feat: Reject unsupported parameters with 400 Bad Request (/v1/completions) (#4140)

Signed-off-by: Krishnan Prashanth <[email protected]>

Author: KrishnanPrash

lib/bindings/python/Cargo.lock

@@ -315,6 +315,7 @@ impl TryFrom<inference::ModelInferRequest> for NvCreateCompletionRequest {
             common: Default::default(),
             nvext: None,
             metadata: None,
+            unsupported_fields: Default::default(),
         })
     }
 }

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

@@ -1469,6 +1469,7 @@ mod tests {
             common: Default::default(),
             nvext: None,
             metadata: None,
+            unsupported_fields: Default::default(),
         };
 
         let result = validate_completion_fields_generic(&request);
@@ -1492,6 +1493,7 @@ mod tests {
             common: Default::default(),
             nvext: None,
             metadata: None,
+            unsupported_fields: Default::default(),
         };
         let result = validate_completion_fields_generic(&request);
         assert!(result.is_err());
@@ -1514,6 +1516,7 @@ mod tests {
             common: Default::default(),
             nvext: None,
             metadata: None,
+            unsupported_fields: Default::default(),
         };
         let result = validate_completion_fields_generic(&request);
         assert!(result.is_err());
@@ -1536,6 +1539,7 @@ mod tests {
             common: Default::default(),
             nvext: None,
             metadata: None,
+            unsupported_fields: Default::default(),
         };
         let result = validate_completion_fields_generic(&request);
         assert!(result.is_err());
@@ -1560,6 +1564,7 @@ mod tests {
                 .unwrap(),
             nvext: None,
             metadata: None,
+            unsupported_fields: Default::default(),
         };
         let result = validate_completion_fields_generic(&request);
         assert!(result.is_err());
@@ -1582,6 +1587,7 @@ mod tests {
             common: Default::default(),
             nvext: None,
             metadata: None,
+            unsupported_fields: Default::default(),
         };
         let result = validate_completion_fields_generic(&request);
         assert!(result.is_err());
@@ -1612,6 +1618,7 @@ mod tests {
                 "session": {"id": "session-1", "timestamp": 1640995200}
             })
             .into(),
+            unsupported_fields: Default::default(),
         };
 
         let result = validate_completion_fields_generic(&request);
@@ -1797,8 +1804,8 @@ mod tests {
     }
 
     #[test]
-    fn test_unknown_fields_rejected() {
-        // Test that all known unsupported fields are rejected and all shown in error message
+    fn test_chat_completions_unknown_fields_rejected() {
+        // Test that known unsupported fields are rejected and all shown in error message
         let json = r#"{
             "messages": [{"role": "user", "content": "Hello"}],
             "model": "test-model",
@@ -1837,4 +1844,36 @@ mod tests {
             assert!(msg.contains("chat_template_kwargs"));
         }
     }
+
+    #[test]
+    fn test_completions_unsupported_fields_rejected() {
+        // Test that known unsupported fields are rejected and all shown in error message
+        let json = r#"{
+            "model": "test-model",
+            "prompt": "Hello",
+            "add_special_tokens": true,
+            "response_format": {"type": "json_object"}
+        }"#;
+
+        let request: NvCreateCompletionRequest = serde_json::from_str(json).unwrap();
+
+        // Verify both unsupported fields were captured
+        assert!(
+            request
+                .unsupported_fields
+                .contains_key("add_special_tokens")
+        );
+        assert!(request.unsupported_fields.contains_key("response_format"));
+
+        let result = validate_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 both fields appear in error message
+            assert!(msg.contains("add_special_tokens"));
+            assert!(msg.contains("response_format"));
+        }
+    }
 }

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

@@ -37,6 +37,10 @@ pub struct NvCreateCompletionRequest {
     // metadata - passthrough parameter without restrictions
     #[serde(skip_serializing_if = "Option::is_none")]
     pub metadata: Option<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>,
 }
 
 #[derive(Serialize, Deserialize, Validate, Debug, Clone)]
@@ -372,6 +376,7 @@ impl OpenAIOutputOptionsProvider for NvCreateCompletionRequest {
 /// allowing us to validate the data.
 impl ValidateRequest for NvCreateCompletionRequest {
     fn validate(&self) -> Result<(), anyhow::Error> {
+        validate::validate_no_unsupported_fields(&self.unsupported_fields)?;
         validate::validate_model(&self.inner.model)?;
         validate::validate_prompt(&self.inner.prompt)?;
         validate::validate_suffix(self.inner.suffix.as_deref())?;

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

@@ -29,6 +29,7 @@ impl CompletionSample {
             common: Default::default(),
             nvext: None,
             metadata: None,
+            unsupported_fields: Default::default(),
         };
 
         Ok(Self {