使用 libcurl 的分块 HTTP 响应中缺少块大小

Question

我尝试使用 curl 库来构建 HTTP 代理。我现在面临的问题是分块的 HTTP 响应不正确。通过检查保存的 HTTP 响应文件，我发现 HTTP 响应开始和结束时的块大小丢失了。 HTTP 响应来自 curl 回调函数，如下所示。

size_t httpClient::write_data(char *ptr, size_t size, size_t nmemb, void* userdata)
{   

    // get total size   
    size_t realsize = size*nmemb;
    // get object
    struct MemoryStruct* mem = (struct MemoryStruct*)userdata;

    // size of memory block pointerd by the mem->memory is changed to the new bytes
    mem->memory = (char*)realloc(mem->memory, (mem->size + realsize));

    if(mem->memory == NULL)
    {
        printf("not enough memory (realloc returned NULL)\n");
            exit(1);
    }

    // copy to memory structure
    memcpy(&(mem->memory[mem->size]), ptr, realsize);
    mem->size += realsize;
    //mem->memory[mem->size] = 0;

    cout<<"Write ["<<realsize<<"] bytes Data to chunk"<<endl;
    return realsize;

}

希望有人能指出我为这个回调函数犯的错误。谢谢：D

预期的分块 HTTP 响应如下所示：

HTTP/1.1 200 OK^M
Date: Wed, 17 Oct 2012 07:44:54 GMT^M
Expires: -1^M
Cache-Control: private, max-age=0^M
Content-Type: text/html; charset=UTF-8^M
Set-Cookie: PREF=ID=58da9f2271ea2d2b:FF=0:TM=1350459894:LM=1350459894:S=EnJS1hQo2d6_AnPM; expires=Fri, 17-Oct-2014 07:44:54 GMT; path=/; domain=.google.com^M
Set-Cookie: NID=65=RW0txpQSNA4NwlRhp0y1I6iF3L0xfugw8Bv4GMsB1yE1qu7iGoBO_2ZxqS0-DSeS4tJKnV26JlfVZmsnjxnjdUaHTDj3-AFREsvyMiE8wSKyabwYG8x-e18Pj8smdxUs; expires=Thu, 18-Apr-2013 07:44:54 GMT; path=/; domain=.google.com; HttpOnly^M
P3P: CP="This is not a P3P policy! See http://www.google.com/support/accounts/bin/answer.py?hl=en&answer=151657 for more info."^M
Content-Encoding: gzip^M
Transfer-Encoding: chunked^M
Server: gws^M
X-XSS-Protection: 1; mode=block^M
X-Frame-Options: SAMEORIGIN^M
^M
907a^M

十六进制格式的数字 907a 是我的 HTTP 响应文件中遗漏的块大小。

Answer 1

我可以向你提出下一步的建议：

1. 进入您的代码部分，设置回调函数，在堆栈上创建struct MemoryStruct。
2. 将参数写入回调函数原型中，以 struct MemoryStruct *userdata 代替 void *userdata。

3. 您的代码将如下所示：

   MemoryStruct data;
   curl_easy_setopt(curl, CURLOPT_WRITEDATA, &data);
   curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, write_data);
   
   ---------------------------------------------------------------------
   // if you'll used std::string instead char*
   ---------------------------------------------------------------------
   size_t write_data(char *data, size_t size, size_t count, MemoryStruct *userdata)
   {
       int result = 0;
       if(userdata->memory != NULL) {
           userdata->memory->append(data, size*count);
           result = size*count;
           userdata->size += result;
       }
       return result;
   }
   

调用curl库curl_easy_perform(CURL *handler)的函数后可以得到正确的响应。

PS。如果我对您的问题的理解有误，请在调用回调函数的位置显示您的代码