libcurl怎样判断数据接收完成?

Cocos2d-x
#1

rt，一般设置CURLOPT_WRITEFUNCTION回调后，libcurl会多次自动调用这个回调;
size_t cb(void *contents, size_t size, size_t nmemb, void *userp)
curl_easy_setopt(curl_handle, CURLOPT_WRITEFUNCTION, cb );

怎么在这个回调中判断数据接收完毕?

多谢!

#2

比如http get接收json数据，应该怎么判断接收完成?:6:

#3

没人吗?:6::6::6::6:

#4

This function may be called with zero bytes data if the transferred file is empty.