add client

Author: matklad

src/bin/client.rs

@@ -1,3 +1,49 @@
-fn main() {
-    println!("hello, world")
+#![feature(async_await)]
+
+use std::net::ToSocketAddrs;
+
+use futures::select;
+
+use async_std::{
+    prelude::*,
+    net::TcpStream,
+    task,
+    io::{stdin, BufReader},
+};
+
+type Result<T> = std::result::Result<T, Box<dyn std::error::Error + Send + Sync>>;
+
+
+fn main() -> Result<()> {
+    task::block_on(try_main("127.0.0.1:8080"))
+}
+
+async fn try_main(addr: impl ToSocketAddrs) -> Result<()> {
+    let stream = TcpStream::connect(addr).await?;
+    let (reader, mut writer) = (&stream, &stream);
+    let reader = BufReader::new(reader);
+    let mut lines_from_server = futures::StreamExt::fuse(reader.lines());
+
+    let stdin = BufReader::new(stdin());
+    let mut lines_from_stdin = futures::StreamExt::fuse(stdin.lines());
+    loop {
+        select! {
+            line = lines_from_server.next() => match line {
+                Some(line) => {
+                    let line = line?;
+                    println!("{}", line);
+                },
+                None => break,
+            },
+            line = lines_from_stdin.next() => match line {
+                Some(line) => {
+                    let line = line?;
+                    writer.write_all(line.as_bytes()).await?;
+                    writer.write_all(b"\n").await?;
+                }
+                None => break,
+            }
+        }
+    }
+    Ok(())
 }

tutorial.adoc

@@ -865,3 +865,76 @@ where
     It is not strictly necessary in the current setup, where the broker waits for readers' shutdown anyway.
     However, if we add a server-initiated shutdown (for example, kbd:[ctrl+c] handling), this will be a way for the broker to shutdown the writers.
 <6> Finally, we close and drain the disconnections channel.
+
+== Implementing a client
+
+Let's now implement the client for the chat.
+Because the protocol is line-based, the implementation is pretty straightforward:
+
+* Lines read from stdin should be send over the socket.
+* Lines read from the socket should be echoed to stdout.
+
+Unlike the server, the client needs only limited concurrency, as it interacts with only a single user.
+For this reason, async doesn't bring a lot of performance benefits in this case.
+
+However, async is still useful for managing concurrency!
+Specifically, the client should _simultaneously_ read from stdin and from the socket.
+Programming this with threads is cumbersome, especially when implementing clean shutdown.
+With async, we can just use the `select!` macro.
+
+[source,rust]
+----
+#![feature(async_await)]
+
+use std::net::ToSocketAddrs;
+
+use futures::select;
+
+use async_std::{
+    prelude::*,
+    net::TcpStream,
+    task,
+    io::{stdin, BufReader},
+};
+
+type Result<T> = std::result::Result<T, Box<dyn std::error::Error + Send + Sync>>;
+
+
+fn main() -> Result<()> {
+    task::block_on(try_main("127.0.0.1:8080"))
+}
+
+async fn try_main(addr: impl ToSocketAddrs) -> Result<()> {
+    let stream = TcpStream::connect(addr).await?;
+    let (reader, mut writer) = (&stream, &stream); <1>
+    let reader = BufReader::new(reader);
+    let mut lines_from_server = futures::StreamExt::fuse(reader.lines()); <2>
+
+    let stdin = BufReader::new(stdin());
+    let mut lines_from_stdin = futures::StreamExt::fuse(stdin.lines()); <2>
+    loop {
+        select! { <3>
+            line = lines_from_server.next() => match line {
+                Some(line) => {
+                    let line = line?;
+                    println!("{}", line);
+                },
+                None => break,
+            },
+            line = lines_from_stdin.next() => match line {
+                Some(line) => {
+                    let line = line?;
+                    writer.write_all(line.as_bytes()).await?;
+                    writer.write_all(b"\n").await?;
+                }
+                None => break,
+            }
+        }
+    }
+    Ok(())
+}
+----
+
+<1> Here we split `TcpStream` into read and write halfs: there's `impl AsyncRead for &'_ TcpStream`, just like the one in std.
+<2> We crate a steam of lines for both the socket and stdin.
+<3> In the main select loop, we print the lines we receive from server and send the lines we read from the console. 

tutorial.html

@@ -1560,6 +1560,104 @@ <h2 id="_handling_disconnections">Handling Disconnections</h2>
 </div>
 </div>
 </div>
+<div class="sect1">
+<h2 id="_implementing_a_client">Implementing a client</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>Let&#8217;s now implement the client for the chat.
+Because the protocol is line-based, the implementation is pretty straightforward:</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p>Lines read from stdin should be send over the socket.</p>
+</li>
+<li>
+<p>Lines read from the socket should be echoed to stdout.</p>
+</li>
+</ul>
+</div>
+<div class="paragraph">
+<p>Unlike the server, the client needs only limited concurrency, as it interacts with only a single user.
+For this reason, async doesn&#8217;t bring a lot of performance benefits in this case.</p>
+</div>
+<div class="paragraph">
+<p>However, async is still useful for managing concurrency!
+Specifically, the client should <em>simultaneously</em> read from stdin and from the socket.
+Programming this with threads is cumbersome, especially when implementing clean shutdown.
+With async, we can just use the <code>select!</code> macro.</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="pygments highlight"><code data-lang="rust"><span></span><span class="tok-cp">#![feature(async_await)]</span><span class="tok-w"></span>
+
+<span class="tok-k">use</span><span class="tok-w"> </span><span class="tok-n">std</span>::<span class="tok-n">net</span>::<span class="tok-n">ToSocketAddrs</span><span class="tok-p">;</span><span class="tok-w"></span>
+
+<span class="tok-k">use</span><span class="tok-w"> </span><span class="tok-n">futures</span>::<span class="tok-n">select</span><span class="tok-p">;</span><span class="tok-w"></span>
+
+<span class="tok-k">use</span><span class="tok-w"> </span><span class="tok-n">async_std</span>::<span class="tok-p">{</span><span class="tok-w"></span>
+<span class="tok-w">    </span><span class="tok-n">prelude</span>::<span class="tok-o">*</span><span class="tok-p">,</span><span class="tok-w"></span>
+<span class="tok-w">    </span><span class="tok-n">net</span>::<span class="tok-n">TcpStream</span><span class="tok-p">,</span><span class="tok-w"></span>
+<span class="tok-w">    </span><span class="tok-n">task</span><span class="tok-p">,</span><span class="tok-w"></span>
+<span class="tok-w">    </span><span class="tok-n">io</span>::<span class="tok-p">{</span><span class="tok-n">stdin</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-n">BufReader</span><span class="tok-p">},</span><span class="tok-w"></span>
+<span class="tok-p">};</span><span class="tok-w"></span>
+
+<span class="tok-k">type</span> <span class="tok-nb">Result</span><span class="tok-o">&lt;</span><span class="tok-n">T</span><span class="tok-o">&gt;</span><span class="tok-w"> </span><span class="tok-o">=</span><span class="tok-w"> </span><span class="tok-n">std</span>::<span class="tok-n">result</span>::<span class="tok-nb">Result</span><span class="tok-o">&lt;</span><span class="tok-n">T</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-nb">Box</span><span class="tok-o">&lt;</span><span class="tok-n">dyn</span><span class="tok-w"> </span><span class="tok-n">std</span>::<span class="tok-n">error</span>::<span class="tok-n">Error</span><span class="tok-w"> </span><span class="tok-o">+</span><span class="tok-w"> </span><span class="tok-nb">Send</span><span class="tok-w"> </span><span class="tok-o">+</span><span class="tok-w"> </span><span class="tok-nb">Sync</span><span class="tok-o">&gt;&gt;</span><span class="tok-p">;</span><span class="tok-w"></span>
+
+
+<span class="tok-k">fn</span> <span class="tok-nf">main</span><span class="tok-p">()</span><span class="tok-w"> </span>-&gt; <span class="tok-nb">Result</span><span class="tok-o">&lt;</span><span class="tok-p">()</span><span class="tok-o">&gt;</span><span class="tok-w"> </span><span class="tok-p">{</span><span class="tok-w"></span>
+<span class="tok-w">    </span><span class="tok-n">task</span>::<span class="tok-n">block_on</span><span class="tok-p">(</span><span class="tok-n">try_main</span><span class="tok-p">(</span><span class="tok-s">&quot;127.0.0.1:8080&quot;</span><span class="tok-p">))</span><span class="tok-w"></span>
+<span class="tok-p">}</span><span class="tok-w"></span>
+
+<span class="tok-n">async</span><span class="tok-w"> </span><span class="tok-k">fn</span> <span class="tok-nf">try_main</span><span class="tok-p">(</span><span class="tok-n">addr</span>: <span class="tok-nc">impl</span><span class="tok-w"> </span><span class="tok-n">ToSocketAddrs</span><span class="tok-p">)</span><span class="tok-w"> </span>-&gt; <span class="tok-nb">Result</span><span class="tok-o">&lt;</span><span class="tok-p">()</span><span class="tok-o">&gt;</span><span class="tok-w"> </span><span class="tok-p">{</span><span class="tok-w"></span>
+<span class="tok-w">    </span><span class="tok-kd">let</span><span class="tok-w"> </span><span class="tok-n">stream</span><span class="tok-w"> </span><span class="tok-o">=</span><span class="tok-w"> </span><span class="tok-n">TcpStream</span>::<span class="tok-n">connect</span><span class="tok-p">(</span><span class="tok-n">addr</span><span class="tok-p">).</span><span class="tok-n">await</span><span class="tok-o">?</span><span class="tok-p">;</span><span class="tok-w"></span>
+<span class="tok-w">    </span><span class="tok-kd">let</span><span class="tok-w"> </span><span class="tok-p">(</span><span class="tok-n">reader</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-k">mut</span><span class="tok-w"> </span><span class="tok-n">writer</span><span class="tok-p">)</span><span class="tok-w"> </span><span class="tok-o">=</span><span class="tok-w"> </span><span class="tok-p">(</span><span class="tok-o">&amp;</span><span class="tok-n">stream</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-o">&amp;</span><span class="tok-n">stream</span><span class="tok-p">);</span><span class="tok-w"> </span><i class="conum" data-value="1"></i><b>(1)</b>
+<span class="tok-w">    </span><span class="tok-kd">let</span><span class="tok-w"> </span><span class="tok-n">reader</span><span class="tok-w"> </span><span class="tok-o">=</span><span class="tok-w"> </span><span class="tok-n">BufReader</span>::<span class="tok-n">new</span><span class="tok-p">(</span><span class="tok-n">reader</span><span class="tok-p">);</span><span class="tok-w"></span>
+<span class="tok-w">    </span><span class="tok-kd">let</span><span class="tok-w"> </span><span class="tok-k">mut</span><span class="tok-w"> </span><span class="tok-n">lines_from_server</span><span class="tok-w"> </span><span class="tok-o">=</span><span class="tok-w"> </span><span class="tok-n">futures</span>::<span class="tok-n">StreamExt</span>::<span class="tok-n">fuse</span><span class="tok-p">(</span><span class="tok-n">reader</span><span class="tok-p">.</span><span class="tok-n">lines</span><span class="tok-p">());</span><span class="tok-w"> </span><i class="conum" data-value="2"></i><b>(2)</b>
+
+<span class="tok-w">    </span><span class="tok-kd">let</span><span class="tok-w"> </span><span class="tok-n">stdin</span><span class="tok-w"> </span><span class="tok-o">=</span><span class="tok-w"> </span><span class="tok-n">BufReader</span>::<span class="tok-n">new</span><span class="tok-p">(</span><span class="tok-n">stdin</span><span class="tok-p">());</span><span class="tok-w"></span>
+<span class="tok-w">    </span><span class="tok-kd">let</span><span class="tok-w"> </span><span class="tok-k">mut</span><span class="tok-w"> </span><span class="tok-n">lines_from_stdin</span><span class="tok-w"> </span><span class="tok-o">=</span><span class="tok-w"> </span><span class="tok-n">futures</span>::<span class="tok-n">StreamExt</span>::<span class="tok-n">fuse</span><span class="tok-p">(</span><span class="tok-n">stdin</span><span class="tok-p">.</span><span class="tok-n">lines</span><span class="tok-p">());</span><span class="tok-w"> </span><i class="conum" data-value="2"></i><b>(2)</b>
+<span class="tok-w">    </span><span class="tok-k">loop</span><span class="tok-w"> </span><span class="tok-p">{</span><span class="tok-w"></span>
+<span class="tok-w">        </span><span class="tok-n">select</span><span class="tok-o">!</span><span class="tok-w"> </span><span class="tok-p">{</span><span class="tok-w"> </span><i class="conum" data-value="3"></i><b>(3)</b>
+<span class="tok-w">            </span><span class="tok-n">line</span><span class="tok-w"> </span><span class="tok-o">=</span><span class="tok-w"> </span><span class="tok-n">lines_from_server</span><span class="tok-p">.</span><span class="tok-n">next</span><span class="tok-p">()</span><span class="tok-w"> </span><span class="tok-o">=&gt;</span><span class="tok-w"> </span><span class="tok-k">match</span><span class="tok-w"> </span><span class="tok-n">line</span><span class="tok-w"> </span><span class="tok-p">{</span><span class="tok-w"></span>
+<span class="tok-w">                </span><span class="tok-nb">Some</span><span class="tok-p">(</span><span class="tok-n">line</span><span class="tok-p">)</span><span class="tok-w"> </span><span class="tok-o">=&gt;</span><span class="tok-w"> </span><span class="tok-p">{</span><span class="tok-w"></span>
+<span class="tok-w">                    </span><span class="tok-kd">let</span><span class="tok-w"> </span><span class="tok-n">line</span><span class="tok-w"> </span><span class="tok-o">=</span><span class="tok-w"> </span><span class="tok-n">line</span><span class="tok-o">?</span><span class="tok-p">;</span><span class="tok-w"></span>
+<span class="tok-w">                    </span><span class="tok-n">println</span><span class="tok-o">!</span><span class="tok-p">(</span><span class="tok-s">&quot;{}&quot;</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-n">line</span><span class="tok-p">);</span><span class="tok-w"></span>
+<span class="tok-w">                </span><span class="tok-p">},</span><span class="tok-w"></span>
+<span class="tok-w">                </span><span class="tok-nb">None</span><span class="tok-w"> </span><span class="tok-o">=&gt;</span><span class="tok-w"> </span><span class="tok-k">break</span><span class="tok-p">,</span><span class="tok-w"></span>
+<span class="tok-w">            </span><span class="tok-p">},</span><span class="tok-w"></span>
+<span class="tok-w">            </span><span class="tok-n">line</span><span class="tok-w"> </span><span class="tok-o">=</span><span class="tok-w"> </span><span class="tok-n">lines_from_stdin</span><span class="tok-p">.</span><span class="tok-n">next</span><span class="tok-p">()</span><span class="tok-w"> </span><span class="tok-o">=&gt;</span><span class="tok-w"> </span><span class="tok-k">match</span><span class="tok-w"> </span><span class="tok-n">line</span><span class="tok-w"> </span><span class="tok-p">{</span><span class="tok-w"></span>
+<span class="tok-w">                </span><span class="tok-nb">Some</span><span class="tok-p">(</span><span class="tok-n">line</span><span class="tok-p">)</span><span class="tok-w"> </span><span class="tok-o">=&gt;</span><span class="tok-w"> </span><span class="tok-p">{</span><span class="tok-w"></span>
+<span class="tok-w">                    </span><span class="tok-kd">let</span><span class="tok-w"> </span><span class="tok-n">line</span><span class="tok-w"> </span><span class="tok-o">=</span><span class="tok-w"> </span><span class="tok-n">line</span><span class="tok-o">?</span><span class="tok-p">;</span><span class="tok-w"></span>
+<span class="tok-w">                    </span><span class="tok-n">writer</span><span class="tok-p">.</span><span class="tok-n">write_all</span><span class="tok-p">(</span><span class="tok-n">line</span><span class="tok-p">.</span><span class="tok-n">as_bytes</span><span class="tok-p">()).</span><span class="tok-n">await</span><span class="tok-o">?</span><span class="tok-p">;</span><span class="tok-w"></span>
+<span class="tok-w">                    </span><span class="tok-n">writer</span><span class="tok-p">.</span><span class="tok-n">write_all</span><span class="tok-p">(</span><span class="tok-s">b&quot;</span><span class="tok-se">\n</span><span class="tok-s">&quot;</span><span class="tok-p">).</span><span class="tok-n">await</span><span class="tok-o">?</span><span class="tok-p">;</span><span class="tok-w"></span>
+<span class="tok-w">                </span><span class="tok-p">}</span><span class="tok-w"></span>
+<span class="tok-w">                </span><span class="tok-nb">None</span><span class="tok-w"> </span><span class="tok-o">=&gt;</span><span class="tok-w"> </span><span class="tok-k">break</span><span class="tok-p">,</span><span class="tok-w"></span>
+<span class="tok-w">            </span><span class="tok-p">}</span><span class="tok-w"></span>
+<span class="tok-w">        </span><span class="tok-p">}</span><span class="tok-w"></span>
+<span class="tok-w">    </span><span class="tok-p">}</span><span class="tok-w"></span>
+<span class="tok-w">    </span><span class="tok-nb">Ok</span><span class="tok-p">(())</span><span class="tok-w"></span>
+<span class="tok-p">}</span><span class="tok-w"></span></code></pre>
+</div>
+</div>
+<div class="colist arabic">
+<table>
+<tr>
+<td><i class="conum" data-value="1"></i><b>1</b></td>
+<td>Here we split <code>TcpStream</code> into read and write halfs: there&#8217;s <code>impl AsyncRead for &amp;'_ TcpStream</code>, just like the one in std.</td>
+</tr>
+<tr>
+<td><i class="conum" data-value="2"></i><b>2</b></td>
+<td>We crate a steam of lines for both the socket and stdin.</td>
+</tr>
+<tr>
+<td><i class="conum" data-value="3"></i><b>3</b></td>
+<td>In the main select loop, we print the lines we receive from server and send the lines we read from the console.</td>
+</tr>
+</table>
+</div>
+</div>
+</div>
 </div>
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