Add a http server proxy example (#66)

tomasol · web-flow · commit 6c14d5a660b2 · 2025-11-04T10:07:29.000-08:00
* Add a http server proxy example

* Propagate the `Client.finish` error to the proxy server's response

* Add a simplified reverse proxy example

* Fix a typo

* wip: Partially the proxy example to `wstd`

* Finish the streaming proxy example

* Simplify the response creation

* Skip copying request/response body contents through guest memory

* Add `http_server_proxy` test
diff --git a/examples/http_server_proxy.rs b/examples/http_server_proxy.rs
@@ -0,0 +1,64 @@
+//! Run the example with:
+//! ```sh
+//! cargo build --example http_server_proxy --target=wasm32-wasip2
+//! wasmtime serve -Scli -Shttp --env TARGET_URL=https://example.com/ target/wasm32-wasip2/debug/examples/http_server_proxy.wasm
+//! curl --no-buffer -v 127.0.0.1:8080/proxy/
+//! ```
+use wstd::http::body::Body;
+use wstd::http::{Client, Error, Request, Response, StatusCode, Uri};
+
+const PROXY_PREFIX: &str = "/proxy/";
+
+#[wstd::http_server]
+async fn main(server_req: Request<Body>) -> Result<Response<Body>, Error> {
+    match server_req.uri().path_and_query().unwrap().as_str() {
+        api_prefixed_path if api_prefixed_path.starts_with(PROXY_PREFIX) => {
+            // Remove PROXY_PREFIX
+            let target_url =
+                std::env::var("TARGET_URL").expect("missing environment variable TARGET_URL");
+            let target_url: Uri = format!(
+                "{target_url}{}",
+                api_prefixed_path
+                    .strip_prefix(PROXY_PREFIX)
+                    .expect("checked above")
+            )
+            .parse()
+            .expect("final target url should be parseable");
+            println!("Proxying to {target_url}");
+            proxy(server_req, target_url).await
+        }
+        _ => Ok(http_not_found(server_req)),
+    }
+}
+
+async fn proxy(server_req: Request<Body>, target_url: Uri) -> Result<Response<Body>, Error> {
+    let client = Client::new();
+    let mut client_req = Request::builder();
+    client_req = client_req.uri(target_url).method(server_req.method());
+
+    // Copy headers from `server_req` to the `client_req`.
+    for (key, value) in server_req.headers() {
+        client_req = client_req.header(key, value);
+    }
+
+    // Stream the request body.
+    let client_req = client_req.body(server_req.into_body())?;
+    // Send the request.
+    let client_resp = client.send(client_req).await?;
+    // Copy headers from `client_resp` to `server_resp`.
+    let mut server_resp = Response::builder();
+    for (key, value) in client_resp.headers() {
+        server_resp
+            .headers_mut()
+            .expect("no errors could be in ResponseBuilder")
+            .append(key, value.clone());
+    }
+    Ok(server_resp.body(client_resp.into_body())?)
+}
+
+fn http_not_found(_request: Request<Body>) -> Response<Body> {
+    Response::builder()
+        .status(StatusCode::NOT_FOUND)
+        .body(Body::empty())
+        .unwrap()
+}
diff --git a/test-programs/src/lib.rs b/test-programs/src/lib.rs
@@ -6,6 +6,8 @@ use std::process::{Child, Command};
 use std::thread::sleep;
 use std::time::Duration;
 
+const DEFAULT_SERVER_PORT: u16 = 8081;
+
 /// Manages exclusive access to port 8081, and kills the process when dropped
 pub struct WasmtimeServe {
     #[expect(dead_code, reason = "exists to live for as long as wasmtime process")]
@@ -22,26 +24,35 @@ impl WasmtimeServe {
     ///
     /// Kills the wasmtime process, and releases the lock, once dropped.
     pub fn new(guest: &str) -> std::io::Result<Self> {
+        Self::new_with_config(guest, DEFAULT_SERVER_PORT, &[])
+    }
+
+    pub fn new_with_config(guest: &str, port: u16, env_vars: &[&str]) -> std::io::Result<Self> {
         let mut lockfile = std::env::temp_dir();
-        lockfile.push("TEST_PROGRAMS_WASMTIME_SERVE.lock");
+        lockfile.push(format!("TEST_PROGRAMS_WASMTIME_SERVE_{port}.lock"));
         let lockfile = File::create(&lockfile)?;
         lockfile.lock()?;
 
         // Run wasmtime serve.
         // Enable -Scli because we currently don't have a way to build with the
         // proxy adapter, so we build with the default adapter.
-        let process = Command::new("wasmtime")
+        let mut process = Command::new("wasmtime");
+        let listening_addr = format!("127.0.0.1:{port}");
+        process
             .arg("serve")
             .arg("-Scli")
-            .arg("--addr=127.0.0.1:8081")
-            .arg(guest)
-            .spawn()?;
+            .arg("--addr")
+            .arg(&listening_addr);
+        for env_var in env_vars {
+            process.arg("--env").arg(env_var);
+        }
+        let process = process.arg(guest).spawn()?;
         let w = WasmtimeServe { lockfile, process };
 
         // Clumsily wait for the server to accept connections.
         'wait: loop {
             sleep(Duration::from_millis(100));
-            if TcpStream::connect("127.0.0.1:8081").is_ok() {
+            if TcpStream::connect(&listening_addr).is_ok() {
                 break 'wait;
             }
         }
diff --git a/test-programs/tests/http_server_proxy.rs b/test-programs/tests/http_server_proxy.rs
@@ -0,0 +1,20 @@
+use anyhow::Result;
+
+#[test_log::test]
+fn http_server_proxy() -> Result<()> {
+    // Run wasmtime serve for the proxy and the target HTTP server.
+    let _serve_target = test_programs::WasmtimeServe::new(test_programs::HTTP_SERVER)?;
+    let _serve_proxy = test_programs::WasmtimeServe::new_with_config(
+        test_programs::HTTP_SERVER_PROXY,
+        8082,
+        &["TARGET_URL=http://127.0.0.1:8081"],
+    )?;
+
+    // TEST / of the `http_server` example through the proxy
+    let body: String = ureq::get("http://127.0.0.1:8082/proxy/")
+        .call()?
+        .body_mut()
+        .read_to_string()?;
+    assert_eq!(body, "Hello, wasi:http/proxy world!\n");
+    Ok(())
+}
