backend-common: add UrlReaderPredicateMux

2020-10-02 10:35:56 +02:00
parent f2ad1b6f27
commit 0fbe965b43
1 changed files with 48 additions and 0 deletions
@@ -0,0 +1,48 @@
+/*
+ * Copyright 2020 Spotify AB
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { UrlReader } from './types';
+
+export type UrlReaderPredicate = (url: URL) => boolean;
+
+export type UrlReaderPredicateTuple = {
+  predicate: UrlReaderPredicate;
+  reader: UrlReader;
+};
+
+/**
+ * A UrlReader implementation that selects from a set of UrlReaders
+ * based on a predicate tied to each reader.
+ */
+export class UrlReaderPredicateMux implements UrlReader {
+  private readonly readers: UrlReaderPredicateTuple[] = [];
+
+  register(tuple: UrlReaderPredicateTuple): void {
+    this.readers.push(tuple);
+  }
+
+  read(url: string): Promise<Buffer> {
+    const parsed = new URL(url);
+
+    for (const { predicate, reader } of this.readers) {
+      if (predicate(parsed)) {
+        return reader.read(url);
+      }
+    }
+
+    throw new Error(`No reader found that could handle '${url}'`);
+  }
+}