fix: Remove redundant format field from LiteLLM content objects

LiteLLM providers can extract the MIME type from the data URI. Removing the separate `format` field avoids redundancy and potential issues with backends that may reject requests containing this field.

Close #2017

Co-authored-by: George Weale <gweale@google.com>
PiperOrigin-RevId: 828014286

src/google/adk/models/lite_llm.py

@@ -314,33 +314,28 @@ def _get_content(
     ):
       base64_string = base64.b64encode(part.inline_data.data).decode("utf-8")
       data_uri = f"data:{part.inline_data.mime_type};base64,{base64_string}"
+      # LiteLLM providers extract the MIME type from the data URI; avoid
+      # passing a separate `format` field that some backends reject.
 
       if part.inline_data.mime_type.startswith("image"):
-        # Use full MIME type (e.g., "image/png") for providers that validate it
-        format_type = part.inline_data.mime_type
         content_objects.append({
             "type": "image_url",
-            "image_url": {"url": data_uri, "format": format_type},
+            "image_url": {"url": data_uri},
         })
       elif part.inline_data.mime_type.startswith("video"):
-        # Use full MIME type (e.g., "video/mp4") for providers that validate it
-        format_type = part.inline_data.mime_type
         content_objects.append({
             "type": "video_url",
-            "video_url": {"url": data_uri, "format": format_type},
+            "video_url": {"url": data_uri},
         })
       elif part.inline_data.mime_type.startswith("audio"):
-        # Use full MIME type (e.g., "audio/mpeg") for providers that validate it
-        format_type = part.inline_data.mime_type
         content_objects.append({
             "type": "audio_url",
-            "audio_url": {"url": data_uri, "format": format_type},
+            "audio_url": {"url": data_uri},
         })
       elif part.inline_data.mime_type == "application/pdf":
-        format_type = part.inline_data.mime_type
         content_objects.append({
             "type": "file",
-            "file": {"file_data": data_uri, "format": format_type},
+            "file": {"file_data": data_uri},
         })
       else:
         raise ValueError("LiteLlm(BaseLlm) does not support this content part.")
@@ -348,8 +343,6 @@ def _get_content(
       file_object: ChatCompletionFileUrlObject = {
           "file_id": part.file_data.file_uri,
       }
-      if part.file_data.mime_type:
-        file_object["format"] = part.file_data.mime_type
       content_objects.append({
           "type": "file",
           "file": file_object,

tests/unittests/models/test_litellm.py

@@ -1107,7 +1107,7 @@ def test_content_to_message_param_user_message_with_file_uri():
   assert message["content"][0]["text"] == "Summarize this file."
   assert message["content"][1]["type"] == "file"
   assert message["content"][1]["file"]["file_id"] == "gs://bucket/document.pdf"
-  assert message["content"][1]["file"]["format"] == "application/pdf"
+  assert "format" not in message["content"][1]["file"]
 
 
 def test_content_to_message_param_user_message_file_uri_only():
@@ -1126,7 +1126,7 @@ def test_content_to_message_param_user_message_file_uri_only():
   assert isinstance(message["content"], list)
   assert message["content"][0]["type"] == "file"
   assert message["content"][0]["file"]["file_id"] == "gs://bucket/only.pdf"
-  assert message["content"][0]["file"]["format"] == "application/pdf"
+  assert "format" not in message["content"][0]["file"]
 
 
 def test_content_to_message_param_multi_part_function_response():
@@ -1278,7 +1278,7 @@ def test_get_content_image():
       content[0]["image_url"]["url"]
       == "data:image/png;base64,dGVzdF9pbWFnZV9kYXRh"
   )
-  assert content[0]["image_url"]["format"] == "image/png"
+  assert "format" not in content[0]["image_url"]
 
 
 def test_get_content_video():
@@ -1291,7 +1291,7 @@ def test_get_content_video():
       content[0]["video_url"]["url"]
       == "data:video/mp4;base64,dGVzdF92aWRlb19kYXRh"
   )
-  assert content[0]["video_url"]["format"] == "video/mp4"
+  assert "format" not in content[0]["video_url"]
 
 
 def test_get_content_pdf():
@@ -1304,7 +1304,7 @@ def test_get_content_pdf():
       content[0]["file"]["file_data"]
       == "data:application/pdf;base64,dGVzdF9wZGZfZGF0YQ=="
   )
-  assert content[0]["file"]["format"] == "application/pdf"
+  assert "format" not in content[0]["file"]
 
 
 def test_get_content_file_uri():
@@ -1317,7 +1317,7 @@ def test_get_content_file_uri():
   content = _get_content(parts)
   assert content[0]["type"] == "file"
   assert content[0]["file"]["file_id"] == "gs://bucket/document.pdf"
-  assert content[0]["file"]["format"] == "application/pdf"
+  assert "format" not in content[0]["file"]
 
 
 def test_get_content_audio():
@@ -1330,7 +1330,7 @@ def test_get_content_audio():
       content[0]["audio_url"]["url"]
       == "data:audio/mpeg;base64,dGVzdF9hdWRpb19kYXRh"
   )
-  assert content[0]["audio_url"]["format"] == "audio/mpeg"
+  assert "format" not in content[0]["audio_url"]
 
 
 def test_to_litellm_role():