Prob with binary files using sockets - c

Question

This is not the total code.
This is working fine for normal files like text files, but not working for tar.gz and binary files transfer please help me.
And how to send the chunks of memory using sockets.
server.c
void main()
{
int sockfd, new_fd; // listen on sock_fd, new connection on new_fd
struct sockaddr_in my_addr; // my address information
struct sockaddr_in their_addr; // connector's address information
socklen_t sin_size;
struct sigaction sa;
int yes=1;
char buf[16384];
char remotefile[MAXDATASIZE];
if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{
perror("socket");
exit(1);
}
if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1)
{
perror("setsockopt");
exit(1);
}
my_addr.sin_family = AF_INET; // host byte order
my_addr.sin_port = htons(MYPORT); // short, network byte order
my_addr.sin_addr.s_addr = INADDR_ANY; // automatically fill with my IP
memset(my_addr.sin_zero, '\0', sizeof my_addr.sin_zero);
printf("call binding\n");
if (bind(sockfd, (struct sockaddr *)&my_addr, sizeof my_addr) == -1)
{
perror("bind");
exit(1);
}
if (listen(sockfd, BACKLOG) == -1)
{
perror("listen");
exit(1);
}
sa.sa_handler = sigchld_handler; // reap all dead processes
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_RESTART;
if (sigaction(SIGCHLD, &sa, NULL) == -1)
{
perror("sigaction");
exit(1);
}
while(1)
{ // main accept() loop
sin_size = sizeof their_addr;
if ((new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size)) == -1)
{
perror("accept");
exit(1);
continue;
}
printf("server: got connection from %s\n",inet_ntoa(their_addr.sin_addr));
if (!fork())
{ // this is the child process
if ((byt=recv(new_fd, remotefile, MAXDATASIZE-1, 0)) == -1)
{
perror("server recv");
exit(1);
}
int serverfile_fd;
size_t result;
printf("\nremotefile in val1 is %s\n",remotefile);
if((serverfile_fd = open(remotefile,O_RDONLY)) < 0)
{
printf("error at remotefile\n");
exit(1);
}
else
{
read(serverfile_fd, &buf[0], sizeof(buf));
}
//printf("file is\n%s", buf);
/* 3. sending buf in val 0*/
if (send(new_fd, buf, 16384, 0) == -1)
perror("send");
close(new_fd);
exit(0);
}
client.c
int remote_to_local(const char *remotehost,const char *remotefile,const char *localfile)
{
int sockfd, numbytes,i = 0,j = 0;
char buf[16384];
struct hostent *he;
struct sockaddr_in s_addr; // connector's address information
printf("\n");
printf("Remotehost is %s\n", remotehost);
if ((he=gethostbyname(remotehost)) == NULL)
{ // get the host info
perror("gethostbyname");
exit(1);
}
if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{
perror("socket");
exit(1);
}
s_addr.sin_family = AF_INET; // host byte order
s_addr.sin_port = htons(PORT); // short, network byte order
s_addr.sin_addr = *((struct in_addr *)he->h_addr);
//inet_aton(he->h_addr, &s_addr.sin_addr);
memset(s_addr.sin_zero, '\0', sizeof s_addr.sin_zero);
if (connect(sockfd, (struct sockaddr *)&s_addr, sizeof s_addr) == -1)
{
perror("connect");
exit(1);
}
//send(sockfd, remotefile, MAXDATASIZE-1, 0);
val[0] = 1;
printf("Val 0 is %d\n", val[0]);
printf("Val 1 is %d\n", val[1]);
/*1 sending val in r to l*/
if (send(sockfd, val, MAXDATASIZE-1, 0) == -1)
perror("send");
printf("remotefile is %s\n",remotefile);
/* 2 sending remotefile in r to l*/
if (send(sockfd, remotefile, MAXDATASIZE-1, 0) == -1)
perror("send");
/* 3. recieve buf in r to l */
if ((numbytes=recv(sockfd, buf, 16384, 0)) == -1)
{
perror("recv");
exit(1);
}
buf[numbytes] = '\0';
//printf("Received: \n%s",buf);
int clientfile_fd;
printf("Local file is %s\n",localfile);
if((clientfile_fd = open(localfile,O_CREAT|O_WRONLY,0777)) < 0)
{
printf("error at remotefile\n");
exit(1);
}
else
{
//read(clientfile_fd, &buf[0], sizeof(buf));
int result = strlen(buf);
//printf("Result size is %d\n",result);
open(localfile,O_TRUNC);
write(clientfile_fd, &buf[0], result);
}
close(sockfd);
return 0;
}

Answer 1

Go through ALL your code and fix/change ALL the places where you:
don't correctly handle the results returned by system calls like
recv(). If a positive value is returned, that value is the ONLY safe
way of finding out how much data has been read into the buffer.
Get rid of all the strlen(), printf("%s...) etc. that are either
useless, (the binary data may contain nulls and so the action will
complete early), or dangerous, (binary data contains no nulls at all
and so the calls are UB).

Answer 2

Following logic for receiving a file is already a lot better than what you have. But there are a lot more problems with your code than just this :
FILE *received_file;
received_file = fopen(FILENAME, "w");
...
//copy logic, copies data received from the socket into the file as is.
while (((len = recv(client_socket, buffer, BUFSIZ, 0)) > 0))
{
fwrite(buffer, sizeof(char), len, received_file);
}
fclose(received_file);
close(client_socket);
The receive is continuously called until your receive 0 or a negative number, if you receive 0 that means you need to close the socket because the transfer is finished and the peer has closed its end of the connection too.
The file handle should be created right after accept.
Bottom line is that your code needs a total revision because it is too lengthy for what it is supposed to do, and it is based on totally wrong assumptions. Read first about network programming before attempting anything like this. Socket programming is an advanced topic, without proper understanding you will fail.