storage/Plugin: add "prefixes"

src/storage/plugins/CurlStorage.cxx

@@ -570,14 +570,15 @@ CurlStorage::OpenDirectory(std::string_view uri_utf8)
 static std::unique_ptr<Storage>
 CreateCurlStorageURI(EventLoop &event_loop, const char *uri)
 {
-	if (!StringStartsWithCaseASCII(uri, "http://") &&
-	    !StringStartsWithCaseASCII(uri, "https://"))
-		return nullptr;
-
 	return std::make_unique<CurlStorage>(event_loop, uri);
 }
 
+static constexpr const char *curl_prefixes[] = {
+	"http://", "https://", nullptr
+};
+
 const StoragePlugin curl_storage_plugin = {
 	"curl",
+	curl_prefixes,
 	CreateCurlStorageURI,
 };

src/storage/plugins/LocalStorage.cxx

@@ -173,4 +173,5 @@ CreateLocalStorage(Path base_fs)
 constexpr StoragePlugin local_storage_plugin = {
 	"local",
 	nullptr,
+	nullptr,
 };

src/storage/plugins/NfsStorage.cxx

@@ -425,7 +425,10 @@ CreateNfsStorageURI(EventLoop &event_loop, const char *base)
 					    server.c_str(), mount);
 }
 
+static constexpr const char *nfs_prefixes[] = { "nfs://", nullptr };
+
 const StoragePlugin nfs_storage_plugin = {
 	"nfs",
+	nfs_prefixes,
 	CreateNfsStorageURI,
 };

src/storage/plugins/UdisksStorage.cxx

@@ -377,7 +377,10 @@ CreateUdisksStorageURI(EventLoop &event_loop, const char *base_uri)
 					       std::move(inside_path));
 }
 
+static constexpr const char *udisks_prefixes[] = { "udisks://", nullptr };
+
 const StoragePlugin udisks_storage_plugin = {
 	"udisks",
+	udisks_prefixes,
 	CreateUdisksStorageURI,
 };