Add actix-gcd example, from the tour.

README.md

@@ -15,8 +15,8 @@ terms of the MIT license. See [LICENSE-MIT](LICENSE-MIT) for details.
 - The `gcd` directory holds the command-line program for computing the greatest
   common denominator of a list of numbers.
 
-- The `iron-gcd` directory holds the code for the simple web service,
-  implemented using the [`iron`] framework, that computes greatest common
+- The `actix-gcd` directory holds the code for the simple web service,
+  implemented using the [`actix-web`] framework, that computes greatest common
   denominators.
 
 - The Mandelbrot plotting program has its own repository, at

actix-gcd/.gitignore

@@ -0,0 +1,2 @@
+/target/
+

actix-gcd/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "actix-gcd"
+version = "0.1.0"
+authors = ["You <you@example.com>"]
+edition = "2018"
+
+# See more keys and their definitions at
+# https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+actix-web = "1.0.8"
+serde = { version = "1.0", features = ["derive"] }

actix-gcd/src/main.rs

@@ -0,0 +1,66 @@
+use actix_web::{web, App, HttpResponse, HttpServer};
+
+fn main() {
+    let server = HttpServer::new(|| {
+        App::new()
+            .route("/", web::get().to(get_index))
+            .route("/gcd", web::post().to(post_gcd))
+    });
+
+    println!("Serving on http://localhost:3000...");
+    server
+        .bind("127.0.0.1:3000").expect("error binding server to address")
+        .run().expect("error running server");
+}
+
+fn get_index() -> HttpResponse {
+    HttpResponse::Ok()
+        .content_type("text/html")
+        .body(
+            r#"
+                <title>GCD Calculator</title>
+                <form action="/gcd" method="post">
+                <input type="text" name="n"/>
+                <input type="text" name="m"/>
+                <button type="submit">Compute GCD</button>
+                </form>
+            "#,
+        )
+}
+
+use serde::Deserialize;
+#[derive(Deserialize)]
+struct GcdParameters {
+    n: u64,
+    m: u64,
+}
+
+fn post_gcd(form: web::Form<GcdParameters>) -> HttpResponse {
+    if form.n == 0 || form.m == 0 {
+        return HttpResponse::BadRequest()
+            .content_type("text/html")
+            .body("Computing the GCD with zero is boring.");
+    }
+
+    let response =
+        format!("The greatest common divisor of the numbers {} and {} \
+                 is <b>{}</b>\n",
+                form.n, form.m, gcd(form.n, form.m));
+
+    HttpResponse::Ok()
+        .content_type("text/html")
+        .body(response)
+}
+
+fn gcd(mut n: u64, mut m: u64) -> u64 {
+    assert!(n != 0 && m != 0);
+    while m != 0 {
+        if m < n {
+            let t = m;
+            m = n;
+            n = t;
+        }
+        m = m % n;
+    }
+    n
+}