JSONPath: Query expressions for JSON
draft-ietf-jsonpath-base-02
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (jsonpath WG) | |
|---|---|---|---|
| Authors | Stefan Gössner , Glyn Normington , Carsten Bormann | ||
| Last updated | 2021-10-25 | ||
| Replaces | draft-normington-jsonpath | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text html xml htmlized pdfized bibtex | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-jsonpath-base-02
JSONPath WG S. Gössner, Ed.
Internet-Draft Fachhochschule Dortmund
Intended status: Standards Track G. Normington, Ed.
Expires: 28 April 2022
C. Bormann, Ed.
Universität Bremen TZI
25 October 2021
JSONPath: Query expressions for JSON
draft-ietf-jsonpath-base-02
Abstract
JSONPath defines a string syntax for identifying values within a
JavaScript Object Notation (JSON) document.
Contributing
This document picks up the popular JSONPath specification dated
2007-02-21 and provides a normative definition for it. In its
current state, it is a strawman document showing what needs to be
covered.
Comments and issues may be directed to this document's github
repository (https://github.com/ietf-wg-jsonpath/draft-ietf-jsonpath-
jsonpath).
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 28 April 2022.
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Copyright Notice
Copyright (c) 2021 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
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Inspired by XPath . . . . . . . . . . . . . . . . . . . . 4
1.3. Overview of JSONPath Expressions . . . . . . . . . . . . 5
2. JSONPath Examples . . . . . . . . . . . . . . . . . . . . . . 8
3. JSONPath Syntax and Semantics . . . . . . . . . . . . . . . . 11
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2. Processing Model . . . . . . . . . . . . . . . . . . . . 11
3.3. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.4. Semantics . . . . . . . . . . . . . . . . . . . . . . . . 12
3.5. Selectors . . . . . . . . . . . . . . . . . . . . . . . . 13
3.5.1. Root Selector . . . . . . . . . . . . . . . . . . . . 14
3.5.2. Dot Selector . . . . . . . . . . . . . . . . . . . . 14
3.5.3. Dot Wild Card Selector . . . . . . . . . . . . . . . 15
3.5.4. Index Selector . . . . . . . . . . . . . . . . . . . 15
3.5.5. Index Wild Card Selector . . . . . . . . . . . . . . 18
3.5.6. Array Slice Selector . . . . . . . . . . . . . . . . 18
3.5.7. Descendant Selector . . . . . . . . . . . . . . . . . 22
3.5.8. Union Selector . . . . . . . . . . . . . . . . . . . 22
3.5.8.1. Syntax . . . . . . . . . . . . . . . . . . . . . 22
3.5.8.2. Semantics . . . . . . . . . . . . . . . . . . . . 23
3.5.9. Filter Selector . . . . . . . . . . . . . . . . . . . 23
3.5.9.1. Syntax . . . . . . . . . . . . . . . . . . . . . 23
3.5.9.2. Semantics . . . . . . . . . . . . . . . . . . . . 26
4. Expression Language . . . . . . . . . . . . . . . . . . . . . 27
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
6. Security Considerations . . . . . . . . . . . . . . . . . . . 28
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
7.1. Normative References . . . . . . . . . . . . . . . . . . 28
7.2. Informative References . . . . . . . . . . . . . . . . . 28
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 29
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 29
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction
This document picks up the popular JSONPath specification dated
2007-02-21 [JSONPath-orig] and provides a normative definition for
it. In its current state, it is a strawman document showing what
needs to be covered.
JSON is defined by [RFC8259].
JSONPath is not intended as a replacement, but as a more powerful
companion, to JSON Pointer [RFC6901]. [insert reference to section
where the relationship is detailed. The purposes of the two syntaxes
are different. Pointer is for isolating a single location within a
document. Path is a query syntax that can also be used to pull
multiple locations.]
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 containers,
namely JSON objects and arrays, and atomic data, namely null,
true, false, numbers, and text strings.
Member: A name/value pair in an object. (Not itself a value.)
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Name: The name in a name/value pair constituting a member. (Also
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. (Also used with a distinct meaning in
XML context for XML elements.)
Index: A non-negative integer that identifies a specific element in
an array.
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.
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
identifies a node by providing a query that results in exactly
that node. Similar to, but syntactically different from, a JSON
Pointer [RFC6901].
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. Inspired by XPath
A frequently emphasized advantage of XML is the availability of
powerful tools to analyse, 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:
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* 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.
So what does such a tool look like for JSON? When defining a
JSONPath, how should expressions look?
The XPath expression
/store/book[1]/title
looks like
x.store.book[0].title
or
x['store']['book'][0]['title']
in popular programming languages such as JavaScript, Python and PHP,
with a variable x holding the argument. Here we observe that such
languages already have a fundamentally XPath-like feature built in.
The JSONPath tool in question should:
* be naturally based on those language characteristics.
* cover only essential parts of XPath 1.0.
* be lightweight in code size and memory consumption.
* be runtime efficient.
1.3. Overview of JSONPath Expressions
JSONPath expressions always apply to a value in the same way as XPath
expressions are used in combination with an XML document. Since a
value is anonymous, JSONPath uses the abstract name $ to refer to the
root node of the argument.
JSONPath expressions can use the _dot notation_
$.store.book[0].title
or the _bracket notation_
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$['store']['book'][0]['title']
for paths input to a JSONPath processor. [1] Where a JSONPath
processor uses JSONPath expressions as output paths, these will
always be converted to Output Paths which employ the more general
_bracket notation_. [2] Bracket notation is more general than dot
notation and can serve as a canonical form when a JSONPath processor
uses JSONPath expressions as output paths.
JSONPath allows the wildcard symbol * for member names and array
indices. It borrows the descendant operator .. from [E4X] and the
array slice syntax proposal [start:end:step] [SLICE] from ECMASCRIPT
4.
JSONPath was originally designed to employ an _underlying scripting
language_ for computing expressions. The present specification
defines a simple expression language that is independent from any
scripting language in use on the platform.
JSONPath can use expressions, written in parentheses: (<expr>), as an
alternative to explicit names or indices as in:
$.store.book[(@.length-1)].title
The symbol @ is used for the current node. Filter expressions are
supported via the syntax ?(<boolean expr>) as in
$.store.book[?(@.price < 10)].title
Here is a complete overview and a side by side comparison of the
JSONPath syntax elements with their XPath counterparts.
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+=======+==================+=====================================+
| XPath | JSONPath | Description |
+=======+==================+=====================================+
| / | $ | the root element/node |
+-------+------------------+-------------------------------------+
| . | @ | the current element/node |
+-------+------------------+-------------------------------------+
| / | . or [] | child operator |
+-------+------------------+-------------------------------------+
| .. | n/a | parent operator |
+-------+------------------+-------------------------------------+
| // | .. | nested descendants (JSONPath |
| | | borrows this syntax from E4X) |
+-------+------------------+-------------------------------------+
| * | * | wildcard: All elements/nodes |
| | | regardless of their names |
+-------+------------------+-------------------------------------+
| @ | n/a | attribute access: JSON values do |
| | | not have attributes |
+-------+------------------+-------------------------------------+
| [] | [] | subscript operator: XPath uses it |
| | | to iterate over element collections |
| | | and for predicates; native array |
| | | indexing as in JavaScript here |
+-------+------------------+-------------------------------------+
| | | [,] | Union operator in XPath (results in |
| | | a combination of node sets); |
| | | JSONPath allows alternate names or |
| | | array indices as a set |
+-------+------------------+-------------------------------------+
| n/a | [start:end:step] | array slice operator borrowed from |
| | | ES4 |
+-------+------------------+-------------------------------------+
| [] | ?() | applies a filter (script) |
| | | expression |
+-------+------------------+-------------------------------------+
| n/a | () | expression engine |
+-------+------------------+-------------------------------------+
| () | n/a | grouping in Xpath |
+-------+------------------+-------------------------------------+
Table 1: Overview over JSONPath, comparing to XPath
XPath has a lot more to offer (location paths in unabbreviated
syntax, operators and functions) than listed here. Moreover there is
a significant difference how the subscript operator works in Xpath
and JSONPath:
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* 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.
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,
which was patterned after a typical XML example 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
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The examples in Table 2 use the expression mechanism to obtain the
number of elements in an array, to test for the presence of a member
in a object, and to perform numeric comparisons of member values with
a constant.
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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[(@.length-1)] | the last book |
| | $..book[-1] | 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 2: Example JSONPath expressions applied to the example JSON
value
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3. JSONPath Syntax and Semantics
3.1. Overview
A JSONPath query is a string which selects zero or more nodes of a
piece of JSON. A valid query conforms to the ABNF syntax defined by
this document.
A query MUST be encoded using UTF-8. To parse a query according to
the grammar in this document, its UTF-8 form SHOULD first be decoded
into Unicode code points as described in [RFC3629].
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 syntax of JSONPath. A well-formed JSONPath query is valid if it
also fulfills all semantic requirements posed by this document.
The well-formedness and the validity of JSONPath queries are
independent of the value the query is applied to; no further errors
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.)
3.2. Processing Model
In this specification, the semantics of a JSONPath query are defined
in terms of a _processing model_. That model is not prescriptive of
the internal workings of an implementation: Implementations may wish
(or need) to design a different process that yields results that
conform to the model.
In the processing model, 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 sequence of zero or more _selectors_, each of which is
applied to the result of the previous selector and provides input to
the next selector. These results and inputs take the form of a
_nodelist_, i.e., a sequence of zero or more nodes.
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The nodelist going into the first selector contains a single node,
the argument. The nodelist resulting from the last selector 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 Output 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 selector 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 into the result of the
selector.
The processing within a selector may execute nested queries, which
are in turn handled with the processing model defined here.
Typically, the argument to that query will be the current node of the
selector or a set of nodes subordinate to that current node.
3.3. Syntax
Syntactically, a JSONPath query consists of a root selector ($),
which stands for a nodelist that contains the root node of the
argument, followed by a possibly empty sequence of _selectors_.
json-path = root-selector *(dot-selector /
dot-wild-selector /
index-selector /
index-wild-selector /
union-selector /
slice-selector /
descendant-selector /
filter-selector)
The syntax and semantics of each selector is defined below.
3.4. Semantics
The root selector $ not only selects the root node of the argument,
but it also produces as output a list consisting of one node: the
argument itself.
A selector may select zero or more nodes for further processing. A
syntactically valid selector MUST NOT produce errors. This means
that some operations which might be considered erroneous, such as
indexing beyond the end of an array, simply result in fewer nodes
being selected.
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But a selector doesn't just act on a single node: a selector acts on
each of the nodes in its input nodelist and concatenates the
resultant nodelists to form the result nodelist of the selector.
For each node in the list, the selector selects zero or more nodes,
each of which is a descendant of the node or the node itself.
For instance, 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). Let's walk through this in detail.
The query consists of $ followed by three selectors: .a, [*], and .b.
Firstly, $ selects the root node which is the argument. So the
result is a list consisting of just the root node.
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 any input node which is an array and selects
all the elements of the input node. 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 selectors selects no
nodes, then the whole query selects no nodes.
In what follows, the semantics of each selector are defined for each
type of node.
3.5. Selectors
A JSONPath query consists of a sequence of selectors. Valid
selectors are
* Root selector $
* Dot selector .<name>, used with object member names exclusively.
* Dot wild card selector .*.
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* Index selector [<index>], where <index> is either an (possibly
negative) array index or an object member name.
* Index wild card selector [*].
* Array slice selector [<start>:<end>:<step>], where <start>, <end>,
<step> are integer literals.
* Nested descendants selector ...
* Union selector [<sel1>,<sel2>,...,<selN>], holding a comma
delimited list of index, index wild card, array slice, and filter
selectors.
* Filter selector [?(<expr>)]
* Current item selector @
3.5.1. Root Selector
Syntax
Every valid JSONPath query MUST begin with the root selector $.
root-selector = "$"
Semantics
The Argument -- the root JSON value -- becomes the root node, which
is addressed by the root selector $.
3.5.2. Dot Selector
Syntax
A dot selector starts with a dot . followed by an object's member
name.
dot-selector = "." 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
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Member names containing other characters than allowed by dot-selector
-- such as space ` ` and minus - characters -- MUST NOT be used with
the dot-selector. (Such member names can be addressed by the index-
selector instead.)
Semantics
The dot-selector selects the node of the member value corresponding
to the member name from any JSON object. It selects no nodes from
any other JSON value.
Note that the dot-selector follows the philosophy of JSON strings and
is allowed to contain bit sequences that cannot encode Unicode
characters (a single unpaired UTF-16 surrogate, for example). The
behaviour of an implementation is undefined for member names which do
not encode Unicode characters.
3.5.3. Dot Wild Card Selector
Syntax
The dot wild card selector has the form .*.
dot-wild-selector = "." "*" ; dot followed by asterisk
Semantics
A dot-wild-selector acts as a wild card by selecting the nodes of all
member values of an object as well as all element nodes of an array.
Applying the dot-wild-selector to a primitive JSON value (number,
string, or true/false/null) selects no node.
3.5.4. Index Selector
Syntax
An index selector [<index>] addresses at most one object member value
or at most one array element value.
index-selector = "[" (quoted-member-name / element-index) "]"
Applying the index-selector to an object value, a quoted-member-name
string is required. JSONPath allows it to be enclosed in _single_ or
_double_ quotes.
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quoted-member-name = 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)
"\" / ; \ backslash (reverse solidus)
(%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
Applying the index-selector to an array, a numerical element-index is
required. JSONPath allows it to be negative.
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element-index = int ; decimal integer
int = ["-"] ( "0" / (DIGIT1 *DIGIT) ) ; - optional
DIGIT1 = %x31-39 ; 1-9 non-zero digit
Notes: 1. double-quoted strings follow JSON in [RFC8259]; single-
quoted strings follow an analogous pattern. 2. An element-index is
an integer (in base 10, as in JSON numbers). 3. As in JSON numbers,
the syntax does not allow octal-like integers with leading zeros such
as 01 or -01.
Semantics
A quoted-member-name 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 3: Escape Sequence Replacements
The index-selector applied with a quoted-member-name 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 which is not a object.
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Array indexing via element-index is a way of selecting a particular
array element using a zero-based index. For example, selector [0]
selects the first and selector [4] the fifth element of a
sufficiently long array.
A negative element-index counts from the array end. For example,
selector [-1] selects the last and selector [-2] selects the last but
one element of an array with at least two elements.
3.5.5. Index Wild Card Selector
Syntax
The index wild card selector has the form [*].
index-wild-selector = "[" "*" "]" ; asterisk enclosed by brackets
Semantics
An index-wild-selector selects the nodes of all member values of an
object as well as of all elements of an array. Applying the index-
wild-selector to a primitive JSON value (such as a number, string, or
true/false/null) selects no node.
The index-wild-selector behaves identically to the dot-wild-selector.
3.5.6. Array Slice Selector
Syntax
The array slice selector has the form [<start>:<end>:<step>]. It
selects elements starting at index <start>, ending at -- but not
including -- <end>, while incrementing by step.
slice-selector = "[" slice-index "]"
slice-index = ws [start] ws ":" ws [end] [ws ":" ws [step] ws]
start = int ; included in selection
end = int ; not included in selection
step = int ; default: 1
ws = *( %x20 / ; Space
%x09 / ; Horizontal tab
%x0A / ; Line feed or New line
%x0D ) ; Carriage return
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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 indexing is a way of selecting a particular element of an array
using a 0-based index. For example, the expression [0] selects the
first element of a non-empty array.
Negative indices index from the end of an array. For example, the
expression [-2] selects the last but one element of an array with at
least two elements.
Array slicing is inspired by the behaviour 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.
When step is 0, no elements are selected. This is the one case which
differs from the behaviour of Python, which raises an error in this
case.
The following section specifies the behaviour fully, without
depending on JavaScript or Python behaviour.
Detailed Semantics
An array selector is either an array slice or an array index, which
is defined in terms of an array slice.
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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
which 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 4: 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 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:
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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.
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.
An implementation MUST raise an error if any of the slice expression
parameters does not fit in the implementation's representation of an
integer. If a successfully parsed slice expression is evaluated
against an array whose size doesn't fit in the implementation's
representation of an integer, the implementation MUST raise an error.
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3.5.7. Descendant Selector
Syntax
The descendant selector starts with a double dot .. and can be
followed by an object member name (similar to the dot-selector), by
an index-selector acting on objects or arrays, or by a wild card.
descendant-selector = ".." ( dot-member-name / ; ..<name>
index-selector / ; ..[<index>]
index-wild-selector / ; ..[*]
"*" ; ..*
)
Semantics
The descendant-selector is inspired by ECMAScript for XML (E4X). It
selects the node and all its descendants.
3.5.8. Union Selector
3.5.8.1. Syntax
The union selector is syntactically related to the index-selector.
It contains multiple, comma separated entries.
union-selector = "[" ws union-entry 1*(ws "," ws union-entry) ws "]"
union-entry = ( quoted-member-name /
element-index /
slice-index
)
Task (T1): This, besides slice-index, is currently one of only two
places in the document that mentions whitespace. Whitespace needs
to be handled throughout the ABNF syntax. Room Consensus at the
2021-06-15 interim was that JSONPath generally is generous with
allowing insignificant whitespace throughout. Minimizing the
impact of the many whitespace insertion points by choosing a rule
name such as "S" was mentioned. Some conventions will probably
help with minimizing the number of places where S needs to be
inserted.
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3.5.8.2. Semantics
A union selects any node which is selected by at least one of the
union selectors and selects the concatenation of the lists (in the
order of the selectors) of nodes selected by the union elements.
Note that any node selected in more than one of the union selectors
is kept as many times in the node list.
3.5.9. Filter Selector
3.5.9.1. Syntax
The filter selector has the form [?<expr>]. It works via iterating
over structured values, i.e. arrays and objects.
filter-selector = "[?" boolean-expr "]"
During 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 result is true.
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boolean-expr = logical-or-expr
logical-or-expr = logical-and-expr *("||" logical-and-expr)
; disjunction
; binds less tightly than conjunction
logical-and-expr = basic-expr *("&&" basic-expr) ; conjunction
; binds more tightly than disjunction
basic-expr = exist-expr / paren-expr / (neg-op paren-expr) / relation-expr
exist-expr = [neg-op] path ; path existence or non-existence
path = rel-path / json-path
rel-path = "@" *(dot-selector / index-selector)
paren-expr = "(" boolean-expr ")" ; parenthesized expression
neg-op = "!" ; not operator
relation-expr = comp-expr / ; comparison test
regex-expr / ; regular expression test
contain-expr ; containment test
comp-expr = comparable comp-op comparable
comparable = number / string-literal / ; primitive ...
true / false / null / ; values only
path ; path value
comp-op = "==" / "!=" / ; comparison ...
"<" / ">" / ; operators
"<=" / ">="
regex-expr = regex-op regex
regex-op = "=~" ; regular expression match
regex = <TO BE DEFINED>
contain-expr = containable in-op container
containable = rel-path / json-path / ; path to primitive value
number / string-literal
in-op = " in " ; in operator
container = rel-path / json-path / array-literal ; resolves to array
Notes:
* 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.
* Comparisons are restricted to primitive values (such as number,
string, true, false, null). Comparisons with complex values will
fail, i.e. no selection occurs.
* Types are not implicitly converted in comparisons. So "13 ==
'13'" selects no node.
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* A member or element value by itself is _falsy_ only, if it does
not exist. Otherwise it is _truthy_, resulting in its value. To
be more specific explicit comparisons are necessary. This
existence test -- as an exception of the general rule -- also
works with structured values.
* Regular expression tests can be applied to string values only.
* The value of the first operand (containable) of a contain-expr is
compared to every single element of the RHS container. In case of
a match a selection occurs. Containment tests -- like comparisons
-- are restricted to primitive values. So even if a structured
containable value is equal to a certain structured value in
container, no selection is done.
* The value of the second operand (container) of a contain-expr
needs to be resolved to an array. Otherwise nothing is selected.
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 | == != |
| | | < <= > >= |
| | | =~ |
| | | in |
+------------+-----------+-----------+
| 2 | Logical | && |
| | AND | |
+------------+-----------+-----------+
| 1 | Logical | \|\| |
| | OR | |
+------------+-----------+-----------+
Table 5: Filter expression
operator precedence
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3.5.9.2. Semantics
The filter-selector works with arrays and objects exclusively. Its
result might be a list of _zero_, _one_, _multiple_ or _all_ of their
element or member values then. Applied to other value types, it will
select nothing.
Negation operator neg-op allows to test _falsiness_ of values.
+========+==========+========+===========================+
| Type | Negation | Result | Comment |
+========+==========+========+===========================+
| Number | !0 | true | false for non-zero number |
+--------+----------+--------+---------------------------+
| String | !"" | true | false for non-empty |
| | !'' | | string |
+--------+----------+--------+---------------------------+
| null | !null | true | -- |
+--------+----------+--------+---------------------------+
| true | !true | false | -- |
+--------+----------+--------+---------------------------+
| false | !false | true | -- |
+--------+----------+--------+---------------------------+
| Object | !{} | false | always false |
| | !{a:0} | | |
+--------+----------+--------+---------------------------+
| Array | ![] | false | always false |
| | ![0] | | |
+--------+----------+--------+---------------------------+
Table 6: Test falsiness of JSON values
Applying negation operator twice !! gives us _truthiness_ of values.
Some examples:
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+===================+=======================+===============+===========+
|JSON | Query | Result |Comment |
+===================+=======================+===============+===========+
|{"a":1,"b":2} | $[?@] | [1,2] |Same as $.*|
|[2,3,4] | | [2,3,4] |or $[*] |
+-------------------+-----------------------+---------------+-----------+
|./. | $[?@==2] | [2] |Select by |
| | | [2] |value. |
+-------------------+-----------------------+---------------+-----------+
|{"a":{"b":{"c":{}}}| $[?@.b] |[{"b":{"c":{}}]|Existence |
| | $[?@.b.c] | | |
+-------------------+-----------------------+---------------+-----------+
|{"key":false} | $[?index(@)=='key'] | [false] |Select |
| | $[?index(@)==0] | [] |object |
| | | |member |
+-------------------+-----------------------+---------------+-----------+
|[3,4,5] | $[?index(@)==2] | [5] |Select |
| | $[?index(@)==17] | [] |array |
| | | |element |
+-------------------+-----------------------+---------------+-----------+
|{"col":"red"} | $[?@ in | ["red"] |Containment|
| |['red','green','blue']]| | |
+-------------------+-----------------------+---------------+-----------+
|{"a":{"b":{5},c:0}}| $[?@.b==5 && !@.c] |[{"b":{5},c:0}]|Existence |
+-------------------+-----------------------+---------------+-----------+
Table 7
4. Expression Language
Task (T2): Separate out expression language. For now, this
section is a repository for ABNF taken from [RFC8259]. This needs
to be deduplicated with definitions above.
number = [ minus ] jsint [ frac ] [ exp ]
decimal-point = %x2E ; .
digit1-9 = %x31-39 ; 1-9
e = %x65 / %x45 ; e E
exp = e [ minus / plus ] 1*DIGIT
frac = decimal-point 1*DIGIT
jsint = zero / ( digit1-9 *DIGIT )
minus = %x2D ; -
plus = %x2B ; +
zero = %x30 ; 0
false = %x66.61.6c.73.65 ; false
null = %x6e.75.6c.6c ; null
true = %x74.72.75.65 ; true
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5. IANA Considerations
TBD: Define a media type for JSONPath expressions.
6. Security Considerations
This section gives security considerations, as required by [RFC3552].
7. References
7.1. Normative References
[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>.
[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>.
7.2. Informative References
[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>.
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[JSONPath-orig]
Gössner, S., "JSONPath — XPath for JSON", 21 February
2007, <https://goessner.net/articles/JsonPath/>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/info/rfc3552>.
[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>.
[SLICE] "Slice notation", n.d.,
<https://github.com/tc39/proposal-slice-notation>.
[XPath] Berglund, A., Boag, S., Chamberlin, D., Fernandez, M.,
Kay, M., Robie, J., and J. Simeon, "XML Path Language
(XPath) 2.0 (Second Edition)", World Wide Web Consortium
Recommendation REC-xpath20-20101214, 14 December 2010,
<https://www.w3.org/TR/2010/REC-xpath20-20101214>.
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
Marko Mikulicic
InfluxData, Inc.
Pisa
Italy
Email: mmikulicic@gmail.com
Edward Surov
TheSoul Publishing Ltd.
Limassol
Cyprus
Email: esurov.tsp@gmail.com
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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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