Add a http server proxy example

Author: tomasol

Cargo.toml

@@ -31,6 +31,7 @@ serde_json = { workspace = true, optional = true }
 [dev-dependencies]
 anyhow.workspace = true
 clap.workspace = true
+futures-concurrency.workspace = true
 futures-lite.workspace = true
 humantime.workspace = true
 serde = { workspace = true, features = ["derive"] }
@@ -61,6 +62,7 @@ authors = [
 anyhow = "1"
 cargo_metadata = "0.18.1"
 clap = { version = "4.5.26", features = ["derive"] }
+futures-concurrency = "7.6.3"
 futures-core = "0.3.19"
 futures-lite = "1.12.0"
 humantime = "2.1.0"

examples/http_server_proxy.rs

@@ -0,0 +1,90 @@
+// Run the example with:
+// wasmtime serve -Scli -Shttp --env TARGET_URL=https://example.com http_server_proxy.wasm
+use futures_concurrency::prelude::*;
+use wstd::http::body::{BodyForthcoming, IncomingBody};
+use wstd::http::server::{Finished, Responder};
+use wstd::http::{Client, Request, Response, StatusCode, Uri};
+use wstd::io::{copy, empty};
+
+const PROXY_PREFIX: &str = "/proxy";
+
+#[wstd::http_server]
+async fn main(mut server_req: Request<IncomingBody>, responder: Responder) -> Finished {
+    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");
+
+            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 request to the client request.
+            for (key, value) in server_req.headers() {
+                client_req = client_req.header(key, value);
+            }
+
+            // Send the request.
+            let client_req = client_req
+                .body(BodyForthcoming)
+                .expect("client_req.body failed");
+            let (mut client_request_body, client_resp) = client
+                .start_request(client_req)
+                .await
+                .expect("client.start_request failed");
+
+            // Copy the server request body to client's request body.
+            let server_req_to_client_req = async {
+                let res = copy(server_req.body_mut(), &mut client_request_body).await;
+                // TODO: Convert to io error if necessary
+                let _ = Client::finish(client_request_body, None);
+                res
+            };
+
+            // Copy the client response headers to server response.
+            let client_resp_to_server_resp = async {
+                let client_resp = client_resp.await.unwrap();
+                let mut server_resp = Response::builder();
+                for (key, value) in client_resp.headers() {
+                    server_resp
+                        .headers_mut()
+                        .unwrap()
+                        .append(key, value.clone());
+                }
+                // Start sending the server response.
+                let server_resp = server_resp.body(BodyForthcoming).unwrap();
+                let mut server_resp = responder.start_response(server_resp);
+
+                (
+                    copy(client_resp.into_body(), &mut server_resp).await,
+                    server_resp,
+                )
+            };
+
+            let (server_req_to_client_req, (client_resp_to_server_resp, server_resp)) =
+                (server_req_to_client_req, client_resp_to_server_resp)
+                    .join()
+                    .await;
+            let is_success = server_req_to_client_req.and(client_resp_to_server_resp);
+            Finished::finish(server_resp, is_success, None)
+        }
+        _ => http_not_found(server_req, responder).await,
+    }
+}
+
+async fn http_not_found(_request: Request<IncomingBody>, responder: Responder) -> Finished {
+    let response = Response::builder()
+        .status(StatusCode::NOT_FOUND)
+        .body(empty())
+        .unwrap();
+    responder.respond(response).await
+}