[PATCH] Added hook in git-receive-pack

Just before updating a ref,

    $GIT_DIR/hooks/update refname old-sha1 new-sha1

is called if executable.  The hook can decline the ref to be
updated by exiting with a non-zero status, or allow it to be
updated by exiting with a zero status.  The mechanism also
allows e.g sending of a mail with pushed commits on the remote
repository.

Documentation update with an example hook is included.

jc: The credits of the basic idea and initial implementation go
to Josef, but I ended up rewriting major parts of his patch, so
bugs are all mine.  Also I changed the semantics for the hook
from his original version (which were post-update hook) so that
the hook can optionally decline to update the ref, and also can
be used to implement the overall cleanups.  The latter was
primarily to implement a suggestion from Linus that calling
update-server-info should be made optional.

Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-receive-pack.txt

@@ -22,6 +22,55 @@ program pair is meant to be used to push updates to remote
 repository.  For pull operations, see 'git-fetch-pack' and
 'git-clone-pack'.
 
+The command allows for creation and fast forwarding of sha1 refs
+(heads/tags) on the remote end (strictly speaking, it is the
+local end receive-pack runs, but to the user who is sitting at
+the send-pack end, it is updating the remote.  Confused?)
+
+Before each ref is updated, if $GIT_DIR/hooks/update file exists
+and executable, it is called with three parameters:
+
+       $GIT_DIR/hooks/update refname sha1-old sha1-new
+
+The refname parameter is relative to $GIT_DIR; e.g. for the
+master head this is "refs/heads/master".  Two sha1 are the
+object names for the refname before and after the update.  Note
+that the hook is called before the refname is updated, so either
+sha1-old is 0{40} (meaning there is no such ref yet), or it
+should match what is recorded in refname.
+
+The hook should exit with non-zero status if it wants to
+disallow updating the named ref.  Otherwise it should exit with
+zero.
+
+The same hook is also called with an empty string as refname and
+no other arguments just before git-receive-pack exits.  This can
+be used to implement repository wide cleanup task if needed.
+The exit code from this hook invocation is ignored; the only
+thing left for git-receive-pack to do at that point is to exit
+itself anyway.
+
+Using this hook, it is easy to generate mails on updates to
+the local repository. This example script sends a mail with
+the commits pushed to the repository:
+
+	#!/bin/sh
+	case "$#,$1" in
+	1,) # help packed repository pulled via dumb protocol.
+	    git-update-server-info
+	    ;;
+	*)  # mail out commit update information.
+	    if expr "$2" : '0*$' >/dev/null
+	    then
+		echo "Created now ref."
+		git-rev-list --pretty "$2"
+	    else
+		echo "New commits"
+		git-rev-list --pretty "$3" "^$2"
+	    fi |
+	    mail -s "Changes to ref $1" commit-list@mydomain
+        esac
+	exit 0
 
 OPTIONS
 -------

Makefile

@@ -98,6 +98,9 @@ LIB_OBJS=read-cache.o sha1_file.o usage.o object.o commit.o tree.o blob.o \
 LIB_H += rev-cache.h
 LIB_OBJS += rev-cache.o
 
+LIB_H += run-command.h
+LIB_OBJS += run-command.o
+
 LIB_H += strbuf.h
 LIB_OBJS += strbuf.o
 

receive-pack.c

@@ -1,11 +1,12 @@
 #include "cache.h"
 #include "refs.h"
 #include "pkt-line.h"
+#include "run-command.h"
 #include <sys/wait.h>
 
 static const char receive_pack_usage[] = "git-receive-pack <git-dir>";
 
-static const char *unpacker = "git-unpack-objects";
+static const char unpacker[] = "git-unpack-objects";
 
 static int show_ref(const char *path, const unsigned char *sha1)
 {
@@ -55,6 +56,38 @@ static int verify_old_ref(const char *name, char *hex_contents)
 	return 0;
 }
 
+static char update_hook[] = "hooks/update";
+
+static int run_update_hook(const char *refname,
+			   char *old_hex, char *new_hex)
+{
+	int code;
+
+	if (access(update_hook, X_OK) < 0)
+		return 0;
+	code = run_command(update_hook, refname, old_hex, new_hex, NULL);
+	switch (code) {
+	case 0:
+		return 0;
+	case -ERR_RUN_COMMAND_FORK:
+		die("hook fork failed");
+	case -ERR_RUN_COMMAND_EXEC:
+		die("hook execute failed");
+	case -ERR_RUN_COMMAND_WAITPID:
+		die("waitpid failed");
+	case -ERR_RUN_COMMAND_WAITPID_WRONG_PID:
+		die("waitpid is confused");
+	case -ERR_RUN_COMMAND_WAITPID_SIGNAL:
+		fprintf(stderr, "%s died of signal", update_hook);
+		return -1;
+	case -ERR_RUN_COMMAND_WAITPID_NOEXIT:
+		die("%s died strangely", update_hook);
+	default:
+		error("%s exited with error code %d", update_hook, -code);
+		return -code;
+	}
+}
+
 static void update(const char *name, unsigned char *old_sha1, unsigned char *new_sha1)
 {
 	char new_hex[60], *old_hex, *lock_name;
@@ -90,11 +123,16 @@ static void update(const char *name, unsigned char *old_sha1, unsigned char *new
 		unlink(lock_name);
 		die("%s changed during push", name);
 	}
-	if (rename(lock_name, name) < 0) {
+	if (run_update_hook(name, old_hex, new_hex)) {
+		unlink(lock_name);
+		fprintf(stderr, "hook declined to update %s\n", name);
+	}
+	else if (rename(lock_name, name) < 0) {
 		unlink(lock_name);
 		die("unable to replace %s", name);
 	}
-	fprintf(stderr, "%s: %s -> %s\n", name, old_hex, new_hex);
+	else
+		fprintf(stderr, "%s: %s -> %s\n", name, old_hex, new_hex);
 }
 
 
@@ -110,7 +148,7 @@ static void execute_commands(void)
 		update(cmd->ref_name, cmd->old_sha1, cmd->new_sha1);
 		cmd = cmd->next;
 	}
-	update_server_info(0);
+	run_update_hook("", NULL, NULL);
 }
 
 static void read_head_info(void)
@@ -145,34 +183,24 @@ static void read_head_info(void)
 
 static void unpack(void)
 {
-	pid_t pid = fork();
-
-	if (pid < 0)
+	int code = run_command(unpacker, NULL);
+	switch (code) {
+	case 0:
+		return 0;
+	case -ERR_RUN_COMMAND_FORK:
 		die("unpack fork failed");
-	if (!pid) {
-		execlp(unpacker, unpacker, NULL);
+	case -ERR_RUN_COMMAND_EXEC:
 		die("unpack execute failed");
-	}
-
-	for (;;) {
-		int status, code;
-		int retval = waitpid(pid, &status, 0);
-
-		if (retval < 0) {
-			if (errno == EINTR)
-				continue;
-			die("waitpid failed (%s)", strerror(retval));
-		}
-		if (retval != pid)
-			die("waitpid is confused");
-		if (WIFSIGNALED(status))
-			die("%s died of signal %d", unpacker, WTERMSIG(status));
-		if (!WIFEXITED(status))
-			die("%s died out of really strange complications", unpacker);
-		code = WEXITSTATUS(status);
-		if (code)
-			die("%s exited with error code %d", unpacker, code);
-		return;
+	case -ERR_RUN_COMMAND_WAITPID:
+		die("waitpid failed");
+	case -ERR_RUN_COMMAND_WAITPID_WRONG_PID:
+		die("waitpid is confused");
+	case -ERR_RUN_COMMAND_WAITPID_SIGNAL:
+		die("%s died of signal", unpacker);
+	case -ERR_RUN_COMMAND_WAITPID_NOEXIT:
+		die("%s died strangely", unpacker);
+	default:
+		die("%s exited with error code %d", unpacker, -code);
 	}
 }
 

run-command.c

@@ -0,0 +1,60 @@
+#include "cache.h"
+#include "run-command.h"
+#include <sys/wait.h>
+
+static int run_external_command(int argc, const char **argv)
+{
+	pid_t pid = fork();
+
+	if (pid < 0)
+		return -ERR_RUN_COMMAND_FORK;
+	if (!pid) {
+		execvp(argv[0], (char *const*) argv);
+		return -ERR_RUN_COMMAND_EXEC;
+	}
+	for (;;) {
+		int status, code;
+		int retval = waitpid(pid, &status, 0);
+
+		if (retval < 0) {
+			if (errno == EINTR)
+				continue;
+			error("waitpid failed (%s)", strerror(retval));
+			return -ERR_RUN_COMMAND_WAITPID;
+		}
+		if (retval != pid)
+			return -ERR_RUN_COMMAND_WAITPID_WRONG_PID;
+		if (WIFSIGNALED(status))
+			return -ERR_RUN_COMMAND_WAITPID_SIGNAL;
+
+		if (!WIFEXITED(status))
+			return -ERR_RUN_COMMAND_WAITPID_NOEXIT;
+		code = WEXITSTATUS(status);
+		if (code)
+			return -code;
+		return 0;
+	}
+}
+
+int run_command(const char *cmd, ...)
+{
+	int argc;
+	const char *argv[MAX_RUN_COMMAND_ARGS];
+	const char *arg;
+	va_list param;
+
+	fprintf(stderr, "run-command %s (%d)\n", cmd, ERR_RUN_COMMAND_EXEC);
+
+	va_start(param, cmd);
+	argv[0] = cmd;
+	argc = 1;
+	while (argc < MAX_RUN_COMMAND_ARGS) {
+		arg = argv[argc++] = va_arg(param, char *);
+		if (!arg)
+			break;
+	}
+	va_end(param);
+	if (MAX_RUN_COMMAND_ARGS <= argc)
+		return error("too many args to run %s", cmd);
+	return run_external_command(argc, argv);
+}

run-command.h

@@ -0,0 +1,16 @@
+#ifndef RUN_COMMAND_H
+#define RUN_COMMAND_H
+
+#define MAX_RUN_COMMAND_ARGS 256
+enum {
+	ERR_RUN_COMMAND_FORK = 10000,
+	ERR_RUN_COMMAND_EXEC,
+	ERR_RUN_COMMAND_WAITPID,
+	ERR_RUN_COMMAND_WAITPID_WRONG_PID,
+	ERR_RUN_COMMAND_WAITPID_SIGNAL,
+	ERR_RUN_COMMAND_WAITPID_NOEXIT,
+};
+
+int run_command(const char *cmd, ...);
+
+#endif