fix: prevent unsafe url rewrites

tests/Unit/Url/UrlTransformerTest.php

@@ -81,4 +81,65 @@ class UrlTransformerTest extends TestCase {
 			$transformer->transformString( 'https://example.test https://cdn.example.test/image.jpg', $mappings )
 		);
 	}
+
+	public function test_it_does_not_cascade_mapping_destinations_into_other_sources(): void {
+		$transformer = new UrlTransformer();
+		$mappings    = new UrlMappingCollection(
+			array(
+				new UrlMapping( 'https://a.example.test', 'https://b.example.test' ),
+				new UrlMapping( 'https://b.example.test', 'https://c.example.test' ),
+			)
+		);
+
+		self::assertSame(
+			'https://b.example.test/page https://c.example.test/page',
+			$transformer->transformString( 'https://a.example.test/page https://b.example.test/page', $mappings )
+		);
+	}
+
+	public function test_it_does_not_rewrite_partial_host_matches(): void {
+		$transformer = new UrlTransformer();
+		$mappings    = new UrlMappingCollection(
+			array(
+				new UrlMapping( 'https://example.test', 'https://staging.example.test' ),
+			)
+		);
+
+		self::assertSame(
+			'https://example.test.evil/path https://staging.example.test/path',
+			$transformer->transformString(
+				'https://example.test.evil/path https://example.test/path',
+				$mappings
+			)
+		);
+	}
+
+	public function test_it_prefers_more_specific_overlapping_mappings(): void {
+		$transformer = new UrlTransformer();
+		$mappings    = new UrlMappingCollection(
+			array(
+				new UrlMapping( 'https://example.test', 'https://staging.example.test' ),
+				new UrlMapping( 'https://example.test/uploads', 'https://media.staging.example.test/uploads' ),
+			)
+		);
+
+		self::assertSame(
+			'https://media.staging.example.test/uploads/image.jpg',
+			$transformer->transformString( 'https://example.test/uploads/image.jpg', $mappings )
+		);
+	}
+
+	public function test_it_rewrites_escaped_protocol_relative_urls(): void {
+		$transformer = new UrlTransformer();
+		$mappings    = new UrlMappingCollection(
+			array(
+				new UrlMapping( 'https://example.test/path?a=1&b=2', 'https://staging.example.test/path?a=1&b=2' ),
+			)
+		);
+
+		self::assertSame(
+			'//staging.example.test/path?a=1&b=2',
+			$transformer->transformString( '//example.test/path?a=1&b=2', $mappings )
+		);
+	}
 }