pmomusic/BROWSEMETADATA_FIX.md

BrowseMetadata Fix for Radio Paradise - PMO Music

Date: 2025-11-27 Issue: gupnp-av-cp failed to get metadata for live streams and history containers

Problem

UPnP clients (like gupnp-av-cp) were unable to get metadata for:

• Live stream items (e.g., radio-paradise:channel:mellow:live)
• History containers (e.g., radio-paradise:channel:mellow:history)

Error:

Failed to get metadata for 'radio-paradise:channel:mellow:live'
Failed to get metadata for 'radio-paradise:channel:mellow:history'

Root Cause

The UPnP ContentDirectory service has two browse modes:

• BrowseMetadata: Get metadata for a specific object (item or container)
• BrowseDirectChildren: Get the children of a container

The ContentHandler::browse_metadata() was calling source.browse() for all objects, but:

1. The MusicSource::browse() trait method is designed to return children, not object metadata
2. For leaf items (LiveStream, HistoryTrack), RadioParadiseSource::browse() was rejecting them as "cannot be browsed"
3. The trait doesn't provide a way to distinguish between BrowseMetadata and BrowseDirectChildren requests

Solution

1. Modified ContentHandler (pmomediaserver/src/content_handler.rs)

• browse_metadata() now tries get_item() first for leaf items before falling back to browse()
• This allows proper metadata retrieval for items (LiveStream, HistoryTrack)

2. Modified RadioParadiseSource (pmoparadise/src/source.rs)

For LiveStream items:

• browse() now returns BrowseResult::Items([live_item]) with the item's metadata
• This supports both BrowseMetadata (via ContentHandler) and direct browse calls

For HistoryTrack items:

• browse() now returns BrowseResult::Items([track]) using get_item() internally
• Properly retrieves track metadata from the history playlist

For History containers:

• browse() now returns BrowseResult::Mixed { containers: [history_container], items: [tracks] }
• Provides both container metadata and its children in one result

3. Added Container Filtering (pmomediaserver/src/content_handler.rs)

• browse_result_to_didl() now filters out containers that match the browsed object_id
• Prevents containers from appearing as children of themselves
• For History: BrowseDirectChildren returns only tracks, not the container

Files Modified

1. ✅ pmomediaserver/src/content_handler.rs

   • Lines 120-135: Try get_item() first in browse_metadata()
   • Lines 290-310: Added object_id parameter and container filtering in browse_result_to_didl()
   • Lines 212, 286: Updated callers to pass object_id

2. ✅ pmoparadise/src/source.rs

   • Lines 345-369: Modified History browse to return Mixed (container + items)
   • Lines 371-377: Modified LiveStream browse to return item metadata
   • Lines 379-383: Modified HistoryTrack browse to return track metadata

Validation

Live Stream Metadata ✅

curl -X POST -H "SOAPAction: ..." BrowseMetadata radio-paradise:channel:mellow:live

Returns:

<item id="radio-paradise:channel:mellow:live" parentID="radio-paradise:channel:mellow">
  <dc:title>Unknown Title</dc:title>
  <upnp:class>object.item.audioItem.audioBroadcast</upnp:class>
  <res protocolInfo="http-get:*:audio/flac:*">http://.../radioparadise/stream/mellow/flac</res>
</item>

History Container Metadata ✅

curl -X POST -H "SOAPAction: ..." BrowseMetadata radio-paradise:channel:mellow:history

Returns:

<container id="radio-paradise:channel:mellow:history" parentID="radio-paradise:channel:mellow">
  <dc:title>Mellow Mix - History</dc:title>
  <upnp:class>object.container.playlistContainer</upnp:class>
</container>

History Children ✅

curl -X POST -H "SOAPAction: ..." BrowseDirectChildren radio-paradise:channel:mellow:history

Returns only track items (not the container itself)

Design Notes

This solution works around a fundamental limitation in the MusicSource trait:

• The browse() method doesn't receive the browse_flag parameter
• It can't distinguish between BrowseMetadata and BrowseDirectChildren
• We use get_item() for items and browse() for containers
• Container filtering ensures correct BrowseDirectChildren behavior

Testing Checklist

• BrowseMetadata works for LiveStream items
• BrowseMetadata works for History containers
• BrowseDirectChildren works for History (returns only tracks)
• Container filtering prevents self-reference
• Test with BubbleUPnP (user to verify)
• Test with gupnp-av-cp (user to verify)

References

• Original issue report: UPNP_FIX_SUMMARY.md
• UPnP AV Architecture: https://openconnectivity.org/developer/specifications/upnp-resources/upnp/