1 files changed, 173 insertions, 0 deletions
diff --git a/man/notify-selfcontained-example.c b/man/notify-selfcontained-example.c
new file mode 100644
index 0000000..9a7553e
--- /dev/null
+++ b/man/notify-selfcontained-example.c
@@ -0,0 +1,173 @@
+/* SPDX-License-Identifier: MIT-0 */
+
+/* Implement the systemd notify protocol without external dependencies.
+ * Supports both readiness notification on startup and on reloading,
+ * according to the protocol defined at:
+ * https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html
+ * This protocol is guaranteed to be stable as per:
+ * https://systemd.io/PORTABILITY_AND_STABILITY/ */
+
+#include <errno.h>
+#include <inttypes.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <time.h>
+#include <unistd.h>
+
+#define _cleanup_(f) __attribute__((cleanup(f)))
+
+static void closep(int *fd) {
+  if (!fd || *fd < 0)
+    return;
+
+  close(*fd);
+  *fd = -1;
+}
+
+static int notify(const char *message) {
+  union sockaddr_union {
+    struct sockaddr sa;
+    struct sockaddr_un sun;
+  } socket_addr = {
+    .sun.sun_family = AF_UNIX,
+  };
+  size_t path_length, message_length;
+  _cleanup_(closep) int fd = -1;
+  const char *socket_path;
+
+  socket_path = getenv("NOTIFY_SOCKET");
+  if (!socket_path)
+    return 0; /* Not running under systemd? Nothing to do */
+
+  if (!message)
+    return -EINVAL;
+
+  message_length = strlen(message);
+  if (message_length == 0)
+    return -EINVAL;
+
+  /* Only AF_UNIX is supported, with path or abstract sockets */
+  if (socket_path[0] != '/' && socket_path[0] != '@')
+    return -EAFNOSUPPORT;
+
+  path_length = strlen(socket_path);
+  /* Ensure there is room for NUL byte */
+  if (path_length >= sizeof(socket_addr.sun.sun_path))
+    return -E2BIG;
+
+  memcpy(socket_addr.sun.sun_path, socket_path, path_length);
+
+  /* Support for abstract socket */
+  if (socket_addr.sun.sun_path[0] == '@')
+    socket_addr.sun.sun_path[0] = 0;
+
+  fd = socket(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0);
+  if (fd < 0)
+    return -errno;
+
+  if (connect(fd, &socket_addr.sa, offsetof(struct sockaddr_un, sun_path) + path_length) != 0)
+    return -errno;
+
+  ssize_t written = write(fd, message, message_length);
+  if (written != (ssize_t) message_length)
+    return written < 0 ? -errno : -EPROTO;
+
+  return 1; /* Notified! */
+}
+
+static int notify_ready(void) {
+  return notify("READY=1");
+}
+
+static int notify_reloading(void) {
+  /* A buffer with length sufficient to format the maximum UINT64 value. */
+  char reload_message[sizeof("RELOADING=1\nMONOTONIC_USEC=18446744073709551615")];
+  struct timespec ts;
+  uint64_t now;
+
+  /* Notify systemd that we are reloading, including a CLOCK_MONOTONIC timestamp in usec
+   * so that the program is compatible with a Type=notify-reload service. */
+
+  if (clock_gettime(CLOCK_MONOTONIC, &ts) < 0)
+    return -errno;
+
+  if (ts.tv_sec < 0 || ts.tv_nsec < 0 ||
+      (uint64_t) ts.tv_sec > (UINT64_MAX - (ts.tv_nsec / 1000ULL)) / 1000000ULL)
+    return -EINVAL;
+
+  now = (uint64_t) ts.tv_sec * 1000000ULL + (uint64_t) ts.tv_nsec / 1000ULL;
+
+  if (snprintf(reload_message, sizeof(reload_message), "RELOADING=1\nMONOTONIC_USEC=%" PRIu64, now) < 0)
+    return -EINVAL;
+
+  return notify(reload_message);
+}
+
+static volatile sig_atomic_t reloading = 0;
+static volatile sig_atomic_t terminating = 0;
+
+static void signal_handler(int sig) {
+  if (sig == SIGHUP)
+    reloading = 1;
+  else if (sig == SIGINT || sig == SIGTERM)
+    terminating = 1;
+}
+
+int main(int argc, char **argv) {
+  struct sigaction sa = {
+    .sa_handler = signal_handler,
+    .sa_flags = SA_RESTART,
+  };
+  int r;
+
+  /* Setup signal handlers */
+  sigemptyset(&sa.sa_mask);
+  sigaction(SIGHUP, &sa, NULL);
+  sigaction(SIGINT, &sa, NULL);
+  sigaction(SIGTERM, &sa, NULL);
+
+  /* Do more service initialization work here … */
+
+  /* Now that all the preparations steps are done, signal readiness */
+
+  r = notify_ready();
+  if (r < 0) {
+    fprintf(stderr, "Failed to notify readiness to $NOTIFY_SOCKET: %s\n", strerror(-r));
+    return EXIT_FAILURE;
+  }
+
+  while (!terminating) {
+    if (reloading) {
+      reloading = false;
+
+      /* As a separate but related feature, we can also notify the manager
+       * when reloading configuration. This allows accurate state-tracking,
+       * and also automated hook-in of 'systemctl reload' without having to
+       * specify manually an ExecReload= line in the unit file. */
+
+      r = notify_reloading();
+      if (r < 0) {
+        fprintf(stderr, "Failed to notify reloading to $NOTIFY_SOCKET: %s\n", strerror(-r));
+        return EXIT_FAILURE;
+      }
+
+      /* Do some reconfiguration work here … */
+
+      r = notify_ready();
+      if (r < 0) {
+        fprintf(stderr, "Failed to notify readiness to $NOTIFY_SOCKET: %s\n", strerror(-r));
+        return EXIT_FAILURE;
+      }
+    }
+
+    /* Do some daemon work here … */
+    sleep(5);
+  }
+
+  return EXIT_SUCCESS;
+}