网络

## 简介
提供一系列联网函数。

## 安装/配置

### 需求
Functions checkdnsrr(), getmxrr() and dns_get_record() requires Bind on Linux.

### 安装
使用这些函数不需要安装，它们是 PHP 核心的一部分。

### 运行时配置
此扩展没有在 `php.ini` 中定义配置指令。

### 资源类型
This extension defines a file pointer resource returned by fsockopen() and pfsockopen().

## 预定义常量
下列常量作为 PHP 核心的一部分总是可用的。

**openlog() Options**

| Constant   | Description                                                                                                              |
|------------|-------------------------|
| LOG_CONS   | if there is an error while sending data to the system logger, write directly to the system console|
| LOG_NDELAY | open the connection to the logger immediately |
| LOG_ODELAY | (default) delay opening the connection until the first message is logged |
| LOG_NOWAIT |  |
| LOG_PERROR | print log message also to standard error         |
| LOG_PID    | include PID with each message                    |

**openlog() Facilities**

| Constant     | Description                                                                                                                |
|--------------|------------------------------|
| LOG_AUTH     | security/authorization messages (use LOG_AUTHPRIV instead in systems where that constant is defined) |
| LOG_AUTHPRIV | security/authorization messages (private)     |
| LOG_CRON     | clock daemon (cron and at)     |
| LOG_DAEMON   | other system daemons          |
| LOG_KERN     | kernel messages              |
| LOG_LOCAL0   | reserved for local use, not available in Windows     |
| LOG_LOCAL1   | reserved for local use, not available in Windows    |
| LOG_LOCAL2   | reserved for local use, not available in Windows |
| LOG_LOCAL3   | reserved for local use, not available in Windows |
| LOG_LOCAL4   | reserved for local use, not available in Windows |
| LOG_LOCAL5   | reserved for local use, not available in Windows |
| LOG_LOCAL6   | reserved for local use, not available in Windows |
| LOG_LOCAL7   | reserved for local use, not available in Windows |
| LOG_LPR      | line printer subsystem |
| LOG_MAIL     | mail subsystem |
| LOG_NEWS     | USENET news subsystem |
| LOG_SYSLOG   | messages generated internally by syslogd |
| LOG_USER     | generic user-level messages |
| LOG_UUCP     | UUCP subsystem |

**syslog() Priorities (in descending order)**

| Constant    | Description                        |
|-------------|------------------------------------|
| LOG_EMERG   | system is unusable                 |
| LOG_ALERT   | action must be taken immediately   |
| LOG_CRIT    | critical conditions                |
| LOG_ERR     | error conditions                   |
| LOG_WARNING | warning conditions                 |
| LOG_NOTICE  | normal, but significant, condition |
| LOG_INFO    | informational message              |
| LOG_DEBUG   | debug-level message                |

**dns_get_record() Options**

| Constant  | Description |
|-----------|----------------------------------------|
| DNS_A     | IPv4 Address Resource |
| DNS_CAA   | Certification Authority Authorization Resource (available as of PHP 7.0.16 and 7.1.2)    |
| DNS_MX    | Mail Exchanger Resource |
| DNS_CNAME | Alias (Canonical Name) Resource |
| DNS_NS    | Authoritative Name Server Resource |
| DNS_PTR   | Pointer Resource |
| DNS_HINFO | Host Info Resource (See IANA's [» Operating System Names](http://www.iana.org/assignments/operating-system-names/operating-system-names.xhtml "» Operating System Names") for the meaning of these values)      |
| DNS_SOA   | Start of Authority Resource |
| DNS_TXT   | Text Resource |
| DNS_ANY   | Any Resource Record.  On most systems this returns all resource records, however it should not be counted upon for critical uses. Try DNS_ALL instead. |
| DNS_AAAA  | IPv6 Address Resource |
| DNS_ALL   | Iteratively query the name server for each available record type. |