Support server option from configuration

We manage some internal repositories with numerous CI tasks, each requiring code preparation through git-clone or git-fetch. These tasks, triggered by post-receive hooks, often fetch the same copy of code concurrently using --depth=1, causing extremely high load spikes on our Git servers.

To reduce performance impacts caused by these tasks, we plan to deploy a specially designed pack-objects-hook [1]. This hook would allow the packs generated by git-pack-objects(during git-clone or git-fetch) to be reused. Since not all clone/fetch operations will benefit from this caching (e.g., pulls from developer environments), clients need to pass a special identifier to indicate whether caching should be enabled. Using server options [2] is suitable for this purpose.

However, server options can only be specified via the command line option (via --server-option or -o), which is inconvenient and requires modifications to CI scripts. A configuration-based approach is preferable, as it can be propagated through global configuration (e.g. ~/.gitconfig) and avoids compatibility issues with older Git versions that don't support --server-option.

This patch series introduces a new multi-valued configuration, remote.<name>.serverOption, similar to push.pushOption, to specify default server options for the corresponding remote.

* Patches 1~3 contain the main changes for introducing the new configuration.
* Patch 4 fixes a issue for git-fetch not sending server-options when fetching from multiple remotes.
* Patch 5 is a minor fix for a server options-related memory leak.

1. https://git-scm.com/docs/git-config#Documentation/git-config.txt-uploadpackpackObjectsHook
2. https://git-scm.com/docs/gitprotocol-v2#_server_option

Xing Xin (5):
transport: introduce parse_transport_option() method
remote: introduce remote.<name>.serverOption configuration transport.c::handshake: make use of server options from remote
fetch: respect --server-option when fetching multiple remotes
ls-remote: leakfix for not clearing server_options

 Documentation/config/remote.txt |  10 +++
 Documentation/fetch-options.txt |   3 +
 Documentation/git-clone.txt     |   3 +
 Documentation/git-ls-remote.txt |   3 +
 builtin/fetch.c                 |   2 +
 builtin/ls-remote.c             |   1 +
 builtin/push.c                  |   9 +--
 remote.c                        |   6 ++
 remote.h                        |   3 +
 t/t5702-protocol-v2.sh          | 133 ++++++++++++++++++++++++++++++++
 transport.c                     |  15 ++++
 transport.h                     |   4 +
 12 files changed, 184 insertions(+), 8 deletions(-)

base-commit: 6258f68c3c1092c901337895c864073dcdea9213
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1776%2Fblanet%2Fxx%2Fadd-server-option-from-config-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1776/blanet/xx/add-server-option-from-config-v3
Pull-Request: https://github.com/git/git/pull/1776

Range-diff vs v2:

 1:  c95ed5e0dd5 = 1:  b44face42e1 transport: introduce parse_transport_option() method
 2:  2474b4c69d6 ! 2:  3c6b129d368 remote: introduce remote.<name>.serverOption configuration

@@ Documentation/config/remote.txt: remote.<name>.partialclonefilter::
database, use the --refetch option of linkgit:git-fetch[1].
+
+remote.<name>.serverOption::
-+ When no --server-option=<option> argument is given from the command
-+ line, git will use the values from this configuration as a default list of
-+ server options for this remote.
++ The default set of server options used when fetching from this remote.
++ These server options can be overridden by the --server-option= command
++ line arguments.
++
+This is a multi-valued variable, and an empty value can be used in a higher +priority configuration file (e.g. .git/config in a repository) to clear
@@ remote.c

enum map_direction { FROM_SRC, FROM_DST };

-@@ remote.c: static struct remote *make_remote(struct remote_state *remote_state,
- struct remote *ret;
- struct remotes_hash_key lookup;
- struct hashmap_entry lookup_entry, *e;
-+ struct string_list server_options = STRING_LIST_INIT_DUP;
-
- if (!len)
- len = strlen(name);
@@ remote.c: static struct remote *make_remote(struct remote_state *remote_state,
ret->name = xstrndup(name, len);
refspec_init(&ret->push, REFSPEC_PUSH);
refspec_init(&ret->fetch, REFSPEC_FETCH);
-+ ret->server_options = server_options;
++ string_list_init_dup(&ret->server_options);

ALLOC_GROW(remote_state->remotes, remote_state->remotes_nr + 1,
remote_state->remotes_alloc);
@@ remote.c: static void remote_clear(struct remote *remote)

static void add_merge(struct branch *branch, const char *name)
@@ remote.c: static int handle_config(const char *key, const char *value,
- key, value);
} else if (!strcmp(subkey, "vcs")) {
+ FREE_AND_NULL(remote->foreign_vcs);
return git_config_string(&remote->foreign_vcs, key, value);
+ } else if (!strcmp(subkey, "serveroption")) {
+ return parse_transport_option(key, value,

 3:  a7f3e458501 = 3:  f0835259b06 transport.c::handshake: make use of server options from remote
 4:  39ee8dbef78 = 4:  420b15d9f37 fetch: respect --server-option when fetching multiple remotes
 5:  39c07a6c8ee ! 5:  2528d929c7e ls-remote: leakfix for not clearing server_options

@@ Commit message

## builtin/ls-remote.c ##
-@@ builtin/ls-remote.c: int cmd_ls_remote(int argc, const char **argv, const char *prefix) +@@ builtin/ls-remote.c: int cmd_ls_remote(int argc,
transport_ls_refs_options_release(&transport_options);

strvec_clear(&pattern);

gitgitgadget