bundle-uri: create base key-value pair parsing

There will be two primary ways to advertise a bundle list: as a list of
packet lines in Git's protocol v2 and as a config file served from a
bundle URI. Both of these fundamentally use a list of key-value pairs.
We will use the same set of key-value pairs across these formats.

Create a new bundle_list_update() method that is currently unusued, but
will be used in the next change. It inspects each key to see if it is
understood and then applies it to the given bundle_list. Here are the
keys that we teach Git to understand:

* bundle.version: This value should be an integer. Git currently
  understands only version 1 and will ignore the list if the version is
  any other value. This version can be increased in the future if we
  need to add new keys that Git should not ignore. We can add new
  "heuristic" keys without incrementing the version.

* bundle.mode: This value should be one of "all" or "any". If this
  mode is not understood, then Git will ignore the list. This mode
  indicates whether Git needs all of the bundle list items to make a
  complete view of the content or if any single item is sufficient.

The rest of the keys use a bundle identifier "<id>" as part of the key
name. Keys using the same "<id>" describe a single bundle list item.

* bundle.<id>.uri: This stores the URI of the bundle item. This
  currently is expected to be an absolute URI, but will be relaxed to be
  a relative URI in the future.

While parsing, return an error if a URI key is repeated, since we can
make that restriction with bundle lists.

Make the git_parse_int() method global so we can parse the integer
version value carefully.

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

Documentation/config.txt

@@ -387,6 +387,8 @@ include::config/branch.txt[]
 
 include::config/browser.txt[]
 
+include::config/bundle.txt[]
+
 include::config/checkout.txt[]
 
 include::config/clean.txt[]

Documentation/config/bundle.txt

@@ -0,0 +1,24 @@
+bundle.*::
+	The `bundle.*` keys may appear in a bundle list file found via the
+	`git clone --bundle-uri` option. These keys currently have no effect
+	if placed in a repository config file, though this will change in the
+	future. See link:technical/bundle-uri.html[the bundle URI design
+	document] for more details.
+
+bundle.version::
+	This integer value advertises the version of the bundle list format
+	used by the bundle list. Currently, the only accepted value is `1`.
+
+bundle.mode::
+	This string value should be either `all` or `any`. This value describes
+	whether all of the advertised bundles are required to unbundle a
+	complete understanding of the bundled information (`all`) or if any one
+	of the listed bundle URIs is sufficient (`any`).
+
+bundle.<id>.*::
+	The `bundle.<id>.*` keys are used to describe a single item in the
+	bundle list, grouped under `<id>` for identification purposes.
+
+bundle.<id>.uri::
+	This string value defines the URI by which Git can reach the contents
+	of this `<id>`. This URI may be a bundle file or another bundle list.

bundle-uri.c

@@ -6,6 +6,7 @@
 #include "run-command.h"
 #include "hashmap.h"
 #include "pkt-line.h"
+#include "config.h"
 
 static int compare_bundles(const void *hashmap_cmp_fn_data,
 			   const struct hashmap_entry *he1,
@@ -65,6 +66,81 @@ int for_all_bundles_in_list(struct bundle_list *list,
 	return 0;
 }
 
+/**
+ * Given a key-value pair, update the state of the given bundle list.
+ * Returns 0 if the key-value pair is understood. Returns -1 if the key
+ * is not understood or the value is malformed.
+ */
+MAYBE_UNUSED
+static int bundle_list_update(const char *key, const char *value,
+			      struct bundle_list *list)
+{
+	struct strbuf id = STRBUF_INIT;
+	struct remote_bundle_info lookup = REMOTE_BUNDLE_INFO_INIT;
+	struct remote_bundle_info *bundle;
+	const char *subsection, *subkey;
+	size_t subsection_len;
+
+	if (parse_config_key(key, "bundle", &subsection, &subsection_len, &subkey))
+		return -1;
+
+	if (!subsection_len) {
+		if (!strcmp(subkey, "version")) {
+			int version;
+			if (!git_parse_int(value, &version))
+				return -1;
+			if (version != 1)
+				return -1;
+
+			list->version = version;
+			return 0;
+		}
+
+		if (!strcmp(subkey, "mode")) {
+			if (!strcmp(value, "all"))
+				list->mode = BUNDLE_MODE_ALL;
+			else if (!strcmp(value, "any"))
+				list->mode = BUNDLE_MODE_ANY;
+			else
+				return -1;
+			return 0;
+		}
+
+		/* Ignore other unknown global keys. */
+		return 0;
+	}
+
+	strbuf_add(&id, subsection, subsection_len);
+
+	/*
+	 * Check for an existing bundle with this <id>, or create one
+	 * if necessary.
+	 */
+	lookup.id = id.buf;
+	hashmap_entry_init(&lookup.ent, strhash(lookup.id));
+	if (!(bundle = hashmap_get_entry(&list->bundles, &lookup, ent, NULL))) {
+		CALLOC_ARRAY(bundle, 1);
+		bundle->id = strbuf_detach(&id, NULL);
+		hashmap_entry_init(&bundle->ent, strhash(bundle->id));
+		hashmap_add(&list->bundles, &bundle->ent);
+	}
+	strbuf_release(&id);
+
+	if (!strcmp(subkey, "uri")) {
+		if (bundle->uri)
+			return -1;
+		bundle->uri = xstrdup(value);
+		return 0;
+	}
+
+	/*
+	 * At this point, we ignore any information that we don't
+	 * understand, assuming it to be hints for a heuristic the client
+	 * does not currently understand.
+	 */
+	return 0;
+}
+
 static char *find_temp_filename(void)
 {
 	int fd;

config.c

@@ -1214,7 +1214,7 @@ static int git_parse_unsigned(const char *value, uintmax_t *ret, uintmax_t max)
 	return 0;
 }
 
-static int git_parse_int(const char *value, int *ret)
+int git_parse_int(const char *value, int *ret)
 {
 	intmax_t tmp;
 	if (!git_parse_signed(value, &tmp, maximum_signed_value_of_type(int)))

config.h

@@ -206,6 +206,7 @@ int config_with_options(config_fn_t fn, void *,
 
 int git_parse_ssize_t(const char *, ssize_t *);
 int git_parse_ulong(const char *, unsigned long *);
+int git_parse_int(const char *value, int *ret);
 
 /**
  * Same as `git_config_bool`, except that it returns -1 on error rather