Internet DRAFT - draft-normington-jsonpath
draft-normington-jsonpath
JSONPath WG G. Normington, Ed.
Internet-Draft VMware, Inc.
Intended status: Standards Track E. Surov, Ed.
Expires: 10 June 2021 TheSoul Publishing Ltd.
M. Mikulicic
VMware, Inc.
S. Gössner
Fachhochschule Dortmund
7 December 2020
JavaScript Object Notation (JSON) Path
draft-normington-jsonpath-00
Abstract
JSONPath defines a string syntax for identifying values within a
JavaScript Object Notation (JSON) document.
Note
*This document is a work in progress and has not yet been published
as an Internet Draft* (which needs to be fixed soon).
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 can be directed at the github repository _insert
repo here_ as well as (for the time when the more permanent home is
being decided) at the dispatch@ietf.org mailing list.
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/.
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on 10 June 2021.
Copyright Notice
Copyright (c) 2020 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 . . . . . . . . . . . . . . . . . . . . . . 7
3. JSONPath Syntax and Semantics . . . . . . . . . . . . . . . . 10
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 10
3.3. Implementation . . . . . . . . . . . . . . . . . . . . . 10
3.4. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.5. Semantics . . . . . . . . . . . . . . . . . . . . . . . . 11
3.6. Selectors . . . . . . . . . . . . . . . . . . . . . . . . 12
3.6.1. Dot Child Selector . . . . . . . . . . . . . . . . . 12
3.6.2. Union Selector . . . . . . . . . . . . . . . . . . . 13
3.6.2.1. Syntax . . . . . . . . . . . . . . . . . . . . . 13
3.6.2.2. Semantics . . . . . . . . . . . . . . . . . . . . 13
3.6.2.3. Child . . . . . . . . . . . . . . . . . . . . . . 13
3.6.2.4. Array Selector . . . . . . . . . . . . . . . . . 15
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
5. Security Considerations . . . . . . . . . . . . . . . . . . . 19
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
6.1. Normative References . . . . . . . . . . . . . . . . . . 19
6.2. Informative References . . . . . . . . . . . . . . . . . 19
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 20
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 20
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
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.
Data Item: A structure complying to the generic data model of JSON,
i.e., composed of containers such as arrays and maps (JSON
objects), and of atomic data such as null, true, false, numbers,
and text strings.
Object: Used in its generic sense, e.g., for programming language
objects. When a JSON Object as defined in [RFC8259] is meant, we
specifically say JSON Object.
Query: Short name for JSONPath expression.
Argument: Short name for the JSON data item a JSONPath expression is
applied to.
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Output Path: A simple form of JSONPath expression that identifies a
Position by providing a query that results in exactly that
position. Similar to, but syntactically different from, a JSON
Pointer [RFC6901].
Position: A JSON data item identical to or nested within the JSON
data item to which the query is applied to, expressed either by
the value of that data item or by providing a JSONPath Output
Path.
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:
* Finding data interactively and extracting them out of [RFC8259]
data items 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 JSON data item. Here we observe that
such languages already have a fundamentally XPath-like feature built
in.
The JSONPath tool in question should:
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* 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 JSON data item in the same way
as XPath expressions are used in combination with an XML document.
Since a JSON data item is usually anonymous and doesn't necessarily
have a "root member object", JSONPath used the abstract name "$" to
refer to the top level object of the data item.
JSONPath expressions can use the _dot-notation_
$.store.book[0].title
or the _bracket-notation_
$['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 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:
$.store.book[(@.length-1)].title
The symbol "@" is used for the current object. Filter expressions
are supported via the syntax "?(<boolean expr>)" as in
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$.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.
+=======+==================+=====================================+
| XPath | JSONPath | Description |
+=======+==================+=====================================+
| / | $ | the root object/element |
+-------+------------------+-------------------------------------+
| . | @ | the current object/element |
+-------+------------------+-------------------------------------+
| / | "." or "[]" | child operator |
+-------+------------------+-------------------------------------+
| .. | n/a | parent operator |
+-------+------------------+-------------------------------------+
| // | .. | nested descendants (JSONPath |
| | | borrows this syntax from E4X) |
+-------+------------------+-------------------------------------+
| * | * | wildcard: All objects/elements |
| | | regardless of their names |
+-------+------------------+-------------------------------------+
| @ | n/a | attribute access: JSON data items |
| | | 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
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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:
* 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 a simple JSON data item patterned after a
typical XML example representing a bookstore (that also has
bicycles):
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{ "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 data item
The examples in Table 2 use the expression mechanism to obtain the
number of items in an array, to test for the presence of a map
member, and to perform numeric comparisons of map 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 |
| | | members of |
| | | JSON data item |
+----------------------+-------------------------+------------------+
Table 2: Example JSONPath expressions applied to the example JSON
data item
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3. JSONPath Syntax and Semantics
3.1. Overview
A JSONPath is a string which selects zero or more nodes of a piece of
JSON. A valid JSONPath conforms to the ABNF syntax defined by this
document.
A JSONPath MUST be encoded using UTF-8. To parse a JSONPath
according to the grammar in this document, its UTF-8 form SHOULD
first be decoded into Unicode code points as described in [RFC3629].
3.2. Terminology
A JSON value is logically a tree of nodes.
Each node holds a JSON value (as defined by [RFC8259]) of one of the
types object, array, number, string, or one of the literals "true",
"false", or "null". The type of the JSON value held by a node is
sometimes referred to as the type of the node.
3.3. Implementation
An implementation of this specification, from now on referred to
simply as "an implementation", SHOULD takes two inputs, a JSONPath
and a JSON value, and produce a possibly empty list of nodes of the
JSON value which are selected by the JSONPath or an error (but not
both).
If no node is selected and no error has occurred, an implementation
MUST return an empty list of nodes.
Syntax errors in the JSONPath SHOULD be detected before selection is
attempted since these errors do not depend on the JSON value.
Therefore, an implementation SHOULD take a JSONPath and produce an
optional syntax error and then, if and only if an error was not
produced, SHOULD take a JSON value and produce a list of nodes or an
error (but not both).
Alternatively, an implementation MAY take a JSONPath and a JSON value
and produce a list of nodes or an optional error (but not both).
For any implementation, if a syntactically invalid JSONPath is
provided, the implementation MUST return an error.
If a syntactially invalid JSON value is provided, any implementation
SHOULD return an error.
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3.4. Syntax
Syntactically, a JSONPath consists of a root selector ("$"), which
selects the root node of a JSON value, followed by a possibly empty
sequence of _selectors_.
json-path = root-selector *selector
root-selector = %x24 ; $ selects document root node
The syntax and semantics of each selector is defined below.
3.5. Semantics
The root selector "$" not only selects the root node of the input
document, but it also produces as output a list consisting of one
node: the input document.
A selector may select zero or more nodes for further processing. A
syntactically valid selector MUST NOT produce errors. This means
that some operations which might be considered erroneous, such as
indexing beyond the end of an array, simply result in fewer nodes
being selected.
But a selector doesn't just act on a single node: each selector acts
on a list of nodes and produces a list of nodes, as follows.
After the root selector, the remainder of the JSONPath is processed
by passing lists of nodes from one selector to the next ending up
with a list of nodes which is the result of applying the JSONPath to
the input JSON value.
Each selector acts on its input list of nodes as follows. For each
node in the list, the selector selects zero or more nodes, each of
which is a descendant of the node or the node itself. The output
list of nodes of a selector is the concatenation of the lists of
selected nodes for each input node.
A specific, non-normative example will make this clearer. Suppose
the input document is: "{"a":[{"b":0},{"b":1},{"c":2}]}". As we will
see later, the JSONPath "$.a[*].b" selects the following list of
nodes: "0", "1". Let's walk through this in detail.
The JSONPath consists of "$" followed by three selectors: ".a",
"[*]", and ".b".
Firstly, "$" selects the root node which is the input document. So
the result is a list consisting of just the root node.
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Next, ".a" selects from any input node of type object and selects any
value of the input node corresponding to the key ""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 key
"b" and selects the value of the input node corresponding to that
key. 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 JSONPath selects no nodes.
In what follows, the semantics of each selector are defined for each
type of node.
3.6. Selectors
3.6.1. Dot Child Selector
Syntax
A dot child selector has a key known as a dot child name or a single
asterisk ("*").
A dot child name corresponds to a name in a JSON object.
selector = dot-child ; see below for alternatives
dot-child = %x2E dot-child-name / ; .<dot-child-name>
%x2E %x2A ; .*
dot-child-name = 1*(
%x2D / ; -
DIGIT /
ALPHA /
%x5F / ; _
%x80-10FFFF ; any non-ASCII Unicode character
)
DIGIT = %x30-39 ; 0-9
ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
More general child names, such as the empty string, are supported by
"Union Child" (Section 3.6.2.3).
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Note that the "dot-child-name" rule 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 child names which
do not encode Unicode characters.
Semantics
A dot child name which is not a single asterisk ("*") is considered
to have a key. It selects the value corresponding to the key from
any object node. It selects no nodes from a node which is not an
object.
The key of a dot child name is the sequence of Unicode characters
contained in that name.
A dot child name consisting of a single asterisk is a wild card. It
selects all the values of any object node. It also selects all the
elements of any array node. It selects no nodes from number, string,
or literal nodes.
3.6.2. Union Selector
3.6.2.1. Syntax
A union selector consists of one or more union elements.
selector =/ union
union = %x5B ws union-elements ws %x5D ; [...]
ws = *%x20 ; zero or more spaces
union-elements = union-element /
union-element ws %x2C ws union-elements
; ,-separated list
3.6.2.2. 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.
3.6.2.3. Child
Syntax
A child is a quoted string.
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union-element = child ; see below for more alternatives
child = %x22 *double-quoted %x22 / ; "string"
%x27 *single-quoted %x27 ; 'string'
double-quoted = dq-unescaped /
escape (
%x22 / ; " quotation mark U+0022
%x2F / ; / solidus U+002F
%x5C / ; \ reverse solidus U+005C
%x62 / ; b backspace U+0008
%x66 / ; f form feed U+000C
%x6E / ; n line feed U+000A
%x72 / ; r carriage return U+000D
%x74 / ; t tab U+0009
%x75 4HEXDIG ) ; uXXXX U+XXXX
dq-unescaped = %x20-21 / %x23-5B / %x5D-10FFFF
single-quoted = sq-unescaped /
escape (
%x27 / ; ' apostrophe U+0027
%x2F / ; / solidus U+002F
%x5C / ; \ reverse solidus U+005C
%x62 / ; b backspace U+0008
%x66 / ; f form feed U+000C
%x6E / ; n line feed U+000A
%x72 / ; r carriage return U+000D
%x74 / ; t tab U+0009
%x75 4HEXDIG ) ; uXXXX U+XXXX
sq-unescaped = %x20-26 / %x28-5B / %x5D-10FFFF
escape = %x5C ; \
HEXDIG = DIGIT / "A" / "B" / "C" / "D" / "E" / "F"
; case insensitive hex digit
Notes: 1. double-quoted strings follow JSON in [RFC8259]. Single-
quoted strings follow an analogous pattern. 2. "HEXDIG" includes A-F
and a-f.
Semantics
If the child is a quoted string, the string MUST be converted to a
key by removing the surrounding quotes and replacing each escape
sequence with its equivalent Unicode character, as in the table
below:
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+=================+===================+
| Escape Sequence | Unicode Character |
+=================+===================+
| %x5C %x22 | U+0022 |
+-----------------+-------------------+
| %x5C %x27 | U+0027 |
+-----------------+-------------------+
| %x5C %x2F | U+002F |
+-----------------+-------------------+
| %x5C %x5C | U+005C |
+-----------------+-------------------+
| %x5C %x62 | U+0008 |
+-----------------+-------------------+
| %x5C %x66 | U+000C |
+-----------------+-------------------+
| %x5C %x6E | U+000A |
+-----------------+-------------------+
| %x5C %x72 | U+000D |
+-----------------+-------------------+
| %x5C %x74 | U+0009 |
+-----------------+-------------------+
| %x5C uXXXX | U+XXXX |
+-----------------+-------------------+
Table 3: Escape Sequence Replacements
The child selects the value corresponding to the key from any object
node with the key as a name. It selects no nodes from a node which
is not an object.
3.6.2.4. Array Selector
Syntax
An array selector selects zero or more elements of an array node. An
array selector takes the form of an index, which selects at most one
element, or a slice, which selects zero or more elements.
union-element =/ array-index / array-slice
An array index is an integer (in base 10).
array-index = integer
integer = ["-"] ("0" / (DIGIT1 *DIGIT))
; optional - followed by 0 or
; sequence of digits with no leading zero
DIGIT1 = %x31-39 ; non-zero digit
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Note: the syntax does not allow integers with leading zeros such as
"01" and "-01".
An array slice consists of three optional integers (in base 10)
separated by colons.
array-slice = [ start ] ws ":" ws [ end ]
[ ws ":" ws [ step ] ]
start = integer
end = integer
step = integer
Note: the array slices ":" and "::" are both syntactically valid, as
are ":2:2", "2::2", and "2:4:".
Semantics
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.
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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.
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 is
defined as:
FUNCTION Normalize(i):
IF i >= 0 THEN
RETURN i
ELSE
RETURN len + i
END IF
The result of the array indexing expression "[i]" is defined to be
the result of the array slicing expression "[i:Normalize(i)+1:1]".
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Slice expression parameters "start" and "end" are used to derive
slice bounds "lower" and "upper". The direction of the iteration,
defined by the sign of "step", determines which of the parameters is
the lower bound and which is the upper bound:
FUNCTION Bounds(start, end, step, len):
n_start = Normalize(start)
n_end = Normalize(end)
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.
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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.
4. IANA Considerations
TBD: Define a media type for JSON Path expressions.
5. Security Considerations
This section gives security considerations, as required by [RFC3552].
6. References
6.1. 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>.
6.2. Informative References
[E4X] ISO, "Information technology — ECMAScript for XML (E4X)
specification", ISO/IEC 22537:2006 , 2006.
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[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/>.
[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
Carsten Bormann
Universität Bremen TZI
Postfach 330440
D-28359 Bremen
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
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Authors' Addresses
Glyn Normington (editor)
VMware, Inc.
Winchester
United Kingdom
Email: glyn.normington@gmail.com
Edward Surov (editor)
TheSoul Publishing Ltd.
Limassol
Cyprus
Email: esurov.tsp@gmail.com
Marko Mikulicic
VMware, Inc.
Pisa
Italy
Email: mmikulicic@gmail.com
Stefan Gössner
Fachhochschule Dortmund
Sonnenstraße 96
D-44139 Dortmund
Germany
Email: stefan.goessner@fh-dortmund.de
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