Issue with C++ UDP Client Hanging Up - c++

Question

The project I am working on uses TCP and UDP to create a file transport protocol. The TCP connection generates a random port in which it returns to the client and the client then connects to the server on that port number using UDP. UDP is then used to transfer a text file four characters a time to the server and the server will send back the characters capitalized in which will then be displayed on the client. The issue is that the client is hanging up when waiting for the server to send back the capitalized version of the characters. I will leave the code below. The part of the code that is not working is commented out towards the end of the client and server files. Any help is appreciated!
Client Code
// Libraries
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <iostream>
#include <unistd.h>
using namespace std;
int main(int argc, char* argv[]) {
// Variables
int port = strtol(argv[2], NULL, 10);
string file = argv[3];
int r_port;
FILE* fp;
string fileString;
string dataBuffer;
int charCounter = 0;
char c;
// *** Declare TCP socket ***
int tcpsocket = 0;
tcpsocket = socket(AF_INET, SOCK_STREAM, 0);
if (tcpsocket == -1) {
cerr << "Can't create a socket";
return 1;
}
// Get host IP address
struct hostent *s;
s = gethostbyname(argv[1]);
// Setting destination info
struct sockaddr_in server;
memset((char *) &server, 0, sizeof(server));
server.sin_family = AF_INET;
server.sin_port = htons(port);
bcopy((char *) s->h_addr, (char *) &server.sin_addr.s_addr, s->h_length);
// Connect to server
int connectRes = connect(tcpsocket, (sockaddr*)&server, sizeof(server));
if (connectRes == -1) {
cerr << "Can't connect to socket";
return 1;
}
// Sending data to server
char payload[512] = "117";
int sendRes = send(tcpsocket, payload, 512, 0);
if (sendRes == -1) {
cerr << "Could not send to server";
return 1;
}
// Receive r_port from server
memset(payload, 0, sizeof(payload));
recv(tcpsocket, payload, 512, 0);
r_port = strtol(payload, NULL, 10);
close(tcpsocket);
// *** Declare UDP socket ***
int udpsocket = 0;
udpsocket = socket(AF_INET, SOCK_DGRAM, 0);
if (udpsocket == -1) {
cerr << "Can't create a socket";
return 1;
}
// Get host IP address
s = gethostbyname(argv[1]);
// Setting destination info
memset((char *) &server, 0, sizeof(server));
server.sin_family = AF_INET;
server.sin_port = htons(r_port);
bcopy((char *) s->h_addr, (char *) &server.sin_addr.s_addr, s->h_length);
// File manipulation
fp = fopen(file.c_str(), "r");
while (c != EOF) {
c = fgetc(fp);
fileString += c;
charCounter++;
}
fclose(fp);
// UDP file transfer
for (int i = 4; i < 8; i++) {
dataBuffer += fileString[i];
}
socklen_t slen = sizeof(server);
memset(payload, 0, sizeof(payload));
strcpy(payload, dataBuffer.c_str());
sendRes = sendto(udpsocket, payload, 32, 0, (struct sockaddr *) &server, slen);
if (sendRes == -1) {
cerr << "Could not send to server";
return 1;
}
// Receive ack
// slen = sizeof(server);
// memset(payload, 0, sizeof(payload));
// recvfrom(udpsocket, payload, 32, 0, (sockaddr*)&server, &slen);
// cout << "Capitalized data: " << payload;
close(udpsocket);
return 0;
}
Server Code
// Libraries
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <iostream>
#include <stdlib.h>
#include <unistd.h>
#include <cstdlib>
#include <time.h>
#include <ctype.h>
using namespace std;
// Variables
int r_port;
string fileData;
// Generate Random Port
int randomPort() {
srand(time(NULL));
return rand() % ((65535 - 1024) + 1) + 1024;
}
// Capitalization Function
string capitalize(char* payload) {
int i = 0;
char c;
string charArr;
while(payload[i]) {
c = payload[i];
charArr += toupper(c);
i++;
}
return charArr;
}
int main(int argc, char* argv[]) {
// Variables
int port = strtol(argv[1], NULL, 10);
// *** Declare TCP socket ***
int tcpsocket = 0;
tcpsocket = socket(AF_INET, SOCK_STREAM, 0);
if (tcpsocket == -1) {
cerr << "Can't create a socket";
return -1;
}
// Receive data
struct sockaddr_in server;
memset((char *) &server, 0, sizeof(server));
server.sin_family = AF_INET;
server.sin_port = htons(port);
server.sin_addr.s_addr = htonl(INADDR_ANY);
if (bind(tcpsocket, (struct sockaddr *) &server, sizeof(server)) == -1) {
cerr << "Can't bind to IP/Port";
return -2;
}
if (listen(tcpsocket, SOMAXCONN) == -1) {
cerr << "Can't listen";
return -3;
}
struct sockaddr_in client;
char payload[512];
socklen_t clen = sizeof(client);
int clientSocket = accept(tcpsocket, (sockaddr*)&client, &clen);
if (clientSocket == -1) {
cerr << "Problem with client connecting";
return -4;
}
recv(clientSocket, payload, 512, 0);
// Check client data
if (strtol(payload,NULL,10) == 117) {
r_port = randomPort();
cout << "Handshake detected. Selected the random port " << r_port << "\n";
}
else {
cout << "Error occurred\n";
}
// Return random port
memset(payload, 0, sizeof(payload));
sprintf(payload,"%ld",r_port);
int sendRes = send(clientSocket, payload, 512, 0);
if (sendRes == -1) {
cerr << "Could not send to server\n";
return 1;
}
close(clientSocket);
close(tcpsocket);
// *** Declare UDP socket ***
int udpsocket = 0;
udpsocket = socket(AF_INET, SOCK_DGRAM, 0);
if (udpsocket == -1) {
cerr << "Can't create a socket";
return -1;
}
// Receive data
memset((char *) &server, 0, sizeof(server));
server.sin_family = AF_INET;
server.sin_port = htons(r_port);
server.sin_addr.s_addr = htonl(INADDR_ANY);
if (bind(udpsocket, (struct sockaddr *) &server, sizeof(server)) == -1) {
cerr << "Can't bind to IP/Port";
return -2;
}
clen = sizeof(client);
memset(payload, 0, sizeof(payload));
recvfrom(udpsocket, payload, 32, 0, (sockaddr*)&client, &clen);
fileData = capitalize(payload);
cout << "Payload: " << fileData << "\n";
// Send ack
// socklen_t slen = sizeof(server);
// memset(payload, 0, sizeof(payload));
// strcpy(payload, fileData.c_str());
// sendRes = sendto(udpsocket, payload, 32, 0, (struct sockaddr *) &server, slen);
// if (sendRes == -1) {
// cerr << "Could not send to server";
// return 1;
// }
close(udpsocket);
return 0;
}

Answer 1

ssize_t sendto(**int sockfd**, const void *buf, size_t len, int flags,
const struct **sockaddr *dest_addr**, socklen_t addrlen);
Reference : https://linux.die.net/man/2/sendto
Your destination address should be : (sockaddr *) &client