From 631a3056f48bcd4d87adf6e720bfc41667bee498 Mon Sep 17 00:00:00 2001
From: Runxi Yu <me@runxiyu.org>
Date: Mon, 17 Feb 2025 12:46:10 +0800
Subject: [PATCH] git_hooks_client.c: Splice socket to stderr

This allows the daemon to send status messages to the hook handler.

---
 git_hooks_client/git_hooks_client.c | 57 +++++++++++++++++++++++++++++++++++++++--------------

diff --git a/git_hooks_client/git_hooks_client.c b/git_hooks_client/git_hooks_client.c
index 98269ad2d5d904207f98b2c87226dbaefc0ab2a9..4d62c910beee8beeb8fc5f609e5889f47afc539d 100644
--- a/git_hooks_client/git_hooks_client.c
+++ b/git_hooks_client/git_hooks_client.c
@@ -10,36 +10,54 @@
 int main(void) {
 	const char *socket_path = getenv("LINDENII_FORGE_HOOKS_SOCKET_PATH");
 	if (socket_path == NULL) {
-	        dprintf(STDERR_FILENO, "environment variable LINDENII_FORGE_HOOKS_SOCKET_PATH undefined\n");
+		dprintf(STDERR_FILENO, "environment variable LINDENII_FORGE_HOOKS_SOCKET_PATH undefined\n");
 		return EXIT_FAILURE;
 	}
 
-        /*
-         * All hooks in git (see builtin/receive-pack.c) use a pipe by setting
-         * .in = -1 on the child_process struct, which enables us to use
-         * splice(2) to move the data to the UNIX domain socket. Just to be
+	/*
+	 * All hooks in git (see builtin/receive-pack.c) use a pipe by setting
+	 * .in = -1 on the child_process struct, which enables us to use
+	 * splice(2) to move the data to the UNIX domain socket. Just to be
 	 * safe, we check that stdin is a pipe; and additionally we fetch the
 	 * buffer size of the pipe to use as the maximum size for the splice.
 	 *
 	 * We connect to the UNIX domain socket after ensuring that standard
 	 * input matches our expectations.
-         */
+	 */
 
-        struct stat stdin_stat;
+	struct stat stdin_stat;
 	if (fstat(STDIN_FILENO, &stdin_stat) == -1) {
 		perror("fstat on stdin");
 		return EXIT_FAILURE;
 	}
 	if (!S_ISFIFO(stdin_stat.st_mode)) {
-	        dprintf(STDERR_FILENO, "stdin must be a pipe\n");
-	        return EXIT_FAILURE;
+		dprintf(STDERR_FILENO, "stdin must be a pipe\n");
+		return EXIT_FAILURE;
 	}
-	int pipe_size = fcntl(STDIN_FILENO, F_GETPIPE_SZ);
-	if (pipe_size == -1) {
+	int stdin_pipe_size = fcntl(STDIN_FILENO, F_GETPIPE_SZ);
+	if (stdin_pipe_size == -1) {
 		perror("fcntl on stdin");
 		return EXIT_FAILURE;
 	}
 
+	/* ... And we do the same for stderr */
+
+	struct stat stderr_stat;
+	if (fstat(STDERR_FILENO, &stderr_stat) == -1) {
+		perror("fstat on stderr");
+		return EXIT_FAILURE;
+	}
+	if (!S_ISFIFO(stderr_stat.st_mode)) {
+		dprintf(STDERR_FILENO, "stderr must be a pipe\n");
+		return EXIT_FAILURE;
+	}
+	int stderr_pipe_size = fcntl(STDERR_FILENO, F_GETPIPE_SZ);
+	if (stderr_pipe_size == -1) {
+		perror("fcntl on stderr");
+		return EXIT_FAILURE;
+	}
+
+
 	int sock;
 	struct sockaddr_un addr;
 	sock = socket(AF_UNIX, SOCK_STREAM, 0);
@@ -57,12 +75,11 @@ 		close(sock);
 		return EXIT_FAILURE;
 	}
 
-
-	ssize_t bytes_spliced;
-	while ((bytes_spliced = splice(STDIN_FILENO, NULL, sock, NULL, pipe_size, SPLICE_F_MORE)) > 0) {
+	ssize_t stdin_bytes_spliced;
+	while ((stdin_bytes_spliced = splice(STDIN_FILENO, NULL, sock, NULL, stdin_pipe_size, SPLICE_F_MORE)) > 0) {
 	}
 
-	if (bytes_spliced == -1) {
+	if (stdin_bytes_spliced == -1) {
 		perror("splice stdin to internal socket");
 		close(sock);
 		return EXIT_FAILURE;
@@ -83,6 +100,16 @@ 	case 1:
 		break;
 	default:
 		dprintf(STDERR_FILENO, "read returned unexpected value on internal socket\n");
+		close(sock);
+		return EXIT_FAILURE;
+	}
+
+	ssize_t stderr_bytes_spliced;
+	while ((stderr_bytes_spliced = splice(sock, NULL, STDERR_FILENO, NULL, stderr_pipe_size, SPLICE_F_MORE)) > 0) {
+	}
+
+	if (stdin_bytes_spliced == -1) {
+		perror("splice internal socket to stderr");
 		close(sock);
 		return EXIT_FAILURE;
 	}

-- 
2.48.1