Added json_error example. (#146)

Cargo.toml

@@ -16,6 +16,7 @@ members = [
   "http-proxy",
   "http-full-proxy",
   "json",
+  "json_error",
   "jsonrpc",
   "juniper",
   "middleware",

json_error/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "json_error"
+version = "0.1.0"
+authors = ["Kai Yao <kai.b.yao@gmail.com>"]
+edition = "2018"
+
+[dependencies]
+actix = "0.8"
+actix-web = "1.0"
+failure = "0.1"
+futures = "0.1"
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"

json_error/src/main.rs

@@ -0,0 +1,53 @@
+// This example is meant to show how to automatically generate a json error response when something goes wrong.
+
+use actix::System;
+use actix_web::http::StatusCode;
+use actix_web::web::{get, resource, HttpRequest, HttpResponse};
+use actix_web::{App, HttpServer, ResponseError};
+use futures::future::err;
+use futures::Future;
+use serde::Serialize;
+use serde_json::{json, to_string_pretty};
+use std::fmt::{Display, Formatter, Result as FmtResult};
+use std::io;
+
+#[derive(Debug, Serialize)]
+struct Error {
+  msg: String,
+  status: u16,
+}
+
+impl Display for Error {
+  fn fmt(&self, f: &mut Formatter) -> FmtResult {
+    write!(f, "{}", to_string_pretty(self).unwrap())
+  }
+}
+
+impl ResponseError for Error {
+  // builds the actual response to send back when an error occurs
+  fn render_response(&self) -> HttpResponse {
+    let err_json = json!({ "error": self.msg });
+    HttpResponse::build(StatusCode::from_u16(self.status).unwrap()).json(err_json)
+  }
+}
+
+fn index(_: HttpRequest) -> impl Future<Item = HttpResponse, Error = Error> {
+  err(Error {
+    msg: "an example error message".to_string(),
+    status: 400,
+  })
+}
+
+fn main() -> io::Result<()> {
+  let sys = System::new("json_error_example");
+  let ip_address = "127.0.0.1:8000";
+
+  HttpServer::new(|| App::new().service(resource("/").route(get().to_async(index))))
+    .bind(ip_address)
+    .expect("Can not bind to port 8000")
+    .start();
+
+  println!("Running server on {}", ip_address);
+
+  sys.run()
+}