如何使用 NSURLProtocol 模拟 AJAX 调用？

Question

我有 UIWebview 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。

我实现了一个 NSURLProtocol 并且我设法捕获了 AJAX 请求，问题是 jquery 总是返回一个 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，我尝试在我的 html 中模拟一张图片，效果很好。

• 从 google.fr 对图像的 HTML 请求 => 工作正常
• 在亚马逊上对 json 的 AJAX 调用 => 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，它因为跨域源请求而阻塞了响应。由于我们模拟了响应，我们必须强制使用 Access-Control-Allow-Origin。

然后我们还需要强制响应的内容类型。

这就是神奇发生的地方：

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];

协议的最终实现：

#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 没什么特别的：

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 );
      }
  });
}

Answer 2

前段时间我不得不做类似的事情。

首先我设法找到可以使 UIWebViewDelegate 捕获 ajax 调用的代码，所以在我的 webapp 部分中我有：

//code to extend XMLHttpRequest, and have ajax call available in uiwebviewdelegate.

var s_ajaxListener = new Object();
s_ajaxListener.tempOpen = XMLHttpRequest.prototype.open;
s_ajaxListener.tempSend = XMLHttpRequest.prototype.send;
s_ajaxListener.callback = function () {
    window.location=this.url;
};

XMLHttpRequest.prototype.open = function(a,b) {
  if (!a) var a='';
  if (!b) var b='';
  s_ajaxListener.tempOpen.apply(this, arguments);
  s_ajaxListener.method = a;  
  s_ajaxListener.url = b;
  if (a.toLowerCase() == 'get') {
    s_ajaxListener.data = b.split('?');
    s_ajaxListener.data = s_ajaxListener.data[1];
  }
}

XMLHttpRequest.prototype.send = function(a,b) {
  if (!a) var a='';
  if (!b) var b='';
  s_ajaxListener.tempSend.apply(this, arguments);
  if(s_ajaxListener.method.toLowerCase() == 'post')s_ajaxListener.data = a;
  s_ajaxListener.callback();
}

然后在 iOS 中，我在 UIWebViewDelegate shouldStartLoad 中返回 NO（我的情况有点难看）：

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType
{
    if ([[[request URL] scheme] rangeOfString:@"https"].length > 0) 
    {
        return NO;
    }

    return YES;
}

最重要的是我会注册我的协议：

[NSURLProtocol registerClass:[MyProtocol class]];

使用 StartLoad 实现。 您还应该将 canInitWithRequest 子类化

+ (BOOL)canInitWithRequest:(NSURLRequest *)request 
{
    if ([request.URL.scheme rangeOfString:@"https"].length > 0) 
    {
        return YES;
    }

    return NO;
}

告诉协议它应该用于请求。

当你有网络时不要忘记取消注册。

如果您不想打扰 NSURLProtocol 实现，可以使用我自己的：https://github.com/bcharp/BOURLProtocol ;)

希望对你有帮助！