1、httpc支持stream下载文件
参见erlang官方文档：
- stream
-
Streams the body of a 200 or 206 response to the calling process or to a file. When streaming to the calling process using the option self the following stream messages will be sent to that process: {http, {RequestId, stream_start, Headers}, {http, {RequestId, stream, BinBodyPart}, {http, {RequestId, stream_end, Headers}. When streaming to to the calling processes using the option {self, once} the first message will have an additional element e.i. {http, {RequestId, stream_start, Headers, Pid}, this is the process id that should be used as an argument to http:stream_next/1 to trigger the next message to be sent to the calling process.
Note that it is possible that chunked encoding will add headers so that there are more headers in the stream_end message than in the stream_start. When streaming to a file and the request is asynchronous the message {http, {RequestId, saved_to_file}} will be sent.
Defaults to none.
{ok, _RequestId} = httpc:request(get,{Url,[{"User-Agent", "RYT"}]}, [],[{sync, false}, {body_format, binary}, {stream, self}]),
loop_recv() ->
receive
{http, {RequestId, stream_start, _Headers}} ->
io:format("recv data ~p stream_start ~n",[RequestId]),
loop_recv();
{http, {_RequestId, stream, BinBodyPart}}->
io:format("recv data ~p BinBodyPart: ~n~p~n",[RequestId,BinBodyPart]),
loop_recv();
{http, {RequestId, stream_end, _Headers}} ->
io:format("recv data ~p stream_end ~n",[RequestId]);
R ->
io:format("recv error data: ~p~n",[R])
end.
{sync,false} 异步请求
{body_format, binary} body为二进制格式
{steam， self} 支持steam方式，且发送到请求进程
loop_recv() 发送完异步下载请求后，循环等待接收，直到收到stream_end