fix(mcpserver): normalize Image and Audio format to registered MIME types

Closes #3585

Author: MustafaKemal0146

src/mcp/server/mcpserver/utilities/types.py

@@ -5,6 +5,23 @@
 
 from mcp_types import AudioContent, ImageContent
 
+IMAGE_MIME_TYPES: dict[str, str] = {
+    "png": "image/png",
+    "jpg": "image/jpeg",
+    "jpeg": "image/jpeg",
+    "gif": "image/gif",
+    "webp": "image/webp",
+}
+
+AUDIO_MIME_TYPES: dict[str, str] = {
+    "wav": "audio/wav",
+    "mp3": "audio/mpeg",
+    "ogg": "audio/ogg",
+    "flac": "audio/flac",
+    "aac": "audio/aac",
+    "m4a": "audio/mp4",
+}
+
 
 class Image:
     """Helper class for returning images from tools."""
@@ -28,17 +45,12 @@ def __init__(
     def _get_mime_type(self) -> str:
         """Get MIME type from format or guess from file extension."""
         if self._format:
-            return f"image/{self._format.lower()}"
+            fmt = self._format.lower().lstrip(".")
+            return IMAGE_MIME_TYPES.get(fmt, f"image/{fmt}")
 
         if self.path:
-            suffix = self.path.suffix.lower()
-            return {
-                ".png": "image/png",
-                ".jpg": "image/jpeg",
-                ".jpeg": "image/jpeg",
-                ".gif": "image/gif",
-                ".webp": "image/webp",
-            }.get(suffix, "application/octet-stream")
+            suffix = self.path.suffix.lower().lstrip(".")
+            return IMAGE_MIME_TYPES.get(suffix, "application/octet-stream")
         return "image/png"  # default for raw binary data
 
     def to_image_content(self) -> ImageContent:
@@ -74,18 +86,12 @@ def __init__(
     def _get_mime_type(self) -> str:
         """Get MIME type from format or guess from file extension."""
         if self._format:
-            return f"audio/{self._format.lower()}"
+            fmt = self._format.lower().lstrip(".")
+            return AUDIO_MIME_TYPES.get(fmt, f"audio/{fmt}")
 
         if self.path:
-            suffix = self.path.suffix.lower()
-            return {
-                ".wav": "audio/wav",
-                ".mp3": "audio/mpeg",
-                ".ogg": "audio/ogg",
-                ".flac": "audio/flac",
-                ".aac": "audio/aac",
-                ".m4a": "audio/mp4",
-            }.get(suffix, "application/octet-stream")
+            suffix = self.path.suffix.lower().lstrip(".")
+            return AUDIO_MIME_TYPES.get(suffix, "application/octet-stream")
         return "audio/wav"  # default for raw binary data
 
     def to_audio_content(self) -> AudioContent:

tests/server/mcpserver/test_media_types.py

@@ -0,0 +1,89 @@
+from pathlib import Path
+
+import pytest
+
+from mcp.server.mcpserver import Audio, Image
+
+
+@pytest.mark.parametrize(
+    ("format_val", "expected_mime"),
+    [
+        ("jpg", "image/jpeg"),
+        ("jpeg", "image/jpeg"),
+        ("png", "image/png"),
+        ("gif", "image/gif"),
+        ("webp", "image/webp"),
+        ("bmp", "image/bmp"),
+        (".jpg", "image/jpeg"),
+        ("JPG", "image/jpeg"),
+    ],
+)
+def test_image_format_mime_types(format_val: str, expected_mime: str) -> None:
+    img = Image(data=b"\x00", format=format_val)
+    assert img.to_image_content().mime_type == expected_mime
+
+
+@pytest.mark.parametrize(
+    ("filename", "expected_mime"),
+    [
+        ("chart.jpg", "image/jpeg"),
+        ("chart.jpeg", "image/jpeg"),
+        ("chart.png", "image/png"),
+        ("chart.gif", "image/gif"),
+        ("chart.webp", "image/webp"),
+        ("chart.unknown", "application/octet-stream"),
+    ],
+)
+def test_image_path_mime_types(filename: str, expected_mime: str, tmp_path: Path) -> None:
+    file_path = tmp_path / filename
+    file_path.write_bytes(b"\x00")
+    img = Image(path=file_path)
+    assert img.to_image_content().mime_type == expected_mime
+
+
+def test_image_raw_data_default_mime_type() -> None:
+    img = Image(data=b"\x00")
+    assert img.to_image_content().mime_type == "image/png"
+
+
+@pytest.mark.parametrize(
+    ("format_val", "expected_mime"),
+    [
+        ("mp3", "audio/mpeg"),
+        ("m4a", "audio/mp4"),
+        ("wav", "audio/wav"),
+        ("ogg", "audio/ogg"),
+        ("flac", "audio/flac"),
+        ("aac", "audio/aac"),
+        ("opus", "audio/opus"),
+        (".mp3", "audio/mpeg"),
+        ("MP3", "audio/mpeg"),
+    ],
+)
+def test_audio_format_mime_types(format_val: str, expected_mime: str) -> None:
+    audio = Audio(data=b"\x00", format=format_val)
+    assert audio.to_audio_content().mime_type == expected_mime
+
+
+@pytest.mark.parametrize(
+    ("filename", "expected_mime"),
+    [
+        ("chime.mp3", "audio/mpeg"),
+        ("chime.m4a", "audio/mp4"),
+        ("chime.wav", "audio/wav"),
+        ("chime.ogg", "audio/ogg"),
+        ("chime.flac", "audio/flac"),
+        ("chime.aac", "audio/aac"),
+        ("chime.unknown", "application/octet-stream"),
+    ],
+)
+def test_audio_path_mime_types(filename: str, expected_mime: str, tmp_path: Path) -> None:
+    file_path = tmp_path / filename
+    file_path.write_bytes(b"\x00")
+    audio = Audio(path=file_path)
+    assert audio.to_audio_content().mime_type == expected_mime
+
+
+def test_audio_raw_data_default_mime_type() -> None:
+    audio = Audio(data=b"\x00")
+    assert audio.to_audio_content().mime_type == "audio/wav"