C++ socket recv why so slowly

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recently , I meet a question about the function recv of socket programming, let me introduce the background of the question ,
now I have a client and server in different pc , the client is linux OS without any 3th network libray, such ACE , curl ... and the server is Window OS - and I have deployed the http server - Apache , in my project , I will send http post request from socket programming to server which is a php website timely (about 1 time 2 seconds), and the post data is encapluted with Json format , that is the http Content-Type:application/json, but when I send the request , then I recv the response with Json format from server (in fact the response data is not big < 5*1024), but in the next , very slowly , about more than 10 seconds ,then I can get the response wholly , sometimes can not the any response Json , I suppose the reason is bacause the unfit buf length , I tried 1024 , 2048 , 512 ... , and the result is disappointed , the below is my recv code , could you help to see it ? thanks in advance , BTW , I use SOCK_STREAM in the socket

C++

      void Communication::receive(char buffer[], int BUFFER_SIZE){
        static const int small_buf = 512;
        char buf[small_buf];
        bzero(buf,small_buf);
        int length = 0;
        char* pp = buffer;
        do{
            length = recv(socket_,buf,small_buf,0);
             if(length < 0)
                {
                connect_state_ = false;
                break;
                }else if(length == small_buf){
                connect_state_ = true;
                memcpy(pp, buf, small_buf);
                pp = pp+small_buf;  
            }else if(length < small_buf && length > 0)
            {
                connect_state_ = true;
                memcpy(pp, buf, length);
                pp = pp + length;
            }else if(length == 0)
            {
                break;
            }
        }while(length > 0);
//merge the small_buf into a big buffer which is big enough (50*1024), which is one of function's param 
}

What I have tried:

I changed the buf length , 512, 1024 ,2048 , even I change SOCK_DGRAW to send json and then recv , but the result is same , recv is very very slow , I use sync to communicate with a php website in apache server

Posted 23-Jun-16 23:31pm

Member 12601798

Updated 24-Jun-16 1:01am

Richard MacCutchan

v2

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Mohibur Rashid 24-Jun-16 6:15am

Are you sure that your query is working fast?

Member 12601798 26-Jun-16 20:50pm

yes , the server response is very short , and i write the server code

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KarstenK · Answer 1 · 2016-06-24T00:58:00

Solution 1

Your code looks straitforward, as in many other places I have seen. The influence of buffer size is smaller as you think. You should also use a 8k buffer, so you get all data at once.

My tip is that your server or network is slow. Take a look at it. You need to find the bottleneck. Try a local fetch on the server.

Tip 2: Use Wireshark for investigating the network traffic.

Posted 24-Jun-16 0:58am

KarstenK

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Member 12601798 26-Jun-16 5:49am

thank your advance , but I I find the reason why the reponse is so slowly , in face , I use the below c++ code to send Post request,

string PostString::prepare_send(const string& host, const string& path , const string& content_type){
string stream;
int content_length = str_.length();
//cout << "content length is " << content_length << endl;
char buffer[20] = { 0 };
num_to_buffer(content_length, buffer, 10);
string str;
cp_buffer_string(buffer, 20, str);
stream += "POST ";
stream += path;
stream += " HTTP/1.1\r\n";
stream += "Host: ";
stream += host;
stream += "\r\n";
stream += "User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.3\r\n";
if("json" == content_type){

stream += "Content-Type: application/json\r\n";
}else{
stream += "Content-Type: application/x-www-form-urlencoded\r\n";
}
stream += "Content-Length: ";
stream += str;
stream += "\r\n";
//stream += "Connection: keep-alive\r\n";
stream += "Connection: close\r\n";
stream += "\r\n";
stream += str_;
return stream;

}
please note :Connection: keep-alive\r\n";
stream += "Connection: close\r\n";

I used the keep_alive mode , http will keep to open the connection , the server will suppose the client will continue to send post request, so the server will wait, in fact , I will not send any more in the session, so the server will close the connection when time is out , that is all :)

Jochen Arndt · Answer 2 · 2016-06-24T01:01:00

Solution 2

Is your socket blocking or non-blocking?

With blocking sockets, the recv call will only return when there are data available (return value > 0), a timeout occured (return value 0), or an error occured (return value -1).

Your code will wait for data, receives it, and waits again. This will be an endless loop if you have not set a timeout value. With a timeout value, the recv call will return after that time when no data has been received. According to your description this seems to be the case with a timeout value of 10 seconds.

With non-blocking sockets you should use some kind of signaling when data are available and call recv repeatedly while it returns -1 and errno is EAGAIN or EWOULDBLOCK.

I suggest to use a non-blocking socket. With blocking sockets you have to analyse the received data immediately to detect if all data has been received or there are more to come.

Posted 24-Jun-16 1:01am

Jochen Arndt

Comments

Member 12601798 26-Jun-16 5:52am

thank your advance , sync and async has nothing to improve the situation, I find the reason why the reponse is so slowly , in fact , I use the below c++ code to send Post request,

string PostString::prepare_send(const string& host, const string& path , const string& content_type){
string stream;
int content_length = str_.length();
//cout << "content length is " << content_length << endl;
char buffer[20] = { 0 };
num_to_buffer(content_length, buffer, 10);
string str;
cp_buffer_string(buffer, 20, str);
stream += "POST ";
stream += path;
stream += " HTTP/1.1\r\n";
stream += "Host: ";
stream += host;
stream += "\r\n";
stream += "User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.3\r\n";
if("json" == content_type){

stream += "Content-Type: application/json\r\n";
}else{
stream += "Content-Type: application/x-www-form-urlencoded\r\n";
}
stream += "Content-Length: ";
stream += str;
stream += "\r\n";
//stream += "Connection: keep-alive\r\n";
stream += "Connection: close\r\n";
stream += "\r\n";
stream += str_;
return stream;

}
please note :Connection: keep-alive\r\n";
stream += "Connection: close\r\n";

I used the keep_alive mode , http will keep to open the connection , the server will suppose the client will continue to send post request, so the server will wait, in fact , I will not send any more in the session, so the server will close the connection when time is out , that is all :)