使用低级 C++ 网络库发送 GET 请求时网站无响应

Question

I am trying to create a program that downloads data from websites using c++ low level networking. Here is the code:

#include <iostream>
#include <string>

#include <string.h>
#include <netdb.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>

#include <sys/types.h>
#include <sys/socket.h>

#include <arpa/inet.h>



int status, sock;
struct addrinfo hints;
struct addrinfo *servinfo;
int main(int argc, char** argv){
  memset(&hints, 0, sizeof hints);
  hints.ai_family = AF_UNSPEC;
  hints.ai_socktype = SOCK_STREAM;
  int MAXDATASIZE = 100;
  char request[] = "GET /robots.txt HTTP/1.1\n";
  char buf[MAXDATASIZE];
  if((status = getaddrinfo(argv[1], argv[2], &hints, &servinfo)) != 0){
    std::cout << "getaddrinfo: " << gai_strerror(status) << "\n";
    return 2;
  }
  if((sock = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol)) == -1){
    std::cout << "Error creating socket\n";
    return 2;
  }
  if(connect(sock, servinfo->ai_addr, servinfo->ai_addrlen) == -1){
    std::cout << "Error connecting to host " << argv[1] << " at port " << argv[2] << "\n";
    return 2;
  }
  if((send(sock, request,strlen(request), 0)) == -1){
     std::cout << "Error communicating with website\n";
     return 2;
  }
  if(recv(sock, buf, MAXDATASIZE, 0) == -1){
     std::cout << "Error recciving data from " << argv[1] << " at port " << argv[2] << "\n";
  }
  std::cout << buf << std::endl;
  close(sock);

  freeaddrinfo(servinfo);
}

When I try to connect to google, using www.google.com as the host and 80 as the port, it hangs at the recv() call.To test whether the request was the problem, I connected to google using telnet with the same request, and it worked. I also tried binding netcat to a port on my computer, and then connected to that port using my program. The request was sent properly to netcat, and when I responded with a test message, my program reccived it.

Does anyone know why google isn't sending the data?

I'm using fedora 32, if that might help

Answer 1

Your software is not hanging. Rather, the server is waiting for an indication that the client has finished sending the headers, which is indicated by sending an empty line. Until the client sends the blank line, the server cannot respond.

Change your request to:

char request[] = "GET /robots.txt HTTP/1.1\r\n\r\n";