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upload-pack: provide a hook for running pack-objects
When upload-pack serves a client request, it turns to pack-objects to do the heavy lifting of creating a packfile. There's no easy way to intercept the call to pack-objects, but there are a few good reasons to want to do so: 1. If you're debugging a client or server issue with fetching, you may want to store a copy of the generated packfile. 2. If you're gathering data from real-world fetches for performance analysis or debugging, storing a copy of the arguments and stdin lets you replay the pack generation at your leisure. 3. You may want to insert a caching layer around pack-objects; it is the most CPU- and memory-intensive part of serving a fetch, and its output is a pure function[1] of its input, making it an ideal place to consolidate identical requests. This patch adds a simple "hook" interface to intercept calls to pack-objects. The new test demonstrates how it can be used for debugging (using it for caching is a straightforward extension; the tricky part is writing the actual caching layer). This hook is unlike the normal hook scripts found in the "hooks/" directory of a repository. Because we promise that upload-pack is safe to run in an untrusted repository, we cannot execute arbitrary code or commands found in the repository (neither in hooks/, nor in the config). So instead, this hook is triggered from a config variable that is explicitly ignored in the per-repo config. The config variable holds the actual shell command to run as the hook. Another approach would be to simply treat it as a boolean: "should I respect the upload-pack hooks in this repo?", and then run the script from "hooks/" as we usually do. However, that isn't as flexible; there's no way to run a hook approved by the site administrator (e.g., in "/etc/gitconfig") on a repository whose contents are not trusted. The approach taken by this patch is more fine-grained, if a little less conventional for git hooks (it does behave similar to other configured commands like diff.external, etc). [1] Pack-objects isn't _actually_ a pure function. Its output depends on the exact packing of the object database, and if multi-threading is used for delta compression, can even differ racily. But for the purposes of caching, that's OK; of the many possible outputs for a given input, it is sufficient only that we output one of them. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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@ -2880,6 +2880,21 @@ uploadpack.keepAlive::
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`uploadpack.keepAlive` seconds. Setting this option to 0
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disables keepalive packets entirely. The default is 5 seconds.
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uploadpack.packObjectsHook::
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If this option is set, when `upload-pack` would run
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`git pack-objects` to create a packfile for a client, it will
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run this shell command instead. The `pack-objects` command and
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arguments it _would_ have run (including the `git pack-objects`
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at the beginning) are appended to the shell command. The stdin
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and stdout of the hook are treated as if `pack-objects` itself
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was run. I.e., `upload-pack` will feed input intended for
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`pack-objects` to the hook, and expects a completed packfile on
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stdout.
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+
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Note that this configuration variable is ignored if it is seen in the
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repository-level config (this is a safety measure against fetching from
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untrusted repositories).
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url.<base>.insteadOf::
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Any URL that starts with this value will be rewritten to
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start, instead, with <base>. In cases where some site serves a
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62
t/t5544-pack-objects-hook.sh
Executable file
62
t/t5544-pack-objects-hook.sh
Executable file
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@ -0,0 +1,62 @@
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#!/bin/sh
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test_description='test custom script in place of pack-objects'
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. ./test-lib.sh
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test_expect_success 'create some history to fetch' '
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test_commit one &&
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test_commit two
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'
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test_expect_success 'create debugging hook script' '
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write_script .git/hook <<-\EOF
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echo >&2 "hook running"
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echo "$*" >hook.args
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cat >hook.stdin
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"$@" <hook.stdin >hook.stdout
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cat hook.stdout
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EOF
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'
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clear_hook_results () {
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rm -rf .git/hook.* dst.git
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}
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test_expect_success 'hook runs via global config' '
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clear_hook_results &&
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test_config_global uploadpack.packObjectsHook ./hook &&
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git clone --no-local . dst.git 2>stderr &&
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grep "hook running" stderr
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'
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test_expect_success 'hook outputs are sane' '
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# check that we recorded a usable pack
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git index-pack --stdin <.git/hook.stdout &&
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# check that we recorded args and stdin. We do not check
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# the full argument list or the exact pack contents, as it would make
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# the test brittle. So just sanity check that we could replay
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# the packing procedure.
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grep "^git" .git/hook.args &&
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$(cat .git/hook.args) <.git/hook.stdin >replay
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'
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test_expect_success 'hook runs from -c config' '
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clear_hook_results &&
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git clone --no-local \
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-u "git -c uploadpack.packObjectsHook=./hook upload-pack" \
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. dst.git 2>stderr &&
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grep "hook running" stderr
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'
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test_expect_success 'hook does not run from repo config' '
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clear_hook_results &&
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test_config uploadpack.packObjectsHook "./hook" &&
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git clone --no-local . dst.git 2>stderr &&
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! grep "hook running" stderr &&
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test_path_is_missing .git/hook.args &&
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test_path_is_missing .git/hook.stdin &&
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test_path_is_missing .git/hook.stdout
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'
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test_done
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@ -52,6 +52,7 @@ static int keepalive = 5;
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static int use_sideband;
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static int advertise_refs;
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static int stateless_rpc;
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static const char *pack_objects_hook;
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static void reset_timeout(void)
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{
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@ -93,6 +94,14 @@ static void create_pack_file(void)
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int i;
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FILE *pipe_fd;
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if (!pack_objects_hook)
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pack_objects.git_cmd = 1;
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else {
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argv_array_push(&pack_objects.args, pack_objects_hook);
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argv_array_push(&pack_objects.args, "git");
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pack_objects.use_shell = 1;
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}
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if (shallow_nr) {
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argv_array_push(&pack_objects.args, "--shallow-file");
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argv_array_push(&pack_objects.args, "");
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@ -115,7 +124,6 @@ static void create_pack_file(void)
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pack_objects.in = -1;
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pack_objects.out = -1;
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pack_objects.err = -1;
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pack_objects.git_cmd = 1;
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if (start_command(&pack_objects))
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die("git upload-pack: unable to fork git-pack-objects");
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@ -812,6 +820,9 @@ static int upload_pack_config(const char *var, const char *value, void *unused)
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keepalive = git_config_int(var, value);
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if (!keepalive)
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keepalive = -1;
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} else if (current_config_scope() != CONFIG_SCOPE_REPO) {
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if (!strcmp("uploadpack.packobjectshook", var))
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return git_config_string(&pack_objects_hook, var, value);
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}
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return parse_hide_refs_config(var, value, "uploadpack");
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}
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