Skip the pure-PHP DoS tests when the extension is loaded

These tests assert the pure-PHP decoder's "exceeds the maximum payload
size" message. When the maxminddb extension is loaded, Reader decodes
through libmaxminddb, which reports different text, so the assertions
failed. They also fed the large amplification and fan-out fixtures to the
extension's decoder, which on a libmaxminddb without the fix would exhaust
memory.

Skip them when the extension is loaded. The extension path is covered
safely by ExtensionDosTest, which probes a small fixture first and runs the
large fixtures only against a libmaxminddb that enforces the limits.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: oschwald

tests/MaxMind/Db/Test/ReaderTest.php

@@ -291,8 +291,24 @@ public function testBrokenDataPointer(): void
         $reader->get('1.1.1.16');
     }
 
+    // The DoS and payload-limit tests below assert the pure-PHP decoder's
+    // messages, so they skip when the maxminddb extension is loaded: that path
+    // decodes through libmaxminddb, which reports different text, and
+    // ExtensionDosTest covers it. Skipping also keeps the large amplification
+    // and fan-out fixtures away from a possibly-unpatched extension, whose
+    // decoder would otherwise exhaust memory.
+    private function skipIfExtensionLoaded(): void
+    {
+        if (\extension_loaded('maxminddb')) {
+            $this->markTestSkipped(
+                'covers the pure-PHP decoder; the extension path is covered by ExtensionDosTest'
+            );
+        }
+    }
+
     public function testPayloadAmplificationDosIsRejected(): void
     {
+        $this->skipIfExtensionLoaded();
         // An array of pointers to one large value. The value count stays low,
         // but a reader that copies each target materializes the value once per
         // pointer. The produced-payload byte budget rejects it.
@@ -304,6 +320,7 @@ public function testPayloadAmplificationDosIsRejected(): void
 
     public function testStringPayloadAmplificationDosIsRejected(): void
     {
+        $this->skipIfExtensionLoaded();
         // The string variant, so the UTF-8 path is charged as well as bytes.
         $this->expectException(InvalidDatabaseException::class);
         $this->expectExceptionMessage("The MaxMind DB file's data section exceeds the maximum payload size");
@@ -313,6 +330,7 @@ public function testStringPayloadAmplificationDosIsRejected(): void
 
     public function testWorstCasePayloadAmplificationDosIsRejected(): void
     {
+        $this->skipIfExtensionLoaded();
         // The worst case keeps the produced payload just under the byte budget
         // while fanning out through tens of thousands of pointers, so a bound
         // on decoded values rejects it.
@@ -332,6 +350,7 @@ public function testPayloadAtLimitDecodes(): void
 
     public function testPayloadOverLimitIsRejected(): void
     {
+        $this->skipIfExtensionLoaded();
         // One byte past the limit must be rejected.
         $this->expectException(InvalidDatabaseException::class);
         $this->expectExceptionMessage("The MaxMind DB file's data section exceeds the maximum payload size");
@@ -341,6 +360,7 @@ public function testPayloadOverLimitIsRejected(): void
 
     public function testMetadataPayloadLimitIsRejectedOnOpen(): void
     {
+        $this->skipIfExtensionLoaded();
         // Metadata is decoded while opening the database, so the same bound
         // must guard that path.
         $this->expectException(InvalidDatabaseException::class);