TCPServerFork.c

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

int writeFile(int socketDescriptor);
void DieWithError(char *errorMessage);

int main(int argc, char *argv[]){
  int serverSocket, clientSocket, addr_size;
  unsigned int clientLen;
  pid_t processID;
  struct sockaddr_in server, client;
  unsigned int childProcCount = 0;

  if ((serverSocket = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    DieWithError(" socket () failed") ;

  printf("[+]Server socket created successfully.\n");

  memset(&server, 0, sizeof(server));
  server.sin_family = AF_INET;    
  server.sin_addr.s_addr = INADDR_ANY;
  server.sin_port = htons(8888);

  if (bind(serverSocket, (struct sockaddr *)&server, sizeof(server)) < 0)
    DieWithError ("bind () failed");

  printf("[+]Binding successfull.\n");

  if (listen(serverSocket, 5) < 0)
    DieWithError("listen() failed") ;

  printf("[+]Listening....\n");
  addr_size = sizeof(struct sockaddr_in);

  for (;;){
  if ((clientSocket = accept(serverSocket, (struct sockaddr *) &client, (socklen_t*)&addr_size)) < 0)
      DieWithError( "accept () failed");
    
    printf("Handling client %s\n", inet_ntoa(client.sin_addr));

  if ((processID = fork()) < 0)
    DieWithError("fork() failed");
  else if (processID == 0){
    close(serverSocket);
    exit(writeFile(clientSocket));
  }

  printf("with child process' %d\n", (int) processID);
  close(clientSocket);
  childProcCount ++;

  while (childProcCount)
    {
      processID = waitpid((pid_t)-1, NULL, WNOHANG);
      if (processID < 0)
        DieWithError("waitpid() failed");
      else if (processID == 0)
         break;
      else
        childProcCount--;
    }
  }
  exit(0);
}

void DieWithError(char *errorMessage){
  perror (errorMessage);
  exit(1);
}

int writeFile(int socketDescriptor){
  int bytesReceived = 0;
  FILE *uploadedFile;
  char buffer[512];

if (recv(socketDescriptor, buffer, sizeof(buffer), 0) < 0)
  DieWithError ("Error receiving name");

int fileNameSize = buffer[0];
char fileName[fileNameSize];

strcpy(fileName, buffer+1);

uploadedFile = fopen(fileName, "wb"); //overwrite if exists and create if not
 if(NULL == uploadedFile){
    DieWithError ("Error creating file");
  }
  
  printf("Created filename: %s\n", fileName);

  puts("waiting\n");
  sleep(10);

  while((bytesReceived=recv(socketDescriptor, buffer, sizeof(buffer),0)) > 0){
    printf("Received %d bytes\n", bytesReceived);
    fwrite(buffer, 1, bytesReceived, uploadedFile);
  }

  if(bytesReceived == 0) {
    puts("Client disconnected");
  } else if(bytesReceived == -1) {
    DieWithError("Error recieving file");
  }
  close(socketDescriptor);
  fclose(uploadedFile);
  return 0;
}