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<h1>HTTPS Client</h1>
<p>前章でOpenSSLのセットアップが済んだので、さっそくHTTPSクライアントを使ってみましょう。2章で使った <code>httplib::Client</code> がそのまま使えます。コンストラクタに <code>https://</code> 付きのURLを渡すだけです。</p>
<h2>GETリクエスト</h2>
<p>実在するHTTPSサイトにアクセスしてみましょう。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#b48ead;">#define </span><span style="color:#c0c5ce;">CPPHTTPLIB_OPENSSL_SUPPORT
</span><span style="color:#b48ead;">#include </span><span style="color:#c0c5ce;">&quot;</span><span style="color:#a3be8c;">httplib.h</span><span style="color:#c0c5ce;">&quot;
</span><span style="color:#b48ead;">#include </span><span style="color:#c0c5ce;">&lt;</span><span style="color:#a3be8c;">iostream</span><span style="color:#c0c5ce;">&gt;
</span><span style="color:#c0c5ce;">
</span><span style="color:#b48ead;">int </span><span style="color:#8fa1b3;">main</span><span style="color:#c0c5ce;">() {
</span><span style="color:#c0c5ce;"> httplib::Client </span><span style="color:#8fa1b3;">cli</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">https://nghttp2.org</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">
</span><span style="color:#c0c5ce;"> </span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> res = cli.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;"> </span><span style="color:#b48ead;">if </span><span style="color:#c0c5ce;">(res) {
</span><span style="color:#c0c5ce;"> std::cout &lt;&lt; res-&gt;</span><span style="color:#bf616a;">status </span><span style="color:#c0c5ce;">&lt;&lt; std::endl; </span><span style="color:#65737e;">// 200
</span><span style="color:#c0c5ce;"> std::cout &lt;&lt; res-&gt;</span><span style="color:#bf616a;">body</span><span style="color:#c0c5ce;">.</span><span style="color:#8fa1b3;">substr</span><span style="color:#c0c5ce;">(</span><span style="color:#d08770;">0</span><span style="color:#c0c5ce;">, </span><span style="color:#d08770;">100</span><span style="color:#c0c5ce;">) &lt;&lt; std::endl; </span><span style="color:#65737e;">// HTMLの先頭部分
</span><span style="color:#c0c5ce;"> } </span><span style="color:#b48ead;">else </span><span style="color:#c0c5ce;">{
</span><span style="color:#c0c5ce;"> std::cout &lt;&lt; &quot;</span><span style="color:#a3be8c;">Error: </span><span style="color:#c0c5ce;">&quot; &lt;&lt; </span><span style="color:#8fa1b3;">httplib::to_string</span><span style="color:#c0c5ce;">(res.</span><span style="color:#8fa1b3;">error</span><span style="color:#c0c5ce;">()) &lt;&lt; std::endl;
</span><span style="color:#c0c5ce;"> }
</span><span style="color:#c0c5ce;">}
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="font-weight:bold;color:#a71d5d;">#define </span><span style="color:#323232;">CPPHTTPLIB_OPENSSL_SUPPORT
</span><span style="font-weight:bold;color:#a71d5d;">#include </span><span style="color:#183691;">&quot;httplib.h&quot;
</span><span style="font-weight:bold;color:#a71d5d;">#include </span><span style="color:#183691;">&lt;iostream&gt;
</span><span style="color:#323232;">
</span><span style="font-weight:bold;color:#a71d5d;">int </span><span style="font-weight:bold;color:#795da3;">main</span><span style="color:#323232;">() {
</span><span style="color:#323232;"> httplib::Client cli(</span><span style="color:#183691;">&quot;https://nghttp2.org&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">
</span><span style="color:#323232;"> </span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> res </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> cli.Get(</span><span style="color:#183691;">&quot;/&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;"> </span><span style="font-weight:bold;color:#a71d5d;">if </span><span style="color:#323232;">(res) {
</span><span style="color:#323232;"> std::cout </span><span style="font-weight:bold;color:#a71d5d;">&lt;&lt;</span><span style="color:#323232;"> res-&gt;status </span><span style="font-weight:bold;color:#a71d5d;">&lt;&lt;</span><span style="color:#323232;"> std::endl; </span><span style="font-style:italic;color:#969896;">// 200
</span><span style="color:#323232;"> std::cout </span><span style="font-weight:bold;color:#a71d5d;">&lt;&lt;</span><span style="color:#323232;"> res-&gt;body.substr(</span><span style="color:#0086b3;">0</span><span style="color:#323232;">, </span><span style="color:#0086b3;">100</span><span style="color:#323232;">) </span><span style="font-weight:bold;color:#a71d5d;">&lt;&lt;</span><span style="color:#323232;"> std::endl; </span><span style="font-style:italic;color:#969896;">// HTMLの先頭部分
</span><span style="color:#323232;"> } </span><span style="font-weight:bold;color:#a71d5d;">else </span><span style="color:#323232;">{
</span><span style="color:#323232;"> std::cout </span><span style="font-weight:bold;color:#a71d5d;">&lt;&lt; </span><span style="color:#183691;">&quot;Error: &quot; </span><span style="font-weight:bold;color:#a71d5d;">&lt;&lt; </span><span style="color:#323232;">httplib::to_string(res.error()) </span><span style="font-weight:bold;color:#a71d5d;">&lt;&lt;</span><span style="color:#323232;"> std::endl;
</span><span style="color:#323232;"> }
</span><span style="color:#323232;">}
</span></pre>
</div></div>
<p>2章では <code>httplib::Client cli("http://localhost:8080")</code> と書きましたよね。スキームを <code>https://</code> に変えるだけです。<code>Get()</code> や <code>Post()</code> など、2章で学んだAPIはすべてそのまま使えます。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#8fa1b3;">curl</span><span style="color:#c0c5ce;"> https://nghttp2.org/
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">curl https://nghttp2.org/
</span></pre>
</div></div>
<h2>ポートの指定</h2>
<p>HTTPSのデフォルトポートは443です。別のポートを使いたい場合は、URLにポートを含めます。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">httplib::Client </span><span style="color:#8fa1b3;">cli</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">https://localhost:8443</span><span style="color:#c0c5ce;">&quot;);
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">httplib::Client </span><span style="font-weight:bold;color:#795da3;">cli</span><span style="color:#323232;">(</span><span style="color:#183691;">&quot;https://localhost:8443&quot;</span><span style="color:#323232;">);
</span></pre>
</div></div>
<h2>CA証明書の検証</h2>
<p><code>httplib::Client</code> はHTTPS接続時、デフォルトでサーバー証明書を検証します。信頼できるCA（認証局）が発行した証明書を持つサーバーにしか接続しません。</p>
<p>CA証明書は、macOSならKeychain、LinuxならシステムのCA証明書ストア、WindowsならWindowsの証明書ストアから自動で読み込みます。ほとんどの場合、追加の設定は要りません。</p>
<h3>CA証明書ファイルの指定</h3>
<p>環境によってはシステムのCA証明書が見つからないこともあります。そのときは <code>set_ca_cert_path()</code> でパスを直接指定してください。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">httplib::Client </span><span style="color:#8fa1b3;">cli</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">https://nghttp2.org</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">cli.</span><span style="color:#8fa1b3;">set_ca_cert_path</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/etc/ssl/certs/ca-certificates.crt</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">
</span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> res = cli.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/</span><span style="color:#c0c5ce;">&quot;);
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">httplib::Client </span><span style="font-weight:bold;color:#795da3;">cli</span><span style="color:#323232;">(</span><span style="color:#183691;">&quot;https://nghttp2.org&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">cli.set_ca_cert_path(</span><span style="color:#183691;">&quot;/etc/ssl/certs/ca-certificates.crt&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;"> res </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> cli.Get(</span><span style="color:#183691;">&quot;/&quot;</span><span style="color:#323232;">);
</span></pre>
</div></div><div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#8fa1b3;">curl</span><span style="color:#bf616a;"> --cacert</span><span style="color:#c0c5ce;"> /etc/ssl/certs/ca-certificates.crt https://nghttp2.org/
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">curl --cacert /etc/ssl/certs/ca-certificates.crt https://nghttp2.org/
</span></pre>
</div></div>
<h3>証明書検証の無効化</h3>
<p>開発中、自己署名証明書のサーバーに接続したいときは、検証を無効にできます。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">httplib::Client </span><span style="color:#8fa1b3;">cli</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">https://localhost:8443</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">cli.</span><span style="color:#8fa1b3;">enable_server_certificate_verification</span><span style="color:#c0c5ce;">(</span><span style="color:#d08770;">false</span><span style="color:#c0c5ce;">);
</span><span style="color:#c0c5ce;">
</span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> res = cli.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/</span><span style="color:#c0c5ce;">&quot;);
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">httplib::Client </span><span style="font-weight:bold;color:#795da3;">cli</span><span style="color:#323232;">(</span><span style="color:#183691;">&quot;https://localhost:8443&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">cli.enable_server_certificate_verification(</span><span style="color:#0086b3;">false</span><span style="color:#323232;">);
</span><span style="color:#323232;">
</span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> res </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> cli.Get(</span><span style="color:#183691;">&quot;/&quot;</span><span style="color:#323232;">);
</span></pre>
</div></div><div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#8fa1b3;">curl</span><span style="color:#bf616a;"> -k</span><span style="color:#c0c5ce;"> https://localhost:8443/
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">curl -k https://localhost:8443/
</span></pre>
</div></div>
<p>本番では絶対に無効にしないでください。中間者攻撃のリスクがあります。</p>
<h2>リダイレクトの追跡</h2>
<p>HTTPSサイトへのアクセスでは、リダイレクトに遭遇することがよくあります。たとえば <code>http://</code> から <code>https://</code> へ、あるいは <code>www</code> なしから <code>www</code> ありへ転送されるケースです。</p>
<p>デフォルトではリダイレクトを追跡しません。リダイレクト先は <code>Location</code> ヘッダーで確認できます。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">httplib::Client </span><span style="color:#8fa1b3;">cli</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">https://nghttp2.org</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">
</span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> res = cli.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/httpbin/redirect/3</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#b48ead;">if </span><span style="color:#c0c5ce;">(res) {
</span><span style="color:#c0c5ce;"> std::cout &lt;&lt; res-&gt;</span><span style="color:#bf616a;">status </span><span style="color:#c0c5ce;">&lt;&lt; std::endl; </span><span style="color:#65737e;">// 302
</span><span style="color:#c0c5ce;"> std::cout &lt;&lt; res-&gt;</span><span style="color:#8fa1b3;">get_header_value</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">Location</span><span style="color:#c0c5ce;">&quot;) &lt;&lt; std::endl;
</span><span style="color:#c0c5ce;">}
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">httplib::Client </span><span style="font-weight:bold;color:#795da3;">cli</span><span style="color:#323232;">(</span><span style="color:#183691;">&quot;https://nghttp2.org&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;"> res </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> cli.Get(</span><span style="color:#183691;">&quot;/httpbin/redirect/3&quot;</span><span style="color:#323232;">);
</span><span style="font-weight:bold;color:#a71d5d;">if </span><span style="color:#323232;">(res) {
</span><span style="color:#323232;"> std::cout </span><span style="font-weight:bold;color:#a71d5d;">&lt;&lt;</span><span style="color:#323232;"> res-&gt;status </span><span style="font-weight:bold;color:#a71d5d;">&lt;&lt;</span><span style="color:#323232;"> std::endl; </span><span style="font-style:italic;color:#969896;">// 302
</span><span style="color:#323232;"> std::cout </span><span style="font-weight:bold;color:#a71d5d;">&lt;&lt;</span><span style="color:#323232;"> res-&gt;get_header_value(</span><span style="color:#183691;">&quot;Location&quot;</span><span style="color:#323232;">) </span><span style="font-weight:bold;color:#a71d5d;">&lt;&lt;</span><span style="color:#323232;"> std::endl;
</span><span style="color:#323232;">}
</span></pre>
</div></div><div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#8fa1b3;">curl</span><span style="color:#c0c5ce;"> https://nghttp2.org/httpbin/redirect/3
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">curl https://nghttp2.org/httpbin/redirect/3
</span></pre>
</div></div>
<p><code>set_follow_location(true)</code> を設定すると、リダイレクトを自動で追跡して、最終的なレスポンスを返してくれます。</p>
<div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#c0c5ce;">httplib::Client </span><span style="color:#8fa1b3;">cli</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">https://nghttp2.org</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#c0c5ce;">cli.</span><span style="color:#8fa1b3;">set_follow_location</span><span style="color:#c0c5ce;">(</span><span style="color:#d08770;">true</span><span style="color:#c0c5ce;">);
</span><span style="color:#c0c5ce;">
</span><span style="color:#b48ead;">auto</span><span style="color:#c0c5ce;"> res = cli.</span><span style="color:#8fa1b3;">Get</span><span style="color:#c0c5ce;">(&quot;</span><span style="color:#a3be8c;">/httpbin/redirect/3</span><span style="color:#c0c5ce;">&quot;);
</span><span style="color:#b48ead;">if </span><span style="color:#c0c5ce;">(res) {
</span><span style="color:#c0c5ce;"> std::cout &lt;&lt; res-&gt;</span><span style="color:#bf616a;">status </span><span style="color:#c0c5ce;">&lt;&lt; std::endl; </span><span style="color:#65737e;">// 200（最終的なレスポンス）
</span><span style="color:#c0c5ce;">}
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">httplib::Client </span><span style="font-weight:bold;color:#795da3;">cli</span><span style="color:#323232;">(</span><span style="color:#183691;">&quot;https://nghttp2.org&quot;</span><span style="color:#323232;">);
</span><span style="color:#323232;">cli.set_follow_location(</span><span style="color:#0086b3;">true</span><span style="color:#323232;">);
</span><span style="color:#323232;">
</span><span style="font-weight:bold;color:#a71d5d;">auto</span><span style="color:#323232;"> res </span><span style="font-weight:bold;color:#a71d5d;">=</span><span style="color:#323232;"> cli.Get(</span><span style="color:#183691;">&quot;/httpbin/redirect/3&quot;</span><span style="color:#323232;">);
</span><span style="font-weight:bold;color:#a71d5d;">if </span><span style="color:#323232;">(res) {
</span><span style="color:#323232;"> std::cout </span><span style="font-weight:bold;color:#a71d5d;">&lt;&lt;</span><span style="color:#323232;"> res-&gt;status </span><span style="font-weight:bold;color:#a71d5d;">&lt;&lt;</span><span style="color:#323232;"> std::endl; </span><span style="font-style:italic;color:#969896;">// 200（最終的なレスポンス）
</span><span style="color:#323232;">}
</span></pre>
</div></div><div class="code-block-wrapper"><div data-code-theme="dark"><pre style="background-color:#2b303b;">
<span style="color:#8fa1b3;">curl</span><span style="color:#bf616a;"> -L</span><span style="color:#c0c5ce;"> https://nghttp2.org/httpbin/redirect/3
</span></pre>
</div><div data-code-theme="light"><pre style="background-color:#ffffff;">
<span style="color:#323232;">curl -L https://nghttp2.org/httpbin/redirect/3
</span></pre>
</div></div>
<h2>次のステップ</h2>
<p>HTTPSクライアントの使い方がわかりましたね。次は自分でHTTPSサーバーを立ててみましょう。自己署名証明書の作り方から始めます。</p>
<p><strong>次:</strong> <a href="../07-https-server">HTTPS Server</a></p>
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