Package org.pgpainless.decryption_verification.syntax_check

Class PDA

java.lang.Object

org.pgpainless.decryption_verification.syntax_check.PDA

public class PDA
extends java.lang.Object

Pushdown Automaton for validating context-free languages. In PGPainless, this class is used to validate OpenPGP message packet sequences against the allowed syntax.

See Also:

OpenPGP Message Syntax

Constructor Summary

Constructors

Constructor	Description
PDA()	Default constructor which initializes the PDA to work with the OpenPgpMessageSyntax.
PDA(Syntax syntax, State initialState, StackSymbol... initialStack)	Construct a PDA with a custom Syntax, initial State and initial StackSymbols.

Method Summary

Modifier and Type	Method	Description
void	assertValid()	Throw a MalformedOpenPgpMessageException if the pda is not in a valid state right now.
State	getState()	Return the current state of the PDA.
boolean	isValid()	Return true, if the PDA is in a valid state (the OpenPGP message is valid).
void	next(InputSymbol input)	Process the next InputSymbol.
StackSymbol	peekStack()	Peek at the stack, returning the topmost stack item without changing the stack.
java.lang.String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

PDA

public PDA()

Default constructor which initializes the PDA to work with the OpenPgpMessageSyntax.

PDA

public PDA(@Nonnull
           Syntax syntax,
           @Nonnull
           State initialState,
           @Nonnull
           StackSymbol... initialStack)

Construct a PDA with a custom Syntax, initial State and initial StackSymbols.

Parameters:

syntax - syntax

initialState - initial state

initialStack - zero or more initial stack items (get pushed onto the stack in order of appearance)

Method Detail

next

public void next(@Nonnull
                 InputSymbol input)
          throws MalformedOpenPgpMessageException

Process the next InputSymbol. This will either leave the PDA in the next state, or throw a MalformedOpenPgpMessageException if the input symbol is rejected.

Parameters:

input - input symbol

Throws:

MalformedOpenPgpMessageException - if the input symbol is rejected

getState

@Nonnull
public State getState()

Return the current state of the PDA.

Returns:

state

peekStack

@Nullable
public StackSymbol peekStack()

Peek at the stack, returning the topmost stack item without changing the stack.

Returns:

topmost stack item, or null if stack is empty

isValid

public boolean isValid()

Return true, if the PDA is in a valid state (the OpenPGP message is valid).

Returns:

true if valid, false otherwise

assertValid

public void assertValid()
                 throws MalformedOpenPgpMessageException

Throw a MalformedOpenPgpMessageException if the pda is not in a valid state right now.

Throws:

MalformedOpenPgpMessageException - if the pda is not in an acceptable state

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object