unix socket send() succeeds, but recv() fails - c

Question

I am writing a simple client server program using unix domain sockets, but am having issues with the recv() call in my client program.
The program executes as follows:
Server sets up socket and waits for a connection
Client connects and sends a string
Server receives string, and sends string back to client (like an echo)
Client recv() call fails, returning "resource temporarily unavailable"
Client exits
Server waits for another connection
I have also tried using a poll() call in my client to wait for the response from the server.
In this case however, the recv() call simply receives a 0, implying the connection has been closed serverside, which it has not.
I have exhausted google on this error, but no fixes I came accross seem applicable to my code.
I have included my client (with poll() code commented out) and server code below.
I'm probably missing something obvious... but any insight would be greatly appreciated!
Server code:
/*
* testServer.c
*
*/
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <termios.h>
#include <fcntl.h>
#include <poll.h>
#include <signal.h>
#include <unistd.h>
#include <string.h>
#include <stdbool.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/un.h>
#include <linux/spi/spidev.h>
#include <linux/sockios.h>
#include <errno.h>
#define SOCK_PATH "/var/run/ts.serv"
void handleSockIO(int *sockDesc);
int main ()
{
int sock;
struct sockaddr_un sock_addr;
int len, p;
struct pollfd poll_fd[1];
printf("[TS] testServer Started.\r\n");
if ((sock = socket(AF_UNIX, SOCK_STREAM, 0)) == -1)
{
perror("[TS]wr_sock creation");
}
else
{
printf("[TS] Created socket descriptor.\r\n");
}
sock_addr.sun_family = AF_UNIX;
strcpy(sock_addr.sun_path, SOCK_PATH);
unlink(sock_addr.sun_path);
len = strlen(sock_addr.sun_path) + sizeof(sock_addr.sun_family);
if (bind(sock, (struct sockaddr *)&sock_addr, len) == -1)
{
perror("[TS]sock bind failed\r\n");
}
else
{
printf("[TS] Bound socket to sock_addr.\r\n");
}
if (listen(sock, 5) == -1)
{
perror("[TS] sock listen fail");
}
else
{
printf("[TS] Socket now listening.\r\n");
}
poll_fd[0].fd = sock;
poll_fd[0].events = POLLIN;
printf("[TS] Waiting for a connection...\r\n");
while (1)
{
p = poll(poll_fd, 1, 1); //Wait for 1 ms for data
if (p == -1)
{
perror("[TS] Poll");
}
else if (p == 0)
{
//printf("Timeout occurred!\n");
}
else
{
if (poll_fd[0].revents & POLLIN)//Data available to read without blocking
{
printf("[TS] Data available on sock..\r\n");
handleSockIO(&sock);
printf("[TS] Waiting for another connection...\r\n");
}
}
}//While(1)
return 0;
}
void handleSockIO(int *sockDesc)
{
int ioSock, n;
socklen_t t;
struct sockaddr_un remote_addr;
char str[15];
memset(str, ' ', sizeof(str));
t = sizeof(remote_addr);
if ((ioSock = accept(*sockDesc, (struct sockaddr *)&remote_addr, &t)) == -1)
{
perror("accept failed\r\n");
}
else
{
printf("[TS] Receiving...\r\n");
n = recv(ioSock, str, sizeof(str), 0);
if (n < 0)
printf("[TS] recvfrom failed: %s\r\n", strerror(errno));
else if(n == 0)
{
printf("[TS] Received %d on ioSock...\r\n", n);
}
else if(n > 0)
{
printf("[TS] Received: %s, which is %d long.\r\n", str, strlen(str));
printf("[TS] Echoing response...\r\n");
if (send(ioSock, str, n, 0) == -1) //Echo str back
{
printf("[TS] send failed: %s\r\n", strerror(errno));
}
else
{
printf("[TS] Send successful\r\n");
}
//============Wait to close IO descriptor=================
int r;
char temp[1]; //Arbitrary buffer to satisfy recv()
do
{
printf("[TS] Waiting for client to close connection...\r\n");
r = recv(ioSock, temp, sizeof(temp), 0);
if (r == 0)
{
printf("[TS] Client closed connection, closing ioSock...\r\n");
close(ioSock);
}
} while (r != 0);
//========================================================
}//if(n>0) else...
}
}
Client code:
/*
* testClient.c
*
*/
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <termios.h>
#include <fcntl.h>
#include <poll.h>
#include <signal.h>
#include <unistd.h>
#include <string.h>
#include <stdbool.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/un.h>
#include <linux/sockios.h>
#include <errno.h>
#define CHAR_BUF_SIZE 15
#define SEND_STRING "Hello!"
#define SOCK_PATH "/var/run/ts.serv"
int main ()
{
char str[CHAR_BUF_SIZE] = {0};
int c, len, n, p;
int s; // s will hold a socket descriptor returned by socket()
struct sockaddr_un serv_addr;
struct pollfd poll_fd[1];
printf("[TC] testClient Started.\r\n");
//===============SOCKET SETUP===============================
if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) == -1)
{
printf("[TC] Socket failed: %s\r\n", strerror(errno));
}
memset(&serv_addr, '0', sizeof(serv_addr));
serv_addr.sun_family = AF_UNIX;
strcpy(serv_addr.sun_path, SOCK_PATH);
len = strlen(serv_addr.sun_path) + sizeof(serv_addr.sun_family);
//==========================================================
// printf("[TC]Trying to connect to TS socket...\r\n");
//===============RESPONSE POLL SETUP========================
poll_fd[0].fd = s;
poll_fd[0].events = POLLIN;
//==========================================================
printf("[TC] Connecting to SOCK_PATH...\r\n");
c = connect(s, (struct sockaddr *)&serv_addr, len);
if (c == -1)
{
printf("[TC] Connection failed: %s\r\n", strerror(errno));
}
else
{
printf("[TC] Connected. Sending string....\r\n");
if (send(s, SEND_STRING, strlen(SEND_STRING), 0) == -1)
{
printf("[TC] send() failed: %s\r\n", strerror(errno));
}
else
{
printf("[TC] Send on SOCK_PATH successful.\r\n");
//Sending complete------------------------------------------------
//Wait for response...
printf("[TC] Waiting for server response...\r\n");
// p = poll(poll_fd, 1, -1); //Wait for a response
//
// if (p == -1)
// {
// perror("[TC] Poll");
// }
// else
// {
// if(poll_fd[0].revents & POLLIN)
// {
n = recv(s, str, sizeof(str), 0);
if (n < 0)
{
printf("[TC] Receive on SOCK_PATH failed: %s\r\n",
strerror(errno));
}
else if(n == 0)
{
printf("[TC] %d Received on SOCK_PATH.\r\n", n);
}
else if(n > 0)
{
printf("[TC] Received %d from SOCK_PATH: %s\r\n",
n, str);
}
// }
// }
}//if(send())
}//if(connect())
printf("[TC] Transction complete, closing connection and exiting.\r\n");
close(s);
return 0;
}

Answer 1

len = sizeof(serv_addr) instead of len = strlen(serv_addr.sun_path) + sizeof(serv_addr.sun_family) should solve you problem. Also do not ignore compiler warnings, say n = recv(s, str, strlen(str), 0) with n declared as int and ssize_t returned by recv. It will help you to avoid a future errors.