org.restcomm.media.stun.messages.attributes.general

Class FingerprintAttribute

java.lang.Object

org.restcomm.media.stun.messages.attributes.StunAttribute

org.restcomm.media.stun.messages.attributes.general.FingerprintAttribute

All Implemented Interfaces:

ContextDependentAttribute

public class FingerprintAttribute
extends StunAttribute
implements ContextDependentAttribute

The FINGERPRINT attribute is used to distinguish STUN packets from packets of other protocols. It MAY be present in all STUN messages. The value of the attribute is computed as the CRC-32 of the STUN message up to (but excluding) the FINGERPRINT attribute itself, XOR'ed with the 32-bit value 0x5354554e (the XOR helps in cases where an application packet is also using CRC-32 in it). The 32-bit CRC is the one defined in ITU V.42 [ITU.V42.2002], which has a generator polynomial of x32+x26+x23+x22+x16+x12+x11+x10+x8+x7+x5+x4+x2+x+1. When present, the FINGERPRINT attribute MUST be the last attribute in the message, and thus will appear after MESSAGE-INTEGRITY.

The FINGERPRINT attribute can aid in distinguishing STUN packets from packets of other protocols. See Section 8.

As with MESSAGE-INTEGRITY, the CRC used in the FINGERPRINT attribute covers the length field from the STUN message header. Therefore, this value must be correct and include the CRC attribute as part of the message length, prior to computation of the CRC. When using the FINGERPRINT attribute in a message, the attribute is first placed into the message with a dummy value, then the CRC is computed, and then the value of the attribute is updated. If the MESSAGE-INTEGRITY attribute is also present, then it must be present with the correct message-integrity value before the CRC is computed, since the CRC is done over the value of the MESSAGE-INTEGRITY attribute as well.

Field Summary

Fields

Modifier and Type	Field and Description
static String	NAME
static byte[]	XOR_MASK The value that we need to XOR the CRC with.

Fields inherited from class org.restcomm.media.stun.messages.attributes.StunAttribute

ALTERNATE_SERVER, attributeType, CHANGE_REQUEST, CHANGED_ADDRESS, CHANNEL_NUMBER, DATA, DESTINATION_ADDRESS, DONT_FRAGMENT, ERROR_CODE, EVEN_PORT, FINGERPRINT, HEADER_LENGTH, ICE_CONTROLLED, ICE_CONTROLLING, LIFETIME, MAGIC_COOKIE, MAPPED_ADDRESS, MESSAGE_INTEGRITY, NONCE, PASSWORD, PRIORITY, REALM, REFLECTED_FROM, REMOTE_ADDRESS, REQUESTED_TRANSPORT, RESERVATION_TOKEN, RESPONSE_ADDRESS, SOFTWARE, SOURCE_ADDRESS, UNKNOWN_ATTRIBUTES, UNKNOWN_OPTIONAL_ATTRIBUTE, USE_CANDIDATE, USERNAME, XOR_MAPPED_ADDRESS, XOR_ONLY, XOR_PEER_ADDRESS, XOR_RELAYED_ADDRESS

Constructor Summary

Constructors

Constructor and Description
FingerprintAttribute()

Method Summary

Methods

Modifier and Type	Method and Description
static byte[]	calculateXorCRC32(byte[] message, int offset, int len) Calculates and returns the CRC32 checksum for message after applying the XOR_MASK specified by RFC 5389.
protected void	decodeAttributeBody(byte[] data, char offset, char length) Sets this attribute's fields according to attributeValue array.
byte[]	encode() Returns a binary representation of this attribute.
byte[]	encode(byte[] data, int offset, int length) Returns a binary representation of this attribute.
boolean	equals(Object other) Compares two STUN Attributes.
byte[]	getChecksum() Returns the CRC32 checksum that this attribute is carrying.
char	getDataLength() Returns the length of this attribute's body.
String	getName() Returns the human readable name of this attribute.

Methods inherited from class org.restcomm.media.stun.messages.attributes.StunAttribute

getAttributeType, getLocationInMessage, setAttributeType, setLocationInMessage

Methods inherited from class java.lang.Object

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

Field Detail

NAME

public static final String NAME

See Also:

Constant Field Values

XOR_MASK

public static final byte[] XOR_MASK

The value that we need to XOR the CRC with. The XOR helps in cases where an application packet is also using CRC-32 in it).

Constructor Detail

FingerprintAttribute

public FingerprintAttribute()

Method Detail

getChecksum

public byte[] getChecksum()

Returns the CRC32 checksum that this attribute is carrying. Only makes sense for incoming messages and hence only set for them.

Returns:

the CRC32 checksum that this attribute is carrying or null if it has not been set.

getDataLength

public char getDataLength()

Description copied from class: StunAttribute

Returns the length of this attribute's body.

Specified by:

getDataLength in class StunAttribute

Returns:

the length of this attribute's value.

getName

public String getName()

Description copied from class: StunAttribute

Returns the human readable name of this attribute. Attribute names do not really matter from the protocol point of view. They are only used for debugging and readability.

Specified by:

getName in class StunAttribute

Returns:

this attribute's name.

equals

public boolean equals(Object other)

Description copied from class: StunAttribute

Compares two STUN Attributes. Two attributes are considered equal when they have the same type length and value.

Specified by:

equals in class StunAttribute

Parameters:

other - the object to compare this attribute with.

Returns:

true if the attributes are equal and false otherwise.

encode

public byte[] encode()
              throws UnsupportedOperationException

Description copied from class: StunAttribute

Returns a binary representation of this attribute.

Specified by:

encode in class StunAttribute

Returns:

a binary representation of this attribute.

Throws:

UnsupportedOperationException

decodeAttributeBody

protected void decodeAttributeBody(byte[] data,
                       char offset,
                       char length)
                            throws StunException

Description copied from class: StunAttribute

Sets this attribute's fields according to attributeValue array.

Specified by:

decodeAttributeBody in class StunAttribute

Parameters:

data - a binary array containing this attribute's field values and NOT containing the attribute header.

offset - the position where attribute values begin (most often offset is equal to the index of the first byte after length)

length - the length of the binary array.

Throws:

StunException - if attrubteValue contains invalid data.

encode

public byte[] encode(byte[] data,
            int offset,
            int length)

Description copied from interface: ContextDependentAttribute

Returns a binary representation of this attribute.

Specified by:

encode in interface ContextDependentAttribute

Parameters:

data - the content of the message that this attribute will be transported in

offset - the content-related offset where the actual content starts.

length - the length of the content in the content array.

Returns:

a binary representation of this attribute valid for the message with the specified content.

calculateXorCRC32

public static byte[] calculateXorCRC32(byte[] message,
                       int offset,
                       int len)

Calculates and returns the CRC32 checksum for message after applying the XOR_MASK specified by RFC 5389.

Parameters:

message - the message whose checksum we'd like to have

offset - the location in message where the actual message starts.

len - the number of message bytes in message

Returns:

the CRC value that should be sent in a FINGERPRINT attribute traveling in the message message.