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如何用PHP 的getservbyname 判斷某個服務名稱是否有效？

gitbox 2025-09-12

在PHP 中， getservbyname(string $service, string $protocol)可以根據服務名稱（如http 、 ssh ）和協議（ tcp或udp ）返回對應的端口號（十進制整數）。如果找不到該服務名或發生錯誤，函數會返回false 。因此我們可以用它來判斷某個服務名稱是否在系統服務數據庫（例如Linux 下的/etc/services 、Windows 的services 文件）中存在—— 注意：這是查名字是否有映射到端口，而不是檢測該服務當前是否可連接或可用。

下面示例展示常見用法、封裝函數、注意事項與實際可用性的額外檢測方法（如果你需要確認服務是否真的能連通）。

基本用法

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-variable">$service</span></span><span> = </span><span><span class="hljs-string">'http'</span></span><span>;
</span><span><span class="hljs-variable">$protocol</span></span><span> = </span><span><span class="hljs-string">'tcp'</span></span><span>;

</span><span><span class="hljs-variable">$port</span></span><span> = </span><span><span class="hljs-title function_ invoke__">getservbyname</span></span><span>(</span><span><span class="hljs-variable">$service</span></span><span>, </span><span><span class="hljs-variable">$protocol</span></span><span>);

</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$port</span></span><span> === </span><span><span class="hljs-literal">false</span></span><span>) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"服務名 '<span class="hljs-subst">{$service}</span></span></span><span>'（協定 </span><span><span class="hljs-subst">{$protocol}</span></span><span>）在本機服務數據庫中不存在。\n";
} </span><span><span class="hljs-keyword">else</span></span><span> {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"服務 '<span class="hljs-subst">{$service}</span></span></span><span>'（</span><span><span class="hljs-subst">{$protocol}</span></span><span>）映射到端口：</span><span><span class="hljs-subst">{$port}</span></span><span>\n";
}
</span></span>

推薦的判斷封裝函數

這個函數會更穩健地判斷：既檢查getservbyname返回值，也確保端口號在合法範圍（1–65535）內：

 <span><span><span class="hljs-meta">&lt;?php</span></span><span>
<span class="hljs-comment">/**
 * 判断服務名称是否有效（在本機服務数据库中有对应端口）
 *
 * </span></span><span><span class="hljs-doctag">@param</span></span><span> string $service 服務名称，例如 'http'、'ssh'
 * </span><span><span class="hljs-doctag">@param</span></span><span> string $protocol 協定 'tcp' 或 'udp'
 * </span><span><span class="hljs-doctag">@return</span></span><span> bool 返回 true 表示有效（找到合法端口），false 表示無效或出錯
 */
</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">is_service_name_valid</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-keyword">string</span></span></span><span> </span><span><span class="hljs-variable">$service</span></span><span>, </span><span><span class="hljs-keyword">string</span></span><span> </span><span><span class="hljs-variable">$protocol</span></span><span> = </span><span><span class="hljs-string">'tcp'</span></span><span>): </span><span><span class="hljs-title">bool</span></span><span>
{
    </span><span><span class="hljs-comment">// 規範化參數</span></span><span>
    </span><span><span class="hljs-variable">$protocol</span></span><span> = </span><span><span class="hljs-title function_ invoke__">strtolower</span></span><span>(</span><span><span class="hljs-variable">$protocol</span></span><span>);
    </span><span><span class="hljs-keyword">if</span></span><span> (!</span><span><span class="hljs-title function_ invoke__">in_array</span></span><span>(</span><span><span class="hljs-variable">$protocol</span></span><span>, [</span><span><span class="hljs-string">'tcp'</span></span><span>, </span><span><span class="hljs-string">'udp'</span></span><span>], </span><span><span class="hljs-literal">true</span></span><span>)) {
        </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-literal">false</span></span><span>;
    }

    </span><span><span class="hljs-variable">$port</span></span><span> = @</span><span><span class="hljs-title function_ invoke__">getservbyname</span></span><span>(</span><span><span class="hljs-variable">$service</span></span><span>, </span><span><span class="hljs-variable">$protocol</span></span><span>);
    </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$port</span></span><span> === </span><span><span class="hljs-literal">false</span></span><span>) {
        </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-literal">false</span></span><span>;
    }

    </span><span><span class="hljs-comment">// 確保端口在合法範圍</span></span><span>
    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">is_int</span></span><span>(</span><span><span class="hljs-variable">$port</span></span><span>) &amp;&amp; </span><span><span class="hljs-variable">$port</span></span><span> &gt;= </span><span><span class="hljs-number">1</span></span><span> &amp;&amp; </span><span><span class="hljs-variable">$port</span></span><span> &lt;= </span><span><span class="hljs-number">65535</span></span><span>;
}

</span><span><span class="hljs-comment">// 示例</span></span><span>
</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-title function_ invoke__">is_service_name_valid</span></span><span>(</span><span><span class="hljs-string">'http'</span></span><span>, </span><span><span class="hljs-string">'tcp'</span></span><span>));  </span><span><span class="hljs-comment">// 通常 true</span></span><span>
</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-title function_ invoke__">is_service_name_valid</span></span><span>(</span><span><span class="hljs-string">'nosuchservice'</span></span><span>, </span><span><span class="hljs-string">'tcp'</span></span><span>)); </span><span><span class="hljs-comment">// false</span></span><span>
</span></span>

平台依賴性與限制（重要）

  • getservbyname查詢的是操作系統的服務數據庫（如/etc/ services ）。不同系統、不同安裝環境、不同發行版可能含有不同條目。例如某些自定義服務在一個主機上存在而在另一個主機上不存在。

  • 該函數只告訴你服務名是否有端口映射—— 並不表示該端口上的服務當前正在運行或可連通。如果你需要檢查“服務可用性”，還需要執行網絡連接測試（例如fsockopen 、 stream_socket_client或socket_create / socket_connect ）。

  • 協議必須是'tcp'或'udp' （大小寫不敏感）。其他值會被視為無效。

如果你還想確認服務是否可連接（可選）

判斷服務名存在只是第一步。如果你想檢查遠程主機（或本地主機）是否在該服務端口上接受連接，可以先用getservbyname取端口，然後嘗試建立連接。

 <span><span><span class="hljs-meta">&lt;?php</span></span><span>
<span class="hljs-comment">/**
 * 先用 getservbyname 判断服務名，再嘗試連接目標主機的該端口以確認可達性
 *
 * </span></span><span><span class="hljs-doctag">@param</span></span><span> string $host 目標主機（IP 或 主機名）
 * </span><span><span class="hljs-doctag">@param</span></span><span> string $service 服務名称
 * </span><span><span class="hljs-doctag">@param</span></span><span> string $protocol 'tcp' 或 'udp'（這裡只實現 tcp 的連接檢測）
 * </span><span><span class="hljs-doctag">@param</span></span><span> float $timeout 秒（例如 2.0）
 * </span><span><span class="hljs-doctag">@return</span></span><span> bool true 表示找到端口且能建立 TCP 連接，false 否則
 */
</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">is_service_reachable</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-keyword">string</span></span></span><span> </span><span><span class="hljs-variable">$host</span></span><span>, </span><span><span class="hljs-keyword">string</span></span><span> </span><span><span class="hljs-variable">$service</span></span><span>, </span><span><span class="hljs-keyword">string</span></span><span> </span><span><span class="hljs-variable">$protocol</span></span><span> = </span><span><span class="hljs-string">'tcp'</span></span><span>, </span><span><span class="hljs-keyword">float</span></span><span> </span><span><span class="hljs-variable">$timeout</span></span><span> = </span><span><span class="hljs-number">2.0</span></span><span>): </span><span><span class="hljs-title">bool</span></span><span>
{
    </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">strtolower</span></span><span>(</span><span><span class="hljs-variable">$protocol</span></span><span>) !== </span><span><span class="hljs-string">'tcp'</span></span><span>) {
        </span><span><span class="hljs-comment">// 簡化：這裡只做 TCP 的連通性檢測；UDP 檢測較複雜（无連接/無確認）</span></span><span>
        </span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">InvalidArgumentException</span></span><span>(</span><span><span class="hljs-string">'is_service_reachable 目前只支持 tcp 檢測'</span></span><span>);
    }

    </span><span><span class="hljs-variable">$port</span></span><span> = @</span><span><span class="hljs-title function_ invoke__">getservbyname</span></span><span>(</span><span><span class="hljs-variable">$service</span></span><span>, </span><span><span class="hljs-variable">$protocol</span></span><span>);
    </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$port</span></span><span> === </span><span><span class="hljs-literal">false</span></span><span> || !</span><span><span class="hljs-title function_ invoke__">is_int</span></span><span>(</span><span><span class="hljs-variable">$port</span></span><span>) || </span><span><span class="hljs-variable">$port</span></span><span> &lt; </span><span><span class="hljs-number">1</span></span><span> || </span><span><span class="hljs-variable">$port</span></span><span> &gt; </span><span><span class="hljs-number">65535</span></span><span>) {
        </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-literal">false</span></span><span>;
    }

    </span><span><span class="hljs-variable">$errno</span></span><span> = </span><span><span class="hljs-number">0</span></span><span>;
    </span><span><span class="hljs-variable">$errstr</span></span><span> = </span><span><span class="hljs-string">''</span></span><span>;
    </span><span><span class="hljs-variable">$fp</span></span><span> = @</span><span><span class="hljs-title function_ invoke__">fsockopen</span></span><span>(</span><span><span class="hljs-variable">$host</span></span><span>, </span><span><span class="hljs-variable">$port</span></span><span>, </span><span><span class="hljs-variable">$errno</span></span><span>, </span><span><span class="hljs-variable">$errstr</span></span><span>, </span><span><span class="hljs-variable">$timeout</span></span><span>);
    </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$fp</span></span><span> === </span><span><span class="hljs-literal">false</span></span><span>) {
        </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-literal">false</span></span><span>;
    }

    </span><span><span class="hljs-title function_ invoke__">fclose</span></span><span>(</span><span><span class="hljs-variable">$fp</span></span><span>);
    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-literal">true</span></span><span>;
}

</span><span><span class="hljs-comment">// 示例</span></span><span>
</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-title function_ invoke__">is_service_reachable</span></span><span>(</span><span><span class="hljs-string">'127.0.0.1'</span></span><span>, </span><span><span class="hljs-string">'ssh'</span></span><span>, </span><span><span class="hljs-string">'tcp'</span></span><span>, </span><span><span class="hljs-number">1.5</span></span><span>)); </span><span><span class="hljs-comment">// 本機 ssh 服務是否可达</span></span><span>
</span></span>

注意：UDP 的“可達性”判斷不是簡單的connect：通常需要發送探測包並等待響應，或使用更複雜的socket API（並且可能被防火牆丟棄）。如果確實需要UDP 檢測，要實現應用層探測邏輯或採用專門工具。

常見用例與建議

  1. 配置驗證：當用戶在配置界面輸入服務名（例如smtp 、 imap ），先用getservbyname驗證名字是否被系統識別。如果未識別，可提示用戶使用端口號或選擇其他服務名。

  2. 兼容性：不要硬依賴系統的服務數據庫——在需要跨平台一致性時，維護一個應用內映射表（如'http' => 80 ）作為回退。

  3. 權限與安全：嘗試連接端口進行可達性檢測時，注意網絡策略、防火牆和速率限制，不要在短時間內對大量主機頻繁探測以免造成濫用或觸發安全告警。

  4. 錯誤處理： getservbyname可能返回false ，請在代碼中顯式處理，而不是直接使用返回值。

小結

  • 使用getservbyname($service, $protocol)可以判斷服務名稱在本機系統服務數據庫中是否有端口映射（返回端口號或false ）。

  • 判斷有效性時最好檢查返回值類型並確保端口在1–65535 範圍內。

  • 該方法不代表服務可用；若需確認可用性，還需進一步做網絡連接層面的檢測（如fsockopen等）。

  • 注意平台差異：不同系統的服務數據庫條目不盡相同，如有跨平台需求請準備回退映射或詢問用戶提供端口號。

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