Long messages get cut off when I send them through a tcp socket. It differs depending on the destination. When sending and receiving locally on my machine, all goes through. When sending and receiving locally on my server, it gets cut off after the 21846th byte consistently. When sending from my machine to the server, it gets cut off at the 1441th byte consistently. The server is in Stockholm and I’m in the UK. The same problem is also present when the client is on Windows and uses Windows’ networking code.
Here the client is supposed to send 29 999 zeros and a null terminator, receive them and print them. When I counted them with wc, I got the figures of actual bytes that I received. So the figures represent a two-way transfer but from testing I can say that the problem has the same properties one-way.
The read/write functions are blocking as far as I can tell, so the problem is not that the data has not arrived fully before the functions exit – a problem described in the man page.
How can I fix this?
Go to the bottom to see solution
Here’s the code that I used to test this:
server/main.cpp
#include <filesystem>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <sstream>
#include <string>
#include "aes/aes.hpp"
#include "network.hpp"
#include <thread>
using namespace std;
int main()
{
int server_socket = InitServerSocket(26969);
std::cout << "Listening..." << std::endl;
while (true) {
// accept incomming connections - blocking
int client_socket = accept(server_socket, NULL, NULL);
if (client_socket < 0) {
std::cerr << "Unable to accept";
close(server_socket);
return 1;
}
char long_text[30000];
read(client_socket, long_text, 30000);
std::cout << long_text << std::endl;
write(client_socket, long_text, 30000);
close(client_socket);
}
return 0;
}
InitServerSocket():
int InitServerSocket(int port)
{
struct sockaddr_in server_address;
server_address.sin_family = AF_INET;
server_address.sin_port = htons(port);
server_address.sin_addr.s_addr = htonl(INADDR_ANY);
int server_socket;
server_socket = socket(AF_INET, SOCK_STREAM, 0);
if (server_socket < 0) {
perror("Unable to create socket");
_exit(1);
}
int result = bind(
server_socket,
(struct sockaddr*)&server_address,
sizeof(server_address));
if (result < 0) {
perror("Unable to bind");
_exit(1);
}
if (listen(server_socket, 1000) < 0) {
perror("Unable to listen");
_exit(1);
}
return server_socket;
}
client/main.cpp
#include <arpa/inet.h>
#include <iostream>
#include <netdb.h>
#include <string.h>
#include <string>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>
#include "network.hpp"
using namespace std;
int main()
{
int socket = ConnectToHost("70.34.195.74", 26969);
char long_text[30000];
for (int i = 0; i < 30000; i++)
long_text[i] = '0';
long_text[29999] = '\0';
write(socket, long_text, 30000);
read(socket, long_text, 30000);
std::cout << long_text << std::endl;
CloseConnection(socket);
return 0;
}
ConnectToHost():
int ConnectToHost(char* IPAddress, int PortNo)
{
// create a socket
int network_socket; // socket descriptor ~= pointer ~= fd
network_socket = socket(AF_INET, SOCK_STREAM, 0);
// specify a destination address
struct sockaddr_in server_address;
server_address.sin_family = AF_INET; // specify protocol
server_address.sin_port = htons(PortNo); // specify port
// server_address.sin_addr.s_addr = a.s_addr; // specify resolved ip
server_address.sin_addr.s_addr = inet_addr(IPAddress);
// connect
int connection_status = connect(
network_socket,
(struct sockaddr*)&server_address,
sizeof(server_address));
if (connection_status == -1)
std::cout << "Failed to conect to remote host\n";
return network_socket;
}
Solution:
Here are the wrapper functions I wrote to fix the problem:
int Send(int soc, char* buffer, int size)
{
int ret = -1;
int index = 0;
do {
ret = write(soc, buffer + index, size - index);
index += ret;
} while (ret > 0);
if (ret == -1)
return -1;
else
return 1;
};
int Recv(int soc, char* buffer, int size)
{
int ret = -1;
int index = 0;
do {
ret = read(soc, buffer + index, size - index);
index += ret;
} while (ret > 0);
if (ret == -1)
return -1;
else
return 1;
};