[php] Added a unit test that bad UTF-8 is rejected in the parser.

PiperOrigin-RevId: 632274113

php/src/Google/Protobuf/Internal/Message.php

@@ -394,7 +394,8 @@ class Message
                 }
                 break;
             case GPBType::STRING:
-                // TODO: Add utf-8 check.
+                // We don't check UTF-8 here; that will be validated by the
+                // setter later.
                 if (!GPBWire::readString($input, $value)) {
                     throw new GPBDecodeException(
                         "Unexpected EOF inside string field.");

php/tests/EncodeDecodeTest.php

@@ -683,6 +683,21 @@ class EncodeDecodeTest extends TestBase
         $m->mergeFromString(hex2bin('7201'));
     }
 
+    public function testDecodeInvalidStringDataBadUtf8()
+    {
+        $this->expectException(Exception::class);
+
+        $m = new TestMessage();
+        $m->mergeFromString(hex2bin('720180'));
+    }
+
+    public function testDecodeValidStringData()
+    {
+        $m = new TestMessage();
+        $m->mergeFromString(hex2bin('720161'));
+        $this->assertSame('a', $m->getOptionalString());
+    }
+
     public function testDecodeInvalidBytesLengthMiss()
     {
         $this->expectException(Exception::class);