如何用 PHP 的 getservbyname 判断某个服务名称是否有效？

gitbox 2025-09-12

在 PHP 中，getservbyname(string $service, string $protocol) 可以根据服务名称（如 http、ssh）和协议（tcp 或 udp）返回对应的端口号（十进制整数）。如果找不到该服务名或发生错误，函数会返回 false。因此我们可以用它来判断某个服务名称是否在系统服务数据库（例如 Linux 下的 /etc/services、Windows 的 services 文件）中存在 —— 注意：这是查名字是否有映射到端口，而不是检测该服务当前是否可连接或可用。

下面示例展示常见用法、封装函数、注意事项与实际可用性的额外检测方法（如果你需要确认服务是否真的能连通）。

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">$port</span></span><span> === </span><span><span class="hljs-literal">false</span></span><span>) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"服务名 '<span class="hljs-subst">{$service}</span></span></span><span>'（协议 </span><span><span class="hljs-subst">{$protocol}</span></span><span>）在本机服务数据库中不存在。\n";
} </span><span><span class="hljs-keyword">else</span></span><span> {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"服务 '<span class="hljs-subst">{$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>

推荐的判断封装函数

这个函数会更稳健地判断：既检查 getservbyname 返回值，也确保端口号在合法范围（1–65535）内：

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
<span class="hljs-comment">/**
 * 判断服务名称是否有效（在本机服务数据库中有对应端口）
 *
 * </span></span><span><span class="hljs-doctag">@param</span></span><span> string $service 服务名称，例如 'http'、'ssh'
 * </span><span><span class="hljs-doctag">@param</span></span><span> string $protocol 协议 'tcp' 或 'udp'
 * </span><span><span class="hljs-doctag">@return</span></span><span> bool 返回 true 表示有效（找到合法端口），false 表示无效或出错
 */
</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">is_service_name_valid</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-keyword">string</span></span></span><span> </span><span><span class="hljs-variable">$service</span></span><span>, </span><span><span class="hljs-keyword">string</span></span><span> </span><span><span class="hljs-variable">$protocol</span></span><span> = </span><span><span class="hljs-string">'tcp'</span></span><span>): </span><span><span class="hljs-title">bool</span></span><span>
{
    </span><span><span class="hljs-comment">// 规范化参数</span></span><span>
    </span><span><span class="hljs-variable">$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">// 确保端口在合法范围</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>

平台依赖性与限制（重要）

getservbyname 查询的是 操作系统的服务数据库（如 /etc/services）。不同系统、不同安装环境、不同发行版可能含有不同条目。例如某些自定义服务在一个主机上存在而在另一个主机上不存在。
该函数只告诉你服务名是否有端口映射 —— 并不表示该端口上的服务当前正在运行或可连通。如果你需要检查“服务可用性”，还需要执行网络连接测试（例如 fsockopen、stream_socket_client 或 socket_create/socket_connect）。
协议必须是 'tcp' 或 'udp'（大小写不敏感）。其他值会被视为无效。

如果你还想确认服务是否可连接（可选）

判断服务名存在只是第一步。如果你想检查远程主机（或本地主机）是否在该服务端口上接受连接，可以先用 getservbyname 取端口，然后尝试建立连接。

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
<span class="hljs-comment">/**
 * 先用 getservbyname 判断服务名，再尝试连接目标主机的该端口以确认可达性
 *
 * </span></span><span><span class="hljs-doctag">@param</span></span><span> string $host 目标主机（IP 或 主机名）
 * </span><span><span class="hljs-doctag">@param</span></span><span> string $service 服务名称
 * </span><span><span class="hljs-doctag">@param</span></span><span> string $protocol 'tcp' 或 'udp'（这里只实现 tcp 的连接检测）
 * </span><span><span class="hljs-doctag">@param</span></span><span> float $timeout 秒（例如 2.0）
 * </span><span><span class="hljs-doctag">@return</span></span><span> bool true 表示找到端口且能建立 TCP 连接，false 否则
 */
</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">is_service_reachable</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-keyword">string</span></span></span><span> </span><span><span class="hljs-variable">$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">// 简化：这里只做 TCP 的连通性检测；UDP 检测较复杂（无连接/无确认）</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 检测'</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">// 本机 ssh 服务是否可达</span></span><span>
</span></span>

注意：UDP 的“可达性”判断不是简单的 connect：通常需要发送探测包并等待响应，或使用更复杂的 socket API（并且可能被防火墙丢弃）。如果确实需要 UDP 检测，要实现应用层探测逻辑或采用专门工具。

常见用例与建议

配置验证：当用户在配置界面输入服务名（例如 smtp、imap），先用 getservbyname 验证名字是否被系统识别。如果未识别，可提示用户使用端口号或选择其他服务名。
兼容性：不要硬依赖系统的服务数据库——在需要跨平台一致性时，维护一个应用内映射表（如 'http' => 80）作为回退。
权限与安全：尝试连接端口进行可达性检测时，注意网络策略、防火墙和速率限制，不要在短时间内对大量主机频繁探测以免造成滥用或触发安全告警。
错误处理：getservbyname 可能返回 false，请在代码中显式处理，而不是直接使用返回值。

小结

使用 getservbyname($service, $protocol) 可以判断服务名称在本机系统服务数据库中是否有端口映射（返回端口号或 false）。
判断有效性时最好检查返回值类型并确保端口在 1–65535 范围内。
该方法不代表服务可用；若需确认可用性，还需进一步做网络连接层面的检测（如 fsockopen 等）。
注意平台差异：不同系统的服务数据库条目不尽相同，如有跨平台需求请准备回退映射或询问用户提供端口号。