1 files changed, 125 insertions, 0 deletions
diff --git a/unix-stream-server.c b/unix-stream-server.c
new file mode 100644
index 0000000000..efa2a207ab
--- /dev/null
+++ b/unix-stream-server.c
@@ -0,0 +1,125 @@
+#include "cache.h"
+#include "lockfile.h"
+#include "unix-socket.h"
+#include "unix-stream-server.h"
+
+#define DEFAULT_LOCK_TIMEOUT (100)
+
+/*
+ * Try to connect to a unix domain socket at `path` (if it exists) and
+ * see if there is a server listening.
+ *
+ * We don't know if the socket exists, whether a server died and
+ * failed to cleanup, or whether we have a live server listening, so
+ * we "poke" it.
+ *
+ * We immediately hangup without sending/receiving any data because we
+ * don't know anything about the protocol spoken and don't want to
+ * block while writing/reading data.  It is sufficient to just know
+ * that someone is listening.
+ */
+static int is_another_server_alive(const char *path,
+				   const struct unix_stream_listen_opts *opts)
+{
+	int fd = unix_stream_connect(path, opts->disallow_chdir);
+	if (fd >= 0) {
+		close(fd);
+		return 1;
+	}
+
+	return 0;
+}
+
+int unix_ss_create(const char *path,
+		   const struct unix_stream_listen_opts *opts,
+		   long timeout_ms,
+		   struct unix_ss_socket **new_server_socket)
+{
+	struct lock_file lock = LOCK_INIT;
+	int fd_socket;
+	struct unix_ss_socket *server_socket;
+
+	*new_server_socket = NULL;
+
+	if (timeout_ms < 0)
+		timeout_ms = DEFAULT_LOCK_TIMEOUT;
+
+	/*
+	 * Create a lock at "<path>.lock" if we can.
+	 */
+	if (hold_lock_file_for_update_timeout(&lock, path, 0, timeout_ms) < 0)
+		return -1;
+
+	/*
+	 * If another server is listening on "<path>" give up.  We do not
+	 * want to create a socket and steal future connections from them.
+	 */
+	if (is_another_server_alive(path, opts)) {
+		rollback_lock_file(&lock);
+		errno = EADDRINUSE;
+		return -2;
+	}
+
+	/*
+	 * Create and bind to a Unix domain socket at "<path>".
+	 */
+	fd_socket = unix_stream_listen(path, opts);
+	if (fd_socket < 0) {
+		int saved_errno = errno;
+		rollback_lock_file(&lock);
+		errno = saved_errno;
+		return -1;
+	}
+
+	server_socket = xcalloc(1, sizeof(*server_socket));
+	server_socket->path_socket = strdup(path);
+	server_socket->fd_socket = fd_socket;
+	lstat(path, &server_socket->st_socket);
+
+	*new_server_socket = server_socket;
+
+	/*
+	 * Always rollback (just delete) "<path>.lock" because we already created
+	 * "<path>" as a socket and do not want to commit_lock to do the atomic
+	 * rename trick.
+	 */
+	rollback_lock_file(&lock);
+
+	return 0;
+}
+
+void unix_ss_free(struct unix_ss_socket *server_socket)
+{
+	if (!server_socket)
+		return;
+
+	if (server_socket->fd_socket >= 0) {
+		if (!unix_ss_was_stolen(server_socket))
+			unlink(server_socket->path_socket);
+		close(server_socket->fd_socket);
+	}
+
+	free(server_socket->path_socket);
+	free(server_socket);
+}
+
+int unix_ss_was_stolen(struct unix_ss_socket *server_socket)
+{
+	struct stat st_now;
+
+	if (!server_socket)
+		return 0;
+
+	if (lstat(server_socket->path_socket, &st_now) == -1)
+		return 1;
+
+	if (st_now.st_ino != server_socket->st_socket.st_ino)
+		return 1;
+	if (st_now.st_dev != server_socket->st_socket.st_dev)
+		return 1;
+
+	if (!S_ISSOCK(st_now.st_mode))
+		return 1;
+
+	return 0;
+}