UDP 客户端挂起C++问题

我正在从事的项目使用TCP和UDP来创建文件传输协议。TCP 连接生成一个随机端口，在该端口中它返回到客户端，然后客户端使用 UDP 连接到该端口号上的服务器。然后使用 UDP 将文本文件一次传输四个字符到服务器，服务器将发回大写的字符，然后这些字符将显示在客户端上。问题是客户端在等待服务器发回字符的大写版本时挂起。我将保留下面的代码。代码中不起作用的部分在客户端和服务器文件的末尾被注释掉。任何帮助不胜感激！

客户端代码

// 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;
}

服务器代码

// 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 occurredn";
}
// 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 servern";
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;
}