feat: conditionally toggle chat on invocations route (#1454)

This PR adds support for reading the `OAI_ENABLED` env var which will
changes the function called when the `/invocations` is called.

If `OAI_ENABLED=true` the `chat_completions` method is used otherwise it
defaults to `compat_generate`.

example running the router
```bash
OAI_ENABLED=true \
  cargo run -- \
  --tokenizer-name mistralai/Mistral-7B-Instruct-v0.2
```

example request
```bash
curl localhost:3000/invocations \
    -X POST \
    -d '{ "model": "tgi", "messages": [ { "role": "user", "content": "What is the IP address of the Google DNS servers?" } ], "stream": false, "max_tokens": 20, "logprobs": true, "seed": 0 }' \
    -H 'Content-Type: application/json' | jq 
```

**please let me know if any naming changes are needed or if any other
routes need similar functionality.

router/src/main.rs

@@ -71,6 +71,8 @@ struct Args {
     ngrok_authtoken: Option<String>,
     #[clap(long, env)]
     ngrok_edge: Option<String>,
+    #[clap(long, env, default_value_t = false)]
+    chat_enabled_api: bool,
 }
 
 #[tokio::main]
@@ -102,6 +104,7 @@ async fn main() -> Result<(), RouterError> {
         ngrok,
         ngrok_authtoken,
         ngrok_edge,
+        chat_enabled_api,
     } = args;
 
     // Launch Tokio runtime
@@ -345,6 +348,7 @@ async fn main() -> Result<(), RouterError> {
         ngrok_authtoken,
         ngrok_edge,
         tokenizer_config,
+        chat_enabled_api,
     )
     .await?;
     Ok(())

router/src/server.rs

@@ -708,6 +708,7 @@ pub async fn run(
     ngrok_authtoken: Option<String>,
     ngrok_edge: Option<String>,
     tokenizer_config: HubTokenizerConfig,
+    chat_enabled_api: bool,
 ) -> Result<(), axum::BoxError> {
     // OpenAPI documentation
     #[derive(OpenApi)]
@@ -856,25 +857,32 @@ pub async fn run(
         docker_label: option_env!("DOCKER_LABEL"),
     };
 
-    // Create router
-    let app = Router::new()
-        .merge(SwaggerUi::new("/docs").url("/api-doc/openapi.json", ApiDoc::openapi()))
-        // Base routes
+    // Configure Swagger UI
+    let swagger_ui = SwaggerUi::new("/docs").url("/api-doc/openapi.json", ApiDoc::openapi());
+
+    // Define base and health routes
+    let base_routes = Router::new()
         .route("/", post(compat_generate))
         .route("/info", get(get_model_info))
         .route("/generate", post(generate))
         .route("/generate_stream", post(generate_stream))
         .route("/v1/chat/completions", post(chat_completions))
-        // AWS Sagemaker route
-        .route("/invocations", post(compat_generate))
-        // Base Health route
         .route("/health", get(health))
-        // Inference API health route
-        .route("/", get(health))
-        // AWS Sagemaker health route
         .route("/ping", get(health))
-        // Prometheus metrics route
-        .route("/metrics", get(metrics))
+        .route("/metrics", get(metrics));
+
+    // Conditional AWS Sagemaker route
+    let aws_sagemaker_route = if chat_enabled_api {
+        Router::new().route("/invocations", post(chat_completions)) // Use 'chat_completions' for OAI_ENABLED
+    } else {
+        Router::new().route("/invocations", post(compat_generate)) // Use 'compat_generate' otherwise
+    };
+
+    // Combine routes and layers
+    let app = Router::new()
+        .merge(swagger_ui)
+        .merge(base_routes)
+        .merge(aws_sagemaker_route)
         .layer(Extension(info))
         .layer(Extension(health_ext.clone()))
         .layer(Extension(compat_return_full_text))