Linux C Socket: Blocked on recv call

Question

In my application i have created a thread for a simple http server, then from within my application i tried to connect to http server but control is blocked/hanged on recv call.

But if try to connect to my application's http server using linux GET command, I will be connected to http server successfully.

As per my understanding by searching the google i found that this is not the right approach.

But if i want to do this, in what should i create the sockets so that i can connect o my http server from within the application.

Below is how my http server socket created

pthread_create(&pt_server, NULL, http_srvr, NULL);

//http server handler
void *http_server()
{
    int sockfd, new_fd;             
    struct sockaddr_in my_addr;     
    struct sockaddr_in their_addr;  
    socklen_t sin_size;
    struct sigaction sa;
    int yes=1;

    if ((sockfd = socket(PF_INET, SOCK_STREAM, 0)) == -1)
    {
    perror("socket");
    exit(1);
    }

    if (setsockopt(sockfd,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(int)) == -1)
    {
    perror("setsockopt");
    exit(1);
    }

    my_addr.sin_family = AF_INET;               // host byte order
    my_addr.sin_port = htons(HTTP_PORT);        // short, network byte order
    my_addr.sin_addr.s_addr = INADDR_ANY;       // automatically fill with my IP
    memset(&(my_addr.sin_zero), '\0', 8);       // zero the rest of the struct

    if (bind(sockfd, (struct sockaddr *)&my_addr, sizeof(struct sockaddr))== -1)
    {
    perror("bind");
    exit(1);
    }

    printf("Listening to sockets\n");
    if (listen(sockfd, BACKLOG) == -1)
    {
    perror("listen");
    exit(1);
    }

    sa.sa_handler = sigchld_handler; // reap all dead processes
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_RESTART;
    if (sigaction(SIGCHLD, &sa, NULL) == -1)
    {
    perror("sigaction");
    exit(1);
    }

    printf("server: waiting for connections...\n");

    while(1) {  // main accept() loop
        sin_size = sizeof(struct sockaddr_in);
        if ((new_fd = accept(sockfd, (struct sockaddr *)&their_addr,&sin_size)) == -1)
        {
          perror("accept");
          continue;
        }
        printf("server: got connection from %s\n",inet_ntoa(their_addr.sin_addr));

        handle_connection(new_fd);
    }
}

And following is how i am doing http POST to my http server

  /* create socket */
  if ((s = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    return ERRSOCK;
  setsockopt(s, SOL_SOCKET, SO_KEEPALIVE, 0, 0);


  /* connect to server */
  if (connect(s, &server, sizeof(server)) < 0) 
    ret=ERRCONN;
  else {
    if (pfd) *pfd=s;

    /* create header */
    if (proxy) {
      sprintf(header,
"%s http://%.128s:%d/%.256s HTTP/1.0\015\012User-Agent: %s\015\012%s\015\012",
          command,
          http_server1,
          http_port,
          url,
          http_user_agent,
          additional_header
          );
    } else {
      sprintf(header,
"%s /%.256s HTTP/1.0\015\012User-Agent: %s\015\012%s\015\012",
          command,
          url,
          http_user_agent,
          additional_header
          );
    }

    hlg=strlen(header);


    /* send header */   
    if (send(s,header,hlg,0)!=hlg)
      ret= ERRWRHD;

    /* send data */
    else if (length && data && (send(s,data,length,0)!=length) )
      ret= ERRWRDT;

    else {
      /* read result & check */
      ret=http_read_line(s,header,MAXBUF-1);

and following are the contents of http_read_line, and in this function recv call blocked

static int http_read_line (fd,buffer,max) 
     int fd; /* file descriptor to read from */
     char *buffer; /* placeholder for data */
     int max; /* max number of bytes to read */
{ /* not efficient on long lines (multiple unbuffered 1 char reads) */
  int n=0;
  while (n<max) {
    if (recv(fd,buffer,1,0)!=1) {
      n= -n;
      break;
    }
    n++;
    if (*buffer=='\015') continue; /* ignore CR */
    if (*buffer=='\012') break;    /* LF is the separator */
    buffer++;
  }
  *buffer=0;
  return n;
}

Answer 1

You have told "In my application i have created a thread for a simple http server, then from within my application i tried to connect to http server but control is blocked/hanged on recv call."

That means the recv is never returning 0. Now when the recv function will return a 0? ->When it gets a TCP FIN segment. It seems that your server is never sending a TCP FIN segment to the client. The reason that is most likely here is that, your client code needs modification. You are sending data from from the client, but you are never sending the FIN, so I assume that your server function is continuing forever and it had not sent the FIN. This made the recv wait for ever.

In the current code perhaps the fix is to add a line

else {
  /*Send the FIN segment, but we can still read the socket*/
  shutdown(s, SHUT_WR); 
  /* read result & check */
  ret=http_read_line(s,header,MAXBUF-1);

In this case the shutdown function sends the TCP FIN and the server function can return and possibly then it would do a proper close.

And on a proper close, the FIN from the server will be received by the client. This would make the recv return 0, instead of getting blocked for ever.

Now if you want to continue any further data transfer from the client, you need to again connect or may be you need to have some different algorithm.

I hope my explanation may help fix the current problem.

Answer 2

You need to either send an HTTP 1.0 header, or else read about content-length in HTTP 1.1. You are reading the stream to EOS when the server is under no obligation to close the connection, so you block. The Content-Length header tells you how much data is in the body: you should only try to read that many bytes.

If you specify HTTP 1.0 (and no fancy headers) the server will close the connection after sending the response.