[router] Function call support for openai router Responses API (#12386)

.github/workflows/pr-test-rust.yml

@@ -97,6 +97,7 @@ jobs:
         run: |
           source "$HOME/.cargo/env"
           cd sgl-router/
+          rustup component add clippy
           cargo clippy --all-targets --all-features -- -D warnings
 
       - name: Run fmt

scripts/ci/ci_install_rust.sh

@@ -11,7 +11,7 @@ else
 fi
 
 # Install rustup (Rust installer and version manager)
-curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
+curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --default-toolchain 1.90
 
 
 # Follow the installation prompts, then reload your shell

sgl-router/src/data_connector/core.rs

@@ -268,7 +268,7 @@ pub fn make_item_id(item_type: &str) -> ConversationItemId {
         "reasoning" => "rs".to_string(),
         "mcp_call" => "mcp".to_string(),
         "mcp_list_tools" => "mcpl".to_string(),
-        "function_tool_call" => "ftc".to_string(),
+        "function_call" => "fc".to_string(),
         other => {
             // Fallback: first 3 letters of type or "itm"
             let mut p = other.chars().take(3).collect::<String>();

sgl-router/src/protocols/responses.rs

@@ -9,7 +9,7 @@ use validator::Validate;
 
 // Import shared types from common module
 use super::common::{
-    default_model, default_true, ChatLogProbs, GenerationRequest, PromptTokenUsageInfo,
+    default_model, default_true, ChatLogProbs, Function, GenerationRequest, PromptTokenUsageInfo,
     StringOrArray, ToolChoice, UsageInfo,
 };
 
@@ -22,8 +22,10 @@ pub struct ResponseTool {
     #[serde(rename = "type")]
     pub r#type: ResponseToolType,
     // Function tool fields (used when type == "function")
+    // In Responses API, function fields are flattened at the top level
+    #[serde(flatten)]
     #[serde(skip_serializing_if = "Option::is_none")]
-    pub function: Option<crate::protocols::common::Function>,
+    pub function: Option<Function>,
     // MCP-specific fields (used when type == "mcp")
     #[serde(skip_serializing_if = "Option::is_none")]
     pub server_url: Option<String>,
@@ -123,15 +125,16 @@ pub enum ResponseInputOutputItem {
     #[serde(rename = "reasoning")]
     Reasoning {
         id: String,
-        #[serde(skip_serializing_if = "Vec::is_empty")]
         summary: Vec<String>,
+        #[serde(skip_serializing_if = "Vec::is_empty")]
         content: Vec<ResponseReasoningContent>,
         #[serde(skip_serializing_if = "Option::is_none")]
         status: Option<String>,
     },
-    #[serde(rename = "function_tool_call")]
+    #[serde(rename = "function_call")]
     FunctionToolCall {
         id: String,
+        call_id: String,
         name: String,
         arguments: String,
         #[serde(skip_serializing_if = "Option::is_none")]
@@ -141,6 +144,7 @@ pub enum ResponseInputOutputItem {
     },
     #[serde(rename = "function_call_output")]
     FunctionCallOutput {
+        id: Option<String>,
         call_id: String,
         output: String,
         #[serde(skip_serializing_if = "Option::is_none")]
@@ -207,15 +211,15 @@ pub enum ResponseOutputItem {
     #[serde(rename = "reasoning")]
     Reasoning {
         id: String,
-        #[serde(skip_serializing_if = "Vec::is_empty")]
         summary: Vec<String>,
         content: Vec<ResponseReasoningContent>,
         #[serde(skip_serializing_if = "Option::is_none")]
         status: Option<String>,
     },
-    #[serde(rename = "function_tool_call")]
+    #[serde(rename = "function_call")]
     FunctionToolCall {
         id: String,
+        call_id: String,
         name: String,
         arguments: String,
         #[serde(skip_serializing_if = "Option::is_none")]
@@ -925,6 +929,7 @@ impl ResponseOutputItem {
     /// Create a new function tool call output item
     pub fn new_function_tool_call(
         id: String,
+        call_id: String,
         name: String,
         arguments: String,
         output: Option<String>,
@@ -932,6 +937,7 @@ impl ResponseOutputItem {
     ) -> Self {
         Self::FunctionToolCall {
             id,
+            call_id,
             name,
             arguments,
             output,

sgl-router/src/routers/grpc/harmony/responses.rs

@@ -912,6 +912,7 @@ fn build_next_request_with_tools(
     for tool_call in tool_calls {
         items.push(ResponseInputOutputItem::FunctionToolCall {
             id: tool_call.id.clone(),
+            call_id: tool_call.id.clone(),
             name: tool_call.function.name.clone(),
             arguments: tool_call
                 .function

sgl-router/src/routers/grpc/responses/conversions.rs

@@ -304,6 +304,7 @@ pub fn chat_to_responses(
         for tool_call in tool_calls {
             output.push(ResponseOutputItem::FunctionToolCall {
                 id: tool_call.id.clone(),
+                call_id: tool_call.id.clone(),
                 name: tool_call.function.name.clone(),
                 arguments: tool_call.function.arguments.clone().unwrap_or_default(),
                 output: None, // Tool hasn't been executed yet

sgl-router/src/routers/grpc/responses/handlers.rs

@@ -721,6 +721,7 @@ impl StreamingResponseAccumulator {
                     while self.tool_calls.len() <= index {
                         self.tool_calls.push(ResponseOutputItem::FunctionToolCall {
                             id: String::new(),
+                            call_id: String::new(),
                             name: String::new(),
                             arguments: String::new(),
                             output: None,

sgl-router/src/routers/grpc/responses/tool_loop.rs

@@ -124,6 +124,7 @@ impl ToolLoopState {
         self.conversation_history
             .push(ResponseInputOutputItem::FunctionToolCall {
                 id: call_id.clone(),
+                call_id: call_id.clone(),
                 name: tool_name.clone(),
                 arguments: args_json_str.clone(),
                 output: Some(output_str.clone()),

sgl-router/src/routers/openai/conversations.rs

@@ -384,9 +384,9 @@ const SUPPORTED_ITEM_TYPES: &[&str] = &[
     "mcp_list_tools",
     "mcp_call",
     "item_reference",
-    // Accepted but not yet implemented (stored, warning returned)
-    "function_tool_call",
+    "function_call",
     "function_call_output",
+    // Accepted but not yet implemented (stored, warning returned)
     "file_search_call",
     "computer_call",
     "computer_call_output",
@@ -936,6 +936,26 @@ fn item_to_json(item: &crate::data_connector::ConversationItem) -> Value {
                 }
             }
         }
+        "function_call" => {
+            // Extract function_call fields: call_id, name, arguments, output
+            if let Some(content_obj) = item.content.as_object() {
+                for field in ["call_id", "name", "arguments", "output"] {
+                    if let Some(value) = content_obj.get(field) {
+                        obj.insert(field.to_string(), value.clone());
+                    }
+                }
+            }
+        }
+        "function_call_output" => {
+            // Extract function_call_output fields: call_id, output
+            if let Some(content_obj) = item.content.as_object() {
+                for field in ["call_id", "output"] {
+                    if let Some(value) = content_obj.get(field) {
+                        obj.insert(field.to_string(), value.clone());
+                    }
+                }
+            }
+        }
         _ => {
             // For all other types (message, reasoning, etc.), keep content as-is
             obj.insert("content".to_string(), item.content.clone());
@@ -1144,7 +1164,7 @@ fn extract_input_items(input: &ResponseInput) -> Result<Vec<Value>, String> {
                             }))
                         }
                         _ => {
-                            // For other item types (Message, Reasoning, FunctionToolCall), serialize and ensure ID
+                            // For other item types (Message, Reasoning, FunctionToolCall, FunctionCallOutput), serialize and ensure ID
                             let mut value = serde_json::to_value(item)
                                 .map_err(|e| format!("Failed to serialize item: {}", e))?;
 
@@ -1157,7 +1177,15 @@ fn extract_input_items(input: &ResponseInput) -> Result<Vec<Value>, String> {
                                         .map(|s| s.is_empty())
                                         .unwrap_or(true)
                                 {
-                                    obj.insert("id".to_string(), json!(generate_id("item")));
+                                    // Generate ID with appropriate prefix based on type
+                                    let item_type =
+                                        obj.get("type").and_then(|v| v.as_str()).unwrap_or("item");
+                                    let prefix = match item_type {
+                                        "function_call" | "function_call_output" => "fc",
+                                        "message" => "msg",
+                                        _ => "item",
+                                    };
+                                    obj.insert("id".to_string(), json!(generate_id(prefix)));
                                 }
                             }
 
@@ -1201,17 +1229,31 @@ async fn link_items_to_conversation(
             .get("role")
             .and_then(|v| v.as_str())
             .map(String::from);
-        let content = input_item_value
-            .get("content")
-            .cloned()
-            .unwrap_or(json!([]));
+
+        // For function_call and function_call_output, store the entire item as content
+        // For message types, extract just the content field
+        let content = if item_type == "function_call" || item_type == "function_call_output" {
+            input_item_value.clone()
+        } else {
+            input_item_value
+                .get("content")
+                .cloned()
+                .unwrap_or(json!([]))
+        };
+
         let status = input_item_value
             .get("status")
             .and_then(|v| v.as_str())
             .map(String::from);
 
+        // Extract the original item ID from input if present
+        let item_id = input_item_value
+            .get("id")
+            .and_then(|v| v.as_str())
+            .map(ConversationItemId::from);
+
         let new_item = NewConversationItem {
-            id: None, // Let storage generate ID
+            id: item_id, // Preserve ID if present
             response_id: response_id_opt.clone(),
             item_type: item_type.to_string(),
             role,
@@ -1252,7 +1294,7 @@ async fn link_items_to_conversation(
                 .cloned()
                 .unwrap_or(json!([]))
         } else {
-            // For other types (reasoning, function_tool_call, mcp_call, etc.)
+            // For other types (reasoning, function_call, function_call_output, mcp_call, etc.)
             // store the entire item structure
             output_item_value.clone()
         };

sgl-router/src/routers/openai/router.rs

@@ -810,20 +810,76 @@ impl crate::routers::RouterTrait for OpenAIRouter {
                 Ok(stored_items) => {
                     let mut items: Vec<ResponseInputOutputItem> = Vec::new();
                     for item in stored_items.into_iter() {
-                        // Only use message items for conversation context
-                        // Skip non-message items (reasoning, function calls, etc.)
-                        if item.item_type == "message" {
-                            if let Ok(content_parts) =
-                                serde_json::from_value::<Vec<ResponseContentPart>>(
+                        // Include messages, function calls, and function call outputs
+                        // Skip reasoning items as they're internal processing details
+                        match item.item_type.as_str() {
+                            "message" => {
+                                match serde_json::from_value::<Vec<ResponseContentPart>>(
                                     item.content.clone(),
-                                )
-                            {
-                                items.push(ResponseInputOutputItem::Message {
-                                    id: item.id.0.clone(),
-                                    role: item.role.clone().unwrap_or_else(|| "user".to_string()),
-                                    content: content_parts,
-                                    status: item.status.clone(),
-                                });
+                                ) {
+                                    Ok(content_parts) => {
+                                        items.push(ResponseInputOutputItem::Message {
+                                            id: item.id.0.clone(),
+                                            role: item
+                                                .role
+                                                .clone()
+                                                .unwrap_or_else(|| "user".to_string()),
+                                            content: content_parts,
+                                            status: item.status.clone(),
+                                        });
+                                    }
+                                    Err(e) => {
+                                        tracing::error!(
+                                            "Failed to deserialize message content: {}",
+                                            e
+                                        );
+                                    }
+                                }
+                            }
+                            "function_call" => {
+                                // The entire function_call item is stored in content field
+                                match serde_json::from_value::<ResponseInputOutputItem>(
+                                    item.content.clone(),
+                                ) {
+                                    Ok(func_call) => items.push(func_call),
+                                    Err(e) => {
+                                        tracing::error!(
+                                            "Failed to deserialize function_call: {}",
+                                            e
+                                        );
+                                    }
+                                }
+                            }
+                            "function_call_output" => {
+                                // The entire function_call_output item is stored in content field
+                                tracing::debug!(
+                                    "Loading function_call_output from DB - content: {}",
+                                    serde_json::to_string_pretty(&item.content)
+                                        .unwrap_or_else(|_| "failed to serialize".to_string())
+                                );
+                                match serde_json::from_value::<ResponseInputOutputItem>(
+                                    item.content.clone(),
+                                ) {
+                                    Ok(func_output) => {
+                                        tracing::debug!(
+                                            "Successfully deserialized function_call_output"
+                                        );
+                                        items.push(func_output);
+                                    }
+                                    Err(e) => {
+                                        tracing::error!(
+                                            "Failed to deserialize function_call_output: {}",
+                                            e
+                                        );
+                                    }
+                                }
+                            }
+                            "reasoning" => {
+                                // Skip reasoning items - they're internal processing details
+                            }
+                            _ => {
+                                // Skip unknown item types
+                                warn!("Unknown item type in conversation: {}", item.item_type);
                             }
                         }
                     }
@@ -889,6 +945,10 @@ impl crate::routers::RouterTrait for OpenAIRouter {
 
         // Always set store=false for upstream (we store internally)
         request_body.store = Some(false);
+        // Filter out reasoning items from input - they're internal processing details
+        if let ResponseInput::Items(ref mut items) = request_body.input {
+            items.retain(|item| !matches!(item, ResponseInputOutputItem::Reasoning { .. }));
+        }
 
         // Convert to JSON and strip SGLang-specific fields
         let mut payload = match to_value(&request_body) {