socket connection getting closed abruptly with code 141 - c

Question

What im trying to do is connect to a remote server , read contents from a file on the local machine and send it over to the server. Then capture the server response and save it. I put the GET command in a text file and am trying get the results of the same. Here is some part of the code. Im doing this using sockets and C.
if ( inet_pton(AF_INET,ip, &(nc_args->destaddr.sin_addr.s_addr)) <= 0 )
printf("\n\t\t inet_pton error");
if (connect(sockfd, (struct sockaddr *) &nc_args->destaddr, sizeof(&nc_args->destaddr)) < 0)
{
printf("\n\t\t Connection error");
exit(1);
}
puts("\n\t\t Connection successful to ...");
// file parameter is taken from command line and passéd to this function
fp = fopen(file,"rb");
if ( fp == NULL)
{
printf("\n\t\t File not found");
exit(3);
}
else
{
printf("\n\t\t Found file %s\n", file);
fseek(fp, 0, SEEK_END);
file_size = ftell(fp);
rewind(fp);
//allocate memory to the buffer dynamically
buffer = (char*) malloc (sizeof(char)*file_size);
if (buffer == NULL) {fputs ("Memory error",stderr); exit (2);}
for (i=0 ; i<sizeof(buffer); i++)
{
printf("\n\t\t %s", buffer);
}
printf("\n\t\t File contains %ld bytes!\n", file_size);
printf("\n\t\t Sending the file now");
}
while (1)
{
bytes_read = fread(buffer,1, file_size, fp);
printf("\n\t\t The bytes read is %zd", bytes_read);
if (bytes_read == 0) // We're done reading from the file
{
printf("\n\t\t The bytes read is %zd", bytes_read);
break;
}
if (bytes_read < 0)
{
printf("\n\t\t ERROR reading from file");
}
void *p = buffer;
while (bytes_read > 0)
{
ssize_t bytes_written = send(sockfd, buffer, bytes_read,0);
if (bytes_written <= 0)
{
printf("\n\t\t ERROR writing to socket\n");
}
bytes_read -= bytes_written;
p += bytes_written;
printf("\n\t\t Bytes %zd written", bytes_written);
}
}
printf("\n\n\t\t Sending complete.");
What is happening here is that i get the message "connection successful", then it displays "sending the file now" and then the program quits unexpectedly. if i do echo $? i get 141 as the exit code. I am trying to connect from my server to a different server at work and get the results. These two can communicate correctly, and i can run the GET command from command line without issues. Its just not working from the code. Can someone let me know what the issue could be ?

Answer 1

On Linux, and probably other Unixes, the return code encodes a signal that the process received. Here it is 141 - 128 so 13 which corresponds to SIGPIPE.
If you don't want that signal to be raised because you capture the error return of send, anyhow, on Linux you can use MSG_NOSIGNAL in the flags argument to send to inhibit that signal. On other platforms you might have to program more complicated signal handlers to deal with that situation.

Answer 2

sizeof(&nc_args->destaddr) is the wrong thing to pass to connect. It wants the size of the address, not the size of a pointer to the address.
And this loop:
for (i=0 ; i<sizeof(buffer); i++)
{
printf("\n\t\t %s", buffer);
}
is baffling. buffer is a pointer, as we can see from when it was assigned a vlue returned by malloc. So its size is going to be 4 or 8 bytes on 32-bit and 64-bit architectures respectively; not related to the size of the malloc'ed object it points to. The loop runs 4 or 8 times, and prints... the same thing each time. Why?