Socket Types.

This data type might have different constructors depending on what is supported by the operating system.

Resolve a host or service name to one or more addresses. The AddrInfo values that this function returns contain SockAddr values that you can pass directly to connect or bindSocket.

This function is protocol independent. It can return both IPv4 and IPv6 address information.

The AddrInfo argument specifies the preferred query behaviour, socket options, or protocol. You can override these conveniently using Haskell's record update syntax on defaultHints, for example as follows:

   myHints = defaultHints { addrFlags = [AI_ADDRCONFIG, AI_CANONNAME] }

Values for addrFlags control query behaviour. The supported flags are as follows:

AI_PASSIVE

If no HostName value is provided, the network address in each SockAddr will be left as a wild card, i.e. as either iNADDR_ANY or iN6ADDR_ANY. This is useful for server applications that will accept connections from any client.

AI_CANONNAME

The addrCanonName field of the first returned AddrInfo will contain the canonical name of the host.

AI_NUMERICHOST

The HostName argument must be a numeric address in string form, and network name lookups will not be attempted.

Note: Although the following flags are required by RFC 3493, they may not have an effect on all platforms, because the underlying network stack may not support them. To see whether a flag from the list below will have any effect, call addrInfoFlagImplemented.

AI_NUMERICSERV

The ServiceName argument must be a port number in string form, and service name lookups will not be attempted.

AI_ADDRCONFIG

The list of returned AddrInfo values will only contain IPv4 addresses if the local system has at least one IPv4 interface configured, and likewise for IPv6.

AI_V4MAPPED

If an IPv6 lookup is performed, and no IPv6 addresses are found, IPv6-mapped IPv4 addresses will be returned.

AI_ALL

If AI_ALL is specified, return all matching IPv6 and IPv4 addresses. Otherwise, this flag has no effect.

You must provide a Just value for at least one of the HostName or ServiceName arguments. HostName can be either a numeric network address (dotted quad for IPv4, colon-separated hex for IPv6) or a hostname. In the latter case, its addresses will be looked up unless AI_NUMERICHOST is specified as a hint. If you do not provide a HostName value and do not set AI_PASSIVE as a hint, network addresses in the result will contain the address of the loopback interface.

If the query fails, this function throws an IO exception instead of returning an empty list. Otherwise, it returns a non-empty list of AddrInfo values.

There are several reasons why a query might result in several values. For example, the queried-for host could be multihomed, or the service might be available via several protocols.

Note: the order of arguments is slightly different to that defined for getaddrinfo in RFC 2553. The AddrInfo parameter comes first to make partial application easier.

Example: let hints = defaultHints { addrFlags = [AI_ADDRCONFIG, AI_CANONNAME] } addrs <- getAddrInfo (Just hints) (Just www.haskell.org) (Just http) let addr = head addrs sock <- socket (addrFamily addr) (addrSocketType addr) (addrProtocol addr) connect sock (addrAddress addr)

Resolve an address to a host or service name. This function is protocol independent.

The list of NameInfoFlag values controls query behaviour. The supported flags are as follows:

NI_NOFQDN

If a host is local, return only the hostname part of the FQDN.

NI_NUMERICHOST

The name of the host is not looked up. Instead, a numeric representation of the host's address is returned. For an IPv4 address, this will be a dotted-quad string. For IPv6, it will be colon-separated hexadecimal.

NI_NUMERICSERV

The name of the service is not looked up. Instead, a numeric representation of the service is returned.

NI_NAMEREQD

If the hostname cannot be looked up, an IO error is thrown.

NI_DGRAM

Resolve a datagram-based service name. This is required only for the few protocols that have different port numbers for their datagram-based versions than for their stream-based versions.

Hostname and service name lookups can be expensive. You can specify which lookups to perform via the two Bool arguments. If one of these is False, the corresponding value in the returned tuple will be Nothing, and no lookup will be performed.

If a host or service's name cannot be looked up, then the numeric form of the address or service will be returned.

If the query fails, this function throws an IO exception.

Example: (hostName, _) <- getNameInfo [] True False myAddress