ded
/
cpp-httplib
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    <h1>Basic Server</h1>
    <p>前章ではクライアントからリクエストを送りました。そのとき、テスト用サーバーを用意しましたね。この章では、あのサーバーの仕組みをひとつずつ紐解いていきます。</p>
<h2>サーバーの起動</h2>
<p>ルーティングを登録したら、最後に <code>svr.listen()</code> を呼んでサーバーを起動します。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">listen</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">0.0.0.0</span><span style="color:#c0c5ce;">&quot;, </span><span style="color:#d08770;">8080</span><span style="color:#c0c5ce;">);
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.listen(</span><span style="color:#183691;">&quot;0.0.0.0&quot;</span><span style="color:#323232;">, </span><span style="color:#0086b3;">8080</span><span style="color:#323232;">);
</span></pre>
</div></div>
<p>第1引数はホスト、第2引数はポート番号です。<code>"0.0.0.0"</code> を指定すると、すべてのネットワークインターフェースでリクエストを受け付けます。自分のマシンからのアクセスだけに限定したいときは <code>"127.0.0.1"</code> を使います。</p>
<p><code>listen()</code> はブロッキング呼び出しです。サーバーが停止するまで、この行から先には進みません。ターミナルで <code>Ctrl+C</code> を押すか、別スレッドから <code>svr.stop()</code> を呼ぶまでサーバーは動き続けます。</p>
<h2>ルーティング</h2>
<p>サーバーの核になるのは「ルーティング」です。どのURLに、どのHTTPメソッドでアクセスされたら、何をするか。それを登録する仕組みです。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">httplib::Server svr;
</span><span style="color:#c0c5ce;">
</span><span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/hi</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const</span><span style="color:#c0c5ce;"> httplib::Request &amp;req, httplib::Response &amp;res) {
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">Hello!</span><span style="color:#c0c5ce;">&quot;, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">httplib::Server svr;
</span><span style="color:#323232;">
</span><span style="color:#323232;">svr.Get(</span><span style="color:#183691;">&quot;/hi&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const</span><span style="color:#323232;"> httplib::Request </span><span style="font-weight:bold;color:#a71d5d;">&amp;</span><span style="color:#323232;">req, httplib::Response </span><span style="font-weight:bold;color:#a71d5d;">&amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    res.set_content(</span><span style="color:#183691;">&quot;Hello!&quot;</span><span style="color:#323232;">, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<p><code>svr.Get()</code> は、GETリクエストに対するハンドラーを登録します。第1引数がパス、第2引数がハンドラー関数です。<code>/hi</code> にGETリクエストが来たら、このラムダが呼ばれます。</p>
<p>HTTPメソッドごとにメソッドが用意されています。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/path</span><span style="color:#c0c5ce;">&quot;,    handler);  </span><span style="color:#65737e;">// GET
</span><span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Post</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/path</span><span style="color:#c0c5ce;">&quot;,   handler);  </span><span style="color:#65737e;">// POST
</span><span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Put</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/path</span><span style="color:#c0c5ce;">&quot;,    handler);  </span><span style="color:#65737e;">// PUT
</span><span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Delete</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/path</span><span style="color:#c0c5ce;">&quot;, handler);  </span><span style="color:#65737e;">// DELETE
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Get(</span><span style="color:#183691;">&quot;/path&quot;</span><span style="color:#323232;">,    handler);  </span><span style="font-style:italic;color:#969896;">// GET
</span><span style="color:#323232;">svr.Post(</span><span style="color:#183691;">&quot;/path&quot;</span><span style="color:#323232;">,   handler);  </span><span style="font-style:italic;color:#969896;">// POST
</span><span style="color:#323232;">svr.Put(</span><span style="color:#183691;">&quot;/path&quot;</span><span style="color:#323232;">,    handler);  </span><span style="font-style:italic;color:#969896;">// PUT
</span><span style="color:#323232;">svr.Delete(</span><span style="color:#183691;">&quot;/path&quot;</span><span style="color:#323232;">, handler);  </span><span style="font-style:italic;color:#969896;">// DELETE
</span></pre>
</div></div>
<p>ハンドラーのシグネチャは <code>(const httplib::Request &amp;req, httplib::Response &amp;res)</code> です。<code>auto</code> を使って短く書くこともできます。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/hi</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">Hello!</span><span style="color:#c0c5ce;">&quot;, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Get(</span><span style="color:#183691;">&quot;/hi&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    res.set_content(</span><span style="color:#183691;">&quot;Hello!&quot;</span><span style="color:#323232;">, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<p>パスが一致したときだけハンドラーが呼ばれます。登録されていないパスにアクセスすると、自動的に404が返ります。</p>
<h2>リクエストオブジェクト</h2>
<p>ハンドラーの第1引数 <code>req</code> から、クライアントが送ってきた情報を読み取れます。</p>
<h3>ボディ</h3>
<p><code>req.body</code> でリクエストボディを取得できます。型は <code>std::string</code> です。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Post</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/post</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    </span><span style="color:#65737e;">// クライアントが送ったボディをそのまま返す
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(req.</span><span style="color:#bf616a;">body</span><span style="color:#c0c5ce;">, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Post(</span><span style="color:#183691;">&quot;/post&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    </span><span style="font-style:italic;color:#969896;">// クライアントが送ったボディをそのまま返す
</span><span style="color:#323232;">    res.set_content(req.body, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<h3>ヘッダー</h3>
<p><code>req.get_header_value()</code> でリクエストヘッダーの値を取得できます。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/check</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    </span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> auth = req.</span><span style="color:#8fa1b3;">get_header_value</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">Authorization</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">Auth: </span><span style="color:#c0c5ce;">&quot; + auth, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Get(</span><span style="color:#183691;">&quot;/check&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    </span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> auth </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> req.get_header_value(</span><span style="color:#183691;">&quot;Authorization&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">    res.set_content(</span><span style="color:#183691;">&quot;Auth: &quot; </span><span style="font-weight:bold;color:#a71d5d;">+</span><span style="color:#323232;"> auth, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<h3>クエリパラメーターとフォームデータ</h3>
<p><code>req.get_param_value()</code> でパラメーターを取得できます。GETのクエリパラメーターと、POSTのフォームデータの両方に使えます。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/search</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    </span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> q = req.</span><span style="color:#8fa1b3;">get_param_value</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">q</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">Query: </span><span style="color:#c0c5ce;">&quot; + q, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Get(</span><span style="color:#183691;">&quot;/search&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    </span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> q </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> req.get_param_value(</span><span style="color:#183691;">&quot;q&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">    res.set_content(</span><span style="color:#183691;">&quot;Query: &quot; </span><span style="font-weight:bold;color:#a71d5d;">+</span><span style="color:#323232;"> q, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<p><code>/search?q=cpp-httplib</code> にアクセスすると、<code>q</code> の値は <code>"cpp-httplib"</code> になります。</p>
<p>すべてのパラメーターをループで処理したいときは、<code>req.params</code> を使います。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Post</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/submit</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    std::string result;
</span><span style="color:#c0c5ce;">    </span><span style="color:#b48ead;">for </span><span style="color:#c0c5ce;">(</span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;[key, val] : req.</span><span style="color:#bf616a;">params</span><span style="color:#c0c5ce;">) {
</span><span style="color:#c0c5ce;">        result += key + &quot;</span><span style="color:#a3be8c;"> = </span><span style="color:#c0c5ce;">&quot; + val + &quot;</span><span style="color:#96b5b4;">\n</span><span style="color:#c0c5ce;">&quot;;
</span><span style="color:#c0c5ce;">    }
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(result, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Post(</span><span style="color:#183691;">&quot;/submit&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    std::string result;
</span><span style="color:#323232;">    </span><span style="font-weight:bold;color:#a71d5d;">for </span><span style="color:#323232;">(</span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">[key, val] </span><span style="font-weight:bold;color:#a71d5d;">:</span><span style="color:#323232;"> req.params) {
</span><span style="color:#323232;">        result </span><span style="font-weight:bold;color:#a71d5d;">+=</span><span style="color:#323232;"> key </span><span style="font-weight:bold;color:#a71d5d;">+ </span><span style="color:#183691;">&quot; = &quot; </span><span style="font-weight:bold;color:#a71d5d;">+</span><span style="color:#323232;"> val </span><span style="font-weight:bold;color:#a71d5d;">+ </span><span style="color:#183691;">&quot;</span><span style="color:#0086b3;">\n</span><span style="color:#183691;">&quot;</span><span style="color:#323232;">;
</span><span style="color:#323232;">    }
</span><span style="color:#323232;">    res.set_content(result, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<h3>ファイルアップロード</h3>
<p>マルチパートフォームでアップロードされたファイルは、<code>req.form.get_file()</code> で取得します。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Post</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/upload</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    </span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> f = req.</span><span style="color:#bf616a;">form</span><span style="color:#c0c5ce;">.</span><span style="color:#8fa1b3;">get_file</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">file</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">    </span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> content = f.</span><span style="color:#bf616a;">filename </span><span style="color:#c0c5ce;">+ &quot;</span><span style="color:#a3be8c;"> (</span><span style="color:#c0c5ce;">&quot; + </span><span style="color:#8fa1b3;">std::to_string</span><span style="color:#c0c5ce;">(f.</span><span style="color:#bf616a;">content</span><span style="color:#c0c5ce;">.</span><span style="color:#8fa1b3;">size</span><span style="color:#c0c5ce;">()) + &quot;</span><span style="color:#a3be8c;"> bytes)</span><span style="color:#c0c5ce;">&quot;;
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(content, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Post(</span><span style="color:#183691;">&quot;/upload&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    </span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> f </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> req.form.get_file(</span><span style="color:#183691;">&quot;file&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">    </span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> content </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> f.filename </span><span style="font-weight:bold;color:#a71d5d;">+ </span><span style="color:#183691;">&quot; (&quot; </span><span style="font-weight:bold;color:#a71d5d;">+ </span><span style="color:#323232;">std::to_string(f.content.size()) </span><span style="font-weight:bold;color:#a71d5d;">+ </span><span style="color:#183691;">&quot; bytes)&quot;</span><span style="color:#323232;">;
</span><span style="color:#323232;">    res.set_content(content, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<p><code>f.filename</code> でファイル名、<code>f.content</code> でファイルの中身にアクセスできます。</p>
<h2>パスパラメーター</h2>
<p>URLの一部を変数として受け取りたいことがあります。たとえば <code>/users/42</code> の <code>42</code> を取得したい場合です。<code>:param</code> 記法を使うと、URLの一部をキャプチャできます。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/users/:id</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    </span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> id = req.</span><span style="color:#bf616a;">path_params</span><span style="color:#c0c5ce;">.</span><span style="color:#8fa1b3;">at</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">id</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">User ID: </span><span style="color:#c0c5ce;">&quot; + id, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Get(</span><span style="color:#183691;">&quot;/users/:id&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    </span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> id </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> req.path_params.at(</span><span style="color:#183691;">&quot;id&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">    res.set_content(</span><span style="color:#183691;">&quot;User ID: &quot; </span><span style="font-weight:bold;color:#a71d5d;">+</span><span style="color:#323232;"> id, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<p><code>/users/42</code> にアクセスすると、<code>req.path_params.at("id")</code> は <code>"42"</code> を返します。<code>/users/100</code> なら <code>"100"</code> です。</p>
<p>複数のパスパラメーターも使えます。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/users/:user_id/posts/:post_id</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    </span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> user_id = req.</span><span style="color:#bf616a;">path_params</span><span style="color:#c0c5ce;">.</span><span style="color:#8fa1b3;">at</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">user_id</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">    </span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> post_id = req.</span><span style="color:#bf616a;">path_params</span><span style="color:#c0c5ce;">.</span><span style="color:#8fa1b3;">at</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">post_id</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">User: </span><span style="color:#c0c5ce;">&quot; + user_id + &quot;</span><span style="color:#a3be8c;">, Post: </span><span style="color:#c0c5ce;">&quot; + post_id, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Get(</span><span style="color:#183691;">&quot;/users/:user_id/posts/:post_id&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    </span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> user_id </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> req.path_params.at(</span><span style="color:#183691;">&quot;user_id&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">    </span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> post_id </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> req.path_params.at(</span><span style="color:#183691;">&quot;post_id&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">    res.set_content(</span><span style="color:#183691;">&quot;User: &quot; </span><span style="font-weight:bold;color:#a71d5d;">+</span><span style="color:#323232;"> user_id </span><span style="font-weight:bold;color:#a71d5d;">+ </span><span style="color:#183691;">&quot;, Post: &quot; </span><span style="font-weight:bold;color:#a71d5d;">+</span><span style="color:#323232;"> post_id, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<h3>正規表現パターン</h3>
<p><code>:param</code> の代わりに正規表現をパスに書くこともできます。キャプチャグループの値は <code>req.matches</code> で取得します。型は <code>std::smatch</code> です。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#65737e;">// 数字のみのIDを受け付ける
</span><span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(</span><span style="color:#b48ead;">R</span><span style="color:#c0c5ce;">&quot;(</span><span style="color:#a3be8c;">/files/(\d+)</span><span style="color:#c0c5ce;">)&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    </span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> id = req.</span><span style="color:#bf616a;">matches</span><span style="color:#c0c5ce;">[</span><span style="color:#d08770;">1</span><span style="color:#c0c5ce;">];  </span><span style="color:#65737e;">// 最初のキャプチャグループ
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">File ID: </span><span style="color:#c0c5ce;">&quot; + </span><span style="color:#8fa1b3;">std::string</span><span style="color:#c0c5ce;">(id), &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="font-style:italic;color:#969896;">// 数字のみのIDを受け付ける
</span><span style="color:#323232;">svr.Get(</span><span style="font-weight:bold;color:#a71d5d;">R</span><span style="color:#183691;">&quot;(/files/(\d+))&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    </span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> id </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> req.matches[</span><span style="color:#0086b3;">1</span><span style="color:#323232;">];  </span><span style="font-style:italic;color:#969896;">// 最初のキャプチャグループ
</span><span style="color:#323232;">    res.set_content(</span><span style="color:#183691;">&quot;File ID: &quot; </span><span style="font-weight:bold;color:#a71d5d;">+ </span><span style="color:#323232;">std::string(id), </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<p><code>/files/42</code> にはマッチしますが、<code>/files/abc</code> にはマッチしません。入力値を絞り込みたいときに便利です。</p>
<h2>レスポンスの組み立て</h2>
<p>ハンドラーの第2引数 <code>res</code> を使って、クライアントに返すレスポンスを組み立てます。</p>
<h3>ボディとContent-Type</h3>
<p><code>res.set_content()</code> でボディとContent-Typeを設定します。これだけでステータスコード200のレスポンスが返ります。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/hi</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">Hello!</span><span style="color:#c0c5ce;">&quot;, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Get(</span><span style="color:#183691;">&quot;/hi&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    res.set_content(</span><span style="color:#183691;">&quot;Hello!&quot;</span><span style="color:#323232;">, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<h3>ステータスコード</h3>
<p>ステータスコードを変えたいときは、<code>res.status</code> に代入します。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/not-found</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#bf616a;">status </span><span style="color:#c0c5ce;">= </span><span style="color:#d08770;">404</span><span style="color:#c0c5ce;">;
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">Not found</span><span style="color:#c0c5ce;">&quot;, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Get(</span><span style="color:#183691;">&quot;/not-found&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    res.status </span><span style="font-weight:bold;color:#a71d5d;">= </span><span style="color:#0086b3;">404</span><span style="color:#323232;">;
</span><span style="color:#323232;">    res.set_content(</span><span style="color:#183691;">&quot;Not found&quot;</span><span style="color:#323232;">, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<h3>レスポンスヘッダー</h3>
<p><code>res.set_header()</code> でレスポンスヘッダーを追加できます。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/with-header</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_header</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">X-Custom</span><span style="color:#c0c5ce;">&quot;, &quot;</span><span style="color:#a3be8c;">my-value</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">Hello!</span><span style="color:#c0c5ce;">&quot;, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Get(</span><span style="color:#183691;">&quot;/with-header&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    res.set_header(</span><span style="color:#183691;">&quot;X-Custom&quot;</span><span style="color:#323232;">, </span><span style="color:#183691;">&quot;my-value&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">    res.set_content(</span><span style="color:#183691;">&quot;Hello!&quot;</span><span style="color:#323232;">, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<h2>前章のサーバーを読み解く</h2>
<p>ここまでの知識を使って、前章で用意したテスト用サーバーを改めて見てみましょう。</p>
<h3>GET /hi</h3>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/hi</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">Hello!</span><span style="color:#c0c5ce;">&quot;, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Get(</span><span style="color:#183691;">&quot;/hi&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    res.set_content(</span><span style="color:#183691;">&quot;Hello!&quot;</span><span style="color:#323232;">, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<p>最もシンプルなハンドラーです。リクエストの情報は使わないので、<code>req</code> の変数名を省略しています。<code>"Hello!"</code> というテキストをそのまま返します。</p>
<h3>GET /search</h3>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/search</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    </span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> q = req.</span><span style="color:#8fa1b3;">get_param_value</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">q</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">Query: </span><span style="color:#c0c5ce;">&quot; + q, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Get(</span><span style="color:#183691;">&quot;/search&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    </span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> q </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> req.get_param_value(</span><span style="color:#183691;">&quot;q&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">    res.set_content(</span><span style="color:#183691;">&quot;Query: &quot; </span><span style="font-weight:bold;color:#a71d5d;">+</span><span style="color:#323232;"> q, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<p><code>req.get_param_value("q")</code> でクエリパラメーター <code>q</code> の値を取り出します。<code>/search?q=cpp-httplib</code> なら、レスポンスは <code>"Query: cpp-httplib"</code> になります。</p>
<h3>POST /post</h3>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Post</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/post</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(req.</span><span style="color:#bf616a;">body</span><span style="color:#c0c5ce;">, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Post(</span><span style="color:#183691;">&quot;/post&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    res.set_content(req.body, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<p>クライアントが送ったリクエストボディを、そのままレスポンスとして返すエコーサーバーです。<code>req.body</code> にボディが丸ごと入っています。</p>
<h3>POST /submit</h3>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Post</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/submit</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    std::string result;
</span><span style="color:#c0c5ce;">    </span><span style="color:#b48ead;">for </span><span style="color:#c0c5ce;">(</span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;[key, val] : req.</span><span style="color:#bf616a;">params</span><span style="color:#c0c5ce;">) {
</span><span style="color:#c0c5ce;">        result += key + &quot;</span><span style="color:#a3be8c;"> = </span><span style="color:#c0c5ce;">&quot; + val + &quot;</span><span style="color:#96b5b4;">\n</span><span style="color:#c0c5ce;">&quot;;
</span><span style="color:#c0c5ce;">    }
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(result, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Post(</span><span style="color:#183691;">&quot;/submit&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    std::string result;
</span><span style="color:#323232;">    </span><span style="font-weight:bold;color:#a71d5d;">for </span><span style="color:#323232;">(</span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">[key, val] </span><span style="font-weight:bold;color:#a71d5d;">:</span><span style="color:#323232;"> req.params) {
</span><span style="color:#323232;">        result </span><span style="font-weight:bold;color:#a71d5d;">+=</span><span style="color:#323232;"> key </span><span style="font-weight:bold;color:#a71d5d;">+ </span><span style="color:#183691;">&quot; = &quot; </span><span style="font-weight:bold;color:#a71d5d;">+</span><span style="color:#323232;"> val </span><span style="font-weight:bold;color:#a71d5d;">+ </span><span style="color:#183691;">&quot;</span><span style="color:#0086b3;">\n</span><span style="color:#183691;">&quot;</span><span style="color:#323232;">;
</span><span style="color:#323232;">    }
</span><span style="color:#323232;">    res.set_content(result, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<p>フォームデータとして送られたキーと値のペアを、<code>req.params</code> でループ処理しています。構造化束縛 <code>auto &amp;[key, val]</code> を使って、各ペアを取り出しています。</p>
<h3>POST /upload</h3>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Post</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/upload</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    </span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> f = req.</span><span style="color:#bf616a;">form</span><span style="color:#c0c5ce;">.</span><span style="color:#8fa1b3;">get_file</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">file</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">    </span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> content = f.</span><span style="color:#bf616a;">filename </span><span style="color:#c0c5ce;">+ &quot;</span><span style="color:#a3be8c;"> (</span><span style="color:#c0c5ce;">&quot; + </span><span style="color:#8fa1b3;">std::to_string</span><span style="color:#c0c5ce;">(f.</span><span style="color:#bf616a;">content</span><span style="color:#c0c5ce;">.</span><span style="color:#8fa1b3;">size</span><span style="color:#c0c5ce;">()) + &quot;</span><span style="color:#a3be8c;"> bytes)</span><span style="color:#c0c5ce;">&quot;;
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(content, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Post(</span><span style="color:#183691;">&quot;/upload&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    </span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> f </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> req.form.get_file(</span><span style="color:#183691;">&quot;file&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">    </span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> content </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> f.filename </span><span style="font-weight:bold;color:#a71d5d;">+ </span><span style="color:#183691;">&quot; (&quot; </span><span style="font-weight:bold;color:#a71d5d;">+ </span><span style="color:#323232;">std::to_string(f.content.size()) </span><span style="font-weight:bold;color:#a71d5d;">+ </span><span style="color:#183691;">&quot; bytes)&quot;</span><span style="color:#323232;">;
</span><span style="color:#323232;">    res.set_content(content, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<p>マルチパートフォームで送られたファイルを受け取ります。<code>req.form.get_file("file")</code> で <code>"file"</code> という名前のフィールドを取得し、<code>f.filename</code> と <code>f.content.size()</code> でファイル名とサイズを返しています。</p>
<h3>GET /users/:id</h3>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/users/:id</span><span style="color:#c0c5ce;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    </span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> id = req.</span><span style="color:#bf616a;">path_params</span><span style="color:#c0c5ce;">.</span><span style="color:#8fa1b3;">at</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">id</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">User ID: </span><span style="color:#c0c5ce;">&quot; + id, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Get(</span><span style="color:#183691;">&quot;/users/:id&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    </span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> id </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> req.path_params.at(</span><span style="color:#183691;">&quot;id&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">    res.set_content(</span><span style="color:#183691;">&quot;User ID: &quot; </span><span style="font-weight:bold;color:#a71d5d;">+</span><span style="color:#323232;"> id, </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<p><code>:id</code> の部分がパスパラメーターです。<code>req.path_params.at("id")</code> で値を取り出しています。<code>/users/42</code> なら <code>"42"</code>、<code>/users/alice</code> なら <code>"alice"</code> が得られます。</p>
<h3>GET /files/(\d+)</h3>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(</span><span style="color:#b48ead;">R</span><span style="color:#c0c5ce;">&quot;(</span><span style="color:#a3be8c;">/files/(\d+)</span><span style="color:#c0c5ce;">)&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#c0c5ce;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#c0c5ce;">&amp;res) {
</span><span style="color:#c0c5ce;">    </span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> id = req.</span><span style="color:#bf616a;">matches</span><span style="color:#c0c5ce;">[</span><span style="color:#d08770;">1</span><span style="color:#c0c5ce;">];
</span><span style="color:#c0c5ce;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">File ID: </span><span style="color:#c0c5ce;">&quot; + </span><span style="color:#8fa1b3;">std::string</span><span style="color:#c0c5ce;">(id), &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">});
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">svr.Get(</span><span style="font-weight:bold;color:#a71d5d;">R</span><span style="color:#183691;">&quot;(/files/(\d+))&quot;</span><span style="color:#323232;">, [](</span><span style="font-weight:bold;color:#a71d5d;">const auto &amp;</span><span style="color:#323232;">req, </span><span style="font-weight:bold;color:#a71d5d;">auto &amp;</span><span style="color:#323232;">res) {
</span><span style="color:#323232;">    </span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> id </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> req.matches[</span><span style="color:#0086b3;">1</span><span style="color:#323232;">];
</span><span style="color:#323232;">    res.set_content(</span><span style="color:#183691;">&quot;File ID: &quot; </span><span style="font-weight:bold;color:#a71d5d;">+ </span><span style="color:#323232;">std::string(id), </span><span style="color:#183691;">&quot;text/plain&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">});
</span></pre>
</div></div>
<p>正規表現 <code>(\d+)</code> で数字だけのIDにマッチします。<code>/files/42</code> にはマッチしますが、<code>/files/abc</code> は404になります。<code>req.matches[1]</code> で最初のキャプチャグループの値を取得しています。</p>
<h2>次のステップ</h2>
<p>サーバーの基本がわかりましたね。ルーティング、リクエストの読み取り、レスポンスの組み立て。これだけで、十分に実用的なAPIサーバーが作れます。</p>
<p>次は、静的ファイルの配信を見てみましょう。HTMLやCSSを配信するサーバーを作ります。</p>
<p><strong>次:</strong> <a href="../04-static-file-server">Static File Server</a></p>

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