docs(examples): Update client_json example to use async await

Cargo.toml

@@ -55,9 +55,9 @@ spmc = "0.2"
 url = "1.0"
 #tokio-fs = "0.1"
 #tokio-mockstream = "1.1.0"
-#serde = "1.0"
-#serde_derive = "1.0"
-#serde_json = "1.0"
+serde = "1.0"
+serde_derive = "1.0"
+serde_json = "1.0"
 
 [features]
 default = [

examples/client_json.rs

@@ -1,3 +1,4 @@
+#![feature(async_await)]
 #![deny(warnings)]
 extern crate hyper;
 #[macro_use]
@@ -6,56 +7,35 @@ extern crate serde;
 extern crate serde_json;
 
 use hyper::Client;
-use hyper::rt::{self, Future, Stream};
+use futures_util::TryStreamExt;
 
-fn main() {
+// A simple type alias so as to DRY.
+type Result<T> = std::result::Result<T, Box<dyn std::error::Error + Send + Sync>>;
+
+#[hyper::rt::main]
+async fn main() -> Result<()> {
     let url = "http://jsonplaceholder.typicode.com/users".parse().unwrap();
+    let users = fetch_json(url).await?;
+    // print users
+    println!("users: {:#?}", users);
 
-    let fut = fetch_json(url)
-        // use the parsed vector
-        .map(|users| {
-            // print users
-            println!("users: {:#?}", users);
-
-            // print the sum of ids
-            let sum = users.iter().fold(0, |acc, user| acc + user.id);
-            println!("sum of ids: {}", sum);
-        })
-        // if there was an error print it
-        .map_err(|e| {
-            match e {
-                FetchError::Http(e) => eprintln!("http error: {}", e),
-                FetchError::Json(e) => eprintln!("json parsing error: {}", e),
-            }
-        });
-
-    // Run the runtime with the future trying to fetch, parse and print json.
-    //
-    // Note that in more complicated use cases, the runtime should probably
-    // run on its own, and futures should just be spawned into it.
-    rt::run(fut);
+    // print the sum of ids
+    let sum = users.iter().fold(0, |acc, user| acc + user.id);
+    println!("sum of ids: {}", sum);
+    Ok(())
 }
 
-fn fetch_json(url: hyper::Uri) -> impl Future<Item=Vec<User>, Error=FetchError> {
+async fn fetch_json(url: hyper::Uri) -> Result<Vec<User>> {
     let client = Client::new();
 
-    client
-        // Fetch the url...
-        .get(url)
-        // And then, if we get a response back...
-        .and_then(|res| {
-            // asynchronously concatenate chunks of the body
-            res.into_body().concat2()
-        })
-        .from_err::<FetchError>()
-        // use the body after concatenation
-        .and_then(|body| {
-            // try to parse as json with serde_json
-            let users = serde_json::from_slice(&body)?;
+    // Fetch the url...
+    let res = client.get(url).await?;
+    // asynchronously concatenate chunks of the body
+    let body = res.into_body().try_concat().await?;
+    // try to parse as json with serde_json
+    let users = serde_json::from_slice(&body)?;
 
-            Ok(users)
-        })
-        .from_err()
+    Ok(users)
 }
 
 #[derive(Deserialize, Debug)]
@@ -63,21 +43,3 @@ struct User {
     id: i32,
     name: String,
 }
-
-// Define a type so we can return multiple types of errors
-enum FetchError {
-    Http(hyper::Error),
-    Json(serde_json::Error),
-}
-
-impl From<hyper::Error> for FetchError {
-    fn from(err: hyper::Error) -> FetchError {
-        FetchError::Http(err)
-    }
-}
-
-impl From<serde_json::Error> for FetchError {
-    fn from(err: serde_json::Error) -> FetchError {
-        FetchError::Json(err)
-    }
-}