Improve exception when user tries to open dir

CHANGELOG.md

@@ -1,6 +1,12 @@
 CHANGELOG
 =========
 
+1.12.0
+-------------------
+
+* Improve the error handling when the user tries to open a directory
+  with the pure PHP reader.
+
 1.11.1 (2023-12-01)
 -------------------
 

src/MaxMind/Db/Reader.php

@@ -79,6 +79,13 @@ public function __construct(string $database)
             );
         }
 
+        if (is_dir($database)) {
+            // This matches the error that the C extension throws.
+            throw new InvalidDatabaseException(
+                "Error opening database file ($database). Is this a valid MaxMind DB file?"
+            );
+        }
+
         $fileHandle = @fopen($database, 'rb');
         if ($fileHandle === false) {
             throw new \InvalidArgumentException(

tests/MaxMind/Db/Test/ReaderTest.php

@@ -305,6 +305,13 @@ public function testNonDatabase(): void
         new Reader('README.md');
     }
 
+    public function testOpeningDir(): void
+    {
+        $this->expectException(InvalidDatabaseException::class);
+        $this->expectExceptionMessage('Error opening database file (tests/). Is this a valid MaxMind DB file?');
+        new Reader('tests/');
+    }
+
     public function testTooManyConstructorArgs(): void
     {
         $this->expectException(\ArgumentCountError::class);