feat(CBOR): Implement decode method for TextString and improve test suite

Author: shahmal1yev

src/CBOR/MajorTypes/TextString.php

@@ -34,6 +34,40 @@ public static function encode(string $input): string
 
     public static function decode(string $input): string
     {
-        // TODO
+        $initialByte = ord($input[0]);
+        $majorType = ($initialByte >> 5) & 0x07;
+
+        if ($majorType !== 0x03) {
+            throw new \ValueError('Invalid CBOR TextString major type.');
+        }
+
+        $additionalInfo = $initialByte & 0x1F;
+        $offset = 1;
+
+        if ($additionalInfo <= 23) {
+            $length = $additionalInfo;
+        } elseif ($additionalInfo === 24) {
+            $length = ord($input[$offset]);
+            $offset += 1;
+        } elseif ($additionalInfo === 25) {
+            $length = unpack('n', substr($input, $offset, 2))[1];
+            $offset += 2;
+        } elseif ($additionalInfo === 26) {
+            $length = unpack('N', substr($input, $offset, 4))[1];
+            $offset += 4;
+        } elseif ($additionalInfo === 27) {
+            $length = unpack('J', substr($input, $offset, 8))[1];
+            $offset += 8;
+        } else {
+            throw new \ValueError('Invalid CBOR TextString length information.');
+        }
+
+        $text = substr($input, $offset, $length);
+
+        if (strlen($text) !== $length) {
+            throw new \ValueError('Invalid CBOR TextString length mismatch.');
+        }
+
+        return $text;
     }
-}
+}

tests/Unit/CBOR/MajorTypes/TextStringTest.php

@@ -17,27 +17,27 @@
 
 class TextStringTest extends TestCase
 {
-    #[DataProvider('provideCases')]
-    public function testItCanEncodeCorrectly(string $case, string $header): void
+    #[DataProvider('provideValidCases')]
+    public function testEncodeProducesCorrectCBORRepresentation(string $input, string $expectedHeader): void
     {
-        $actual = bin2hex(TextString::encode($case));
-        $expected = bin2hex($header . $case);
+        $actual = bin2hex(TextString::encode($input));
+        $expected = bin2hex($expectedHeader . $input);
 
         $this->assertSame($expected, $actual);
     }
 
-    #[DataProvider('provideCases')]
-    public function testItCanDecodeCorrectly(string $case, string $header): void
+    #[DataProvider('provideValidCases')]
+    public function testDecodeExtractsOriginalStringFromCBORRepresentation(string $input, string $header): void
     {
-        $target = $header . $case;
+        $encoded = $header . $input;
 
-        $actual = TextString::decode($target);
-        $expected = $case;
+        $actual = TextString::decode($encoded);
+        $expected = $input;
 
         $this->assertSame($expected, $actual);
     }
 
-    public static function provideCases(): array
+    public static function provideValidCases(): array
     {
         return [
             ["f", "\x61"],
@@ -54,4 +54,30 @@ public static function provideCases(): array
             ]
         ];
     }
+
+    public function testDecodeThrowsExceptionForInvalidMajorType(): void
+    {
+        $this->expectException(\ValueError::class);
+        $this->expectExceptionMessage("Invalid CBOR TextString major type.");
+
+        TextString::decode("\x0C");
+    }
+
+    public function testDecodeThrowsExceptionForLengthMismatch(): void
+    {
+        $this->expectException(\ValueError::class);
+        $this->expectExceptionMessage("Invalid CBOR TextString length mismatch.");
+
+        // Encoded length is 5, but actual length is 4
+        TextString::decode("\x65\x66\x6F\x6F\x62");
+    }
+
+    public function testDecodeThrowsExceptionForInvalidAdditionalInformation(): void
+    {
+        $this->expectException(\ValueError::class);
+        $this->expectExceptionMessage("Invalid CBOR TextString length information.");
+
+        // Additional info 28 is invalid for text strings
+        TextString::decode("\x7C\x01");
+    }
 }