C-Raft

C-Raft is a fully asynchronous C implementation of the Raft consensus protocol.

Design

The library has modular design: its core part implements only the core Raft algorithm logic, in a fully platform independent way. On top of that, a pluggable interface defines the I/O implementation for networking and disk persistence.

A stock implementation of the I/O interface is provided when building the library with default options. It is based on libuv and should fit the vast majority of use cases.

Features

C-Raft implements all the basic features described in the Raft dissertation:

  • Leader election

  • Log replication

  • Log compaction

  • Membership changes

It also includes a few optional enhancements:

  • Optimistic pipelining to reduce log replication latency

  • Writing to leader’s disk in parallel

  • Automatic stepping down when the leader loses quorum

  • Leadership transfer extension

  • Non-voting servers

Quick start

Make sure that libuv is installed on your system, then run:

1autoreconf -i
2./configure --enable-example
3make

Then create a main.c file with this simple test program that just runs a single raft server and implements a basic state machine for incrementing a counter:

 1#include <raft.h>
 2#include <raft/uv.h>
 3
 4static raft_id id = 12345;
 5static const char *address = "127.0.0.1:8080";
 6static const char *dir = "/tmp/raft-quick-start";
 7static struct uv_loop_s loop;
 8static struct raft_uv_transport transport;
 9static struct raft_io io;
10static struct raft_fsm fsm;
11static struct raft raft;
12static struct raft_configuration conf;
13static struct uv_timer_s timer;
14static struct raft_apply apply;
15static unsigned counter = 0;
16static uint64_t command;
17
18static int applyCommand(struct raft_fsm *fsm,
19                        const struct raft_buffer *buf,
20                        void **result) {
21    counter += *(uint64_t *)buf->base;
22    printf("counter: %u\n", counter);
23    return 0;
24}
25
26static void submitCommand(uv_timer_t *timer) {
27    struct raft_buffer buf;
28    command = uv_now(timer->loop) % 10;
29    buf.len = sizeof command;
30    buf.base = &command;
31    raft_apply(&raft, &apply, &buf, 1, NULL);
32}
33
34int main() {
35    mkdir(dir, 0755);
36    uv_loop_init(&loop);
37    raft_uv_tcp_init(&transport, &loop);
38    raft_uv_init(&io, &loop, dir, &transport);
39    fsm.apply = applyCommand;
40    raft_init(&raft, &io, &fsm, id, address);
41    raft_configuration_init(&conf);
42    raft_configuration_add(&conf, id, address, RAFT_VOTER);
43    raft_bootstrap(&raft, &conf);
44    raft_start(&raft);
45    uv_timer_init(&loop, &timer);
46    uv_timer_start(&timer, submitCommand, 0, 1000);
47    uv_run(&loop, UV_RUN_DEFAULT);
48}

You can compile and run it with:

1cc main.c -o main -lraft -luv && ./main

Licence

This raft C library is released under a slightly modified version of LGPLv3, that includes a copyright exception letting users to statically link the library code in their project and release the final work under their own terms. See the full license text.

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