getsockopt/setsockopt备忘

getsockopt和setsockopt的选项很多，但对于一些不常用的但又重要的很容易忘记，先记下。

头文件：

#include <sys/socket.h>

函数声明

int setsockopt(int socket, int level, int option_name, const void *option_value, socklen_t option_len);

int getsockopt(int socket, int level, int option_name, void *option_value, socklen_t* option_len);

选项（英文原文）

SO_DEBUG

Turns on recording of debugging information. This option enables or disables debugging in the underlying protocolmodules. This option takes an int value. This is a Boolean option.

SO_BROADCAST

Permits sending of broadcast messages, if this is supported by the protocol. This option takes an int value. This isa Boolean option.

SO_REUSEADDR

Specifies that the rules used in validating addresses supplied to bind() should allow reuse of local addresses, if this is supported by the protocol. This option takes an intvalue. This is a Boolean option.

SO_KEEPALIVE

Keeps connections active by enabling the periodic transmission of messages, if this is supported by the protocol.This option takes an int value.

If the connected socket fails to respond to these messages, the connection is broken and threads writing to thatsocket are notified with a SIGPIPE signal. This is a Boolean option.

SO_LINGER

Lingers on a close() if data is present. This option controls the action taken when unsent messages queue on a socket and close() is performed. If SO_LINGER is set, the system shall block the calling thread during close() untilit can transmit the data or until the time expires. If SO_LINGER is not specified, and close() is issued, the system handles the call in a way that allows the calling thread to continue as quickly as possible. This option takesa linger structure, as defined in the <sys/socket.h> header, to specify the state of the option and linger interval.

SO_OOBINLINE

Leaves received out-of-band data (data marked urgent) inline. This option takes an int value. This is a Booleanoption.

SO_SNDBUF

Sets send buffer size. This option takes an int value.

SO_RCVBUF

Sets receive buffer size. This option takes an int value.

SO_DONTROUTE

Requests that outgoing messages bypass the standard routing facilities. The destination shall be on a directly-connected network, and messages are directed to the appropriate network interface according to the destinationaddress. The effect, if any, of this option depends on what protocol is in use. This option takes an int value. Thisis a Boolean option.

SO_RCVLOWAT

Sets the minimum number of bytes to process for socket input operations. The default value for SO_RCVLOWATis 1. If SO_RCVLOWAT is set to a larger value, blocking receive calls normally wait until they have received thesmaller of the low water mark value or the requested amount. (They may return less than the low water mark ifan error occurs, a signal is caught, or the type of data next in the receive queue is different from that returned;for example, out-of-band data.) This option takes anint value. Note that not all implementations allow this optionto be set.

SO_RCVTIMEO

Sets the timeout value that specifies the maximum amount of time an input function waits until it completes. Itaccepts a timeval structure with the number of seconds and microseconds specifying the limit on how long towait for an input operation to complete. If a receive operation has blocked for this much time without receivingadditional data, it shall return with a partial count or errno set to [EAGAIN] or [EWOULDBLOCK] if no data isreceived. The default for this option is zero, which indicates that a receive operation shall not time out. Thisoption takes a timeval structure. Note that not all implementations allow this option to be set.

SO_SNDLOWAT

Sets the minimum number of bytes to process for socket output operations. Non-blocking output operationsshall process no data if flow control does not allow the smaller of the send low water mark value or the entirerequest to be processed. This option takes an int value. Note that not all implementations allow this option to beset.

SO_SNDTIMEO

Sets the timeout value specifying the amount of time that an output function blocks because flow controlprevents data from being sent. If a send operation has blocked for this time, it shall return with a partial count orwith errno set to [EAGAIN] or [EWOULDBLOCK] if no data is sent. The default for this option is zero, whichindicates that a send operation shall not time out. This option stores a timeval structure. Note that not allimplementations allow this option to be set.

For Boolean options, 0 indicates that the option is disabled and 1 indicates that the option is enabled.

Options at other protocol levels vary in format and name.

返回值

成功返回0，失败返回-1。错误信息可以查看errno。以下是英文原文：

The setsockopt() function shall fail if:

[EBADF]

The socket argument is not a valid file descriptor.

[EDOM]

The send and receive timeout values are too big to fit into the timeout fields in the socket structure.

[EINVAL]

The specified option is invalid at the specified socket level or the socket has been shut down.

[EISCONN]

The socket is already connected, and a specified option cannot be set while the socket is connected.

[ENOPROTOOPT]

The option is not supported by the protocol.

[ENOTSOCK]

The socket argument does not refer to a socket.

The setsockopt() function may fail if:

[ENOMEM]

There was insufficient memory available for the operation to complete.

[ENOBUFS]

Insufficient resources are available in the system to complete the call.