[olejnjak]

Problem

When a source has sideloaded subtitles, the connector rewrites the HLS playlists. If the master
playlist lists variant playlists as relative URIs with a query string, playback fails.

Example of a variant URI in the master playlist:

video=391132.m3u8?hdntl=<token>

The connector requests it as:

https://example.com/path/video=391132.m3u8%3Fhdntl=<token>

The ? is percent-encoded, so the query becomes part of the path. The CDN returns HTTP 400 for
each variant playlist, and THEOplayer reports a network error (6400). The same stream plays
correctly without sideloaded subtitles.

Cause

PlaylistParser.getFullURL(from:) builds the absolute URL of a relative URI with
manifestURL.deletingLastPathComponent().appendingPathComponent(path).
appendingPathComponent treats its whole argument as a path component, so it percent-encodes ?
to %3F.

Fix

Resolve a relative URI against the manifest URL with URL(string:relativeTo:). This keeps the
query string as a query and also handles ../ and subdirectory paths. If that initializer
returns nil, the code falls back to the previous appendingPathComponent behavior. Absolute
URIs are not affected.

A relative URI without its own query no longer gets the playlist's query string. The previous
code added it as a side effect of appendingPathComponent. The new result follows RFC 3986
section 5.2.2, which RFC 8216bis section 4.1 refers to for resolving relative URIs, and matches
AVPlayer's own resolution. A stream that needs the playlist's query on other URIs can use
EXT-X-DEFINE with QUERYPARAM.

Tests

Added PlaylistParserTests with these cases, resolved against
https://cdn.example.com/vod/movie/index.m3u8?token=abc:

Relative URI	Result
video=391132.m3u8?hdntl=…	…/movie/video=391132.m3u8?hdntl=…
keyframes/video.m3u8?accountId=1	…/movie/keyframes/video.m3u8?accountId=1
../other/video.m3u8?accountId=1	…/vod/other/video.m3u8?accountId=1
video.m3u8	…/movie/video.m3u8
https://other.example.com/video.m3u8?token=xyz (absolute)	unchanged

All five pass with the fix. With the previous getFullURL, the four relative cases fail.

Also checked on an iOS device with an HLS VOD stream whose master playlist has relative variant
URIs with a signed hdntl query, plus sideloaded WebVTT subtitles. Before the fix every variant
playlist request returned HTTP 400 and playback failed. After the fix the variant playlists load
with their query string, and the stream plays.

Changelog

Added an entry under Unreleased → Fixed → SideloadedSubtitle.

[ceyhun-o]

Hi @olejnjak,

Thank you very much for your PR!

This is indeed fixing a real problem with signed playlists URLs being broken, but it seems to introduce an edge case where ? in file names are escaped.

While reviewing this PR, we also found 3 other edge cases where some encoding/decoding issues happen. Instead of merging this PR, we will work on a more robust solution that fixes all the cases we have found so that we fix the root cause and not a specific case.

Would you please create a ticket on our Service Desk in the meantime with a source description that reproduced an issue on your end so that we can also use it to test the fix?