network- Networking-related facilities





The Network.Socket module is for when you want full control over sockets. Essentially the entire C socket API is exposed through this module; in general the operations follow the behaviour of the C functions of the same name (consult your favourite Unix networking book).

A higher level interface to networking operations is provided through the module Network.



data Family Source

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

data SocketType Source

Socket Types.

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

defaultProtocol :: ProtocolNumberSource

This is the default protocol for a given service.

Address operations

addrInfoFlagImplemented :: AddrInfoFlag -> BoolSource

Indicate whether the given AddrInfoFlag will have any effect on this system.

defaultHints :: AddrInfoSource

Default hints for address lookup with getAddrInfo. The values of the addrAddress and addrCanonName fields are undefined, and are never inspected by getAddrInfo.



:: Maybe AddrInfo

preferred socket type or protocol

-> Maybe HostName

host name to look up

-> Maybe ServiceName

service name to look up

-> IO [AddrInfo]

resolved addresses, with best first

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:

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

The ServiceName argument must be a port number in string form, and service name lookups will not be attempted.
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.
If an IPv6 lookup is performed, and no IPv6 addresses are found, IPv6-mapped IPv4 addresses will be returned.
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 (Just http) let addr = head addrs sock <- socket (addrFamily addr) (addrSocketType addr) (addrProtocol addr) connect sock (addrAddress addr)



:: [NameInfoFlag]

flags to control lookup behaviour

-> Bool

whether to look up a hostname

-> Bool

whether to look up a service name

-> SockAddr

the address to look up

-> IO (Maybe HostName, Maybe ServiceName) 

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:

If a host is local, return only the hostname part of the FQDN.
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.
The name of the service is not looked up. Instead, a numeric representation of the service is returned.
If the hostname cannot be looked up, an IO error is thrown.
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

Socket Operations

getPeerCred :: Socket -> IO (CUInt, CUInt, CUInt)Source

Returns the processID, userID and groupID of the socket's peer.

Only available on platforms that support SO_PEERCRED on domain sockets.

socketToHandle :: Socket -> IOMode -> IO HandleSource

turns a Socket into an Handle. By default, the new handle is unbuffered. Use hSetBuffering to change the buffering.

Note that since a Handle is automatically closed by a finalizer when it is no longer referenced, you should avoid doing any more operations on the Socket after calling socketToHandle. To close the Socket after socketToHandle, call hClose on the Handle.

sendTo :: Socket -> String -> SockAddr -> IO IntSource

NOTE: blocking on Windows unless you compile with -threaded (see GHC ticket #1129)

recvFrom :: Socket -> Int -> IO (String, Int, SockAddr)Source

NOTE: blocking on Windows unless you compile with -threaded (see GHC ticket #1129)

sClose :: Socket -> IO ()Source

Closes a socket

Predicates on sockets

Socket options

File descriptor transmission

sendAncillary :: Socket -> Int -> Int -> Int -> Ptr a -> Int -> IO ()Source

Special Constants

iNADDR_ANY :: HostAddressSource

The IPv4 wild card address.

iN6ADDR_ANY :: HostAddress6Source

The IPv6 wild card address.


withSocketsDo :: IO a -> IO aSource

On Windows operating systems, the networking subsystem has to be initialised using withSocketsDo before any networking operations can be used. eg.

 main = withSocketsDo $ do {...}

Although this is only strictly necessary on Windows platforms, it is harmless on other platforms, so for portability it is good practice to use it all the time.

Very low level operations


The following are exported ONLY for use in the BSD module and should not be used anywhere else.



:: Num a 
=> String

textual description of the location

-> IO a

the IO operation to be executed

-> IO () 

Throw an IOError corresponding to the current socket error if the IO action returns a result of -1. Discards the result of the IO action after error handling.