codec: move into tokio-util (#1675)

Related to #1318, Tokio APIs that are "less stable" are moved into a new
`tokio-util` crate. This crate will mirror `tokio` and provide
additional APIs that may require a greater rate of breaking changes.

As examples require `tokio-util`, they are moved into a separate
crate (`examples`). This has the added advantage of being able to avoid
example only dependencies in the `tokio` crate.

1 files changed, 104 insertions, 0 deletions

diff --git a/examples/print_each_packet.rs b/examples/print_each_packet.rs
new file mode 100644
index 00000000..0a275545
--- /dev/null
+++ b/examples/print_each_packet.rs
@@ -0,0 +1,104 @@
+//! A "print-each-packet" server with Tokio
+//!
+//! This server will create a TCP listener, accept connections in a loop, and
+//! put down in the stdout everything that's read off of each TCP connection.
+//!
+//! Because the Tokio runtime uses a thread pool, each TCP connection is
+//! processed concurrently with all other TCP connections across multiple
+//! threads.
+//!
+//! To see this server in action, you can run this in one terminal:
+//!
+//!     cargo run --example print\_each\_packet
+//!
+//! and in another terminal you can run:
+//!
+//!     cargo run --example connect 127.0.0.1:8080
+//!
+//! Each line you type in to the `connect` terminal should be written to terminal!
+//!
+//! Minimal js example:
+//!
+//! ```js
+//! var net = require("net");
+//!
+//! var listenPort = 8080;
+//!
+//! var server = net.createServer(function (socket) {
+//!     socket.on("data", function (bytes) {
+//!         console.log("bytes", bytes);
+//!     });
+//!
+//!     socket.on("end", function() {
+//!         console.log("Socket received FIN packet and closed connection");
+//!     });
+//!     socket.on("error", function (error) {
+//!         console.log("Socket closed with error", error);
+//!     });
+//!
+//!     socket.on("close", function (with_error) {
+//!         if (with_error) {
+//!             console.log("Socket closed with result: Err(SomeError)");
+//!         } else {
+//!             console.log("Socket closed with result: Ok(())");
+//!         }
+//!     });
+//!
+//! });
+//!
+//! server.listen(listenPort);
+//!
+//! console.log("Listening on:", listenPort);
+//! ```
+//!
+
+#![warn(rust_2018_idioms)]
+
+use tokio::net::TcpListener;
+use tokio::prelude::*;
+use tokio_util::codec::{BytesCodec, Decoder};
+
+use std::env;
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    // Allow passing an address to listen on as the first argument of this
+    // program, but otherwise we'll just set up our TCP listener on
+    // 127.0.0.1:8080 for connections.
+    let addr = env::args().nth(1).unwrap_or("127.0.0.1:8080".to_string());
+
+    // Next up we create a TCP listener which will listen for incoming
+    // connections. This TCP listener is bound to the address we determined
+    // above and must be associated with an event loop, so we pass in a handle
+    // to our event loop. After the socket's created we inform that we're ready
+    // to go and start accepting connections.
+    let mut listener = TcpListener::bind(&addr).await?;
+    println!("Listening on: {}", addr);
+
+    loop {
+        // Asynchronously wait for an inbound socket.
+        let (socket, _) = listener.accept().await?;
+
+        // And this is where much of the magic of this server happens. We
+        // crucially want all clients to make progress concurrently, rather than
+        // blocking one on completion of another. To achieve this we use the
+        // `tokio::spawn` function to execute the work in the background.
+        //
+        // Essentially here we're executing a new task to run concurrently,
+        // which will allow all of our clients to be processed concurrently.
+        tokio::spawn(async move {
+            // We're parsing each socket with the `BytesCodec` included in `tokio::codec`.
+            let mut framed = BytesCodec::new().framed(socket);
+
+            // We loop while there are messages coming from the Stream `framed`.
+            // The stream will return None once the client disconnects.
+            while let Some(message) = framed.next().await {
+                match message {
+                    Ok(bytes) => println!("bytes: {:?}", bytes),
+                    Err(err) => println!("Socket closed with error: {:?}", err),
+                }
+            }
+            println!("Socket received FIN packet and closed connection");
+        });
+    }
+}