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    80. 

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    81. 

  81.     <h1>Basic Server</h1>
    82. 

  82.     <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>
    83. 

  83. <h2>サーバーの起動</h2>
    84. 

  84. <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>
    85. 

  85. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    86. 

  86. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">listen</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">0.0.0.0</span><span style="color:#d3d0c8;">&quot;, </span><span style="color:#f99157;">8080</span><span style="color:#d3d0c8;">);
    87. 

  87. </span></pre>
    88. 

  88. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    89. 

  89. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">listen</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">0.0.0.0</span><span style="color:#4f5b66;">&quot;, </span><span style="color:#d08770;">8080</span><span style="color:#4f5b66;">);
    90. 

  90. </span></pre>
    91. 

  91. </div>
    92. 

  92. <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>
    93. 

  93. <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>
    94. 

  94. <h2>ルーティング</h2>
    95. 

  95. <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>
    96. 

  96. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    97. 

  97. <span style="color:#d3d0c8;">httplib::Server svr;
    98. 

  98. </span><span style="color:#d3d0c8;">
    99. 

  99. </span><span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Get</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/hi</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const</span><span style="color:#d3d0c8;"> httplib::Request &amp;req, httplib::Response &amp;res) {
    100. 

  100. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">Hello!</span><span style="color:#d3d0c8;">&quot;, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    101. 

  101. </span><span style="color:#d3d0c8;">});
    102. 

  102. </span></pre>
    103. 

  103. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    104. 

  104. <span style="color:#4f5b66;">httplib::Server svr;
    105. 

  105. </span><span style="color:#4f5b66;">
    106. 

  106. </span><span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/hi</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const</span><span style="color:#4f5b66;"> httplib::Request &amp;req, httplib::Response &amp;res) {
    107. 

  107. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">Hello!</span><span style="color:#4f5b66;">&quot;, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    108. 

  108. </span><span style="color:#4f5b66;">});
    109. 

  109. </span></pre>
    110. 

  110. </div>
    111. 

  111. <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>
    112. 

  112. <p>HTTPメソッドごとにメソッドが用意されています。</p>
    113. 

  113. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    114. 

  114. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Get</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/path</span><span style="color:#d3d0c8;">&quot;,    handler);  </span><span style="color:#747369;">// GET
    115. 

  115. </span><span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Post</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/path</span><span style="color:#d3d0c8;">&quot;,   handler);  </span><span style="color:#747369;">// POST
    116. 

  116. </span><span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Put</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/path</span><span style="color:#d3d0c8;">&quot;,    handler);  </span><span style="color:#747369;">// PUT
    117. 

  117. </span><span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Delete</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/path</span><span style="color:#d3d0c8;">&quot;, handler);  </span><span style="color:#747369;">// DELETE
    118. 

  118. </span></pre>
    119. 

  119. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    120. 

  120. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/path</span><span style="color:#4f5b66;">&quot;,    handler);  </span><span style="color:#a7adba;">// GET
    121. 

  121. </span><span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Post</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/path</span><span style="color:#4f5b66;">&quot;,   handler);  </span><span style="color:#a7adba;">// POST
    122. 

  122. </span><span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Put</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/path</span><span style="color:#4f5b66;">&quot;,    handler);  </span><span style="color:#a7adba;">// PUT
    123. 

  123. </span><span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Delete</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/path</span><span style="color:#4f5b66;">&quot;, handler);  </span><span style="color:#a7adba;">// DELETE
    124. 

  124. </span></pre>
    125. 

  125. </div>
    126. 

  126. <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>
    127. 

  127. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    128. 

  128. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Get</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/hi</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    129. 

  129. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">Hello!</span><span style="color:#d3d0c8;">&quot;, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    130. 

  130. </span><span style="color:#d3d0c8;">});
    131. 

  131. </span></pre>
    132. 

  132. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    133. 

  133. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/hi</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    134. 

  134. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">Hello!</span><span style="color:#4f5b66;">&quot;, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    135. 

  135. </span><span style="color:#4f5b66;">});
    136. 

  136. </span></pre>
    137. 

  137. </div>
    138. 

  138. <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>
    139. 

  139. <h2>リクエストオブジェクト</h2>
    140. 

  140. <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>
    141. 

  141. <h3>ボディ</h3>
    142. 

  142. <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>
    143. 

  143. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    144. 

  144. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Post</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/post</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    145. 

  145. </span><span style="color:#d3d0c8;">    </span><span style="color:#747369;">// クライアントが送ったボディをそのまま返す
    146. 

  146. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(req.</span><span style="color:#f2777a;">body</span><span style="color:#d3d0c8;">, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    147. 

  147. </span><span style="color:#d3d0c8;">});
    148. 

  148. </span></pre>
    149. 

  149. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    150. 

  150. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Post</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/post</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    151. 

  151. </span><span style="color:#4f5b66;">    </span><span style="color:#a7adba;">// クライアントが送ったボディをそのまま返す
    152. 

  152. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(req.</span><span style="color:#bf616a;">body</span><span style="color:#4f5b66;">, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    153. 

  153. </span><span style="color:#4f5b66;">});
    154. 

  154. </span></pre>
    155. 

  155. </div>
    156. 

  156. <h3>ヘッダー</h3>
    157. 

  157. <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>
    158. 

  158. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    159. 

  159. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Get</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/check</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    160. 

  160. </span><span style="color:#d3d0c8;">    </span><span style="color:#cc99cc;">auto</span><span style="color:#d3d0c8;"> auth = req.</span><span style="color:#6699cc;">get_header_value</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">Authorization</span><span style="color:#d3d0c8;">&quot;);
    161. 

  161. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">Auth: </span><span style="color:#d3d0c8;">&quot; + auth, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    162. 

  162. </span><span style="color:#d3d0c8;">});
    163. 

  163. </span></pre>
    164. 

  164. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    165. 

  165. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/check</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    166. 

  166. </span><span style="color:#4f5b66;">    </span><span style="color:#b48ead;">auto</span><span style="color:#4f5b66;"> auth = req.</span><span style="color:#8fa1b3;">get_header_value</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">Authorization</span><span style="color:#4f5b66;">&quot;);
    167. 

  167. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">Auth: </span><span style="color:#4f5b66;">&quot; + auth, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    168. 

  168. </span><span style="color:#4f5b66;">});
    169. 

  169. </span></pre>
    170. 

  170. </div>
    171. 

  171. <h3>クエリパラメーターとフォームデータ</h3>
    172. 

  172. <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>
    173. 

  173. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    174. 

  174. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Get</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/search</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    175. 

  175. </span><span style="color:#d3d0c8;">    </span><span style="color:#cc99cc;">auto</span><span style="color:#d3d0c8;"> q = req.</span><span style="color:#6699cc;">get_param_value</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">q</span><span style="color:#d3d0c8;">&quot;);
    176. 

  176. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">Query: </span><span style="color:#d3d0c8;">&quot; + q, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    177. 

  177. </span><span style="color:#d3d0c8;">});
    178. 

  178. </span></pre>
    179. 

  179. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    180. 

  180. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/search</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    181. 

  181. </span><span style="color:#4f5b66;">    </span><span style="color:#b48ead;">auto</span><span style="color:#4f5b66;"> q = req.</span><span style="color:#8fa1b3;">get_param_value</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">q</span><span style="color:#4f5b66;">&quot;);
    182. 

  182. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">Query: </span><span style="color:#4f5b66;">&quot; + q, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    183. 

  183. </span><span style="color:#4f5b66;">});
    184. 

  184. </span></pre>
    185. 

  185. </div>
    186. 

  186. <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>
    187. 

  187. <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>
    188. 

  188. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    189. 

  189. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Post</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/submit</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    190. 

  190. </span><span style="color:#d3d0c8;">    std::string result;
    191. 

  191. </span><span style="color:#d3d0c8;">    </span><span style="color:#cc99cc;">for </span><span style="color:#d3d0c8;">(</span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;[key, val] : req.</span><span style="color:#f2777a;">params</span><span style="color:#d3d0c8;">) {
    192. 

  192. </span><span style="color:#d3d0c8;">        result += key + &quot;</span><span style="color:#99cc99;"> = </span><span style="color:#d3d0c8;">&quot; + val + &quot;</span><span style="color:#66cccc;">\n</span><span style="color:#d3d0c8;">&quot;;
    193. 

  193. </span><span style="color:#d3d0c8;">    }
    194. 

  194. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(result, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    195. 

  195. </span><span style="color:#d3d0c8;">});
    196. 

  196. </span></pre>
    197. 

  197. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    198. 

  198. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Post</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/submit</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    199. 

  199. </span><span style="color:#4f5b66;">    std::string result;
    200. 

  200. </span><span style="color:#4f5b66;">    </span><span style="color:#b48ead;">for </span><span style="color:#4f5b66;">(</span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;[key, val] : req.</span><span style="color:#bf616a;">params</span><span style="color:#4f5b66;">) {
    201. 

  201. </span><span style="color:#4f5b66;">        result += key + &quot;</span><span style="color:#a3be8c;"> = </span><span style="color:#4f5b66;">&quot; + val + &quot;</span><span style="color:#96b5b4;">\n</span><span style="color:#4f5b66;">&quot;;
    202. 

  202. </span><span style="color:#4f5b66;">    }
    203. 

  203. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(result, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    204. 

  204. </span><span style="color:#4f5b66;">});
    205. 

  205. </span></pre>
    206. 

  206. </div>
    207. 

  207. <h3>ファイルアップロード</h3>
    208. 

  208. <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>
    209. 

  209. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    210. 

  210. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Post</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/upload</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    211. 

  211. </span><span style="color:#d3d0c8;">    </span><span style="color:#cc99cc;">auto</span><span style="color:#d3d0c8;"> f = req.</span><span style="color:#f2777a;">form</span><span style="color:#d3d0c8;">.</span><span style="color:#6699cc;">get_file</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">file</span><span style="color:#d3d0c8;">&quot;);
    212. 

  212. </span><span style="color:#d3d0c8;">    </span><span style="color:#cc99cc;">auto</span><span style="color:#d3d0c8;"> content = f.</span><span style="color:#f2777a;">filename </span><span style="color:#d3d0c8;">+ &quot;</span><span style="color:#99cc99;"> (</span><span style="color:#d3d0c8;">&quot; + </span><span style="color:#6699cc;">std::to_string</span><span style="color:#d3d0c8;">(f.</span><span style="color:#f2777a;">content</span><span style="color:#d3d0c8;">.</span><span style="color:#6699cc;">size</span><span style="color:#d3d0c8;">()) + &quot;</span><span style="color:#99cc99;"> bytes)</span><span style="color:#d3d0c8;">&quot;;
    213. 

  213. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(content, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    214. 

  214. </span><span style="color:#d3d0c8;">});
    215. 

  215. </span></pre>
    216. 

  216. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    217. 

  217. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Post</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/upload</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    218. 

  218. </span><span style="color:#4f5b66;">    </span><span style="color:#b48ead;">auto</span><span style="color:#4f5b66;"> f = req.</span><span style="color:#bf616a;">form</span><span style="color:#4f5b66;">.</span><span style="color:#8fa1b3;">get_file</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">file</span><span style="color:#4f5b66;">&quot;);
    219. 

  219. </span><span style="color:#4f5b66;">    </span><span style="color:#b48ead;">auto</span><span style="color:#4f5b66;"> content = f.</span><span style="color:#bf616a;">filename </span><span style="color:#4f5b66;">+ &quot;</span><span style="color:#a3be8c;"> (</span><span style="color:#4f5b66;">&quot; + </span><span style="color:#8fa1b3;">std::to_string</span><span style="color:#4f5b66;">(f.</span><span style="color:#bf616a;">content</span><span style="color:#4f5b66;">.</span><span style="color:#8fa1b3;">size</span><span style="color:#4f5b66;">()) + &quot;</span><span style="color:#a3be8c;"> bytes)</span><span style="color:#4f5b66;">&quot;;
    220. 

  220. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(content, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    221. 

  221. </span><span style="color:#4f5b66;">});
    222. 

  222. </span></pre>
    223. 

  223. </div>
    224. 

  224. <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>
    225. 

  225. <h2>パスパラメーター</h2>
    226. 

  226. <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>
    227. 

  227. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    228. 

  228. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Get</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/users/:id</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    229. 

  229. </span><span style="color:#d3d0c8;">    </span><span style="color:#cc99cc;">auto</span><span style="color:#d3d0c8;"> id = req.</span><span style="color:#f2777a;">path_params</span><span style="color:#d3d0c8;">.</span><span style="color:#6699cc;">at</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">id</span><span style="color:#d3d0c8;">&quot;);
    230. 

  230. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">User ID: </span><span style="color:#d3d0c8;">&quot; + id, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    231. 

  231. </span><span style="color:#d3d0c8;">});
    232. 

  232. </span></pre>
    233. 

  233. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    234. 

  234. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/users/:id</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    235. 

  235. </span><span style="color:#4f5b66;">    </span><span style="color:#b48ead;">auto</span><span style="color:#4f5b66;"> id = req.</span><span style="color:#bf616a;">path_params</span><span style="color:#4f5b66;">.</span><span style="color:#8fa1b3;">at</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">id</span><span style="color:#4f5b66;">&quot;);
    236. 

  236. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">User ID: </span><span style="color:#4f5b66;">&quot; + id, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    237. 

  237. </span><span style="color:#4f5b66;">});
    238. 

  238. </span></pre>
    239. 

  239. </div>
    240. 

  240. <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>
    241. 

  241. <p>複数のパスパラメーターも使えます。</p>
    242. 

  242. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    243. 

  243. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Get</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/users/:user_id/posts/:post_id</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    244. 

  244. </span><span style="color:#d3d0c8;">    </span><span style="color:#cc99cc;">auto</span><span style="color:#d3d0c8;"> user_id = req.</span><span style="color:#f2777a;">path_params</span><span style="color:#d3d0c8;">.</span><span style="color:#6699cc;">at</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">user_id</span><span style="color:#d3d0c8;">&quot;);
    245. 

  245. </span><span style="color:#d3d0c8;">    </span><span style="color:#cc99cc;">auto</span><span style="color:#d3d0c8;"> post_id = req.</span><span style="color:#f2777a;">path_params</span><span style="color:#d3d0c8;">.</span><span style="color:#6699cc;">at</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">post_id</span><span style="color:#d3d0c8;">&quot;);
    246. 

  246. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">User: </span><span style="color:#d3d0c8;">&quot; + user_id + &quot;</span><span style="color:#99cc99;">, Post: </span><span style="color:#d3d0c8;">&quot; + post_id, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    247. 

  247. </span><span style="color:#d3d0c8;">});
    248. 

  248. </span></pre>
    249. 

  249. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    250. 

  250. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/users/:user_id/posts/:post_id</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    251. 

  251. </span><span style="color:#4f5b66;">    </span><span style="color:#b48ead;">auto</span><span style="color:#4f5b66;"> user_id = req.</span><span style="color:#bf616a;">path_params</span><span style="color:#4f5b66;">.</span><span style="color:#8fa1b3;">at</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">user_id</span><span style="color:#4f5b66;">&quot;);
    252. 

  252. </span><span style="color:#4f5b66;">    </span><span style="color:#b48ead;">auto</span><span style="color:#4f5b66;"> post_id = req.</span><span style="color:#bf616a;">path_params</span><span style="color:#4f5b66;">.</span><span style="color:#8fa1b3;">at</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">post_id</span><span style="color:#4f5b66;">&quot;);
    253. 

  253. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">User: </span><span style="color:#4f5b66;">&quot; + user_id + &quot;</span><span style="color:#a3be8c;">, Post: </span><span style="color:#4f5b66;">&quot; + post_id, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    254. 

  254. </span><span style="color:#4f5b66;">});
    255. 

  255. </span></pre>
    256. 

  256. </div>
    257. 

  257. <h3>正規表現パターン</h3>
    258. 

  258. <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>
    259. 

  259. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    260. 

  260. <span style="color:#747369;">// 数字のみのIDを受け付ける
    261. 

  261. </span><span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Get</span><span style="color:#d3d0c8;">(</span><span style="color:#cc99cc;">R</span><span style="color:#d3d0c8;">&quot;(</span><span style="color:#99cc99;">/files/(\d+)</span><span style="color:#d3d0c8;">)&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    262. 

  262. </span><span style="color:#d3d0c8;">    </span><span style="color:#cc99cc;">auto</span><span style="color:#d3d0c8;"> id = req.</span><span style="color:#f2777a;">matches</span><span style="color:#d3d0c8;">[</span><span style="color:#f99157;">1</span><span style="color:#d3d0c8;">];  </span><span style="color:#747369;">// 最初のキャプチャグループ
    263. 

  263. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">File ID: </span><span style="color:#d3d0c8;">&quot; + </span><span style="color:#6699cc;">std::string</span><span style="color:#d3d0c8;">(id), &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    264. 

  264. </span><span style="color:#d3d0c8;">});
    265. 

  265. </span></pre>
    266. 

  266. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    267. 

  267. <span style="color:#a7adba;">// 数字のみのIDを受け付ける
    268. 

  268. </span><span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#4f5b66;">(</span><span style="color:#b48ead;">R</span><span style="color:#4f5b66;">&quot;(</span><span style="color:#a3be8c;">/files/(\d+)</span><span style="color:#4f5b66;">)&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    269. 

  269. </span><span style="color:#4f5b66;">    </span><span style="color:#b48ead;">auto</span><span style="color:#4f5b66;"> id = req.</span><span style="color:#bf616a;">matches</span><span style="color:#4f5b66;">[</span><span style="color:#d08770;">1</span><span style="color:#4f5b66;">];  </span><span style="color:#a7adba;">// 最初のキャプチャグループ
    270. 

  270. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">File ID: </span><span style="color:#4f5b66;">&quot; + </span><span style="color:#8fa1b3;">std::string</span><span style="color:#4f5b66;">(id), &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    271. 

  271. </span><span style="color:#4f5b66;">});
    272. 

  272. </span></pre>
    273. 

  273. </div>
    274. 

  274. <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>
    275. 

  275. <h2>レスポンスの組み立て</h2>
    276. 

  276. <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>
    277. 

  277. <h3>ボディとContent-Type</h3>
    278. 

  278. <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>
    279. 

  279. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    280. 

  280. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Get</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/hi</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    281. 

  281. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">Hello!</span><span style="color:#d3d0c8;">&quot;, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    282. 

  282. </span><span style="color:#d3d0c8;">});
    283. 

  283. </span></pre>
    284. 

  284. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    285. 

  285. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/hi</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    286. 

  286. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">Hello!</span><span style="color:#4f5b66;">&quot;, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    287. 

  287. </span><span style="color:#4f5b66;">});
    288. 

  288. </span></pre>
    289. 

  289. </div>
    290. 

  290. <h3>ステータスコード</h3>
    291. 

  291. <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>
    292. 

  292. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    293. 

  293. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Get</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/not-found</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    294. 

  294. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#f2777a;">status </span><span style="color:#d3d0c8;">= </span><span style="color:#f99157;">404</span><span style="color:#d3d0c8;">;
    295. 

  295. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">Not found</span><span style="color:#d3d0c8;">&quot;, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    296. 

  296. </span><span style="color:#d3d0c8;">});
    297. 

  297. </span></pre>
    298. 

  298. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    299. 

  299. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/not-found</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    300. 

  300. </span><span style="color:#4f5b66;">    res.</span><span style="color:#bf616a;">status </span><span style="color:#4f5b66;">= </span><span style="color:#d08770;">404</span><span style="color:#4f5b66;">;
    301. 

  301. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">Not found</span><span style="color:#4f5b66;">&quot;, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    302. 

  302. </span><span style="color:#4f5b66;">});
    303. 

  303. </span></pre>
    304. 

  304. </div>
    305. 

  305. <h3>レスポンスヘッダー</h3>
    306. 

  306. <p><code>res.set_header()</code> でレスポンスヘッダーを追加できます。</p>
    307. 

  307. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    308. 

  308. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Get</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/with-header</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    309. 

  309. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_header</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">X-Custom</span><span style="color:#d3d0c8;">&quot;, &quot;</span><span style="color:#99cc99;">my-value</span><span style="color:#d3d0c8;">&quot;);
    310. 

  310. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">Hello!</span><span style="color:#d3d0c8;">&quot;, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    311. 

  311. </span><span style="color:#d3d0c8;">});
    312. 

  312. </span></pre>
    313. 

  313. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    314. 

  314. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/with-header</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    315. 

  315. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_header</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">X-Custom</span><span style="color:#4f5b66;">&quot;, &quot;</span><span style="color:#a3be8c;">my-value</span><span style="color:#4f5b66;">&quot;);
    316. 

  316. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">Hello!</span><span style="color:#4f5b66;">&quot;, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    317. 

  317. </span><span style="color:#4f5b66;">});
    318. 

  318. </span></pre>
    319. 

  319. </div>
    320. 

  320. <h2>前章のサーバーを読み解く</h2>
    321. 

  321. <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>
    322. 

  322. <h3>GET /hi</h3>
    323. 

  323. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    324. 

  324. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Get</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/hi</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    325. 

  325. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">Hello!</span><span style="color:#d3d0c8;">&quot;, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    326. 

  326. </span><span style="color:#d3d0c8;">});
    327. 

  327. </span></pre>
    328. 

  328. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    329. 

  329. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/hi</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    330. 

  330. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">Hello!</span><span style="color:#4f5b66;">&quot;, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    331. 

  331. </span><span style="color:#4f5b66;">});
    332. 

  332. </span></pre>
    333. 

  333. </div>
    334. 

  334. <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>
    335. 

  335. <h3>GET /search</h3>
    336. 

  336. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    337. 

  337. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Get</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/search</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    338. 

  338. </span><span style="color:#d3d0c8;">    </span><span style="color:#cc99cc;">auto</span><span style="color:#d3d0c8;"> q = req.</span><span style="color:#6699cc;">get_param_value</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">q</span><span style="color:#d3d0c8;">&quot;);
    339. 

  339. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">Query: </span><span style="color:#d3d0c8;">&quot; + q, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    340. 

  340. </span><span style="color:#d3d0c8;">});
    341. 

  341. </span></pre>
    342. 

  342. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    343. 

  343. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/search</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    344. 

  344. </span><span style="color:#4f5b66;">    </span><span style="color:#b48ead;">auto</span><span style="color:#4f5b66;"> q = req.</span><span style="color:#8fa1b3;">get_param_value</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">q</span><span style="color:#4f5b66;">&quot;);
    345. 

  345. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">Query: </span><span style="color:#4f5b66;">&quot; + q, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    346. 

  346. </span><span style="color:#4f5b66;">});
    347. 

  347. </span></pre>
    348. 

  348. </div>
    349. 

  349. <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>
    350. 

  350. <h3>POST /post</h3>
    351. 

  351. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    352. 

  352. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Post</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/post</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    353. 

  353. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(req.</span><span style="color:#f2777a;">body</span><span style="color:#d3d0c8;">, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    354. 

  354. </span><span style="color:#d3d0c8;">});
    355. 

  355. </span></pre>
    356. 

  356. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    357. 

  357. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Post</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/post</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    358. 

  358. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(req.</span><span style="color:#bf616a;">body</span><span style="color:#4f5b66;">, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    359. 

  359. </span><span style="color:#4f5b66;">});
    360. 

  360. </span></pre>
    361. 

  361. </div>
    362. 

  362. <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>
    363. 

  363. <h3>POST /submit</h3>
    364. 

  364. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    365. 

  365. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Post</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/submit</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    366. 

  366. </span><span style="color:#d3d0c8;">    std::string result;
    367. 

  367. </span><span style="color:#d3d0c8;">    </span><span style="color:#cc99cc;">for </span><span style="color:#d3d0c8;">(</span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;[key, val] : req.</span><span style="color:#f2777a;">params</span><span style="color:#d3d0c8;">) {
    368. 

  368. </span><span style="color:#d3d0c8;">        result += key + &quot;</span><span style="color:#99cc99;"> = </span><span style="color:#d3d0c8;">&quot; + val + &quot;</span><span style="color:#66cccc;">\n</span><span style="color:#d3d0c8;">&quot;;
    369. 

  369. </span><span style="color:#d3d0c8;">    }
    370. 

  370. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(result, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    371. 

  371. </span><span style="color:#d3d0c8;">});
    372. 

  372. </span></pre>
    373. 

  373. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    374. 

  374. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Post</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/submit</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    375. 

  375. </span><span style="color:#4f5b66;">    std::string result;
    376. 

  376. </span><span style="color:#4f5b66;">    </span><span style="color:#b48ead;">for </span><span style="color:#4f5b66;">(</span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;[key, val] : req.</span><span style="color:#bf616a;">params</span><span style="color:#4f5b66;">) {
    377. 

  377. </span><span style="color:#4f5b66;">        result += key + &quot;</span><span style="color:#a3be8c;"> = </span><span style="color:#4f5b66;">&quot; + val + &quot;</span><span style="color:#96b5b4;">\n</span><span style="color:#4f5b66;">&quot;;
    378. 

  378. </span><span style="color:#4f5b66;">    }
    379. 

  379. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(result, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    380. 

  380. </span><span style="color:#4f5b66;">});
    381. 

  381. </span></pre>
    382. 

  382. </div>
    383. 

  383. <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>
    384. 

  384. <h3>POST /upload</h3>
    385. 

  385. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    386. 

  386. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Post</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/upload</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    387. 

  387. </span><span style="color:#d3d0c8;">    </span><span style="color:#cc99cc;">auto</span><span style="color:#d3d0c8;"> f = req.</span><span style="color:#f2777a;">form</span><span style="color:#d3d0c8;">.</span><span style="color:#6699cc;">get_file</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">file</span><span style="color:#d3d0c8;">&quot;);
    388. 

  388. </span><span style="color:#d3d0c8;">    </span><span style="color:#cc99cc;">auto</span><span style="color:#d3d0c8;"> content = f.</span><span style="color:#f2777a;">filename </span><span style="color:#d3d0c8;">+ &quot;</span><span style="color:#99cc99;"> (</span><span style="color:#d3d0c8;">&quot; + </span><span style="color:#6699cc;">std::to_string</span><span style="color:#d3d0c8;">(f.</span><span style="color:#f2777a;">content</span><span style="color:#d3d0c8;">.</span><span style="color:#6699cc;">size</span><span style="color:#d3d0c8;">()) + &quot;</span><span style="color:#99cc99;"> bytes)</span><span style="color:#d3d0c8;">&quot;;
    389. 

  389. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(content, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    390. 

  390. </span><span style="color:#d3d0c8;">});
    391. 

  391. </span></pre>
    392. 

  392. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    393. 

  393. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Post</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/upload</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    394. 

  394. </span><span style="color:#4f5b66;">    </span><span style="color:#b48ead;">auto</span><span style="color:#4f5b66;"> f = req.</span><span style="color:#bf616a;">form</span><span style="color:#4f5b66;">.</span><span style="color:#8fa1b3;">get_file</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">file</span><span style="color:#4f5b66;">&quot;);
    395. 

  395. </span><span style="color:#4f5b66;">    </span><span style="color:#b48ead;">auto</span><span style="color:#4f5b66;"> content = f.</span><span style="color:#bf616a;">filename </span><span style="color:#4f5b66;">+ &quot;</span><span style="color:#a3be8c;"> (</span><span style="color:#4f5b66;">&quot; + </span><span style="color:#8fa1b3;">std::to_string</span><span style="color:#4f5b66;">(f.</span><span style="color:#bf616a;">content</span><span style="color:#4f5b66;">.</span><span style="color:#8fa1b3;">size</span><span style="color:#4f5b66;">()) + &quot;</span><span style="color:#a3be8c;"> bytes)</span><span style="color:#4f5b66;">&quot;;
    396. 

  396. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(content, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    397. 

  397. </span><span style="color:#4f5b66;">});
    398. 

  398. </span></pre>
    399. 

  399. </div>
    400. 

  400. <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>
    401. 

  401. <h3>GET /users/:id</h3>
    402. 

  402. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    403. 

  403. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Get</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">/users/:id</span><span style="color:#d3d0c8;">&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    404. 

  404. </span><span style="color:#d3d0c8;">    </span><span style="color:#cc99cc;">auto</span><span style="color:#d3d0c8;"> id = req.</span><span style="color:#f2777a;">path_params</span><span style="color:#d3d0c8;">.</span><span style="color:#6699cc;">at</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">id</span><span style="color:#d3d0c8;">&quot;);
    405. 

  405. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">User ID: </span><span style="color:#d3d0c8;">&quot; + id, &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    406. 

  406. </span><span style="color:#d3d0c8;">});
    407. 

  407. </span></pre>
    408. 

  408. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    409. 

  409. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">/users/:id</span><span style="color:#4f5b66;">&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    410. 

  410. </span><span style="color:#4f5b66;">    </span><span style="color:#b48ead;">auto</span><span style="color:#4f5b66;"> id = req.</span><span style="color:#bf616a;">path_params</span><span style="color:#4f5b66;">.</span><span style="color:#8fa1b3;">at</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">id</span><span style="color:#4f5b66;">&quot;);
    411. 

  411. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">User ID: </span><span style="color:#4f5b66;">&quot; + id, &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    412. 

  412. </span><span style="color:#4f5b66;">});
    413. 

  413. </span></pre>
    414. 

  414. </div>
    415. 

  415. <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>
    416. 

  416. <h3>GET /files/(\d+)</h3>
    417. 

  417. <div class="code-dark"><pre style="background-color:#2d2d2d;">
    418. 

  418. <span style="color:#d3d0c8;">svr.</span><span style="color:#6699cc;">Get</span><span style="color:#d3d0c8;">(</span><span style="color:#cc99cc;">R</span><span style="color:#d3d0c8;">&quot;(</span><span style="color:#99cc99;">/files/(\d+)</span><span style="color:#d3d0c8;">)&quot;, [](</span><span style="color:#cc99cc;">const auto </span><span style="color:#d3d0c8;">&amp;req, </span><span style="color:#cc99cc;">auto </span><span style="color:#d3d0c8;">&amp;res) {
    419. 

  419. </span><span style="color:#d3d0c8;">    </span><span style="color:#cc99cc;">auto</span><span style="color:#d3d0c8;"> id = req.</span><span style="color:#f2777a;">matches</span><span style="color:#d3d0c8;">[</span><span style="color:#f99157;">1</span><span style="color:#d3d0c8;">];
    420. 

  420. </span><span style="color:#d3d0c8;">    res.</span><span style="color:#6699cc;">set_content</span><span style="color:#d3d0c8;">(&quot;</span><span style="color:#99cc99;">File ID: </span><span style="color:#d3d0c8;">&quot; + </span><span style="color:#6699cc;">std::string</span><span style="color:#d3d0c8;">(id), &quot;</span><span style="color:#99cc99;">text/plain</span><span style="color:#d3d0c8;">&quot;);
    421. 

  421. </span><span style="color:#d3d0c8;">});
    422. 

  422. </span></pre>
    423. 

  423. </div><div class="code-light"><pre style="background-color:#eff1f5;">
    424. 

  424. <span style="color:#4f5b66;">svr.</span><span style="color:#8fa1b3;">Get</span><span style="color:#4f5b66;">(</span><span style="color:#b48ead;">R</span><span style="color:#4f5b66;">&quot;(</span><span style="color:#a3be8c;">/files/(\d+)</span><span style="color:#4f5b66;">)&quot;, [](</span><span style="color:#b48ead;">const auto </span><span style="color:#4f5b66;">&amp;req, </span><span style="color:#b48ead;">auto </span><span style="color:#4f5b66;">&amp;res) {
    425. 

  425. </span><span style="color:#4f5b66;">    </span><span style="color:#b48ead;">auto</span><span style="color:#4f5b66;"> id = req.</span><span style="color:#bf616a;">matches</span><span style="color:#4f5b66;">[</span><span style="color:#d08770;">1</span><span style="color:#4f5b66;">];
    426. 

  426. </span><span style="color:#4f5b66;">    res.</span><span style="color:#8fa1b3;">set_content</span><span style="color:#4f5b66;">(&quot;</span><span style="color:#a3be8c;">File ID: </span><span style="color:#4f5b66;">&quot; + </span><span style="color:#8fa1b3;">std::string</span><span style="color:#4f5b66;">(id), &quot;</span><span style="color:#a3be8c;">text/plain</span><span style="color:#4f5b66;">&quot;);
    427. 

  427. </span><span style="color:#4f5b66;">});
    428. 

  428. </span></pre>
    429. 

  429. </div>
    430. 

  430. <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>
    431. 

  431. <h2>次のステップ</h2>
    432. 

  432. <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>
    433. 

  433. <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>
    434. 

  434. <p><strong>次:</strong> <a href="../04-static-file-server">Static File Server</a></p>
    435. 

  435. 

  436.   </article>
    437. 

  437. </main>
    438. 

  438. 

  439.   </div>
    440. 

  440. 

  441.   <footer class="footer">
    442. 

  442.     &copy; 2026 yhirose. All rights reserved.
    443. 

  443.   </footer>
    444. 

  444. 

  445.   <script src="&#x2F;cpp-httplib/js/main.js"></script>
    446. 

  446. </body>
    447. 

  447. </html>
    448.