backend-common: print warning if supplied readers do not implement readUrl

Co-authored-by: Johan Haals <johan.haals@gmail.com>
Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/backend-common/src/reading/UrlReaderPredicateMux.ts

@@ -15,6 +15,7 @@
  */
 
 import { NotAllowedError } from '@backstage/errors';
+import { Logger } from 'winston';
 import {
   ReadTreeOptions,
   ReadTreeResponse,
@@ -26,12 +27,17 @@ import {
   UrlReaderPredicateTuple,
 } from './types';
 
+const MIN_WARNING_INTERVAL_MS = 1000 * 60 * 15;
+
 /**
  * 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[] = [];
+  private readonly readerWarnings: Map<UrlReader, number> = new Map();
+
+  constructor(private readonly logger: Logger) {}
 
   register(tuple: UrlReaderPredicateTuple): void {
     this.readers.push(tuple);
@@ -60,6 +66,16 @@ export class UrlReaderPredicateMux implements UrlReader {
         if (reader.readUrl) {
           return reader.readUrl(url, options);
         }
+        const now = Date.now();
+        const lastWarned = this.readerWarnings.get(reader) ?? 0;
+        if (now > lastWarned + MIN_WARNING_INTERVAL_MS) {
+          this.readerWarnings.set(reader, now);
+          this.logger.warn(
+            `No implementation of readUrl found for ${reader}, this method will be required in the ` +
+              `future and will replace the 'read' method. See the changelog for more details here: ` +
+              'https://github.com/backstage/backstage/blob/master/packages/backend-common/CHANGELOG.md#085',
+          );
+        }
         const buffer = await reader.read(url);
         return {
           buffer: async () => buffer,

packages/backend-common/src/reading/UrlReaders.ts

@@ -43,7 +43,7 @@ export class UrlReaders {
    * Creates a UrlReader without any known types.
    */
   static create({ logger, config, factories }: CreateOptions): UrlReader {
-    const mux = new UrlReaderPredicateMux();
+    const mux = new UrlReaderPredicateMux(logger);
     const treeResponseFactory = DefaultReadTreeResponseFactory.create({
       config,
     });