logahawk.formatters
Class RollingHashedMessageFormatter

java.lang.Object
  logahawk.formatters.HashedMessageFormatter
      logahawk.formatters.RollingHashedMessageFormatter

All Implemented Interfaces:

MessageFormatter

@ThreadSafe
public class RollingHashedMessageFormatter
extends HashedMessageFormatter

Hashes log messages using a rolling hash -- that is the hash of the previous message is part of the hash for the following hash. This means the hash can be used to detect when a log messages have been added, removed, or reordered.

Nested Class Summary

Nested classes/interfaces inherited from class logahawk.formatters.HashedMessageFormatter

HashedMessageFormatter.HashMessagePair

Field Summary

protected String

previousDigest

Fields inherited from class logahawk.formatters.HashedMessageFormatter

hashPrefix, hashSuffix, messageDigest, messageFormatter

Constructor Summary

RollingHashedMessageFormatter(MessageFormatter messageFormatter, MessageDigest messageDigest)

Method Summary

protected String	createDigest(String message) Creates a digest from the provided message.
int	verify(List<String> messages) Verifies that the hash contained within the messages is the correct hash.

Methods inherited from class logahawk.formatters.HashedMessageFormatter

encode, format, getHashPrefix, getHashSuffix, setHashPrefix, setHashSuffix, splitMessage

Methods inherited from class java.lang.Object

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

Field Detail

previousDigest

protected String previousDigest

Constructor Detail

RollingHashedMessageFormatter

public RollingHashedMessageFormatter(MessageFormatter messageFormatter,
                                     MessageDigest messageDigest)
                              throws CloneNotSupportedException

Throws:

CloneNotSupportedException - The MessageDigest must be cloneable for verify(List) to work correctly. The constructor tests cloning by calling MessageDigest.clone() and letting the exception go uncaught.

Method Detail

createDigest

protected String createDigest(String message)

Description copied from class: HashedMessageFormatter

Creates a digest from the provided message. This method may not be idempotent depending on the implementation.

Overrides:

createDigest in class HashedMessageFormatter

verify

public int verify(List<String> messages)
           throws IllegalArgumentException

Description copied from class: HashedMessageFormatter

Verifies that the hash contained within the messages is the correct hash.

Overrides:

verify in class HashedMessageFormatter

Returns:

The index of the first invalid message. If the returned index equals the length of the provided List, then all messages are valid.

Throws:

IllegalArgumentException - Thrown if the message does not contain a hash in the expected location.