From ca830519e17e0b3fae6697839bc5e7347a1299a5 Mon Sep 17 00:00:00 2001
From: Runxi Yu <me@runxiyu.org>
Date: Mon, 17 Feb 2025 06:56:18 +0800
Subject: [PATCH] git_hooks_client: Restructure for clarity

---
 git_hooks_client/git_hooks_client.c | 51 ++++++++++++++++++++++++++++-----------------------

diff --git a/git_hooks_client/git_hooks_client.c b/git_hooks_client/git_hooks_client.c
index 0d736a9ae736518afac27bc8f7089ef3cea7f8fe..01af1966ba90241f42f76a26f71b0f7732f2df67 100644
--- a/git_hooks_client/git_hooks_client.c
+++ b/git_hooks_client/git_hooks_client.c
@@ -8,21 +8,45 @@ #include <string.h>
 #include <fcntl.h>
 
 int main(void) {
-	int sock;
-	struct sockaddr_un addr;
 	const char *socket_path = getenv("LINDENII_FORGE_HOOKS_SOCKET_PATH");
-
 	if (socket_path == NULL) {
 	        dprintf(STDERR_FILENO, "fatal: 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
+	 * 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;
+	if (fstat(STDIN_FILENO, &stdin_stat) == -1) {
+		perror("fstat");
+		return EXIT_FAILURE;
+	}
+	if (!S_ISFIFO(stdin_stat.st_mode)) {
+	        dprintf(STDERR_FILENO, "fatal: stdin must be a pipe\n");
+	        return EXIT_FAILURE;
+	}
+	int pipe_size = fcntl(STDIN_FILENO, F_GETPIPE_SZ);
+	if (pipe_size == -1) {
+		perror("fcntl");
+		return EXIT_FAILURE;
+	}
+
+	int sock;
+	struct sockaddr_un addr;
 	sock = socket(AF_UNIX, SOCK_STREAM, 0);
 	if (sock == -1) {
 		perror("socket");
 		return EXIT_FAILURE;
 	}
-
 	memset(&addr, 0, sizeof(struct sockaddr_un));
 	addr.sun_family = AF_UNIX;
 	strncpy(addr.sun_path, socket_path, sizeof(addr.sun_path) - 1);
@@ -33,25 +57,6 @@ 		close(sock);
 		return EXIT_FAILURE;
 	}
 
-	struct stat stdin_stat;
-	if (fstat(STDIN_FILENO, &stdin_stat) == -1) {
-		perror("fstat");
-		close(sock);
-		return EXIT_FAILURE;
-	}
-
-	if (!S_ISFIFO(stdin_stat.st_mode)) {
-	        dprintf(STDERR_FILENO, "fatal: stdin must be a pipe\n");
-	        close(sock);
-	        return EXIT_FAILURE;
-	}
-
-	int pipe_size = fcntl(STDIN_FILENO, F_GETPIPE_SZ);
-	if (pipe_size == -1) {
-		perror("fcntl");
-		close(sock);
-		return EXIT_FAILURE;
-	}
 
 	ssize_t bytes_spliced;
 	while ((bytes_spliced = splice(STDIN_FILENO, NULL, sock, NULL, pipe_size, SPLICE_F_MORE)) > 0) {

-- 
2.48.1