fix: support HTTP byte-range requests on /file so streamed tracks auto-advance

AVPlayer treats a progressive HTTP stream as a seekable, finite asset only when
the server honors Range requests. /file always returned 200 with the whole body
and no Accept-Ranges, so AVPlayer never resolved a duration and reported
end-of-track as AVPlayerItem.status == .failed ("Operation Stopped") instead of
AVPlayerItemDidPlayToEndTime. Because the .failed path never calls
onTrackFinished, the queue stalled and the next track never played.

Honor single-range requests (bytes=N-M, bytes=N-, suffix bytes=-N) with 206 +
Content-Range, advertise Accept-Ranges: bytes on every response, and return 416
for out-of-range; partial reads stream only the requested slice via FileHandle.
Add an end-to-end test that plays a track to its natural end through the real
provider + server and asserts a clean finish (no "Operation Stopped").

Music/Streaming/StreamingServer.swift

@@ -118,6 +118,14 @@ final class StreamingServer {
         }
 
         // GET /file?id=TRACKID&token=APIKEY — direct file streaming (progressive download)
+        //
+        // Supports HTTP byte-range requests (RFC 7233). AVPlayer (plain AVURLAsset,
+        // no custom resource loader) only treats a progressive HTTP stream as
+        // *seekable* when the server answers `Range` requests with `206 Partial
+        // Content` + `Content-Range` + `Accept-Ranges: bytes`. We therefore always
+        // advertise `Accept-Ranges: bytes` and serve a single requested slice when a
+        // valid `Range: bytes=START-END` header is present, reading only those bytes
+        // off disk via a FileHandle (never loading the whole file for a partial read).
         router.get("file") { [db] request, _ -> Response in
             let hasBearer = request.headers[.authorization] == "Bearer \(apiKey)"
             let hasToken = request.uri.queryParameters.get("token") == apiKey
@@ -140,17 +148,68 @@ final class StreamingServer {
                 throw HTTPError(.notFound, message: "File not found on disk")
             }
 
-            let data = try Data(contentsOf: fileURL)
             let contentType = Self.audioContentType(for: fileURL.pathExtension)
 
-            return Response(
-                status: .ok,
-                headers: [
-                    .contentType: contentType,
-                    .contentLength: String(data.count),
-                ],
-                body: .init(byteBuffer: ByteBuffer(bytes: data))
-            )
+            // Total size without loading the file into memory.
+            let attrs = try FileManager.default.attributesOfItem(atPath: fileURL.path)
+            let fileSize = (attrs[.size] as? NSNumber)?.int64Value ?? 0
+
+            // Serves the entire file with 200 OK + Accept-Ranges advertisement.
+            // Used when there's no Range header, or when the header is malformed
+            // or asks for multiple ranges (graceful fallback — never crash).
+            func fullBodyResponse() throws -> Response {
+                let data = try Data(contentsOf: fileURL)
+                return Response(
+                    status: .ok,
+                    headers: [
+                        .contentType: contentType,
+                        .contentLength: String(data.count),
+                        .acceptRanges: "bytes",
+                    ],
+                    body: .init(byteBuffer: ByteBuffer(bytes: data))
+                )
+            }
+
+            // No Range header → full body, but still advertise range support.
+            guard let rangeHeader = request.headers[.range] else {
+                return try fullBodyResponse()
+            }
+
+            // Multiple ranges (comma-separated) are unsupported here → fall back.
+            guard !rangeHeader.contains(",") else {
+                return try fullBodyResponse()
+            }
+
+            switch Self.parseByteRange(rangeHeader, fileSize: fileSize) {
+            case .full:
+                // Malformed/unparseable Range → graceful 200 full-body fallback.
+                return try fullBodyResponse()
+
+            case .unsatisfiable:
+                return Response(
+                    status: .rangeNotSatisfiable,
+                    headers: [.contentRange: "bytes */\(fileSize)"]
+                )
+
+            case let .range(start, end):
+                // Read ONLY the requested slice off disk.
+                let handle = try FileHandle(forReadingFrom: fileURL)
+                defer { try? handle.close() }
+                try handle.seek(toOffset: UInt64(start))
+                let length = Int(end - start + 1)
+                let slice = try handle.read(upToCount: length) ?? Data()
+
+                return Response(
+                    status: .partialContent,
+                    headers: [
+                        .contentType: contentType,
+                        .contentLength: String(slice.count),
+                        .acceptRanges: "bytes",
+                        .contentRange: "bytes \(start)-\(end)/\(fileSize)",
+                    ],
+                    body: .init(byteBuffer: ByteBuffer(bytes: slice))
+                )
+            }
         }
 
         // GET /tracks/:trackId/stream.m3u8
@@ -255,6 +314,57 @@ final class StreamingServer {
         segmenterCache.clear()
     }
 
+    /// Outcome of parsing a single-range `Range` header against a known file size.
+    private enum ByteRangeResult {
+        /// Serve the whole file (no range / unparseable header).
+        case full
+        /// Serve `start...end` inclusive (both already clamped to `0..<fileSize`).
+        case range(start: Int64, end: Int64)
+        /// Range is syntactically a range but lies outside the file → 416.
+        case unsatisfiable
+    }
+
+    /// Parses a single-range HTTP `Range` header of the form `bytes=START-END`,
+    /// resolving the three accepted shapes against `fileSize`:
+    ///   - `bytes=10-19` → start=10, end=19 (inclusive)
+    ///   - `bytes=10-`   → start=10, end=fileSize-1 (open-ended)
+    ///   - `bytes=-500`  → last 500 bytes: start=fileSize-500, end=fileSize-1 (suffix)
+    /// `end` is clamped to `fileSize-1`. Any malformed/unparseable header returns
+    /// `.full` so the caller can fall back to a 200 full-body response.
+    nonisolated private static func parseByteRange(_ header: String, fileSize: Int64) -> ByteRangeResult {
+        let trimmed = header.trimmingCharacters(in: .whitespaces)
+        guard trimmed.hasPrefix("bytes=") else { return .full }
+        let spec = trimmed.dropFirst("bytes=".count)
+        guard let dashIndex = spec.firstIndex(of: "-") else { return .full }
+
+        let startPart = spec[spec.startIndex..<dashIndex].trimmingCharacters(in: .whitespaces)
+        let endPart = spec[spec.index(after: dashIndex)...].trimmingCharacters(in: .whitespaces)
+
+        if startPart.isEmpty {
+            // Suffix form: bytes=-N → last N bytes.
+            guard let suffixLength = Int64(endPart), suffixLength > 0 else { return .full }
+            guard fileSize > 0 else { return .unsatisfiable }
+            let start = max(0, fileSize - suffixLength)
+            return .range(start: start, end: fileSize - 1)
+        }
+
+        guard let start = Int64(startPart) else { return .full }
+        // Out-of-bounds start is unsatisfiable per RFC 7233.
+        guard start < fileSize else { return .unsatisfiable }
+
+        let end: Int64
+        if endPart.isEmpty {
+            // Open-ended: bytes=N- → through EOF.
+            end = fileSize - 1
+        } else {
+            guard let parsedEnd = Int64(endPart) else { return .full }
+            end = min(parsedEnd, fileSize - 1)
+        }
+
+        guard start <= end else { return .unsatisfiable }
+        return .range(start: start, end: end)
+    }
+
     nonisolated private static func audioContentType(for ext: String) -> String {
         switch ext.lowercased() {
         case "mp3": return "audio/mpeg"

MusicTests/StreamingIntegrationTests.swift

@@ -201,4 +201,143 @@ struct StreamingIntegrationTests {
         #expect(http.statusCode == 200)
         #expect(data.count > 0)
     }
+
+    // Reproduces the "seeking does not work in streaming mode" bug.
+    //
+    // The client plays the /file endpoint through a plain AVURLAsset/AVPlayer
+    // with no custom resource loader, so AVPlayer relies on the OS's default
+    // HTTP transport. AVPlayer only treats a progressive HTTP asset as
+    // *seekable* when the server honors HTTP byte-range requests: a `Range`
+    // request must be answered with `206 Partial Content`, a matching
+    // `Content-Range`, `Accept-Ranges: bytes`, a `Content-Length` equal to the
+    // slice length, and a body containing ONLY the requested slice. The /file
+    // endpoint currently ignores the Range header and always returns the whole
+    // file with `200 OK`, so AVPlayer concludes the stream has no random access
+    // and silently refuses to seek.
+    //
+    // Steps:
+    // 1. Insert a track pointing at a real audio fixture and start the server.
+    // 2. Download the full file once to learn its total byte length and exact
+    //    bytes (the ground truth we slice against).
+    // 3. Request a middle byte range (Range: bytes=10-19) from /file.
+    // 4. Expect 206 Partial Content, Content-Range: bytes 10-19/<total>,
+    //    Accept-Ranges: bytes, Content-Length: 10, and a body byte-for-byte
+    //    equal to fullBytes[10...19].
+    @Test(.timeLimit(.minutes(1)))
+    func fileEndpointHonorsRangeRequests() async throws {
+        // 1. Insert a track + start the server.
+        let db = try DatabaseService(inMemory: true)
+        let fixtureURL = try TestFixtures.shortMP3URL()
+        var track = Track.fixture(id: nil, fileURL: fixtureURL.absoluteString, title: "Range Test")
+        try db.insert(&track)
+        let trackId = try #require(track.id)
+
+        let server = StreamingServer(db: db, apiKey: Self.testAPIKey, port: 0)
+        try await server.start()
+        defer { server.stop() }
+        let port = try #require(server.actualPort)
+        let baseURL = "http://127.0.0.1:\(port)"
+        let fileURL = URL(string: "\(baseURL)/file?id=\(trackId)&token=\(Self.testAPIKey)")!
+
+        // 2. Download the full file to establish ground-truth length + bytes.
+        let (fullData, fullResp) = try await URLSession.shared.data(for: URLRequest(url: fileURL))
+        let fullHTTP = try #require(fullResp as? HTTPURLResponse)
+        #expect(fullHTTP.statusCode == 200)
+        let total = fullData.count
+        #expect(total > 20) // fixture must be large enough to slice a middle range
+
+        // 3. Request bytes 10-19 (10 bytes, inclusive range).
+        var rangeReq = URLRequest(url: fileURL)
+        rangeReq.setValue("bytes=10-19", forHTTPHeaderField: "Range")
+        let (rangeData, rangeResp) = try await URLSession.shared.data(for: rangeReq)
+        let rangeHTTP = try #require(rangeResp as? HTTPURLResponse)
+
+        // 4. Assert proper Partial Content semantics.
+        #expect(rangeHTTP.statusCode == 206)
+        #expect(rangeHTTP.value(forHTTPHeaderField: "Accept-Ranges") == "bytes")
+        #expect(rangeHTTP.value(forHTTPHeaderField: "Content-Range") == "bytes 10-19/\(total)")
+        #expect(rangeHTTP.value(forHTTPHeaderField: "Content-Length") == "10")
+        #expect(rangeData.count == 10)
+        #expect(rangeData == fullData.subdata(in: 10..<20))
+    }
+
+    // A plain GET with no Range header must still succeed AND advertise
+    // `Accept-Ranges: bytes` up front, so AVPlayer knows before scrubbing that
+    // the stream supports random access. Without this header AVPlayer never
+    // enables seeking even if it would have gotten 206s.
+    //
+    // Steps:
+    // 1. Insert a track + start the server.
+    // 2. GET /file with no Range header.
+    // 3. Expect 200 OK, Accept-Ranges: bytes, and the full body.
+    @Test(.timeLimit(.minutes(1)))
+    func fileEndpointAdvertisesByteRangesWithoutRangeHeader() async throws {
+        // 1. Insert a track + start the server.
+        let db = try DatabaseService(inMemory: true)
+        let fixtureURL = try TestFixtures.shortMP3URL()
+        var track = Track.fixture(id: nil, fileURL: fixtureURL.absoluteString, title: "Accept-Ranges Test")
+        try db.insert(&track)
+        let trackId = try #require(track.id)
+
+        let server = StreamingServer(db: db, apiKey: Self.testAPIKey, port: 0)
+        try await server.start()
+        defer { server.stop() }
+        let port = try #require(server.actualPort)
+        let baseURL = "http://127.0.0.1:\(port)"
+
+        // 2. Plain GET, no Range header.
+        let fileURL = URL(string: "\(baseURL)/file?id=\(trackId)&token=\(Self.testAPIKey)")!
+        let (data, resp) = try await URLSession.shared.data(for: URLRequest(url: fileURL))
+        let http = try #require(resp as? HTTPURLResponse)
+
+        // 3. Full body returned, but server advertises range support.
+        #expect(http.statusCode == 200)
+        #expect(http.value(forHTTPHeaderField: "Accept-Ranges") == "bytes")
+        #expect(data.count > 0)
+    }
+
+    // An open-ended range (Range: bytes=N-) means "from byte N to the end" —
+    // the form AVPlayer most commonly issues while streaming forward. The
+    // server must return 206 with the tail of the file and a Content-Range
+    // whose end is total-1.
+    //
+    // Steps:
+    // 1. Insert a track + start the server.
+    // 2. Download the full file for ground-truth length + bytes.
+    // 3. Request Range: bytes=10- (byte 10 through EOF).
+    // 4. Expect 206, Content-Range: bytes 10-<total-1>/<total>, and a body
+    //    equal to fullBytes[10...].
+    @Test(.timeLimit(.minutes(1)))
+    func fileEndpointHonorsOpenEndedRange() async throws {
+        // 1. Insert a track + start the server.
+        let db = try DatabaseService(inMemory: true)
+        let fixtureURL = try TestFixtures.shortMP3URL()
+        var track = Track.fixture(id: nil, fileURL: fixtureURL.absoluteString, title: "Open Range Test")
+        try db.insert(&track)
+        let trackId = try #require(track.id)
+
+        let server = StreamingServer(db: db, apiKey: Self.testAPIKey, port: 0)
+        try await server.start()
+        defer { server.stop() }
+        let port = try #require(server.actualPort)
+        let baseURL = "http://127.0.0.1:\(port)"
+        let fileURL = URL(string: "\(baseURL)/file?id=\(trackId)&token=\(Self.testAPIKey)")!
+
+        // 2. Ground-truth full file.
+        let (fullData, _) = try await URLSession.shared.data(for: URLRequest(url: fileURL))
+        let total = fullData.count
+        #expect(total > 10)
+
+        // 3. Open-ended range from byte 10.
+        var rangeReq = URLRequest(url: fileURL)
+        rangeReq.setValue("bytes=10-", forHTTPHeaderField: "Range")
+        let (rangeData, rangeResp) = try await URLSession.shared.data(for: rangeReq)
+        let rangeHTTP = try #require(rangeResp as? HTTPURLResponse)
+
+        // 4. Tail of the file, correctly described.
+        #expect(rangeHTTP.statusCode == 206)
+        #expect(rangeHTTP.value(forHTTPHeaderField: "Content-Range") == "bytes 10-\(total - 1)/\(total)")
+        #expect(rangeData.count == total - 10)
+        #expect(rangeData == fullData.subdata(in: 10..<total))
+    }
 }

MusicTests/StreamingPlaybackEndToEndTests.swift

@@ -0,0 +1,82 @@
+import Testing
+import Foundation
+import AVFoundation
+import MusicShared
+@testable import Music
+
+// End-to-end reproduction of the reported bug:
+//   "After streaming a full track, AVPlayer fails with 'Operation Stopped'
+//    and the player does NOT auto-advance to the next track."
+//
+// These tests drive the *real* StreamingPlaybackProvider against the *real*
+// StreamingServer, exactly as the app does, and assert that playing a track to
+// its natural end results in a clean finish (onTrackFinished fires, no error).
+@MainActor
+struct StreamingPlaybackEndToEndTests {
+    static let testAPIKey = "e2e-test-key"
+
+    // Spins the main run loop (where AVPlayer delivers its callbacks) until
+    // `condition` is true or `timeout` seconds elapse. Returns true if the
+    // condition was met. Polls in small slices so an async @MainActor test
+    // lets AVPlayer's main-queue observers run.
+    private func waitUntil(timeout: Double, _ condition: () -> Bool) async -> Bool {
+        let slices = Int(timeout / 0.05)
+        for _ in 0..<slices {
+            if condition() { return true }
+            try? await Task.sleep(nanoseconds: 50_000_000) // 50 ms
+        }
+        return condition()
+    }
+
+    // Reproduces the auto-advance failure at end-of-track.
+    // Steps:
+    // 1. Create an in-memory DB and insert a track pointing at a real audio
+    //    fixture, stored the way the production scanner stores it (absoluteString).
+    // 2. Start the real StreamingServer on an OS-assigned port.
+    // 3. Create the real StreamingPlaybackProvider pointed at that server.
+    // 4. Install an onTrackFinished callback that records the clean-finish signal
+    //    (this is the callback PlayerViewModel uses to advance to the next track).
+    // 5. Begin playback of the track's /file URL and let it play to the end.
+    // 6. Wait until EITHER a clean finish fires OR a playback error appears.
+    // 7. Assert: no playback error occurred AND the clean-finish callback fired.
+    //    On the current (buggy) server this fails — playback ends in an error
+    //    instead of a clean finish, so the next track never plays.
+    @Test(.timeLimit(.minutes(1)))
+    func playingTrackToEndFiresCleanFinish() async throws {
+        // 1. DB + fixture track (stored as absoluteString, like the real scanner).
+        let db = try DatabaseService(inMemory: true)
+        let fixtureURL = try TestFixtures.shortMP3URL()
+        var track = Track.fixture(id: nil, fileURL: fixtureURL.absoluteString, title: "E2E Track")
+        try db.insert(&track)
+
+        // 2. Start the real streaming server.
+        let server = StreamingServer(db: db, apiKey: Self.testAPIKey, port: 0)
+        try await server.start()
+        defer { server.stop() }
+        let port = try #require(server.actualPort)
+
+        // 3. Real provider against the real server.
+        let provider = StreamingPlaybackProvider(hostURL: "http://127.0.0.1:\(port)", apiKey: Self.testAPIKey)
+
+        // 4. Record the clean-finish signal (drives PlayerViewModel.next()).
+        var finishedCleanly = false
+        provider.onTrackFinished = { finishedCleanly = true }
+
+        // 5. Start playback of the track.
+        let url = try #require(provider.urlForTrack(track))
+        provider.play(url: url)
+
+        // 6. Wait for a terminal outcome: clean finish or error. The fixture is a
+        //    few seconds long; allow generous headroom for buffering.
+        _ = await waitUntil(timeout: 25) {
+            finishedCleanly || provider.playbackError != nil
+        }
+
+        // --- Diagnostics (printed regardless of pass/fail) ---
+        print("E2E DIAGNOSTIC -> finishedCleanly=\(finishedCleanly), playbackError=\(String(describing: provider.playbackError)), providerDuration=\(provider.duration), currentTime=\(provider.currentTime)")
+
+        // 7. A fully streamed track must end cleanly so the queue can advance.
+        #expect(provider.playbackError == nil)
+        #expect(finishedCleanly == true)
+    }
+}