File size changes after sending it through socket - c

Question

When sending a file through socket from client to server the file size changes. Where the problem may be?
Here is the client's side code:
char chunk[512];
host_info = gethostbyname(server);
if (host_info == NULL) {
perror("get host by name");
exit(errno);
}
socket_desc = socket(AF_INET, SOCK_STREAM, 0);
if (socket_desc < 0) {
perror("socket");
exit(errno);
}
server_address.sin_family = host_info->h_addrtype;
memcpy((char *) &server_address.sin_addr.s_addr, host_info->h_addr_list[0], host_info->h_length);
server_address.sin_port = htons(PORT);
if (connect(socket_desc, (struct sockaddr *) &server_address, sizeof(server_address)) < 0) {
perror("connect");
exit(errno);
}
file_to_send = fopen (lfile,"rb");
if(!file_to_send) {
perror("fopen");
close(socket_desc);
exit(errno);
} else {
long file_size;
fseek (file_to_send, 0, SEEK_END);
file_size = ftell (file_to_send);
rewind(file_to_send);
while(totally_read < file_size){
chunk[0] = '\0';
bytes_read = fread(chunk, sizeof(char), sizeof(chunk), file_to_send);
totally_read += bytes_read;
int sent = send(socket_desc, chunk, bytes_read, 0);
if(sent < 0){
perror("connect");
exit(errno);
}
totally_sent += sent;
printf("read: %7db sent: %7db totally read: %7db totally sent: %7db\n", bytes_read, sent, totally_read, totally_sent);
}
And here is the server side:
char chunk[512];
listen_socket = socket(AF_INET, SOCK_STREAM, 0);
if (listen_socket < 0) {
perror("socket");
close(listen_socket);
exit(errno);
}
server_address.sin_family = AF_INET;
server_address.sin_addr.s_addr = htonl(INADDR_ANY);
server_address.sin_port = htons(PORT);
if (bind(listen_socket, (struct sockaddr *) &server_address, sizeof(server_address)) < 0) {
perror("bind");
close(listen_socket);
exit(errno);
}
listen(listen_socket, 5);
client_address_length = sizeof(client_address);
while(1){
connect_socket = accept(listen_socket, (struct sockaddr *) &client_address, &client_address_length);
if (connect_socket < 0) {
perror("accept");
close(listen_socket);
exit(errno);
}
recv_file = fopen(filename,"wb");
int received = 0;
int totally_wrote = 0, totally_received = 0;
while(1){
chunk[0] = '\0';
received = recv(connect_socket, chunk, sizeof(chunk), 0);
if(received < 0) {
perror("recv");
} else if(received > 0) {
int wrote = fwrite(chunk, sizeof(char), received, recv_file);
totally_wrote +=wrote;
totally_received += received;
printf("received: %7db wrote: %7db totally received: %7db torally wrote: %7db\n", received, wrote, totally_received, totally_wrote);
} else {
printf("Complete!\n");
break;
}
}
When sending a text file I get the following output
on the client side:
totally read: 299695b | totally sent: 299695b
but on the server side:
totally received: 303279b | torally wrote: 303279b
I've opened the file with the editor. The transmitted file is practically the same with the source file, except for some strange data in the beginning. The transmitted file 3584 bytes of additionsl binary data in the beginning if the chunk size is 512 bytes. It adds 3840 bytes if i change the chunk size to 256 bytes.

Answer 1

You are not checking the return value from send()
Send() can return any value between -1 and the third (length) argument, inclusive. You assume any return value > 0 to be equal to the 3rd argument. They need not be.
to deal with short send()s (or recv()s (or read() / write()) you'll need something like:
int sent, pos, bytes_read;
bytes_read = fread(chunk, sizeof(char), sizeof(chunk), file_to_send);
totally_read += bytes_read;
for (pos = 0; pos < bytes_read; pos += sent) {
sent = send(socket_desc, chunk+pos, bytes_read-pos, 0)
switch(sent) {
case -1: /* handle errno here, especially EAGAIN/EINTR */
case 0: /*handle EOF here */
break;
default:
break;
}
}
totally_sent += pos;