test/sockets/test_unix_server.c

/*
 * Copyright 2026 The Emscripten Authors.  All rights reserved.
 * Emscripten is available under two separate licenses, the MIT license and the
 * University of Illinois/NCSA Open Source License.  Both these licenses can be
 * found in the LICENSE file.
 *
 * Self-contained AF_UNIX (named pathname) loopback accept+echo. A listener and
 * a client live in one process, both non-blocking, driven by select. Exercises
 * bind(path), listen, getsockname (the bound path), accept, getpeername,
 * non-blocking connect-by-path, send and recv. Plain POSIX, so it also builds
 * and runs natively against the host stack.
 */

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>

#ifdef __EMSCRIPTEN__
#include <emscripten.h>
#endif

static const char* SOCK_PATH = "/tmp/emscripten_unix_server.sock";

int listen_fd = -1;
int client_fd = -1;
int peer_fd = -1; // accepted (server-side) connection
struct sockaddr_un dest;
bool connected = false;
bool ping_sent = false;
bool pong_sent = false;

void set_nonblocking(int fd) {
  fcntl(fd, F_SETFL, O_NONBLOCK);
}

void test_success(void) {
  printf("done\n");
  if (listen_fd >= 0) close(listen_fd);
  if (client_fd >= 0) close(client_fd);
  if (peer_fd >= 0) close(peer_fd);
  unlink(SOCK_PATH);
#ifdef __EMSCRIPTEN__
  emscripten_cancel_main_loop();
#else
  exit(0);
#endif
}

void start_client(void) {
  if (client_fd >= 0) close(client_fd);
  client_fd = socket(AF_UNIX, SOCK_STREAM, 0);
  assert(client_fd >= 0);
  set_nonblocking(client_fd);
  connected = false;
  ping_sent = false;
  int r = connect(client_fd, (struct sockaddr*)&dest, sizeof(dest));
  assert((r == 0 || errno == EINPROGRESS) && "connect");
}

void main_loop(void) {
  fd_set fdr, fdw;
  struct timeval tv = {0};
  FD_ZERO(&fdr);
  FD_ZERO(&fdw);
  FD_SET(listen_fd, &fdr);
  FD_SET(client_fd, &fdr);
  FD_SET(client_fd, &fdw);
  if (peer_fd >= 0) FD_SET(peer_fd, &fdr);
  select(64, &fdr, &fdw, NULL, &tv);

  // server: accept the incoming connection
  if (peer_fd < 0 && FD_ISSET(listen_fd, &fdr)) {
    struct sockaddr_un ca;
    socklen_t cl = sizeof(ca);
    peer_fd = accept(listen_fd, (struct sockaddr*)&ca, &cl);
    if (peer_fd >= 0) {
      set_nonblocking(peer_fd);
      printf("accepted\n");
    }
  }

  // client: connect completion (retry while the listener is coming up)
  if (!connected && FD_ISSET(client_fd, &fdw)) {
    int err = 0;
    socklen_t l = sizeof(err);
    getsockopt(client_fd, SOL_SOCKET, SO_ERROR, &err, &l);
    if (err == ECONNREFUSED || err == ECONNRESET || err == ENOENT) {
      start_client();
      return;
    }
    assert(err == 0 && "connect failed");
    connected = true;
    // The connected client's peer name is the listener's path.
    struct sockaddr_un pa;
    socklen_t pl = sizeof(pa);
    if (getpeername(client_fd, (struct sockaddr*)&pa, &pl) == 0) {
      assert(pa.sun_family == AF_UNIX);
      assert(strcmp(pa.sun_path, SOCK_PATH) == 0 && "peer path");
      printf("connected to %s\n", pa.sun_path);
    }
  }

  // client: send ping
  if (connected && !ping_sent && FD_ISSET(client_fd, &fdw)) {
    if (send(client_fd, "ping", 4, 0) == 4) ping_sent = true;
  }

  // server: echo ping -> pong
  if (peer_fd >= 0 && !pong_sent && FD_ISSET(peer_fd, &fdr)) {
    char buf[4];
    ssize_t n = recv(peer_fd, buf, sizeof(buf), 0);
    if (n == 4 && memcmp(buf, "ping", 4) == 0) {
      send(peer_fd, "pong", 4, 0);
      pong_sent = true;
    }
  }

  // client: receive pong
  if (ping_sent && FD_ISSET(client_fd, &fdr)) {
    char buf[4];
    ssize_t n = recv(client_fd, buf, sizeof(buf), 0);
    if (n == 4 && memcmp(buf, "pong", 4) == 0) {
      test_success();
    } else if (n == 0) {
      assert(false && "peer closed unexpectedly");
    }
  }
}

int main(void) {
  // Remove any stale socket file from a previous run (a lingering file makes
  // bind() fail with EADDRINUSE).
  unlink(SOCK_PATH);

  listen_fd = socket(AF_UNIX, SOCK_STREAM, 0);
  assert(listen_fd >= 0);

  struct sockaddr_un addr;
  memset(&addr, 0, sizeof(addr));
  addr.sun_family = AF_UNIX;
  strcpy(addr.sun_path, SOCK_PATH);
  if (bind(listen_fd, (struct sockaddr*)&addr, sizeof(addr)) != 0) {
    perror("bind");
    return 1;
  }
  if (listen(listen_fd, 4) != 0) {
    perror("listen");
    return 1;
  }

  // getsockname() must report the bound path synchronously.
  struct sockaddr_un la;
  socklen_t ll = sizeof(la);
  if (getsockname(listen_fd, (struct sockaddr*)&la, &ll) != 0) {
    perror("getsockname");
    return 1;
  }
  assert(la.sun_family == AF_UNIX);
  assert(strcmp(la.sun_path, SOCK_PATH) == 0 && "bound path");
  printf("listening on %s\n", la.sun_path);
  set_nonblocking(listen_fd);

  memset(&dest, 0, sizeof(dest));
  dest.sun_family = AF_UNIX;
  strcpy(dest.sun_path, SOCK_PATH);
  start_client();

#ifdef __EMSCRIPTEN__
  emscripten_set_main_loop(main_loop, 0, 0);
#else
  while (1) {
    main_loop();
    usleep(1000);
  }
#endif
  return 0;
}