Add request-id header example (LukeMathWalker#108)

* Add request-id header example

* Apply cargo fmt

Cargo.toml

@@ -1,5 +1,5 @@
 [workspace]
-members = [".", "examples/opentelemetry", "examples/custom-root-span"]
+members = [".", "examples/opentelemetry", "examples/custom-root-span", "examples/request-id-response-header"]
 
 [package]
 name = "tracing-actix-web"

examples/request-id-response-header/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "request-id-response-header"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+actix-web = "4"
+tracing-actix-web = { path = "../.." }

examples/request-id-response-header/README.md

@@ -0,0 +1,25 @@
+# Request ID in Response Header
+
+This example shows how to set the `RequestId` as a response header.
+
+## Running
+
+You can launch this example with
+
+```bash
+cargo run
+```
+
+An `actix-web` application will be listening on port `8080`.
+You can fire requests to it with:
+
+```bash
+curl -v http://localhost:8080/hello
+```
+```text
+...
+< HTTP/1.1 200 OK
+< content-length: 12
+< x-request-id: 1d5c5448-44d2-4051-ab59-985868875f94
+...
+```

examples/request-id-response-header/src/main.rs

@@ -0,0 +1,41 @@
+use actix_web::{
+    dev::Service,
+    http::header::{HeaderName, HeaderValue},
+    web, App, HttpMessage, HttpServer,
+};
+use std::io;
+use tracing_actix_web::{RequestId, TracingLogger};
+
+async fn hello() -> &'static str {
+    "Hello world!"
+}
+
+#[actix_web::main]
+async fn main() -> io::Result<()> {
+    HttpServer::new(move || {
+        App::new()
+            // set the request id in the `x-request-id` response header
+            .wrap_fn(|req, srv| {
+                let request_id = req.extensions().get::<RequestId>().copied();
+                let res = srv.call(req);
+                async move {
+                    let mut res = res.await?;
+                    if let Some(request_id) = request_id {
+                        res.headers_mut().insert(
+                            HeaderName::from_static("x-request-id"),
+                            // this unwrap never fails, since UUIDs are valid ASCII strings
+                            HeaderValue::from_str(&request_id.to_string()).unwrap(),
+                        );
+                    }
+                    Ok(res)
+                }
+            })
+            .wrap(TracingLogger::default())
+            .service(web::resource("/hello").to(hello))
+    })
+    .bind("127.0.0.1:8080")?
+    .run()
+    .await?;
+
+    Ok(())
+}