bundle-uri: parse bundle list in config format

When a bundle provider wants to operate independently from a Git remote,
they want to provide a single, consistent URI that users can use in
their 'git clone --bundle-uri' commands. At this point, the Git client
expects that URI to be a single bundle that can be unbundled and used to
bootstrap the rest of the clone from the Git server. This single bundle
cannot be re-used to assist with future incremental fetches.

To allow for the incremental fetch case, teach Git to understand a
bundle list that could be advertised at an independent bundle URI. Such
a bundle list is likely to be inspected by human readers, even if only
by the bundle provider creating the list. For this reason, we can take
our expected "key=value" pairs and instead format them using Git config
format.

Create bundle_uri_parse_config_format() to parse a file in config format
and convert that into a 'struct bundle_list' filled with its
understanding of the contents.

Be careful to use error_action CONFIG_ERROR_ERROR when calling
git_config_from_file_with_options() because the default action for
git_config_from_file() is to die() on a parsing error.  The current
warning isn't particularly helpful if it arises to a user, but it will
be made more verbose at a higher layer later.

Update 'test-tool bundle-uri' to take this config file format as input.
It uses a filename instead of stdin because there is no existing way to
parse a FILE pointer in the config machinery. Using
git_config_from_mem() is overly complicated and more likely to introduce
bugs than this simpler version.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

bundle-uri.c

@@ -173,6 +173,33 @@ static int bundle_list_update(const char *key, const char *value,
 	return 0;
 }
 
+static int config_to_bundle_list(const char *key, const char *value, void *data)
+{
+	struct bundle_list *list = data;
+	return bundle_list_update(key, value, list);
+}
+
+int bundle_uri_parse_config_format(const char *uri,
+				   const char *filename,
+				   struct bundle_list *list)
+{
+	int result;
+	struct config_options opts = {
+		.error_action = CONFIG_ERROR_ERROR,
+	};
+
+	result = git_config_from_file_with_options(config_to_bundle_list,
+						   filename, list,
+						   &opts);
+
+	if (!result && list->mode == BUNDLE_MODE_NONE) {
+		warning(_("bundle list at '%s' has no mode"), uri);
+		result = 1;
+	}
+
+	return result;
+}
+
 static char *find_temp_filename(void)
 {
 	int fd;