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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