bundle-uri: create "key=value" line parsing

When advertising a bundle list over Git's protocol v2, we will use
packet lines. Each line will be of the form "key=value" representing a
bundle list. Connect the API necessary for Git's transport to the
key-value pair parsing created in the previous change.

We are not currently implementing this protocol v2 functionality, but
instead preparing to expose this parsing to be unit-testable.

Co-authored-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

bundle-uri.c

@@ -71,7 +71,6 @@ int for_all_bundles_in_list(struct bundle_list *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)
 {
@@ -306,3 +305,29 @@ cleanup:
 	free(filename);
 	return result;
 }
+
+/**
+ * General API for {transport,connect}.c etc.
+ */
+int bundle_uri_parse_line(struct bundle_list *list, const char *line)
+{
+	int result;
+	const char *equals;
+	struct strbuf key = STRBUF_INIT;
+
+	if (!strlen(line))
+		return error(_("bundle-uri: got an empty line"));
+
+	equals = strchr(line, '=');
+
+	if (!equals)
+		return error(_("bundle-uri: line is not of the form 'key=value'"));
+	if (line == equals || !*(equals + 1))
+		return error(_("bundle-uri: line has empty key or value"));
+
+	strbuf_add(&key, line, equals - line);
+	result = bundle_list_update(key.buf, equals + 1, list);
+	strbuf_release(&key);
+
+	return result;
+}

bundle-uri.h

@@ -67,4 +67,16 @@ int for_all_bundles_in_list(struct bundle_list *list,
  */
 int fetch_bundle_uri(struct repository *r, const char *uri);
 
+/**
+ * General API for {transport,connect}.c etc.
+ */
+
+/**
+ * Parse a "key=value" packet line from the bundle-uri verb.
+ *
+ * Returns 0 on success and non-zero on error.
+ */
+int bundle_uri_parse_line(struct bundle_list *list,
+			  const char *line);
+
 #endif