Re: [PATCH v2] fetch-pack: optionally save packs to disk

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Am 11.06.2015 um 20:59 schrieb Augie Fackler:
When developing server software, it's often helpful to save a
potentially-bogus pack for later analysis. This makes that trivial,
instead of painful.

When you develop server software, shouldn't you test drive the server via the bare metal protocol anyway? That *is* painful, but unavoidable because you must harden the server against any garbage that a potentially malicous client could throw at it. Restricting yourself to a well-behaved client such as fetch-pack is only half the deal.

That said, I do think that fetch-pack could learn a mode that makes it easier to debug the normal behavior of a server (if such a mode is missing currently).

What is the problem with the current fetch-pack implementation? Does it remove a bogus packfile after download? Does it abort during download when it detects a broken packfile? Does --keep not do what you need?

Instead of your approach (which forks off tee to dump a copy of the packfile), would it not be simpler to add an option --debug-pack (probably not the best name) that skips the cleanup step when a broken packfile is detected and prints the name of the downloaded packfile?

diff --git a/fetch-pack.c b/fetch-pack.c
index a912935..fe6ba58 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -684,7 +684,7 @@ static int get_pack(struct fetch_pack_args *args,
  	const char *argv[22];
  	char keep_arg[256];
  	char hdr_arg[256];
-	const char **av, *cmd_name;
+	const char **av, *cmd_name, *savepath;
  	int do_keep = args->keep_pack;
  	struct child_process cmd = CHILD_PROCESS_INIT;
  	int ret;
@@ -708,9 +708,8 @@ static int get_pack(struct fetch_pack_args *args,
  	cmd.argv = argv;
  	av = argv;
  	*hdr_arg = 0;
+	struct pack_header header;
  	if (!args->keep_pack && unpack_limit) {
-		struct pack_header header;
-
  		if (read_pack_header(demux.out, &header))
  			die("protocol error: bad pack header");
  		snprintf(hdr_arg, sizeof(hdr_arg),
@@ -762,7 +761,44 @@ static int get_pack(struct fetch_pack_args *args,
  		*av++ = "--strict";
  	*av++ = NULL;

-	cmd.in = demux.out;
+	savepath = getenv("GIT_SAVE_FETCHED_PACK_TO");
+	if (savepath) {
+		struct child_process cmd2 = CHILD_PROCESS_INIT;
+		const char *argv2[22];
+		int pipefds[2];
+		int e;
+		const char **av2;
+		cmd2.argv = argv2;
+		av2 = argv2;
+		*av2++ = "tee";
+		if (*hdr_arg) {
+			/* hdr_arg being nonempty means we already read the
+			 * pack header from demux, so we need to drop a pack
+			 * header in place for tee to append to, otherwise
+			 * we'll end up with a broken pack on disk.
+			 */

			/*
			 * Write multi-line comments
			 * like this (/* on its own line)
			 */

+			int fp;
+			struct sha1file *s;
+			fp = open(savepath, O_CREAT | O_TRUNC | O_WRONLY, 0666);
+			s = sha1fd_throughput(fp, savepath, NULL);
+			sha1write(s, &header, sizeof(header));
+			sha1flush(s);

Are you abusing sha1write() and sha1flush() to write a byte sequence to a file? Is write_in_full() not sufficient?

+			close(fp);
+			/* -a is supported by both GNU and BSD tee */
+			*av2++ = "-a";
+		}
+		*av2++ = savepath;
+		*av2++ = NULL;
+		cmd2.in = demux.out;
+		e = pipe(pipefds);
+		if (e != 0)
+			die("couldn't make pipe to save pack");

start_command() can create the pipe for you. Just say cmd2.out = -1.

+		cmd2.out = pipefds[1];
+		cmd.in = pipefds[0];
+		if (start_command(&cmd2))
+			die("couldn't start tee to save a pack");

When you call start_command(), you must also call finish_command(). start_command() prints an error message for you; you don't have to do that (the start_command() in the context below is a bad example).

+	} else
+		cmd.in = demux.out;
  	cmd.git_cmd = 1;
  	if (start_command(&cmd))
  		die("fetch-pack: unable to fork off %s", cmd_name);
diff --git a/t/t5551-http-fetch-smart.sh b/t/t5551-http-fetch-smart.sh
index 58207d8..bf4640d 100755
--- a/t/t5551-http-fetch-smart.sh
+++ b/t/t5551-http-fetch-smart.sh
@@ -82,11 +82,23 @@ test_expect_success 'fetch changes via http' '
  	test_cmp file clone/file
  '

+test_expect_success 'fetch changes via http and save pack' '
+	echo content >>file &&
+	git commit -a -m two &&
+	git push public &&
+	GIT_SAVE_FETCHED_PACK_TO=saved.pack &&
+	export GIT_SAVE_FETCHED_PACK_TO &&
+	(cd clone && git pull) &&

This can be written as

	(
		cd clone &&
		GIT_SAVE_FETCHED_PACK_TO=../saved.pack git pull
	) &&

without 'export'.

+	git index-pack clone/saved.pack
+'
+
  cat >exp <<EOF
  GET  /smart/repo.git/info/refs?service=git-upload-pack HTTP/1.1 200
  POST /smart/repo.git/git-upload-pack HTTP/1.1 200
  GET  /smart/repo.git/info/refs?service=git-upload-pack HTTP/1.1 200
  POST /smart/repo.git/git-upload-pack HTTP/1.1 200
+GET  /smart/repo.git/info/refs?service=git-upload-pack HTTP/1.1 200
+POST /smart/repo.git/git-upload-pack HTTP/1.1 200
  EOF
  test_expect_success 'used upload-pack service' '
  	sed -e "
diff --git a/t/t5601-clone.sh b/t/t5601-clone.sh
index bfdaf75..73f9e1c 100755
--- a/t/t5601-clone.sh
+++ b/t/t5601-clone.sh
@@ -40,6 +40,15 @@ test_expect_success C_LOCALE_OUTPUT 'output from clone' '
  	test $(grep Clon output | wc -l) = 1
  '

+test_expect_success 'clone allows saving a pack' '
+	rm -fr dst saved.pack &&
+	GIT_SAVE_FETCHED_PACK_TO=saved.pack &&
+	export GIT_SAVE_FETCHED_PACK_TO &&
+	git clone -n "file://$(pwd)/src" dst >output 2>&1 &&

Same here.

+	test -e saved.pack &&
+	git index-pack saved.pack
+'
+
  test_expect_success 'clone does not keep pack' '

  	rm -fr dst &&


-- Hannes

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