restructure folders

templating/handlebars/Cargo.toml

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+[package]
+name = "template_handlebars"
+version = "1.0.0"
+edition = "2021"
+
+[dependencies]
+actix-web = "4.0.0-beta.21"
+handlebars = { version = "4.2.1", features = ["dir_source"] }
+serde_json = "1.0"

templating/handlebars/README.md

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+# Handlebars
+
+This is an example of how to use Actix Web with the [Handlebars](https://crates.io/crates/handlebars) templating language, which is currently the most popular crate that achieves this.
+
+## Usage
+
+```bash
+cd template_engines/handlebars
+cargo run
+```
+
+After starting the server, you may visit the following pages:
+
+- http://localhost:8080
+- http://localhost:8080/Emma/documents
+- http://localhost:8080/Bob/passwords
+- http://localhost:8080/some-non-existing-page - 404 error rendered using template

templating/handlebars/src/main.rs

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+use actix_web::body::BoxBody;
+use actix_web::dev::ServiceResponse;
+use actix_web::http::header::ContentType;
+use actix_web::http::StatusCode;
+use actix_web::middleware::{ErrorHandlerResponse, ErrorHandlers};
+use actix_web::{get, web, App, HttpResponse, HttpServer, Result};
+use handlebars::Handlebars;
+use serde_json::json;
+use std::io;
+
+// Macro documentation can be found in the actix_web_codegen crate
+#[get("/")]
+async fn index(hb: web::Data<Handlebars<'_>>) -> HttpResponse {
+    let data = json!({
+        "name": "Handlebars"
+    });
+    let body = hb.render("index", &data).unwrap();
+
+    HttpResponse::Ok().body(body)
+}
+
+#[get("/{user}/{data}")]
+async fn user(
+    hb: web::Data<Handlebars<'_>>,
+    path: web::Path<(String, String)>,
+) -> HttpResponse {
+    let info = path.into_inner();
+    let data = json!({
+        "user": info.0,
+        "data": info.1
+    });
+    let body = hb.render("user", &data).unwrap();
+
+    HttpResponse::Ok().body(body)
+}
+
+#[actix_web::main]
+async fn main() -> io::Result<()> {
+    // Handlebars uses a repository for the compiled templates. This object must be
+    // shared between the application threads, and is therefore passed to the
+    // Application Builder as an atomic reference-counted pointer.
+    let mut handlebars = Handlebars::new();
+    handlebars
+        .register_templates_directory(".html", "./static/templates")
+        .unwrap();
+    let handlebars_ref = web::Data::new(handlebars);
+
+    HttpServer::new(move || {
+        App::new()
+            .wrap(error_handlers())
+            .app_data(handlebars_ref.clone())
+            .service(index)
+            .service(user)
+    })
+    .bind(("127.0.0.1", 8080))?
+    .run()
+    .await
+}
+
+// Custom error handlers, to return HTML responses when an error occurs.
+fn error_handlers() -> ErrorHandlers<BoxBody> {
+    ErrorHandlers::new().handler(StatusCode::NOT_FOUND, not_found)
+}
+
+// Error handler for a 404 Page not found error.
+fn not_found<B>(res: ServiceResponse<B>) -> Result<ErrorHandlerResponse<BoxBody>> {
+    let response = get_error_response(&res, "Page not found");
+    Ok(ErrorHandlerResponse::Response(ServiceResponse::new(
+        res.into_parts().0,
+        response.map_into_left_body(),
+    )))
+}
+
+// Generic error handler.
+fn get_error_response<B>(
+    res: &ServiceResponse<B>,
+    error: &str,
+) -> HttpResponse<BoxBody> {
+    let request = res.request();
+
+    // Provide a fallback to a simple plain text response in case an error occurs during the
+    // rendering of the error page.
+    let fallback = |e: &str| {
+        HttpResponse::build(res.status())
+            .content_type(ContentType::plaintext())
+            .body(e.to_string())
+    };
+
+    let hb = request
+        .app_data::<web::Data<Handlebars>>()
+        .map(|t| t.get_ref());
+    match hb {
+        Some(hb) => {
+            let data = json!({
+                "error": error,
+                "status_code": res.status().as_str()
+            });
+            let body = hb.render("error", &data);
+
+            match body {
+                Ok(body) => HttpResponse::build(res.status())
+                    .content_type(ContentType::html())
+                    .body(body),
+                Err(_) => fallback(error),
+            }
+        }
+        None => fallback(error),
+    }
+}

templating/handlebars/static/templates/error.html

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+<!DOCTYPE html>
+<html>
+<head>
+  <meta charset="utf-8" />
+  <title>{{error}}</title>
+</head>
+<body>
+  <h1>{{status_code}} {{error}}</h1>
+</body>
+</html>

templating/handlebars/static/templates/index.html

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+<!DOCTYPE html>
+<html>
+
+<head>
+    <title>{{name}} Example</title>
+</head>
+
+<body>
+    <h1>{{name}} example</h1>
+    <p>This is an example of how to use {{name}} with Actix-Web.</p>
+</body>
+</html>

templating/handlebars/static/templates/user.html

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+<!DOCTYPE html>
+<html>
+
+<head>
+    <title>{{user}}'s homepage</title>
+</head>
+
+<body>
+    <h1>Welcome back, {{user}}</h1>
+    <p>Here's your {{data}}.</p>
+</body>
+</html>