cant send file through socket C - c

Question

it works only when i do it with my own Computer , but when i use another Computer the file recieved is a mess and the size is always another.
Server:
while (1) {
ZeroMemory(r_buf, MAX_BUFF_RECV - 1);
bytesReceived = recv(sock, r_buf, FILE_DOWNLOAD_SIZE, 0);
if (bytesReceived < 0) {
// ERROR
puts("[!] recv failed");
return;
}
else if (bytesReceived < FILE_DOWNLOAD_SIZE) {
// LAST CHUNCK
if (WriteFile(out, r_buf, bytesReceived, &n, NULL) == FALSE) {
printf("WriteFile() error %d\n", GetLastError());
}
break;
}
else {
if (WriteFile(out, r_buf, bytesReceived, &n, NULL) == FALSE) {
printf("WriteFile() error %d\n", GetLastError());
}
}
}
Client:
while (1)
{
ZeroMemory(buff, FILE_DOWNLOAD_SIZE);
nread = fread(buff, 1, FILE_DOWNLOAD_SIZE, f);
if (nread != FILE_DOWNLOAD_SIZE) {
send(s, buff, nread, 0);
break;
}
else {
send(s, buff, nread, 0);
}
}
im for hours on it , pls tell me whats wrong

Answer 1

In connection-oriented transports, like TCP, send() and recv() are not 1-to-1. There is no guarantee that what you send() will be transmitted in a single data packet, or that recv() will receive everything that you send() in a single go.
There is no guarantee that send() will even accept everything that you give it. It will copy whatever it can into the socket's outbound buffer and return the actual number of bytes copied. So it can accept fewer bytes than requested.
Likewise, recv() will copy whatever data is currently available in the socket's inbound buffer, at least 1 byte but not more than the specified number of bytes, into your specified buffer and will return the actual number of bytes copied. So it can receive fewer bytes than requested.
You also need to know how much file data is actually being transmitted so you know when to stop reading the data. Since recv() can return fewer bytes than requested, you cannot rely on buffer sizes alone to indicate EOF.
You are not taking any of this into account in your code.
Try something more like this instead:
Server:
bool readRaw(SOCKET sock, void *buf, int bufSize)
{
char *pbuf = (char*) buf;
while (bufSize > 0)
{
int bytesReceived = recv(sock, pbuf, bufSize, 0);
if (bytesReceived < 0)
{
printf("[!] recv() error %d\n", WSAGetLastError());
return false;
}
else if (bytesReceived == 0)
{
puts("[!] client disconnected");
return false;
}
else
{
pBuf += bytesReceived;
bufSize -= bytesReceived;
}
}
return true;
}
...
unsigned __int64 fileSize = 0;
if (readRaw(sock, &fileSize, sizeof(fileSize)))
{
while (fileSize > 0)
{
int bufSize = min(fileSize, MAX_BUFF_RECV);
if (!readRaw(sock, r_buf, bufSize))
break;
if (!WriteFile(out, r_buf, bufSize, &n, NULL))
{
printf("[!] WriteFile() error %d\n", GetLastError());
break;
}
fileSize -= bufSize;
}
}
Client:
bool sendRaw(SOCKET sock, void *buf, int bufSize)
{
char *pbuf = (char*) buf;
while (bufSize > 0)
{
int bytesSent = send(sock, pbuf, bufSize, 0);
if (bytesSent < 0)
{
printf("[!] send() error %d\n", WSAGetLastError());
return false;
}
else
{
pBuf += bytesSent;
bufSize -= bytesSent;
}
}
return true;
}
...
fseek(f, 0, SEEK_END);
long int pos = ftell(f);
fseek(f, 0, SEEK_SET);
if (pos == -1)
printf("[!] ftell() error\n");
else
{
unsigned __int64 fileSize = pos;
if (sendRaw(s, &fileSize, sizeof(fileSize)))
{
while (fileSize > 0)
{
int bufSize = min(FILE_DOWNLOAD_SIZE, fileSize);
nread = fread(buff, 1, bufSize, f);
if (nread == 0)
{
printf("[!] fread() error\n");
break;
}
if (!sendRaw(s, buff, nread))
break;
uifileSize -= nread;
}
}
}