A basic NSURLProtocol subclass useful for capturing and mocking JSON responses

SCMockURLProtocol.m

#import "SCMockURLProtocol.h"

#define HARVEST_MODE NO
#define MOCK_MODE YES

@interface SCMockURLProtocol()<NSURLConnectionDelegate>

@property (nonatomic, strong) NSURLRequest *currentRequest;
@property (nonatomic, strong) NSURLSessionTask *currentTask;
@property (nonatomic, strong) NSURLConnection *connection;
@property (nonatomic, strong) NSMutableData *responseData;

@end


@implementation SCMockURLProtocol

+ (BOOL)canInitWithRequest:(NSURLRequest *)request {
    
    if (!MOCK_MODE) return NO;
    
    if (!HARVEST_MODE) {
        
        // Check if request is one we want to handle
        NSLog(@"%s, %s called %ld times, with request: %@", __FILE__, __FUNCTION__,(long)0, request.URL.absoluteString);
        if ([SCMockURLProtocol haveMockJSONForURL:request.URL]) {
            return YES;
        } else {
            return NO;
        }
        
    } else {
        
        static NSInteger callCount = 0;
        
        callCount++;
        
        NSLog(@"%s, %s called %ld times, with request: %@", __FILE__, __FUNCTION__,(long)callCount, request.URL.absoluteString);
        
        if ([NSURLProtocol propertyForKey:@"MyURLProtocolHandledKey" inRequest:request]) {
            return NO;
        }
        
        return YES;
    }
}

+ (NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request {
    return request;
}

+ (BOOL)requestIsCacheEquivalent:(NSURLRequest *)a toRequest:(NSURLRequest *)b {
    return [super requestIsCacheEquivalent:a toRequest:b];
}


- (void)startLoading {
    
    if (!HARVEST_MODE) {
        
        // Call got response
        NSHTTPURLResponse *response = [self getResponseForURL:self.request.URL];
        [self.client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed];
        
        // Call did load data
        NSData *responseData = [self getResponseDataForURL:self.request.URL];
        [self.client URLProtocol:self didLoadData:responseData];
        
        // Finish the load
        [self.client URLProtocolDidFinishLoading:self];
        
    } else {
        
        // Let the connection pass through and load from NSURL connection
        NSMutableURLRequest *newRequest = [self.request mutableCopy];
        [NSURLProtocol setProperty:@YES forKey:@"MyURLProtocolHandledKey" inRequest:newRequest];
        
        self.connection = [NSURLConnection connectionWithRequest:newRequest delegate:self];
    }
}

- (void)stopLoading {
    [self.connection cancel];
    self.connection = nil;
}


#pragma mark - NSURLConnectionDelegate

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    
    if (HARVEST_MODE) {
        // Dump Response
        NSLog(@"Response of URL %@: %@", self.request.URL, response);
    }
    
    [self.client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    
    // We are only interested in capturing data in harvest mode
    
    if (HARVEST_MODE) {
        
        if (self.responseData == nil) {
            self.responseData = [[NSMutableData alloc] initWithData:data];
        } else {
            [self.responseData appendData:data];
        }
        
    }
    
    [self.client URLProtocol:self didLoadData:data];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    
    if (HARVEST_MODE) {
        [self dumpJSONData:self.responseData];
    }
    
    [self.client URLProtocolDidFinishLoading:self];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    [self.client URLProtocol:self didFailWithError:error];
}


#pragma mark - Helpers

- (NSHTTPURLResponse *)getResponseForURL:(NSURL *)URL {
    
    NSString *fileLocation = URL.absoluteString.lastPathComponent;
    
    NSString *filePath = [[NSBundle mainBundle] pathForResource:[fileLocation stringByDeletingPathExtension] ofType:@"json"];
    NSData* data = [NSData dataWithContentsOfFile:filePath];
    __autoreleasing NSError* error = nil;
    NSDictionary *responseDict = [NSJSONSerialization JSONObjectWithData:data
                                                                 options:kNilOptions
                                                                   error:&error][@"response"];
    
    /*
    {
        "status code": 200,
        "headers" : {
            "Access-Control-Allow-Methods" : "*",
            "Access-Control-Allow-Origin" : "*",
            "Connection" : "keep-alive",
            "Content-Encoding" : "gzip",
            "Content-Length" : 13696,
            "Content-Type" : "application/json; charset=utf-8",
            "Date" : "Sun, 31 Jan 2016 15:11:13 GMT",
            "Server" : "nginx/1.6.0",
            "X-Parse-Platform" : "G1",
            "X-Runtime" : "0.981976"
        }
    }
     */
    
    if (error != nil) {
        return nil;
    } else {
        
        return [[NSHTTPURLResponse alloc] initWithURL:self.request.URL
                                           statusCode:[responseDict[@"status code"] integerValue]
                                          HTTPVersion:@"HTTP/1.1"
                                         headerFields:responseDict[@"headers"]];
    }
}

- (NSData *)getResponseDataForURL:(NSURL *)URL {
    
    NSString *fileLocation = URL.absoluteString.lastPathComponent;
    
    NSString *filePath = [[NSBundle mainBundle] pathForResource:[fileLocation stringByDeletingPathExtension] ofType:@"json"];
    
    NSData* data = [NSData dataWithContentsOfFile:filePath];
    __autoreleasing NSError* error = nil;
    NSDictionary *responseDict = [NSJSONSerialization JSONObjectWithData:data
                                                                 options:kNilOptions
                                                                   error:&error][@"response_data"];
    
    return [NSJSONSerialization dataWithJSONObject:responseDict options:NSJSONWritingPrettyPrinted error:nil];
}

+ (BOOL)haveMockJSONForURL:(NSURL *)URL {
    
    NSString *fileLocation = URL.absoluteString.lastPathComponent;
    
    NSString *filePath = [[NSBundle mainBundle] pathForResource:[fileLocation stringByDeletingPathExtension] ofType:@"json"];
    
    if (filePath != nil) {
        return YES;
    } else {
        return NO;
    }
}

- (void)dumpJSONData:(NSData *)responseData {
    
    NSString *JSONString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];

    NSLog(@"/n/n/n ****** /n Response for URL: %@ /n/n %@, /n/n *******", self.request.URL.absoluteString, JSONString);
}

@end