读取套接字缓冲区不读取

Question

this maybe is a simple question but I'm trying to just read a server response using the sockets API adapting the code from Geeks for Geeks [site] 1 , when I try to read the data, it becomes blocked forever in the valread = read(server_fd, buffer, 2048); line, and doesn't execute any of the prints. Am I doing something wrong?

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

int send_request() {
  int server_fd, new_socket, valread;
  struct sockaddr_in address;
  int opt = 1;
  int addrlen = sizeof(address);
  char buffer[512] = {0};
  char *hello = "Hello from server";

  // Creating socket file descriptor
  if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
    perror("socket failed");
    exit(EXIT_FAILURE);
  }

  // Forcefully attaching socket to the port 8080
  if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))) {
    perror("setsockopt");
    exit(EXIT_FAILURE);
  }

  // CONNECT TO HOST
  struct hostent *he;
  char* host = "www.columbia.edu";
  he = gethostbyname(host);

  if(!he) {
    printf("Host doesn't exist!\n");
    return 0;
  }

  address.sin_family = AF_INET;
  bcopy(he->h_addr, &address.sin_addr, sizeof(struct in_addr));
  address.sin_port = htons(80);


  if(connect(server_fd, (struct sockaddr *) &address, sizeof(struct sockaddr_in)) < 0) {
  printf("Error in the connection");
    return 0;
  }

  valread = read(server_fd, buffer, 2048);

  printf("%s\n", buffer);
  printf("%d\n", valread);
  printf("%d\n", errno);
  return 0;
}

int main(int argc, char const *argv[]) {
  send_request();
    return 0;
}

Answer 1

You are connecting to an HTTP server. The HTTP protocol specifies that the client (that is, the side that makes the connection to the server) must send a request first. You aren't sending a request, so the server is not going to send you a reply.

Also, this is a bug:

valread = read(server_fd, buffer, 2048);

printf("%s\n", buffer);

The %s format specifier can only be used with C-style strings. It can't be used for arbitrary data. For one thing, how would it know how many bytes to output? The only place that information is currently contained is in valread , and you didn't pass it to printf .