Add UDP client example (send/recv_dgram) (#239)

examples/README.md

@@ -47,6 +47,8 @@ A high level description of each example is:
 * [`tinydb`](tinydb.rs) - an in-memory database which shows sharing state
   between all connected clients, notably the key/value store of this database.
 
+* [`udp-client`](udp-client.rs) - a simple `send_dgram`/`recv_dgram` example.
+
 If you've got an example you'd like to see here, please feel free to open an
 issue. Otherwise if you've got an example you'd like to add, please feel free
 to make a PR!

examples/udp-client.rs

@@ -0,0 +1,74 @@
+//! A UDP client that just sends everything it gets via `stdio` in a single datagram, and then
+//! waits for a reply.
+//!
+//! For the reasons of simplicity data from `stdio` is read until `EOF` in a blocking manner.
+//!
+//! You can test this out by running an echo server:
+//!
+//! ```
+//!     $ cargo run --example echo-udp -- 127.0.0.1:8080
+//! ```
+//!
+//! and running the client in another terminal:
+//!
+//! ```
+//!     $ cargo run --example udp-client
+//! ```
+//!
+//! You can optionally provide any custom endpoint address for the client:
+//!
+//! ```
+//!     $ cargo run --example udp-client -- 127.0.0.1:8080
+//! ```
+//!
+//! Don't forget to pass `EOF` to the standard input of the client!
+//!
+//! Please mind that since the UDP protocol doesn't have any capabilities to detect a broken
+//! connection the server needs to be run first, otherwise the client will block forever.
+
+extern crate futures;
+extern crate tokio;
+
+use std::env;
+use std::io::stdin;
+use std::net::SocketAddr;
+use tokio::net::UdpSocket;
+use tokio::prelude::*;
+
+fn get_stdin_data() -> Vec<u8> {
+    let mut buf = Vec::new();
+    stdin().read_to_end(&mut buf).unwrap();
+    buf
+}
+
+fn main() {
+    let remote_addr: SocketAddr = env::args()
+        .nth(1)
+        .unwrap_or("127.0.0.1:8080".into())
+        .parse()
+        .unwrap();
+    // We use port 0 to let the operating system allocate an available port for us.
+    let local_addr: SocketAddr = if remote_addr.is_ipv4() {
+        "0.0.0.0:0"
+    } else {
+        "[::]:0"
+    }.parse()
+        .unwrap();
+    let socket = UdpSocket::bind(&local_addr).unwrap();
+    const MAX_DATAGRAM_SIZE: usize = 65_507;
+    let processing = socket
+        .send_dgram(get_stdin_data(), &remote_addr)
+        .and_then(|(socket, _)| socket.recv_dgram(vec![0u8; MAX_DATAGRAM_SIZE]))
+        .map(|(_, data, len, _)| {
+            println!(
+                "Received {} bytes:\n{}",
+                len,
+                String::from_utf8_lossy(&data[..len])
+            )
+        })
+        .wait();
+    match processing {
+        Ok(_) => {}
+        Err(e) => eprintln!("Encountered an error: {}", e),
+    }
+}