C Socket Write Too many times

Question

After the user as entered data it writes out a part of the data entered before the data just enetered if that makes sense? I've only included a snippet, but can anyone see any reason why it would reply multiple times?

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<sys/socket.h>
#include<arpa/inet.h> //inet_addr
#include<unistd.h> // write

#include<pthread.h> // For Threading

#include<wiringPi.h>
void *connection_handler(void *);
void lightLED(int pin,int status);
int maxConnections = 1;
int totalConnections = 0;
int main(int argc , char *argv[])
{
    int socket_desc , new_socket , c, *new_sock;
    struct sockaddr_in server , client;
    char *message;     
    //Create socket
    socket_desc = socket(AF_INET , SOCK_STREAM , 0);
    if (socket_desc == -1)
    {
        printf("Could not create socket");
    }

    //Prepare the sockaddr_in structure
    server.sin_family = AF_INET;
    server.sin_addr.s_addr = INADDR_ANY;
    server.sin_port = htons( 8888 );

    //Bind
    if( bind(socket_desc,(struct sockaddr *)&server , sizeof(server)) < 0)
    {
        puts("bind failed");
    }
    puts("bind done");

    //Listen
    listen(socket_desc , 3);

    //Accept and incoming connection
    puts("Waiting for incoming connections...");
    c = sizeof(struct sockaddr_in);
    while( (new_socket = accept(socket_desc, (struct sockaddr *)&client, (socklen_t*)&c)) )
    {
     if(new_socket > 0)
     {
      if(totalConnections < maxConnections){
      totalConnections++;
     }
      else
      {
       message = "Sorry Maximum Users Reached\n";
       write(new_socket,message,strlen(message));
       puts("Too many Users");
       close(new_socket);
       continue;
      }
    }
     puts("Connection Accepted");
    char *client_ip = inet_ntoa(client.sin_addr);
    int client_port = ntohs(client.sin_port);
    printf("ClientIP:%s\n",client_ip);
     message = "Hello you have been accepted!\n";
     write(new_socket, message , strlen(message));

    pthread_t sniffer_thread;
    new_sock = malloc(1);
    *new_sock = new_socket;

    if(pthread_create( &sniffer_thread, NULL , connection_handler , (void*) new_sock) <0)
    {
     perror("Could not create thread");
    return 1;
    }
    puts("Handler Assigned");
    }

    if (new_socket<0)
    {
        perror("accept failed");
    return 1;
    }
    return 0;
}

void *connection_handler(void *socket_desc)
{
    int sock = *(int*)socket_desc;
    int read_size;
    char *message , client_message[2000];

    message = "Greeting! I am your Connection Handler\n";
    write(sock , message,strlen(message));

    message =  "What do you want to do\n";
    write(sock,message,strlen(message));

    while( (read_size = recv(sock , client_message , 2000 , 0)) > 0)
    {
     write(sock , client_message , strlen(client_message));
     printf("User Entered:%s\n",client_message);
     int pin = client_message[0]-'0';
     int status = client_message[1]-'0';
     lightLED(pin,status);
    }
    if(read_size == 0)
    {
    puts("Client Disconnected\n");
    fflush(stdout);
    totalConnections--;
    }else if(read_size == -1)
    {
     perror("recv Failed");
    }

    free(socket_desc);
    return 0;
}

void lightLED(int pin,int status)
{
    char message;
    if(wiringPiSetup() == -1){
    puts("wiringPi Error");
        exit(1);
    }

    //pinMode(pin,OUTPUT);
    printf("Changing LED Pin- %d Status- %d\n",pin,status);
    //digitalWrite(pin,status);
}

Answer 1

First pass

I'm not sure what problem you're seeing. I've taken your code (which was in pretty good shape — well done; I've looked at a lot of code with many worse problems in it) and compiled it and run it and it seemed to work for me:

$ nc localhost 8888
Connection Accepted
ClientIP:127.0.0.1
Handler Assigned
Hello you have been accepted!
Greeting! I am your Connection Handler
What do you want to do
01
User Entered:01

Changing LED Pin- 0 Status- 1
01
21
User Entered:21

Changing LED Pin- 2 Status- 1
21
31
User Entered:31

Changing LED Pin- 3 Status- 1
31
we wish you a merry Christmas
User Entered:we wish you a merry Christmas

Changing LED Pin- 71 Status- 53
we wish you a merry Christmas
Client Disconnected

$

The code as run was:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <pthread.h>
//#include <wiringPi.h>

void *connection_handler(void *);
void lightLED(int pin, int status);

int maxConnections = 1;
int totalConnections = 0;

int main(void)
{
    int socket_desc, new_socket, c, *new_sock;
    struct sockaddr_in server, client;
    char *message;

    socket_desc = socket(AF_INET, SOCK_STREAM, 0);
    if (socket_desc == -1)
    {
        printf("Could not create socket");
        return 1;
    }

    server.sin_family = AF_INET;
    server.sin_addr.s_addr = INADDR_ANY;
    server.sin_port = htons(8888);

    if ( bind(socket_desc, (struct sockaddr *)&server, sizeof(server)) < 0)
    {
        puts("bind failed");
        return 1;
    }
    puts("bind done");

    if (listen(socket_desc, 3) != 0)
    {
        perror("listen() failed");
        return 1;
    }

    puts("Waiting for incoming connections...");
    c = sizeof(struct sockaddr_in);
    while ((new_socket = accept(socket_desc, (struct sockaddr *)&client, (socklen_t*)&c)))
    {
        if (new_socket > 0)
        {
            if (totalConnections < maxConnections)
                totalConnections++;
            else
            {
                message = "Sorry Maximum Users Reached\n";
                write(new_socket, message, strlen(message));
                puts("Too many Users");
                close(new_socket);
                continue;
            }
        }
        puts("Connection Accepted");
        char *client_ip = inet_ntoa(client.sin_addr);
        //int client_port = ntohs(client.sin_port);

        printf("ClientIP:%s\n", client_ip);
        message = "Hello you have been accepted!\n";
        write(new_socket, message, strlen(message));

        pthread_t sniffer_thread;
        new_sock = malloc(1 * sizeof(int));       // Oops!
        if (new_sock == 0) { perror("out of memory"); return 1; }
        *new_sock = new_socket;

        if (pthread_create( &sniffer_thread, NULL, connection_handler, (void*) new_sock) <0)
        {
            perror("Could not create thread");
            return 1;
        }
        puts("Handler Assigned");
    }

    if (new_socket<0)
    {
        perror("accept failed");
        return 1;
    }
    return 0;
}

void *connection_handler(void *socket_desc)
{
    int sock = *(int*)socket_desc;
    int read_size;
    char *message, client_message[2000];

    message = "Greeting! I am your Connection Handler\n";
    write(sock, message, strlen(message));

    message =  "What do you want to do\n";
    write(sock, message, strlen(message));

    while ((read_size = recv(sock, client_message, 2000, 0)) > 0)
    {
        write(sock, client_message, strlen(client_message));
        printf("User Entered:%s\n", client_message);
        int pin = client_message[0]-'0';
        int status = client_message[1]-'0';
        lightLED(pin, status);
    }
    if (read_size == 0)
    {
        puts("Client Disconnected\n");
        fflush(stdout);
        totalConnections--;
    }
    else if (read_size == -1)
    {
        perror("recv Failed");
    }

    free(socket_desc);
    return 0;
}

void lightLED(int pin, int status)
{
//    if (wiringPiSetup() == -1)
//    {
//        puts("wiringPi Error");
//        exit(1);
//    }

    printf("Changing LED Pin- %d Status- %d\n", pin, status);
}

If you still have problems, maybe the trouble is in your client code. As you can see, I used netcat (nc) as a surrogate for your client. Note that 'we wish you a merry Christmas' was accepted as a valid command, though the pin was 73 and the status was 53. That might not work with the real LEDs.

Note that I added an error check for the malloc() and allocated a more correct amount of space (sizeof(int) instead of just 1 byte). I also made sure that reported error conditions are followed by a more-or-less appropriate error return, rather than continuing as if no error had occurred.

Also, I've not fixed some of the issues highlighted in the comments — checking write() and not relying on null termination, etc. These should still be addressed.

My test was on Mac OS X 10.7.5 with GCC 4.7.1:

gcc -O3 -g -std=c99 -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes -Wold-style-definition server.c -o server

---

Second pass

Another test run — showing the problem with inputs that are not null terminated:

$ nc localhost 8888
Connection Accepted
ClientIP:127.0.0.1
Hello you have been accepted!
Handler Assigned
Greeting! I am your Connection Handler
What do you want to do
this is a long string - what will you do with it?
User Entered:this is a long string - what will you do with it?

Changing LED Pin- 68 Status- 56
this is a long string - what will you do with it?
01
User Entered:01
s is a long string - what will you do with it?

Changing LED Pin- 0 Status- 1
01
s is a long string - what will you do with it?
Client Disconnected

$

When I ran it with telnet instead of nc, I got the misbehaviour you were seeing, I think:

$ telnet localhost 8888
Trying 127.0.0.1...
Connection Accepted
ClientIP:127.0.0.1
Handler Assigned
Connected to localhost.
Escape character is '^]'.
Hello you have been accepted!
Greeting! I am your Connection Handler
What do you want to do
Would you like a biscuit?
User Entered:Would you like a biscuit?

Changing LED Pin- 39 Status- 63
Would you like a biscuit?
93
User Entered:93
d you like a biscuit?

Changing LED Pin- 9 Status- 3
93
d you like a biscuit?
Intriguing
User Entered:Intriguing
ke a biscuit?

Changing LED Pin- 25 Status- 62
Intriguing
ke a biscuit?
Bye
User Entered:Bye
guing
ke a biscuit?

Changing LED Pin- 18 Status- 73
Bye
guing
ke a biscuit?
User Entered:ye
guing
ke a biscuit?

Changing LED Pin- -44 Status- 73
ye
guing
ke a biscuit?
^CUser Entered:????guing
ke a biscuit?

Changing LED Pin- -49 Status- -60
User Entered:???guing
ke a biscuit?

Changing LED Pin- -49 Status- -53
?guing
ke a biscuit?
User Entered:??guing
ke a biscuit?

...continued attempts with control-C (interrupt)...
...and control-D (EOF) not producing anything useful...

^]
telnet> qConnection closed.
Client Disconnected

$

So, telnet may have been misleading you...nothing up with your server, just the client (telnet) not behaving as you expected.

Updated code

Conversation with updated server code:

$ nc localhost 8888
Connection Accepted
ClientIP: 127.0.0.1
Handler Assigned
Hello you have been accepted!
Greetings! I am your Connection Handler
What do you want to do
13
User Entered:13

Changing LED Pin 1 status 3
13
21
User Entered:21

Changing LED Pin 2 status 1
21
elephants?
User Entered:elephants?

Changing LED Pin 53 status 60
elephants?
21
User Entered:21

Changing LED Pin 2 status 1
21
quit 
User Entered:quit

Changing LED Pin 65 status 69
quit
Client Disconnected

$

Updated server code

This version pays attention to lengths and ensures that strings are null terminated.

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <pthread.h>
//#include <wiringPi.h>

void *connection_handler(void *);
void lightLED(int pin, int status);
static void write_sock(int sock, const char *msg);

int maxConnections = 1;
int totalConnections = 0;

int main(void)
{
    int socket_desc, new_socket, c, *new_sock;
    struct sockaddr_in server, client;

    socket_desc = socket(AF_INET, SOCK_STREAM, 0);
    if (socket_desc == -1)
    {
        printf("Could not create socket");
        return 1;
    }

    server.sin_family = AF_INET;
    server.sin_addr.s_addr = INADDR_ANY;
    server.sin_port = htons(8888);

    if (bind(socket_desc, (struct sockaddr *)&server, sizeof(server)) < 0)
    {
        puts("bind failed");
        return 1;
    }
    puts("bind done");

    if (listen(socket_desc, 3) != 0)
    {
        perror("listen() failed");
        return 1;
    }

    puts("Waiting for incoming connections...");
    c = sizeof(struct sockaddr_in);
    while ((new_socket = accept(socket_desc, (struct sockaddr *)&client, (socklen_t*)&c)))
    {
        if (new_socket > 0)
        {
            if (totalConnections < maxConnections)
                totalConnections++;
            else
            {
                write_sock(new_socket, "Sorry Maximum Users Reached\n");
                puts("Too many Users");
                close(new_socket);
                continue;
            }
        }

        puts("Connection Accepted");
        char *client_ip = inet_ntoa(client.sin_addr);
        //int client_port = ntohs(client.sin_port);

        printf("ClientIP: %s\n", client_ip);
        write_sock(new_socket, "Hello you have been accepted!\n");

        pthread_t sniffer_thread;
        new_sock = malloc(1 * sizeof(int));       // Oops!
        if (new_sock == 0) { perror("out of memory"); return 1; }
        *new_sock = new_socket;

        if (pthread_create(&sniffer_thread, NULL, connection_handler, (void *)new_sock) < 0)
        {
            perror("Could not create thread");
            return 1;
        }
        puts("Handler Assigned");
    }

    if (new_socket < 0)
    {
        perror("accept failed");
        return 1;
    }
    return 0;
}

// Avoid repetition - use functions!
static void write_sock(int sock, const char *msg)
{
    int len = strlen(msg);
    if (write(sock, msg, len) != len)
    {
        perror("short write on socket");
        exit(1);
    }
}

void *connection_handler(void *socket_desc)
{
    int sock = *(int*)socket_desc;
    int read_size;
    char client_message[2000];

    write_sock(sock, "Greetings! I am your Connection Handler\n");
    write_sock(sock, "What do you want to do\n");

    while ((read_size = recv(sock, client_message, 2000, 0)) > 0)
    {
        client_message[read_size] = '\0';
        write_sock(sock, client_message);
        printf("User Entered:%s\n", client_message);
        int pin = client_message[0]-'0';
        int status = client_message[1]-'0';
        lightLED(pin, status);
    }

    if (read_size == 0)
    {
        puts("Client Disconnected\n");
        fflush(stdout);
        totalConnections--;
    }
    else if (read_size == -1)
    {
        perror("recv Failed");
    }

    free(socket_desc);
    return 0;
}

void lightLED(int pin, int status)
{
//    if (wiringPiSetup() == -1)
//    {
//        puts("wiringPi Error");
//        exit(1);
//    }
    printf("Changing LED Pin %d status %d\n", pin, status);
}

Note the use of the write_sock() function to encapsulate repeated code (which has the side benefit of only requiring the code to be written once, so it can be correct every time it is used).

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <pthread.h>
//#include <wiringPi.h>

void *connection_handler(void *);
void lightLED(int pin, int status);
static void write_sock(int sock, const char *msg);

int maxConnections = 1;
int totalConnections = 0;

int main(void)
{
    int socket_desc, new_socket, c, *new_sock;
    struct sockaddr_in server, client;

    socket_desc = socket(AF_INET, SOCK_STREAM, 0);
    if (socket_desc == -1)
    {
        printf("Could not create socket");
        return 1;
    }

    server.sin_family = AF_INET;
    server.sin_addr.s_addr = INADDR_ANY;
    server.sin_port = htons(8888);

    if (bind(socket_desc, (struct sockaddr *)&server, sizeof(server)) < 0)
    {
        puts("bind failed");
        return 1;
    }
    puts("bind done");

    if (listen(socket_desc, 3) != 0)
    {
        perror("listen() failed");
        return 1;
    }

    puts("Waiting for incoming connections...");
    c = sizeof(struct sockaddr_in);
    while ((new_socket = accept(socket_desc, (struct sockaddr *)&client, (socklen_t*)&c)))
    {
        if (new_socket > 0)
        {
            if (totalConnections < maxConnections)
                totalConnections++;
            else
            {
                write_sock(new_socket, "Sorry Maximum Users Reached\n");
                puts("Too many Users");
                close(new_socket);
                continue;
            }
        }

        puts("Connection Accepted");
        char *client_ip = inet_ntoa(client.sin_addr);
        //int client_port = ntohs(client.sin_port);

        printf("ClientIP: %s\n", client_ip);
        write_sock(new_socket, "Hello you have been accepted!\n");

        pthread_t sniffer_thread;
        new_sock = malloc(1 * sizeof(int));       // Oops!
        if (new_sock == 0) { perror("out of memory"); return 1; }
        *new_sock = new_socket;

        if (pthread_create(&sniffer_thread, NULL, connection_handler, (void *)new_sock) < 0)
        {
            perror("Could not create thread");
            return 1;
        }
        puts("Handler Assigned");
    }

    if (new_socket < 0)
    {
        perror("accept failed");
        return 1;
    }
    return 0;
}

// Avoid repetition - use functions!
static void write_sock(int sock, const char *msg)
{
    int len = strlen(msg);
    if (write(sock, msg, len) != len)
    {
        perror("short write on socket");
        exit(1);
    }
}

void *connection_handler(void *socket_desc)
{
    int sock = *(int*)socket_desc;
    int read_size;
    char client_message[2000];

    write_sock(sock, "Greetings! I am your Connection Handler\n");
    write_sock(sock, "What do you want to do\n");

    while ((read_size = recv(sock, client_message, 2000, 0)) > 0)
    {
        client_message[read_size] = '\0';
        write_sock(sock, client_message);
        printf("User Entered:%s\n", client_message);
        int pin = client_message[0]-'0';
        int status = client_message[1]-'0';
        lightLED(pin, status);
    }

    if (read_size == 0)
    {
        puts("Client Disconnected\n");
        fflush(stdout);
        totalConnections--;
    }
    else if (read_size == -1)
    {
        perror("recv Failed");
    }

    free(socket_desc);
    return 0;
}

void lightLED(int pin, int status)
{
//    if (wiringPiSetup() == -1)
//    {
//        puts("wiringPi Error");
//        exit(1);
//    }
    printf("Changing LED Pin %d status %d\n", pin, status);
}