Notes

#include <stdio.h>

#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netdb.h>
#include <netinet/in.h>
#include <unistd.h>
#include <signal.h>
#include <stdbool.h>

typedef unsigned long ip_address;
typedef unsigned short uint16;

static const int BUFFER_SIZE = 16*1024;

static void UsageExit()
{
printf("Usage: xfer (send/receive) filename [host:Port]n");
exit(10);
}

static ip_address GetHostByName(const char * name)
{
struct hostent * he = gethostbyname(name);
return ntohl(he ? *((ip_address*)he->h_addr) : 0);
}

static void SendFile(ip_address ipAddress, uint16 port, const char * fileName)
{
FILE * fpIn = fopen(fileName, "r");
if (fpIn)
{
int s = socket(AF_INET, SOCK_STREAM, 0);
if (s >= 0)
{
struct sockaddr_in saAddr; memset(&saAddr, 0, sizeof(saAddr));
saAddr.sin_family = AF_INET;
saAddr.sin_addr.s_addr = htonl(ipAddress);
saAddr.sin_port = htons(port);

if (connect(s, (struct sockaddr *) &saAddr, sizeof(saAddr)) == 0)
{
printf("Connected to remote host, sending file [%s]n", fileName);

char buf[BUFFER_SIZE];
while(1)
{
ssize_t bytesRead = fread(buf, 1, sizeof(buf), fpIn);
if (bytesRead <= 0) break; // EOF

printf("Read %i bytes from file, sending them to network...n", (int)bytesRead);
if (send(s, buf, bytesRead, 0) != bytesRead)
{
perror("send");
break;
}
}
}
else perror("connect");

close(s);
}
else perror("socket");

fclose(fpIn);
}
else printf("Error, couldn't open file [%s] to send!n", fileName);
}

static void ReceiveFile(uint16 port, const char * fileName)
{
int s = socket(AF_INET, SOCK_STREAM, 0);
if (s >= 0)
{
#ifndef WIN32
// (Not necessary under windows -- it has the behaviour we want by default)
const int trueValue = 1;
(void) setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &trueValue, sizeof(trueValue));
#endif

struct sockaddr_in saAddr; memset(&saAddr, 0, sizeof(saAddr));
saAddr.sin_family = AF_INET;
saAddr.sin_addr.s_addr = htonl(0); // (IPADDR_ANY)
saAddr.sin_port = htons(port);

if ((bind(s, (struct sockaddr *) &saAddr, sizeof(saAddr)) == 0)&&(listen(s, 10) == 0))
{
memset(&saAddr, 0, sizeof(saAddr));
socklen_t len = sizeof(saAddr);
printf("Waiting for incoming TCP connection on port %u, to write file [%s]n", port, fileName);
int connectSocket = accept(s, (struct sockaddr *) &saAddr, &len);
if (connectSocket >= 0)
{
FILE * fpIn = fopen(fileName, "w");
if (fpIn)
{
char buf[BUFFER_SIZE];
while(1)
{
ssize_t bytesReceived = recv(connectSocket, buf, sizeof(buf), 0);
if (bytesReceived < 0) perror("recv"); // network error?
if (bytesReceived == 0) break; // sender closed connection, must be end of file

printf("Received %i bytes from network, writing them to file...n", (int) bytesReceived);
if (fwrite(buf, 1, bytesReceived, fpIn) != (size_t) bytesReceived)
{
perror("fwrite");
break;
}
}
fclose(fpIn);
}
else printf("Error, couldn't open file [%s] to receive!n", fileName);

close(connectSocket);
}
}
else perror("bind");
close(s);
}
else perror("socket");
}
int main(int argc, char ** argv)
{
if (argc < 4) UsageExit();

#ifdef WIN32
// Windows requires this to start up the networking API
WORD versionWanted = MAKEWORD(1, 1);
WSADATA wsaData;
(void) WSAStartup(versionWanted, &wsaData);
#else
// avoid SIGPIPE signals caused by sending on a closed socket

signal(SIGPIPE, SIG_IGN);
#endif

bool isSend = false;
if (strcmp(argv[1], "send") == 0) isSend = true;
else if (strcmp(argv[1], "receive") != 0) UsageExit();

const char * fileName = argv[2];

ip_address ip = isSend ? GetHostByName(argv[3]) : 0;
uint16 port = 0;
const char * portColon = strchr(argv[3], ':');
port = portColon ? atoi(portColon+1) : 0;
if (port == 0) port = 9999;

if (isSend) SendFile(ip, port, fileName);
else ReceiveFile(port, fileName);

printf("Exiting, bye!n");
return 0;
}