Refactor the relationship between the servers and handles

crates/re_viewer/src/web.rs

@@ -148,7 +148,10 @@ fn get_url(info: &eframe::IntegrationInfo) -> String {
         url = param.clone();
     }
     if url.is_empty() {
-        re_ws_comms::default_server_url(&info.web_info.location.hostname)
+        re_ws_comms::server_url(
+            &info.web_info.location.hostname,
+            re_ws_comms::DEFAULT_WS_SERVER_PORT,
+        )
     } else {
         url
     }

crates/re_web_viewer_server/Cargo.toml

@@ -51,6 +51,7 @@ ctrlc.workspace = true
 document-features = "0.2"
 futures-util = "0.3"
 hyper = { version = "0.14", features = ["full"] }
+thiserror.workspace = true
 tokio = { workspace = true, default-features = false, features = [
   "macros",
   "rt-multi-thread",

crates/re_web_viewer_server/src/lib.rs

@@ -12,6 +12,8 @@ use std::task::{Context, Poll};
 use futures_util::future;
 use hyper::{server::conn::AddrIncoming, service::Service, Body, Request, Response};
 
+pub const DEFAULT_WEB_VIEWER_PORT: u16 = 9090;
+
 #[cfg(not(feature = "__ci"))]
 mod data {
     // If you add/remove/change the paths here, also update the include-list in `Cargo.toml`!
@@ -32,6 +34,18 @@ mod data {
     pub const VIEWER_WASM_RELEASE: &[u8] = include_bytes!("../web_viewer/re_viewer_bg.wasm");
 }
 
+#[derive(thiserror::Error, Debug)]
+pub enum WebViewerServerError {
+    #[error("Could not parse address: {0}")]
+    AddrParseFailed(#[from] std::net::AddrParseError),
+    #[error("failed to bind to port {0}: {1}")]
+    BindFailed(u16, hyper::Error),
+    #[error("failed to join web viewer server task: {0}")]
+    JoinError(#[from] tokio::task::JoinError),
+    #[error("failed to serve web viewer: {0}")]
+    ServeFailed(hyper::Error),
+}
+
 struct Svc {
     // NOTE: Optional because it is possible to have the `analytics` feature flag enabled
     // while at the same time opting-out of analytics at run-time.
@@ -149,27 +163,72 @@ impl<T> Service<T> for MakeSvc {
 
 // ----------------------------------------------------------------------------
 
-/// Hosts the Web Viewer Wasm+HTML
+/// HTTP host for the Rerun Web Viewer application
+/// This serves the HTTP+WASM+JS files that make up the web-viewer.
 pub struct WebViewerServer {
     server: hyper::Server<AddrIncoming, MakeSvc>,
 }
 
 impl WebViewerServer {
-    pub fn new(port: u16) -> Self {
-        let bind_addr = format!("0.0.0.0:{port}").parse().unwrap();
-        let server = hyper::Server::bind(&bind_addr).serve(MakeSvc);
-        Self { server }
+    pub fn new(port: u16) -> Result<Self, WebViewerServerError> {
+        let bind_addr = format!("0.0.0.0:{port}").parse()?;
+        let server = hyper::Server::try_bind(&bind_addr)
+            .map_err(|e| WebViewerServerError::BindFailed(port, e))?
+            .serve(MakeSvc);
+        Ok(Self { server })
     }
 
     pub async fn serve(
         self,
         mut shutdown_rx: tokio::sync::broadcast::Receiver<()>,
-    ) -> anyhow::Result<()> {
+    ) -> Result<(), WebViewerServerError> {
         self.server
             .with_graceful_shutdown(async {
                 shutdown_rx.recv().await.ok();
             })
-            .await?;
+            .await
+            .map_err(WebViewerServerError::ServeFailed)?;
         Ok(())
     }
 }
+
+/// Sync handle for the [`WebViewerServer`]
+///
+/// When dropped, the server will be shut down.
+pub struct WebViewerServerHandle {
+    port: u16,
+    shutdown_tx: tokio::sync::broadcast::Sender<()>,
+}
+
+impl Drop for WebViewerServerHandle {
+    fn drop(&mut self) {
+        re_log::info!("Shutting down web server on port {}.", self.port);
+        self.shutdown_tx.send(()).ok();
+    }
+}
+
+impl WebViewerServerHandle {
+    /// Create new [`WebViewerServer`] to host the Rerun Web Viewer on a specified port.
+    ///
+    /// A port of 0 will let the OS choose a free port.
+    ///
+    /// The caller needs to ensure that there is a `tokio` runtime running.
+    pub fn new(requested_port: u16) -> Result<Self, WebViewerServerError> {
+        let (shutdown_tx, shutdown_rx) = tokio::sync::broadcast::channel(1);
+
+        let web_server = WebViewerServer::new(requested_port)?;
+
+        let port = web_server.server.local_addr().port();
+
+        tokio::spawn(async move { web_server.serve(shutdown_rx).await });
+
+        re_log::info!("Started web server on port {}.", port);
+
+        Ok(Self { port, shutdown_tx })
+    }
+
+    /// Get the port where the web assets are hosted
+    pub fn port(&self) -> u16 {
+        self.port
+    }
+}

crates/re_web_viewer_server/src/main.rs

@@ -16,6 +16,7 @@ async fn main() {
     .expect("Error setting Ctrl-C handler");
 
     re_web_viewer_server::WebViewerServer::new(port)
+        .expect("Could not create web server")
         .serve(shutdown_rx)
         .await
         .unwrap();

crates/re_ws_comms/Cargo.toml

@@ -59,6 +59,7 @@ futures-util = { version = "0.3", optional = true, default-features = false, fea
   "std",
 ] }
 parking_lot = { workspace = true, optional = true }
+thiserror.workspace = true
 tokio-tungstenite = { version = "0.17.1", optional = true }
 tokio = { workspace = true, optional = true, default-features = false, features = [
   "io-std",

crates/re_ws_comms/src/lib.rs

@@ -12,7 +12,7 @@ pub use client::Connection;
 #[cfg(feature = "server")]
 mod server;
 #[cfg(feature = "server")]
-pub use server::Server;
+pub use server::{RerunServer, RerunServerHandle};
 
 use re_log_types::LogMsg;
 
@@ -26,8 +26,8 @@ pub const PROTOCOL: &str = "wss";
 #[cfg(not(feature = "tls"))]
 pub const PROTOCOL: &str = "ws";
 
-pub fn default_server_url(hostname: &str) -> String {
-    format!("{PROTOCOL}://{hostname}:{DEFAULT_WS_SERVER_PORT}")
+pub fn server_url(hostname: &str, port: u16) -> String {
+    format!("{PROTOCOL}://{hostname}:{port}")
 }
 
 const PREFIX: [u8; 4] = *b"RR00";

crates/re_ws_comms/src/server.rs

@@ -16,22 +16,32 @@ use tokio_tungstenite::{accept_async, tungstenite::Error};
 use re_log_types::LogMsg;
 use re_smart_channel::Receiver;
 
+use crate::server_url;
+
 // ----------------------------------------------------------------------------
 
-pub struct Server {
+#[derive(thiserror::Error, Debug)]
+pub enum RerunServerError {
+    #[error("failed to bind to port {0}: {1}")]
+    BindFailed(u16, std::io::Error),
+    #[error("failed to join web viewer server task: {0}")]
+    JoinError(#[from] tokio::task::JoinError),
+    #[error("tokio error: {0}")]
+    TokioIoError(#[from] tokio::io::Error),
+}
+
+pub struct RerunServer {
     listener: TcpListener,
 }
 
-impl Server {
+impl RerunServer {
     /// Start a pub-sub server listening on the given port
-    pub async fn new(port: u16) -> anyhow::Result<Self> {
-        use anyhow::Context as _;
-
+    pub async fn new(port: u16) -> Result<Self, RerunServerError> {
         let bind_addr = format!("0.0.0.0:{port}");
 
         let listener = TcpListener::bind(&bind_addr)
             .await
-            .with_context(|| format!("Can't listen on {bind_addr:?}"))?;
+            .map_err(|e| RerunServerError::BindError(port, e))?;
 
         re_log::info!(
             "Listening for websocket traffic on {bind_addr}. Connect with a web Rerun Viewer."
@@ -45,9 +55,7 @@ impl Server {
         self,
         rx: Receiver<LogMsg>,
         mut shutdown_rx: tokio::sync::broadcast::Receiver<()>,
-    ) -> anyhow::Result<()> {
-        use anyhow::Context as _;
-
+    ) -> Result<(), RerunServerError> {
         let history = Arc::new(Mutex::new(Vec::new()));
 
         let log_stream = to_broadcast_stream(rx, history.clone());
@@ -60,9 +68,7 @@ impl Server {
                 }
             };
 
-            let peer = tcp_stream
-                .peer_addr()
-                .context("connected streams should have a peer address")?;
+            let peer = tcp_stream.peer_addr()?;
             tokio::spawn(accept_connection(
                 log_stream.clone(),
                 peer,
@@ -73,6 +79,51 @@ impl Server {
     }
 }
 
+pub struct RerunServerHandle {
+    port: u16,
+    shutdown_tx: tokio::sync::broadcast::Sender<()>,
+}
+
+impl Drop for RerunServerHandle {
+    fn drop(&mut self) {
+        re_log::info!("Shutting down Rerun server on port {}.", self.port);
+        self.shutdown_tx.send(()).ok();
+    }
+}
+
+impl RerunServerHandle {
+    /// Create new [`RerunServer`] to relay [`LogMsg`]s to a web viewer.
+    ///
+    /// A port of 0 will let the OS choose a free port.
+    ///
+    /// The caller needs to ensure that there is a `tokio` runtime running.
+    pub fn new(rerun_rx: Receiver<LogMsg>, requested_port: u16) -> Result<Self, RerunServerError> {
+        let (shutdown_tx, shutdown_rx) = tokio::sync::broadcast::channel(1);
+
+        let rt = tokio::runtime::Handle::current();
+
+        let ws_server = rt.block_on(tokio::spawn(async move {
+            let ws_server = RerunServer::new(requested_port).await;
+            ws_server
+        }))??;
+
+        let port = ws_server.listener.local_addr()?.port();
+
+        tokio::spawn(async move { ws_server.listen(rerun_rx, shutdown_rx).await });
+
+        Ok(Self { port, shutdown_tx })
+    }
+
+    /// Get the port where the web assets are hosted
+    pub fn port(&self) -> u16 {
+        self.port
+    }
+
+    pub fn server_url(&self) -> String {
+        server_url("localhost", self.port)
+    }
+}
+
 fn to_broadcast_stream(
     log_rx: Receiver<LogMsg>,
     history: Arc<Mutex<Vec<Arc<[u8]>>>>,

crates/rerun/src/clap.rs

@@ -103,7 +103,7 @@ impl RerunArgs {
             #[cfg(feature = "web_viewer")]
             RerunBehavior::Serve => {
                 let open_browser = true;
-                crate::web_viewer::new_sink(open_browser)
+                crate::web_viewer::new_sink(open_browser)?
             }
 
             #[cfg(feature = "native_viewer")]

crates/rerun/src/run.rs

@@ -303,8 +303,15 @@ async fn run_impl(
                 if args.web_viewer {
                     #[cfg(feature = "web_viewer")]
                     {
-                        let web_viewer =
-                            host_web_viewer(true, rerun_server_ws_url, shutdown_rx.resubscribe());
+                        let web_port = re_web_viewer_server::DEFAULT_WEB_VIEWER_PORT;
+                        let web_viewer = host_web_viewer(
+                            web_port,
+                            true,
+                            rerun_server_ws_url,
+                            shutdown_rx.resubscribe(),
+                        );
+                        // We return here because the running [`WebViewerServer`] is all we need.
+                        // The page we open will be pointed at a websocket url hosted by a *different* server.
                         return web_viewer.await;
                     }
                     #[cfg(not(feature = "web_viewer"))]
@@ -369,17 +376,23 @@ async fn run_impl(
             let shutdown_web_viewer = shutdown_rx.resubscribe();
 
             // This is the server which the web viewer will talk to:
-            let ws_server = re_ws_comms::Server::new(re_ws_comms::DEFAULT_WS_SERVER_PORT).await?;
+            let ws_server =
+                re_ws_comms::RerunServer::new(re_ws_comms::DEFAULT_WS_SERVER_PORT).await?;
             let ws_server_handle = tokio::spawn(ws_server.listen(rx, shutdown_ws_server));
-            let ws_server_url = re_ws_comms::default_server_url("127.0.0.1");
+            let ws_server_url =
+                re_ws_comms::server_url("127.0.0.1", re_ws_comms::DEFAULT_WS_SERVER_PORT);
 
             // This is the server that serves the Wasm+HTML:
-            let web_server_handle =
-                tokio::spawn(host_web_viewer(true, ws_server_url, shutdown_web_viewer));
+            let web_server_handle = tokio::spawn(host_web_viewer(
+                re_web_viewer_server::DEFAULT_WEB_VIEWER_PORT,
+                true,
+                ws_server_url,
+                shutdown_web_viewer,
+            ));
 
             // Wait for both servers to shutdown.
             web_server_handle.await?.ok();
-            return ws_server_handle.await?;
+            return ws_server_handle.await?.map_err(anyhow::Error::from);
         }
 
         #[cfg(not(feature = "web_viewer"))]