JSONPath: Query expressions for JSON
draft-ietf-jsonpath-base-11
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9535.
|
|
|---|---|---|---|
| Authors | Stefan Gössner , Glyn Normington , Carsten Bormann | ||
| Last updated | 2023-03-12 | ||
| Replaces | draft-normington-jsonpath | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Associated WG milestone |
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||
| Document shepherd | Tim Bray | ||
| IESG | IESG state | Became RFC 9535 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | tbray@textuality.com |
draft-ietf-jsonpath-base-11
JSONPath WG S. Gössner, Ed.
Internet-Draft Fachhochschule Dortmund
Intended status: Standards Track G. Normington, Ed.
Expires: 13 September 2023
C. Bormann, Ed.
Universität Bremen TZI
12 March 2023
JSONPath: Query expressions for JSON
draft-ietf-jsonpath-base-11
Abstract
JSONPath defines a string syntax for selecting and extracting JSON
(RFC 8259) values from a JSON value.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-jsonpath-base/.
Discussion of this document takes place on the JSON Path Working
Group mailing list (mailto:jsonpath@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/jsonpath/. Subscribe at
https://www.ietf.org/mailman/listinfo/jsonpath/.
Source for this draft and an issue tracker can be found at
https://github.com/ietf-wg-jsonpath/draft-ietf-jsonpath-base.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 13 September 2023.
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Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.1. JSON Values as Trees of Nodes . . . . . . . . . . . . 6
1.2. History . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3. JSON Values . . . . . . . . . . . . . . . . . . . . . . . 7
1.4. Overview of JSONPath Expressions . . . . . . . . . . . . 7
1.4.1. Identifiers . . . . . . . . . . . . . . . . . . . . . 7
1.4.2. Segments . . . . . . . . . . . . . . . . . . . . . . 7
1.4.3. Selectors . . . . . . . . . . . . . . . . . . . . . . 8
1.4.4. Summary . . . . . . . . . . . . . . . . . . . . . . . 8
1.5. JSONPath Examples . . . . . . . . . . . . . . . . . . . . 10
2. JSONPath Syntax and Semantics . . . . . . . . . . . . . . . . 11
2.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3. Semantics . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.1. Worked Example . . . . . . . . . . . . . . . . . . . 13
2.4. Root Identifier . . . . . . . . . . . . . . . . . . . . . 14
2.5. Selectors . . . . . . . . . . . . . . . . . . . . . . . . 15
2.5.1. Name Selector . . . . . . . . . . . . . . . . . . . . 15
2.5.2. Wildcard Selector . . . . . . . . . . . . . . . . . . 18
2.5.3. Index Selector . . . . . . . . . . . . . . . . . . . 20
2.5.4. Array Slice selector . . . . . . . . . . . . . . . . 21
2.5.5. Filter selector . . . . . . . . . . . . . . . . . . . 25
2.6. Function Extensions . . . . . . . . . . . . . . . . . . . 35
2.6.1. Type System for Function Expressions . . . . . . . . 36
2.6.2. Type Conversion . . . . . . . . . . . . . . . . . . . 38
2.6.3. Well-Typedness of Function Expressions . . . . . . . 38
2.6.4. length Function Extension . . . . . . . . . . . . . . 39
2.6.5. count Function Extension . . . . . . . . . . . . . . 39
2.6.6. match Function Extension . . . . . . . . . . . . . . 40
2.6.7. search Function Extension . . . . . . . . . . . . . . 40
2.6.8. value Function Extension . . . . . . . . . . . . . . 41
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2.7. Segments . . . . . . . . . . . . . . . . . . . . . . . . 42
2.7.1. Child Segment . . . . . . . . . . . . . . . . . . . . 42
2.7.2. Descendant Segment . . . . . . . . . . . . . . . . . 44
2.8. Semantics of null . . . . . . . . . . . . . . . . . . . . 47
2.9. Normalized Paths . . . . . . . . . . . . . . . . . . . . 48
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 51
3.1. Registration of Media Type application/jsonpath . . . . . 51
3.2. Function Extensions . . . . . . . . . . . . . . . . . . . 52
4. Security Considerations . . . . . . . . . . . . . . . . . . . 53
4.1. Attack Vectors on JSONPath Implementations . . . . . . . 54
4.2. Attack Vectors on How JSONPath Queries are Formed . . . . 54
4.3. Attacks on Security Mechanisms that Employ JSONPath . . . 54
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.1. Normative References . . . . . . . . . . . . . . . . . . 55
5.2. Informative References . . . . . . . . . . . . . . . . . 56
Appendix A. Inspired by XPath . . . . . . . . . . . . . . . . . 57
A.1. JSONPath and XPath . . . . . . . . . . . . . . . . . . . 58
Appendix B. JSON Pointer . . . . . . . . . . . . . . . . . . . . 61
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 61
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 62
1. Introduction
JSON [RFC8259] is a popular representation format for structured data
values. JSONPath defines a string syntax for selecting and
extracting JSON values from a JSON value.
JSONPath is not intended as a replacement for, but as a more powerful
companion to, JSON Pointer [RFC6901]. See Appendix B.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
The grammatical rules in this document are to be interpreted as ABNF,
as described in [RFC5234]. ABNF terminal values in this document
define Unicode code points rather than their UTF-8 encoding. For
example, the Unicode PLACE OF INTEREST SIGN (U+2318) would be defined
in ABNF as %x2318.
The terminology of [RFC8259] applies except where clarified below.
The terms "Primitive" and "Structured" are used to group different
kinds of values as in Section 1 of [RFC8259]; JSON Objects and Arrays
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are structured, all other values are primitive. Definitions for
"Object", "Array", "Number", and "String" remain unchanged.
Importantly "object" and "array" in particular do not take on a
generic meaning, such as they would in a general programming context.
Additional terms used in this document are defined below.
Value: As per [RFC8259], a structure conforming to the generic data
model of JSON, i.e., composed of constituents such as structured
values, namely JSON objects and arrays, and primitive data, namely
numbers and text strings as well as the special values null, true,
and false. [RFC8259] focuses on the textual representation of
JSON values and does not fully define the value abstraction
assumed here.
Member: A name/value pair in an object. (A member is not itself a
value.)
Name: The name (a string) in a name/value pair constituting a
member. This is also used in [RFC8259], but that specification
does not formally define it. It is included here for
completeness.
Element: A value in a JSON array.
Index: An integer that identifies a specific element in an array.
Query: Short name for a JSONPath expression.
Argument: Short name for the value a JSONPath expression is applied
to. (Also used for actual parameters of function-expressions.)
Location: the position of a value within the argument. This can be
thought of as a sequence of names and indexes navigating to the
value through the objects and arrays in the argument, with the
empty sequence indicating the argument itself. A location can be
represented as a Normalized Path (defined below).
Node: The pair of a value along with its location within the
argument.
Root Node: The unique node whose value is the entire argument.
Root Node Identifier: The expression $ which refers to the root node
of the argument.
Current Node Identifier: The expression @ which refers to the
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current node in the context of the evaluation of a filter
expression (described later).
Children (of a node): If the node is an array, the nodes of its
elements. If the node is an object, the nodes of its member
values. If the node is neither an array nor an object, it has no
children.
Descendants (of a node): The children of the node, together with the
children of its children, and so forth recursively. More
formally, the descendants relation between nodes is the transitive
closure of the children relation.
Depth (of a descendant node within a value): The number of ancestors
of the node within the value. The root node of the value has
depth zero, the children of the root node have depth one, their
children have depth two, and so forth.
Segment: One of the constructs which select children ([]) or
descendants (..[]) of an input value.
Nodelist: A list of nodes. While a nodelist can be represented in
JSON, e.g. as an array, this document does not require or assume
any particular representation.
Parameter: Formal parameter that can take Arguments (actual
parameters) in a function-expression.
Normalized Path: A simple form of JSONPath expression that
identifies a node in a value by providing a query that results in
exactly that node. Similar to, but syntactically different from,
a JSON Pointer [RFC6901].
Unicode Scalar Value: Any Unicode [UNICODE] code point except high-
surrogate and low-surrogate code points. In other words, integers
in either of the inclusive base 16 ranges 0 to D7FF and E000 to
10FFFF. JSON string values are sequences of Unicode scalar
values.
Singular Nodelist: A nodelist containing at most one node.
Singular Query: A JSONPath expression built from segments each of
which, regardless of the input value, produces a Singular
Nodelist.
Selector: A single item within a segment that takes the input value
and produces a nodelist consisting of child nodes of the input
value.
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1.1.1. JSON Values as Trees of Nodes
This document models the argument as a tree of JSON values, each with
its own node. A node is either the root node or one of its
descendants.
This document models the result of applying a query to the argument
as a nodelist (a list of nodes).
Nodes are the selectable parts of the argument. The only parts of an
object that can be selected by a query are the member values. Member
names and members (name/value pairs) cannot be selected. Thus,
member values have nodes, but members and member names do not.
Similarly, member values are children of an object, but members and
member names are not.
1.2. History
This section is informative.
This document picks up Stefan Gössner's popular JSONPath proposal
dated 2007-02-21 [JSONPath-orig], builds on the experience from the
widespread deployment of its implementations, and provides a
normative specification for it.
Appendix A describes how JSONPath was inspired by XML's XPath
[XPath].
JSONPath was intended as a light-weight companion to JSON
implementations in programming languages such as PHP and JavaScript,
so instead of defining its own expression language, like XPath did,
JSONPath delegated parts of a query to the underlying runtime, e.g.,
JavaScript's eval() function. As JSONPath was implemented in more
environments, JSONPath expressions became decreasingly portable. For
example, regular expression processing was often delegated to a
convenient regular expression engine.
This document aims to remove such implementation-specific
dependencies and serve as a common JSONPath specification that can be
used across programming languages and environments. This means that
backwards compatibility is not always achieved; a design principle of
this document is to go with a "consensus" between implementations
even if it is rough, as long as that does not jeopardize the
objective of obtaining a usable, stable JSON query language.
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1.3. JSON Values
The JSON value a JSONPath query is applied to is, by definition, a
valid JSON value. A JSON value is often constructed by parsing a
JSON text.
The parsing of a JSON text into a JSON value and what happens if a
JSON text does not represent valid JSON are not defined by this
document. Sections 4 and 8 of [RFC8259] identify specific situations
that may conform to the grammar for JSON texts but are not
interoperable uses of JSON, as they may cause unpredictable behavior.
This document does not attempt to define predictable behavior for
JSONPath queries in these situations.
Specifically, the "Semantics" subsections of Sections 2.5.1, 2.5.2,
2.5.5, and 2.7.2 describe behavior that becomes unpredictable when
the JSON value for one of the objects under consideration was
constructed out of JSON text that exhibits multiple members for a
single object that share the same member name ("duplicate names", see
Section 4 of [RFC8259]). Also, selecting a child by name
(Section 2.5.1) and comparing strings (Section "Comparisons" in
Section 2.5.5) assume these strings are sequences of Unicode scalar
values, becoming unpredictable if they are not (Section 8.2 of
[RFC8259]).
1.4. Overview of JSONPath Expressions
This section is informative.
A JSONPath expression is applied to a JSON value, known as the
argument. The output is a nodelist.
A JSONPath expression consists of an identifier followed by a series
of zero or more segments each of which contains one or more
selectors.
1.4.1. Identifiers
The root node identifier $ refers to the root node of the argument,
i.e., to the argument as a whole.
The current node identifier @ refers to the current node in the
context of the evaluation of a filter expression (described later).
1.4.2. Segments
Segments select children ([]) or descendants (..[]) of an input
value.
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Segments can use _bracket notation_, for example:
$['store']['book'][0]['title']
or the more compact _dot notation_, for example:
$.store.book[0].title
A JSONPath expression may use a combination of bracket and dot
notations.
This document treats the bracket notations as canonical and defines
the shorthand dot notation in terms of bracket notation. Examples
and descriptions use shorthands where convenient.
1.4.3. Selectors
A name selector, e.g. 'name', selects a named child of an object.
An index selector, e.g. 3, selects an indexed child of an array.
A wildcard * (Section 2.5.2) in the expression [*] selects all
children of a node and in the expression ..[*] selects all
descendants of a node.
An array slice start:end:step (Section 2.5.4) selects a series of
elements from an array, giving a start position, an end position, and
an optional step value that moves the position from the start to the
end.
Filter expressions ?<logical-expr> select certain children of an
object or array, as in:
$.store.book[?@.price < 10].title
1.4.4. Summary
Table 1 provides a brief overview of JSONPath syntax.
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+=================+==============================================+
| Syntax Element | Description |
+=================+==============================================+
| $ | root node identifier (Section 2.4) |
+-----------------+----------------------------------------------+
| @ | current node identifier (Section 2.5.5) |
| | (valid only within filter selectors) |
+-----------------+----------------------------------------------+
| [<selectors>] | child segment (Section 2.7.1) selects zero |
| | or more children of a node; contains one or |
| | more selectors, separated by commas |
+-----------------+----------------------------------------------+
| .name | shorthand for ['name'] |
+-----------------+----------------------------------------------+
| .* | shorthand for [*] |
+-----------------+----------------------------------------------+
| ..[<selectors>] | descendant segment (Section 2.7.2): selects |
| | zero or more descendants of a node; contains |
| | one or more selectors, separated by commas |
+-----------------+----------------------------------------------+
| ..name | shorthand for ..['name'] |
+-----------------+----------------------------------------------+
| ..* | shorthand for ..[*] |
+-----------------+----------------------------------------------+
| 'name' | name selector (Section 2.5.1): selects a |
| | named child of an object |
+-----------------+----------------------------------------------+
| * | wildcard selector (Section 2.5.1): selects |
| | all children of a node |
+-----------------+----------------------------------------------+
| 3 | index selector (Section 2.5.3): selects an |
| | indexed child of an array (from 0) |
+-----------------+----------------------------------------------+
| 0:100:5 | array slice selector (Section 2.5.4): |
| | start:end:step for arrays |
+-----------------+----------------------------------------------+
| ?<logical-expr> | filter selector (Section 2.5.5): selects |
| | particular children using a logical |
| | expression |
+-----------------+----------------------------------------------+
| length(@.foo) | function extension (Section 2.6): invokes a |
| | function in a filter expression |
+-----------------+----------------------------------------------+
Table 1: Overview of JSONPath syntax
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1.5. JSONPath Examples
This section is informative. It provides examples of JSONPath
expressions.
The examples are based on the simple JSON value shown in Figure 1,
representing a bookstore (that also has a bicycle).
{ "store": {
"book": [
{ "category": "reference",
"author": "Nigel Rees",
"title": "Sayings of the Century",
"price": 8.95
},
{ "category": "fiction",
"author": "Evelyn Waugh",
"title": "Sword of Honour",
"price": 12.99
},
{ "category": "fiction",
"author": "Herman Melville",
"title": "Moby Dick",
"isbn": "0-553-21311-3",
"price": 8.99
},
{ "category": "fiction",
"author": "J. R. R. Tolkien",
"title": "The Lord of the Rings",
"isbn": "0-395-19395-8",
"price": 22.99
}
],
"bicycle": {
"color": "red",
"price": 399
}
}
}
Figure 1: Example JSON value
Table 2 shows some JSONPath queries that might be applied to this
example and their intended results.
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+========================+=======================================+
| JSONPath | Intended result |
+========================+=======================================+
| $.store.book[*].author | the authors of all books in the store |
+------------------------+---------------------------------------+
| $..author | all authors |
+------------------------+---------------------------------------+
| $.store.* | all things in store, which are some |
| | books and a red bicycle |
+------------------------+---------------------------------------+
| $.store..price | the prices of everything in the store |
+------------------------+---------------------------------------+
| $..book[2] | the third book |
+------------------------+---------------------------------------+
| $..book[-1] | the last book in order |
+------------------------+---------------------------------------+
| $..book[0,1] | the first two books |
| $..book[:2] | |
+------------------------+---------------------------------------+
| $..book[?(@.isbn)] | all books with an ISBN number |
+------------------------+---------------------------------------+
| $..book[?(@.price<10)] | all books cheaper than 10 |
+------------------------+---------------------------------------+
| $..* | all member values and array elements |
| | contained in the input value |
+------------------------+---------------------------------------+
Table 2: Example JSONPath expressions and their intended
results when applied to the example JSON value
2. JSONPath Syntax and Semantics
2.1. Overview
A JSONPath _expression_ is a string which, when applied to a JSON
value, the _argument_, selects zero or more nodes of the argument and
outputs these nodes as a nodelist.
A query MUST be encoded using UTF-8. The grammar for queries given
in this document assumes that its UTF-8 form is first decoded into
Unicode code points as described in [RFC3629]; implementation
approaches that lead to an equivalent result are possible.
A string to be used as a JSONPath query needs to be _well-formed_ and
_valid_. A string is a well-formed JSONPath query if it conforms to
the ABNF syntax in this document. A well-formed JSONPath query is
valid if it also fulfills all semantic requirements posed by this
document, which are:
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1. Integer numbers in the JSONPath query that are relevant to the
JSONPath processing (e.g., index values and steps) MUST be within
the range of exact values defined in I-JSON [RFC7493], namely
within the interval [-(2^53)+1, (2^53)-1].
2. Uses of function extensions must be _well-typed_, as described in
Section 2.6.
A JSONPath implementation MUST raise an error for any query which is
not well-formed and valid. The well-formedness and the validity of
JSONPath queries are independent of the JSON value the query is
applied to; no further errors relating to the well-formedness and the
validity of a JSONPath query can be raised during application of the
query to a value.
Obviously, an implementation can still fail when executing a JSONPath
query, e.g., because of resource depletion, but this is not modeled
in this document. However, the implementation MUST NOT silently
malfunction. Specifically, if a valid JSONPath query is evaluated
against a structured value whose size does not fit in the range of
exact values, interfering with the correct interpretation of the
query, the implementation MUST provide an indication of overflow.
(Readers familiar with the HTTP error model may be reminded of 400
type errors when pondering well-formedness and validity, while
resource depletion and related errors are comparable to 500 type
errors.)
2.2. Syntax
Syntactically, a JSONPath query consists of a root identifier ($),
which stands for a nodelist that contains the root node of the
argument, followed by a possibly empty sequence of _segments_.
jsonpath-query = root-identifier segments
segments = *(S segment)
The syntax and semantics of segments are defined in Section 2.7.
2.3. Semantics
In this document, the semantics of a JSONPath query define the
required results and do not prescribe the internal workings of an
implementation. This document may describe semantics in a procedural
step-by-step fashion, but such descriptions are normative only in the
sense that any implementation MUST produce an identical result, but
not in the sense that implementors are required to use the same
algorithms.
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The semantics are that a valid query is executed against a value, the
_argument_, and produces a nodelist (i.e., a list of zero or more
nodes of the value).
The query is a root identifier followed by a sequence of zero or more
segments, each of which is applied to the result of the previous root
identifier or segment and provides input to the next segment. These
results and inputs take the form of a nodelist.
Segments can be added to a query to drill further into the structure
of the input value.
The nodelist resulting from the root identifier contains a single
node, the argument. The nodelist resulting from the last segment is
presented as the result of the query. Depending on the specific API,
it might be presented as an array of the JSON values at the nodes, an
array of Normalized Paths referencing the nodes, or both — or some
other representation as desired by the implementation. Note that an
empty nodelist is a valid query result.
A segment operates on each of the nodes in its input nodelist in
turn, and the resultant nodelists are concatenated in the order of
the input nodelist they were derived from to produce the result of
the segment. A node may be selected more than once and appears that
number of times in the nodelist. Duplicate nodes are not removed.
A syntactically valid segment MUST NOT produce errors when executing
the query. This means that some operations that might be considered
erroneous, such as using an index lying outside the range of an
array, simply result in fewer nodes being selected.
As a consequence of this approach, if any of the segments produces an
empty nodelist, then the whole query produces an empty nodelist.
If a query may produce a nodelist with more than one possible
ordering, a particular implementation may also produce distinct
orderings in successive runs of the query.
2.3.1. Worked Example
Consider this example. With the argument
{"a":[{"b":0},{"b":1},{"c":2}]}, the query $.a[*].b selects the
following list of nodes: 0, 1 (denoted here by their value).
The query consists of $ followed by three segments: .a, [*], and .b.
Firstly, $ produces a nodelist consisting of just the argument.
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Next, .a selects from any object input node and selects the node of
any member value of the input node corresponding to the member name
"a". The result is again a list of one node:
[{"b":0},{"b":1},{"c":2}].
Next, [*] selects from any array input node all its elements (for an
object input node, it would select all its member values, but not the
member names). The result is a list of three nodes: {"b":0},
{"b":1}, and {"c":2}.
Finally, .b selects from any object input node with a member name b
and selects the node of the member value of the input node
corresponding to that name. The result is a list containing 0, 1.
This is the concatenation of three lists, two of length one
containing 0, 1, respectively, and one of length zero.
2.4. Root Identifier
Syntax
Every JSONPath query (except those inside filter expressions, see
Section 2.5.5) MUST begin with the root identifier $.
root-identifier = "$"
Semantics
The root identifier $ represents the root node of the argument and
produces a nodelist consisting of that root node.
Examples
JSON:
{"k": "v"}
Queries:
+=======+============+=============+===========+
| Query | Result | Result Path | Comment |
+=======+============+=============+===========+
| $ | {"k": "v"} | $ | Root node |
+-------+------------+-------------+-----------+
Table 3: Root identifier examples
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2.5. Selectors
Selectors appear only inside child segments (Section 2.7.1) and
descendant segments (Section 2.7.2).
A selector produces a nodelist consisting of zero or more children of
the input value.
There are various kinds of selectors which produce children of
objects, children of arrays, or children of either objects or arrays.
selector = name-selector /
wildcard-selector /
slice-selector /
index-selector /
filter-selector
The syntax and semantics of each kind of selector are defined below.
2.5.1. Name Selector
Syntax
A name selector '<name>' selects at most one object member value.
In contrast to JSON, the JSONPath syntax allows strings to be
enclosed in _single_ or _double_ quotes.
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name-selector = string-literal
string-literal = %x22 *double-quoted %x22 / ; "string"
%x27 *single-quoted %x27 ; 'string'
double-quoted = unescaped /
%x27 / ; '
ESC %x22 / ; \"
ESC escapable
single-quoted = unescaped /
%x22 / ; "
ESC %x27 / ; \'
ESC escapable
ESC = %x5C ; \ backslash
unescaped = %x20-21 / ; see RFC 8259
; omit 0x22 "
%x23-26 /
; omit 0x27 '
%x28-5B /
; omit 0x5C \
%x5D-10FFFF
escapable = %x62 / ; b BS backspace U+0008
%x66 / ; f FF form feed U+000C
%x6E / ; n LF line feed U+000A
%x72 / ; r CR carriage return U+000D
%x74 / ; t HT horizontal tab U+0009
"/" / ; / slash (solidus) U+002F
"\" / ; \ backslash (reverse solidus) U+005C
(%x75 hexchar) ; uXXXX U+XXXX
hexchar = non-surrogate /
(high-surrogate "\" %x75 low-surrogate)
non-surrogate = ((DIGIT / "A"/"B"/"C" / "E"/"F") 3HEXDIG) /
("D" %x30-37 2HEXDIG )
high-surrogate = "D" ("8"/"9"/"A"/"B") 2HEXDIG
low-surrogate = "D" ("C"/"D"/"E"/"F") 2HEXDIG
HEXDIG = DIGIT / "A" / "B" / "C" / "D" / "E" / "F"
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Note: double-quoted strings follow the JSON string syntax (Section 7
of [RFC8259]); single-quoted strings follow an analogous pattern
(Section "Syntax"). No attempt was made to improve on this syntax,
so if it is desired to escape characters with scalar values above
0x10000, such as U+1F914 ("🤔", THINKING FACE), they need to be
represented by a pair of surrogate escapes ("\uD83E\uDD14" in this
case).
Semantics
A name-selector string MUST be converted to a member name M by
removing the surrounding quotes and replacing each escape sequence
with its equivalent Unicode character, as in the table below:
+=================+===================+=============================+
| Escape Sequence | Unicode Character | Description |
+=================+===================+=============================+
| \b | U+0008 | BS backspace |
+-----------------+-------------------+-----------------------------+
| \t | U+0009 | HT horizontal tab |
+-----------------+-------------------+-----------------------------+
| \n | U+000A | LF line feed |
+-----------------+-------------------+-----------------------------+
| \f | U+000C | FF form feed |
+-----------------+-------------------+-----------------------------+
| \r | U+000D | CR carriage return |
+-----------------+-------------------+-----------------------------+
| \" | U+0022 | quotation mark |
+-----------------+-------------------+-----------------------------+
| \' | U+0027 | apostrophe |
+-----------------+-------------------+-----------------------------+
| \/ | U+002F | slash (solidus) |
+-----------------+-------------------+-----------------------------+
| \\ | U+005C | backslash (reverse |
| | | solidus) |
+-----------------+-------------------+-----------------------------+
| \uXXXX | U+XXXX | unicode character |
+-----------------+-------------------+-----------------------------+
Table 4: Escape Sequence Replacements
Applying the name-selector to an object node selects a member value
whose name equals the member name M, or selects nothing if there is
no such member value. Nothing is selected from a value that is not
an object.
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Note that processing the name selector requires comparing the member
name string M with member name strings in the JSON to which the
selector is being applied. Two strings MUST be considered equal if
and only if they are identical sequences of Unicode scalar values.
In other words, normalization operations MUST NOT be applied to
either the member name string M from the JSONPath or to the member
name strings in the JSON prior to comparison.
Examples
JSON:
{
"o": {"j j": {"k.k": 3}},
"'": {"@": 2}
}
Queries:
The following examples show the name selector in use by child
segments.
+===================+========+======================+=============+
| Query | Result | Result Paths | Comment |
+===================+========+======================+=============+
| $.o['j j']['k.k'] | 3 | $['o']['j j']['k.k'] | Named value |
| | | | in nested |
| | | | object |
+-------------------+--------+----------------------+-------------+
| $.o["j j"]["k.k"] | 3 | $['o']['j j']['k.k'] | Named value |
| | | | in nested |
| | | | object |
+-------------------+--------+----------------------+-------------+
| $["'"]["@"] | 2 | $['\'']['@'] | Unusual |
| | | | member |
| | | | names |
+-------------------+--------+----------------------+-------------+
Table 5: Name selector examples
2.5.2. Wildcard Selector
Syntax
The wildcard selector consists of an asterisk.
wildcard-selector = "*"
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Semantics
A wildcard selector selects the nodes of all children of an object or
array. The order in which the children of an object appear in the
resultant nodelist is not stipulated, since JSON objects are
unordered. Children of an array appear in array order in the
resultant nodelist.
The wildcard selector selects nothing from a primitive JSON value
(that is, a number, a string, true, false, or null).
Examples
JSON:
{
"o": {"j": 1, "k": 2},
"a": [5, 3]
}
Queries:
The following examples show the wildcard selector in use by a child
segment.
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+========+==========+=============+===================+
| Query | Result | Result | Comment |
| | | Paths | |
+========+==========+=============+===================+
| $[*] | {"j": 1, | $['o'] | Object values |
| | "k": 2} | $['a'] | |
| | [5, 3] | | |
+--------+----------+-------------+-------------------+
| $.o[*] | 1 | $['o']['j'] | Object values |
| | 2 | $['o']['k'] | |
+--------+----------+-------------+-------------------+
| $.o[*] | 2 | $['o']['k'] | Alternative |
| | 1 | $['o']['j'] | result |
+--------+----------+-------------+-------------------+
| $.o[*, | 1 | $['o']['j'] | Non-deterministic |
| *] | 2 | $['o']['k'] | ordering |
| | 2 | $['o']['k'] | |
| | 1 | $['o']['j'] | |
+--------+----------+-------------+-------------------+
| $.a[*] | 5 | $['a'][0] | Array members |
| | 3 | $['a'][1] | |
+--------+----------+-------------+-------------------+
Table 6: Wildcard selector examples
The example above with the query $.o[*, *] shows that the wildcard
selector may produce nodelists in distinct orders each time it
appears in the child segment, when it is applied to an object node
with two or more members (but not when it is applied to object nodes
with fewer than two members or to array nodes).
2.5.3. Index Selector
Syntax
An index selector <index> matches at most one array element value.
index-selector = int ; decimal integer
int = "0" /
(["-"] DIGIT1 *DIGIT) ; - optional
DIGIT1 = %x31-39 ; 1-9 non-zero digit
Applying the numerical index-selector selects the corresponding
element. JSONPath allows it to be negative (see
Section "Semantics").
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To be valid, the index selector value MUST be in the I-JSON range of
exact values, see Section 2.1.
Notes: 1. An index-selector is an integer (in base 10, as in JSON
numbers). 2. As in JSON numbers, the syntax does not allow octal-
like integers with leading zeros such as 01 or -01.
Semantics
A non-negative index-selector applied to an array selects an array
element using a zero-based index. For example, the selector 0
selects the first and the selector 4 selects the fifth element of a
sufficiently long array. Nothing is selected, and it is not an
error, if the index lies outside the range of the array. Nothing is
selected from a value that is not an array.
A negative index-selector counts from the array end. For example,
the selector -1 selects the last and the selector -2 selects the
penultimate element of an array with at least two elements. As with
non-negative indexes, it is not an error if such an element does not
exist; this simply means that no element is selected.
Examples
JSON:
["a","b"]
Queries:
The following examples show the index selector in use by a child
segment.
+=======+========+==============+================================+
| Query | Result | Result Paths | Comment |
+=======+========+==============+================================+
| $[1] | "b" | $[1] | Element of array |
+-------+--------+--------------+--------------------------------+
| $[-2] | "a" | $[0] | Element of array, from the end |
+-------+--------+--------------+--------------------------------+
Table 7: Index selector examples
2.5.4. Array Slice selector
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Syntax
The array slice selector has the form <start>:<end>:<step>. It
matches elements from arrays starting at index <start>, ending at —
but not including — <end>, while incrementing by step with a default
of 1.
slice-selector = [start S] ":" S [end S] [":" [S step ]]
start = int ; included in selection
end = int ; not included in selection
step = int ; default: 1
B = %x20 / ; Space
%x09 / ; Horizontal tab
%x0A / ; Line feed or New line
%x0D ; Carriage return
S = *B ; optional blank space
The slice selector consists of three optional decimal integers
separated by colons.
To be valid, the integers provided MUST be in the I-JSON range of
exact values, see Section 2.1.
Semantics
The slice selector was inspired by the slice operator of ECMAScript 4
(ES4), which was deprecated in 2014, and that of Python.
Informal Introduction
This section is informative.
Array slicing is inspired by the behavior of the
Array.prototype.slice method of the JavaScript language as defined by
the ECMA-262 standard [ECMA-262], with the addition of the step
parameter, which is inspired by the Python slice expression.
The array slice expression start:end:step selects elements at indices
starting at start, incrementing by step, and ending with end (which
is itself excluded). So, for example, the expression 1:3 (where step
defaults to 1) selects elements with indices 1 and 2 (in that order)
whereas 1:5:2 selects elements with indices 1 and 3.
When step is negative, elements are selected in reverse order. Thus,
for example, 5:1:-2 selects elements with indices 5 and 3, in that
order and ::-1 selects all the elements of an array in reverse order.
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When step is 0, no elements are selected. (This is the one case that
differs from the behavior of Python, which raises an error in this
case.)
The following section specifies the behavior fully, without depending
on JavaScript or Python behavior.
Normative Semantics
A slice expression selects a subset of the elements of the input
array, in the same order as the array or the reverse order, depending
on the sign of the step parameter. It selects no nodes from a node
that is not an array.
A slice is defined by the two slice parameters, start and end, and an
iteration delta, step. Each of these parameters is optional. In the
rest of this section, len denotes the length of the input array.
The default value for step is 1. The default values for start and
end depend on the sign of step, as follows:
+===========+=========+==========+
| Condition | start | end |
+===========+=========+==========+
| step >= 0 | 0 | len |
+-----------+---------+----------+
| step < 0 | len - 1 | -len - 1 |
+-----------+---------+----------+
Table 8: Default array slice
start and end values
Slice expression parameters start and end are not directly usable as
slice bounds and must first be normalized. Normalization for this
purpose is defined as:
FUNCTION Normalize(i, len):
IF i >= 0 THEN
RETURN i
ELSE
RETURN len + i
END IF
The result of the array index expression i applied to an array of
length len is the result of the array slicing expression Normalize(i,
len):Normalize(i, len)+1:1.
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Slice expression parameters start and end are used to derive slice
bounds lower and upper. The direction of the iteration, defined by
the sign of step, determines which of the parameters is the lower
bound and which is the upper bound:
FUNCTION Bounds(start, end, step, len):
n_start = Normalize(start, len)
n_end = Normalize(end, len)
IF step >= 0 THEN
lower = MIN(MAX(n_start, 0), len)
upper = MIN(MAX(n_end, 0), len)
ELSE
upper = MIN(MAX(n_start, -1), len-1)
lower = MIN(MAX(n_end, -1), len-1)
END IF
RETURN (lower, upper)
The slice expression selects elements with indices between the lower
and upper bounds. In the following pseudocode, a(i) is the i+1th
element of the array a (i.e., a(0) is the first element, a(1) the
second, and so forth).
IF step > 0 THEN
i = lower
WHILE i < upper:
SELECT a(i)
i = i + step
END WHILE
ELSE if step < 0 THEN
i = upper
WHILE lower < i:
SELECT a(i)
i = i + step
END WHILE
END IF
When step = 0, no elements are selected and the result array is
empty.
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Examples
JSON:
["a", "b", "c", "d", "e", "f", "g"]
Queries:
The following examples show the array slice selector in use by a
child segment.
+===========+========+========+==========+
| Query | Result | Result | Comment |
| | | Paths | |
+===========+========+========+==========+
| $[1:3] | "b" | $[1] | Slice |
| | "c" | $[2] | with |
| | | | default |
| | | | step |
+-----------+--------+--------+----------+
| $[1:5:2] | "b" | $[1] | Slice |
| | "d" | $[3] | with |
| | | | step 2 |
+-----------+--------+--------+----------+
| $[5:1:-2] | "f" | $[5] | Slice |
| | "d" | $[3] | with |
| | | | negative |
| | | | step |
+-----------+--------+--------+----------+
| $[::-1] | "g" | $[6] | Slice in |
| | "f" | $[5] | reverse |
| | "e" | $[4] | order |
| | "d" | $[3] | |
| | "c" | $[2] | |
| | "b" | $[1] | |
| | "a" | $[0] | |
+-----------+--------+--------+----------+
Table 9: Array slice selector examples
2.5.5. Filter selector
Filter selectors are used to iterate over the elements or members of
structured values, i.e., JSON arrays and objects. The structured
values are identified in the nodelist offered by the child or
descendant segment using the filter selector.
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For each iteration (element/member), a logical expression, the
_filter expression_, is evaluated which decides whether the node of
the element/member is selected. (While a logical expression
evaluates to what mathematically is a Boolean value, this
specification uses the term _logical_ to maintain a distinction from
the Boolean values that JSON can represent.)
During the iteration process, the filter expression receives the node
of each array element or object member value of the structured value
being filtered; this element or member value is then known as the
_current node_.
The current node can be used as the start of one or more JSONPath
queries in subexpressions of the filter expression, notated via the
current-node-identifier @. Each JSONPath query can be used either for
testing existence of a result of the query, for obtaining a specific
JSON value resulting from that query that can then be used in a
comparison, or as a _function argument_.
Within the logical expression for a filter selector, function
expressions can be used to operate on nodelists and values. The set
of available functions is extensible, with a number of functions
predefined, see Section 2.6, and the ability to register further
functions provided by the Function Extensions sub-registry
(Section 3.2). When a function is defined, it is given a unique
name, and its return value and each of its parameters is given a
_declared type_. The type system is limited in scope; its purpose is
to express restrictions that, without functions, are implicit in the
grammar of filter expressions. The type system also guides
conversions (Section 2.6.2) that mimic the way different kinds of
expressions are handled in the grammar when function expressions are
not in use.
Syntax
The filter selector has the form ?<logical-expr>.
filter-selector = "?" S logical-expr
As the filter expression is composed of side-effect free
constituents, the order of evaluation does not need to be (and is
not) defined. Similarly, for conjunction (&&) and disjunction (||)
(defined later), both a short-circuiting and a fully evaluating
implementation will lead to the same result; both implementation
strategies are therefore valid.
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The current node is accessible via the current node identifier @.
This identifier addresses the current node of the filter-selector
that is directly enclosing the identifier; note that within nested
filter-selectors, there is no syntax to address the current node of
any other than the directly enclosing filter-selector (i.e., of
filter-selectors enclosing the filter-selector that is directly
enclosing the identifier).
Logical expressions offer the usual Boolean operators (|| for OR, &&
for AND, and ! for NOT). Parentheses MAY be used within logical-expr
for grouping.
logical-expr = logical-or-expr
logical-or-expr = logical-and-expr *(S "||" S logical-and-expr)
; disjunction
; binds less tightly than conjunction
logical-and-expr = basic-expr *(S "&&" S basic-expr)
; conjunction
; binds more tightly than disjunction
basic-expr = paren-expr /
comparison-expr /
test-expr
paren-expr = [logical-not-op S] "(" S logical-expr S ")"
; parenthesized expression
logical-not-op = "!" ; logical NOT operator
A test expression either tests the existence of a node designated by
an embedded query (see Section "Existence Tests") or tests the result
of a function expression (see Section 2.6). In the latter case, if
the function result type is declared as LogicalType (see
Section 2.6.1), it tests whether the result is LogicalTrue; if the
function result type is declared as NodesType, it tests whether the
result is non-empty. If the declared function result type is
ValueType, its use in a test expression is not well-typed.
test-expr = [logical-not-op S]
(filter-query / ; existence/non-existence
function-expr) ; LogicalType or
; NodesType
filter-query = rel-query / jsonpath-query
rel-query = current-node-identifier segments
current-node-identifier = "@"
Comparison expressions are available for comparisons between
primitive values (that is, numbers, strings, true, false, and null).
These can be obtained via literal values; Singular Queries, each of
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which selects at most one node the value of which is then used; and
function expressions (see Section 2.6) of type ValueType or NodesType
(see Section 2.6.2).
comparison-expr = comparable S comparison-op S comparable
literal = number / string-literal /
true / false / null
comparable = literal /
singular-query / ; Singular Query value
function-expr ; ValueType
comparison-op = "==" / "!=" /
"<=" / ">=" /
"<" / ">"
singular-query = rel-singular-query / abs-singular-query
rel-singular-query = current-node-identifier singular-query-segments
abs-singular-query = root-identifier singular-query-segments
singular-query-segments = *(S (name-segment / index-segment))
name-segment = ("[" name-selector "]") /
("." member-name-shorthand)
index-segment = "[" index-selector "]"
Literals can be notated in the way that is usual for JSON (with the
extension that strings can use single-quote delimiters). Alphabetic
characters in ABNF are case-insensitive, so within a floating point
number the ABNF expression "e" can be either the value 'e' or 'E'.
true, false, and null are lower-case only (case-sensitive).
number = (int / "-0") [ frac ] [ exp ] ; decimal number
frac = "." 1*DIGIT ; decimal fraction
exp = "e" [ "-" / "+" ] 1*DIGIT ; decimal exponent
true = %x74.72.75.65 ; true
false = %x66.61.6c.73.65 ; false
null = %x6e.75.6c.6c ; null
The following table lists filter expression operators in order of
precedence from highest (binds most tightly) to lowest (binds least
tightly).
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+============+===============+===========+
| Precedence | Operator type | Syntax |
+============+===============+===========+
| 5 | Grouping | (...) |
+------------+---------------+-----------+
| 4 | Logical NOT | ! |
+------------+---------------+-----------+
| 3 | Relations | == != |
| | | < <= > >= |
+------------+---------------+-----------+
| 2 | Logical AND | && |
+------------+---------------+-----------+
| 1 | Logical OR | || |
+------------+---------------+-----------+
Table 10: Filter expression operator
precedence
Semantics
The filter selector works with arrays and objects exclusively. Its
result is a list of _zero_, _one_, _multiple_ or _all_ of their array
elements or member values, respectively. Applied to primitive
values, it selects nothing.
The order in which the children of an object appear in the resultant
nodelist is not stipulated, since JSON objects are unordered.
Children of an array appear in array order in the resultant nodelist.
Existence Tests
A query by itself in a Logical context is an existence test which
yields true if the query selects at least one node and yields false
if the query does not select any nodes.
Existence tests differ from comparisons in that:
* they work with arbitrary relative or absolute queries (not just
Singular Queries).
* they work with queries that select structured values.
To examine the value of a node selected by a query, an explicit
comparison is necessary. For example, to test whether the node
selected by the query @.foo has the value null, use @.foo == null
(see Section 2.8) rather than the negated existence test !@.foo
(which yields false if @.foo selects a node, regardless of the node's
value).
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Comparisons
The comparison operators == and < are defined first and then these
are used to define !=, <=, >, and >=.
When either side of a comparison results in an empty nodelist or
Nothing:
* a comparison using the operator == yields true if and only the
other side also results in an empty nodelist or Nothing.
* a comparison using the operator < yields false.
When any query or function expression on either side of a comparison
results in a nodelist consisting of a single node, that side is
replaced by the value of its node and then:
* a comparison using the operator == yields true if and only if the
comparison is between:
- numbers expected to interoperate as per Section 2.2 of I-JSON
[RFC7493] that compare equal using normal mathematical
equality,
- numbers at least one of which is not expected to interoperate
as per I-JSON, where the numbers compare equal using an
implementation specific equality,
- equal primitive values which are not numbers,
- equal arrays, that is arrays of the same length where each
element of the first array is equal to the corresponding
element of the second array, or
- equal objects with no duplicate names, that is where:
o both objects have the same collection of names (with no
duplicates), and
o for each of those names, the values associated with the name
by the objects are equal.
* a comparison using the operator < yields true if and only if the
comparison is between values which are both numbers or both
strings and which satisfy the comparison:
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- numbers expected to interoperate as per Section 2.2 of I-JSON
[RFC7493] MUST compare using the normal mathematical ordering;
numbers not expected to interoperate as per I-JSON MAY compare
using an implementation specific ordering
- the empty string compares less than any non-empty string
- a non-empty string compares less than another non-empty string
if and only if the first string starts with a lower Unicode
scalar value than the second string or if both strings start
with the same Unicode scalar value and the remainder of the
first string compares less than the remainder of the second
string.
Note that comparisons using the operator < yield false if either
value being compared is an object, array, boolean, or null.
!=, <=, >, and >= are defined in terms of the other comparison
operators. For any a and b:
* The comparison a != b yields true if and only if a == b yields
false.
* The comparison a <= b yields true if and only if a < b yields true
or a == b yields true.
* The comparison a > b yields true if and only if b < a yields true.
* The comparison a >= b yields true if and only if b < a yields true
or a == b yields true.
Logical Operators
The logical AND, OR, and NOT operators have the normal semantics of
Boolean algebra and obey its laws (see, for example, [BOOLEAN-LAWS]).
Function Extensions
Filter selectors may use function extensions, which are covered in
Section 2.6.
Examples
The first set of examples shows some comparison expressions and their
result with a given JSON value as input.
JSON:
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{
"obj": {"x": "y"},
"arr": [2, 3]
}
Comparisons:
+========================+========+============================+
| Comparison | Result | Comment |
+========================+========+============================+
| $.absent1 == $.absent2 | true | Empty nodelists |
+------------------------+--------+----------------------------+
| $.absent1 <= $.absent2 | true | == implies <= |
+------------------------+--------+----------------------------+
| $.absent == 'g' | false | Empty nodelist |
+------------------------+--------+----------------------------+
| $.absent1 != $.absent2 | false | Empty nodelists |
+------------------------+--------+----------------------------+
| $.absent != 'g' | true | Empty nodelist |
+------------------------+--------+----------------------------+
| 1 <= 2 | true | Numeric comparison |
+------------------------+--------+----------------------------+
| 1 > 2 | false | Strict, numeric comparison |
+------------------------+--------+----------------------------+
| 13 == '13' | false | Type mismatch |
+------------------------+--------+----------------------------+
| 'a' <= 'b' | true | String comparison |
+------------------------+--------+----------------------------+
| 'a' > 'b' | false | Strict, string comparison |
+------------------------+--------+----------------------------+
| $.obj == $.arr | false | Type mismatch |
+------------------------+--------+----------------------------+
| $.obj != $.arr | true | Type mismatch |
+------------------------+--------+----------------------------+
| $.obj == $.obj | true | Object comparison |
+------------------------+--------+----------------------------+
| $.obj != $.obj | false | Object comparison |
+------------------------+--------+----------------------------+
| $.arr == $.arr | true | Array comparison |
+------------------------+--------+----------------------------+
| $.arr != $.arr | false | Array comparison |
+------------------------+--------+----------------------------+
| $.obj == 17 | false | Type mismatch |
+------------------------+--------+----------------------------+
| $.obj != 17 | true | Type mismatch |
+------------------------+--------+----------------------------+
| $.obj <= $.arr | false | Objects and arrays are not |
| | | ordered |
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+------------------------+--------+----------------------------+
| $.obj < $.arr | false | Objects and arrays are not |
| | | ordered |
+------------------------+--------+----------------------------+
| $.obj <= $.obj | true | == implies <= |
+------------------------+--------+----------------------------+
| $.arr <= $.arr | true | == implies <= |
+------------------------+--------+----------------------------+
| 1 <= $.arr | false | Arrays are not ordered |
+------------------------+--------+----------------------------+
| 1 >= $.arr | false | Arrays are not ordered |
+------------------------+--------+----------------------------+
| 1 > $.arr | false | Arrays are not ordered |
+------------------------+--------+----------------------------+
| 1 < $.arr | false | Arrays are not ordered |
+------------------------+--------+----------------------------+
| true <= true | true | == implies <= |
+------------------------+--------+----------------------------+
| true > true | false | Booleans are not ordered |
+------------------------+--------+----------------------------+
Table 11: Comparison examples
The second set of examples shows some complete JSONPath queries that
make use of filter selectors, and the results of evaluating these
queries on a given JSON value as input. (Note that two of the
queries employ function extensions; please see Sections 2.6.6 and
2.6.7 below for details about these.)
JSON:
{
"a": [3, 5, 1, 2, 4, 6, {"b": "j"}, {"b": "k"},
{"b": {}}, {"b": "kilo"}],
"o": {"p": 1, "q": 2, "r": 3, "s": 5, "t": {"u": 6}},
"e": "f"
}
Queries:
The following examples show the filter selector in use by a child
segment.
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+==================+==============+=============+===================+
| Query | Result | Result | Comment |
| | | Paths | |
+==================+==============+=============+===================+
| $.a[?@.b == | {"b": | $['a'][9] | Member value |
| 'kilo'] | "kilo"} | | comparison |
+------------------+--------------+-------------+-------------------+
| $.a[?@>3.5] | 5 | $['a'][1] | Array value |
| | 4 | $['a'][4] | comparison |
| | 6 | $['a'][5] | |
+------------------+--------------+-------------+-------------------+
| $.a[?@.b] | {"b": "j"} | $['a'][6] | Array value |
| | {"b": "k"} | $['a'][7] | existence |
| | {"b": {}} | $['a'][8] | |
| | {"b": | $['a'][9] | |
| | "kilo"} | | |
+------------------+--------------+-------------+-------------------+
| $[?@.*] | [3, 5, 1, | $['a'] | Existence of non- |
| | 2, 4, 6, | $['o'] | singular queries |
| | {"b": "j"}, | | |
| | {"b": "k"}, | | |
| | {"b": {}}, | | |
| | {"b": | | |
| | "kilo"}] | | |
| | {"p": 1, | | |
| | "q": 2, | | |
| | "r": 3, | | |
| | "s": 5, | | |
| | "t": {"u": | | |
| | 6}} | | |
+------------------+--------------+-------------+-------------------+
| $[?@[?@.b]] | [3, 5, 1, | $['a'] | Nested filters |
| | 2, 4, 6, | | |
| | {"b": "j"}, | | |
| | {"b": "k"}, | | |
| | {"b": {}}, | | |
| | {"b": | | |
| | "kilo"}] | | |
+------------------+--------------+-------------+-------------------+
| $.o[?@<3, ?@<3] | 1 | $['o']['p'] | Non-deterministic |
| | 2 | $['o']['q'] | ordering |
| | 2 | $['o']['q'] | |
| | 1 | $['o']['p'] | |
+------------------+--------------+-------------+-------------------+
| $.a[?@<2 || @.b | 1 | $['a'][2] | Array value |
| == "k"] | {"b": "k"} | $['a'][7] | logical OR |
+------------------+--------------+-------------+-------------------+
| $.a[?match(@.b, | {"b": "j"} | $['a'][6] | Array value |
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| "[jk]")] | {"b": "k"} | $['a'][7] | regular |
| | | | expression match |
+------------------+--------------+-------------+-------------------+
| $.a[?search(@.b, | {"b": "j"} | $['a'][6] | Array value |
| "[jk]")] | {"b": "k"} | $['a'][7] | regular |
| | {"b": | $['a'][9] | expression search |
| | "kilo"} | | |
+------------------+--------------+-------------+-------------------+
| $.o[?@>1 && @<4] | 2 | $['o']['q'] | Object value |
| | 3 | $['o']['r'] | logical AND |
+------------------+--------------+-------------+-------------------+
| $.o[?@>1 && @<4] | 3 | $['o']['r'] | Alternative |
| | 2 | $['o']['q'] | result |
+------------------+--------------+-------------+-------------------+
| $.o[?@.u || @.x] | {"u": 6} | $['o']['t'] | Object value |
| | | | logical OR |
+------------------+--------------+-------------+-------------------+
| $.a[?(@.b == | 3 | $['a'][0] | Comparison of |
| $.x)] | 5 | $['a'][1] | queries with no |
| | 1 | $['a'][2] | values |
| | 2 | $['a'][3] | |
| | 4 | $['a'][4] | |
| | 6 | $['a'][5] | |
+------------------+--------------+-------------+-------------------+
| $.a[?(@ == @)] | 3 | $['a'][0] | Comparisons of |
| | 5 | $['a'][1] | primitive and of |
| | 1 | $['a'][2] | structured values |
| | 2 | $['a'][3] | |
| | 4 | $['a'][4] | |
| | 6 | $['a'][5] | |
| | {"b": "j"} | $['a'][6] | |
| | {"b": "k"} | $['a'][7] | |
| | {"b": {}} | $['a'][8] | |
| | {"b": | $['a'][9] | |
| | "kilo"} | | |
+------------------+--------------+-------------+-------------------+
Table 12: Filter selector examples
The example above with the query $.o[?@<3, ?@<3] shows that a filter
selector may produce nodelists in distinct orders each time it
appears in the child segment.
2.6. Function Extensions
Beyond the filter expression functionality defined in the preceding
subsections, JSONPath defines an extension point that can be used to
add filter expression functionality: "Function Extensions".
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This section defines the extension point as well as four function
extensions that use this extension point. While these mechanisms are
designed to use the extension point, they are an integral part of the
JSONPath specification and are expected to be implemented like any
other integral part of this specification.
A function extension defines a registered name (see Section 3.2) that
can be applied to a sequence of zero or more arguments, producing a
result.
A function extension MUST be defined such that its evaluation is
side-effect free, i.e., all possible orders of evaluation and choices
of short-circuiting or full evaluation of an expression containing it
must lead to the same result. (Note that memoization or logging are
not side effects in this sense as they are visible at the
implementation level only — they do not influence the result of the
evaluation.)
function-name = function-name-first *function-name-char
function-name-first = LCALPHA
function-name-char = function-name-first / "_" / DIGIT
LCALPHA = %x61-7A ; "a".."z"
function-expr = function-name "(" S [function-argument
*(S "," S function-argument)] S ")"
function-argument = literal /
filter-query / ; (includes singular-query)
function-expr
A function argument is a filter-query or a comparable.
According to Section 2.5.5, a function-expr is valid as a filter-
query or a comparable.
Any function expressions in a query must be well-formed (by
conforming to the above ABNF) and well-typed, otherwise the JSONPath
implementation MUST raise an error (see Section 2.1). To define
which function expressions are well-typed, a type system is first
introduced.
2.6.1. Type System for Function Expressions
Each parameter as well as the result of a function extension must
have a declared type.
A type is a set of instances. Declared types enable checking a
JSONPath query for well-typedness independent of any argument the
JSONPath query is applied to.
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Table 13 defines the available types in terms of abstract instances,
where v denotes a value, and nl denotes a nodelist.
+=============+===========================+
| Type | Abstract Instances |
+=============+===========================+
| ValueType | Value(v), Nothing |
+-------------+---------------------------+
| LogicalType | LogicalTrue, LogicalFalse |
+-------------+---------------------------+
| NodesType | Nodes(nl) |
+-------------+---------------------------+
Table 13: Function extension type system
Notes:
* ValueType is an abstraction of a JSON value or Nothing.
* LogicalType is an abstraction of the result of a logical-expr.
Its two instances, LogicalTrue and LogicalFalse, are not related
to the JSON literals true and false and have no direct syntactical
representation in JSONPath.
* NodesType is an abstraction of a filter-query (which appears in a
test expression or as a function argument). Members of NodesType
have no direct syntactical representation in JSONPath.
The abstract instances above can be obtained from the concrete
representations in Table 14.
+===========+=============================================+
| Abstract | Concrete Representations |
| Instance | |
+===========+=============================================+
| Value(v) | JSON value v |
+-----------+---------------------------------------------+
| Nothing | A representation of the absence of a JSON |
| | value, distinct from the JSON literal null, |
| | e.g., from a Singular Query or filter-query |
| | resulting in an empty nodelist |
+-----------+---------------------------------------------+
| Nodes(nl) | A list of zero or more nodes, e.g., from a |
| | filter-query resulting in the nodelist nl, |
| | which may or may not be empty |
+-----------+---------------------------------------------+
Table 14: Concrete representations of abstract instances
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2.6.2. Type Conversion
The following implicit type conversion may occur:
* Where a member of NodesType needs to be converted to a
LogicalType, the conversion proceeds as follows:
- If the nodelist contains one or more nodes, the conversion
result is LogicalTrue.
- If the nodelist is empty, the conversion result is
LogicalFalse.
Given an expression with a declared type of NodesType, a ValueType
can be obtained using a function such as value() (see Section 2.6.8).
The well-typedness of function expressions can now be defined in
terms of this type system.
2.6.3. Well-Typedness of Function Expressions
A function expression is well-typed if all of the following are true:
* If it occurs directly in a test expression, the function is
declared to have a result type of LogicalType, or (conversion
applies) NodesType.
* If it occurs directly as a comparable in a comparison, the
function is declared to have a result type of ValueType, or
(conversion applies) NodesType.
* Otherwise, it occurs as an argument in another function
expression, and the following rules for function arguments apply
to its declared result type.
* Each argument of the function can be used for the declared type of
the corresponding declared parameter according to one of the
following rules:
- The argument is a function expression with declared result type
that is the same as the declared type of the parameter.
- The argument is a literal primitive value and the defined type
of the parameter is ValueType.
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- The argument is a Singular Query or filter-query (which
includes Singular Queries), or a function expression with
declared result type NodesType and the defined type of the
parameter is NodesType. Where the declared type of the
parameter is not NodesType, a conversion applies.
2.6.4. length Function Extension
Parameters:
1. ValueType
Result: ValueType (unsigned integer or Nothing)
The "length" function extension provides a way to compute the length
of a value and make that available for further processing in the
filter expression:
$[?length(@.authors) >= 5]
Its only argument is an instance of ValueType (possibly taken from a
singular query as in the example above). The result also is an
instance of ValueType: an unsigned integer or Nothing.
* If the argument value is a string, the result is the number of
Unicode scalar values in the string.
* If the argument value is an array, the result is the number of
elements in the array.
* If the argument value is an object, the result is the number of
members in the object.
* For any other argument value, the result is Nothing.
2.6.5. count Function Extension
Parameters:
1. NodesType
Result: ValueType (unsigned integer)
The "count" function extension provides a way to obtain the number of
nodes in a nodelist and make that available for further processing in
the filter expression:
$[?count(@.*.author) >= 5]
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Its only argument is a nodelist. The result is a value, an unsigned
integer, that gives the number of nodes in the nodelist. Note that
there is no deduplication of the nodelist.
2.6.6. match Function Extension
Parameters:
1. ValueType (string)
2. ValueType (string conforming to
[I-D.draft-ietf-jsonpath-iregexp])
Result: LogicalType
The "match" function extension provides a way to check whether (the
entirety of, see Section 2.6.7 below) a given string matches a given
regular expression, which is in [I-D.draft-ietf-jsonpath-iregexp]
form.
$[?match(@.date, "1974-05-..")]
Its arguments are instances of ValueType. If the first argument is
not a string or the second argument is not a string conforming to
[I-D.draft-ietf-jsonpath-iregexp], the result is LogicalFalse.
Otherwise, the string that is the first argument is matched against
the iregexp contained in the string that is the second argument; the
result is LogicalTrue if the string matches the iregexp and
LogicalFalse otherwise.
2.6.7. search Function Extension
Parameters:
1. ValueType (string)
2. ValueType (string conforming to
[I-D.draft-ietf-jsonpath-iregexp])
Result: LogicalType
The "search" function extension provides a way to check whether a
given string contains a substring that matches a given regular
expression, which is in [I-D.draft-ietf-jsonpath-iregexp] form.
$[?search(@.author, "[BR]ob")]
Its arguments are instances of ValueType. If the first argument is
not a string or the second argument is not a string conforming to
[I-D.draft-ietf-jsonpath-iregexp], the result is LogicalFalse.
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Otherwise, the string that is the first argument is searched for at
least one substring that matches the iregexp contained in the string
that is the second argument; the result is LogicalTrue if such a
substring exists and LogicalFalse otherwise.
2.6.8. value Function Extension
Parameters:
1. NodesType
Result: ValueType
The "value" function extension provides a way to convert an instance
of NodesType to a value and make that available for further
processing in the filter expression:
$[?value(@..color) == "red"]
Its only argument is an instance of NodesType (possibly taken from a
filter-query as in the example above). The result is an instance of
ValueType.
* If the argument contains a single node, the result is the value of
the node.
* If the argument is Nothing or contains multiple nodes, the result
is Nothing.
Examples
+======================+=====================================+
| Query | Comment |
+======================+=====================================+
| $[?length(@) < 3] | well-typed |
+----------------------+-------------------------------------+
| $[?length(@.*) < 3] | not well-typed since @.* is a non- |
| | singular query |
+----------------------+-------------------------------------+
| $[?count(@.*) == 1] | well-typed |
+----------------------+-------------------------------------+
| $[?count(1) == 1] | not well-typed since 1 is not a |
| | query or function expression |
+----------------------+-------------------------------------+
| $[?count(foo(@.*)) | well-typed, where foo is a function |
| == 1] | extension with a parameter of type |
| | NodesType and result type NodesType |
+----------------------+-------------------------------------+
| $[?match(@.timezone, | well-typed |
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| 'Europe/.*')] | |
+----------------------+-------------------------------------+
| $[?match(@.timezone, | not well-typed as LogicalType may |
| 'Europe/.*') == | not be used in comparisons |
| true] | |
+----------------------+-------------------------------------+
| $[?value(@..color) | well-typed |
| == "red"] | |
+----------------------+-------------------------------------+
| $[?value(@..color)] | not well-typed as ValueType may not |
| | be used in a test expression |
+----------------------+-------------------------------------+
Table 15: Function expression examples
2.7. Segments
For each node in an input nodelist, segments apply one or more
selectors to the node and concatenate the results of each selector
into per-input-node nodelists, which are then concatenated in the
order of the input nodelist to form a single segment result nodelist.
It turns out that the more segments there are in a query, the greater
the depth in the input value of the nodes of the resultant nodelist:
* A query with N segments, where N >= 0, produces a nodelist
consisting of nodes at depth in the input value of N or greater.
* A query with N segments, where N >= 0, all of which are child
segments (Section 2.7.1), produces a nodelist consisting of nodes
precisely at depth N in the input value.
There are two kinds of segment: child segments and descendant
segments.
segment = child-segment / descendant-segment
The syntax and semantics of each kind of segment are defined below.
2.7.1. Child Segment
Syntax
The child segment consists of a non-empty, comma-separated sequence
of selectors enclosed in square brackets.
Shorthand notations are also provided for when there is a single
wildcard or name selector.
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child-segment = bracketed-selection /
("."
(wildcard-selector /
member-name-shorthand))
bracketed-selection = "[" S selector *(S "," S selector) S "]"
member-name-shorthand = name-first *name-char
name-first = ALPHA /
"_" /
%x80-10FFFF ; any non-ASCII Unicode character
name-char = DIGIT / name-first
DIGIT = %x30-39 ; 0-9
ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
.*, a child-segment directly built from a wildcard-selector, is
shorthand for [*].
.<member-name>, a child-segment built from a member-name-shorthand,
is shorthand for ['<member-name>']. Note that this can only be used
with member names that are composed of certain characters, as
specified in the ABNF rule member-name-shorthand. Thus, for example,
$.foo.bar is shorthand for $['foo']['bar'] (but not for
$['foo.bar']).
Semantics
A child segment contains a sequence of selectors, each of which
selects zero or more children of the input value.
Selectors of different kinds may be combined within a single child
segment.
For each node in the input nodelist, the resulting nodelist of a
child segment is the concatenation of the nodelists from each of its
selectors in the order that the selectors appear in the list. Note
that any node matched by more than one selector is kept as many times
in the nodelist.
Where a selector can produce a nodelist in more than one possible
order, each occurrence of the selector in the child segment may
evaluate to produce a nodelist in a distinct order.
So a child segment drills down one more level into the structure of
the input value.
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Examples
JSON:
["a", "b", "c", "d", "e", "f", "g"]
Queries:
+========+========+========+============+
| Query | Result | Result | Comment |
| | | Paths | |
+========+========+========+============+
| $[0, | "a" | $[0] | Indices |
| 3] | "d" | $[3] | |
+--------+--------+--------+------------+
| $[0:2, | "a" | $[0] | Slice and |
| 5] | "b" | $[1] | index |
| | "f" | $[5] | |
+--------+--------+--------+------------+
| $[0, | "a" | $[0] | Duplicated |
| 0] | "a" | $[0] | entries |
+--------+--------+--------+------------+
Table 16: Child segment examples
2.7.2. Descendant Segment
Syntax
The descendant segment consists of a double dot .. followed by a
child segment (using bracket notation).
Shortand notations are also provided that correspond to the shorthand
forms of the child segment.
descendant-segment = ".." (bracketed-selection /
wildcard-selector /
member-name-shorthand)
..*, the descendant-segment directly built from a wildcard-selector,
is shorthand for ..[*].
..<member-name>, a descendant-segment built from a member-name-
shorthand, is shorthand for ..['<member-name>']. As with the similar
shorthand of a child-segment, note that this can only be used with
member names that are composed of certain characters, as specified in
the ABNF rule member-name-shorthand.
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Note that .. on its own is not a valid segment.
Semantics
A descendant segment produces zero or more descendants of an input
value.
For each node in the input nodelist, a descendant selector visits the
input node and each of its descendants such that:
* nodes of any array are visited in array order, and
* nodes are visited before their descendants.
The order in which the children of an object are visited is not
stipulated, since JSON objects are unordered.
Suppose the descendant segment is of the form ..[<selectors>] (after
converting any shorthand form to bracket notation) and the nodes, in
the order visited, are D1, ..., Dn (where n >= 1). Note that D1 is
the input value.
For each i such that 1 <= i <= n, the nodelist Ri is defined to be a
result of applying the child segment [<selectors>] to the node Di.
For each node in the input nodelist, the result of the descendant
segment is the concatenation of R1, ..., Rn (in that order). These
results are then concatenated in input nodelist order to form the
result of the segment.
So a descendant segment drills down one or more levels into the
structure of each input value.
Examples
JSON:
{
"o": {"j": 1, "k": 2},
"a": [5, 3, [{"j": 4}, {"k": 6}]]
}
Queries:
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+==========+================+===================+===================+
| Query | Result | Result Paths | Comment |
+==========+================+===================+===================+
| $..j | 1 | $['o']['j'] | Object values |
| | 4 | $['a'][2][0]['j'] | |
+----------+----------------+-------------------+-------------------+
| $..j | 4 | $['a'][2][0]['j'] | Alternative |
| | 1 | $['o']['j'] | result |
+----------+----------------+-------------------+-------------------+
| $..[0] | 5 | $['a'][0] | Array values |
| | {"j": 4} | $['a'][2][0] | |
+----------+----------------+-------------------+-------------------+
| $..[*] | {"j": 1, | $['o'] | All values |
| $..* | "k" : 2} | $['a'] | |
| | [5, 3, | $['o']['j'] | |
| | [{"j": 4}, | $['o']['k'] | |
| | {"k": 6}]] | $['a'][0] | |
| | 1 | $['a'][1] | |
| | 2 | $['a'][2] | |
| | 5 | $['a'][2][0] | |
| | 3 | $['a'][2][1] | |
| | [{"j": 4}, | $['a'][2][0]['j'] | |
| | {"k": 6}] | $['a'][2][1]['k'] | |
| | {"j": 4} | | |
| | {"k": 6} | | |
| | 4 | | |
| | 6 | | |
+----------+----------------+-------------------+-------------------+
| $..o | {"j": 1, | $['o'] | Input value is |
| | "k": 2} | | visited |
+----------+----------------+-------------------+-------------------+
| $.o..[*, | 1 | $['o']['j'] | Non-deterministic |
| *] | 2 | $['o']['k'] | ordering |
| | 2 | $['o']['k'] | |
| | 1 | $['o']['j'] | |
+----------+----------------+-------------------+-------------------+
| $.a..[0, | 5 | $['a'][0] | Multiple segments |
| 1] | 3 | $['a'][1] | |
| | {"j": 4} | $['a'][2][0] | |
| | {"k": 6} | $['a'][2][1] | |
+----------+----------------+-------------------+-------------------+
Table 17: Descendant segment examples
Note: The ordering of the results for the $..[*] and $..* examples
above is not guaranteed, except that:
* {"j": 1, "k": 2} must appear before 1 and 2,
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* [5, 3, [{"j": 4}, {"k": 6}]] must appear before 5, 3, and [{"j":
4}, {"k": 6}],
* 5 must appear before 3 which must appear before [{"j": 4}, {"k":
6}],
* 5 and 3 must appear before {"j": 4}, 4, , {"k": 6}, and 6,
* [{"j": 4}, {"k": 6}] must appear before {"j": 4} and {"k": 6},
* {"j": 4} must appear before {"k": 6},
* {"k": 6} must appear before 4, and
* 4 must appear before 6.
The example above with the query $.o..[*, *] shows that a selector
may produce nodelists in distinct orders each time it appears in the
descendant segment.
The example above with the query $.a..[0, 1] shows that the child
segment [0, 1] is applied to each node in turn (rather than the nodes
being visited once per selector, which is the case for some JSONPath
implementations that do not conform to this specification).
2.8. Semantics of null
Note that JSON null is treated the same as any other JSON value: it
is not taken to mean "undefined" or "missing".
Examples
JSON:
{"a": null, "b": [null], "c": [{}], "null": 1}
Queries:
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+===================+========+===========+====================+
| Query | Result | Result | Comment |
| | | Paths | |
+===================+========+===========+====================+
| $.a | null | $['a'] | Object value |
+-------------------+--------+-----------+--------------------+
| $.a[0] | | | null used as array |
+-------------------+--------+-----------+--------------------+
| $.a.d | | | null used as |
| | | | object |
+-------------------+--------+-----------+--------------------+
| $.b[0] | null | $['b'][0] | Array value |
+-------------------+--------+-----------+--------------------+
| $.b[*] | null | $['b'][0] | Array value |
+-------------------+--------+-----------+--------------------+
| $.b[?@] | null | $['b'][0] | Existence |
+-------------------+--------+-----------+--------------------+
| $.b[?@==null] | null | $['b'][0] | Comparison |
+-------------------+--------+-----------+--------------------+
| $.c[?(@.d==null)] | | | Comparison with |
| | | | "missing" value |
+-------------------+--------+-----------+--------------------+
| $.null | 1 | $['null'] | Not JSON null at |
| | | | all, just a member |
| | | | name string |
+-------------------+--------+-----------+--------------------+
Table 18: Examples involving (or not involving) null
2.9. Normalized Paths
A Normalized Path is a canonical representation of the location of a
node in a value and uniquely identifies the node in the value.
Specifically, a Normalized Path is a JSONPath query with restricted
syntax (defined below), e.g., $['book'][3], which when applied to the
value results in a nodelist consisting of just the node identified by
the Normalized Path. Note that a Normalized Path represents the
identity of a node _in a specific value_. There is precisely one
Normalized Path identifying any particular node in a value.
A canonical representation of a nodelist is as a JSON arrays of
strings, where the strings are Normalized Paths.
Normalized Paths provide a predictable format that simplifies testing
and post-processing of nodelists, e.g., to remove duplicate nodes.
Normalized Paths are used in this document as result paths in
examples.
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Normalized Paths use the canonical bracket notation, rather than dot
notation.
Single quotes are used to delimit string member names. This reduces
the number of characters that need escaping when Normalized Paths
appear in double quote delimited strings, e.g., in JSON texts.
Certain characters are escaped, in one and only one way; all other
characters are unescaped.
Note: Normalized Paths are Singular Queries, but not all Singular
Queries are Normalized Paths. For example, $[-3] is a Singular
Query, but is not a Normalized Path. The Normalized Path equivalent
to $[-3] would have an index equal to the array length minus 3. (The
array length must be at least 3 if $[-3] is to identify a node.)
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normalized-path = root-identifier *(normal-index-segment)
normal-index-segment = "[" normal-selector "]"
normal-selector = normal-name-selector / normal-index-selector
normal-name-selector = %x27 *normal-single-quoted %x27 ; 'string'
normal-single-quoted = normal-unescaped /
ESC normal-escapable
normal-unescaped = ; omit %x0-1F control codes
%x20-26 /
; omit 0x27 '
%x28-5B /
; omit 0x5C \
%x5D-10FFFF
normal-escapable = %x62 / ; b BS backspace U+0008
%x66 / ; f FF form feed U+000C
%x6E / ; n LF line feed U+000A
%x72 / ; r CR carriage return U+000D
%x74 / ; t HT horizontal tab U+0009
"'" / ; ' apostrophe U+0027
"\" / ; \ backslash (reverse solidus) U+005C
(%x75 normal-hexchar)
; certain values u00xx U+00XX
normal-hexchar = "0" "0"
(
("0" %x30-37) / ; "00"-"07"
; omit U+0008-U+000A BS HT LF
("0" %x62) / ; "0b"
; omit U+000C-U+000D FF CR
("0" %x65-66) / ; "0e"-"0f"
("1" normal-HEXDIG)
)
normal-HEXDIG = DIGIT / %x61-66 ; "0"-"9", "a"-"f"
normal-index-selector = "0" / (DIGIT1 *DIGIT)
; non-negative decimal integer
Since there can only be one Normalized Path identifying a given node,
the syntax stipulates which characters are escaped and which are not.
So the definition of normal-hexchar is designed for hex escaping of
characters which are not straightforwardly-printable, for example
U+000B LINE TABULATION, but for which no standard JSON escape, such
as \n, is available.
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Examples
+=============+=================+==========================+
| Path | Normalized Path | Comment |
+=============+=================+==========================+
| $.a | $['a'] | Object value |
+-------------+-----------------+--------------------------+
| $[1] | $[1] | Array index |
+-------------+-----------------+--------------------------+
| $[-3] | $[2] | Negative array index for |
| | | an array of length 5 |
+-------------+-----------------+--------------------------+
| $.a.b[1:2] | $['a']['b'][1] | Nested structure |
+-------------+-----------------+--------------------------+
| $["\u000B"] | $['\u000b'] | Unicode escape |
+-------------+-----------------+--------------------------+
| $["\u0061"] | $['a'] | Unicode character |
+-------------+-----------------+--------------------------+
Table 19: Normalized Path examples
3. IANA Considerations
3.1. Registration of Media Type application/jsonpath
IANA is requested to register the following media type [RFC6838]:
Type name: application
Subtype name: jsonpath
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: binary (UTF-8)
Security considerations: See the Security Considerations section of
RFCXXXX.
Interoperability considerations: N/A
Published specification: RFCXXXX
Applications that use this media type: Applications that need to
convey queries in JSON data
Fragment identifier considerations: N/A
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Additional information: Deprecated alias names for this type: N/A
Magic number(s): N/A
File extension(s): N/A
Macintosh file type code(s): N/A
Person & email address to contact for further information:
iesg@ietf.org
Intended usage: COMMON
Restrictions on usage: N/A
Author: JSONPath WG
Change controller: IESG
Provisional registration? (standards tree only): no
3.2. Function Extensions
This specification defines a new "Function Extensions sub-registry"
in a new "JSONPath Parameters registry", with the policy "expert
review" (Section 4.5 of [BCP26]).
The experts are instructed to be frugal in the allocation of function
extension names that are suggestive of generally applicable
semantics, keeping them in reserve for functions that are likely to
enjoy wide use and can make good use of their conciseness. The
expert is also instructed to direct the registrant to provide a
specification (Section 4.6 of [BCP26]), but can make exceptions, for
instance when a specification is not available at the time of
registration but is likely forthcoming. If the expert becomes aware
of function extensions that are deployed and in use, they may also
initiate a registration on their own if they deem such a registration
can avert potential future collisions.
Each entry in the registry must include:
Function Name:
a lower case ASCII [STD80] string that starts with a letter and
can contain letters, digits and underscore characters afterwards
([a-z][_a-z0-9]*).
Brief description:
a brief description
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Parameters:
A comma-separated list of zero or more declared types, one for
each of the arguments expected for this function extension
Result:
The declared type of the result for this function extension
Change Controller:
(see Section 2.3 of [BCP26])
Reference:
a reference document that provides a description of the function
extension
Initial entries in this sub-registry are as listed in Table 20; the
Column "Change Controller" always has the value "IESG" and the column
"Reference" always has the value "Section 2.6 of RFCthis":
+===============+====================+============+=============+
| Function Name | Brief description | Parameters | Result |
+===============+====================+============+=============+
| length | length of array | ValueType | ValueType |
+---------------+--------------------+------------+-------------+
| count | size of nodelist | NodesType | ValueType |
+---------------+--------------------+------------+-------------+
| match | regular expression | ValueType, | LogicalType |
| | full match | ValueType | |
+---------------+--------------------+------------+-------------+
| search | regular expression | ValueType, | LogicalType |
| | substring match | ValueType | |
+---------------+--------------------+------------+-------------+
Table 20: Initial Entries in the Function Extensions Subregistry
4. Security Considerations
Security considerations for JSONPath can stem from
* attack vectors on JSONPath implementations,
* attack vectors on how JSONPath queries are formed, and
* the way JSONPath is used in security-relevant mechanisms.
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4.1. Attack Vectors on JSONPath Implementations
Historically, JSONPath has often been implemented by feeding parts of
the query to an underlying programming language engine, e.g.,
JavaScript's eval() function. This approach is well known to lead to
injection attacks and would require perfect input validation to
prevent these attacks (see Section 12 of [RFC8259] for similar
considerations for JSON itself). Instead, JSONPath implementations
need to implement the entire syntax of the query without relying on
the parsers of programming language engines.
Attacks on availability may attempt to trigger unusually expensive
runtime performance exhibited by certain implementations in certain
cases. (See Section 10 of [RFC8949] for issues in hash-table
implementations, and Section 8 of [I-D.draft-ietf-jsonpath-iregexp]
for performance issues in regular expression implementations.)
Implementers need to be aware that good average performance is not
sufficient as long as an attacker can choose to submit specially
crafted JSONPath queries or arguments that trigger surprisingly high,
possibly exponential, CPU usage or, for example via a naive recursive
implementation of the descendant segment, stack overflow.
Implementations need to have appropriate resource management to
mitigate these attacks.
4.2. Attack Vectors on How JSONPath Queries are Formed
JSONPath queries are often not static, but formed from variables that
provide index values, member names, or values to compare with in a
filter expression. These variables need to be translated into the
form they take in a JSONPath query, e.g., by escaping string
delimiters, or by only allowing specific constructs such as .name to
be formed when the given values allow that. Failure to perform these
translations correctly can lead to unexpected failures, which can
lead to Availability, Confidentiality, and Integrity breaches, in
particular if an adversary has control over the values (e.g., by
entering them into a Web form). The resulting class of attacks,
_injections_ (e.g., SQL injections), is consistently found among the
top causes of application security vulnerabilities and requires
particular attention.
4.3. Attacks on Security Mechanisms that Employ JSONPath
Where JSONPath is used as a part of a security mechanism, attackers
can attempt to provoke unexpected or unpredictable behavior, or take
advantage of differences in behavior between JSONPath
implementations.
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Unexpected or unpredictable behavior can arise from an argument with
certain constructs described as unpredictable by [RFC8259].
Predictable behavior can be expected, except in relation to the
ordering of objects, for any argument conforming with [RFC7493].
Other attacks can target the behavior of underlying technologies such
as UTF-8 (see Section 10 of [RFC3629]) and the Unicode character set.
5. References
5.1. Normative References
[BCP26] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[I-D.draft-ietf-jsonpath-iregexp]
Bormann, C. and T. Bray, "I-Regexp: An Interoperable
Regexp Format", Work in Progress, Internet-Draft, draft-
ietf-jsonpath-iregexp-03, 6 February 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-
jsonpath-iregexp-03>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/rfc/rfc3629>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/rfc/rfc5234>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/rfc/rfc6838>.
[RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
DOI 10.17487/RFC7493, March 2015,
<https://www.rfc-editor.org/rfc/rfc7493>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/rfc/rfc8259>.
[STD80] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969,
<https://www.rfc-editor.org/rfc/rfc20>.
[UNICODE] The Unicode Consortium, "The Unicode® Standard: Version
14.0 - Core Specification", September 2021,
<https://www.unicode.org/versions/Unicode14.0.0/
UnicodeStandard-14.0.pdf>.
5.2. Informative References
[BOOLEAN-LAWS]
"Boolean algebra laws", n.d.,
<https://en.wikipedia.org/wiki/Boolean_algebra#Laws>.
[E4X] ISO, "Information technology — ECMAScript for XML (E4X)
specification", ISO/IEC 22537:2006 , 2006.
[ECMA-262] Ecma International, "ECMAScript Language Specification,
Standard ECMA-262, Third Edition", December 1999,
<http://www.ecma-international.org/publications/files/
ECMA-ST-ARCH/ECMA-
262,%203rd%20edition,%20December%201999.pdf>.
[JSONPath-orig]
Gössner, S., "JSONPath — XPath for JSON", 21 February
2007, <https://goessner.net/articles/JsonPath/>.
[RFC6901] Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
"JavaScript Object Notation (JSON) Pointer", RFC 6901,
DOI 10.17487/RFC6901, April 2013,
<https://www.rfc-editor.org/rfc/rfc6901>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/rfc/rfc8949>.
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[SLICE] "Slice notation", n.d.,
<https://github.com/tc39/proposal-slice-notation>.
[XPath] Berglund, A., Ed., Chamberlin, D., Ed., Simeon, J., Ed.,
Robie, J., Ed., Fernandez, M., Ed., Kay, M., Ed., and S.
Boag, Ed., "XML Path Language (XPath) 2.0 (Second
Edition)", W3C REC REC-xpath20-20101214, W3C REC-
xpath20-20101214, 14 December 2010,
<https://www.w3.org/TR/2010/REC-xpath20-20101214/>.
Appendix A. Inspired by XPath
This appendix is informative.
At the time JSONPath was invented, XML was noted for the availability
of powerful tools to analyze, transform and selectively extract data
from XML documents. [XPath] is one of these tools.
In 2007, the need for something solving the same class of problems
for the emerging JSON community became apparent, specifically for:
* Finding data interactively and extracting them out of [RFC8259]
JSON values without special scripting.
* Specifying the relevant parts of the JSON data in a request by a
client, so the server can reduce the amount of data in its
response, minimizing bandwidth usage.
(Note that XPath has evolved since 2007, and recent versions even
nominally support operating inside JSON values. This appendix only
discusses the more widely used version of XPath that was available in
2007.)
JSONPath picks up the overall feeling of XPath, but maps the concepts
to syntax (and partially semantics) that would be familiar to someone
using JSON in a dynamic language.
E.g., in popular dynamic programming languages such as JavaScript,
Python and PHP, the semantics of the XPath expression
/store/book[1]/title
can be realized in the expression
x.store.book[0].title
or, in bracket notation,
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x['store']['book'][0]['title']
with the variable x holding the argument.
The JSONPath language was designed to:
* be naturally based on those language characteristics;
* cover only the most essential parts of XPath 1.0;
* be lightweight in code size and memory consumption;
* be runtime efficient.
A.1. JSONPath and XPath
JSONPath expressions apply to JSON values in the same way as XPath
expressions are used in combination with an XML document. JSONPath
uses $ to refer to the root node of the argument, similar to XPath's
/ at the front.
JSONPath expressions move further down the hierarchy using _dot
notation_ ($.store.book[0].title) or the _bracket notation_
($['store']['book'][0]['title']), a lightweight/limited, and a more
heavyweight syntax replacing XPath's / within query expressions.
Both JSONPath and XPath use * for a wildcard. The descendant
operators, starting with .., borrowed from [E4X], are similar to
XPath's //. The array slicing construct [start:end:step] is unique to
JSONPath, inspired by [SLICE] from ECMASCRIPT 4.
Filter expressions are supported via the syntax ?<logical-expr> as in
$.store.book[?@.price < 10].title
Table 21 extends Table 1 by providing a comparison with similar XPath
concepts.
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+==========+==================+===================================+
| XPath | JSONPath | Description |
+==========+==================+===================================+
| / | $ | the root XML element |
+----------+------------------+-----------------------------------+
| . | @ | the current XML element |
+----------+------------------+-----------------------------------+
| / | . or [] | child operator |
+----------+------------------+-----------------------------------+
| .. | n/a | parent operator |
+----------+------------------+-----------------------------------+
| // | ..name, | descendants (JSONPath borrows |
| | ..[index], ..*, | this syntax from E4X) |
| | or ..[*] | |
+----------+------------------+-----------------------------------+
| * | * | wildcard: All XML elements |
| | | regardless of their names |
+----------+------------------+-----------------------------------+
| @ | n/a | attribute access: JSON values do |
| | | not have attributes |
+----------+------------------+-----------------------------------+
| [] | [] | subscript operator used to |
| | | iterate over XML element |
| | | collections and for predicates |
+----------+------------------+-----------------------------------+
| | | [,] | Union operator (results in a |
| | | combination of node sets); called |
| | | list operator in JSONPath, allows |
| | | combining member names, array |
| | | indices, and slices |
+----------+------------------+-----------------------------------+
| n/a | [start:end:step] | array slice operator borrowed |
| | | from ES4 |
+----------+------------------+-----------------------------------+
| [] | ? | applies a filter (script) |
| | | expression |
+----------+------------------+-----------------------------------+
| seamless | n/a | expression engine |
+----------+------------------+-----------------------------------+
| () | n/a | grouping |
+----------+------------------+-----------------------------------+
Table 21: XPath syntax compared to JSONPath
For further illustration, Table 22 shows some XPath expressions and
their JSONPath equivalents.
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+======================+========================+===================+
| XPath | JSONPath | Result |
+======================+========================+===================+
| /store/book/author | $.store.book[*].author | the authors of |
| | | all books in |
| | | the store |
+----------------------+------------------------+-------------------+
| //author | $..author | all authors |
+----------------------+------------------------+-------------------+
| /store/* | $.store.* | all things in |
| | | store, which |
| | | are some books |
| | | and a red |
| | | bicycle |
+----------------------+------------------------+-------------------+
| /store//price | $.store..price | the prices of |
| | | everything in |
| | | the store |
+----------------------+------------------------+-------------------+
| //book[3] | $..book[2] | the third book |
+----------------------+------------------------+-------------------+
| //book[last()] | $..book[-1] | the last book |
| | | in order |
+----------------------+------------------------+-------------------+
| //book[position()<3] | $..book[0,1] | the first two |
| | $..book[:2] | books |
+----------------------+------------------------+-------------------+
| //book[isbn] | $..book[?@.isbn] | filter all |
| | | books with isbn |
| | | number |
+----------------------+------------------------+-------------------+
| //book[price<10] | $..book[?@.price<10] | filter all |
| | | books cheaper |
| | | than 10 |
+----------------------+------------------------+-------------------+
| //* | $..* | all elements in |
| | | XML document; |
| | | all member |
| | | values and |
| | | array elements |
| | | contained in |
| | | input value |
+----------------------+------------------------+-------------------+
Table 22: Example XPath expressions and their JSONPath equivalents
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XPath has a lot more functionality (location paths in unabbreviated
syntax, operators and functions) than listed in this comparison.
Moreover, there are significant differences in how the subscript
operator works in XPath and JSONPath:
* Square brackets in XPath expressions always operate on the _node
set_ resulting from the previous path fragment. Indices always
start at 1.
* With JSONPath, square brackets operate on each of the nodes in the
_nodelist_ resulting from the previous query segment. Array
indices always start at 0.
Appendix B. JSON Pointer
This appendix is informative.
JSONPath is not intended as a replacement for, but as a more powerful
companion to, JSON Pointer [RFC6901]. The purposes of the two
standards are different.
JSON Pointer is for identifying a single value within a JSON value
whose structure is known.
JSONPath can identify a single value within a JSON value, for example
by using a Normalized Path. But JSONPath is also a query syntax that
can be used to search for and extract multiple values from JSON
values whose structure is known only in a general way.
A Normalized JSONPath can be converted into a JSON Pointer by
converting the syntax, without knowledge of any JSON value. The
inverse is not generally true: a numeric reference token (path
component) in a JSON Pointer may identify a member value of an object
or an element of an array. For conversion to a JSONPath query,
knowledge of the structure of the JSON value is needed to distinguish
these cases.
Acknowledgements
This document is based on Stefan Gössner's original online article
defining JSONPath [JSONPath-orig].
The books example was taken from http://coli.lili.uni-
bielefeld.de/~andreas/Seminare/sommer02/books.xml — a dead link now.
Contributors
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Marko Mikulicic
InfluxData, Inc.
Pisa
Italy
Email: mmikulicic@gmail.com
Edward Surov
TheSoul Publishing Ltd.
Limassol
Cyprus
Email: esurov.tsp@gmail.com
Greg Dennis
Auckland
New Zealand
Email: gregsdennis@yahoo.com
URI: https://github.com/gregsdennis
Authors' Addresses
Stefan Gössner (editor)
Fachhochschule Dortmund
Sonnenstraße 96
D-44139 Dortmund
Germany
Email: stefan.goessner@fh-dortmund.de
Glyn Normington (editor)
Winchester
United Kingdom
Email: glyn.normington@gmail.com
Carsten Bormann (editor)
Universität Bremen TZI
Postfach 330440
D-28359 Bremen
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
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