Kotlin conversion: Syntax checking

pgpainless-core/src/main/java/org/pgpainless/decryption_verification/syntax_check/OpenPgpMessageSyntax.java

@@ -1,142 +0,0 @@
-// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
-//
-// SPDX-License-Identifier: Apache-2.0
-
-package org.pgpainless.decryption_verification.syntax_check;
-
-import org.pgpainless.exception.MalformedOpenPgpMessageException;
-
-import javax.annotation.Nonnull;
-import javax.annotation.Nullable;
-
-/**
- * This class describes the syntax for OpenPGP messages as specified by rfc4880.
- *
- * @see <a href="https://www.rfc-editor.org/rfc/rfc4880#section-11.3">
- *     rfc4880 - §11.3. OpenPGP Messages</a>
- * @see <a href="https://blog.jabberhead.tk/2022/09/14/using-pushdown-automata-to-verify-packet-sequences/">
- *     Blog post about theoretic background and translation of grammar to PDA syntax</a>
- * @see <a href="https://blog.jabberhead.tk/2022/10/26/implementing-packet-sequence-validation-using-pushdown-automata/">
- *     Blog post about practically implementing the PDA for packet syntax validation</a>
- */
-public class OpenPgpMessageSyntax implements Syntax {
-
-    @Override
-    public @Nonnull Transition transition(@Nonnull State from, @Nonnull InputSymbol input, @Nullable StackSymbol stackItem)
-            throws MalformedOpenPgpMessageException {
-        switch (from) {
-            case OpenPgpMessage:
-                return fromOpenPgpMessage(input, stackItem);
-            case LiteralMessage:
-                return fromLiteralMessage(input, stackItem);
-            case CompressedMessage:
-                return fromCompressedMessage(input, stackItem);
-            case EncryptedMessage:
-                return fromEncryptedMessage(input, stackItem);
-            case Valid:
-                return fromValid(input, stackItem);
-        }
-
-        throw new MalformedOpenPgpMessageException(from, input, stackItem);
-    }
-
-    @Nonnull
-    Transition fromOpenPgpMessage(@Nonnull InputSymbol input, @Nullable StackSymbol stackItem)
-            throws MalformedOpenPgpMessageException {
-        if (stackItem != StackSymbol.msg) {
-            throw new MalformedOpenPgpMessageException(State.OpenPgpMessage, input, stackItem);
-        }
-
-        switch (input) {
-            case LiteralData:
-                return new Transition(State.LiteralMessage);
-
-            case Signature:
-                return new Transition(State.OpenPgpMessage, StackSymbol.msg);
-
-            case OnePassSignature:
-                return new Transition(State.OpenPgpMessage, StackSymbol.ops, StackSymbol.msg);
-
-            case CompressedData:
-                return new Transition(State.CompressedMessage);
-
-            case EncryptedData:
-                return new Transition(State.EncryptedMessage);
-
-            case EndOfSequence:
-            default:
-                throw new MalformedOpenPgpMessageException(State.OpenPgpMessage, input, stackItem);
-        }
-    }
-
-    @Nonnull
-    Transition fromLiteralMessage(@Nonnull InputSymbol input, @Nullable StackSymbol stackItem)
-            throws MalformedOpenPgpMessageException {
-        switch (input) {
-            case Signature:
-                if (stackItem == StackSymbol.ops) {
-                    return new Transition(State.LiteralMessage);
-                }
-                break;
-
-            case EndOfSequence:
-                if (stackItem == StackSymbol.terminus) {
-                    return new Transition(State.Valid);
-                }
-                break;
-        }
-
-        throw new MalformedOpenPgpMessageException(State.LiteralMessage, input, stackItem);
-    }
-
-    @Nonnull
-    Transition fromCompressedMessage(@Nonnull InputSymbol input, @Nullable StackSymbol stackItem)
-            throws MalformedOpenPgpMessageException {
-        switch (input) {
-            case Signature:
-                if (stackItem == StackSymbol.ops) {
-                    return new Transition(State.CompressedMessage);
-                }
-                break;
-
-            case EndOfSequence:
-                if (stackItem == StackSymbol.terminus) {
-                    return new Transition(State.Valid);
-                }
-                break;
-        }
-
-        throw new MalformedOpenPgpMessageException(State.CompressedMessage, input, stackItem);
-    }
-
-    @Nonnull
-    Transition fromEncryptedMessage(@Nonnull InputSymbol input, @Nullable StackSymbol stackItem)
-            throws MalformedOpenPgpMessageException {
-        switch (input) {
-            case Signature:
-                if (stackItem == StackSymbol.ops) {
-                    return new Transition(State.EncryptedMessage);
-                }
-                break;
-
-            case EndOfSequence:
-                if (stackItem == StackSymbol.terminus) {
-                    return new Transition(State.Valid);
-                }
-                break;
-        }
-
-        throw new MalformedOpenPgpMessageException(State.EncryptedMessage, input, stackItem);
-    }
-
-    @Nonnull
-    Transition fromValid(@Nonnull InputSymbol input, @Nullable StackSymbol stackItem)
-            throws MalformedOpenPgpMessageException {
-        if (input == InputSymbol.EndOfSequence) {
-            // allow subsequent read() calls.
-            return new Transition(State.Valid);
-        }
-        // There is no applicable transition rule out of Valid
-        throw new MalformedOpenPgpMessageException(State.Valid, input, stackItem);
-    }
-}

pgpainless-core/src/main/java/org/pgpainless/decryption_verification/syntax_check/Syntax.java

@@ -1,33 +0,0 @@
-// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
-//
-// SPDX-License-Identifier: Apache-2.0
-
-package org.pgpainless.decryption_verification.syntax_check;
-
-import org.pgpainless.exception.MalformedOpenPgpMessageException;
-
-import javax.annotation.Nonnull;
-import javax.annotation.Nullable;
-
-/**
- * This interface can be used to define a custom syntax for the {@link PDA}.
- */
-public interface Syntax {
-
-    /**
-     * Describe a transition rule from {@link State} <pre>from</pre> for {@link InputSymbol} <pre>input</pre>
-     * with {@link StackSymbol} <pre>stackItem</pre> from the top of the {@link PDA PDAs} stack.
-     * The resulting {@link Transition} contains the new {@link State}, as well as a list of
-     * {@link StackSymbol StackSymbols} that get pushed onto the stack by the transition rule.
-     * If there is no applicable rule, a {@link MalformedOpenPgpMessageException} is thrown, since in this case
-     * the {@link InputSymbol} must be considered illegal.
-     *
-     * @param from current state of the PDA
-     * @param input input symbol
-     * @param stackItem item that got popped from the top of the stack
-     * @return applicable transition rule containing the new state and pushed stack symbols
-     * @throws MalformedOpenPgpMessageException if there is no applicable transition rule (the input symbol is illegal)
-     */
-    @Nonnull Transition transition(@Nonnull State from, @Nonnull InputSymbol input, @Nullable StackSymbol stackItem)
-        throws MalformedOpenPgpMessageException;
-}

pgpainless-core/src/main/java/org/pgpainless/decryption_verification/syntax_check/Transition.java

@@ -1,48 +0,0 @@
-// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
-//
-// SPDX-License-Identifier: Apache-2.0
-
-package org.pgpainless.decryption_verification.syntax_check;
-
-import javax.annotation.Nonnull;
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.List;
-
-/**
- * Result of applying a transition rule.
- * Transition rules can be described by implementing the {@link Syntax} interface.
- */
-public class Transition {
-
-    private final List<StackSymbol> pushedItems = new ArrayList<>();
-    private final State newState;
-
-    public Transition(@Nonnull State newState, @Nonnull StackSymbol... pushedItems) {
-        this.newState = newState;
-        this.pushedItems.addAll(Arrays.asList(pushedItems));
-    }
-
-    /**
-     * Return the new {@link State} that is reached by applying the transition.
-     *
-     * @return new state
-     */
-    @Nonnull
-    public State getNewState() {
-        return newState;
-    }
-
-    /**
-     * Return a list of {@link StackSymbol StackSymbols} that are pushed onto the stack
-     * by applying the transition.
-     * The list contains items in the order in which they are pushed onto the stack.
-     * The list may be empty.
-     *
-     * @return list of items to be pushed onto the stack
-     */
-    @Nonnull
-    public List<StackSymbol> getPushedItems() {
-        return new ArrayList<>(pushedItems);
-    }
-}

pgpainless-core/src/main/java/org/pgpainless/decryption_verification/syntax_check/package-info.java

@@ -1,8 +0,0 @@
-// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
-//
-// SPDX-License-Identifier: Apache-2.0
-
-/**
- * Pushdown Automaton to verify validity of packet sequences according to the OpenPGP Message format.
- */
-package org.pgpainless.decryption_verification.syntax_check;

pgpainless-core/src/main/kotlin/org/pgpainless/decryption_verification/syntax_check/InputSymbol.kt

@@ -1,36 +1,30 @@
-// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
 //
 // SPDX-License-Identifier: Apache-2.0
 
-package org.pgpainless.decryption_verification.syntax_check;
+package org.pgpainless.decryption_verification.syntax_check
 
-import org.bouncycastle.openpgp.PGPCompressedData;
+enum class InputSymbol {
-import org.bouncycastle.openpgp.PGPEncryptedDataList;
-import org.bouncycastle.openpgp.PGPLiteralData;
-import org.bouncycastle.openpgp.PGPOnePassSignatureList;
-import org.bouncycastle.openpgp.PGPSignatureList;
-
-public enum InputSymbol {
     /**
-     * A {@link PGPLiteralData} packet.
+     * A [PGPLiteralData] packet.
      */
     LiteralData,
     /**
-     * A {@link PGPSignatureList} object.
+     * A [PGPSignatureList] object.
      */
     Signature,
     /**
-     * A {@link PGPOnePassSignatureList} object.
+     * A [PGPOnePassSignatureList] object.
      */
     OnePassSignature,
     /**
-     * A {@link PGPCompressedData} packet.
+     * A [PGPCompressedData] packet.
      * The contents of this packet MUST form a valid OpenPGP message, so a nested PDA is opened to verify
      * its nested packet sequence.
      */
     CompressedData,
     /**
-     * A {@link PGPEncryptedDataList} object.
+     * A [PGPEncryptedDataList] object.
      * This object combines multiple ESKs and the corresponding Symmetrically Encrypted
      * (possibly Integrity Protected) Data packet.
      */

pgpainless-core/src/main/kotlin/org/pgpainless/decryption_verification/syntax_check/OpenPgpMessageSyntax.kt

@@ -0,0 +1,88 @@
+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.pgpainless.decryption_verification.syntax_check
+
+import org.pgpainless.exception.MalformedOpenPgpMessageException
+
+/**
+ * This class describes the syntax for OpenPGP messages as specified by rfc4880.
+ *
+ * See [rfc4880 - §11.3. OpenPGP Messages](https://www.rfc-editor.org/rfc/rfc4880#section-11.3)
+ * See [Blog post about theoretic background and translation of grammar to PDA syntax](https://blog.jabberhead.tk/2022/09/14/using-pushdown-automata-to-verify-packet-sequences/)
+ * See [Blog post about practically implementing the PDA for packet syntax validation](https://blog.jabberhead.tk/2022/10/26/implementing-packet-sequence-validation-using-pushdown-automata/)
+ */
+class OpenPgpMessageSyntax : Syntax {
+
+    override fun transition(from: State, input: InputSymbol, stackItem: StackSymbol?): Transition {
+        return when (from) {
+            State.OpenPgpMessage -> fromOpenPgpMessage(input, stackItem)
+            State.LiteralMessage -> fromLiteralMessage(input, stackItem)
+            State.CompressedMessage -> fromCompressedMessage(input, stackItem)
+            State.EncryptedMessage -> fromEncryptedMessage(input, stackItem)
+            State.Valid -> fromValid(input, stackItem)
+            else -> throw MalformedOpenPgpMessageException(from, input, stackItem)
+        }
+    }
+
+    fun fromOpenPgpMessage(input: InputSymbol, stackItem: StackSymbol?): Transition {
+        if (stackItem !== StackSymbol.msg) {
+            throw MalformedOpenPgpMessageException(State.OpenPgpMessage, input, stackItem)
+        }
+        return when (input) {
+            InputSymbol.LiteralData -> Transition(State.LiteralMessage)
+            InputSymbol.Signature -> Transition(State.OpenPgpMessage, StackSymbol.msg)
+            InputSymbol.OnePassSignature -> Transition(State.OpenPgpMessage, StackSymbol.ops, StackSymbol.msg)
+            InputSymbol.CompressedData -> Transition(State.CompressedMessage)
+            InputSymbol.EncryptedData -> Transition(State.EncryptedMessage)
+            InputSymbol.EndOfSequence -> throw MalformedOpenPgpMessageException(State.OpenPgpMessage, input, stackItem)
+            else -> throw MalformedOpenPgpMessageException(State.OpenPgpMessage, input, stackItem)
+        }
+    }
+
+    @Throws(MalformedOpenPgpMessageException::class)
+    fun fromLiteralMessage(input: InputSymbol, stackItem: StackSymbol?): Transition {
+        if (input == InputSymbol.Signature && stackItem == StackSymbol.ops) {
+            return Transition(State.LiteralMessage)
+        }
+        if (input == InputSymbol.EndOfSequence && stackItem == StackSymbol.terminus) {
+            return Transition(State.Valid)
+        }
+
+        throw MalformedOpenPgpMessageException(State.LiteralMessage, input, stackItem)
+    }
+
+    @Throws(MalformedOpenPgpMessageException::class)
+    fun fromCompressedMessage(input: InputSymbol, stackItem: StackSymbol?): Transition {
+        if (input == InputSymbol.Signature && stackItem == StackSymbol.ops) {
+            return Transition(State.CompressedMessage)
+        }
+        if (input == InputSymbol.EndOfSequence && stackItem == StackSymbol.terminus) {
+            return Transition(State.Valid)
+        }
+
+        throw MalformedOpenPgpMessageException(State.CompressedMessage, input, stackItem)
+    }
+
+    @Throws(MalformedOpenPgpMessageException::class)
+    fun fromEncryptedMessage(input: InputSymbol, stackItem: StackSymbol?): Transition {
+        if (input == InputSymbol.Signature && stackItem == StackSymbol.ops) {
+            return Transition(State.EncryptedMessage)
+        }
+        if (input == InputSymbol.EndOfSequence && stackItem == StackSymbol.terminus) {
+            return Transition(State.Valid)
+        }
+
+        throw MalformedOpenPgpMessageException(State.EncryptedMessage, input, stackItem)
+    }
+
+    @Throws(MalformedOpenPgpMessageException::class)
+    fun fromValid(input: InputSymbol, stackItem: StackSymbol?): Transition {
+        if (input == InputSymbol.EndOfSequence) {
+            // allow subsequent read() calls.
+            return Transition(State.Valid)
+        }
+        throw MalformedOpenPgpMessageException(State.Valid, input, stackItem)
+    }
+}

pgpainless-core/src/main/kotlin/org/pgpainless/decryption_verification/syntax_check/StackSymbol.kt

@@ -1,10 +1,10 @@
-// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
 //
 // SPDX-License-Identifier: Apache-2.0
 
-package org.pgpainless.decryption_verification.syntax_check;
+package org.pgpainless.decryption_verification.syntax_check
 
-public enum StackSymbol {
+enum class StackSymbol {
     /**
      * OpenPGP Message.
      */

pgpainless-core/src/main/kotlin/org/pgpainless/decryption_verification/syntax_check/State.kt

@@ -1,13 +1,13 @@
-// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
 //
 // SPDX-License-Identifier: Apache-2.0
 
-package org.pgpainless.decryption_verification.syntax_check;
+package org.pgpainless.decryption_verification.syntax_check
 
 /**
  * Set of states of the automaton.
  */
-public enum State {
+enum class State {
     OpenPgpMessage,
     LiteralMessage,
     CompressedMessage,

pgpainless-core/src/main/kotlin/org/pgpainless/decryption_verification/syntax_check/Syntax.kt

@@ -0,0 +1,30 @@
+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.pgpainless.decryption_verification.syntax_check
+
+import org.pgpainless.exception.MalformedOpenPgpMessageException
+
+/**
+ * This interface can be used to define a custom syntax for the [PDA].
+ */
+interface Syntax {
+
+    /**
+     * Describe a transition rule from [State] <pre>from</pre> for [InputSymbol] <pre>input</pre>
+     * with [StackSymbol] <pre>stackItem</pre> from the top of the [PDAs][PDA] stack.
+     * The resulting [Transition] contains the new [State], as well as a list of
+     * [StackSymbols][StackSymbol] that get pushed onto the stack by the transition rule.
+     * If there is no applicable rule, a [MalformedOpenPgpMessageException] is thrown, since in this case
+     * the [InputSymbol] must be considered illegal.
+     *
+     * @param from current state of the PDA
+     * @param input input symbol
+     * @param stackItem item that got popped from the top of the stack
+     * @return applicable transition rule containing the new state and pushed stack symbols
+     * @throws MalformedOpenPgpMessageException if there is no applicable transition rule (the input symbol is illegal)
+     */
+    @Throws(MalformedOpenPgpMessageException::class)
+    fun transition(from: State, input: InputSymbol, stackItem: StackSymbol?): Transition
+}

pgpainless-core/src/main/kotlin/org/pgpainless/decryption_verification/syntax_check/Transition.kt

@@ -0,0 +1,22 @@
+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.pgpainless.decryption_verification.syntax_check
+
+/**
+ * Result of applying a transition rule.
+ * Transition rules can be described by implementing the [Syntax] interface.
+ *
+ * @param newState new [State] that is reached by applying the transition.
+ * @param pushedItems list of [StackSymbol] that are pushed onto the stack by applying the transition.
+ * The list contains items in the order in which they are pushed onto the stack.
+ * The list may be empty.
+ */
+class Transition private constructor(
+        val pushedItems: List<StackSymbol>,
+        val newState: State
+) {
+
+    constructor(newState: State, vararg pushedItems: StackSymbol): this(pushedItems.toList(), newState)
+}