org.jnetpcap.protocol.tcpip
Class Tcp.AlternateChecksum

java.lang.Object
  org.jnetpcap.nio.JMemory
      org.jnetpcap.nio.JBuffer
          org.jnetpcap.packet.JHeader
              org.jnetpcap.packet.JSubHeader<Tcp>
                  org.jnetpcap.protocol.tcpip.Tcp.TcpOption
                      org.jnetpcap.protocol.tcpip.Tcp.AlternateChecksum

All Implemented Interfaces:

JPayloadAccessor

Enclosing class:

Tcp

@Header(id=15)
public static class Tcp.AlternateChecksum
extends Tcp.TcpOption

The option described in this memo provides a mechanism to negotiate the use of an alternate checksum at connection-establishment time, as well as a mechanism to carry additional checksum information for algorithms that utilize checksums that are longer than 16 bits.

Definition of the option: the TCP Alternate Checksum Request Option may be sent in a SYN segment by a TCP to indicate that the TCP is prepared to both generate and receive checksums based on an alternate algorithm. During communication, the alternate checksum replaces the regular TCP checksum in the checksum field of the TCP header. Should the alternate checksum require more than 2 bytes to transmit, the checksum may either be moved into a TCP Alternate Checksum Data Option and the checksum field of the TCP header be sent as 0, or the data may be split between the header field and the option. Alternate checksums are computed over the same data as the regular TCP checksum.

Author:

Mark Bednarczyk, Sly Technologies, Inc.

Nested Class Summary

Nested classes/interfaces inherited from class org.jnetpcap.protocol.tcpip.Tcp.TcpOption

Tcp.TcpOption.OptionCode

Nested classes/interfaces inherited from class org.jnetpcap.packet.JHeader

JHeader.State

Nested classes/interfaces inherited from class org.jnetpcap.nio.JMemory

JMemory.Type

Field Summary

Fields inherited from class org.jnetpcap.packet.JHeader

annotatedHeader, BYTE, EMPTY_HEADER_ARRAY, isSubHeader, packet, state

Fields inherited from class org.jnetpcap.nio.JMemory

JNETPCAP_LIBRARY_NAME, MAX_DIRECT_MEMORY_DEFAULT, POINTER

Constructor Summary

Tcp.AlternateChecksum()

Method Summary

byte[]	data() This field is used only when the alternate checksum that is negotiated is longer than 16 bits.
int	dataLength() Determines the length of this dynamic field.
byte[]	dataToArray(byte[] array) This field is used only when the alternate checksum that is negotiated is longer than 16 bits.

Methods inherited from class org.jnetpcap.protocol.tcpip.Tcp.TcpOption

code, code, length, length, lengthCheck, lengthDescription

Methods inherited from class org.jnetpcap.packet.JSubHeader

getLength, getOffset, getParent, setLength, setOffset, setParent

Methods inherited from class org.jnetpcap.packet.JHeader

decode, decodeHeader, getAnnotatedHeader, getDescription, getFields, getGap, getGapLength, getGapOffset, getHeader, getHeaderLength, getHeaderOffset, getId, getIndex, getName, getNextHeaderId, getNextHeaderOffset, getNicname, getPacket, getPayload, getPayloadLength, getPayloadOffset, getPostfix, getPostfixLength, getPostfixOffset, getPrefix, getPrefixLength, getPrefixOffset, getPreviousHeaderId, getPreviousHeaderOffset, getState, getSubHeaders, hasDescription, hasGap, hasNextHeader, hasPayload, hasPostfix, hasPrefix, hasPreviousHeader, hasSubHeaders, isFragmented, isGapTruncated, isHeaderTruncated, isPayloadTruncated, isPostfixTruncated, isPrefixTruncated, peer, peer, peerPayloadTo, setPacket, setSubHeaders, sizeof, toString, transferPayloadTo, transferPayloadTo, transferPayloadTo, validateHeader

Methods inherited from class org.jnetpcap.nio.JBuffer

findUTF8String, getByte, getByteArray, getByteArray, getByteArray, getDouble, getFloat, getInt, getLong, getShort, getUByte, getUInt, getUShort, getUTF8Char, getUTF8String, getUTF8String, getUTF8String, getUTF8String, isReadonly, order, order, peer, peer, peer, peer, setByte, setByteArray, setByteBuffer, setDouble, setFloat, setInt, setLong, setShort, setShort0, setUByte, setUInt, setUShort, transferFrom, transferFrom, transferFrom, transferTo, transferTo, transferTo

Methods inherited from class org.jnetpcap.nio.JMemory

availableDirectMemory, check, cleanup, createReference, isInitialized, isJMemoryBasedOwner, isOwner, maxDirectMemory, peer, reservedDirectMemory, setSize, size, softDirectMemory, toDebugString, toHexdump, toHexdump, totalActiveAllocated, totalAllocateCalls, totalAllocated, totalAllocatedSegments0To255Bytes, totalAllocatedSegments256OrAbove, totalDeAllocateCalls, totalDeAllocated, transferFrom, transferFrom, transferFromDirect, transferOwnership, transferTo, transferTo, transferTo, transferTo, transferTo, transferTo0

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

Tcp.AlternateChecksum

public Tcp.AlternateChecksum()

Method Detail

data

@Field(offset=16,
       format="#hexdump#")
public byte[] data()

This field is used only when the alternate checksum that is negotiated is longer than 16 bits. These checksums will not fit in the checksum field of the TCP header and thus at least part of them must be put in an option. Whether the checksum is split between the checksum field in the TCP header and the option or the entire checksum is placed in the option is determined on a checksum by checksum basis.

Returns:

variable length alternate checksum data

dataToArray

public byte[] dataToArray(byte[] array)

This field is used only when the alternate checksum that is negotiated is longer than 16 bits. These checksums will not fit in the checksum field of the TCP header and thus at least part of them must be put in an option. Whether the checksum is split between the checksum field in the TCP header and the option or the entire checksum is placed in the option is determined on a checksum by checksum basis.

Parameters:

array - copies data into the supplied array

Returns:

the supplied array

dataLength

@Dynamic(value=LENGTH)
public int dataLength()

Determines the length of this dynamic field.

Returns:

length of the data field in bits