EV

Light event-loop library loosely inspired by the excellent libuv, in a single small (< 700 sloc) header, based on the common IO multiplexing implementations available, epoll on linux, kqueue on BSD-like and OSX, poll/select as a fallback, dependencies-free. A common usage of the library is to craft event-driven TCP servers, ev_tcp.h exposes a set of APIs to fulfill this purpose in a simple manner.

TLS is supported as well through OpenSSL, and source have to be compiled adding a -DHAVE_OPENSSL=1 to enable it. Of course it requires libssl-dev installed on the host machine to work.

In conclusion the library is composed of 2 distinct modules

• ev.h a generic eventloop for I/O bound concurrency on a single-thread:
  • Based on the best multiplexing IO implementation available on the host, supporting epoll/poll/select on linux and kqueue on BSD
  • All IO operations are done in a non-blocking way
  • Support for time based repeated tasks
• ev_tcp.h exposes a set of APIs to simply create an event-driven TCP server using ev.h as the main engine:
  • TCP/UNIX socket connections
  • Basic TLS support through OpenSSL
  • Callback oriented design

To adopt these libraries it's required to define a value just before inclusion in one file only in the project:

#define EV_SOURCE
#include "ev.h"

Or in case of ev_tcp.h

#define EV_SOURCE
#define EV_TCP_SOURCE
#include "ev_tcp.h"

Running examples

A simple event-driven echo server

$ make echo-server

Write periodically on the screen ping and pong on different frequencies, referred as cron tasks

$ make ping-pong

Helper APIs

Lightweight event-driven hello world TCP server

#include <stdio.h>
#include <stdlib.h>
#define EV_SOURCE      // add before ev_tcp
#define EV_TCP_SOURCE  // add before ev_tcp
#include "../ev_tcp.h"

#define HOST    "127.0.0.1"
#define PORT    5959
#define BACKLOG 128

static void on_close(ev_tcp_handle *client, int err) {
    (void) client;
    if (err == EV_TCP_SUCCESS)
        printf("Connection closed\n");
    else
        printf("Connection closed: %s\n", ev_tcp_err(err));
    free(client);
}

static void on_write(ev_tcp_handle *client) {
    (void) client;
    printf("Written response\n");
}

static void on_data(ev_tcp_handle *client) {
    printf("Received %li bytes\n", client->buffer.size);
    if (strncmp(client->buffer.buf, "quit", 4) == 0)
        ev_tcp_close_handle(client);
    else
        // Enqueue a write of the buffer content for the next loop cycle
        ev_tcp_queue_write(client);
        // If want to respond on the same loop cycle
        // ev_tcp_write(client);
}

static void on_connection(ev_tcp_handle *server) {
    ev_tcp_handle *client = malloc(sizeof(*client));
    if (!client) {
        fprintf(stderr, "On connection failed: Out of memory");
        exit(EXIT_FAILURE);
    }
    int err = ev_tcp_server_accept(server, client, on_data, on_write);
    if (err < 0)
        free(client);
    else
        ev_tcp_handle_set_on_close(client, on_close);
}

int main(void) {

    ev_context *ctx = ev_get_context();
    ev_tcp_server server;
    int err = 0;
    if ((err = ev_tcp_server_init(&server, ctx, 128)) < 0) {
        fprintf(stderr, "ev_tcp_server_init failed: %s", ev_tcp_err(err));
        exit(EXIT_FAILURE);
    }
    // To set TLS using OpenSSL
    // struct ev_tls_options tls_opt = {
    //     .ca = CA,
    //     .cert = CERT,
    //     .key = KEY
    // };
    // tls_opt.protocols = EV_TLSv1_2|EV_TLSv1_3;
    // ev_tcp_server_set_tls(&server, &tls_opt);
    int err = ev_tcp_server_listen(&server, HOST, PORT, on_connection);
    if (err < 0)
        exit(EXIT_FAILURE);
    // Blocking call
    ev_tcp_server_run(&server);
    // This could be registered to a SIGINT|SIGTERM signal notification
    // to stop the server with Ctrl+C
    ev_tcp_server_stop(&server);

    return 0;
}

Simple hello-world TCP client reading from STDIN

#include <stdio.h>
#include <stdlib.h>
#define EV_SOURCE     // add before ev_tcp
#define EV_TCP_SOURCE // add before ev_tcp
#include "../ev.h"
#include "../ev_tcp.h"

#define HOST "127.0.0.1"
#define PORT 5959
#define BUFSIZE 256

// STDIN buffer
static unsigned char buf[BUFSIZE];

// STDIN handling callback
static void on_stdin(ev_context *, void *);

// TCP handling callback
static void on_tcp_recv(ev_tcp_handle *);
static void on_tcp_send(ev_tcp_handle *);
static void on_tcp_close(ev_tcp_handle *, int);

static void on_tcp_close(ev_tcp_handle *client, int err) {
    (void)client;
    if (err == EV_TCP_SUCCESS)
        printf("Connection closed\n");
    else
        printf("Connection closed: %s\n", ev_tcp_err(err));
}

static void on_tcp_send(ev_tcp_handle *client) {
    printf("Written %s", client->buffer.buf);
    ev_tcp_zero_buffer(client);
    // Re-arm TCP client for read
    (void)ev_tcp_queue_read(client);
}

static void on_tcp_recv(ev_tcp_handle *client) {
    printf("Response (%li bytes) => %s", client->buffer.size, client->buffer.buf);
    ev_tcp_zero_buffer(client);
}

static void on_stdin(ev_context *ctx, void *ptr) {
    ssize_t n = 0;
    ev_tcp_handle *handle = ptr;
    int fd = fileno(stdin);

    // Read incoming stream of bytes from user input
    n = read(fd, buf, sizeof(buf));
    if (n < 0) {
        if (errno != EAGAIN && errno != EWOULDBLOCK)
            goto err;
    }

    // 0 bytes read means disinput by the client
    if (n == 0) {
        ev_del_fd(ctx, fd);
        return;
    }

    // Close the input and release the resource
    if (strncmp((char *)buf, "quit", 4) == 0) {
        ev_del_fd(ctx, fd);
        exit(EXIT_SUCCESS);
    }

    ev_tcp_fill_buffer(handle, buf, n);

    ev_tcp_queue_write(handle);

    return;

err:
    fprintf(stderr, "read(2) - error reading data: %s\n", strerror(errno));
}

int main(void) {

    ev_context *ctx = ev_get_context();
    ev_tcp_handle client = {.ctx = ctx, .addr = HOST, .port = PORT};

    int err = 0;
    if ((err = ev_tcp_connect(&client, on_tcp_recv, on_tcp_send)) < 0) {
        fprintf(stderr, "ev_tcp_connect failed: %s", ev_tcp_err(err));
        exit(EXIT_FAILURE);
    }

    ev_tcp_handle_set_on_close(&client, on_tcp_close);

    err = ev_register_event(ctx, fileno(stdin), EV_READ, on_stdin, &client);
    if (err < 0) {
        fprintf(stderr, "ev_register_event failed: %s", ev_tcp_err(err));
        exit(EXIT_FAILURE);
    }
    // Blocking call
    ev_run(ctx);

    return 0;
}

Take a look to examples/ directory for more snippets.

Roadmap

• (Re)Move server abstraction on generic ev_tcp_handle, add client
• UDP helper APIs
• Improve error handling
• Documentation