如何使用NSURLProtocol模拟AJAX调用？

Question

我有UIWebview,它对外部服务进行AJAX调用.离线时我需要捕获这些请求并返回本地json.

我实现了NSURLProtocol,我设法捕获AJAX请求,问题是jquery总是返回0错误代码:

$.ajax({
  url: url,
  dataType: 'json',
  contentType: "application/json",
  success: function(jsonData){
    alert("success :");
  },
  error: function (request, status, error) {
    alert("failure :" + request.status );
  }

});

我总是得到一个request.status = 0

为了测试我的协议,我试图在我的html中模拟一个图像并且效果很好.

• 来自google.fr =>的图片的HTML请求正常工作
• AJAX调用amazon上的json => 失败

这是我的完整实现:

#import "EpubProtocol.h"

@implementation EpubProtocol

#pragma mark - NSURLProtocol

+ (BOOL)canInitWithRequest:(NSURLRequest *)request {
    BOOL awsRequest = [self request:request contains:@"s3.amazonaws.com"];
    BOOL imgRequest = [self request:request contains:@"google.fr"];
    BOOL match = awsRequest || imgRequest;

    return match;
}


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


- (void)startLoading {
    NSURLRequest *request = [self request];

    //Mock Amazon call
    if([EpubProtocol request:request contains:@"s3.amazonaws.com"]) {
        NSString *path = [[NSBundle bundleForClass:self.class] pathForResource:@"epub1" ofType:@"json"];
        NSData *data = [NSData dataWithContentsOfFile:path];

        [self mockRequest:request mimeType:@"application/json" data:data];
    }
    //Mock image call
    else if([EpubProtocol request:request contains:@"google.fr"]) {
        NSOperationQueue *queue = [[NSOperationQueue alloc] init];

        [NSURLConnection sendAsynchronousRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.itespresso.fr/wp-content/gallery/yahoo/1-yahoo-logo.jpg"]] queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
            [self mockRequest:request mimeType:@"image/jpeg" data:data];
        }];
    }
}

- (void)stopLoading
{
    NSLog(@"Did stop loading");
}


#pragma mark - Request utils

+ (BOOL) request:(NSURLRequest*)request contains:(NSString*)domain {
    NSString *str = [[request URL] absoluteString];
    NSPredicate *pred = [NSPredicate predicateWithFormat:@"SELF contains[cd] %@", domain];
    return [pred evaluateWithObject:str];
}


#pragma mark - Mock responses


-(void) mockRequest:(NSURLRequest*)request mimeType:(NSString*)mimeType data:(NSData*)data {
    id client = [self client];

    NSHTTPURLResponse *response = [[NSHTTPURLResponse alloc] initWithURL:[request URL] MIMEType:mimeType expectedContentLength:-1 textEncodingName:nil];

    [client URLProtocol:self didReceiveResponse:response
     cacheStoragePolicy:NSURLCacheStorageNotAllowed];
    [client URLProtocol:self didLoadData:data];
    [client URLProtocolDidFinishLoading:self];
}

@end

Answer 1

问题来自webkit,它因跨域请求而阻止响应.由于我们模拟了响应,因此必须强制使用Access-Control-Allow-Origin.

然后我们还需要强制响应的内容类型.

这是神奇发生的地方:

NSDictionary *headers = @{@"Access-Control-Allow-Origin" : @"*", @"Access-Control-Allow-Headers" : @"Content-Type"};
NSHTTPURLResponse *response = [[NSHTTPURLResponse alloc] initWithURL:request.URL statusCode:200 HTTPVersion:@"1.1" headerFields:headers];

协议的最终实施:

#import "EpubProtocol.h"

@implementation EpubProtocol

#pragma mark - NSURLProtocol

+ (BOOL)canInitWithRequest:(NSURLRequest *)request {
    BOOL isAwsRequest = [self request:request contains:@"s3.amazonaws.com"];

    return isAwsRequest;
}

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

- (void)startLoading {
    NSURLRequest *request = [self request];

    //Mock Amazon call
    if([EpubProtocol request:request contains:@"s3.amazonaws.com"]) {
        NSString *path = [[NSBundle bundleForClass:self.class] pathForResource:@"epub1" ofType:@"json"];
        NSData *data = [NSData dataWithContentsOfFile:path];

        [self mockRequest:request data:data];
    }
}

- (void)stopLoading
{
    NSLog(@"Did stop loading");
}


#pragma mark - Request utils

+ (BOOL) request:(NSURLRequest*)request contains:(NSString*)domain {
    NSString *str = [[request URL] absoluteString];
    NSPredicate *pred = [NSPredicate predicateWithFormat:@"SELF contains[cd] %@", domain];
    return [pred evaluateWithObject:str];
}


#pragma mark - Mock responses


-(void) mockRequest:(NSURLRequest*)request data:(NSData*)data {
    id client = [self client];

    NSDictionary *headers = @{@"Access-Control-Allow-Origin" : @"*", @"Access-Control-Allow-Headers" : @"Content-Type"};
    NSHTTPURLResponse *response = [[NSHTTPURLResponse alloc] initWithURL:request.URL statusCode:200 HTTPVersion:@"1.1" headerFields:headers];

    [client URLProtocol:self didReceiveResponse:response
     cacheStoragePolicy:NSURLCacheStorageNotAllowed];
    [client URLProtocol:self didLoadData:data];
    [client URLProtocolDidFinishLoading:self];
}

@end

JS中没什么特别之处:

function loadJSONDoc()
{
  var url = "https://s3.amazonaws.com/youboox_recette/epub.json";

  $.ajax({
      url: url,
      dataType: 'json',
       contentType: "application/json",
      success: function(jsonData){
        alert('success');
        document.getElementById("myDiv").innerHTML='<p>'+$.param(jsonData)+'</p>';
      },
      error: function (request, status, error) {
        alert("failure :" + request.status );
      }
  });
}