patch: fix "strict mode" error when getting prefix on short string

resolved #1

Author: beenotung

src/Core/Value.php

@@ -34,6 +34,9 @@ public function isString(): bool
     public function getStringPrefix(): string
     {
         $str = $this->value;
+        if (strlen($str) < 2) {
+            return '';
+        }
         return $str[0] . $str[1];
     }
 

src/DataTypes/JsonString.php

@@ -7,6 +7,9 @@ class JsonString
     // encodeStr
     public static function encodeString(string $str): string
     {
+        if (strlen($str) < 2) {
+            return $str;
+        }
         $prefix = $str[0] . $str[1];
         switch ($prefix) {
             case 'b|':
@@ -22,6 +25,9 @@ public static function encodeString(string $str): string
     // decodeStr
     public static function decodeString(string $str): string
     {
+        if (strlen($str) < 2) {
+            return $str;
+        }
         $prefix = $str[0] . $str[1];
         return $prefix === 's|' ? substr($str, 2) : $str;
     }

tests/CompressJsonBaseTest.php

@@ -100,4 +100,21 @@ public function testNestedWithSameKey()
         // Assert
         $this->assertEquals($data, $decompressed);
     }
+
+    public function testShortString()
+    {
+        $data = [
+            '',
+            'p',
+            'pp'
+        ];
+        $compressed = Compressor::create()
+            ->compress($data);
+        $compressedJson = $compressed
+            ->toJson();
+        $decompressed = Compressor::create()
+            ->decompressJson($compressedJson);
+        // Assert
+        $this->assertEquals($data, $decompressed);
+    }
 }