Properly handle subrequests for redirected URLs

src/hls/hls-demuxer.ts

@@ -77,12 +77,15 @@ export class HlsDemuxer extends Demuxer {
 	readMetadata() {
 		return this.metadataPromise ??= (async () => {
 			assert(this.input._rootSource instanceof PathedSource);
-			const { rootPath } = this.input._rootSource;
 
 			const slice = await this.input._reader.requestEntireFile();
 			assert(slice);
 			const lines = readAllLines(slice, slice.length, { ignore: canIgnoreLine });
 
+			// Important: get the root path AFTER reading data to get the final root path, possibly affected by
+			// redirects. Any follow requests should be related to the redirected path, not the original one.
+			const { rootPath } = this.input._rootSource;
+
 			const variantStreams: {
 				fullPath: string;
 				attributes: AttributeList;

src/hls/hls-segmented-input.ts

@@ -20,7 +20,7 @@ import {
 	base64ToBytes,
 } from '../misc';
 import { readAllLines, readBytes, Reader } from '../reader';
-import { CustomPathedSource, ReadableStreamSource, SourceRef, SourceRequest } from '../source';
+import { CustomPathedSource, PathedSource, ReadableStreamSource, SourceRef, SourceRequest } from '../source';
 import { HlsDemuxer } from './hls-demuxer';
 import {
 	AttributeList,
@@ -68,6 +68,7 @@ export type HlsSegmentLocation = {
 };
 
 export class HlsSegmentedInput extends SegmentedInput {
+	rootPath: string;
 	demuxer: HlsDemuxer;
 	segments: HlsSegment[] = [];
 	nextLines: string[] | null = null;
@@ -84,6 +85,7 @@ export class HlsSegmentedInput extends SegmentedInput {
 	) {
 		super(demuxer.input, path, trackDeclarations);
 
+		this.rootPath = path;
 		this.demuxer = demuxer;
 		this.nextLines = lines;
 	}
@@ -126,12 +128,17 @@ export class HlsSegmentedInput extends SegmentedInput {
 		this.nextLines = null;
 
 		if (!lines) {
-			using ref = await this.demuxer.input._getSourceUncached({ path: this.path, isRoot: false });
+			using ref = await this.demuxer.input._getSourceUncached({ path: this.rootPath, isRoot: false });
 			const reader = new Reader(ref.source);
 
 			const slice = await reader.requestEntireFile();
 			assert(slice);
 			lines = readAllLines(slice, slice.length, { ignore: canIgnoreLine });
+
+			if (ref.source instanceof PathedSource) {
+				// Copy back the source's path to become aware of potential redirects
+				this.rootPath = ref.source.rootPath;
+			}
 		}
 
 		let headerRead = false;
@@ -219,7 +226,7 @@ export class HlsSegmentedInput extends SegmentedInput {
 						key = { ...key, iv };
 					}
 
-					const fullPath = joinPaths(this.path, line);
+					const fullPath = joinPaths(this.rootPath, line);
 					const location: HlsSegmentLocation = {
 						path: fullPath,
 						offset: nextByteRange?.offset ?? 0,
@@ -299,7 +306,7 @@ export class HlsSegmentedInput extends SegmentedInput {
 				}
 
 				if (!prevLastSegment) {
-					const fullPath = joinPaths(this.path, uri);
+					const fullPath = joinPaths(this.rootPath, uri);
 					const location: HlsSegmentLocation = {
 						path: fullPath,
 						offset: parsedByteRange?.offset ?? 0,
@@ -375,7 +382,7 @@ export class HlsSegmentedInput extends SegmentedInput {
 
 					currentKey = {
 						method: 'AES-128',
-						keyUri: joinPaths(this.path, uri),
+						keyUri: joinPaths(this.rootPath, uri),
 						iv,
 						keyFormat,
 					};

src/source.ts

@@ -289,10 +289,15 @@ export class SourceRef<S extends Source = Source> implements Disposable {
  */
 export abstract class PathedSource extends Source {
 	constructor(
-		/** The path that points to the root file; the entry file of the media. */
+		/**
+		 * The path that points to the root file; the entry file of the media.
+		 *
+		 * This path may be modified by the source to indicate a redirect: an updated path to perform new requests
+		 * relative to.
+		 */
 		public rootPath: FilePath,
 		/** The callback that is called for each requested file; must return a {@link Source} or {@link SourceRef}. */
-		public requestHandler: (request: SourceRequest) => MaybePromise<Source | SourceRef>,
+		public readonly requestHandler: (request: SourceRequest) => MaybePromise<Source | SourceRef>,
 	) {
 		if (typeof rootPath !== 'string') {
 			throw new TypeError('rootPath must be a string.');
@@ -778,7 +783,10 @@ export class UrlSource extends PathedSource {
 				? url.href
 				: url;
 
-		super(urlString, request => new UrlSource(request.path, this._options));
+		super(
+			urlString,
+			request => new UrlSource(request.path, this._options),
+		);
 
 		this._url = url;
 		this._options = options;
@@ -905,6 +913,11 @@ export class UrlSource extends PathedSource {
 				throw new Error(`Error fetching ${String(this._url)}: ${response.status} ${response.statusText}`);
 			}
 
+			if (response.redirected) {
+				// Modify our own root path so that future subrequests get made relative to the redirected URL
+				this.rootPath = response.url;
+			}
+
 			outer:
 			if (this._orchestrator.fileSize === null) {
 				// See if we can deduce the file size from the response