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authorLibravatar Jeff King <peff@peff.net>2016-05-18 18:45:37 -0400
committerLibravatar Junio C Hamano <gitster@pobox.com>2016-06-02 15:22:24 -0700
commit20b20a22f8f7c1420e259c97ef790cb93091f475 (patch)
tree9b4262a0b8bf6de105f5f24773406c511712d686 /t
parentt1308: do not get fooled by symbolic links to the source tree (diff)
downloadtgif-20b20a22f8f7c1420e259c97ef790cb93091f475.tar.xz
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>
Diffstat (limited to 't')
-rwxr-xr-xt/t5544-pack-objects-hook.sh62
1 files changed, 62 insertions, 0 deletions
diff --git a/t/t5544-pack-objects-hook.sh b/t/t5544-pack-objects-hook.sh
new file mode 100755
index 0000000000..4357af1525
--- /dev/null
+++ b/t/t5544-pack-objects-hook.sh
@@ -0,0 +1,62 @@
+#!/bin/sh
+
+test_description='test custom script in place of pack-objects'
+. ./test-lib.sh
+
+test_expect_success 'create some history to fetch' '
+ test_commit one &&
+ test_commit two
+'
+
+test_expect_success 'create debugging hook script' '
+ write_script .git/hook <<-\EOF
+ echo >&2 "hook running"
+ echo "$*" >hook.args
+ cat >hook.stdin
+ "$@" <hook.stdin >hook.stdout
+ cat hook.stdout
+ EOF
+'
+
+clear_hook_results () {
+ rm -rf .git/hook.* dst.git
+}
+
+test_expect_success 'hook runs via global config' '
+ clear_hook_results &&
+ test_config_global uploadpack.packObjectsHook ./hook &&
+ git clone --no-local . dst.git 2>stderr &&
+ grep "hook running" stderr
+'
+
+test_expect_success 'hook outputs are sane' '
+ # check that we recorded a usable pack
+ git index-pack --stdin <.git/hook.stdout &&
+
+ # check that we recorded args and stdin. We do not check
+ # the full argument list or the exact pack contents, as it would make
+ # the test brittle. So just sanity check that we could replay
+ # the packing procedure.
+ grep "^git" .git/hook.args &&
+ $(cat .git/hook.args) <.git/hook.stdin >replay
+'
+
+test_expect_success 'hook runs from -c config' '
+ clear_hook_results &&
+ git clone --no-local \
+ -u "git -c uploadpack.packObjectsHook=./hook upload-pack" \
+ . dst.git 2>stderr &&
+ grep "hook running" stderr
+'
+
+test_expect_success 'hook does not run from repo config' '
+ clear_hook_results &&
+ test_config uploadpack.packObjectsHook "./hook" &&
+ git clone --no-local . dst.git 2>stderr &&
+ ! grep "hook running" stderr &&
+ test_path_is_missing .git/hook.args &&
+ test_path_is_missing .git/hook.stdin &&
+ test_path_is_missing .git/hook.stdout
+'
+
+test_done