feat: Reject unsupported parameters with 400 Bad Request (#4021)

Signed-off-by: Krishnan Prashanth <kprashanth@nvidia.com>

lib/llm/src/entrypoint/input/batch.rs

@@ -229,6 +229,7 @@ async fn evaluate(
         common: Default::default(),
         nvext: None,
         chat_template_args: None,
+        unsupported_fields: Default::default(),
     };
     let mut stream = engine.generate(Context::new(req)).await?;
     let mut output = String::new();

lib/llm/src/entrypoint/input/text.rs

@@ -112,6 +112,7 @@ async fn main_loop(
             common: Default::default(),
             nvext: None,
             chat_template_args: None,
+            unsupported_fields: Default::default(),
         };
 
         // Call the model

lib/llm/src/http/service/openai.rs

@@ -1403,6 +1403,7 @@ mod tests {
             common: Default::default(),
             nvext: None,
             chat_template_args: None,
+            unsupported_fields: Default::default(),
         };
         let result = validate_chat_completion_required_fields(&request);
         assert!(result.is_err());
@@ -1431,6 +1432,7 @@ mod tests {
             common: Default::default(),
             nvext: None,
             chat_template_args: None,
+            unsupported_fields: Default::default(),
         };
         let result = validate_chat_completion_required_fields(&request);
         assert!(result.is_ok());
@@ -1451,7 +1453,7 @@ mod tests {
     // 11. Repetition Penalty: Should be a float between 0.0 and 2.0 : Done
     // 12. Logprobs: Should be a positive integer between 0 and 5 : Done
     // invalid or non existing user : Only empty string is not allowed validation is there. How can we check non-extisting user ?
-    // add_special_tokens null or invalid : Not Done
+    // Unknown fields : Done (rejected via extra_fields catch-all)
     // guided_whitespace_pattern null or invalid : Not Done
     // "response_format": { "type": "invalid_format" } : Not Done
     // "logit_bias": { "invalid_token": "not_a_number" }, : Partial Validation is already there
@@ -1638,6 +1640,7 @@ mod tests {
             common: Default::default(),
             nvext: None,
             chat_template_args: None,
+            unsupported_fields: Default::default(),
         };
 
         let result = validate_chat_completion_fields_generic(&request);
@@ -1666,6 +1669,7 @@ mod tests {
             common: Default::default(),
             nvext: None,
             chat_template_args: None,
+            unsupported_fields: Default::default(),
         };
         let result = validate_chat_completion_fields_generic(&request);
         assert!(result.is_err());
@@ -1693,6 +1697,7 @@ mod tests {
             common: Default::default(),
             nvext: None,
             chat_template_args: None,
+            unsupported_fields: Default::default(),
         };
         let result = validate_chat_completion_fields_generic(&request);
         assert!(result.is_err());
@@ -1720,6 +1725,7 @@ mod tests {
             common: Default::default(),
             nvext: None,
             chat_template_args: None,
+            unsupported_fields: Default::default(),
         };
         let result = validate_chat_completion_fields_generic(&request);
         assert!(result.is_err());
@@ -1749,6 +1755,7 @@ mod tests {
                 .unwrap(),
             nvext: None,
             chat_template_args: None,
+            unsupported_fields: Default::default(),
         };
         let result = validate_chat_completion_fields_generic(&request);
         assert!(result.is_err());
@@ -1776,6 +1783,7 @@ mod tests {
             common: Default::default(),
             nvext: None,
             chat_template_args: None,
+            unsupported_fields: Default::default(),
         };
         let result = validate_chat_completion_fields_generic(&request);
         assert!(result.is_err());
@@ -1787,4 +1795,46 @@ mod tests {
             );
         }
     }
+
+    #[test]
+    fn test_unknown_fields_rejected() {
+        // Test that all known unsupported fields are rejected and all shown in error message
+        let json = r#"{
+            "messages": [{"role": "user", "content": "Hello"}],
+            "model": "test-model",
+            "add_special_tokens": true,
+            "documents": ["doc1"],
+            "chat_template": "custom",
+            "chat_template_kwargs": {"key": "val"}
+        }"#;
+
+        let request: NvCreateChatCompletionRequest = serde_json::from_str(json).unwrap();
+
+        // Verify all unsupported fields were captured
+        assert!(
+            request
+                .unsupported_fields
+                .contains_key("add_special_tokens")
+        );
+        assert!(request.unsupported_fields.contains_key("documents"));
+        assert!(request.unsupported_fields.contains_key("chat_template"));
+        assert!(
+            request
+                .unsupported_fields
+                .contains_key("chat_template_kwargs")
+        );
+
+        let result = validate_chat_completion_fields_generic(&request);
+        assert!(result.is_err());
+        if let Err(error_response) = result {
+            assert_eq!(error_response.0, StatusCode::BAD_REQUEST);
+            let msg = &error_response.1.message;
+            assert!(msg.contains("Unsupported parameter"));
+            // Verify all fields appear in the error message
+            assert!(msg.contains("add_special_tokens"));
+            assert!(msg.contains("documents"));
+            assert!(msg.contains("chat_template"));
+            assert!(msg.contains("chat_template_kwargs"));
+        }
+    }
 }

lib/llm/src/protocols/openai/chat_completions.rs

@@ -44,6 +44,10 @@ pub struct NvCreateChatCompletionRequest {
     /// Extra args to pass to the chat template rendering context
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub chat_template_args: Option<std::collections::HashMap<String, serde_json::Value>>,
+
+    /// Catch-all for unsupported fields - checked during validation
+    #[serde(flatten, default, skip_serializing)]
+    pub unsupported_fields: std::collections::HashMap<String, serde_json::Value>,
 }
 
 /// A response structure for unary chat completion responses, embedding OpenAI's
@@ -271,6 +275,7 @@ impl OpenAIOutputOptionsProvider for NvCreateChatCompletionRequest {
 /// allowing us to validate the data.
 impl ValidateRequest for NvCreateChatCompletionRequest {
     fn validate(&self) -> Result<(), anyhow::Error> {
+        validate::validate_no_unsupported_fields(&self.unsupported_fields)?;
         validate::validate_messages(&self.inner.messages)?;
         validate::validate_model(&self.inner.model)?;
         // none for store

lib/llm/src/protocols/openai/chat_completions/delta.rs

@@ -393,6 +393,7 @@ mod tests {
             common: Default::default(),
             nvext: None,
             chat_template_args: None,
+            unsupported_fields: Default::default(),
         }
     }
 

lib/llm/src/protocols/openai/responses.rs

@@ -189,6 +189,7 @@ impl TryFrom<NvCreateResponse> for NvCreateChatCompletionRequest {
             common: Default::default(),
             nvext: resp.nvext,
             chat_template_args: None,
+            unsupported_fields: Default::default(),
         })
     }
 }

lib/llm/src/protocols/openai/validate.rs

@@ -96,6 +96,20 @@ pub const MAX_REPETITION_PENALTY: f32 = 2.0;
 // Shared Fields
 //
 
+/// Validates that no unsupported fields are present in the request
+pub fn validate_no_unsupported_fields(
+    unsupported_fields: &std::collections::HashMap<String, serde_json::Value>,
+) -> Result<(), anyhow::Error> {
+    if !unsupported_fields.is_empty() {
+        let fields: Vec<_> = unsupported_fields
+            .keys()
+            .map(|s| format!("`{}`", s))
+            .collect();
+        anyhow::bail!("Unsupported parameter(s): {}", fields.join(", "));
+    }
+    Ok(())
+}
+
 /// Validates the temperature parameter
 pub fn validate_temperature(temperature: Option<f32>) -> Result<(), anyhow::Error> {
     if let Some(temp) = temperature

lib/llm/tests/http-service.rs

@@ -770,6 +770,7 @@ async fn test_nv_custom_client() {
         common: Default::default(),
         nvext: None,
         chat_template_args: None,
+        unsupported_fields: Default::default(),
     };
 
     let result = nv_custom_client.chat_stream(request).await;
@@ -810,6 +811,7 @@ async fn test_nv_custom_client() {
         common: Default::default(),
         nvext: None,
         chat_template_args: None,
+        unsupported_fields: Default::default(),
     };
 
     let result = nv_custom_client.chat_stream(request).await;
@@ -851,6 +853,7 @@ async fn test_nv_custom_client() {
         common: Default::default(),
         nvext: None,
         chat_template_args: None,
+        unsupported_fields: Default::default(),
     };
 
     let result = nv_custom_client

lib/llm/tests/parallel_tool_call_integration.rs

@@ -91,6 +91,7 @@ fn create_mock_chat_completion_request() -> NvCreateChatCompletionRequest {
         common: CommonExt::default(),
         nvext: None,
         chat_template_args: None,
+        unsupported_fields: Default::default(),
     }
 }
 

lib/llm/tests/preprocessor.rs

@@ -272,6 +272,7 @@ impl Request {
             common: Default::default(),
             nvext: None,
             chat_template_args: None,
+            unsupported_fields: Default::default(),
         }
     }
 }

lib/llm/tests/test_common_ext.rs

@@ -68,6 +68,7 @@ fn test_sampling_parameters_include_stop_str_in_output_extraction() {
             .unwrap(),
         nvext: None,
         chat_template_args: None,
+        unsupported_fields: Default::default(),
     };
 
     let sampling = request.extract_sampling_options().unwrap();
@@ -296,6 +297,7 @@ fn test_serialization_preserves_structure() {
             ..Default::default()
         }),
         chat_template_args: None,
+        unsupported_fields: Default::default(),
     };
 
     let json = serde_json::to_value(&request).unwrap();
@@ -346,6 +348,7 @@ fn test_sampling_parameters_extraction() {
             .unwrap(),
         nvext: None,
         chat_template_args: None,
+        unsupported_fields: Default::default(),
     };
 
     let sampling_options = request.extract_sampling_options().unwrap();

lib/llm/tests/test_streaming_usage.rs

@@ -150,6 +150,7 @@ fn create_chat_request(include_usage: Option<bool>) -> NvCreateChatCompletionReq
         common: Default::default(),
         nvext: None,
         chat_template_args: None,
+        unsupported_fields: Default::default(),
     }
 }
 
@@ -329,6 +330,7 @@ fn create_nonstreaming_chat_request() -> NvCreateChatCompletionRequest {
         common: Default::default(),
         nvext: None,
         chat_template_args: None,
+        unsupported_fields: Default::default(),
     }
 }