de.intarsys.tools.locator.trusted

Interface ITrustedLocator

All Superinterfaces:

ILocator, ISynchronizable

All Known Implementing Classes:

HashedTrustedLocator, MemoryTrustedLocator, TrustedLocator

public interface ITrustedLocator
extends ILocator

This ILocator guarantees that a change to its physical resource while its is used by application code will be detected or healed.

This behavior is for example important for an application creating a signature for a document, where it is crucial that no one will change the data to be signed while the user verifies and accepts the original version.

An ITrustedLocator guarantess that

• Any input stream acquired after the first input stream will read exactly the same data OR fail.
• If the client code changes data via an OutputStream or IRandomAccess acquired from this ITrustedLocator, the new data stream will become valid at least after a "close" or "flush" operation. After the data is written to the physical resource it will contain exactly the new data where changed and exactly the old data where not. Otherwise the write will fail. Subsequent input stream will read the new data as described above.
• These constraints provide secure access from on the first read/write access to the resource. Sometimes a resource must be "freezed" before a physical access is done. This can be achieved by calling "checkpoint". An access to the resource after "checkpoint" behaves as described above, but the ITrustedLocator is free to implement "checkpoint" in a more performant way.

Method Summary

Methods

Modifier and Type	Method and Description
void	checkpoint() Make sure current state of the resource is still the same as seen with last "checkpoint".
void	ensureEqual(ILocator locator) Check if locator references data that is equal to the one referenced by this.

Methods inherited from interface de.intarsys.tools.locator.ILocator

delete, exists, getChild, getFullName, getInputStream, getLength, getLocalName, getOutputStream, getParent, getRandomAccess, getReader, getReader, getType, getTypedName, getWriter, getWriter, isDirectory, isReadOnly, listLocators, rename, setReadOnly, toURL

Methods inherited from interface de.intarsys.tools.component.ISynchronizable

isOutOfSynch, synch

Method Detail

checkpoint

void checkpoint()
                throws IOException

Make sure current state of the resource is still the same as seen with last "checkpoint". If this is called without any prior state information available, an implicit initial "checkpoint" is made. Subsequent access to the resources data will see exactly the state as seen at this moment or FAIL.

Most likely the ITrustedLocator will take a hash value here which it uses to compare when a physical access is made later. Be sure to understand the documentation on the measures taken by a concrete implementation as this is crucial for security level and performance.

Throws:

IOException

ensureEqual

void ensureEqual(ILocator locator)
                 throws IOException

Check if locator references data that is equal to the one referenced by this.

Parameters:

locator - The ILocator to the data to be checked against this.

Throws:

IOException