JSONPath: Query expressions for JSON
draft-ietf-jsonpath-base-07
The information below is for an old version of the document.
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|---|---|---|---|
| Authors | Stefan Gössner , Glyn Normington , Carsten Bormann | ||
| Last updated | 2022-10-17 | ||
| Replaces | draft-normington-jsonpath | ||
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draft-ietf-jsonpath-base-07
JSONPath WG S. Gössner, Ed.
Internet-Draft Fachhochschule Dortmund
Intended status: Standards Track G. Normington, Ed.
Expires: 20 April 2023
C. Bormann, Ed.
Universität Bremen TZI
17 October 2022
JSONPath: Query expressions for JSON
draft-ietf-jsonpath-base-07
Abstract
JSONPath defines a string syntax for selecting and extracting values
within a JSON (RFC 8259) 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 20 April 2023.
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Copyright Notice
Copyright (c) 2022 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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. History . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Overview of JSONPath Expressions . . . . . . . . . . . . 6
2. JSONPath Examples . . . . . . . . . . . . . . . . . . . . . . 8
3. JSONPath Syntax and Semantics . . . . . . . . . . . . . . . . 9
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3. Semantics . . . . . . . . . . . . . . . . . . . . . . . . 11
3.4. Root Identifier . . . . . . . . . . . . . . . . . . . . . 12
3.5. Selectors . . . . . . . . . . . . . . . . . . . . . . . . 13
3.5.1. Name Selector . . . . . . . . . . . . . . . . . . . . 13
3.5.2. Wildcard Selector . . . . . . . . . . . . . . . . . . 17
3.5.3. Index selector . . . . . . . . . . . . . . . . . . . 18
3.5.4. Array Slice selector . . . . . . . . . . . . . . . . 19
3.5.5. Filter selector . . . . . . . . . . . . . . . . . . . 23
3.6. Segments . . . . . . . . . . . . . . . . . . . . . . . . 31
3.6.1. Child Segment . . . . . . . . . . . . . . . . . . . . 31
3.6.2. Descendant Segment . . . . . . . . . . . . . . . . . 32
3.7. Semantics of null . . . . . . . . . . . . . . . . . . . . 34
3.8. Normalized Paths . . . . . . . . . . . . . . . . . . . . 35
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
4.1. Registration of Media Type application/jsonpath . . . . . 37
5. Security Considerations . . . . . . . . . . . . . . . . . . . 38
5.1. Attack vectors on JSONPath Implementations . . . . . . . 38
5.2. Attacks on Security Mechanisms that Employ JSONPath . . . 38
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.1. Normative References . . . . . . . . . . . . . . . . . . 39
6.2. Informative References . . . . . . . . . . . . . . . . . 40
Appendix A. Inspired by XPath . . . . . . . . . . . . . . . . . 40
A.1. JSONPath and XPath . . . . . . . . . . . . . . . . . . . 42
Appendix B. JSON Pointer . . . . . . . . . . . . . . . . . . . . 45
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Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 45
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46
1. Introduction
JSON [RFC8259] is a popular representation format for structured data
values. JSONPath defines a string syntax for identifying values
within 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 the types as
in Section 1 of [RFC8259]. 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 specification are defined below.
Value: As per [RFC8259], a structure complying to the generic data
model of JSON, i.e., composed of components 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.
Type: As per [RFC8259], one of the six JSON types (strings, numbers,
booleans, null, objects, arrays).
Member: A name/value pair in an object. (Not itself a value.)
Name: The name in a name/value pair constituting a member. (Also
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known as "key", "tag", or "label".) This is also used in
[RFC8259], but that specification does not formally define it. It
is included here for completeness.
Element: A value in an array. (Not to be confused with XML
element.)
Index: A non-negative integer that identifies a specific element in
an array. Note that the term _indexing_ is also used for
accessing elements using negative integers (Section "Semantics"),
and for accessing member values in an object using their member
name.
Query: Short name for JSONPath expression.
Argument: Short name for the value a JSONPath expression is applied
to.
Node: The pair of a value along with its location within the
argument.
Root Node: The unique node whose value is the entire argument.
Children (of a node): If the node is an array, each of its elements,
or if the node is an object, each of its member values (but not
its member names). 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. The output of applying a query to an
argument is manifested as a list of nodes. While this list can be
represented in JSON, e.g. as an array, the nodelist is an abstract
concept unrelated to JSON values.
Normalized Path: A simple form of JSONPath expression that
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identifies a node 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 values of type string are sequences of Unicode
scalar values.
Singular Path: A JSONPath expression built from segments which each
produce at most one node.
Selector: A single item within a segment that takes the input value
and produces a nodelist consisting of child nodes of the input
value.
For the purposes of this specification, a value as defined by
[RFC8259] is also viewed as a tree of nodes. Each node, in turn,
holds a value. Further nodes within each value are the elements of
arrays and the member values of objects and are themselves values.
(The type of the value held by a node may also be referred to as the
type of the node.)
A query is applied to an argument, and the output is a nodelist.
1.2. History
This document picks up Stefan Gössner's popular JSONPath proposal
dated 2007-02-21 [JSONPath-orig] and provides a normative definition
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 on platforms such as PHP and JavaScript, so instead
of defining its own expression language like XPath did, JSONPath
delegated this to the expression language of the platform. While the
languages in which JSONPath is used do have significant
commonalities, over time this caused non-portability of JSONPath
expressions between the ensuing platform-specific dialects.
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The present specification intends to remove platform dependencies and
serve as a common JSONPath specification that can be used across
platforms. Obviously, this means that backwards compatibility could
not always be achieved; a design principle of this specification 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.
1.3. Overview of JSONPath Expressions
JSONPath expressions are applied to a JSON value, the _argument_.
Within the JSONPath expression, the abstract name $ is used to refer
to the _root node_ of the argument, i.e., to the argument as a whole.
JSONPath expressions use the _bracket notation_, for example:
$['store']['book'][0]['title']
or the more compact _dot notation_, for example:
$.store.book[0].title
to build paths that are input to a JSONPath implementation. A single
path may use a combination of bracket and dot notations.
Dot notation is merely a shorthand way of writing certain bracket
notations.
A wildcard * (Section 3.5.2) in the expression [*] selects all
children of an object or an array and in the expression ..[*] selects
all descendants of an object or an array.
An array slice start:end:step (Section 3.5.4) selects a series of
elements from an array, giving a start position, an end position, and
possibly a step value that moves the position from the start to the
end.
Filter expressions ?<boolean expr> select certain children of an
object or array as in
$.store.book[?@.price < 10].title
Table 1 provides a quick overview of the JSONPath syntax elements.
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+=================+========================================+
| JSONPath | Description |
+=================+========================================+
| $ | root node identifier (Section 3.4) |
+-----------------+----------------------------------------+
| @ | current node identifier |
| | (Section 3.5.5) (valid only within |
| | filter selectors) |
+-----------------+----------------------------------------+
| [<selectors>] | child segment (Section 3.6.1) selects |
| | zero or more children of JSON objects |
| | and arrays; contains one or more |
| | selectors, separated by commas |
+-----------------+----------------------------------------+
| ..[<selectors>] | descendant segment (Section 3.6.2): |
| | selects zero or more descendants of |
| | JSON objects and arrays; contains one |
| | or more selectors, separated by commas |
+-----------------+----------------------------------------+
| 'name' | name selector (Section 3.5.1): selects |
| | a named child of an object |
+-----------------+----------------------------------------+
| * | wildcard selector (Section 3.5.1): |
| | selects all children of an array or |
| | object |
+-----------------+----------------------------------------+
| 3 | index selector (Section 3.5.3): |
| | selects an indexed child of an array |
| | (from 0) |
+-----------------+----------------------------------------+
| 0:100:5 | array slice selector (Section 3.5.4): |
| | start:end:step for arrays |
+-----------------+----------------------------------------+
| ?<expr> | filter selector (Section 3.5.5): |
| | selects particular children using a |
| | boolean expression |
+-----------------+----------------------------------------+
| .name | shorthand for ['name'] |
+-----------------+----------------------------------------+
| .* | shorthand for [*] |
+-----------------+----------------------------------------+
| ..name | shorthand for ..['name'] |
+-----------------+----------------------------------------+
| ..* | shorthand for ..[*] |
+-----------------+----------------------------------------+
Table 1: Overview of JSONPath
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2. JSONPath Examples
This section provides some more examples for JSONPath expressions.
The examples are based on the simple JSON value shown in Figure 1,
representing a bookstore (that also has bicycles).
{ "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": 19.95
}
}
}
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)] | filter all books with ISBN number |
+------------------------+---------------------------------------+
| $..book[?(@.price<10)] | filter all books cheaper than 10 |
+------------------------+---------------------------------------+
| $..* | all member values and array elements |
| | contained in input value |
+------------------------+---------------------------------------+
Table 2: Example JSONPath expressions and their intended
results when applied to the example JSON value
3. JSONPath Syntax and Semantics
3.1. Overview
A JSONPath query is a string which selects zero or more nodes of a
JSON value.
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.
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To be valid, 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]).
To be valid, strings on the right-hand side of the =~ regex matching
operator need to conform to [I-D.draft-ietf-jsonpath-iregexp].
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 the present specification. However, the implementation MUST NOT
silently malfunction. Specifically, if a valid JSONPath query is
evaluated against a structured value whose size doesn't 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.)
The JSON value the JSONPath query is applied to is, by definition, a
valid JSON value. 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 specification. 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, for instance as they
may cause unpredictable behavior. The present specification does not
attempt to define predictable behavior for JSONPath queries in these
situations. (Note that another warning about interoperability, in
Section 2 of [RFC8259], at the time of writing is generally
considered to be overtaken by events and causes no issues with the
present specification.)
Specifically, the "Semantics" subsections of Sections 3.5.1, 3.5.2,
3.5.5, and 3.6.2 describe behavior that turns 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 (3.5.1) and comparing
strings (Section "Comparisons" in Section 3.5.5) assume these strings
are sequences of Unicode scalar values, turning unpredictable if they
aren't (Section 8.2 of [RFC8259]).
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3.2. 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_.
json-path = root-identifier *(S (child-segment /
descendant-segment))
The syntax and semantics of each segment are defined below.
3.3. Semantics
In this specification, the semantics of a JSONPath query define the
required results and do not prescribe the internal workings of an
implementation.
The semantics are that a valid query is executed against a value, the
_argument_, and produces 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_, i.e., a
sequence of zero or more nodes.
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 the
API must be capable of presenting an empty nodelist as the result of
the query.
A segment performs its function on each of the nodes in its input
nodelist, during such a function execution, such a node is referred
to as the "current node". Each of these function executions produces
a nodelist, which are then concatenated 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 indexing beyond the end of an array, simply result
in fewer nodes being selected.
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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.
Next, .a selects from any input node of type object 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 an input node of type array all its elements
(if the input node were of type object, 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 input node of type object 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.
As a consequence of this approach, if any of the segments produces an
empty nodelist, then the whole query produces an empty nodelist.
In what follows, the semantics of each segment are defined for each
type of node. It will turn out that the more segments there are in a
query, the greater the depth of the nodes of the resultant nodelist
in the input value:
* 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 3.6.1), produces a nodelist consisting of nodes
precisely at depth N in the input value.
3.4. Root Identifier
Syntax
Every JSONPath query MUST begin with the root identifier $.
root-identifier = "$"
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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
3.5. Selectors
Selectors appear only inside child segments (Section 3.6.1) and
descendant segments (Section 3.6.2).
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 or arrays, or children of either objects or arrays.
selector = ( name-selector /
index-selector /
slice-selector /
filter-selector
)
The syntax and semantics of each kind of selector are defined below.
3.5.1. Name Selector
Syntax
A name selector '<name>' selects at most one object member value.
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Applying the name-selector to an object value in its input nodelist,
its string is required to match the corresponding member value. In
contrast to JSON, the JSONPath syntax allows strings to be enclosed
in _single_ or _double_ quotes.
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 / ; s. RFC 8259
%x23-26 / ; omit "
%x28-5B / ; omit '
%x5D-10FFFF ; omit \
escapable = ( %x62 / %x66 / %x6E / %x72 / %x74 / ; \b \f \n \r \t
; b / ; BS backspace U+0008
; t / ; HT horizontal tab U+0009
; n / ; LF line feed U+000A
; f / ; FF form feed U+000C
; r / ; CR carriage return U+000D
"/" / ; / 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"
; Task from 2021-06-15 interim: update ABNF later
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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").
Semantics
A name-selector string MUST be converted to a member name 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
The name selector applied to an object selects the node of the
corresponding member value from it, if and only if that object has a
member with that name. Nothing is selected from a value that is not
a object.
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Note that processing the name selector potentially requires matching
strings against strings, with those strings coming from the JSONPath
and from member names and string values in the JSON to which it 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
string from the JSONPath or from the JSON prior to comparison.
Examples
JSON:
{
"o": {"j j": {"k.k": 3}},
"'": {"@": 2}
}
Queries:
+===================+========+======================+=============+
| 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 |
+-------------------+--------+----------------------+-------------+
| $.j | {"k": | $['j'] | Named value |
| | 3} | | of an |
| | | | object |
+-------------------+--------+----------------------+-------------+
| $.j.k | 3 | $['j']['k'] | Named value |
| | | | in nested |
| | | | object |
+-------------------+--------+----------------------+-------------+
Table 5: Name selector examples
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3.5.2. Wildcard Selector
Syntax
The wildcard selector consists of an asterisk.
wildcard = "*"
Semantics
A wildcard selector selects the nodes of all children of an object or
array.
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.
+========+==================+==============+=============+
| Query | Result | Result Paths | Comment |
+========+==================+==============+=============+
| $[*] | {"j": 1, "k": 2} | $['o'] | Object |
| | [5, 3] | $['a'] | values |
+--------+------------------+--------------+-------------+
| $.o[*] | 1 | $['o']['j'] | Object |
| | 2 | $['o']['k'] | values |
+--------+------------------+--------------+-------------+
| $.o[*] | 2 | $['o']['k'] | Alternative |
| | 1 | $['o']['j'] | result |
+--------+------------------+--------------+-------------+
| $.a[*] | 5 | $['a'][0] | Array |
| | 3 | $['a'][1] | members |
+--------+------------------+--------------+-------------+
Table 6: Wildcard selector examples
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3.5.3. 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").
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
The 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 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.
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+=======+========+==============+===============================+
| Query | Result | Result Paths | Comment |
+=======+========+==============+===============================+
| $[1] | "b" | $[1] | Member of array |
+-------+--------+--------------+-------------------------------+
| $[-2] | "a" | $[0] | Member of array, from the end |
+-------+--------+--------------+-------------------------------+
Table 7: Index selector examples
3.5.4. Array Slice selector
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.
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
RS = 1*B ; required blank space
The slice selector consists of three optional decimal integers
separated by colons.
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 non-normative.
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.
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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.
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.
Detailed 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. len is
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:
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FUNCTION Normalize(i, len):
IF i >= 0 THEN
RETURN i
ELSE
RETURN len + i
END IF
The result of the array indexing expression i applied to an array of
length len is defined to be the result of the array slicing
expression i:Normalize(i, len)+1:1.
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, the a(i) construct
expresses the 0-based indexing operation on the underlying array.
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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.
To be valid, the slice expression parameters MUST be in the I-JSON
range of exact values, see Section 3.1.
Examples
JSON:
["a", "b", "c", "d", "e", "f", "g"]
Queries:
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+===========+========+========+==========+
| 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
3.5.5. Filter selector
Syntax
The filter selector has the form ?<expr>. It works via iterating
over structured values, i.e. arrays and objects.
filter-selector = "?" S boolean-expr
During the iteration process each array element or object member is
visited and its value -- accessible via symbol @ -- or one of its
descendants -- uniquely defined by a relative path -- is tested
against a boolean expression boolean-expr.
The current item is selected if and only if the boolean expression
yields true.
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boolean-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 = exist-expr /
paren-expr /
relation-expr
exist-expr = [logical-not-op S] singular-path ; path existence or non-existence
Paths in filter expressions are Singular Paths, each of which selects
at most one node.
singular-path = rel-singular-path / abs-singular-path
rel-singular-path = "@" *(S (name-segment / index-segment))
abs-singular-path = root-identifier *(S (name-segment / index-segment))
name-segment = "[" name-selector "]" / dot-member-name-shorthand
index-segment = "[" index-selector "]"
Parentheses can be used with boolean-expr for grouping. So filter
selection syntax in the original proposal ?(<expr>) is naturally
contained in the current lean syntax ?<expr> as a special case.
paren-expr = [logical-not-op S] "(" S boolean-expr S ")"
; parenthesized expression
logical-not-op = "!" ; logical NOT operator
relation-expr = comp-expr / ; comparison test
regex-expr ; regular expression test
Comparisons are restricted to Singular Path values and primitive
values (that is, numbers, strings, true, false, and null).
comp-expr = comparable S comp-op S comparable
comparable = number / string-literal / ; primitive ...
true / false / null / ; values only
singular-path ; Singular Path value
comp-op = "==" / "!=" / ; comparison ...
"<" / ">" / ; operators
"<=" / ">="
Alphabetic characters in ABNF are case-insensitive, so "e" can be
either "e" or "E".
true, false, and null are lower-case only (case-sensitive).
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number = int [ 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 syntax of regular expressions in the string-literals on the
right-hand side of =~ is as defined in
[I-D.draft-ietf-jsonpath-iregexp].
regex-expr = (singular-path / string-literal) S regex-op S regex
regex-op = "=~" ; regular expression match
regex = string-literal ; I-Regexp
The following table lists filter expression operators in order of
precedence from highest (binds most tightly) to lowest (binds least
tightly).
+============+===========+===========+
| Precedence | Operator | Syntax |
| | type | |
+============+===========+===========+
| 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 other value
types, it will select nothing.
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A relative path, beginning with @, refers to the current array
element or member value as the filter selector iterates over the
array or object.
Existence Tests
A singular path by itself in a Boolean context is an existence test
which yields true if the path selects a node and yields false if the
path does not select a node. This existence test -- as an exception
to the general rule -- also works with nodes with structured values.
To test the value of a node selected by a path, an explicit
comparison is necessary. For example, to test whether the node
selected by the path @.foo has the value null, use @.foo == null (see
Section 3.7) rather than the negated existence test !@.foo (which
yields false if @.foo selects a node, regardless of the node's
value).
Comparisons
The comparison operators == and < are defined first and then these
are used to define !=, <=, >, and >=.
When a path resulting in an empty nodelist appears on either side of
a comparison:
* a comparison using the operator == yields true if and only if the
comparison is between two paths each of which result in an empty
nodelist.
* a comparison using the operator < yields false.
When any path on either side of a comparison results in a nodelist
consisting of a single node, each such path 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:
- values of the same primitive type (numbers, strings, booleans,
and null) which are equal,
- 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:
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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 of the same type which are both
numbers or both strings and which satisfy the comparison:
- 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.
Regular Expressions
A regular-expression test yields true if and only if the value on the
left-hand side of =~ is a string value and it matches the regular
expression on the right-hand side according to the semantics of
[I-D.draft-ietf-jsonpath-iregexp].
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The semantics of regular expressions are as defined in
[I-D.draft-ietf-jsonpath-iregexp].
Boolean Operators
The logical AND, OR, and NOT operators have the normal semantics of
Boolean algebra and obey its laws (see, for example, [BOOLEAN-LAWS]).
Examples
JSON:
{
"obj": {"x": "y"},
"arr": [2, 3]
}
+========================+========+============================+
| 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 |
+------------------------+--------+----------------------------+
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| $.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 |
+------------------------+--------+----------------------------+
| $.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
JSON:
{
"a": [3, 5, 1, 2, 4, 6, {"b": "j"}, {"b": "k"}],
"o": {"p": 1, "q": 2, "r": 3, "s": 5, "t": {"u": 6}}
}
Queries:
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+=============+========+=============+=============+
| Query | Result | Result | Comment |
| | | Paths | |
+=============+========+=============+=============+
| $.a[?@>3.5] | 5 | $['a'][1] | Array value |
| | 4 | $['a'][4] | comparison |
| | 6 | $['a'][5] | |
+-------------+--------+-------------+-------------+
| $.a[?@.b] | {"b": | $['a'][6] | Array value |
| | "j"} | $['a'][7] | existence |
| | {"b": | | |
| | "k"} | | |
+-------------+--------+-------------+-------------+
| $.a[?@<2 || | 1 | $['a'][2] | Array value |
| @.b == "k"] | {"b": | $['a'][7] | logical OR |
| | "k"} | | |
+-------------+--------+-------------+-------------+
| $.a[?@.b =~ | {"b": | $['a'][6] | Array value |
| "i.*"] | "j"} | $['a'][7] | regular |
| | {"b": | | expression |
| | "k"} | | |
+-------------+--------+-------------+-------------+
| $.o[?@>1 && | 2 | $['o']['q'] | Object |
| @<4] | 3 | $['o']['r'] | value |
| | | | logical AND |
+-------------+--------+-------------+-------------+
| $.o[?@>1 && | 3 | $['o']['r'] | Alternative |
| @<4] | 2 | $['o']['q'] | result |
+-------------+--------+-------------+-------------+
| $.o[?@.u || | {"u": | $['o']['t'] | Object |
| @.x] | 6} | | value |
| | | | logical OR |
+-------------+--------+-------------+-------------+
| $.a[?(@.b | 3 | $['a'][0] | Comparison |
| == $.x)] | 5 | $['a'][1] | of paths |
| | 1 | $['a'][2] | with no |
| | 2 | $['a'][3] | values |
| | 4 | $['a'][4] | |
| | 6 | | |
+-------------+--------+-------------+-------------+
| $[?(@ == | | | Comparison |
| @)] | | | of |
| | | | structured |
| | | | values |
+-------------+--------+-------------+-------------+
Table 12: Filter selector examples
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3.6. Segments
Segments apply one or more selectors to an input value and
concatenate the results into a single nodelist.
The syntax and semantics of each segment are defined below.
3.6.1. Child Segment
Syntax
The child segment consists of a non-empty, comma-delimited sequence
of selectors enclosed in square brackets.
Shorthand notations are also provided for when there is a single
wildcard or name selector.
child-segment = (child-longhand /
dot-wildcard-shorthand /
dot-member-name-shorthand)
child-longhand = "[" S selector 1*(S "," S selector) S "]"
dot-wildcard-shorthand = "." wildcard
dot-member-name-shorthand = "." dot-member-name
dot-member-name = 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
The dot-wildcard-shorthand is shorthand for [*].
A dot-member-name-shorthand of the form .<member-name> is shorthand
for ['<member-name>'], but can only be used with member names that
are composed of certain characters.
Semantics
A child segment contains a comma-delimited 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.
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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.
3.6.2. Descendant Segment
Syntax
The descendant segment consists of a double dot .. followed by a
child segment (descendant-segment).
Shortand notations are also provided that correspond to the shorthand
forms of the child segment.
descendant-segment = (descendant-child /
descendant-wildcard-shorthand /
descendant-member-name-shorthand)
descendant-child = ".." child-segment
descendant-wildcard-shorthand = ".." wildcard
descendant-member-name-shorthand = ".." dot-member-name
The descendant-wildcard-shorthand is shorthand for ..[*].
A descendant-member-name-shorthand of the form ..<member-name> is
shorthand for ..['<member-name>'].
Note that .. on its own is not a valid segment.
Semantics
A descendant segment produces zero or more descendants of the input
value.
A nodelist enumerating the descendants is known as a _descendant
nodelist_ when:
* nodes of any array appear in array order,
* nodes appear immediately before all their descendants.
This definition does not stipulate the order in which the children of
an object appear, since JSON objects are unordered.
The resultant nodelist of a descendant segment of the form
..[<selectors>] is the result of applying the child segment
[<selectors>] to a descendant nodelist.
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Examples
JSON:
{
"o": {"j": 1, "k": 2},
"a": [5, 3, [{"j": 4}]]
}
Queries:
+========+====================+===================+=============+
| Query | Result | Result Paths | Comment |
+========+====================+===================+=============+
| $..j | 1 | $['o']['j'] | Object |
| | 4 | $['a'][2][0]['j'] | values |
+--------+--------------------+-------------------+-------------+
| $..j | 4 | $['a'][2][0]['j'] | Alternative |
| | 1 | $['o']['j'] | result |
+--------+--------------------+-------------------+-------------+
| $..[0] | 5 | $['a'][0] | Array |
| | {"j": 4} | $['a'][2][0] | values |
+--------+--------------------+-------------------+-------------+
| $..[0] | {"j": 4} | $['a'][2][0] | Alternative |
| | 5 | $['a'][0] | result |
+--------+--------------------+-------------------+-------------+
| $..[*] | {"j": 1, "k" : 2} | $['o'] | All values |
| $..* | [5, 3, [{"j": 4}]] | $['a'] | |
| | 1 | $['o']['j'] | |
| | 2 | $['o']['k'] | |
| | 5 | $['a'][0] | |
| | 3 | $['a'][1] | |
| | [{"j": 4}] | $['a'][2] | |
| | {"j": 4} | $['a'][2][0] | |
| | 4 | $['a'][2][0]['j'] | |
+--------+--------------------+-------------------+-------------+
Table 13: 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,
* [5, 3, [{"j": 4}]] must appear before 5, 3, and [{"j": 4}],
* 5 must appear before 3 which must appear before [{"j": 4}],
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* 5 and 3 must appear before {"j": 4} and 4,
* [{"j": 4}] must appear before {"j": 4}, and
* {"j": 4} must appear before 4.
3.7. 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:
+===================+========+===========+====================+
| 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 string |
| | | | as object key |
+-------------------+--------+-----------+--------------------+
Table 14: Examples involving (or not involving) null
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3.8. Normalized Paths
A Normalized Path is a JSONPath with restricted syntax that
identifies a node by providing a query that results in exactly that
node. For example, the JSONPath expression $.book[?(@.price<10)]
could select two values with Normalized Paths $['book'][3] and
$['book'][5]. For a given JSON value, there is a one to one
correspondence between the value's nodes and the Normalized Paths
that identify these nodes.
A JSONPath implementation may output Normalized Paths instead of, or
in addition to, the values identified by these paths.
Since bracket notation is more general than dot notation, it is used
to construct Normalized Paths. Single quotes are used to delimit
string member names. This reduces the number of characters that need
escaping when Normalized Paths appear as strings (which are delimited
with double quotes) in JSON texts.
Certain characters are escaped, in one and only one way; all other
characters are unescaped.
Normalized Paths are Singular Paths. Not all Singular Paths are
Normalized Paths: $[-3], for example, is a Singular Path, but not a
Normalized Path.
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normalized-path = root-identifier *(normal-index-segment)
normal-index-segment = "[" (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 = %x20-26 / ; omit control codes
%x28-5B / ; omit '
%x5D-10FFFF ; omit \
normal-escapable = ( %x62 / %x66 / %x6E / %x72 / %x74 / ; \b \f \n \r \t
; b / ; BS backspace U+0008
; t / ; HT horizontal tab U+0009
; n / ; LF line feed U+000A
; f / ; FF form feed U+000C
; r / ; CR carriage return U+000D
"'" / ; ' 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"
("0" %x62) / ; "0b" ; omit U+0008-U+000A
("0" %x65-66) / ; "0e"-"0f" ; omit U+000C-U+000D
("1" normal-HEXDIG)
)
normal-HEXDIG = DIGIT / %x61-66 ; "0"-"9", "a"-"f"
normal-index-selector = "0" / (DIGIT1 *DIGIT) ; non-negative decimal integer
Examples
+=============+==============================+===================+
| Path | Normalized Path | Comment |
+=============+==============================+===================+
| $.a | $['a'] | Object value |
+-------------+------------------------------+-------------------+
| $[1] | $[1] | Array index |
+-------------+------------------------------+-------------------+
| $.a.b[1:2] | $['a']['b'][1] | Nested structure |
+-------------+------------------------------+-------------------+
| $["\u000B"] | $['\u000b'] | Unicode escape |
+-------------+------------------------------+-------------------+
| $["\u0061"] | $['a'] | Unicode character |
+-------------+------------------------------+-------------------+
| $["\u00b1"] | $['±'] (U+0024 U+005B U+0027 | Unicode character |
| | U+00B1 U+0027 U+005D) | |
+-------------+------------------------------+-------------------+
Table 15: Normalized Path examples
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$["\u00b1"] is normalized into $['±'] (noise in the table and lack of
typewriter font is due to RFCXMLv3 limitations).
4. IANA Considerations
4.1. 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
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
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Change controller: IESG
Provisional registration? (standards tree only): no
5. Security Considerations
Security considerations for JSONPath can stem from
* attack vectors on JSONPath implementations, and
* the way JSONPath is used in security-relevant mechanisms.
5.1. 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. 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.
5.2. 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.
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].
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Other attacks can target the behavior of underlying technologies such
as UTF-8 (see Section 10 of [RFC3629]) and the Unicode character set.
6. References
6.1. Normative References
[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-01, 11 July 2022,
<https://www.ietf.org/archive/id/draft-ietf-jsonpath-
iregexp-01.txt>.
[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/info/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/info/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/info/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/info/rfc6838>.
[RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
DOI 10.17487/RFC7493, March 2015,
<https://www.rfc-editor.org/info/rfc7493>.
[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/info/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/info/rfc8259>.
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[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>.
6.2. 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/info/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/info/rfc8949>.
[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.
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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,
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.
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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 ?(<boolean expr>) as
in
$.store.book[?(@.price < 10)].title
Table 16 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 16: XPath syntax compared to JSONPath
For further illustration, Table 17 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 17: 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 the _object_ or _array_
addressed by the previous path fragment. 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 path component in a JSON
Pointer may identify a member of a JSON object or may index an array.
For conversion to a JSONPath query, knowledge of the structure of the
JSON value is needed to distinguish these cases.
Acknowledgements
This specification 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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