From e4a87f2afea87962533634403bb08488877ccf06 Mon Sep 17 00:00:00 2001
From: Aman Gupta <aman07112006@gmail.com>
Date: Sun, 26 Jul 2026 23:45:08 +0530
Subject: [PATCH] fix : canonical mime type mapping from formats to remove
 inconsistency #4627 (#4628)

* fix : canonical mime type mapping from formats to remove inconsistency

* Apply ruff format to _get_mime_type

---------

Co-authored-by: Jeremiah Lowin <153965+jlowin@users.noreply.github.com>
---
 fastmcp_slim/fastmcp/utilities/types.py | 21 ++++++++++++---------
 tests/utilities/test_types.py           | 19 +++++++++++++++++--
 2 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/fastmcp_slim/fastmcp/utilities/types.py b/fastmcp_slim/fastmcp/utilities/types.py
index 47d132e63..ea2024d85 100644
--- a/fastmcp_slim/fastmcp/utilities/types.py
+++ b/fastmcp_slim/fastmcp/utilities/types.py
@@ -335,18 +335,21 @@ class Audio:
 
     def _get_mime_type(self) -> str:
         """Get MIME type from format or guess from file extension."""
+        mapping = {
+            "wav": "audio/wav",
+            "mp3": "audio/mpeg",
+            "ogg": "audio/ogg",
+            "m4a": "audio/mp4",
+            "flac": "audio/flac",
+        }
+
         if self._format:
-            return f"audio/{self._format.lower()}"
+            return mapping.get(self._format.lower(), f"audio/{self._format.lower()}")
 
         if self.path:
-            suffix = self.path.suffix.lower()
-            return {
-                ".wav": "audio/wav",
-                ".mp3": "audio/mpeg",
-                ".ogg": "audio/ogg",
-                ".m4a": "audio/mp4",
-                ".flac": "audio/flac",
-            }.get(suffix, "application/octet-stream")
+            return mapping.get(
+                self.path.suffix.lower().lstrip("."), "application/octet-stream"
+            )
         return "audio/wav"  # default for raw binary data
 
     def to_audio_content(
diff --git a/tests/utilities/test_types.py b/tests/utilities/test_types.py
index 85aa8c2be..5ad8d16f7 100644
--- a/tests/utilities/test_types.py
+++ b/tests/utilities/test_types.py
@@ -282,10 +282,25 @@ class TestAudio:
         assert audio.data == b"test"
         assert audio._mime_type == "audio/wav"  # Default for raw data
 
+    def test_mime_type_from_format(self):
+        """Test MIME type normalization from audio format."""
+
+        expected = {
+            "wav": "audio/wav",
+            "mp3": "audio/mpeg",
+            "ogg": "audio/ogg",
+            "m4a": "audio/mp4",
+            "flac": "audio/flac",
+        }
+
+        for fmt, mime in expected.items():
+            audio = Audio(data=b"test", format=fmt)
+            assert audio._mime_type == mime
+
     def test_audio_initialization_with_format(self):
         """Test audio initialization with a specific format."""
         audio = Audio(data=b"test", format="mp3")
-        assert audio._mime_type == "audio/mp3"
+        assert audio._mime_type == "audio/mpeg"
 
     def test_missing_data_and_path_raises_error(self):
         """Test that error is raised when neither path nor data is provided."""
@@ -335,7 +350,7 @@ class TestAudio:
         content = audio.to_audio_content()
 
         assert content.type == "audio"
-        assert content.mime_type == "audio/mp3"
+        assert content.mime_type == "audio/mpeg"
         assert content.data == base64.b64encode(test_data).decode()
 
     def test_to_audio_content_error(self, monkeypatch):