getsockopt, setsockopt


`getsockopt`, `setsockopt`
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`getsockopt`, `setsockopt`

getsockopt, setsockopt — get and set a socket option.

Synopsis

getsockopt (socket, option)
setsockopt (socket, option, value₁, value₂? = nil)

Arguments

socket: The file descriptor of a socket.
option: The option being queried. Supported options and their possible values are listed below.
value: The value to set the socket option to. There may be one or two values, depending on the option. If a socket option requires two values, both must be specified.

Returns

getsockopt returns the socket option value(s) on success, as shown below, or nil on failure. When the option has two values, they are returned as a list.

setsockopt returns 0 on success, otherwise -1.

Description

These functions get and set a socket option, using the socket's file descriptor. The supported socket options are given below.


	`SO_SNDTIMEO`, `SO_RCVTIMEO`, `SO_SNDLOWAT` and `SO_RCVLOWAT` are not supported by all operating systems.

Option	Possible Values	Comments
`SO_BROADCAST`	`0` for off, non-zero for on.	Allows for broadcasting datagrams from the socket.
`SO_DEBUG`	`0` for off, non-zero for on.	Records debugging information.
`SO_DONTROUTE`	`0` for off, non-zero for on.	Sends messages directly to the network interface instead of using normal message routing.
`SO_ERROR`	A number.	Resets the error status (for `getsockopt` only).
`SO_KEEPALIVE`	`0` for off, non-zero for on.	Transmits messages periodically on a connected socket. No response means the connection is broken.
`SO_LINGER`	Two values: `on_or_off` and `linger_time`, where `on_or_off` is `0` for off, non-zero for on. If on, a value for `linger_time` is required.	Keeps the socket open after a `close()` call, to deliver untransmitted messages. If `on_or_off` is non-zero, the socket will block for the duration of the `linger_time` or until all messages have been sent.
`TCP_NODELAY`	`0` for enable, non-zero for disable.	Disables the Nagle algorithm for sending data.
`SO_OOBINLINE`	`0` for off, non-zero for on.	Puts out-of-band data in the normal input queue.
`SO_REUSEADDR`	`0` for off, non-zero for on.	Permits the reuse of local addresses for this socket.
`SO_RCVBUF`	A number.	The size of the input buffer.
`SO_RCVLOWAT`	A number.	Sets the minimum count for input operations.
`SO_RCVTIMEO`	Two values: `seconds` and `nanoseconds`.	Sets a timeout value for input.
`SO_SNDBUF`	A number.	The size of the output buffer.
`SO_SNDLOWAT`	A number.	Sets the minimum count for output operations.
`SO_SNDTIMEO`	Two values: `seconds` and `nanoseconds`.	Sets a timeout value for output.
`SO_TYPE`	A number.	The type of socket (for `getsockopt` only).

Example

Gamma> skt = tcp_connect("localhost", 22);
8
Gamma> getsockopt(skt, SO_KEEPALIVE);
0
Gamma> setsockopt(skt, SO_KEEPALIVE, 1);
0
Gamma> getsockopt(skt, SO_KEEPALIVE);
1
Gamma> getsockopt(skt, SO_DEBUG);
0
Gamma> setsockopt(skt, SO_DEBUG, 1);
-1
Gamma> getsockopt(skt, SO_DEBUG);
0
Gamma>

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