Data Transfer Protocol for C

Modern cross-platform networking interfaces for C.

Data Transfer Protocol

The Data Transfer Protocol (DTP) is a larger project to make ergonomic network programming available in any language. See the full project here.

Creating a server

A server can be built using the CDTPServer implementation:

#include "cdtp.h"
#include <stdio.h>
#include <string.h>
#include <assert.h>

// Create a server that receives strings and returns the length of each string
void server_on_recv(CDTPServer *server, size_t client_id, void *data, size_t data_size, void *arg)
{
    // Send back the length of the string
    char *str_data = (char *) data;
    size_t str_len = strlen(str_data) + 1;
    assert(str_len == data_size);
    cdtp_server_send(server, client_id, &str_len, sizeof(size_t));
    // `free` always needs to be called on received data
    free(data);
}

void server_on_connect(CDTPServer *server, size_t client_id, void *arg)
{
    printf("Client with ID %zu connected\n", client_id);
}

void server_on_disconnect(CDTPServer *server, size_t client_id, void *arg)
{
    printf("Client with ID %zu disconnected\n", client_id);
}

int main(void)
{
    // Start the server
    CDTPServer *server = cdtp_server(server_on_recv, server_on_connect, server_on_disconnect, NULL, NULL, NULL);
    cdtp_server_start(server, "127.0.0.1", 29275);

    // Stop the server
    cdtp_sleep(1.0);
    cdtp_server_stop(server);
    cdtp_server_free(server);

    return 0;
}

Creating a client

A client can be built using the CDTPClient implementation:

#include "cdtp.h"
#include <stdio.h>
#include <string.h>
#include <assert.h>

// Create a client that sends a message to the server and receives the length of the message
void client_on_recv(CDTPClient *client, void *data, size_t data_size, void *arg)
{
    // Validate the response
    size_t *str_len = (size_t *) data;
    char *message = (char *) arg;
    printf("Received response from server: %zu\n", *str_len);
    assert(*str_len == strlen(message) + 1);
    // `free` always needs to be called on received data
    free(data);
}

void client_on_disconnected(CDTPClient *client, void *arg)
{
    printf("Unexpectedly disconnected from server\n");
}

int main(void) {
    // Connect to the server
    char *message = "Hello, server!";
    CDTPClient *client = cdtp_client(client_on_recv, client_on_disconnected, message, NULL);
    cdtp_client_connect(client, "127.0.0.1", 29275);

    // Send a message to the server
    cdtp_client_send(client, message, strlen(message) + 1);

    // Disconnect from the server
    cdtp_sleep(1.0);
    cdtp_client_disconnect(client);
    cdtp_client_free(client);

    return 0;
}

Memory management

All data received is allocated on the heap. To prevent memory leaks, those who use the library must call free(...) on these pieces of data at some point. The same goes for strings returned from the following functions:

• cdtp_server_get_host(...)
• cdtp_server_get_client_host(...)
• cdtp_client_get_host(...)
• cdtp_client_get_server_host(...)

Serialization

Unlike the C++ implementation, the protocol cannot serialize types for you. All send and receive operations deal with void pointers (void *) and their sizes (size_t).

Compilation

The protocol has a few dependencies that must be included when compiling:

Compiling on Windows

• Link Winsock (-lWs2_32)
• Link and provide headers for OpenSSL 3.0

Compiling on other platforms

• Link pthread (-lpthread)
• Link and provide headers for OpenSSL 3.0

For more information on the compilation process, see the Makefile.

Security

Information security comes included. Every message sent over a network interface is encrypted with AES-256. Key exchanges are performed using a 2048-bit RSA key-pair.