Question

I am trying to wrap unix socket api calls in a C++ class to make it easier to work with. I have taken a minimal working example written in C and duplicated the code in a class. As you can see from below the code is identical whether I am calling the function version or method versions of the wrapper code. See ugly temporary code below:

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

static int sockfd;
static int rec_sock;
static int len;

typedef struct sockaddr_in sockaddr_in;
static sockaddr_in addr;
static sockaddr_in recaddr;

int ServerSocket_socket(int family, int type, int protocol)
{
    sockfd = socket(AF_INET, SOCK_STREAM, 0)
    return sockfd;
}

void ServerSocket_bind(int port)
{
    addr.sin_addr.s_addr = INADDR_ANY;
    addr.sin_family = AF_INET;
    addr.sin_port = port;

    bind(sockfd, (struct sockaddr *)&addr, sizeof(addr));
}

void ServerSocket_printInfo(void)
{
    len = sizeof(addr);
    getsockname(sockfd, (struct sockaddr *)&addr, (socklen_t *)&len);
    printf("ip = %s, port = %d\n", inet_ntoa(addr.sin_addr), (addr.sin_port));
}

void ServerSocket_listen(int backlog)
{
    listen(sockfd, backlog);
}

void ServerSocket_accept(void)
{
  rec_sock = accept(sockfd, (struct sockaddr *)(&recaddr), (socklen_t *)&len);
}

void ServerSocket_printPeerInfo(void)
{
    printf("remote machine = %s, port = %x, %x.\n", inet_ntoa(recaddr.sin_addr), recaddr.sin_port, ntohs(recaddr.sin_port));
    memset(&recaddr, 0, sizeof(recaddr));
    len = sizeof(addr);
    getpeername(rec_sock, (struct sockaddr *)&recaddr, (socklen_t *) &len);
}

void ServerSocket_write(void)
{
  write(rec_sock, "hi, there", 10);
  sleep(20);
  exit(1);
}

struct ServerSocket
{
  int socket(int family, int type, int protocol)
  {
      sockfd = socket(AF_INET, SOCK_STREAM, 0);
      return sockfd;  
  }

  void bind(int port)
  {
    addr.sin_addr.s_addr = INADDR_ANY;
    addr.sin_family = AF_INET;
    addr.sin_port = port;

    ::bind(sockfd, (struct sockaddr *)&addr, sizeof(addr));
  }

  void printInfo(void)
  {
      len = sizeof(addr);
      getsockname(sockfd, (struct sockaddr *)&addr, (socklen_t *)&len);
      printf("ip = %s, port = %d\n", inet_ntoa(addr.sin_addr), (addr.sin_port));
  }

  void listen(int backlog)
  {
      ::listen(sockfd, backlog);
  }

  void accept(void)
  {
    rec_sock = ::accept(sockfd, (struct sockaddr *)(&recaddr), (socklen_t *)&len);
  }

  void printPeerInfo(void)
  {
      printf("remote machine = %s, port = %x, %x.\n", inet_ntoa(recaddr.sin_addr), recaddr.sin_port, ntohs(recaddr.sin_port));
      memset(&recaddr, 0, sizeof(recaddr));
      len = sizeof(addr);
      getpeername(rec_sock, (struct sockaddr *)&recaddr, (socklen_t *) &len);
      printf("remote machine = %s, port = %d, %d.\n", inet_ntoa(recaddr.sin_addr), recaddr.sin_port, ntohs(recaddr.sin_port));
  }

  void write(void)
  {
    ::write(rec_sock, "hi, there", 10);
    sleep(20);
    exit(1);
  }
};

When I call the functions the code works like a champ. However when I run the almost identical code wrapped in methods I get a connection refused. Any idea what this minimal code change is doing to cause the example not to work?

   ServerSocket_socket(AF_INET, SOCK_STREAM, 0);
    ServerSocket_bind(1031);
    ServerSocket_printInfo();
    ServerSocket_listen(5);
    ServerSocket_accept();
    ServerSocket_printPeerInfo();
    ServerSocket_write();
  /*
    ServerSocket sock;
    sock.socket(AF_INET, SOCK_STREAM, 0);
    sock.bind(1031);
    sock.printInfo();
    sock.listen(5);
    sock.accept();
    sock.printPeerInfo();
    sock.write();
  */

Answer 1

In ServerSocket_bind change:

addr.sin_port = port;

to

addr.sin_port = htons(port);

And it should work. Also, use strace to debug syscalls (or ltrace for libc) like:

strace -f ./a.out

ltrace ./a.out