raop: honor relative seeks in streaming audio sources

docs/development/stream.md

@@ -171,6 +171,10 @@ be passed instead of a file path:
 await stream.stream_file("https://foo.bar/test.mp3")
 ```
 
+Metadata (title, artist, etc.) is extracted from the first ~32 KB of the HTTP
+response before playback begins.  Sources smaller than that window return metadata
+as usual; larger sources return empty metadata without blocking playback.
+
 #### File Compatibility
 
 It is possible to verify if a file is supported programmatically using

pyatv/protocols/raop/audio_source.py

@@ -130,6 +130,10 @@ def __init__(self, reader: io.BufferedIOBase, buffer: SemiSeekableBuffer) -> Non
         self.reader: io.BufferedIOBase = reader
         self.buffer: SemiSeekableBuffer = buffer
         self.name = "stream"
+        # Tracks the logical position when seek(0, SEEK_END) parks the cursor
+        # past the last buffer index (which SemiSeekableBuffer cannot represent).
+        # Cleared by every other seek so that tell() stays consistent.
+        self._virtual_position: Optional[int] = None
 
     def read(self, size=-1):
         """Read bytes from stream."""
@@ -147,12 +151,38 @@ def read(self, size=-1):
 
     def seek(self, pos, origin=io.SEEK_SET):
         """Seek to position in stream."""
+        self._virtual_position = None
         if origin == io.SEEK_SET:
-            self.buffer.seek(pos)
+            if not self.buffer.seek(pos):
+                raise OSError(f"cannot seek to absolute position {pos}")
+        elif origin == io.SEEK_CUR:
+            absolute = self.buffer.position + pos
+            if not self.buffer.seek(absolute):
+                raise OSError(f"cannot seek to position {absolute} (SEEK_CUR)")
+        elif origin == io.SEEK_END:
+            # Total bytes currently held in the buffer.  For a small stream that
+            # has been fully downloaded this equals the file size; for a larger
+            # stream it is however many bytes have been buffered so far.
+            total = self.buffer.position + self.buffer.size
+            absolute = total + pos
+            if absolute > total:
+                raise OSError(f"cannot seek past end of buffered data (pos={pos})")
+            if absolute == total:
+                # End-of-stream is not a valid buffer position (the buffer holds
+                # indices 0..N-1).  Park a virtual position so tell() reflects
+                # the correct offset; the next seek will clear it.
+                self._virtual_position = absolute
+                return absolute
+            if not self.buffer.seek(absolute):
+                raise OSError(f"cannot seek to position {absolute} (SEEK_END)")
+        else:
+            raise OSError(f"seek whence={origin} is not supported on streaming source")
         return self.buffer.position
 
     def tell(self):
         """Return current position in stream."""
+        if self._virtual_position is not None:
+            return self._virtual_position
         return self.buffer.position
 
     def seekable(self):
@@ -226,19 +256,49 @@ def __init__(
         self.buffer = buffer
         # Medafile uses this in error messages, so it helps for debugging
         self.name = name
+        # Tracks the logical position when seek(0, SEEK_END) parks the cursor
+        # past the last buffer index (which SemiSeekableBuffer cannot represent).
+        # Cleared by every other seek so that tell() stays consistent.
+        self._virtual_position: Optional[int] = None
 
     def read(self, size=-1):
         """Read bytes from stream."""
         return self.source.read(size)
 
     def seek(self, pos, origin=io.SEEK_SET):
         """Seek to position in stream."""
+        self._virtual_position = None
         if origin == io.SEEK_SET:
-            self.source.seek(pos, miniaudio.SeekOrigin.START)
+            if not self.source.seek(pos, miniaudio.SeekOrigin.START):
+                raise OSError(f"cannot seek to absolute position {pos}")
+        elif origin == io.SEEK_CUR:
+            absolute = self.buffer.position + pos
+            if not self.source.seek(absolute, miniaudio.SeekOrigin.START):
+                raise OSError(f"cannot seek to position {absolute} (SEEK_CUR)")
+        elif origin == io.SEEK_END:
+            # Total bytes currently held in the buffer.  For a small stream that
+            # has been fully downloaded this equals the file size; for a larger
+            # stream it is however many bytes have been buffered so far.
+            total = self.buffer.position + self.buffer.size
+            absolute = total + pos
+            if absolute > total:
+                raise OSError(f"cannot seek past end of buffered data (pos={pos})")
+            if absolute == total:
+                # End-of-stream is not a valid buffer position (the buffer holds
+                # indices 0..N-1).  Park a virtual position so tell() reflects
+                # the correct offset; the next seek will clear it.
+                self._virtual_position = absolute
+                return absolute
+            if not self.source.seek(absolute, miniaudio.SeekOrigin.START):
+                raise OSError(f"cannot seek to position {absolute} (SEEK_END)")
+        else:
+            raise OSError(f"seek whence={origin} is not supported on streaming source")
         return self.buffer.position
 
     def tell(self):
         """Return current position in stream."""
+        if self._virtual_position is not None:
+            return self._virtual_position
         return self.buffer.position
 
     def seekable(self):
@@ -263,11 +323,14 @@ async def get_buffered_io_metadata(buffer: io.BufferedIOBase) -> MediaMetadata:
     try:
         return await get_metadata(buffer)
     except Exception:
-        logging.exception("Failed to parse metadata")
+        _LOGGER.exception("Failed to parse metadata")
     finally:
-        buffer.seek(0)
-        if buffer.seek(before) != before:
-            logging.warning("Failed to restore position to %d", before)
+        try:
+            buffer.seek(0)
+            if buffer.seek(before) != before:
+                _LOGGER.warning("Failed to restore position to %d", before)
+        except OSError:
+            _LOGGER.warning("Failed to restore position to %d", before)
 
     return EMPTY_METADATA