Getting wrong ip address and port number from recvfrom - c

Question

I get the following ip and port "204.204.204.204#52428" no matter what my ip and port are. I am using windows 10 and ipv4 address
#include "stdafx.h"
#undef UNICODE
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <stdio.h>
// Need to link with Ws2_32.lib
#pragma comment (lib, "Ws2_32.lib")
// #pragma comment (lib, "Mswsock.lib")
#define DEFAULT_BUFLEN 512
#define DEFAULT_PORT "27015"
int __cdecl main(int argc, char **argv)
{
WSADATA wsaData;
int iResult;
SOCKET ListenSocket = INVALID_SOCKET;
SOCKET ClientSocket = INVALID_SOCKET;
struct addrinfo *result = NULL;
struct addrinfo hints;
int iSendResult;
char recvbuf[DEFAULT_BUFLEN];
int recvbuflen = DEFAULT_BUFLEN;
// Initialize Winsock
iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
if (iResult != 0) {
printf("WSAStartup failed with error: %d\n", iResult);
return 1;
}
ZeroMemory(&hints, sizeof(hints));
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
hints.ai_flags = AI_PASSIVE;
// Resolve the server address and port
iResult = getaddrinfo(NULL, argv[1], &hints, &result);
if (iResult != 0) {
printf("getaddrinfo failed with error: %d\n", iResult);
WSACleanup();
return 1;
}
// Create a SOCKET for connecting to server
ListenSocket = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
if (ListenSocket == INVALID_SOCKET) {
printf("socket failed with error: %ld\n", WSAGetLastError());
freeaddrinfo(result);
WSACleanup();
return 1;
}
// Setup the TCP listening socket
iResult = bind(ListenSocket, result->ai_addr, (int)result->ai_addrlen);
if (iResult == SOCKET_ERROR) {
printf("bind failed with error: %d\n", WSAGetLastError());
freeaddrinfo(result);
closesocket(ListenSocket);
WSACleanup();
return 1;
}
freeaddrinfo(result);
iResult = listen(ListenSocket, SOMAXCONN);
if (iResult == SOCKET_ERROR) {
printf("listen failed with error: %d\n", WSAGetLastError());
closesocket(ListenSocket);
WSACleanup();
return 1;
}
// Accept a client socket
ClientSocket = accept(ListenSocket, NULL, NULL);
if (ClientSocket == INVALID_SOCKET) {
printf("accept failed with error: %d\n", WSAGetLastError());
closesocket(ListenSocket);
WSACleanup();
return 1;
}
// No longer need server socket
closesocket(ListenSocket);
struct sockaddr_in from_addr;
socklen_t fromlen = sizeof(from_addr);
char from_ip[2048] = "";
int nbytes = 0;
// Receive until the peer shuts down the connection
do {
nbytes = recvfrom(ClientSocket, recvbuf, recvbuflen, 0, (sockaddr *) &from_addr, &fromlen);
InetNtop(AF_INET, &from_addr.sin_addr, from_ip, sizeof(from_ip));
if (nbytes > 0) {
printf("Received %d bytes from %s#%d", nbytes, from_ip, ntohs(from_addr.sin_port));
// Echo the buffer back to the sender
iSendResult = send(ClientSocket, recvbuf, nbytes, 0);
if (iSendResult == SOCKET_ERROR) {
printf("send failed with error: %d\n", WSAGetLastError());
closesocket(ClientSocket);
WSACleanup();
return 1;
}
printf("\tBytes sent: %d\n", iSendResult);
}
else if (nbytes == 0)
printf("Connection closing...\n");
else {
printf("recv failed with error: %d\n", WSAGetLastError());
closesocket(ClientSocket);
WSACleanup();
return 1;
}
fromlen = sizeof(from_addr);
} while (nbytes > 0);
// shutdown the connection since we're done
iResult = shutdown(ClientSocket, SD_SEND);
if (iResult == SOCKET_ERROR) {
printf("shutdown failed with error: %d\n", WSAGetLastError());
closesocket(ClientSocket);
WSACleanup();
return 1;
}
// cleanup
closesocket(ClientSocket);
WSACleanup();
return 0;
}
where printing happens in this block
struct sockaddr_in from_addr;
socklen_t fromlen = sizeof(from_addr);
char from_ip[2048] = "";
int nbytes = 0;
// Receive until the peer shuts down the connection
do {
nbytes = recvfrom(ClientSocket, recvbuf, recvbuflen, 0, (sockaddr *) &from_addr, &fromlen);
InetNtop(AF_INET, &from_addr.sin_addr, from_ip, sizeof(from_ip));
if (nbytes > 0) {
printf("Received %d bytes from %s#%d", nbytes, from_ip, ntohs(from_addr.sin_port));
// Echo the buffer back to the sender
iSendResult = send(ClientSocket, recvbuf, nbytes, 0);
if (iSendResult == SOCKET_ERROR) {
printf("send failed with error: %d\n", WSAGetLastError());
closesocket(ClientSocket);
WSACleanup();
return 1;
}
printf("\tBytes sent: %d\n", iSendResult);
}
else if (nbytes == 0)
printf("Connection closing...\n");
else {
printf("recv failed with error: %d\n", WSAGetLastError());
closesocket(ClientSocket);
WSACleanup();
return 1;
}
fromlen = sizeof(from_addr);
} while (nbytes > 0);
I am not sure how to resolve this problem?

Answer 1

Don't call recvfrom() on a TCP socket. I'm surprised it works at all; I suppose it "reverts" to recv() behavior and ignores the source address & length parameters.
You can get the peer's address info from the accept() call.