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40.18 Misc Network Facilities

These additional functions are useful for creating and operating on network connections. Note that they are supported only on some systems.

Function: network-interface-list &optional full family ¶

This function returns a list describing the network interfaces of the machine you are using. The value is an alist whose elements have the form (ifname . address). ifname is a string naming the interface, address has the same form as the local-address and remote-address arguments to make-network-process, i.e. a vector of integers. By default both IPv4 and IPv6 addresses are returned if possible.

Optional argument full non-nil means to instead return a list of one or more elements of the form (ifname addr bcast netmask). ifname is a non-unique string naming the interface. addr, bcast, and netmask are vectors of integers detailing the IP address, broadcast address, and network mask.

Optional argument family specified as symbol ipv4 or ipv6 restricts the returned information to IPv4 and IPv6 addresses respectively, independently of the value of full. Specifying ipv6 when IPv6 support is not available will result in an error being signaled.

Some examples:

(network-interface-list) ⇒
(("vmnet8" .
  [172 16 76 1 0])
 ("vmnet1" .
  [172 16 206 1 0])
 ("lo0" .
  [65152 0 0 0 0 0 0 1 0])
 ("lo0" .
  [0 0 0 0 0 0 0 1 0])
 ("lo0" .
  [127 0 0 1 0]))

(network-interface-list t) ⇒
(("vmnet8"
  [172 16 76 1 0]
  [172 16 76 255 0]
  [255 255 255 0 0])
 ("vmnet1"
  [172 16 206 1 0]
  [172 16 206 255 0]
  [255 255 255 0 0])
 ("lo0"
  [65152 0 0 0 0 0 0 1 0]
  [65152 0 0 0 65535 65535 65535 65535 0]
  [65535 65535 65535 65535 0 0 0 0 0])
 ("lo0"
  [0 0 0 0 0 0 0 1 0]
  [0 0 0 0 0 0 0 1 0]
  [65535 65535 65535 65535 65535 65535 65535 65535 0])
 ("lo0"
  [127 0 0 1 0]
  [127 255 255 255 0]
  [255 0 0 0 0]))

Function: network-interface-info ifname ¶

This function returns information about the network interface named ifname. The value is a list of the form (addr bcast netmask hwaddr flags).

addr

The Internet protocol address.

bcast

The broadcast address.

netmask

The network mask.

hwaddr

The layer 2 address (Ethernet MAC address, for instance).

flags

The current flags of the interface.

Note that this function returns only IPv4 information.

Function: format-network-address address &optional omit-port ¶

This function converts the Lisp representation of a network address to a string.

A five-element vector [a b c d p] represents an IPv4 address a.b.c.d and port number p. format-network-address converts that to the string "a.b.c.d:p".

A nine-element vector [a b c d e f g h p] represents an IPv6 address along with a port number. format-network-address converts that to the string "[a:b:c:d:e:f:g:h]:p".

If the vector does not include the port number, p, or if omit-port is non-nil, the result does not include the :p suffix.

Function: network-lookup-address-info name &optional family hints ¶

This function perform hostname lookups on name, which is expected to be an ASCII-only string, otherwise it signals an error. Call puny-encode-domain on name first if you wish to lookup internationalized hostnames.

If successful, this function returns a list of Lisp representations of network addresses (see make-network-process, for a description of the format), otherwise return nil. In the latter case, it also logs an error message hopefully explaining what went wrong.

By default, this function attempts both IPv4 and IPv6 lookups. The optional argument family controls this behavior, specifying the symbol ipv4 or ipv6 restricts lookups to IPv4 and IPv6 respectively.

If optional argument hints is numeric, the function treats the name as a numerical IP address (and does not perform DNS lookups). This can be used to check whether a string is a valid numerical representation of an IP address, or to convert a numerical string to its canonical representation. e.g.

(network-lookup-address-info "127.1" 'ipv4 'numeric)
    ⇒ ([127 0 0 1 0])

(network-lookup-address-info "::1" nil 'numeric)
    ⇒ ([0 0 0 0 0 0 0 1 0])

Be warned that there are some surprising valid forms, especially for IPv4, e.g ‘0xe3010203’ and ‘0343.1.2.3’ are both valid, as are ‘0’ and ‘1’ (but they are invalid for IPv6).