fix(gemini): handle Gemini Files API URIs without fetching (#24922)

* fix(gemini): handle Gemini Files API URIs without fetching

Fixes #24907

When a file is uploaded via the Gemini Files API, the returned URI
(https://generativelanguage.googleapis.com/v1beta/files/...) starts
with 'https://' and hits the generic HTTPS handler in
_process_gemini_media(). That handler calls
_get_image_mime_type_from_url() which tries to fetch the URL — but
Gemini Files API URLs return 403 when accessed directly, causing:
  'Unable to determine mime type for file_id: ...'

Fix: add an early elif that matches Gemini Files API URLs and passes
them through as file_data without trying to fetch the URL. When an
explicit format is provided it's included; otherwise the Gemini API
infers the MIME type from its stored metadata.

Exactly matches the fix direction suggested by the issue reporter
(rodriciru).

* fix: anchor Gemini Files API URL check with startswith

Address greptile P2: replace `in` substring check with `startswith`
to prevent query-string injection bypass (e.g.
`https://evil.com/?ref=https://generativelanguage...`).

Also adds trailing slash to match only valid file URIs.

---------

Co-authored-by: voidborne-d <voidborne-d@users.noreply.github.com>

litellm/llms/vertex_ai/gemini/transformation.py

@@ -212,6 +212,21 @@ def _process_gemini_media(
             return _apply_gemini_metadata(
                 part, model, media_resolution_enum, video_metadata
             )
+        elif image_url.startswith(
+            "https://generativelanguage.googleapis.com/v1beta/files/"
+        ):
+            # Gemini Files API URIs — the file is already uploaded to Google's
+            # servers; pass the URI through as file_data without fetching it.
+            # These URLs return 403 when accessed directly, so we must not try
+            # to resolve their MIME type via HTTP.
+            if format:
+                file_data = FileDataType(mime_type=format, file_uri=image_url)
+            else:
+                file_data = FileDataType(file_uri=image_url)
+            part = {"file_data": file_data}
+            return _apply_gemini_3_metadata(
+                part, model, media_resolution_enum, video_metadata
+            )
         elif (
             "https://" in image_url
             and (image_type := format or _get_image_mime_type_from_url(image_url))

tests/test_litellm/llms/vertex_ai/gemini/test_vertex_ai_gemini_transformation.py

@@ -1291,6 +1291,53 @@ def test_file_data_field_order_gcs_urls():
     ), "mime_type must come before file_uri in the file_data dict"
 
 
+def test_gemini_files_api_uri_without_format():
+    """
+    Test that Gemini Files API URIs work WITHOUT an explicit format/mime_type.
+
+    When a user uploads a file via the Gemini Files API and then references it
+    by URI (https://generativelanguage.googleapis.com/v1beta/files/...),
+    the file is already on Google's servers. These URLs return 403 when
+    fetched directly, so _process_gemini_media must NOT try to resolve the
+    MIME type via HTTP.  Instead it should pass the URI through as file_data
+    and let the Gemini API resolve the type from its stored metadata.
+
+    Related issue: https://github.com/BerriAI/litellm/issues/24907
+    """
+    from litellm.llms.vertex_ai.gemini.transformation import _process_gemini_media
+
+    file_url = "https://generativelanguage.googleapis.com/v1beta/files/37eh7rsw1vfe"
+
+    # Should NOT raise — previously this hit the generic https:// handler
+    # which called _get_image_mime_type_from_url() and got a 403.
+    result = _process_gemini_media(image_url=file_url)
+
+    assert "file_data" in result
+    file_data = result["file_data"]
+    assert file_data["file_uri"] == file_url
+    # When no format is provided, mime_type should be absent so the
+    # Gemini API infers it from the stored file metadata.
+    assert "mime_type" not in file_data
+
+
+def test_gemini_files_api_uri_with_format():
+    """
+    Test that Gemini Files API URIs correctly forward an explicit format.
+
+    Related issue: https://github.com/BerriAI/litellm/issues/24907
+    """
+    from litellm.llms.vertex_ai.gemini.transformation import _process_gemini_media
+
+    file_url = "https://generativelanguage.googleapis.com/v1beta/files/n1vhxa28lyaw"
+
+    result = _process_gemini_media(image_url=file_url, format="text/plain")
+
+    assert "file_data" in result
+    file_data = result["file_data"]
+    assert file_data["file_uri"] == file_url
+    assert file_data["mime_type"] == "text/plain"
+
+
 def test_extract_file_data_with_path_object():
     """
     Test that filename is correctly extracted from Path objects for MIME type detection.