full duplex communication between server & client - c

Question

I want to make a code for full duplex communication between server & client using this code.
I got error in receive-message thread from server side & in send-message thread from client side.
please help me to solve this errors & suggest me if any other changes are required.
Thanks :)
server.cpp
int newsockfd, n;
void error(const char *msg)
{
perror(msg);
exit(1);
}
void* recvFn( void* data )
{
char buffer[256];
while(n==0){
memset( buffer, sizeof(buffer), 0);
n = recv(newsockfd,buffer,255,MSG_PEEK);
if(n>0){
printf("cliet: ");
printf("%s",buffer);
}
}
return NULL;
}
void* sendFn( void* data )
{
char temp[255], buffer[255];
while(n==0){
memset( buffer, sizeof(buffer), 0);
fgets(temp,255,stdin);
sprintf(buffer,"clent: %s",temp);
n = send(newsockfd,buffer,strlen(buffer),MSG_EOR);
}
return NULL;
}
int main(int argc, char *argv[])
{
int sockfd, portno;
socklen_t clilen;
struct sockaddr_in serv_addr, cli_addr;
if (argc < 2) {
fprintf(stderr,"ERROR, no port provided\n");
exit(1);
}
pthread_t recvThread, sendThread;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
memset( &serv_addr, sizeof(serv_addr), 0);
portno = atoi(argv[1]);
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = INADDR_ANY;
serv_addr.sin_port = htons(portno);
int on = 1;
if ( setsockopt( sockfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof( on ) ) != 0 ) {
close( sockfd );
return -1;
}
if (bind(sockfd, (struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
error("ERROR on binding");
listen(sockfd,5);
clilen = sizeof(cli_addr);
newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);
if (newsockfd < 0)
error("ERROR on accept");
n = 0;
int rc;
rc = pthread_create( &recvThread, NULL, recvFn, NULL);
if(rc){
printf("error in receive-message thread\n");
return -1;
}
rc = pthread_create( &sendThread, NULL, sendFn, NULL);
if(rc){
printf("error in send-message thread\n");
return -1;
}
close(newsockfd);
close(sockfd);
pthread_cancel(recvThread);
pthread_cancel(sendThread);
return 0;
}
client.cpp
int sockfd, n;
void* recvFn( void* data )
{
char buffer[255];
while( n==0 ){
memset( buffer, sizeof(buffer), 0);
n = recv(sockfd,buffer,255,MSG_PEEK);
if(n>0){
printf("server: ");
printf("%s",buffer);
}
}
return NULL;
}
void* sendFn( void* data )
{
char temp[255], buffer[255];
while( n==0 ){
memset( buffer, sizeof(buffer), 0);
fgets(temp,255,stdin);
sprintf(buffer,"clent: %s",temp);
n = send(sockfd,buffer,strlen(buffer),MSG_EOR);
}
return NULL;
}
void error(const char *msg)
{
perror(msg);
exit(0);
}
int main(int argc, char *argv[])
{
int portno;
struct sockaddr_in serv_addr;
struct hostent *server;
char buffer[256];
if (argc < 3) {
fprintf(stderr,"usage %s hostname port\n", argv[0]);
exit(0);
}
pthread_t recvThread, sendThread;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
portno = atoi(argv[2]);
server = gethostbyname(argv[1]);
if (server == NULL) {
fprintf(stderr,"ERROR, no such host\n");
exit(0);
}
memset( &serv_addr, sizeof(serv_addr), 0);
serv_addr.sin_family = AF_INET;
memcpy((char *)server->h_addr,(char *)&serv_addr.sin_addr.s_addr, server->h_length);
serv_addr.sin_port = htons(portno);
if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
error("ERROR on connecting");
n = 0;
int rc;
rc = pthread_create( &sendThread, NULL, sendFn, NULL);
if(rc){
printf("error in send-message thread\n");
return -1;
}
rc = pthread_create( &recvThread, NULL, recvFn, NULL);
if(rc){
printf("error in receive-message thread\n");
return -1;
}
close(sockfd);
pthread_cancel(recvThread);
pthread_cancel(sendThread);
return 0;
}

Answer 1

Your pthread_mutex operations are completely pointless. You're referring only to local variables inside the mutex lock other than n, which should be local in each thread and newsockfd which also should not be global, see below. (Don't you think that a function which calls recv should have a local variable to capture the number of bytes read, and not share that silly little temporary variable globally with other threads?)
Your main thread is in a while loop, creating threads like crazy. Also, inside that loop it has closed the one and only accepted socket, right after creating the threads.
You forgot to put your accept inside the loop, evidently.
Also you seem to think that the main loop will somehow wait for the pair of threads to terminate before launching new ones. You are missing pthread_join calls to wait for the threads finish communicating. If you want the thread to keep going while the main loop accepts new connections using new threads, you should make those threads detached with pthread_detached or using a thread-creation attribute which makes them detached. Non-detached threads which are not pthread_join-ed continue to occupy resources.
Speaking of shutdown, is it really the correct condition that the threads keep looping while n == 0? As soon as n is set to nonzero by one of the threads, the shutdown condition is met. But a nonzero value is normal: some bytes written or read. Your reader should terminate the loop when there is a fatal receive error on the socket, or the read returns zero.
Also, you are evaluating n == 0 outside of the mutex!
If you want to accept multiple concurrent connections, each with its pair of threads, then you cannot use a single global socket. You have to give each pair of threads their own socket. The two threads within each pair do not have to use a mutex to share the socket. The socket calls are thread-safe in the kernel and the threads are not both doing reads or writes; one is reading and one is writing.
Other problems
Your sender keeps sending uninitialized garbage: a buffer that was never set to contain any data.
You have a bzero of 256 bytes on an array of 255 bytes.
Also
Don't use bzero (or bcopy, etc). It's a BSD-ism from the 1980's. The C language was finally standardized in 1989 by ANSI and soon after in 1990 by ISO. At that time, it already had the library functions memset, memcpy and memmove.
I think 22 years later, it is safe to retire bcopy, dontcha think?