Add HandshakePattern#toString (mostly for fun)

Author: jchambers

src/main/java/com/eatthepath/noise/HandshakePattern.java

@@ -340,6 +340,18 @@ class HandshakePattern {
   }
 
   record MessagePattern(NoiseHandshake.Role sender, Token[] tokens) {
+    @Override
+    public String toString() {
+      final String prefix = switch (sender()) {
+        case INITIATOR -> "  -> ";
+        case RESPONDER -> "  <- ";
+      };
+
+      return prefix + Arrays.stream(tokens())
+          .map(token -> token.name().toLowerCase())
+          .collect(Collectors.joining(", "));
+    }
+
     @Override
     public boolean equals(final Object o) {
       if (this == o) return true;
@@ -691,6 +703,31 @@ boolean requiresRemoteStaticPublicKey(final NoiseHandshake.Role role) {
         .anyMatch(token -> token == Token.S);
   }
 
+  @Override
+  public String toString() {
+    final StringBuilder stringBuilder = new StringBuilder(getName() + ":\n");
+
+    // We know we can't end on a pre-message pattern line, so we can unconditionally append newlines after each
+    // pre-handshake message
+    Arrays.stream(getPreMessagePatterns())
+        .forEach(preMessagePattern -> {
+          stringBuilder.append(preMessagePattern);
+          stringBuilder.append('\n');
+        });
+
+    if (getPreMessagePatterns().length > 0) {
+      stringBuilder.append("  ");
+      stringBuilder.append(PRE_MESSAGE_SEPARATOR);
+      stringBuilder.append('\n');
+    }
+
+    stringBuilder.append(Arrays.stream(getHandshakeMessagePatterns())
+        .map(MessagePattern::toString)
+        .collect(Collectors.joining("\n")));
+
+    return stringBuilder.toString();
+  }
+
   /**
    * Tests whether this handshake pattern is equal to another object. This handshake pattern is equal to the given
    * object if the given object is also a handshake pattern and has the same name and message patterns as this handshake

src/test/java/com/eatthepath/noise/HandshakePatternTest.java

@@ -88,6 +88,23 @@ void fromString() {
     }
   }
 
+  @Test
+  void testToString() throws NoSuchPatternException {
+    assertEquals("""
+        XX:
+          -> e
+          <- e, ee, s, es
+          -> s, se""", HandshakePattern.getInstance("XX").toString());
+
+    assertEquals("""
+        KK:
+          -> s
+          <- s
+          ...
+          -> e, es, ss
+          <- e, ee, se""", HandshakePattern.getInstance("KK").toString());
+  }
+
   @ParameterizedTest
   @CsvSource({
       "XX,XX",