[router] Add OpenAI backend support - core function (#10254)

sgl-router/src/config/types.rs

@@ -101,6 +101,11 @@ pub enum RoutingMode {
         #[serde(skip_serializing_if = "Option::is_none")]
         decode_policy: Option<PolicyConfig>,
     },
+    #[serde(rename = "openai")]
+    OpenAI {
+        /// OpenAI-compatible API base(s), provided via worker URLs
+        worker_urls: Vec<String>,
+    },
 }
 
 impl RoutingMode {
@@ -116,6 +121,8 @@ impl RoutingMode {
                 decode_urls,
                 ..
             } => prefill_urls.len() + decode_urls.len(),
+            // OpenAI mode represents a single upstream
+            RoutingMode::OpenAI { .. } => 1,
         }
     }
 
@@ -380,6 +387,7 @@ impl RouterConfig {
         match self.mode {
             RoutingMode::Regular { .. } => "regular",
             RoutingMode::PrefillDecode { .. } => "prefill_decode",
+            RoutingMode::OpenAI { .. } => "openai",
         }
     }
 

sgl-router/src/config/validation.rs

@@ -95,6 +95,20 @@ impl ConfigValidator {
                     Self::validate_policy(d_policy)?;
                 }
             }
+            RoutingMode::OpenAI { worker_urls } => {
+                // Require exactly one worker URL for OpenAI router
+                if worker_urls.len() != 1 {
+                    return Err(ConfigError::ValidationFailed {
+                        reason: "OpenAI mode requires exactly one --worker-urls entry".to_string(),
+                    });
+                }
+                // Validate URL format
+                if let Err(e) = url::Url::parse(&worker_urls[0]) {
+                    return Err(ConfigError::ValidationFailed {
+                        reason: format!("Invalid OpenAI worker URL '{}': {}", &worker_urls[0], e),
+                    });
+                }
+            }
         }
         Ok(())
     }
@@ -243,6 +257,12 @@ impl ConfigValidator {
                     });
                 }
             }
+            RoutingMode::OpenAI { .. } => {
+                // OpenAI mode doesn't use service discovery
+                return Err(ConfigError::ValidationFailed {
+                    reason: "OpenAI mode does not support service discovery".to_string(),
+                });
+            }
         }
 
         Ok(())

sgl-router/src/main.rs

@@ -1,4 +1,4 @@
-use clap::{ArgAction, Parser};
+use clap::{ArgAction, Parser, ValueEnum};
 use sglang_router_rs::config::{
     CircuitBreakerConfig, ConfigError, ConfigResult, ConnectionMode, DiscoveryConfig,
     HealthCheckConfig, MetricsConfig, PolicyConfig, RetryConfig, RouterConfig, RoutingMode,
@@ -41,6 +41,33 @@ fn parse_prefill_args() -> Vec<(String, Option<u16>)> {
     prefill_entries
 }
 
+#[derive(Copy, Clone, Debug, Eq, PartialEq, ValueEnum)]
+pub enum Backend {
+    #[value(name = "sglang")]
+    Sglang,
+    #[value(name = "vllm")]
+    Vllm,
+    #[value(name = "trtllm")]
+    Trtllm,
+    #[value(name = "openai")]
+    Openai,
+    #[value(name = "anthropic")]
+    Anthropic,
+}
+
+impl std::fmt::Display for Backend {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let s = match self {
+            Backend::Sglang => "sglang",
+            Backend::Vllm => "vllm",
+            Backend::Trtllm => "trtllm",
+            Backend::Openai => "openai",
+            Backend::Anthropic => "anthropic",
+        };
+        write!(f, "{}", s)
+    }
+}
+
 #[derive(Parser, Debug)]
 #[command(name = "sglang-router")]
 #[command(about = "SGLang Router - High-performance request distribution across worker nodes")]
@@ -145,6 +172,10 @@ struct CliArgs {
     #[arg(long)]
     api_key: Option<String>,
 
+    /// Backend to route requests to (sglang, vllm, trtllm, openai, anthropic)
+    #[arg(long, value_enum, default_value_t = Backend::Sglang, alias = "runtime")]
+    backend: Backend,
+
     /// Directory to store log files
     #[arg(long)]
     log_dir: Option<String>,
@@ -339,6 +370,11 @@ impl CliArgs {
             RoutingMode::Regular {
                 worker_urls: vec![],
             }
+        } else if matches!(self.backend, Backend::Openai) {
+            // OpenAI backend mode - use worker_urls as base(s)
+            RoutingMode::OpenAI {
+                worker_urls: self.worker_urls.clone(),
+            }
         } else if self.pd_disaggregation {
             let decode_urls = self.decode.clone();
 
@@ -409,8 +445,14 @@ impl CliArgs {
                 }
                 all_urls.extend(decode_urls.clone());
             }
+            RoutingMode::OpenAI { .. } => {
+                // For connection-mode detection, skip URLs; OpenAI forces HTTP below.
+            }
         }
-        let connection_mode = Self::determine_connection_mode(&all_urls);
+        let connection_mode = match &mode {
+            RoutingMode::OpenAI { .. } => ConnectionMode::Http,
+            _ => Self::determine_connection_mode(&all_urls),
+        };
 
         // Build RouterConfig
         Ok(RouterConfig {
@@ -543,16 +585,28 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     // Print startup info
     println!("SGLang Router starting...");
     println!("Host: {}:{}", cli_args.host, cli_args.port);
-    println!(
-        "Mode: {}",
-        if cli_args.enable_igw {
-            "IGW (Inference Gateway)"
-        } else if cli_args.pd_disaggregation {
-            "PD Disaggregated"
-        } else {
-            "Regular"
+    let mode_str = if cli_args.enable_igw {
+        "IGW (Inference Gateway)".to_string()
+    } else if matches!(cli_args.backend, Backend::Openai) {
+        "OpenAI Backend".to_string()
+    } else if cli_args.pd_disaggregation {
+        "PD Disaggregated".to_string()
+    } else {
+        format!("Regular ({})", cli_args.backend)
+    };
+    println!("Mode: {}", mode_str);
+
+    // Warn for runtimes that are parsed but not yet implemented
+    match cli_args.backend {
+        Backend::Vllm | Backend::Trtllm | Backend::Anthropic => {
+            println!(
+                "WARNING: runtime '{}' not implemented yet; falling back to regular routing. \
+Provide --worker-urls or PD flags as usual.",
+                cli_args.backend
+            );
         }
-    );
+        Backend::Sglang | Backend::Openai => {}
+    }
 
     if !cli_args.enable_igw {
         println!("Policy: {}", cli_args.policy);

sgl-router/src/routers/factory.rs

@@ -1,7 +1,7 @@
 //! Factory for creating router instances
 
 use super::{
-    http::{pd_router::PDRouter, router::Router},
+    http::{openai_router::OpenAIRouter, pd_router::PDRouter, router::Router},
     RouterTrait,
 };
 use crate::config::{ConnectionMode, PolicyConfig, RoutingMode};
@@ -44,6 +44,9 @@ impl RouterFactory {
                         )
                         .await
                     }
+                    RoutingMode::OpenAI { .. } => {
+                        Err("OpenAI mode requires HTTP connection_mode".to_string())
+                    }
                 }
             }
             ConnectionMode::Http => {
@@ -69,6 +72,9 @@ impl RouterFactory {
                         )
                         .await
                     }
+                    RoutingMode::OpenAI { worker_urls, .. } => {
+                        Self::create_openai_router(worker_urls.clone(), ctx).await
+                    }
                 }
             }
         }
@@ -164,6 +170,23 @@ impl RouterFactory {
         Ok(Box::new(router))
     }
 
+    /// Create an OpenAI router
+    async fn create_openai_router(
+        worker_urls: Vec<String>,
+        ctx: &Arc<AppContext>,
+    ) -> Result<Box<dyn RouterTrait>, String> {
+        // Use the first worker URL as the OpenAI-compatible base
+        let base_url = worker_urls
+            .first()
+            .cloned()
+            .ok_or_else(|| "OpenAI mode requires at least one worker URL".to_string())?;
+
+        let router =
+            OpenAIRouter::new(base_url, Some(ctx.router_config.circuit_breaker.clone())).await?;
+
+        Ok(Box::new(router))
+    }
+
     /// Create an IGW router (placeholder for future implementation)
     async fn create_igw_router(_ctx: &Arc<AppContext>) -> Result<Box<dyn RouterTrait>, String> {
         // For now, return an error indicating IGW is not yet implemented

sgl-router/src/routers/http/mod.rs

@@ -1,5 +1,6 @@
 //! HTTP router implementations
 
+pub mod openai_router;
 pub mod pd_router;
 pub mod pd_types;
 pub mod router;

sgl-router/src/routers/http/openai_router.rs

@@ -0,0 +1,379 @@
+//! OpenAI router implementation (reqwest-based)
+
+use crate::config::CircuitBreakerConfig;
+use crate::core::{CircuitBreaker, CircuitBreakerConfig as CoreCircuitBreakerConfig};
+use crate::protocols::spec::{ChatCompletionRequest, CompletionRequest, GenerateRequest};
+use async_trait::async_trait;
+use axum::{
+    body::Body,
+    extract::Request,
+    http::{header::CONTENT_TYPE, HeaderMap, HeaderValue, StatusCode},
+    response::{IntoResponse, Response},
+};
+use futures_util::StreamExt;
+use std::{
+    any::Any,
+    sync::atomic::{AtomicBool, Ordering},
+};
+
+/// Router for OpenAI backend
+#[derive(Debug)]
+pub struct OpenAIRouter {
+    /// HTTP client for upstream OpenAI-compatible API
+    client: reqwest::Client,
+    /// Base URL for identification (no trailing slash)
+    base_url: String,
+    /// Circuit breaker
+    circuit_breaker: CircuitBreaker,
+    /// Health status
+    healthy: AtomicBool,
+}
+
+impl OpenAIRouter {
+    /// Create a new OpenAI router
+    pub async fn new(
+        base_url: String,
+        circuit_breaker_config: Option<CircuitBreakerConfig>,
+    ) -> Result<Self, String> {
+        let client = reqwest::Client::builder()
+            .timeout(std::time::Duration::from_secs(300))
+            .build()
+            .map_err(|e| format!("Failed to create HTTP client: {}", e))?;
+
+        let base_url = base_url.trim_end_matches('/').to_string();
+
+        // Convert circuit breaker config
+        let core_cb_config = circuit_breaker_config
+            .map(|cb| CoreCircuitBreakerConfig {
+                failure_threshold: cb.failure_threshold,
+                success_threshold: cb.success_threshold,
+                timeout_duration: std::time::Duration::from_secs(cb.timeout_duration_secs),
+                window_duration: std::time::Duration::from_secs(cb.window_duration_secs),
+            })
+            .unwrap_or_default();
+
+        let circuit_breaker = CircuitBreaker::with_config(core_cb_config);
+
+        Ok(Self {
+            client,
+            base_url,
+            circuit_breaker,
+            healthy: AtomicBool::new(true),
+        })
+    }
+}
+
+#[async_trait]
+impl super::super::WorkerManagement for OpenAIRouter {
+    async fn add_worker(&self, _worker_url: &str) -> Result<String, String> {
+        Err("Cannot add workers to OpenAI router".to_string())
+    }
+
+    fn remove_worker(&self, _worker_url: &str) {
+        // No-op for OpenAI router
+    }
+
+    fn get_worker_urls(&self) -> Vec<String> {
+        vec![self.base_url.clone()]
+    }
+}
+
+#[async_trait]
+impl super::super::RouterTrait for OpenAIRouter {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    async fn health(&self, _req: Request<Body>) -> Response {
+        // Simple upstream probe: GET {base}/v1/models without auth
+        let url = format!("{}/v1/models", self.base_url);
+        match self
+            .client
+            .get(&url)
+            .timeout(std::time::Duration::from_secs(2))
+            .send()
+            .await
+        {
+            Ok(resp) => {
+                let code = resp.status();
+                // Treat success and auth-required as healthy (endpoint reachable)
+                if code.is_success() || code.as_u16() == 401 || code.as_u16() == 403 {
+                    (StatusCode::OK, "OK").into_response()
+                } else {
+                    (
+                        StatusCode::SERVICE_UNAVAILABLE,
+                        format!("Upstream status: {}", code),
+                    )
+                        .into_response()
+                }
+            }
+            Err(e) => (
+                StatusCode::SERVICE_UNAVAILABLE,
+                format!("Upstream error: {}", e),
+            )
+                .into_response(),
+        }
+    }
+
+    async fn health_generate(&self, _req: Request<Body>) -> Response {
+        // For OpenAI, health_generate is the same as health
+        self.health(_req).await
+    }
+
+    async fn get_server_info(&self, _req: Request<Body>) -> Response {
+        let info = serde_json::json!({
+            "router_type": "openai",
+            "workers": 1,
+            "base_url": &self.base_url
+        });
+        (StatusCode::OK, info.to_string()).into_response()
+    }
+
+    async fn get_models(&self, req: Request<Body>) -> Response {
+        // Proxy to upstream /v1/models; forward Authorization header if provided
+        let headers = req.headers();
+
+        let mut upstream = self.client.get(format!("{}/v1/models", self.base_url));
+
+        if let Some(auth) = headers
+            .get("authorization")
+            .or_else(|| headers.get("Authorization"))
+        {
+            upstream = upstream.header("Authorization", auth);
+        }
+
+        match upstream.send().await {
+            Ok(res) => {
+                let status = StatusCode::from_u16(res.status().as_u16())
+                    .unwrap_or(StatusCode::INTERNAL_SERVER_ERROR);
+                let content_type = res.headers().get(CONTENT_TYPE).cloned();
+                match res.bytes().await {
+                    Ok(body) => {
+                        let mut response = Response::new(axum::body::Body::from(body));
+                        *response.status_mut() = status;
+                        if let Some(ct) = content_type {
+                            response.headers_mut().insert(CONTENT_TYPE, ct);
+                        }
+                        response
+                    }
+                    Err(e) => (
+                        StatusCode::INTERNAL_SERVER_ERROR,
+                        format!("Failed to read upstream response: {}", e),
+                    )
+                        .into_response(),
+                }
+            }
+            Err(e) => (
+                StatusCode::BAD_GATEWAY,
+                format!("Failed to contact upstream: {}", e),
+            )
+                .into_response(),
+        }
+    }
+
+    async fn get_model_info(&self, _req: Request<Body>) -> Response {
+        // Not directly supported without model param; return 501
+        (
+            StatusCode::NOT_IMPLEMENTED,
+            "get_model_info not implemented for OpenAI router",
+        )
+            .into_response()
+    }
+
+    async fn route_generate(
+        &self,
+        _headers: Option<&HeaderMap>,
+        _body: &GenerateRequest,
+    ) -> Response {
+        // Generate endpoint is SGLang-specific, not supported for OpenAI backend
+        (
+            StatusCode::NOT_IMPLEMENTED,
+            "Generate endpoint not supported for OpenAI backend",
+        )
+            .into_response()
+    }
+
+    async fn route_chat(
+        &self,
+        headers: Option<&HeaderMap>,
+        body: &ChatCompletionRequest,
+    ) -> Response {
+        if !self.circuit_breaker.can_execute() {
+            return (StatusCode::SERVICE_UNAVAILABLE, "Circuit breaker open").into_response();
+        }
+
+        // Serialize request body, removing SGLang-only fields
+        let mut payload = match serde_json::to_value(body) {
+            Ok(v) => v,
+            Err(e) => {
+                return (
+                    StatusCode::BAD_REQUEST,
+                    format!("Failed to serialize request: {}", e),
+                )
+                    .into_response();
+            }
+        };
+        if let Some(obj) = payload.as_object_mut() {
+            for key in [
+                "top_k",
+                "min_p",
+                "min_tokens",
+                "regex",
+                "ebnf",
+                "stop_token_ids",
+                "no_stop_trim",
+                "ignore_eos",
+                "continue_final_message",
+                "skip_special_tokens",
+                "lora_path",
+                "session_params",
+                "separate_reasoning",
+                "stream_reasoning",
+                "chat_template_kwargs",
+                "return_hidden_states",
+                "repetition_penalty",
+            ] {
+                obj.remove(key);
+            }
+        }
+
+        let url = format!("{}/v1/chat/completions", self.base_url);
+        let mut req = self.client.post(&url).json(&payload);
+
+        // Forward Authorization header if provided
+        if let Some(h) = headers {
+            if let Some(auth) = h.get("authorization").or_else(|| h.get("Authorization")) {
+                req = req.header("Authorization", auth);
+            }
+        }
+
+        // Accept SSE when stream=true
+        if body.stream {
+            req = req.header("Accept", "text/event-stream");
+        }
+
+        let resp = match req.send().await {
+            Ok(r) => r,
+            Err(e) => {
+                self.circuit_breaker.record_failure();
+                return (
+                    StatusCode::SERVICE_UNAVAILABLE,
+                    format!("Failed to contact upstream: {}", e),
+                )
+                    .into_response();
+            }
+        };
+
+        let status = StatusCode::from_u16(resp.status().as_u16())
+            .unwrap_or(StatusCode::INTERNAL_SERVER_ERROR);
+
+        if !body.stream {
+            // Capture Content-Type before consuming response body
+            let content_type = resp.headers().get(CONTENT_TYPE).cloned();
+            match resp.bytes().await {
+                Ok(body) => {
+                    self.circuit_breaker.record_success();
+                    let mut response = Response::new(axum::body::Body::from(body));
+                    *response.status_mut() = status;
+                    if let Some(ct) = content_type {
+                        response.headers_mut().insert(CONTENT_TYPE, ct);
+                    }
+                    response
+                }
+                Err(e) => {
+                    self.circuit_breaker.record_failure();
+                    (
+                        StatusCode::INTERNAL_SERVER_ERROR,
+                        format!("Failed to read response: {}", e),
+                    )
+                        .into_response()
+                }
+            }
+        } else {
+            // Stream SSE bytes to client
+            let stream = resp.bytes_stream();
+            let (tx, rx) = tokio::sync::mpsc::unbounded_channel();
+            tokio::spawn(async move {
+                let mut s = stream;
+                while let Some(chunk) = s.next().await {
+                    match chunk {
+                        Ok(bytes) => {
+                            if tx.send(Ok(bytes)).is_err() {
+                                break;
+                            }
+                        }
+                        Err(e) => {
+                            let _ = tx.send(Err(format!("Stream error: {}", e)));
+                            break;
+                        }
+                    }
+                }
+            });
+            let mut response = Response::new(Body::from_stream(
+                tokio_stream::wrappers::UnboundedReceiverStream::new(rx),
+            ));
+            *response.status_mut() = status;
+            response
+                .headers_mut()
+                .insert(CONTENT_TYPE, HeaderValue::from_static("text/event-stream"));
+            response
+        }
+    }
+
+    async fn route_completion(
+        &self,
+        _headers: Option<&HeaderMap>,
+        _body: &CompletionRequest,
+    ) -> Response {
+        // Completion endpoint not implemented for OpenAI backend
+        (
+            StatusCode::NOT_IMPLEMENTED,
+            "Completion endpoint not implemented for OpenAI backend",
+        )
+            .into_response()
+    }
+
+    async fn flush_cache(&self) -> Response {
+        (
+            StatusCode::NOT_IMPLEMENTED,
+            "flush_cache not supported for OpenAI router",
+        )
+            .into_response()
+    }
+
+    async fn get_worker_loads(&self) -> Response {
+        (
+            StatusCode::NOT_IMPLEMENTED,
+            "get_worker_loads not supported for OpenAI router",
+        )
+            .into_response()
+    }
+
+    fn router_type(&self) -> &'static str {
+        "openai"
+    }
+
+    fn readiness(&self) -> Response {
+        if self.healthy.load(Ordering::Acquire) && self.circuit_breaker.can_execute() {
+            (StatusCode::OK, "Ready").into_response()
+        } else {
+            (StatusCode::SERVICE_UNAVAILABLE, "Not ready").into_response()
+        }
+    }
+
+    async fn route_embeddings(&self, _headers: Option<&HeaderMap>, _body: Body) -> Response {
+        (
+            StatusCode::NOT_IMPLEMENTED,
+            "Embeddings endpoint not implemented for OpenAI backend",
+        )
+            .into_response()
+    }
+
+    async fn route_rerank(&self, _headers: Option<&HeaderMap>, _body: Body) -> Response {
+        (
+            StatusCode::NOT_IMPLEMENTED,
+            "Rerank endpoint not implemented for OpenAI backend",
+        )
+            .into_response()
+    }
+}

sgl-router/src/routers/mod.rs

@@ -17,6 +17,8 @@ pub mod header_utils;
 pub mod http;
 
 pub use factory::RouterFactory;
+// Re-export HTTP routers for convenience (keeps routers::openai_router path working)
+pub use http::{openai_router, pd_router, pd_types, router};
 
 /// Worker management trait for administrative operations
 ///

sgl-router/tests/common/mock_mcp_server.rs

@@ -63,10 +63,7 @@ impl ServerHandler for MockSearchServer {
         ServerInfo {
             protocol_version: ProtocolVersion::V_2024_11_05,
             capabilities: ServerCapabilities::builder().enable_tools().build(),
-            server_info: Implementation {
-                name: "Mock MCP Server".to_string(),
-                version: "1.0.0".to_string(),
-            },
+            server_info: Implementation::from_build_env(),
             instructions: Some("Mock server for testing".to_string()),
         }
     }

sgl-router/tests/common/mock_openai_server.rs

@@ -0,0 +1,238 @@
+//! Mock servers for testing
+
+#![allow(dead_code)]
+
+use axum::{
+    body::Body,
+    extract::{Request, State},
+    http::{HeaderValue, StatusCode},
+    response::sse::{Event, KeepAlive},
+    response::{IntoResponse, Response, Sse},
+    routing::post,
+    Json, Router,
+};
+use futures_util::stream::{self, StreamExt};
+use serde_json::json;
+use std::net::SocketAddr;
+use std::sync::Arc;
+use tokio::net::TcpListener;
+
+/// Mock OpenAI API server for testing
+pub struct MockOpenAIServer {
+    addr: SocketAddr,
+    _handle: tokio::task::JoinHandle<()>,
+}
+
+#[derive(Clone)]
+struct MockServerState {
+    require_auth: bool,
+    expected_auth: Option<String>,
+}
+
+impl MockOpenAIServer {
+    /// Create and start a new mock OpenAI server
+    pub async fn new() -> Self {
+        Self::new_with_auth(None).await
+    }
+
+    /// Create and start a new mock OpenAI server with optional auth requirement
+    pub async fn new_with_auth(expected_auth: Option<String>) -> Self {
+        let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
+        let addr = listener.local_addr().unwrap();
+
+        let state = Arc::new(MockServerState {
+            require_auth: expected_auth.is_some(),
+            expected_auth,
+        });
+
+        let app = Router::new()
+            .route("/v1/chat/completions", post(mock_chat_completions))
+            .route("/v1/completions", post(mock_completions))
+            .route("/v1/models", post(mock_models).get(mock_models))
+            .with_state(state);
+
+        let handle = tokio::spawn(async move {
+            axum::serve(listener, app).await.unwrap();
+        });
+
+        // Give the server a moment to start
+        tokio::time::sleep(tokio::time::Duration::from_millis(10)).await;
+
+        Self {
+            addr,
+            _handle: handle,
+        }
+    }
+
+    /// Get the base URL for this mock server
+    pub fn base_url(&self) -> String {
+        format!("http://{}", self.addr)
+    }
+}
+
+/// Mock chat completions endpoint
+async fn mock_chat_completions(req: Request<Body>) -> Response {
+    let (_, body) = req.into_parts();
+    let body_bytes = match axum::body::to_bytes(body, usize::MAX).await {
+        Ok(bytes) => bytes,
+        Err(_) => return StatusCode::BAD_REQUEST.into_response(),
+    };
+
+    let request: serde_json::Value = match serde_json::from_slice(&body_bytes) {
+        Ok(req) => req,
+        Err(_) => return StatusCode::BAD_REQUEST.into_response(),
+    };
+
+    // Extract model from request or use default (owned String to satisfy 'static in stream)
+    let model: String = request
+        .get("model")
+        .and_then(|v| v.as_str())
+        .unwrap_or("gpt-3.5-turbo")
+        .to_string();
+
+    // If stream requested, return SSE
+    let is_stream = request
+        .get("stream")
+        .and_then(|v| v.as_bool())
+        .unwrap_or(false);
+
+    if is_stream {
+        let created = 1677652288u64;
+        // Single chunk then [DONE]
+        let model_chunk = model.clone();
+        let event_stream = stream::once(async move {
+            let chunk = json!({
+                "id": "chatcmpl-123456789",
+                "object": "chat.completion.chunk",
+                "created": created,
+                "model": model_chunk,
+                "choices": [{
+                    "index": 0,
+                    "delta": {
+                        "content": "Hello!"
+                    },
+                    "finish_reason": null
+                }]
+            });
+            Ok::<_, std::convert::Infallible>(Event::default().data(chunk.to_string()))
+        })
+        .chain(stream::once(async { Ok(Event::default().data("[DONE]")) }));
+
+        Sse::new(event_stream)
+            .keep_alive(KeepAlive::default())
+            .into_response()
+    } else {
+        // Create a mock non-streaming response
+        let response = json!({
+            "id": "chatcmpl-123456789",
+            "object": "chat.completion",
+            "created": 1677652288,
+            "model": model,
+            "choices": [{
+                "index": 0,
+                "message": {
+                    "role": "assistant",
+                    "content": "Hello! I'm a mock OpenAI assistant. How can I help you today?"
+                },
+                "finish_reason": "stop"
+            }],
+            "usage": {
+                "prompt_tokens": 9,
+                "completion_tokens": 12,
+                "total_tokens": 21
+            }
+        });
+
+        Json(response).into_response()
+    }
+}
+
+/// Mock completions endpoint (legacy)
+async fn mock_completions(req: Request<Body>) -> Response {
+    let (_, body) = req.into_parts();
+    let body_bytes = match axum::body::to_bytes(body, usize::MAX).await {
+        Ok(bytes) => bytes,
+        Err(_) => return StatusCode::BAD_REQUEST.into_response(),
+    };
+
+    let request: serde_json::Value = match serde_json::from_slice(&body_bytes) {
+        Ok(req) => req,
+        Err(_) => return StatusCode::BAD_REQUEST.into_response(),
+    };
+
+    let model = request["model"].as_str().unwrap_or("text-davinci-003");
+
+    let response = json!({
+        "id": "cmpl-123456789",
+        "object": "text_completion",
+        "created": 1677652288,
+        "model": model,
+        "choices": [{
+            "text": " This is a mock completion response.",
+            "index": 0,
+            "logprobs": null,
+            "finish_reason": "stop"
+        }],
+        "usage": {
+            "prompt_tokens": 5,
+            "completion_tokens": 7,
+            "total_tokens": 12
+        }
+    });
+
+    Json(response).into_response()
+}
+
+/// Mock models endpoint
+async fn mock_models(State(state): State<Arc<MockServerState>>, req: Request<Body>) -> Response {
+    // Optionally enforce Authorization header
+    if state.require_auth {
+        let auth = req
+            .headers()
+            .get("authorization")
+            .or_else(|| req.headers().get("Authorization"))
+            .and_then(|v| v.to_str().ok())
+            .map(|s| s.to_string());
+        let auth_ok = match (&state.expected_auth, auth) {
+            (Some(expected), Some(got)) => &got == expected,
+            (None, Some(_)) => true,
+            _ => false,
+        };
+        if !auth_ok {
+            let mut response = Response::new(Body::from(
+                json!({
+                    "error": {
+                        "message": "Unauthorized",
+                        "type": "invalid_request_error"
+                    }
+                })
+                .to_string(),
+            ));
+            *response.status_mut() = StatusCode::UNAUTHORIZED;
+            response
+                .headers_mut()
+                .insert("WWW-Authenticate", HeaderValue::from_static("Bearer"));
+            return response;
+        }
+    }
+
+    let response = json!({
+        "object": "list",
+        "data": [
+            {
+                "id": "gpt-4",
+                "object": "model",
+                "created": 1677610602,
+                "owned_by": "openai"
+            },
+            {
+                "id": "gpt-3.5-turbo",
+                "object": "model",
+                "created": 1677610602,
+                "owned_by": "openai"
+            }
+        ]
+    });
+
+    Json(response).into_response()
+}

sgl-router/tests/common/mod.rs

@@ -2,6 +2,7 @@
 #![allow(dead_code)]
 
 pub mod mock_mcp_server;
+pub mod mock_openai_server;
 pub mod mock_worker;
 pub mod test_app;
 

sgl-router/tests/test_openai_routing.rs

@@ -0,0 +1,419 @@
+//! Comprehensive integration tests for OpenAI backend functionality
+
+use axum::{
+    body::Body,
+    extract::Request,
+    http::{Method, StatusCode},
+    routing::post,
+    Router,
+};
+use serde_json::json;
+use sglang_router_rs::{
+    config::{RouterConfig, RoutingMode},
+    protocols::spec::{
+        ChatCompletionRequest, ChatMessage, CompletionRequest, GenerateRequest, UserMessageContent,
+    },
+    routers::{openai_router::OpenAIRouter, RouterTrait},
+};
+use std::sync::Arc;
+use tower::ServiceExt;
+
+mod common;
+use common::mock_openai_server::MockOpenAIServer;
+
+/// Helper function to create a minimal chat completion request for testing
+fn create_minimal_chat_request() -> ChatCompletionRequest {
+    let val = json!({
+        "model": "gpt-3.5-turbo",
+        "messages": [
+            {"role": "user", "content": "Hello"}
+        ],
+        "max_tokens": 100
+    });
+    serde_json::from_value(val).unwrap()
+}
+
+/// Helper function to create a minimal completion request for testing
+fn create_minimal_completion_request() -> CompletionRequest {
+    CompletionRequest {
+        model: "gpt-3.5-turbo".to_string(),
+        prompt: sglang_router_rs::protocols::spec::StringOrArray::String("Hello".to_string()),
+        suffix: None,
+        max_tokens: Some(100),
+        temperature: None,
+        top_p: None,
+        n: None,
+        stream: false,
+        stream_options: None,
+        logprobs: None,
+        echo: false,
+        stop: None,
+        presence_penalty: None,
+        frequency_penalty: None,
+        best_of: None,
+        logit_bias: None,
+        user: None,
+        seed: None,
+        top_k: None,
+        min_p: None,
+        min_tokens: None,
+        repetition_penalty: None,
+        regex: None,
+        ebnf: None,
+        json_schema: None,
+        stop_token_ids: None,
+        no_stop_trim: false,
+        ignore_eos: false,
+        skip_special_tokens: true,
+        lora_path: None,
+        session_params: None,
+        return_hidden_states: false,
+        other: serde_json::Map::new(),
+    }
+}
+
+// ============= Basic Unit Tests =============
+
+/// Test basic OpenAI router creation and configuration
+#[tokio::test]
+async fn test_openai_router_creation() {
+    let router = OpenAIRouter::new("https://api.openai.com".to_string(), None).await;
+
+    assert!(router.is_ok(), "Router creation should succeed");
+
+    let router = router.unwrap();
+    assert_eq!(router.router_type(), "openai");
+    assert!(!router.is_pd_mode());
+}
+
+/// Test health endpoints
+#[tokio::test]
+async fn test_openai_router_health() {
+    let router = OpenAIRouter::new("https://api.openai.com".to_string(), None)
+        .await
+        .unwrap();
+
+    let req = Request::builder()
+        .method(Method::GET)
+        .uri("/health")
+        .body(Body::empty())
+        .unwrap();
+
+    let response = router.health(req).await;
+    assert_eq!(response.status(), StatusCode::OK);
+}
+
+/// Test server info endpoint
+#[tokio::test]
+async fn test_openai_router_server_info() {
+    let router = OpenAIRouter::new("https://api.openai.com".to_string(), None)
+        .await
+        .unwrap();
+
+    let req = Request::builder()
+        .method(Method::GET)
+        .uri("/info")
+        .body(Body::empty())
+        .unwrap();
+
+    let response = router.get_server_info(req).await;
+    assert_eq!(response.status(), StatusCode::OK);
+
+    let (_, body) = response.into_parts();
+    let body_bytes = axum::body::to_bytes(body, usize::MAX).await.unwrap();
+    let body_str = String::from_utf8(body_bytes.to_vec()).unwrap();
+
+    assert!(body_str.contains("openai"));
+}
+
+/// Test models endpoint
+#[tokio::test]
+async fn test_openai_router_models() {
+    // Use mock server for deterministic models response
+    let mock_server = MockOpenAIServer::new().await;
+    let router = OpenAIRouter::new(mock_server.base_url(), None)
+        .await
+        .unwrap();
+
+    let req = Request::builder()
+        .method(Method::GET)
+        .uri("/models")
+        .body(Body::empty())
+        .unwrap();
+
+    let response = router.get_models(req).await;
+    assert_eq!(response.status(), StatusCode::OK);
+
+    let (_, body) = response.into_parts();
+    let body_bytes = axum::body::to_bytes(body, usize::MAX).await.unwrap();
+    let body_str = String::from_utf8(body_bytes.to_vec()).unwrap();
+    let models: serde_json::Value = serde_json::from_str(&body_str).unwrap();
+
+    assert_eq!(models["object"], "list");
+    assert!(models["data"].is_array());
+}
+
+/// Test router factory with OpenAI routing mode
+#[tokio::test]
+async fn test_router_factory_openai_mode() {
+    let routing_mode = RoutingMode::OpenAI {
+        worker_urls: vec!["https://api.openai.com".to_string()],
+    };
+
+    let router_config =
+        RouterConfig::new(routing_mode, sglang_router_rs::config::PolicyConfig::Random);
+
+    let app_context = common::create_test_context(router_config);
+
+    let router = sglang_router_rs::routers::RouterFactory::create_router(&app_context).await;
+    assert!(
+        router.is_ok(),
+        "Router factory should create OpenAI router successfully"
+    );
+
+    let router = router.unwrap();
+    assert_eq!(router.router_type(), "openai");
+}
+
+/// Test that unsupported endpoints return proper error codes
+#[tokio::test]
+async fn test_unsupported_endpoints() {
+    let router = OpenAIRouter::new("https://api.openai.com".to_string(), None)
+        .await
+        .unwrap();
+
+    // Test generate endpoint (SGLang-specific, should not be supported)
+    let generate_request = GenerateRequest {
+        prompt: None,
+        text: Some("Hello world".to_string()),
+        input_ids: None,
+        parameters: None,
+        sampling_params: None,
+        stream: false,
+        return_logprob: false,
+        lora_path: None,
+        session_params: None,
+        return_hidden_states: false,
+        rid: None,
+    };
+
+    let response = router.route_generate(None, &generate_request).await;
+    assert_eq!(response.status(), StatusCode::NOT_IMPLEMENTED);
+
+    // Test completion endpoint (should also not be supported)
+    let completion_request = create_minimal_completion_request();
+    let response = router.route_completion(None, &completion_request).await;
+    assert_eq!(response.status(), StatusCode::NOT_IMPLEMENTED);
+}
+
+// ============= Mock Server E2E Tests =============
+
+/// Test chat completion with mock OpenAI server
+#[tokio::test]
+async fn test_openai_router_chat_completion_with_mock() {
+    // Start a mock OpenAI server
+    let mock_server = MockOpenAIServer::new().await;
+    let base_url = mock_server.base_url();
+
+    // Create router pointing to mock server
+    let router = OpenAIRouter::new(base_url, None).await.unwrap();
+
+    // Create a minimal chat completion request
+    let mut chat_request = create_minimal_chat_request();
+    chat_request.messages = vec![ChatMessage::User {
+        role: "user".to_string(),
+        content: UserMessageContent::Text("Hello, how are you?".to_string()),
+        name: None,
+    }];
+    chat_request.temperature = Some(0.7);
+
+    // Route the request
+    let response = router.route_chat(None, &chat_request).await;
+
+    // Should get a successful response from mock server
+    assert_eq!(response.status(), StatusCode::OK);
+
+    let (_, body) = response.into_parts();
+    let body_bytes = axum::body::to_bytes(body, usize::MAX).await.unwrap();
+    let body_str = String::from_utf8(body_bytes.to_vec()).unwrap();
+    let chat_response: serde_json::Value = serde_json::from_str(&body_str).unwrap();
+
+    // Verify it's a valid chat completion response
+    assert_eq!(chat_response["object"], "chat.completion");
+    assert_eq!(chat_response["model"], "gpt-3.5-turbo");
+    assert!(!chat_response["choices"].as_array().unwrap().is_empty());
+}
+
+/// Test full E2E flow with Axum server
+#[tokio::test]
+async fn test_openai_e2e_with_server() {
+    // Start mock OpenAI server
+    let mock_server = MockOpenAIServer::new().await;
+    let base_url = mock_server.base_url();
+
+    // Create router
+    let router = OpenAIRouter::new(base_url, None).await.unwrap();
+
+    // Create Axum app with chat completions endpoint
+    let app = Router::new().route(
+        "/v1/chat/completions",
+        post({
+            let router = Arc::new(router);
+            move |req: Request<Body>| {
+                let router = router.clone();
+                async move {
+                    let (parts, body) = req.into_parts();
+                    let body_bytes = axum::body::to_bytes(body, usize::MAX).await.unwrap();
+                    let body_str = String::from_utf8(body_bytes.to_vec()).unwrap();
+
+                    let chat_request: ChatCompletionRequest =
+                        serde_json::from_str(&body_str).unwrap();
+
+                    router.route_chat(Some(&parts.headers), &chat_request).await
+                }
+            }
+        }),
+    );
+
+    // Make a request to the server
+    let request = Request::builder()
+        .method(Method::POST)
+        .uri("/v1/chat/completions")
+        .header("content-type", "application/json")
+        .body(Body::from(
+            json!({
+                "model": "gpt-3.5-turbo",
+                "messages": [
+                    {
+                        "role": "user",
+                        "content": "Hello, world!"
+                    }
+                ],
+                "max_tokens": 100
+            })
+            .to_string(),
+        ))
+        .unwrap();
+
+    let response = app.oneshot(request).await.unwrap();
+    assert_eq!(response.status(), StatusCode::OK);
+
+    let body = axum::body::to_bytes(response.into_body(), usize::MAX)
+        .await
+        .unwrap();
+    let response_json: serde_json::Value = serde_json::from_slice(&body).unwrap();
+
+    // Verify the response structure
+    assert_eq!(response_json["object"], "chat.completion");
+    assert_eq!(response_json["model"], "gpt-3.5-turbo");
+    assert!(!response_json["choices"].as_array().unwrap().is_empty());
+}
+
+/// Test streaming chat completions pass-through with mock server
+#[tokio::test]
+async fn test_openai_router_chat_streaming_with_mock() {
+    let mock_server = MockOpenAIServer::new().await;
+    let base_url = mock_server.base_url();
+    let router = OpenAIRouter::new(base_url, None).await.unwrap();
+
+    // Build a streaming chat request
+    let val = json!({
+        "model": "gpt-3.5-turbo",
+        "messages": [
+            {"role": "user", "content": "Hello"}
+        ],
+        "max_tokens": 10,
+        "stream": true
+    });
+    let chat_request: ChatCompletionRequest = serde_json::from_value(val).unwrap();
+
+    let response = router.route_chat(None, &chat_request).await;
+    assert_eq!(response.status(), StatusCode::OK);
+
+    // Should be SSE
+    let headers = response.headers();
+    let ct = headers
+        .get("content-type")
+        .unwrap()
+        .to_str()
+        .unwrap()
+        .to_ascii_lowercase();
+    assert!(ct.contains("text/event-stream"));
+
+    // Read entire stream body and assert chunks + DONE
+    let body = axum::body::to_bytes(response.into_body(), usize::MAX)
+        .await
+        .unwrap();
+    let text = String::from_utf8(body.to_vec()).unwrap();
+    assert!(text.contains("chat.completion.chunk"));
+    assert!(text.contains("[DONE]"));
+}
+
+/// Test circuit breaker functionality
+#[tokio::test]
+async fn test_openai_router_circuit_breaker() {
+    // Create router with circuit breaker config
+    let cb_config = sglang_router_rs::config::CircuitBreakerConfig {
+        failure_threshold: 2,
+        success_threshold: 1,
+        timeout_duration_secs: 1,
+        window_duration_secs: 10,
+    };
+
+    let router = OpenAIRouter::new(
+        "http://invalid-url-that-will-fail".to_string(),
+        Some(cb_config),
+    )
+    .await
+    .unwrap();
+
+    let chat_request = create_minimal_chat_request();
+
+    // First few requests should fail and record failures
+    for _ in 0..3 {
+        let response = router.route_chat(None, &chat_request).await;
+        // Should get either an error or circuit breaker response
+        assert!(
+            response.status() == StatusCode::INTERNAL_SERVER_ERROR
+                || response.status() == StatusCode::SERVICE_UNAVAILABLE
+        );
+    }
+}
+
+/// Test that Authorization header is forwarded in /v1/models
+#[tokio::test]
+async fn test_openai_router_models_auth_forwarding() {
+    // Start a mock server that requires Authorization
+    let expected_auth = "Bearer test-token".to_string();
+    let mock_server = MockOpenAIServer::new_with_auth(Some(expected_auth.clone())).await;
+    let router = OpenAIRouter::new(mock_server.base_url(), None)
+        .await
+        .unwrap();
+
+    // 1) Without auth header -> expect 401
+    let req = Request::builder()
+        .method(Method::GET)
+        .uri("/models")
+        .body(Body::empty())
+        .unwrap();
+
+    let response = router.get_models(req).await;
+    assert_eq!(response.status(), StatusCode::UNAUTHORIZED);
+
+    // 2) With auth header -> expect 200
+    let req = Request::builder()
+        .method(Method::GET)
+        .uri("/models")
+        .header("Authorization", expected_auth)
+        .body(Body::empty())
+        .unwrap();
+
+    let response = router.get_models(req).await;
+    assert_eq!(response.status(), StatusCode::OK);
+
+    let (_, body) = response.into_parts();
+    let body_bytes = axum::body::to_bytes(body, usize::MAX).await.unwrap();
+    let body_str = String::from_utf8(body_bytes.to_vec()).unwrap();
+    let models: serde_json::Value = serde_json::from_str(&body_str).unwrap();
+    assert_eq!(models["object"], "list");
+}