JSON Tools (Objective-C)

by Gregory Combs
(MIT License - 2014)

JSON Patch, JSON Pointer, and JSON Schema Validation in Objective-C

This Objective-C library is a collection of classes and categories that implement three powerful new features (JSON Patch, JSON Pointer, JSON Schema) that work with JSON data (represented by NSDictionaries and NSArrays in Objective-C). Unit tests are included for each component.

To Run the Tests

To build the test project, be sure to do the following:

1. Install CocoaPods (use homebrew) if you haven't already.
2. Run pod install from the command line.
   
3. Open the newly created JSONToolsTests.xcworkspace document not the JSONToolsTests.xcodeproj document.
4. Hit Command-U to run the tests.

Features

• JSON Patch - IETF RFC6902: Create and apply operation patches (add, remove, copy, move, test, _get) to serially transform JSON Data. This functionality was inspired by Joachim Wester's JavaScript implementation of JSON Patch.

  • Example Patch Copy:

        #import "JSONTools.h"
        #import "JSONDeeplyMutable.h"
    
        - (void)examplePatchCopy
        {
             NSMutableDictionary *obj = nil;
             NSMutableDictionary *expected = nil;
             NSDictionary *patch = nil;
    
             obj = [@{@"foo": @1,
                      @"baz": @[@{@"qux": @"hello"}]} copyAsDeeplyMutableJSON];
    
             patch = @{@"op": @"copy",
                       @"from": @"/foo",
                       @"path": @"/bar"};
    
             [JSONPatch applyPatches:@[patch] toCollection:obj];
    
             expected = [@{@"foo": @1,
                           @"baz": @[@{@"qux": @"hello"}],
                           @"bar": @1} copyAsDeeplyMutableJSON];
        }
    

  • Example Patch Generation (JSON Diff):

        #import "JSONTools.h"
    
        - (void)examplePatchGeneration
        {
            NSDictionary *objA = nil;
            NSDictionary *objB = nil;
            NSArray *patches = nil;
            NSArray *expected = nil;
    
            objA = @{@"user": @{@"firstName": @"Albert",
                                @"lastName": @"Einstein"}};
    
            objB = @{@"user": @{@"firstName": @"Albert"}};
    
            patches = [JSONPatch createPatchesComparingCollectionsOld:objA toNew:objB];
    
            expected = @[@{@"op": @"remove",
                           @"path": @"/user/lastName"}];
    
        }
    

• JSON Pointer - IETF RFC6901: Reference and access values and objects within a hierarchical JSON structure using a concise path pattern notation. This functionality is based on Jonathan Dring's NSDictionary-CWJSONPointer.

  • Example:

        #import "JSONTools.h"
    
        - (void)exampleJSONPointer
        {
            NSDictionary *obj = @{
                @"data": @{
                    @"foo": @[@"bar", @"baz"],
                    @"bork": @{
                        @"crud": @"stuff",
                        @"guts": @"and things"
                    }
                }
            };
    
            NSString *result1 = [_obj valueForJSONPointer: @"/data/foo/1" ];
            // Yields -> "baz"
    
            NSString *result2 = [_obj valueForJSONPointer: @"/data/bork/guts"];
            // Yields -> "and things"
    
            NSDictionary *result3 = [_obj valueForJSONPointer: @"/data/bork"];
            // Yields -> {"crud": "stuff","guts": "and things"}
        }
    

• JSON Schema with Validation - IETF Draft v4, 2013. This functionality is based on Sam Duke's KiteJSONValidator but adds additional validations and tests for the JSON-Schema format parameter.

  • Example #1:

        {
           "schema": {
               "type": "array",
               "items": { "$ref": "#/definitions/positiveInteger" },
               "definitions": {
                   "positiveInteger": {
                       "type": "integer",
                       "minimum": 0,
                       "exclusiveMinimum": true
                   }
               }
           },
           "validData": [0, 1, 2, 3, 4, 5],
           "invalidData": [-12, "Abysmal", null, -141]
        }

        /* 
           Assuming that variables are assigned using JSON above: 
             schema is an NSDictionary
             validData and invalidData are NSArrays
         */
    
        BOOL success = NO;        
        JSONSchemaValidator *validator = [JSONSchemaValidator new];
    
        success = [validator validateJSONInstance:validData withSchema:schema];
        // success == YES, All validData values are positive integers.
    
        success = [validator validateJSONInstance:invalidData withSchema:schema];
        // success == NO, invalidData array isn't comprised of positive integers.
    

  • Example #2:

        NSDictionary *schema = nil;
        id testData = nil;
        BOOL success = NO;
    
        JSONSchemaValidator *validator = [JSONSchemaValidator new];
        validator.formatValidationEnabled = YES;
    
        schema = @{@"format": @"date-time"};
        testData = @"2000-02-29T08:30:06.283185Z";
        success = [validator validateJSONInstance:testData withSchema:schema];
        // success == YES, February 2000 had 29 days.
    
        schema = @{@"format": @"ipv6"};
        testData = @"12345::";
        success = [validator validateJSONInstance:testData withSchema:schema];
        // success == NO, the IPv6 address has out-of-range values.