关于WKWebView的post请求丢失body问题的解决方案

WKWebView的优点这里不做过多介绍，主要说一下最近解决WKWebView的post请求丢失body问题的解决方案。
WKWebView 通过loadrequest方法加载Post请求会丢失请求体（body）中的内容，进而导致服务器拿不到body中的内容的问题的发生。这个问题的产生主要是因为WKWebView的网络请求的进程与APP不是同一个进程，所以网络请求的过程是这样的：
由APP所在的进程发起request，然后通过IPC通信(进程间通信)将请求的相关信息（请求头、请求行、请求体等）传递给webkit网络线进程接收包装，进行数据的HTTP请求，最终再进行IPC的通信回传给APP所在的进程的。这里如果发起的request请求是post请求的话，由于要进行IPC数据传递，传递的请求体body中根据系统调度，将其舍弃，最终在WKWebView网络进程接受的时候请求体body中的内容变成了空，导致此种情况下的服务器获取不到请求体，导致问题的产生。
为了能够获取POST方法请求之后的body内容，这两天整理了一些解决方案，大致分为三种：

1.将网络请求交由Js发起，绕开系统WKWebView的网络的进程请求达到正常请求的目的
2.改变POST请求的方法为GET方法(有风险，不一定服务器会接受GET方法)
3.将Post请求的请求body内容放入请求的Header中，并通过URLProtocol拦截自定义协议，在拦截中通过NSConnection进行重新请求（重新包装请求body），然后通过回调Client客户端来传递数据内容

三种方法中，我采用了第三种方案，这里说一下第三种方案的实现方式，大致分为三步:

1.注册拦截的自定义的scheme
2.重写loadRequest()方法，根据request的method方法是否为POST进行URL的拦截替换
3.在URLProtocol中进行request的重新包装（获取请求的body内容），使用NSURLConnection进行HTTP请求并将数据回传
这里说明一下为什么要自己去注册自定义的scheme，而不是直接拦截https/http。主要原因是：如果注册了https/http的拦截，那么所有的http(s)请求都会交由系统进程处理，那么此时系统进程会通过IPC的形式传递给实现URLProctol协议的类去处理，在通过IPC传递的过程中丢失body体（上面有讲到），所以在拦截的时候是拿不到POST方法的请求体body的。然而并不是所有的http请求都会走loadrequest（）方法（比如js中的ajax请求），所以导致一些POST请求没有被包装（将请求体body内容放到请求头header）就被拦截了，进而丢失请求体body内容，问题一样会产生。所以为了避免这样的问题，我们需要自己去定一个scheme协议，保证不过度拦截并且能够处理我们需要处理的POST请求内容。

以下是具体的实现方式：

1.注册拦截的自定义的scheme

    [NSURLProtocol registerClass:NSClassFromString(@“GCURLProtocol")];
    [NSURLProtocol wk_registerScheme:@"gc"];
    [NSURLProtocol wk_registerScheme:WkCustomHttp];
    [NSURLProtocol wk_registerScheme:WkCustomHttps];

2.重写loadRequest()方法，根据request的method方法是否为POST进行URL的拦截替换

//包装请求头内容
- (WKNavigation *)loadRequest:(NSURLRequest *)request{
    NSLog(@"发起请求:%@ method:%@",request.URL.absoluteString,request.HTTPMethod);
    NSMutableURLRequest *mutableRequest = [request mutableCopy];
    NSMutableDictionary *requestHeaders = [request.allHTTPHeaderFields mutableCopy];
    //判断是否是POST请求，POST请求需要包装request中的body内容到请求头中（会有丢失body问题的产生）
    //,包装完成之后重定向到拦截的协议中自己包装处理请求数据内容，拦截协议是GCURLProtocol，请自行搜索
    if ([mutableRequest.HTTPMethod isEqualToString:@"POST"] && ([mutableRequest.URL.scheme isEqualToString:@"http"] || [mutableRequest.URL.scheme isEqualToString:@"https"])) {
        NSString *absoluteStr = mutableRequest.URL.absoluteString;
        if ([[absoluteStr substringWithRange:NSMakeRange(absoluteStr.length-1, 1)] isEqualToString:@"/"]) {
            absoluteStr = [absoluteStr stringByReplacingCharactersInRange:NSMakeRange(absoluteStr.length-1, 1) withString:@""];
        }
        
        if ([mutableRequest.URL.scheme isEqualToString:@"https"]) {
            absoluteStr = [absoluteStr stringByReplacingOccurrencesOfString:@"https" withString:WkCustomHttps];
        }else{
            absoluteStr = [absoluteStr stringByReplacingOccurrencesOfString:@"http" withString:WkCustomHttp];
        }
        
        mutableRequest.URL = [NSURL URLWithString:absoluteStr];
        NSString *bodyDataStr = [[NSString alloc]initWithData:mutableRequest.HTTPBody encoding:NSUTF8StringEncoding];
        [requestHeaders addEntriesFromDictionary:@{@"httpbody":bodyDataStr}];
        mutableRequest.allHTTPHeaderFields = requestHeaders;
        
        NSLog(@"当前请求为POST请求Header:%@",mutableRequest.allHTTPHeaderFields);
        
    }
    return [super loadRequest:mutableRequest];
}

3.在URLProtocol中进行request的重新包装（获取请求的body内容），使用NSURLConnection进行HTTP请求并将数据回传（以下是主要代码）

+ (BOOL)canInitWithRequest:(NSURLRequest *)request {
    
    NSString *scheme = request.URL.scheme;
    
    if ([scheme isEqualToString:InterceptionSchemeKey]){
        
        if ([self propertyForKey:HaveDealRequest inRequest:request]) {
            NSLog(@"已经处理，放行");
            return NO;
        }
        return YES;
    }
    
    if ([scheme isEqualToString:WkCustomHttp]){
           
           if ([self propertyForKey:HaveDealWkHttpPostBody inRequest:request]) {
               NSLog(@"已经处理，放行");
               return NO;
           }
           return YES;
       }
    
    if ([scheme isEqualToString:WkCustomHttps]){
        
        if ([self propertyForKey:HaveDealWkHttpsPostBody inRequest:request]) {
            NSLog(@"已经处理，放行");
            return NO;
        }
        return YES;
    }
        
    return NO;
    
}
- (void)startLoading {
    
    //截获 gc 链接的所有请求，替换成本地资源或者线上资源
    if ([self.request.URL.scheme isEqualToString:InterceptionSchemeKey]) {
        [self htmlCacheRequstLoad];
    }
    
    else if ([self.request.URL.scheme isEqualToString:WkCustomHttp] || [self.request.URL.scheme isEqualToString:WkCustomHttps]){
        [self postBodyAddLoad];
    }
    else{
        NSMutableURLRequest *newRequest = [self cloneRequest:self.request];
        NSString *urlString = newRequest.URL.absoluteString;
        [self addHttpPostBody:newRequest];
        [NSURLProtocol setProperty:@YES forKey:GCProtocolKey inRequest:newRequest];
        [self sendRequest:newRequest];
    }
    
   
}

- (void)addHttpPostBody:(NSMutableURLRequest *)redirectRequest{
    
    //判断当前的请求是否是Post请求
    if ([self.request.HTTPMethod isEqualToString:@"POST"]) {
        NSLog(@"post请求");
        NSMutableDictionary *headerDict = [redirectRequest.allHTTPHeaderFields mutableCopy];
        NSString *body = headerDict[@"httpbody"]?:@"";
        if (body.length) {
            redirectRequest.HTTPBody = [body dataUsingEncoding:NSUTF8StringEncoding];
            NSLog(@"body:%@",body);
        }
    }
}
- (void)postBodyAddLoad{
    
    NSMutableURLRequest *cloneRequest = [self cloneRequest:self.request];
    if ([cloneRequest.URL.scheme isEqualToString:WkCustomHttps]) {
        cloneRequest.URL = [NSURL URLWithString:[cloneRequest.URL.absoluteString stringByReplacingOccurrencesOfString:WkCustomHttps withString:@"https"]];
        [NSURLProtocol setProperty:@YES forKey:HaveDealWkHttpsPostBody inRequest:cloneRequest];
    }else if ([cloneRequest.URL.scheme isEqualToString:WkCustomHttp]){
        
        cloneRequest.URL = [NSURL URLWithString:[cloneRequest.URL.absoluteString stringByReplacingOccurrencesOfString:WkCustomHttp withString:@"http"]];
        [NSURLProtocol setProperty:@YES forKey:HaveDealWkHttpPostBody inRequest:cloneRequest];
    }
    //添加body内容
    [self addHttpPostBody:cloneRequest];
    NSLog(@"请求body添加完成:%@",[[NSString alloc]initWithData:cloneRequest.HTTPBody encoding:NSUTF8StringEncoding]);
    [self sendRequest:cloneRequest];
    
}
//复制Request对象
- (NSMutableURLRequest *)cloneRequest:(NSURLRequest *)request
{
    NSMutableURLRequest *newRequest = [NSMutableURLRequest requestWithURL:request.URL cachePolicy:request.cachePolicy timeoutInterval:request.timeoutInterval];
    
    newRequest.allHTTPHeaderFields = request.allHTTPHeaderFields;
    [newRequest setValue:@"image/webp,image/*;q=0.8" forHTTPHeaderField:@"Accept"];
    
    if (request.HTTPMethod) {
        newRequest.HTTPMethod = request.HTTPMethod;
    }
    
    if (request.HTTPBodyStream) {
        newRequest.HTTPBodyStream = request.HTTPBodyStream;
    }
    
    if (request.HTTPBody) {
        newRequest.HTTPBody = request.HTTPBody;
    }
    
    newRequest.HTTPShouldUsePipelining = request.HTTPShouldUsePipelining;
    newRequest.mainDocumentURL = request.mainDocumentURL;
    newRequest.networkServiceType = request.networkServiceType;
    
    return newRequest;
}

#pragma mark - NSURLConnectionDataDelegate
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    /**
     * 收到服务器响应
     */
    NSURLResponse *returnResponse = response;
    [self.client URLProtocol:self didReceiveResponse:returnResponse cacheStoragePolicy:NSURLCacheStorageAllowed];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    /**
     * 接收数据
     */
    if (!self.recData) {
        self.recData = [NSMutableData new];
    }
    if (data) {
        [self.recData appendData:data];
    }
}
- (nullable NSURLRequest *)connection:(NSURLConnection *)connection willSendRequest:(NSURLRequest *)request redirectResponse:(nullable NSURLResponse *)response
{
    /**
     * 重定向
     */
    if (response) {
        [self.client URLProtocol:self wasRedirectedToRequest:request redirectResponse:response];
    }
    return request;
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    [self.client URLProtocolDidFinishLoading:self];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    /**
     * 加载失败
     */
    [self.client URLProtocol:self didFailWithError:error];
}