wip: first exception handling for #10

Author: Greg Bowler

src/Message/EncryptedMessage.php

@@ -9,17 +9,27 @@ public function decrypt(
 		PrivateKey $receiverPrivateKey,
 		PublicKey $senderPublicKey,
 	):PlainTextMessage {
-		$unlockingKeyPair = sodium_crypto_box_keypair_from_secretkey_and_publickey(
-			$receiverPrivateKey->getBytes(),
-			$senderPublicKey->getBytes(),
-		);
-		$decrypted = sodium_crypto_box_open(
-			base64_decode($this->data),
-			$this->iv->getBytes(),
-			$unlockingKeyPair,
-		);
+		$errorMessage = "Error decrypting cipher message";
+		$decrypted = false;
+
+		try {
+			$unlockingKeyPair = sodium_crypto_box_keypair_from_secretkey_and_publickey(
+				$receiverPrivateKey->getBytes(),
+				$senderPublicKey->getBytes(),
+			);
+			$decrypted = sodium_crypto_box_open(
+				base64_decode($this->data),
+				$this->iv->getBytes(),
+				$unlockingKeyPair,
+			);
+		}
+		catch(\SodiumException $exception) {
+// TODO: Issue #10 - this is one of the exceptions, but I think it makes sense to parse the message and extract the meaningful information.
+// Friendly exception messages are the future!
+			$errorMessage = $exception->getMessage();
+		}
 		if($decrypted === false) {
-			throw new DecryptionFailureException("Error decrypting cipher message");
+			throw new DecryptionFailureException($errorMessage);
 		}
 		return new PlainTextMessage(
 			$decrypted,

test/phpunit/Message/EncryptedMessageTest.php

@@ -51,4 +51,25 @@ public function testDecrypt_failure():void {
 			$senderPublicKey,
 		);
 	}
+
+	public function testDecrypt_incorrectKeySize():void {
+		$iv = self::createMock(InitVector::class);
+		$iv->method("getBytes")
+			->willReturn(str_repeat("0", SODIUM_CRYPTO_BOX_NONCEBYTES - 2));
+		$sut = new EncryptedMessage("badly formed data", $iv);
+
+		$receiverPrivateKey = self::createMock(PrivateKey::class);
+		$receiverPrivateKey->method("getBytes")
+			->willReturn(str_repeat("0", SODIUM_CRYPTO_BOX_SECRETKEYBYTES));
+		$senderPublicKey = self::createMock(PublicKey::class);
+		$senderPublicKey->method("getBytes")
+			->willReturn(str_repeat("0", SODIUM_CRYPTO_BOX_PUBLICKEYBYTES));
+
+		self::expectExceptionMessage("sodium_crypto_box_open(): Argument #2 (\$nonce) must be SODIUM_CRYPTO_BOX_NONCEBYTES bytes long");
+		self::expectException(DecryptionFailureException::class);
+		$sut->decrypt(
+			$receiverPrivateKey,
+			$senderPublicKey,
+		);
+	}
 }