Wsrtjtyk

i have a server/client application and i am trying to get the server to read each message the client sends to it and send it back to the client to be printed. so far i have the server reading the first message and sending that to the client and that prints fine, but when the second message is sent from the client, i try to print it from the HandleTcpClient function to test it and it just prints null, i am not sure if it is receiving it correctly

client code:

#include <stdio.h> //include standard input/output library

#include <stdlib.h> //include standard libraries

#include <string.h> //include string headers 

#include <unistd.h> //add definitions for constansts and functions 

#include <sys/types.h> // include definitions for different data types

#include <sys/socket.h> //include socket support

#include <netinet/in.h> //define internet protocol functions

#include <arpa/inet.h> //define internet protocol functions

#include "Practical.h" //include practical header file



int main(int argc, char *argv) {



char myIP[16];

unsigned int myPort;

struct sockaddr_in server_addr,myaddr;

char username = "CharlieA";

  if (argc < 2 || argc > 3) // Test for correct number of arguments

    DieWithUserMessage("Parameter(s)",

        "<Server Address> [<Server Port>]");



  char *servIP = argv[1];     // First arg: server IP address (dotted quad)





  // Third arg (optional): server port (numeric).  7 is well-known echo port

  in_port_t servPort = atoi(argv[2]);  //21

printf("serv port: %dn",servPort);





 // Create a reliable, stream socket using TCP  //23

int sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);//this block of code creates a reliable tcp stream socket and checks what the returned integer is from the socket function, the returned function will give a integer that descibes the socket. if this is 0 then kill the socket and show the user an error message.

  if (sock < 0)

    DieWithSystemMessage("socket() failed"); //26



  // Construct the server address structure //28

  struct sockaddr_in servAddr;            // Server address

  memset(&servAddr, 0, sizeof(servAddr)); // Zero out structure

  servAddr.sin_family = AF_INET;          // IPv4 address family

  // Convert address

  int rtnVal = inet_pton(AF_INET, servIP, &servAddr.sin_addr.s_addr);

  if (rtnVal == 0)

    DieWithUserMessage("inet_pton() failed", "invalid address string");

  else if (rtnVal < 0)

    DieWithSystemMessage("inet_pton() failed");

  servAddr.sin_port = htons(servPort);    // Server port

  myaddr.sin_addr.s_addr = INADDR_ANY;



  // Establish the connection to the echo server

  if (connect(sock, (struct sockaddr *) &servAddr, sizeof(servAddr)) < 0)

    DieWithSystemMessage("connect() failed"); 



 //get address of bound socket after connect function call (binds automatically with connect method)

bzero(&myaddr,sizeof(myaddr));

int len = sizeof(myaddr);

getsockname(sock,(struct sockaddr *) &myaddr, &len);

inet_ntop(AF_INET, &myaddr.sin_addr, myIP, sizeof(myIP)); //convert network address to string

myPort = ntohs(myaddr.sin_port); //convert from netshort to hostbyte order



//getlocal ip address to be sent to server

char *echoString=(char*)malloc(13*sizeof(char));

sprintf(echoString,"netsrv type0 %s %s-%urn",username,myIP,myPort); //generate request string

size_t echoStringLen = strlen(echoString); // Determine input length //44

size_t iplen = strlen(myIP);





  // Send the string to the server

  ssize_t numBytes = send(sock,echoString, echoStringLen, 0);

  printf("sent: %s", echoString);



  if (numBytes < 0) //sending string to server, number of bytes of the message is equal to return value of send function, if the number of bytes is less than 0 then do not send and say to user that the send failed

    DieWithSystemMessage("send() failed");

  else if (numBytes != echoStringLen)

    DieWithUserMessage("send()", "sent unexpected number of bytes"); //51



// if the number of bytes is not equal to the input length of the string parsed as an argument then die with the message to the user saying sent unexpected number of bytes.

    //send IP to server

send(sock,myIP,iplen,0); //send client IP

  // Receive the same string back from the server  //53

  unsigned int totalBytesRcvd = 0; // Count of total bytes received



  while (totalBytesRcvd < echoStringLen) {

    char buffer[BUFSIZE]; // I/O buffer

    /* Receive up to the buffer size (minus 1 to leave space for

     a null terminator) bytes from the sender */

    numBytes = recv(sock, buffer, BUFSIZE - 1, 0);

    if (numBytes < 0)

      DieWithSystemMessage("recv() failed");

    else if (numBytes == 0)

      DieWithUserMessage("recv()", "connection closed prematurely");

    totalBytesRcvd += numBytes; // Keep tally of total bytes

    buffer[numBytes] = '';    // Terminate the string!

    fputs("Received: ", stdout);     // Setup to print the echoed string

    fputs(buffer, stdout);      // Print the echo buffer





  }



  fputc('n', stdout); // Print a final linefeed //70



  close(sock);

  exit(0);

}

//closing off connections to clean up data left over.

The second message is the send client IP commented line

Server:

#include <stdio.h> //include standard input/output library

#include <stdlib.h> //include standard libraries

#include <string.h> //include string headers 

#include <sys/types.h> //add definitions for constansts and functions 

#include <sys/socket.h> // include definitions for different data types

#include <netinet/in.h>  //define internet protocol functions

#include <arpa/inet.h> //define internet protocol functions

#include "Practical.h" //include pactical



static const int MAXPENDING = 5; // Maximum outstanding connection requests

static const int servPort = 48031;

int main(int argc) {//run on command line = "echoSvr <port>";argc = 2 command and parameter-  argv[0] = echoSvr and argv[1] = <port>



  // Create socket for incoming connections

  int servSock; // Socket descriptor for server

  if ((servSock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)

    DieWithSystemMessage("socket() failed");

// this block of code is creating a socket stream to accept the incoming connections from clients 



  // Construct local address structure

  struct sockaddr_in servAddr;                  // Local address; internet socket address structure

  memset(&servAddr, 0, sizeof(servAddr));       // Zero out structure

  servAddr.sin_family = AF_INET;                // IPv4 address family

  servAddr.sin_addr.s_addr = htonl(INADDR_ANY); // Any incoming interface; host to network long[integer]

  servAddr.sin_port = htons(servPort);          // Local port; host to network short[integer]



  // Bind to the local address

  if (bind(servSock, (struct sockaddr*) &servAddr, sizeof(servAddr)) < 0)//cast servaddr as generic socket address structure

    DieWithSystemMessage("bind() failed");



  // Mark the socket so it will listen for incoming connections

  if (listen(servSock, MAXPENDING) < 0)

    DieWithSystemMessage("listen() failed");



setvbuf (stdout, NULL, _IONBF, 0);

printf("Listening on port: %d n" , servPort);

printf("awaiting connection from client.... n");

// this block of code binds the socket to the address of the server and tells the binded to socket to begin listening in for connections coming from client machines 

  for (;;) { // Run forever

    struct sockaddr_in clntAddr; // Client address

    // Set length of client address structure (in-out parameter)

    socklen_t clntAddrLen = sizeof(clntAddr);



    // Wait for a client to connect

    int clntSock = accept(servSock, (struct sockaddr *) &clntAddr, &clntAddrLen);

    if (clntSock < 0)

      DieWithSystemMessage("accept() failed");

//this block of code waits for a client to connect to the socket and then accepts the connection from the client and prints the clients details out to screen

    // clntSock is connected to a client!



    char clntName[INET_ADDRSTRLEN]; // String to contain client address

    if (inet_ntop(AF_INET, &clntAddr.sin_addr.s_addr, clntName,

        sizeof(clntName)) != NULL)

      printf("Handling client %s/%dn", clntName, ntohs(clntAddr.sin_port));

    else

      puts("Unable to get client address");



    HandleTCPClient(clntSock);

  }

}

HandleTCPClient Function:

void HandleTCPClient(int clntSocket) {

  char buffer[BUFSIZE]; // Buffer for echo string

  char *clientIP;



  unsigned int clientPort;

  // Receive message from client

  ssize_t numBytesRcvd = recv(clntSocket, buffer, BUFSIZE, 0);

  if (numBytesRcvd < 0)

    DieWithSystemMessage("recv() failed");



//get ip and port of clntSocket to apply to greeting string



  // Send greeting string and receive again until end of stream

  while (numBytesRcvd > 0) { // 0 indicates end of stream

    // Echo message back to client

    ssize_t numBytesSent = send(clntSocket, buffer, numBytesRcvd, 0);

    if (numBytesSent < 0)

      DieWithSystemMessage("send() failed");

    else if (numBytesSent != numBytesRcvd)

      DieWithUserMessage("send()", "sent unexpected number of bytes");



    // See if there is more data to receive

    numBytesRcvd = recv(clntSocket, buffer, BUFSIZE, 0);

    if (numBytesRcvd < 0)

      DieWithSystemMessage("recv() failed");



    //recv client ip and assign to variable to hold

    recv(clntSocket,clientIP,100,0);

    printf("clientIP : %s" ,clientIP);

  }



close(clntSocket); // Close client socket

}

i am trying to print the clientIP with the printf function and this is where i am getting a null, it just does not seem to be receiving it, there is a lot of code here, i am posting it all in case it is needed

That is a lot of code, so I didn't look at most of it. I did, however, notice:

char *echoString=(char*)malloc(13*sizeof(char));

sprintf(echoString,"netsrv type0 %s %s-%urn",username,myIP,myPort);

Nowhere do you explain where that 13 comes from, but it is clearly not enough to hold the formatted string which sprintf will produce. It's enough to hold a 12-character string (plus the NUL terminator) which gets you up to netsrv type0. That needs to be fixed, since the sprintf will clobber random memory which doesn't belong to it, but that's probably not your immediate problem. (Use snprintf. Even simpler, if you're using Linux/OSX/FreeBSD, is asprintf.)

What I think might be your problem is this:

numBytesRcvd = recv(clntSocket, buffer, BUFSIZE, 0);

//recv client ip and assign to variable to hold

recv(clntSocket,clientIP,100,0);

printf("clientIP : %s" ,clientIP);

You never look at the data received by the first recv() call. Perhaps you are under the misapprehension that each send somehow marks the data being sent so that recv will only read exactly the data sent by one send. That's not the case. TCP is a streaming protocol; the data is just an undistinguished series of bytes and each recv() receives whatever is available, subject to the size limit in the call. So it is quite possible that the result of both send() calls will show up in the first recv() call.

I think this is probably explained in whatever text/tutorial/guide you are using to write that code, but if not I strongly recommend finding a copy of W. R. Stevens' Unix Network Programming.

In short: If you want to send "messages", you need to figure out how to delimit them in a way that the receiver can tell where one message ends and the next one begins. A really simple strategy, used by many older internet protocols, is to end each message with a newline sequence and ensure that there are no newlines in any message.