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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://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 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. Snell Expires March 28, 2014 [Page 1] Internet-Draft JSON Predicates September 2013 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 Snell Expires March 28, 2014 [Page 2] Internet-Draft JSON Predicates September 2013 { "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 Snell Expires March 28, 2014 [Page 3] Internet-Draft JSON Predicates September 2013 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. Snell Expires March 28, 2014 [Page 4] Internet-Draft JSON Predicates September 2013 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": Snell Expires March 28, 2014 [Page 5] Internet-Draft JSON Predicates September 2013 { "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. Snell Expires March 28, 2014 [Page 6] Internet-Draft JSON Predicates September 2013 { "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 Snell Expires March 28, 2014 [Page 7] Internet-Draft JSON Predicates September 2013 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": Snell Expires March 28, 2014 [Page 8] Internet-Draft JSON Predicates September 2013 { "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: Snell Expires March 28, 2014 [Page 9] Internet-Draft JSON Predicates September 2013 { "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" } } Snell Expires March 28, 2014 [Page 10] Internet-Draft JSON Predicates September 2013 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" } } Snell Expires March 28, 2014 [Page 11] Internet-Draft JSON Predicates September 2013 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. Snell Expires March 28, 2014 [Page 12] Internet-Draft JSON Predicates September 2013 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. Snell Expires March 28, 2014 [Page 13] Internet-Draft JSON Predicates September 2013 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 Snell Expires March 28, 2014 [Page 14] Internet-Draft JSON Predicates September 2013 "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: Snell Expires March 28, 2014 [Page 15] Internet-Draft JSON Predicates September 2013 { "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" } ] } Snell Expires March 28, 2014 [Page 16] Internet-Draft JSON Predicates September 2013 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" Snell Expires March 28, 2014 [Page 17] Internet-Draft JSON Predicates September 2013 { "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. Snell Expires March 28, 2014 [Page 18] Internet-Draft JSON Predicates September 2013 { "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"}, Snell Expires March 28, 2014 [Page 19] Internet-Draft JSON Predicates September 2013 {"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). Snell Expires March 28, 2014 [Page 20] Internet-Draft JSON Predicates September 2013 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 Snell Expires March 28, 2014 [Page 21] Internet-Draft JSON Predicates September 2013 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 [ { Snell Expires March 28, 2014 [Page 22] Internet-Draft JSON Predicates September 2013 "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 Snell Expires March 28, 2014 [Page 23] Internet-Draft JSON Predicates September 2013 [ { "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] Snell Expires March 28, 2014 [Page 24] Internet-Draft JSON Predicates September 2013 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 Intended usage: COMMON Restrictions on usage: none Author: James M Snell 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. Snell Expires March 28, 2014 [Page 25] Internet-Draft JSON Predicates September 2013 [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 Snell Expires March 28, 2014 [Page 26] Internet-Draft JSON Predicates September 2013 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 Snell Expires March 28, 2014 [Page 27] Internet-Draft JSON Predicates September 2013 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 Snell Expires March 28, 2014 [Page 28] Internet-Draft JSON Predicates September 2013 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] == '-' Snell Expires March 28, 2014 [Page 29] Internet-Draft JSON Predicates September 2013 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 Snell Expires March 28, 2014 [Page 30] Internet-Draft JSON Predicates September 2013 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 Snell Expires March 28, 2014 [Page 31] Internet-Draft JSON Predicates September 2013 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 Snell Expires March 28, 2014 [Page 32] Internet-Draft JSON Predicates September 2013 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'] Snell Expires March 28, 2014 [Page 33] Internet-Draft JSON Predicates September 2013 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| Snell Expires March 28, 2014 [Page 34] Internet-Draft JSON Predicates September 2013 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: Snell Expires March 28, 2014 [Page 35] Internet-Draft JSON Predicates September 2013 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 Snell Expires March 28, 2014 [Page 36]