# Predefined Constants

The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.

`AF_UNIX` (int)
  Socket address family of filesystem pathnames in the Unix Domain.
`AF_INET` (int)
  Socket address family of IPv4 in the Internet Domain.
`AF_INET6` (int)
  Socket address family of IPv6 in the Internet Domain. Only available if compiled with IPv6 support.
`AF_DIVERT` (int)
  Available as of PHP 8.3.0 (FreeBSD only)
`SOCK_STREAM` (int)
`SOCK_DGRAM` (int)
`SOCK_RAW` (int)
`SOCK_SEQPACKET` (int)
`SOCK_RDM` (int)
`SOCK_CONN_DGRAM` (int)
  Set the socket to a connection-oriented datagram. Available as of PHP 8.4.0. (NetBSD only)
`SOCK_DCCP` (int)
  Set the socket to a datagram congestion control protocol. Available as of PHP 8.4.0. (NetBSD only)
`SOCK_NONBLOCK` (int)
  Set the non-blocking socket status flag. Available as of PHP 8.4.0.
`SOCK_CLOEXEC` (int)
  Set the close-on-exec socket status flag. Available as of PHP 8.4.0.
`MSG_OOB` (int)
`MSG_WAITALL` (int)
`MSG_PEEK` (int)
`MSG_DONTROUTE` (int)
`MSG_EOR` (int)
  Not available on Windows platforms.
`MSG_EOF` (int)
  Not available on Windows platforms.
`MSG_ZEROCOPY` (int)
  Available as of PHP 8.2.0
`SO_DEBUG` (int)
`SO_REUSEADDR` (int)
`SO_REUSEPORT` (int)
  This constant is only available on platforms that support the `SO_REUSEPORT` socket option: this includes Linux, macOS and *BSD, but does not include Windows.
`SO_KEEPALIVE` (int)
`SO_DONTROUTE` (int)
`SO_LINGER` (int)
`SO_BROADCAST` (int)
`SO_OOBINLINE` (int)
`SO_SNDBUF` (int)
`SO_RCVBUF` (int)
`SO_SNDLOWAT` (int)
`SO_RCVLOWAT` (int)
`SO_SNDTIMEO` (int)
`SO_RCVTIMEO` (int)
`SO_TYPE` (int)
`SO_ERROR` (int)
`SO_ZEROCOPY` (int)
  Available as of PHP 8.2.0
`TCP_NODELAY` (int)
  Used to disable Nagle TCP algorithm.
`TCP_KEEPCNT` (int)
  Available as of PHP 8.2.0
`TCP_KEEPIDLE` (int)
  Available as of PHP 8.2.0
`TCP_KEEPINTVL` (int)
  Available as of PHP 8.2.0
`TCP_KEEPALIVE` (int)
  Available as of PHP 8.2.0
`TCP_NOTSENT_LOWAT` (int)
  Available as of PHP 8.2.0
`SO_MARK` (int)
  Available as of PHP 8.1.0
`SO_USER_COOKIE` (int)
  Available as of PHP 8.1.0
`SO_RTABLE` (int)
  Available as of PHP 8.2.0
`SO_ACCEPTFILTER` (int)
  Available as of PHP 8.1.0
`SO_DONTTRUNC` (int)
  Available as of PHP 8.1.0
`SO_WANTMORE` (int)
  Available as of PHP 8.1.0
`SO_INCOMING_CPU` (int)
  Available as of PHP 8.2.0
`SO_MEMINFO` (int)
  Available as of PHP 8.2.0
`SO_BPF_EXTENSIONS` (int)
  Available as of PHP 8.2.0
`SO_SETFIB` (int)
  Available as of PHP 8.2.0
`SO_ATTACH_REUSEPORT_CBPF` (int)
  Available as of PHP 8.3.0 (Linux only)
`SO_DETACH_BPF` (int)
  Available as of PHP 8.3.0 (Linux only)
`SO_DETACH_FILTER` (int)
  Available as of PHP 8.3.0 (Linux only)
`SO_RERROR` (int)
  Available as of PHP 8.3.0 (NetBSD only)
`SO_ZEROIZE` (int)
  Available as of PHP 8.3.0 (OpenBSD only)
`SO_SPLICE` (int)
  Available as of PHP 8.3.0 (OpenBSD only)
`SO_REUSEPORT_LB` (int)
  Available as of PHP 8.3.0 (FreeBSD only)
`SOL_FILTER` (int)
  Available as of PHP 8.2.0
`SOL_UDPLITE` (int)
  Available as of PHP 8.3.0
`UDPLITE_RECV_CSCOV` (int)
  Available as of PHP 8.3.0
`UDPLITE_SEND_CSCOV` (int)
  Available as of PHP 8.3.0
`TCP_DEFER_ACCEPT` (int)
  Available as of PHP 8.1.0
`TCP_CONGESTION` (int)
  Available as of PHP 8.2.0
`TCP_QUICKACK` (int)
  Available as of PHP 8.3.0 (Linux only)
`TCP_REPAIR` (int)
  Available as of PHP 8.3.0 (Linux only)
`TCP_SYNCNT` (int)
  Set the number of SYN retransmits that TCP should send before aborting the attempt to connect. Available as of PHP 8.4.0 (Linux only)
`IP_DONTFRAG` (int)
  Available as of PHP 8.3.0 (FreeBSD only)
`IP_MTU_DISCOVER` (int)
  Available as of PHP 8.3.0 (Linux only)
`IP_PMTUDISC_DO` (int)
  Available as of PHP 8.3.0 (Linux only)
`IP_PMTUDISC_DONT` (int)
  Available as of PHP 8.3.0 (Linux only)
`IP_PMTUDISC_WANT` (int)
  Available as of PHP 8.3.0 (Linux only)
`IP_PMTUDISC_PROBE` (int)
  Available as of PHP 8.3.0 (Linux only)
`IP_PMTUDISC_INTERFACE` (int)
  Available as of PHP 8.3.0 (Linux only)
`IP_PMTUDISC_OMIT` (int)
  Available as of PHP 8.3.0 (Linux only)
`IP_BIND_ADDRESS_NO_PORT` (int)
  Available as of PHP 8.3.0 (Linux only)
`SOL_SOCKET` (int)
`PHP_NORMAL_READ` (int)
`PHP_BINARY_READ` (int)
`SOL_TCP` (int)
`SOL_UDP` (int)

The following constants are defined under Windows and UNIX-like platforms. Each constant is only defined if their equal is available on the platform.

`SOCKET_EINTR` (int)
  Interrupted system call.
`SOCKET_EBADF` (int)
  Bad file descriptor number.
`SOCKET_EACCES` (int)
  Permission denied.
`SOCKET_EFAULT` (int)
  Bad address.
`SOCKET_EINVAL` (int)
  Invalid argument.
`SOCKET_EMFILE` (int)
  Too many open files.
`SOCKET_ENAMETOOLONG` (int)
  File name too long.
`SOCKET_ENOTEMPTY` (int)
  Directory not empty.
`SOCKET_ELOOP` (int)
  Too many symbolic links encountered.
`SOCKET_EWOULDBLOCK` (int)
  Operation would block.
`SOCKET_EREMOTE` (int)
  Object is remote.
`SOCKET_EUSERS` (int)
  Too many users.
`SOCKET_ENOTSOCK` (int)
  Socket operation on non-socket.
`SOCKET_EDESTADDRREQ` (int)
  Destination address required.
`SOCKET_EMSGSIZE` (int)
  Message too long.
`SOCKET_EPROTOTYPE` (int)
  Protocol wrong type for socket.
`SOCKET_EPROTONOSUPPORT` (int)
  Protocol not supported.
`SOCKET_ESOCKTNOSUPPORT` (int)
  Socket type not supported.
`SOCKET_EOPNOTSUPP` (int)
  Operation not supported on transport endpoint.
`SOCKET_EPFNOSUPPORT` (int)
  Protocol family not supported.
`SOCKET_EAFNOSUPPORT` (int)
  Address family not supported by protocol.
`SOCKET_EADDRNOTAVAIL` (int)
  Cannot assign requested address.
`SOCKET_ENETDOWN` (int)
  Network is down.
`SOCKET_ENETUNREACH` (int)
  Network is unreachable.
`SOCKET_ENETRESET` (int)
  Network dropped connection because of reset.
`SOCKET_ECONNABORTED` (int)
  Software caused connection abort.
`SOCKET_ECONNRESET` (int)
  Connection reset by peer.
`SOCKET_ENOBUFS` (int)
  No buffer space available.
`SOCKET_EISCONN` (int)
  Transport endpoint is already connected.
`SOCKET_ENOTCONN` (int)
  Transport endpoint is not connected.
`SOCKET_ESHUTDOWN` (int)
  Cannot send after transport endpoint shutdown.
`SOCKET_ETIMEDOUT` (int)
  Connection timed out.
`SOCKET_ECONNREFUSED` (int)
  Connection refused.
`SOCKET_EHOSTDOWN` (int)
  Host is down.
`SOCKET_EHOSTUNREACH` (int)
  No route to host.
`SOCKET_EALREADY` (int)
  Operation already in progress.
`SOCKET_EINPROGRESS` (int)
  Operation now in progress.

The following constants are only defined under Windows.

`SOCKET_ENOPROTOOPT` (int)
`SOCKET_EADDRINUSE` (int)
`SOCKET_ETOOMYREFS` (int)
`SOCKET_EPROCLIM` (int)
`SOCKET_EDUOT` (int)
`SOCKET_ESTALE` (int)
`SOCKET_EDISCON` (int)
`SOCKET_SYSNOTREADY` (int)
`SOCKET_VERNOTSUPPORTED` (int)
`SOCKET_NOTINITIALISED` (int)
`SOCKET_HOST_NOT_FOUND` (int)
`SOCKET_TRY_AGAIN` (int)
`SOCKET_NO_RECOVERY` (int)
`SOCKET_NO_DATA` (int)
`SOCKET_NO_ADDRESS` (int)

The following constants are only available on UNIX-like platforms. Each constant is only defined if their equal is available on the platform.

`SOCKET_EPERM` (int)
  Operation not permitted.
`SOCKET_ENOENT` (int)
  No such file or directory.
`SOCKET_EIO` (int)
  I/O error.
`SOCKET_ENXIO` (int)
  No such device or address.
`SOCKET_E2BIG` (int)
  Arg list too long.
`SOCKET_EAGAIN` (int)
  Try again.
`SOCKET_ENOMEM` (int)
  Out of memory.
`SOCKET_ENOTBLK` (int)
  Block device required.
`SOCKET_EBUSY` (int)
  Device or resource busy.
`SOCKET_EEXIST` (int)
  File exists.
`SOCKET_EXDEV` (int)
  Cross-device link.
`SOCKET_ENODEV` (int)
  No such device.
`SOCKET_ENOTDIR` (int)
  Not a directory.
`SOCKET_EISDIR` (int)
  Is a directory.
`SOCKET_ENFILE` (int)
  File table overflow.
`SOCKET_ENOTTY` (int)
  Not a typewriter.
`SOCKET_ENOSPC` (int)
  No space left on device.
`SOCKET_ESPIPE` (int)
  Illegal seek.
`SOCKET_EROFS` (int)
  Read-only file system.
`SOCKET_EMLINK` (int)
  Too many links.
`SOCKET_EPIPE` (int)
  Broken pipe.
`SOCKET_ENOLCK` (int)
  No record locks available.
`SOCKET_ENOSYS` (int)
  Function not implemented.
`SOCKET_ENOMSG` (int)
  No message of desired type.
`SOCKET_EIDRM` (int)
  Identifier removed.
`SOCKET_ECHRNG` (int)
  Channel number out of range.
`SOCKET_EL2NSYNC` (int)
  Level 2 not synchronized.
`SOCKET_EL3HLT` (int)
  Level 3 halted.
`SOCKET_EL3RST` (int)
  Level 3 reset.
`SOCKET_ELNRNG` (int)
  Link number out of range.
`SOCKET_EUNATCH` (int)
  Protocol driver not attached.
`SOCKET_ENOCSI` (int)
  No CSI structure available.
`SOCKET_EL2HLT` (int)
  Level 2 halted.
`SOCKET_EBADE` (int)
  Invalid exchange.
`SOCKET_EBADR` (int)
  Invalid request descriptor.
`SOCKET_EXFULL` (int)
  Exchange full.
`SOCKET_ENOANO` (int)
  No anode.
`SOCKET_EBADRQC` (int)
  Invalid request code.
`SOCKET_EBADSLT` (int)
  Invalid slot.
`SOCKET_ENOSTR` (int)
  Device not a stream.
`SOCKET_ENODATA` (int)
  No data available.
`SOCKET_ETIME` (int)
  Timer expired.
`SOCKET_ENOSR` (int)
  Out of streams resources.
`SOCKET_ENONET` (int)
  Machine is not on the network.
`SOCKET_ENOLINK` (int)
  Link has been severed.
`SOCKET_EADV` (int)
  Advertise error.
`SOCKET_ESRMNT` (int)
  Srmount error.
`SOCKET_ECOMM` (int)
  Communication error on send.
`SOCKET_EPROTO` (int)
  Protocol error.
`SOCKET_EMULTIHOP` (int)
  Multihop attempted.
`SOCKET_EBADMSG` (int)
  Not a data message.
`SOCKET_ENOTUNIQ` (int)
  Name not unique on network.
`SOCKET_EBADFD` (int)
  File descriptor in bad state.
`SOCKET_EREMCHG` (int)
  Remote address changed.
`SOCKET_ERESTART` (int)
  Interrupted system call should be restarted.
`SOCKET_ESTRPIPE` (int)
  Streams pipe error.
`SOCKET_EPROTOOPT` (int)
  Protocol not available.
`SOCKET_ADDRINUSE` (int)
  Address already in use.
`SOCKET_ETOOMANYREFS` (int)
  Too many references: cannot splice.
`SOCKET_EISNAM` (int)
  Is a named type file.
`SOCKET_EREMOTEIO` (int)
  Remote I/O error.
`SOCKET_EDQUOT` (int)
  Quota exceeded.
`SOCKET_ENOMEDIUM` (int)
  No medium found.
`SOCKET_EMEDIUMTYPE` (int)
  Wrong medium type.
`SCM_RIGHTS` (int)
  Send or receive a set of open file descriptors from another process.
`SCM_CREDENTIALS` (int)
`SCM_CREDS` (int)
  Available as of PHP 8.2.0
`SCM_CREDS2` (int)
  Available as of PHP 8.2.0
`LOCAL_CREDS` (int)
  Available as of PHP 8.2.0
`LOCAL_CREDS_PERSISTENT` (int)
  Available as of PHP 8.2.0
`SKF_AD_OFF` (int)
  Available as of PHP 8.2.0
`SKF_AD_PROTOCOL` (int)
  Available as of PHP 8.2.0
`SKF_AD_PKTTYPE` (int)
  Available as of PHP 8.2.0
`SKF_AD_IFINDEX` (int)
  Available as of PHP 8.2.0
`SKF_AD_NLATTR` (int)
  Available as of PHP 8.2.0
`SKF_AD_NLATTR_NEST` (int)
  Available as of PHP 8.2.0
`SKF_AD_MARK` (int)
  Available as of PHP 8.2.0
`SKF_AD_QUEUE` (int)
  Available as of PHP 8.2.0
`SKF_AD_HATYPE` (int)
  Available as of PHP 8.2.0
`SKF_AD_RXHASH` (int)
  Available as of PHP 8.2.0
`SKF_AD_CPU` (int)
  Available as of PHP 8.2.0
`SKF_AD_ALU_XOR_X` (int)
  Available as of PHP 8.2.0
`SKF_AD_VLAN_TAG` (int)
  Available as of PHP 8.2.0
`SKF_AD_VLAN_TAG_PRESENT` (int)
  Available as of PHP 8.2.0
`SKF_AD_PAY_OFFSET` (int)
  Available as of PHP 8.2.0
`SKF_AD_RANDOM` (int)
  Available as of PHP 8.2.0
`SKF_AD_VLAN_TPID` (int)
  Available as of PHP 8.2.0
`SKF_AD_MAX` (int)
  Available as of PHP 8.2.0
`AI_ADDRCONFIG` (int)
`AI_ALL` (int)
`AI_CANONIDN` (int)
`AI_CANONNAME` (int)
`AI_IDN` (int)
`AI_NUMERICHOST` (int)
`AI_NUMERICSERV` (int)
`AI_PASSIVE` (int)
`AI_V4MAPPED` (int)
`FIL_ATTACH` (int)
`FIL_DETACH` (int)
`IPPROTO_IP` (int)
`IPPROTO_IPV6` (int)
`IPV6_HOPLIMIT` (int)
`IPV6_MULTICAST_HOPS` (int)
`IPV6_MULTICAST_IF` (int)
`IPV6_MULTICAST_LOOP` (int)
`IPV6_PKTINFO` (int)
`IPV6_RECVHOPLIMIT` (int)
`IPV6_RECVPKTINFO` (int)
`IPV6_RECVTCLASS` (int)
`IPV6_TCLASS` (int)
`IPV6_UNICAST_HOPS` (int)
`IPV6_V6ONLY` (int)
`IP_MULTICAST_IF` (int)
`IP_MULTICAST_LOOP` (int)
`IP_MULTICAST_TTL` (int)
`IP_PORTRANGE` (int)
  Set the port range used for selecting a local port number. Available as of PHP 8.4.0. (FreeBSD/NetBSD/OpenBSD only)
`IP_PORTRANGE_DEFAULT` (int)
  Use the default range of port values. Available as of PHP 8.4.0. (FreeBSD/NetBSD/OpenBSD only)
`IP_PORTRANGE_HIGH` (int)
  Use a high range of port values. Available as of PHP 8.4.0. (FreeBSD/NetBSD/OpenBSD only)
`IP_PORTRANGE_LOW` (int)
  Use a low range of port values. Available as of PHP 8.4.0. (FreeBSD/NetBSD/OpenBSD only)
`MCAST_BLOCK_SOURCE` (int)
`MCAST_JOIN_GROUP` (int)
`MCAST_JOIN_SOURCE_GROUP` (int)
`MCAST_LEAVE_GROUP` (int)
`MCAST_LEAVE_SOURCE_GROUP` (int)
`MCAST_UNBLOCK_SOURCE` (int)
`MSG_CMSG_CLOEXEC` (int)
`MSG_CONFIRM` (int)
`MSG_CTRUNC` (int)
`MSG_DONTWAIT` (int)
`MSG_ERRQUEUE` (int)
`MSG_MORE` (int)
`MSG_NOSIGNAL` (int)
`MSG_TRUNC` (int)
`MSG_WAITFORONE` (int)
`SOL_LOCAL` (int)
`SOMAXCONN` (int)
`SO_BINDTODEVICE` (int)
`SO_FAMILY` (int)
`SO_LABEL` (int)
`SO_LISTENQLEN` (int)
`SO_LISTENQLIMIT` (int)
`SO_PASSCRED` (int)
`SO_PEERLABEL` (int)
`SO_EXCLUSIVEADDRUSE` (int)
  Prevents other sockets from being forcibly bound to the same address and port. Available as of PHP 8.4.0. (Windows only)
`SO_EXCLBIND` (int)
  Enable/disable exclusive binding of the socket. Available as of PHP 8.4.0. (Solaris only)
`SO_NOSIGPIPE` (int)
  Controls generation of SIGPIPE for the socket. Available as of PHP 8.4.0. (macOs and FreeBSD only)
`SO_LINGER_SEC` (int)
  Similar to `SO_LINGER` but lingering is in seconds as opposed to time clicks on macOs. Available as of PHP 8.4.0. (macOs only)
`SO_BINDTOIFINDEX` (int)
  Bind a socket to a specific network interface by its index. Available as of PHP 8.4.0.

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