Internet DRAFT - draft-snell-json-test
draft-snell-json-test
Individual Submission J. Snell
Internet-Draft
Intended status: Informational September 24, 2013
Expires: March 28, 2014
JSON Predicates
draft-snell-json-test-07
Abstract
JSON Predicates defines a syntax for serializing various predicate
expressions as JSON Objects.
Status of This Memo
This Internet-Draft is submitted to IETF 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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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 28, 2014.
Copyright Notice
Copyright (c) 2013 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
(http://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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Predicate Objects . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Predicate Context . . . . . . . . . . . . . . . . . . . . 5
2.2. First Order Predicates . . . . . . . . . . . . . . . . . 5
2.2.1. "contains" and "contains-" . . . . . . . . . . . . . 5
2.2.2. defined . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.3. ends . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.4. in . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.5. less . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.6. matches . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.7. more . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.8. starts . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.9. test . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.10. type . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2.11. undefined . . . . . . . . . . . . . . . . . . . . . . 14
2.3. Second-Order Predicates . . . . . . . . . . . . . . . . . 14
2.3.1. and . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.3.2. not . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.3.3. or . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3.4. Nesting Second Order Predicates . . . . . . . . . . . 19
2.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 20
2.5. Using JSON Predicates within JSON Patch Documents . . . . 21
2.5.1. Conditional Patch Operations . . . . . . . . . . . . 22
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
4. Security Considerations . . . . . . . . . . . . . . . . . . . 25
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.1. Normative References . . . . . . . . . . . . . . . . . . 25
5.2. Informative References . . . . . . . . . . . . . . . . . 26
Appendix A. Non-Normative Example Implementation (Ruby) . . . . 26
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction
This specification defines JSON Predicates, a JSON-based [RFC4627]
syntax for the description and serialization of logical boolean
predicate operations intended to be used in conjunction with other
JSON-based mechanisms, such as JSON Patch [RFC6902], as a means of
incorporating conditional processing.
JSON Predicates can be used, for instance, to extend a JSON Patch
[RFC6902] document to provide for a broader range of conditional
processing options not currently supported by JSON Patch.
Example: Given a source JSON document
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{
"a": {
"b": {
"c": "ABC!XYZ"
}
}
}
The following JSON Patch with JSON Predicates document will first
test that the value of the "c" property is a string containing the
character sequence "ABC" prior to applying the specified "replace"
operation.
[
{
"op": "and",
"path": "/a/b/c",
"apply": [
{
"op": "type",
"value": "string"
},
{
"op": "contains",
"value": "ABC"
}
]
},
{
"op": "replace",
"path": "/a/b/c",
"value": 123
}
]
It is important to note this specification does not define a distinct
JSON Predicates Document format. Rather, it is the intent for JSON
Predicates to be used within other JSON-based document formats.
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in [RFC2119].
2. Predicate Objects
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A JSON Predicate is a JSON Object whose members describe a testable
condition that evaluates as either true or false.
The essential components of a JSON Predicate include:
o A label identifying the predicate operation,
o A reference to the value being tested, and
o The condition against which the referenced value is to be
evaluated.
Predicate objects MUST have exactly one "op" member whose value
indicates the type of predicate operation to perform. It's value
MUST be one of: "and", "contains", "contains-", "defined", "ends",
"ends-", "in", "in-", "less", "matches", "matches-", "more", "not",
"or", "starts", "starts-", "test", "test-", "type", or "undefined".
The semantics for each are defined in the sections that follow.
Note that the value of the "op" member is case-sensitive and that
each of the operations listed are in lower-case. The value "Starts",
for example, is not equivalent to "starts".
If the "op" member specifies any value other than one of those listed
above, the evaluation of the predicate operation MUST cease and be
handled as if a boolean value of "false" was returned. The
application processing the predicate operation MAY signal that an
error condition has occurred depending on the specific requirements
of the application within which JSON Predicates are being used.
The remaining structure of each predicate operation depends on the
specific type. There are two basic types of predicates.
o First Order Predicates that are used to test one name value pair
against a single condition, and
o Second Order Predicates that aggregate one or more subordinate
First or Second Order Predicates.
In addition to the required "op" member, First Order Predicates have
exactly one "path" member whose value MUST be a string containing a
JSON-Pointer [RFC6901] value referencing the name value pair that is
to be tested. If the "path" member is not specified within the
predicate object, it's value is assumed to be an empty string.
Second Order Predicates MUST have exactly one "apply" member whose
value is a JSON Array containing one or more First or Second Order
Predicate Objects.
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Additional members can be required depending on the specific
predicate operation. All other members not explicitly defined by
this specification MUST be ignored.
Note that the ordering of members in JSON objects is not significant;
therefore the following operations are equivalent:
{"op": "contains", "path": "/a/b/c", "value": "ABC"}
{"path": "/a/b/c", "op": "contains", "value": "ABC"}
{"value": "ABC", "path": "/a/b/c", "op": "contains"}
2.1. Predicate Context
All JSON Predicates are evaluated against a given base context. The
nature of this context is dependent entirely on the application
within which JSON Predicates is being used. For instance, when used
together with JSON Patch, the JSON Predicate operations are evaluated
relative to the JSON document that is the target of the JSON Patch
operation.
Although Predicate Objects use JSON Pointer references to identify
values against which a predicate operation is evaluated, the base
context is not required to be a JSON object or array. In such cases,
however, it is the responsibility of the application implementation
to determine how to interpret the JSON Pointer reference relative to
the base context.
2.2. First Order Predicates
2.2.1. "contains" and "contains-"
The "contains" predicate evaluates as true if the referenced element
is defined and has a value whose string representation contains the
exact sequence of characters given by the predicate object's "value"
member.
For example, given the JSON document:
{
"a": {
"b": "This is a test"
}
}
The following predicate would evaluate as "true":
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{
"op": "contains",
"path": "/a/b",
"value": " is a "
}
By default, character matching MUST be performed in a case-sensitive
manner. To override this default behavior and perform case-
insensitive matching, use "contains-" as the value of "op".
For instance, the following will evaluate as "true":
{
"op": "contains-",
"path": "/a/b/",
"value": " Is A "
}
2.2.2. defined
The "defined" predicate evaluates as true if the referenced element
exists within the target context.
For example, given the JSON document:
{
"a": {
"b": null
}
}
The following predicate would evaluate as "true" because the path "/a
/b" exist within the document despite being explicitly set to null:
{
"op": "defined",
"path": "/a/b"
}
The following predicate would evaluate as "false" because the path "/
a/c" does exist within the document.
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{
"op": "defined",
"path": "/a/c"
}
2.2.3. ends
The "ends" predicate evaluates as true if the referenced element is
defined and has a value whose string representation ends with the
exact sequence of characters given by the predicate object's "value"
member.
For example, given the JSON document:
{
"a": {
"b": "This is a test"
}
}
The following predicate would evaluate as "true":
{
"op": "ends",
"path": "/a/b",
"value": " test"
}
By default, character matching MUST be performed in a case-sensitive
manner. To override this default behavior and perform case-
insensitive matching, use "ends-" as the value of "op".
For instance, the following will evaluate as "true":
{
"op": "ends-",
"path": "/a/b/",
"value": " TEST"
}
2.2.4. in
The "in" predicate evaluates as true if the referenced element
specifies a value exactly equal to one of the members of a JSON array
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provided by the predicate's "value" member. Equality is determined
following the sames rules specified for the JSON Patch "test"
operation in [RFC6902], Section 4.6, with one exception given for
optional case-insensitive comparisons.
For example, given the JSON document:
{
"a": {
"b": 10
}
}
The following will evaluate as "true":
{
"op": "in",
"path": "/a/b",
"value": [1, "foo", 10, {"z":"y"}]
}
The value specified for the "value" member MUST be a JSON Array.
By default, when comparing string values, character matching MUST be
performed in a case-sensitive manner. To override this default
behavior and perform case-insensitive matching, use "in-" as the
value of "op".
2.2.5. less
The "less" predicate evaluates as true if the referenced element is
defined and specifies a number whose value is less than that
specified by the predicate object's "value" member.
For example, given the JSON document:
{
"a": {
"b": 10
}
}
The following will evaluate as "true":
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{
"op": "less",
"path": "/a/b",
"value": 15
}
2.2.6. matches
The "matches" predicate evaluates as true if the referenced element
is defined and has a value whose completely string representation
matches the regular expression provided by the predicate object's
"value" member.
For example, given the JSON document:
{
"a": {
"b": "this is a test"
}
}
The following evalutes as "true":
{
"op": "matches",
"path": "/a/b",
"value": "[\\w\\s]*"
}
The predicate's matching pattern is expressed as a string value
conforming to the JavaScript Regular Expression syntax (see [1]).
By default, matching against the regular expression MUST be performed
in a case-sensitive manner. To override this default behavior and
perform case-insensitive matching, use "matches-" as the value of
"op". Using this alternative is equivalent to using the "i" modifier
flag within the JavaScript Regular Expression syntax (e.g. "/\w\s/*/
i").
For instance:
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{
"op": "matches-",
"path": "/a/b/",
"value": "[\\w\\s]*"
}
2.2.7. more
The "more" predicate evaluates as true if the referenced element is
defined and specifies a number whose value is greater than that
specified by the predicate object's "value" member.
For example, given the JSON document:
{
"a": {
"b": 10
}
}
The following will evaluate as "true":
{
"op": "more",
"path": "/a/b",
"value": 5
}
2.2.8. starts
The "starts" predicate evaluates as true if the referenced element is
defined and has a value whose string representation begins with the
exact sequence of characters given by the predicate object's "value"
member.
For example, given the JSON document:
{
"a": {
"b": "This is a test"
}
}
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The following predicate would evaluate as "true":
{
"op": "starts",
"path": "/a/b",
"value": "This "
}
By default, character matching MUST be performed in a case-sensitive
manner. To override this default behavior and perform case-
insensitive matching, use "starts-" as the value of "op".
For instance, the following will evaluate as "true":
{
"op": "starts-",
"path": "/a/b/",
"value": "this "
}
2.2.9. test
The JSON Patch "test" operation, as defined by [RFC6902],
Section 4.6, can be used as a First Order Predicate operation. It
evaluates as true if the referenced element exists and specifies a
value that is exactly equal to that provided by the predicate's
"value" member. The rules for evaluating equality are identical to
those defined within [RFC6902], Section 4.6, with one exception given
for optional case-insensitive comparisons.
For example, given the JSON document:
{
"a": {
"b": "this is a test"
}
}
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The following predicate would evaluate as "true"
{
"op": "test",
"path": "/a/b",
"value": "this is a test"
}
By default, when comparing string values, character matching MUST be
performed in a case-sensitive manner To override this default
behavior and perform case-insensitive matching, use "test-" as the
value of "op".
2.2.10. type
The "type" predicate evaluates as true if the referenced element
exists and specifies a value whose value type is equal to that
specified by the predicate's "value" member.
The "value" member MUST specify one of: "number", "string",
"boolean", "object", "array", "null", "undefined", "date", "date-
time", "time", "lang", "lang-range", "iri" or "absolute-iri".
For example, given the JSON document:
{
"a": {
"b": "this is a test",
"c": [1,2,3]
}
}
The following predicate would evaluate as "true"
{
"op": "type",
"path": "/a/b",
"value": "string"
}
When evaluating the type of a value, the following rules apply:
o If the "value" member specifies "number", the type predicate will
evaluate as true if the value referenced by the "path" member is a
JSON number.
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o If the "value" member specifies "string", the type predicate will
evaluate as true if the value referenced by the "path" member is a
JSON string.
o If the "value" member specifies "boolean", the type predicate will
evaluate as true if the value referenced by the "path" member is a
JSON boolean.
o If the "value" member specifies "object", the type predicate will
evaluate as true if the value referenced by the "path" member is a
JSON object.
o If the "value" member specifies "array", the type predicate will
evaluate as true if the value referenced by the "path" member is a
JSON array.
o If the "value" member specifies "null", the type predicate will
evaluate as true if the value referenced by the "path" member is a
JSON null.
o If the "value" member specifies "undefined", the type predicate
will evaluate as true if the member referenced by the "path"
member does not exist.
o If the "value" member specifies "date", the type predicate will
evaluate as true if the value referenced by the "path" member is a
JSON string conforming to the [RFC3339] "full-date" construct.
o If the "value" member specifies "time", the type predicate will
evaluate as true if the value referenced by the "path" member is a
JSON string conforming to the [RFC3339] "full-time" construct.
o If the "value" member specifies "date-time", the type predicate
will evaluate as true if the value referenced by the "path" member
is a JSON string conforming to the [RFC3339] "date-time"
construct.
o If the "value" member specifies "lang", the type predicate will
evaluate as true if the value referenced by the "path" member is a
JSON string conforming to the [RFC5646] "Language-Tag" construct.
o If the "value" member specifies "lang-range", the type predicate
will evaluate as true if the value referenced by the "path" member
is a JSON string conforming to the [RFC4647] "language-range"
construct.
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o If the "value" member specifies "iri", the type predicate will
evaluate as true if the value referenced by the "path" member is a
JSON string conforming to the [RFC3987] "IRI-reference" construct.
o If the "value" member specifies "absolute-iri", the type predicate
will evaluate a true if the value referenced by the "path" member
is a JSON string conforming to the [RFC3987] "IRI" construct.
2.2.11. undefined
The "undefined" predicate evaluates as true if the referenced element
does not exist within the target context.
For example, given the JSON document:
{
"a": {
"b": null
}
}
The following predicate would evaluate as "true" because the path "/a
/c" does not exist within the document:
{
"op": "undefined",
"path": "/a/c"
}
However, the following predicate would evaluate as "false" because
the path "/a/b" does exist within the document, despite specifying an
explicit null value.
{
"op": "undefined",
"path": "/a/b"
}
2.3. Second-Order Predicates
Second Order Predicates are defined as sets of one or more
subordinate First and Second Order Predicates.
All Second Order Predicates MAY contain a "path" member whose value
specifies a root path prefix for all contained predicates. If the
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"path" member is not specified, it's value is assumed to be an empty
string. For example, given the JSON document:
{
"a": {
"b": {
"c": "ABC!"
}
}
}
The following would evaluate as true because the path "/a/b/c" is
defined.
{
"op": "and",
"path": "/a/b",
"apply": [
{
"op": "defined",
"path": "/c"
}
]
}
The above example is equivalent to:
{
"op": "and",
"apply": [
{
"op": "defined",
"path": "/a/b/c"
}
]
}
2.3.1. and
The "and" predicate evaluates as "true" if all of it's contained set
of predicate operations evaluate as "true".
For example, given the JSON document:
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{
"a" : {
"b" : "foo",
"c" : {
"d": 10
}
}
}
The following would evaluate as "true" because the element "/a/b" is
defined and the value of element "/a/c/d" is less than 15.
{
"op": "and",
"apply" [
{
"op": "defined",
"path": "/a/b"
},
{
"op": "less",
"path": "/a/c/d",
"value": 15
}
]
}
However, the following would evaluate as "false" because while the
element "/a/c" exists, the value of that element is not a string.
{
"op": "and",
"apply": [
{
"op": "test",
"path": "/a/c"
},
{
"op": "type",
"path": "/a/c",
"value": "string"
}
]
}
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2.3.2. not
The "not" predicate evaluates as "true" if all of it's contained set
of predicate operations evaluate as "false".
For example, given the JSON document:
{
"a" : {
"b" : "foo",
"c" : {
"d": 10
}
}
}
The following would evaluate as "true" because the element "/a/b/e"
is undefined and the value of element "/a/c/d" is not less than 5.
{
"op": "not",
"apply": [
{
"op": "defined",
"path": "/a/b/e"
},
{
"op": "less",
"path": "/a/c/d",
"value": 5
}
]
}
However, the following would evaluate as "false" because the element
"/a/c" exists and the value for element "/a/b" begins with the letter
"f"
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{
"op": "not",
"apply": [
{
"op": "undefined",
"path": "/a/c"
},
{
"op": "starts",
"path": "/a/b",
"value": "f"
}
]
}
2.3.3. or
The "or" predicate evaluates as "true" if at least one of it's
contained set of predicate operations evaluate as "true".
For example, given the JSON document:
{
"a" : {
"b" : "foo",
"c" : {
"d": 10
}
}
}
The following would evaluate as "true" because the element "/a/b" is
defined.
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{
"op": "or",
"apply": [
{
"op": "defined",
"path": "/a/b"
},
{
"op": "less",
"path": "/a/c/d",
"value": 5
}
]
}
However, the following would evaluate as "false" because neither
elements "/a/e" or "/a/f" exist.
{
"op": "or",
"apply": [
{
"op": "test",
"path": "/a/e"
},
{
"op": "test",
"path": "/a/f"
}
]
}
2.3.4. Nesting Second Order Predicates
Second Order Predicates can be combined in a variety of ways to
define more complex test operations. For example:
{
"op": "or",
"path": "/a/b",
"apply": [
{
"op": "not",
"path": "/c",
"apply": [
{"op": "undefined"},
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{"op": "starts", "value": "f"}
]
},
{
"op": "not",
"path": "/d",
"apply": [
{"op": "defined"},
{"op": "type", "value": "number"}
]
}
]
}
2.4. Error Handling
When an error condition is encounted during the processing of a JSON
Predicate, the predicate MUST evaluate as false. Whether or not the
error condition is reported is dependent on the specific requirements
of the application within which JSON Predicates are being used.
Error conditions can arise in each of the following conditions:
o JSON Predicate Objects contained within a document fail to conform
to any normative requirement of this specification, or
o The Predicate Object specifies an unknown predicate operation, or
o The Predicate Object specifies a JSON Pointer referencing a value
that does not exist and the specified Predicate operation is not
specifically intended to test for the absence of a value (i.e. the
"undefined" and "defined" predicates), or
o A First Order Predicate Object specifies a predicate operation
that requires a "value" member providing the condition to test but
no "value" member is provided.
o The "value" member given for a given predicate operation is of an
unexpected or unsupported type for that operation (e.g.
specifying a string value for the "more" and "less" predicate
operations).
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2.5. Using JSON Predicates within JSON Patch Documents
While JSON Predicate objects can be used in a variety of
applications, the syntax has been specifically designed for
compatibility with the JSON Patch Document format. JSON Predicate
objects MAY be used directly within a JSON Patch Document as tests to
evaluate whether or not the application of a set of patch operations
should succeed or fail.
Because of requirements defined by the JSON Patch specification, when
Second Order Predicates are used as patch test operations within a
JSON Patch document, the "path" member MUST be specified. The value
of the "path" member MAY be an empty string.
For example, given the following JSON document:
{
"a": {
"b": {
"c": "123"
}
}
}
The following JSON Patch + JSON Predicates document will first test
that the path "/a/b/c" references a string value matching the given
regular expression prior to replacing that value:
[
{
"op": "and",
"path": "/a/b/c",
"apply": [
{"op": "type", "value": "string"},
{"op": "matches", "value": "\\d{3}"}
]
},
{
"op": "replace",
"path": "/a/b/c",
"value": "ABC"
}
]
When a JSON Predicate object within a JSON Patch document evaluates
as false, processing of the JSON Patch Document MUST be handled
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exactly the same as an unsuccessful JSON Patch operation would be
handled as defined in JSON-PATCH [RFC6902]. Specifically, processing
of the JSON Patch document SHOULD terminate and application of the
entire patch document SHALL NOT be deemed successful.
The MIME media type "application/json-patch-test" is used to identify
JSON Patch documents that contain predicates.
For example:
PATCH /some-document HTTP/1.1
Host: example.org
Content-Type: application/json-patch-test+json
[
{
"op": "matches",
"path": "/a/b/c",
"value": "\\d{3}"
},
{
"op": "replace",
"path": "/a/b/c",
"value": "ABC"
}
]
JSON Patch implementations that do not implement or recognize JSON
Predicate objects will treat them as unknown patch operations that
will cause evaluation of the Patch document to fail.
2.5.1. Conditional Patch Operations
In addition to being included as top-level operations within a JSON
Patch Document, Predicate objects can be used to make conditional
JSON Patch Operations through the use of the optional "if" and
"unless" properties.
For instance, in the following example, the value at path "/a/b/0" is
only removed if the value at path "/a/b" is an Array.
PATCH /some-document HTTP/1.1
Host: example.org
Content-Type: application/json-patch-test+json
[
{
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"op": "remove",
"path": "/a/b/0",
"if": {
"op": "type",
"path": "/a/b",
"value": "array"
}
}
]
Unlike a typical JSON Patch operation, however, the processing of the
complete Patch document does not fail if the stated condition is not
met. The operation is considered to be successful even if the stated
modification is not performed and processing will continue.
In the following example, the value at path "/a/b/0" is removed
unless the value at path "/a/b" is undefined and missing.
PATCH /some-document HTTP/1.1
Host: example.org
Content-Type: application/json-patch-test
[
{
"op": "remove",
"path": "/a/b/0",
"unless": {
"op": "undefined",
"path": "/a/b"
}
}
]
In a normal JSON Patch document without using predicates, processing
of the "remove" operation would cease and an error would be reported.
Using the "if" and "unless" properties, the error condition can be
avoided and compensated for using a combination of operations. For
instance, in the following example the patch document ensures that
the "/a/b" path exists and is an array before attempting to add new
items. If the existing value of "/a/b" is not an array, it's value
is changed to an array prior to adding items, ensuring that the
second "add" operation will succeed.
PATCH /some-document HTTP/1.1
Host: example.org
Content-Type: application/json-patch-test
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[
{
"op": "add",
"path": "/a/b",
"value": [],
"unless": {
"op": "and",
"apply": [
{"op": "defined"},
{"op": "type", "value": "array"}
]
}
},
{
"op": "add",
"path": "/a/b/-",
"value": "ABC"
}
]
The "if" and "unless" properties can be used with any JSON Patch
operation in a document using the "application/json-patch-test+json"
content type. The "if" and "unless" properties MUST NOT be used in
JSON Predicate objects.
3. IANA Considerations
The Internet media type for a JSON Patch document containing JSON
Predicate objects is application/json-patch-test+json.
Type name: application
Subtype name: json-patch-test+json
Required parameters: none
Optional parameters: none
Encoding considerations: binary
Security considerations:
See Security Considerations in Section 4
Interoperability considerations: N/A
Published specification:
[this memo]
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Applications that use this media type:
Applications that manipulate JSON documents.
Additional information:
Magic number(s): N/A
File extension(s): .json-patch-test
Macintosh file type code(s): TEXT
Person & email address to contact for further information:
James M Snell <jasnell@gmail.com>
Intended usage: COMMON
Restrictions on usage: none
Author: James M Snell <jasnell@gmail.com>
Change controller: IETF
4. Security Considerations
JSON Predicate objects do not, by themselves, introduce any
particular security concerns. Note that JSON documents that consist
of an arbitrary number of nested Second Order Predicate objects can
have a detrimental impact on overall performance and could be
leveraged by a malicious entity as part of a denial of service
attack.
5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the
Internet: Timestamps", RFC 3339, July 2002.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006.
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[RFC4647] Phillips, A. and M. Davis, "Matching of Language Tags",
BCP 47, RFC 4647, September 2006.
[RFC5646] Phillips, A. and M. Davis, "Tags for Identifying
Languages", BCP 47, RFC 5646, September 2009.
[RFC6901] Bryan, P., Zyp, K., and M. Nottingham, "JavaScript Object
Notation (JSON) Pointer", RFC 6901, April 2013.
5.2. Informative References
[RFC6902] Bryan, P. and M. Nottingham, "JavaScript Object Notation
(JSON) Patch", RFC 6902, April 2013.
Appendix A. Non-Normative Example Implementation (Ruby)
Following is a non-normative simple example implementation of JSON
Predicates, JSON Pointer and JSON Patch written in Ruby. This
purpose of this code is to simply illustrate the basic function of
JSON Predicates within a specific context. It should not be
considered to be a reference implementation and has not been
thoroughly tested for every possible case. The code is offered under
the Apache v2.0 license without warranty of any kind and may be used
for any purpose so long as proper attribution is maintained.
####################################
# JSON Tools #
# Implementation of JSON Patch, #
# Pointer and Predicates #
# #
# Author: James M Snell #
# (jasnell@gmail.com) #
# Date: 2013-09-24 #
# License: Apache v2.0 #
####################################
require 'json'
class Hash
# A fairly inefficient means of
# generating a deep copy of the
# hash; but it ensures that our
# hash conforms to the JSON spec
# and does not contain any cycles
def json_deep_copy
JSON.parse to_json
end
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def insert loc,val
self[loc] = val
end
def delete_at loc
self.delete loc
end
end
module JsonTools
def self.fix_key obj, key
if Array === obj
idx = Integer key
fail if not (0...obj.length).cover? idx
key = idx
end
key
end
class Pointer
# Raised when an error occurs during the
# evaluation of the pointer against a
# given context
class PointerError < StandardError; end
def initialize path
@parts = path.split('/').drop(1).map { |p|
p.gsub(/\~1/, '/').gsub(/\~0/, '~')
}
@last = @parts.pop
end
# Returns the last segment of the JSON Pointer
def last; @last; end
# Evaluates the pointer against the given
# context hash object and returns the
# parent. That is, if the Pointer is
# "/a/b/c", parent will return the object
# referenced by "/a/b", or nil if that
# object does not exist.
def parent context
@parts.reduce(context) do |o, p|
o[(o.is_a?(Array) ? p.to_i : p)]
end
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rescue
raise PointerError
end
alias :[] :parent
# Enumerates down the pointer path, yielding
# to the given block each name, value pair
# specified in the path, halting at the first
# nil value encountered. The required block
# will be passed two parameters. The first is
# the accessor name, the second is the value.
# For instance, given the hash {'a'=>{'b'=>{'c'=>123}}},
# and the pointer "/a/b/c", the block will be
# called three times, first with ['a',{'b'=>{'c'=>123}}],
# next with ['b',{'c'=>123}], and finally with
# ['c',123].
def walk context
p = @parts.reduce(context) do |o,p|
n = o[(o.is_a?(Array) ? p.to_i : p)]
yield p, n
return if NilClass === n # exit the loop if the object is nil
n
end
key = JsonTools.fix_key(p,@last)
yield key, (!p ? nil : p[key])
end
# Returns the specific value identified by this
# pointer, if any. Nil is returned if the path
# does not exist. Note that this does not differentiate
# between explicitly null values or missing paths.
def value context
parent = parent context
parent[JsonTools.fix_key(parent,@last)] unless !parent
end
# Alternative to value that raises a PointerError
# if the referenced path does not exist.
def value_with_fail context
parent = parent context
fail if !parent
parent.fetch(JsonTools.fix_key(parent,@last))
rescue
raise PointerError
end
# True if the referenced path exists
def exists? context
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p = parent context
if Array === p
(0...p.length).cover? Integer(@last)
else
p.has_key? @last
end
rescue
false
end
end
class Patch
PATCH_OPERATIONS = {}
class InvalidPatchDocumentError < StandardError; end
class FailedOperationError < StandardError; end
def initialize ops, with_predicates=false
# Parse JSON if necessary
if ops.is_a?(String) || ops.respond_to?(:read)
ops = JSON.load(ops)
end
fail unless Array === ops
@ops = ops
# Should we include the JSON Predicate operations?
# Off by default
extend Predicate if with_predicates
rescue
raise InvalidPatchDocumentError
end
# Initialize a new Patch object with
# JSON Predicate Operations enabled
def self.new_with_predicates ops
new ops, true
end
# Apply the patch to the given target hash
# object. Note that the target will be
# modified in place and changes will not
# be reversable in the case of failure.
def apply_to! target
@ops.each_with_object(target) do |operation, target|
raise 'Invalid Operation' unless operation.key?('op')
op = operation['op']
ic = op.slice!(-1) if op[-1] == '-'
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operation['ignore_case'] = ic != nil
PO = PATCH_OPERATIONS[op.to_sym]
PO[operation, target] rescue raise 'Invalid Operation'
end
end
# Apply the patch to a copy of the given
# target hash. The new, modified hash
# will be returned.
def apply_to target
apply_to! target.json_deep_copy
end
private
# Define the various core patch operations
class << Patch
def add params, target
ptr = Pointer.new params['path']
obj = ptr[target]
fail if not (Array === obj || Hash === obj)
if (Array === obj && ptr.last == '-')
obj.insert -1,params['value']
else
obj.insert JsonTools.fix_key(obj,ptr.last),params['value']
end
rescue
raise FailedOperationError
end
def remove params, target
ptr = Pointer.new params['path']
return if not ptr.exists? target #it's gone, just ignore..
obj = ptr[target]
obj.delete_at JsonTools.fix_key(obj,ptr.last)
rescue
raise FailedOperationError
end
def move params, target
move_or_copy params, target, true
end
def copy params, target
move_or_copy params, target, false
end
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def move_or_copy params, target, move=false
from = Pointer.new params['from']
to = Pointer.new params['path']
fail if !from.exists?(target) #|| to.exists?(target)
obj = from[target]
val = obj[JsonTools.fix_key(obj,from.last)]
remove(({'path'=>params['path']}), target) if move
add ({'path'=>params['to'],'value'=>val}), target
rescue
raise FailedOperationError
end
def replace params, target
ptr = Pointer.new params['path']
fail if not ptr.exists? target
obj = ptr[target]
obj[JsonTools.fix_key(obj,ptr.last)] = params['value']
rescue
raise FailedOperationError
end
def test params, target
ptr = Pointer.new(params['path'])
fail if not ptr.exists? target
obj = ptr[target]
val = obj[JsonTools.fix_key(obj,ptr.last)]
fail unless val == params['value']
rescue
raise FailedOperationError
end
end
# Specify the Patch Operations
[:add,:remove,:replace,:move,:copy,:test].each {
|x| PATCH_OPERATIONS[x] = lambda(&method(x))
}
public
def register_op sym, op
PATCH_OPERATIONS[sym] = op
end
end # End Patch Class
# Define the Predicate methods for use with the Patch object
module Predicate
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def self.string_check params, target, &block
ptr = Pointer.new params['path']
return false if !ptr.exists?(target)
val = ptr.value target
return false unless String === val
ignore_case = params['ignore_case']
test_val = params['value']
if ignore_case
test_val.upcase!
val.upcase!
end
yield val, test_val
end
def self.number_check params, target, &block
ptr = Pointer.new params['path']
return false if !ptr.exists?(target)
val = ptr.value target
test_val = params['value']
return false unless (Numeric === val && Numeric === test_val)
yield val, test_val
end
def self.contains params, target
string_check(params,target) {|x,y| x.include? y }
end
def self.defined params, target
ptr = Pointer.new params['path']
ptr.exists?(target)
end
def self.ends params, target
string_check(params,target) {|x,y| x.end_with? y }
end
def self.matches params, target
ptr = Pointer.new params['path']
return false if !ptr.exists?(target)
val = ptr.value target
return false unless String === val
ignore_case = params['ignore_case']
test_val = params['value']
regex = ignore_case ?
Regexp.new(test_val, Regexp::IGNORECASE) :
Regexp.new(test_val)
regex.match val
end
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def self.less params, target
number_check(params,target) {|x,y| x < y}
end
def self.more params, target
number_check(params,target) {|x,y| x > y}
end
def self.starts params, target
string_check(params,target) {|x,y| x.start_with? y }
end
def self.type params, target
ptr = Pointer.new params['path']
test_val = params['value']
if !ptr.exists? target
test_val == 'undefined'
else
return false if !ptr.exists?(target)
val = ptr.value target
case test_val
when 'number'
Numeric === val
when 'string'
String === val
when 'boolean'
TrueClass === val || FalseClass === val
when 'object'
Hash === val
when 'array'
Array === val
when 'null'
NilClass === val
else
false
end
end
end
def self.undefined params, target
ptr = Pointer.new params['path']
!ptr.exists?(target)
end
def self.and params, target
preds = params['apply']
return false unless preds.all? {|pred|
op = pred['op']
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ic = op.slice! -1 if op[-1] == '-'
pred['ignore_case'] = ic != nil
PREDICATES[op.to_sym][pred,target] rescue return false
}
true
end
def self.not params, target
preds = params['apply']
return false unless preds.none? {|pred|
op = pred['op']
ic = op.slice! -1 if op[-1] == '-'
pred['ignore_case'] = ic != nil
PREDICATES[op.to_sym][pred,target] rescue return false
}
true
end
def self.or params, target
preds = params['apply']
return false unless preds.any? {|pred|
op = pred['op']
ic = op.slice! -1 if op[-1] == '-'
pred['ignore_case'] = ic != nil
PREDICATES[op.to_sym][pred,target] rescue return false
}
true
end
PREDICATES = {}
[:contains,
:defined,
:ends,
:less,
:matches,
:more,
:starts,
:type,
:undefined,
:and,
:not,
:or].each {|x|
PREDICATES[x] = lambda(&method(x))
}
def self.extended other
PREDICATES.each_pair {|x,y|
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other.register_op x, ->(params,target) {
raise Patch::FailedOperationError unless y.call params,target
}
}
end
end
end # End Module
The following illustrates how the Ruby module is used:
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require 'jsontools'
include JsonTools
my_hash = JSON.parse %Q/
{
"a": {
"b": {
"c": "123!ABC"
}
}
}
/
my_patch = JSON.parse %Q!
[
{
"op": "contains",
"path": "/a/b/c",
"value": "ABC"
},
{
"op": "replace",
"path": "/a/b/c",
"value": 123
}
]
!
patch = Patch.new_with_predicates my_patch
# create new modified hash
new_hash = patch.apply_to my_hash
# edit hash in place
patch.apply_to! my_hash
Author's Address
James M Snell
Email: jasnell@gmail.com
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