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<h1 id="构建单线程-web-服务器"><a class="header" href="#构建单线程-web-服务器">构建单线程 Web 服务器</a></h1>
<p>在开始之前先来简单回顾下构建所需的网络协议: HTTP 和 TCP。这两种协议都是请求-应答模式的网络协议,意味着在客户端发起请求后,服务器会监听并处理进入的请求,最后给予应答,至于这个过程怎么进行,取决于具体的协议定义。</p>
<p>与 HTTP 有所不同, TCP 是一个底层协议,它仅描述客户端传递了信息给服务器,至于这个信息长什么样,怎么解析处理,则不在该协议的职责范畴内。</p>
<p>而 HTTP 协议是更高层的通信协议,一般来说都基于 TCP 来构建 (HTTP/3 是基于 UDP 构建的协议),更高层的协议也意味着它会对传输的信息进行解析处理。</p>
<p>更加深入的学习网络协议并不属于本书的范畴,因此让我们从如何读取 TCP 传输的字节流开始吧。</p>
<h2 id="监听-tcp-连接"><a class="header" href="#监听-tcp-连接">监听 TCP 连接</a></h2>
<p>先来创建一个全新的项目:</p>
<pre><code class="language-shell">$ cargo new hello
Created binary (application) `hello` project
$ cd hello
</code></pre>
<p>接下来,使用 <code>std::net</code> 模块监听进入的请求连接IP和端口是 <code>127.0.0.1:7878</code></p>
<pre><pre class="playground"><code class="language-rust edition2021">use std::net::TcpListener;
fn main() {
// 监听地址: 127.0.0.1:7878
let listener = TcpListener::bind(&quot;127.0.0.1:7878&quot;).unwrap();
for stream in listener.incoming() {
let stream = stream.unwrap();
println!(&quot;Connection established!&quot;);
}
}</code></pre></pre>
<p>选择 <code>7878</code> 端口的原因是,<code>80</code><code>8080</code> 往往都被 HTTP 服务器霸占,因此我们需要选择一个跟已经监听的端口不冲突的。</p>
<p><code>bind</code> 非常类似 <code>new</code> ,它返回一个 <code>TcpListener</code> 实例,只不过我们一般都说 &quot;绑定到某个端口&quot;,因此 <code>bind</code> 这个名称会更合适。</p>
<p><code>unwrap</code> 的使用是因为 <code>bind</code> 返回 <code>Result&lt;T,E&gt;</code>,毕竟监听是有可能报错的,例如:如果要监听 <code>80</code> 端口往往需要管理员权限;监听了同样的端口,等等。</p>
<p><code>incoming</code> 会返回一个迭代器,它每一次迭代都会返回一个新的连接 <code>stream</code>(客户端发起web服务器监听接收),因此,接下来要做的就是从 <code>stream</code> 中读取数据,然后返回处理后的结果。</p>
<p>细心的同学可能会注意到,代码中对 <code>stream</code> 还进行了一次 <code>unwrap</code> 处理,原因在于我们并不是在迭代一个一个连接,而是在迭代处理一个一个请求建立连接的尝试,而这种尝试可能会失败!例如,操作系统的最大连接数限制。</p>
<p>现在,启动服务器,然后在你的浏览器中,访问地址 <code>127.0.0.1:7878</code>,这时应该会看到一条错误信息,类似: &quot;Connection reset&quot;,毕竟我们的服务器目前只是接收了连接,并没有回复任何数据。</p>
<pre><code class="language-shell">$ cargo run
Running `target/debug/hello`
Connection established!
Connection established!
Connection established!
</code></pre>
<p>无论浏览器怎么摆烂我们的服务器还是成功打出了信息TCP 连接已经成功建立。</p>
<p>可能大家会疑问,为啥在浏览器访问一次,可能会在终端打印出多次请求建立的信息,难道不是应该一一对应吗?原因在于当 <code>stream</code> 超出作用域时,会触发 <code>drop</code> 的扫尾工作,其中包含了关闭连接。但是,浏览器可能会存在自动重试的情况,因此还会重新建立连接,最终打印了多次。</p>
<p>由于 <code>listener.incoming</code> 会在当前阻塞式监听,也就是 <code>main</code> 线程会被阻塞,我们最后需要通过 <code>ctrl + c</code> 来结束程序进程。</p>
<h2 id="读取请求"><a class="header" href="#读取请求">读取请求</a></h2>
<p>连接建立后,就可以开始读取客户端传来的数据:</p>
<pre><pre class="playground"><code class="language-rust edition2021">use std::{
io::{prelude::*, BufReader},
net::{TcpListener, TcpStream},
};
fn main() {
let listener = TcpListener::bind(&quot;127.0.0.1:7878&quot;).unwrap();
for stream in listener.incoming() {
let stream = stream.unwrap();
handle_connection(stream);
}
}
fn handle_connection(mut stream: TcpStream) {
let buf_reader = BufReader::new(&amp;mut stream);
let http_request: Vec&lt;_&gt; = buf_reader
.lines()
.map(|result| result.unwrap())
.take_while(|line| !line.is_empty())
.collect();
println!(&quot;Request: {:#?}&quot;, http_request);
}</code></pre></pre>
<p>这段代码有几点值得注意:</p>
<ul>
<li>引入 <code>std::io::prelude</code><code>std::io::BufReader</code> 是引入相应的特征和类型,帮助我们读取和写入数据</li>
<li><code>BufReader</code> 可以实现缓冲区读取,底层其实是基于 <code>std::io::Read</code> 实现</li>
<li>可以使用 <code>lines</code> 方法来获取一个迭代器,可以对传输的内容流进行按行迭代读取,要使用该方法,必须先引入 <code>std::io::BufRead</code></li>
<li>最后使用 <code>collect</code> 消费掉迭代器,最终客户端发来的请求数据被存到 <code>http_request</code> 这个动态数组中</li>
</ul>
<p>大家可能会比较好奇,该如何判断客户端发来的 HTTP 数据是否读取完成,答案就在于客户端会在请求数据的结尾附上两个换行符,当我们检测到某一行字符串为空时,就意味着请求数据已经传输完毕,可以 <code>collect</code> 了。</p>
<p>来运行下试试:</p>
<pre><code class="language-shell">$ cargo run
Compiling hello v0.1.0 (file:///projects/hello)
Finished dev [unoptimized + debuginfo] target(s) in 0.42s
Running `target/debug/hello`
Request: [
&quot;GET / HTTP/1.1&quot;,
&quot;Host: 127.0.0.1:7878&quot;,
&quot;User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:99.0) Gecko/20100101 Firefox/99.0&quot;,
&quot;Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8&quot;,
&quot;Accept-Language: en-US,en;q=0.5&quot;,
&quot;Accept-Encoding: gzip, deflate, br&quot;,
&quot;DNT: 1&quot;,
&quot;Connection: keep-alive&quot;,
&quot;Upgrade-Insecure-Requests: 1&quot;,
&quot;Sec-Fetch-Dest: document&quot;,
&quot;Sec-Fetch-Mode: navigate&quot;,
&quot;Sec-Fetch-Site: none&quot;,
&quot;Sec-Fetch-User: ?1&quot;,
&quot;Cache-Control: max-age=0&quot;,
]
</code></pre>
<p>呦,还挺长的,是不是长得很像我们以前见过的 HTTP 请求 JSON来简单分析下。</p>
<h2 id="http-请求长啥样"><a class="header" href="#http-请求长啥样">HTTP 请求长啥样</a></h2>
<p>刚才的文本挺长的,但其实符合以下的格式:</p>
<pre><code class="language-text">Method Request-URI HTTP-Version
headers CRLF
message-body
</code></pre>
<ul>
<li>第一行 Method 是请求的方法,例如 <code>GET</code><code>POST</code>Request-URI 是该请求希望访问的目标资源路径,例如 <code>/</code><code>/hello/world</code></li>
<li>类似 JSON 格式的数据都是 HTTP 请求报头 headers例如 <code>&quot;Host: 127.0.0.1:7878&quot;</code></li>
<li>至于 message-body 是消息体, 它包含了用户请求携带的具体数据,例如更改用户名的请求,就要提交新的用户名数据,至于刚才的 <code>GET</code> 请求,它是没有 message-body 的</li>
</ul>
<p>大家可以尝试换一个浏览器再访问一次,看看不同的浏览器请求携带的 headers 是否不同。</p>
<h2 id="请求应答"><a class="header" href="#请求应答">请求应答</a></h2>
<p>目前为止都是在服务器端的操作浏览器的请求依然还会报错是时候给予相应的请求应答了HTTP 格式类似:</p>
<pre><code class="language-text">HTTP-Version Status-Code Reason-Phrase CRLF
headers CRLF
message-body
</code></pre>
<p>应答的格式与请求相差不大,其中 Status-Code 是最重要的,它用于告诉客户端,当前的请求是否成功,若失败,大概是什么原因,它就是著名的 HTTP 状态码,常用的有 <code>200</code>: 请求成功,<code>404</code> 目标不存在,等等。</p>
<p>为了帮助大家更直观的感受下应答格式第一行长什么样,下面给出一个示例:</p>
<pre><code class="language-text">HTTP/1.1 200 OK\r\n\r\n
</code></pre>
<p>下面将该应答发送回客户端:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>fn handle_connection(mut stream: TcpStream) {
let buf_reader = BufReader::new(&amp;mut stream);
let http_request: Vec&lt;_&gt; = buf_reader
.lines()
.map(|result| result.unwrap())
.take_while(|line| !line.is_empty())
.collect();
let response = &quot;HTTP/1.1 200 OK\r\n\r\n&quot;;
stream.write_all(response.as_bytes()).unwrap();
}
<span class="boring">}</span></code></pre></pre>
<p>由于 <code>write_all</code> 方法接受 <code>&amp;[u8]</code> 类型作为参数,这里需要用 <code>as_bytes</code> 将字符串转换为字节数组。</p>
<p>重新启动服务器,然后再观察下浏览器中的输出,这次应该不再有报错,而是一个空白页面,因为没有返回任何具体的数据( message-body ),上面只是一条最简单的符合 HTTP 格式的数据。</p>
<h2 id="返回-html-页面"><a class="header" href="#返回-html-页面">返回 HTML 页面</a></h2>
<p>空白页面显然会让人不知所措,那就返回一个简单的 HTML 页面,给用户打给招呼。</p>
<p>在项目的根目录下创建 <code>hello.html</code> 文件并写入如下内容:</p>
<pre><code class="language-html">&lt;!DOCTYPE html&gt;
&lt;html lang=&quot;en&quot;&gt;
&lt;head&gt;
&lt;meta charset=&quot;utf-8&quot;&gt;
&lt;title&gt;Hello!&lt;/title&gt;
&lt;/head&gt;
&lt;body&gt;
&lt;h1&gt;Hello!&lt;/h1&gt;
&lt;p&gt;Hi from Rust&lt;/p&gt;
&lt;/body&gt;
&lt;/html&gt;
</code></pre>
<p>看得出来,这是一个非常简单的 HTML5 网页文档,基本上没人读不懂吧 </p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use std::{
fs,
io::{prelude::*, BufReader},
net::{TcpListener, TcpStream},
};
// --snip--
fn handle_connection(mut stream: TcpStream) {
let buf_reader = BufReader::new(&amp;mut stream);
let http_request: Vec&lt;_&gt; = buf_reader
.lines()
.map(|result| result.unwrap())
.take_while(|line| !line.is_empty())
.collect();
let status_line = &quot;HTTP/1.1 200 OK&quot;;
let contents = fs::read_to_string(&quot;hello.html&quot;).unwrap();
let length = contents.len();
let response =
format!(&quot;{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}&quot;);
stream.write_all(response.as_bytes()).unwrap();
}
<span class="boring">}</span></code></pre></pre>
<p>新修改的代码中,读取了新增 HTML 的内容,并按照 HTTP 格式,将内容传回给客户端。</p>
<p>具体的运行验证就不再赘述,我们再来看看如何增加一些验证和选择性回复。</p>
<blockquote>
<p>用这么奇怪的格式返回应答数据,原因只有一个,我们在模拟实现真正的 http web 服务器框架。事实上,写逻辑代码时,只需使用现成的 web 框架( 例如 <a href="https://rocket.rs"><code>rocket</code></a> )去启动 web 服务即可,解析请求数据和返回应答数据都已经被封装在 API 中,非常简单易用</p>
</blockquote>
<h2 id="验证请求和选择性应答"><a class="header" href="#验证请求和选择性应答">验证请求和选择性应答</a></h2>
<p>用户想要获取他的个人信息,你给他 say hi用户想要查看他的某篇文章内容你给他 say hi, 好吧用户想要骂你,你还是给它 say hi。</p>
<p>是的,这种服务态度我们很欣赏,但是这种服务质量属实令人堪忧。因此我们要针对用户的不同请求给出相应的不同回复,让场景模拟更加真实。</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>fn handle_connection(mut stream: TcpStream) {
let buf_reader = BufReader::new(&amp;mut stream);
let request_line = buf_reader.lines().next().unwrap().unwrap();
if request_line == &quot;GET / HTTP/1.1&quot; {
let status_line = &quot;HTTP/1.1 200 OK&quot;;
let contents = fs::read_to_string(&quot;hello.html&quot;).unwrap();
let length = contents.len();
let response = format!(
&quot;{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}&quot;
);
stream.write_all(response.as_bytes()).unwrap();
} else {
// some other request
}
}
<span class="boring">}</span></code></pre></pre>
<p>注意迭代器方法 <code>next</code> 的使用,原因在于我们只需要读取第一行,判断具体的 HTTP METHOD 是什么。</p>
<p>接着判断了用户是否请求了 <code>/</code> 根路径,如果是,返回之前的 <code>hello.html</code> 页面;如果不是...尚未实现。</p>
<p>重新运行服务器,如果你继续访问 <code>127.0.0.1:7878</code> ,那么看到的依然是 <code>hello.html</code> 页面,因为默认访问根路径,但是一旦换一个路径访问,例如 <code>127.0.0.1:7878/something-else</code>,那你将继续看到之前看过多次的连接错误。</p>
<p>下面来完善下,当用户访问根路径之外的页面时,给他展示一个友好的 404 页面( 相比直接报错 )。</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span> // --snip--
} else {
let status_line = &quot;HTTP/1.1 404 NOT FOUND&quot;;
let contents = fs::read_to_string(&quot;404.html&quot;).unwrap();
let length = contents.len();
let response = format!(
&quot;{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}&quot;
);
stream.write_all(response.as_bytes()).unwrap();
}
<span class="boring">}</span></code></pre></pre>
<p>哦对了,别忘了在根路径下创建 <code>404.html</code>并填入下面内容:</p>
<pre><code class="language-html">&lt;!DOCTYPE html&gt;
&lt;html lang=&quot;en&quot;&gt;
&lt;head&gt;
&lt;meta charset=&quot;utf-8&quot;&gt;
&lt;title&gt;你好!&lt;/title&gt;
&lt;/head&gt;
&lt;body&gt;
&lt;h1&gt;很抱歉!&lt;/h1&gt;
&lt;p&gt;由于运维删库跑路我们的数据全部丢失总监也已经准备跑路88&lt;/p&gt;
&lt;/body&gt;
&lt;/html&gt;
</code></pre>
<p>最后,上面的代码其实有很多重复,可以提取出来进行简单重构:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// --snip--
fn handle_connection(mut stream: TcpStream) {
// --snip--
let (status_line, filename) = if request_line == &quot;GET / HTTP/1.1&quot; {
(&quot;HTTP/1.1 200 OK&quot;, &quot;hello.html&quot;)
} else {
(&quot;HTTP/1.1 404 NOT FOUND&quot;, &quot;404.html&quot;)
};
let contents = fs::read_to_string(filename).unwrap();
let length = contents.len();
let response =
format!(&quot;{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}&quot;);
stream.write_all(response.as_bytes()).unwrap();
}
<span class="boring">}</span></code></pre></pre>
<p>至此,单线程版本的服务器已经完成,但是说实话,没啥用,总不能让你的用户排队等待访问吧,那也太糟糕了...</p>
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