Socket Options

A number of properties can be set or modified on the socket, which affects the socket s behavior. An example of a property is how much data the underlying network stack buffers for the socket, which can be important if a socket is receiving very large UDP datagrams and wants the local stack to be able to buffer multiple packets.

Two methods can change certain characteristics of a socket: GetSocketOption and SetSocketOption . GetSocketOption retrieves the current property value, and SetSocketOption sets the property s value. The parameter list for these two methods is the same. The first parameter is a SocketOptionLevel enumerated type, and the second is the SocketOptionName enumerated type. The value of the options can be one of three types, depending on the option level and name : integer, byte array, or object.

SocketOptionLevel indicates on what network level the option name is being applied. Socket options can be applied at the socket level ( Socket ) or at the protocol level (IPv4, IPv6, UDP, or TCP). SocketOptionName is an enumerated type that indicates the property being queried or set. Note that a particular SocketOptionName typically applies to a single SocketOptionLevel , although this is not always the case. Table 8-4 describes some of the common SocketOptionName properties. The multicast- related options will be covered in the IP Multicasting section later in this chapter.

Table 8-4: Common SocketOptionName Options

Option Name	Option Level	Description
Broadcast	Socket	Boolean value that enables the sending of broadcast packets on a socket. Only valid for protocols that support broadcast data.
DontLinger	Socket	Boolean value that disables any linger value set with the Linger option.
ExclusiveAddressUse	Socket	Boolean value that disallows any subsequent socket from binding to the same port regardless of whether the socket sets the ReuseAddress option.
HeaderIncluded	IP or IPv6	Boolean value that s used with raw sockets and indicates that the protocol header is included as part of data to send.
IpTimeToLive	IP or IPv6	Sets the integer time to live (TTL) value in the IP header.
KeepAlive	Tcp	Boolean value that enables TCP keepalives. Note that by default keepalives are sent on the order of hours.
Linger	Socket	Sets a time limit on unacknowledged data after the Close method has been called on a connection-oriented socket. A LingerOption object is passed to the call.
NoDelay	Tcp	Boolean value that disables the Nagle algorithm.
ReceiveBuffer	Socket	Sets the integer size in bytes (default of 8 KB) of the per-socket buffer maintained by the stack for receiving data.
ReceiveTimeout	Socket	Sets the timeout value for receive operations in milliseconds . An exception is thrown if timeout occurs.
ReuseAddress	Socket	When enabled, indicates a socket can be bound to an address even if another socket is bound to the same address and port.
SendBuffer	Socket	Sets the integer size in bytes (default of 8 KB) of the per-socket buffer maintained by the stack for sending data.
SendTimeout	Socket	Sets the timeout value for send operations in milliseconds. If the send can t complete in the specified time, an exception is thrown.

Warning  

The ReceiveTimeout and SendTimeout socket options should never be used on TCP sockets because data might be lost when a timeout occurs.

A few notes about socket options. First, the majority of the options are Boolean values. When setting an option s value, simply pass an integer where zero is false and non-zero is true . Retrieving the option s value is a little more complex because a byte array must be used. The following code illustrates setting the ReceiveBuffer option and then retrieving the value just set:

C#

 SocketmySocket; byte[]optionBuffer=newbyte[4]; intsendBufferSize=16384; //FirstcreateavalidSocketmySocket mySocket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.SendBuffer, sendBufferSize); mySocket.GetSocketOption(SocketOptionLevel.Socket, SocketOptionName.SendBuffer, optionBuffer); sendBufferSize=BitConverter.ToInt32(optionBuffer,0); Console.WriteLine("RetrievedSendBuffersize={0}",sendBufferSize); 

Visual Basic .NET

 DimmySocketAsSocket DimoptionBuffer(4)AsByte DimsendBufferSizeAsInteger=16384