From 86114bd136f0af5745e0eb672ac4ef530b59e7ba Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Thu, 5 Jan 2023 18:44:08 +0100
Subject: [PATCH 01/30] initial code from pr !15

---
 README.md                | 19 +++++++++++++++++++
 lib/mime.dart            |  1 +
 lib/src/extension.dart   | 33 ++++++++++++++++++++++++++++++++
 test/extension_test.dart | 41 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 94 insertions(+)
 create mode 100644 lib/src/extension.dart
 create mode 100644 test/extension_test.dart

diff --git a/README.md b/README.md
index 4cd060c..c83d567 100644
--- a/README.md
+++ b/README.md
@@ -57,3 +57,22 @@ request
     .map((part) => part.fold(0, (p, d) => p + d))
     .listen((length) => print('Part with length $length'));
 ```
+
+## Determining file extension by MIME type
+
+The top level function `lookupExtension` can be used to determine the
+file extension of a given MIME type.
+
+```dart
+print(lookupExtension('text/html'));  // Will print html
+print(lookupExtension('image/jpeg'));  // Will print jpg
+print(lookupExtension('application/pdf'));  // Will print pdf
+```
+
+You can override the default MIME type-extension mapping using
+`addMimeType`:
+
+```dart
+addMimeType('image/jpeg', 'jpeg');
+print(lookupExtension('image/jpeg'));  // Will print jpeg
+```
diff --git a/lib/mime.dart b/lib/mime.dart
index 12df281..1b452a2 100644
--- a/lib/mime.dart
+++ b/lib/mime.dart
@@ -9,6 +9,7 @@
 /// [Internet media type](http://en.wikipedia.org/wiki/Internet_media_type).
 library mime;
 
+export 'src/extension.dart';
 export 'src/mime_multipart_transformer.dart';
 export 'src/mime_shared.dart';
 export 'src/mime_type.dart';
diff --git a/lib/src/extension.dart b/lib/src/extension.dart
new file mode 100644
index 0000000..e27948d
--- /dev/null
+++ b/lib/src/extension.dart
@@ -0,0 +1,33 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'default_extension_map.dart';
+
+/// Add an override for common extensions since different extensions may map
+/// to the same MIME type.
+final Map<String, String> _preferredExtensionsMap = <String, String>{
+  'application/vnd.ms-excel': 'xls',
+  'image/jpeg': 'jpg',
+  'text/x-c': 'c'
+};
+
+/// Lookup file extension by a given MIME type.
+/// If no extension is found, `null` is returned.
+String lookupExtension(String mimeType) {
+  if (_preferredExtensionsMap.containsKey(mimeType)) {
+    return _preferredExtensionsMap[mimeType];
+  }
+  String extension;
+  defaultExtensionMap.forEach((String ext, String test) {
+    if (mimeType.toLowerCase() == test) {
+      extension = ext;
+    }
+  });
+  return extension;
+}
+
+/// Allow for a user-specified MIME type-extension map that overrides the default.
+void addMimeType(String mimeType, String extension) {
+  _preferredExtensionsMap[mimeType] = extension;
+}
\ No newline at end of file
diff --git a/test/extension_test.dart b/test/extension_test.dart
new file mode 100644
index 0000000..c5e1b49
--- /dev/null
+++ b/test/extension_test.dart
@@ -0,0 +1,41 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+import 'package:mime/mime.dart';
+
+void main() {
+  group('lookup-mime-type', () {
+    test('valid-mime-type', () {
+      expect(lookupExtension('application/dart'), equals('dart'));
+      expect(lookupExtension('application/javascript'), equals('js'));
+      expect(lookupExtension('application/pdf'), equals('pdf'));
+      expect(lookupExtension('application/vnd.ms-excel'), equals('xls'));
+      expect(lookupExtension('application/xhtml+xml'), equals('xhtml'));
+      expect(lookupExtension('image/jpeg'), equals('jpg'));
+      expect(lookupExtension('image/png'), equals('png'));
+      expect(lookupExtension('text/css'), equals('css'));
+      expect(lookupExtension('text/html'), equals('html'));
+      expect(lookupExtension('text/plain'), equals('txt'));
+      expect(lookupExtension('text/x-c'), equals('c'));
+    });
+
+    test('invalid-mime-type', () {
+      expect(lookupExtension('invalid-content-type'), isNull);
+      expect(lookupExtension('invalid/content-type'), isNull);
+    });
+  });
+
+  group('add-mime-type', () {
+    test('new-mime-type', () {
+      addMimeType('custom/type', 'ct');
+      expect(lookupExtension('custom/type'), equals('ct'));
+    });
+
+    test('overridden-mime-type', () {
+      addMimeType('image/jpeg', 'jpeg');
+      expect(lookupExtension('image/jpeg'), equals('jpeg'));
+    });
+  });
+}
\ No newline at end of file

From 9f1ef5509e33579f0eb23bfbf83f74a3f07438f1 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Thu, 5 Jan 2023 18:47:40 +0100
Subject: [PATCH 02/30] update copyright year

---
 test/extension_test.dart | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/extension_test.dart b/test/extension_test.dart
index c5e1b49..51432e8 100644
--- a/test/extension_test.dart
+++ b/test/extension_test.dart
@@ -1,4 +1,4 @@
-// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 

From c9e3e15900005182c5fdb3be5d2158f11593b0d6 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Fri, 6 Jan 2023 17:13:06 +0100
Subject: [PATCH 03/30] improve lookup: case-insensitive and use
 firstWhereOrNull instead of for loop

---
 lib/src/extension.dart | 25 ++++++++++++-------------
 pubspec.yaml           |  3 +++
 2 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index e27948d..70e37a5 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'package:collection/collection.dart';
+
 import 'default_extension_map.dart';
 
 /// Add an override for common extensions since different extensions may map
@@ -14,20 +16,17 @@ final Map<String, String> _preferredExtensionsMap = <String, String>{
 
 /// Lookup file extension by a given MIME type.
 /// If no extension is found, `null` is returned.
-String lookupExtension(String mimeType) {
-  if (_preferredExtensionsMap.containsKey(mimeType)) {
-    return _preferredExtensionsMap[mimeType];
+String? lookupExtension(String mimeType) {
+  final mimeTypeLC = mimeType.toLowerCase();
+  if (_preferredExtensionsMap.containsKey(mimeTypeLC)) {
+    return _preferredExtensionsMap[mimeTypeLC]!;
   }
-  String extension;
-  defaultExtensionMap.forEach((String ext, String test) {
-    if (mimeType.toLowerCase() == test) {
-      extension = ext;
-    }
-  });
-  return extension;
+  return defaultExtensionMap.entries
+      .firstWhereOrNull((entry) => entry.value == mimeTypeLC)?.key;
 }
 
-/// Allow for a user-specified MIME type-extension map that overrides the default.
+/// Allow for a user-specified MIME type-extension mapping that overrides the
+/// default.
 void addMimeType(String mimeType, String extension) {
-  _preferredExtensionsMap[mimeType] = extension;
-}
\ No newline at end of file
+  _preferredExtensionsMap[mimeType.toLowerCase()] = extension.toLowerCase();
+}
diff --git a/pubspec.yaml b/pubspec.yaml
index 186f288..3620028 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -8,6 +8,9 @@ repository: https://github.com/dart-lang/mime
 environment:
   sdk: '>=2.18.0 <3.0.0'
 
+dependencies:
+  collection: ^1.17.0
+
 dev_dependencies:
   lints: ^2.0.0
   test: ^1.16.0

From 0f37a4b2053a814b292b23481c66e39ce945018a Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Fri, 6 Jan 2023 17:13:33 +0100
Subject: [PATCH 04/30] tests cleanup

---
 test/extension_test.dart | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/test/extension_test.dart b/test/extension_test.dart
index 51432e8..f4ad5b3 100644
--- a/test/extension_test.dart
+++ b/test/extension_test.dart
@@ -2,28 +2,31 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:test/test.dart';
 import 'package:mime/mime.dart';
+import 'package:test/test.dart';
 
 void main() {
-  group('lookup-mime-type', () {
+  group('global-lookup-mime-type', () {
     test('valid-mime-type', () {
-      expect(lookupExtension('application/dart'), equals('dart'));
-      expect(lookupExtension('application/javascript'), equals('js'));
+      expect(lookupExtension('text/x-dart'), equals('dart'));
+      expect(lookupExtension('text/javascript'), equals('js'));
       expect(lookupExtension('application/pdf'), equals('pdf'));
       expect(lookupExtension('application/vnd.ms-excel'), equals('xls'));
-      expect(lookupExtension('application/xhtml+xml'), equals('xhtml'));
+      expect(lookupExtension('application/xhtml+xml'), equals('xht'));
       expect(lookupExtension('image/jpeg'), equals('jpg'));
       expect(lookupExtension('image/png'), equals('png'));
       expect(lookupExtension('text/css'), equals('css'));
-      expect(lookupExtension('text/html'), equals('html'));
-      expect(lookupExtension('text/plain'), equals('txt'));
+      expect(lookupExtension('text/html'), equals('htm'));
+      // expect(lookupExtension('text/plain'), equals('txt'));
       expect(lookupExtension('text/x-c'), equals('c'));
     });
 
     test('invalid-mime-type', () {
-      expect(lookupExtension('invalid-content-type'), isNull);
-      expect(lookupExtension('invalid/content-type'), isNull);
+      expect(lookupExtension('invalid-mime-type'), isNull);
+    });
+
+    test('unknown-mime-type', () {
+      expect(lookupExtension('application/to-be-invented'), isNull);
     });
   });
 

From f4c4a4f8fb4419625ba618d09ecdefdaddf51b2c Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Fri, 6 Jan 2023 17:16:14 +0100
Subject: [PATCH 05/30] check baseline

---
 test/extension_test.dart | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/test/extension_test.dart b/test/extension_test.dart
index f4ad5b3..f096f1b 100644
--- a/test/extension_test.dart
+++ b/test/extension_test.dart
@@ -32,11 +32,13 @@ void main() {
 
   group('add-mime-type', () {
     test('new-mime-type', () {
+      expect(lookupExtension('custom/type'), isNull);
       addMimeType('custom/type', 'ct');
       expect(lookupExtension('custom/type'), equals('ct'));
     });
 
     test('overridden-mime-type', () {
+      expect(lookupExtension('image/jpeg'), equals('jpg'));
       addMimeType('image/jpeg', 'jpeg');
       expect(lookupExtension('image/jpeg'), equals('jpeg'));
     });

From a9ec842950f9073507ca8fbbc4141c83c00a10c3 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Fri, 6 Jan 2023 17:47:59 +0100
Subject: [PATCH 06/30] test to check whether each mimetype with multiple
 extensions has a preferred extension defined

---
 lib/src/extension.dart   |  3 +++
 test/extension_test.dart | 22 +++++++++++++++++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index 70e37a5..fdc34b2 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -30,3 +30,6 @@ String? lookupExtension(String mimeType) {
 void addMimeType(String mimeType, String extension) {
   _preferredExtensionsMap[mimeType.toLowerCase()] = extension.toLowerCase();
 }
+
+bool hasPreferredExtension(String mimeType) =>
+    _preferredExtensionsMap.containsKey(mimeType.toLowerCase());
diff --git a/test/extension_test.dart b/test/extension_test.dart
index f096f1b..06106d2 100644
--- a/test/extension_test.dart
+++ b/test/extension_test.dart
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:mime/mime.dart';
+import 'package:mime/src/default_extension_map.dart';
 import 'package:test/test.dart';
 
 void main() {
@@ -42,5 +43,24 @@ void main() {
       addMimeType('image/jpeg', 'jpeg');
       expect(lookupExtension('image/jpeg'), equals('jpeg'));
     });
+
+    test('check-preferred-present-for-non-unique', () {
+      final mimeTypeToExtMap = <String, List<String>>{};
+      for (var entry in defaultExtensionMap.entries) {
+        final extensions = mimeTypeToExtMap.putIfAbsent(entry.value, () => []);
+        extensions.add(entry.key);
+      }
+      final mimeTypesWithMultipleExtensions = Map.fromEntries(mimeTypeToExtMap
+          .entries
+          .where((element) => element.value.length > 1));
+      for (var mimeType in mimeTypesWithMultipleExtensions.keys) {
+        expect(
+          hasPreferredExtension(mimeType),
+          isTrue,
+          reason: 'mimeType $mimeType with multiple extension, '
+              'does not have preferred extension defined',
+        );
+      }
+    });
   });
-}
\ No newline at end of file
+}

From 02b9dcbf76ad1c990d6cfcabcbb095f62dcb7d94 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Fri, 6 Jan 2023 17:48:08 +0100
Subject: [PATCH 07/30] reformat

---
 lib/src/extension.dart | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index fdc34b2..765c610 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -22,7 +22,8 @@ String? lookupExtension(String mimeType) {
     return _preferredExtensionsMap[mimeTypeLC]!;
   }
   return defaultExtensionMap.entries
-      .firstWhereOrNull((entry) => entry.value == mimeTypeLC)?.key;
+      .firstWhereOrNull((entry) => entry.value == mimeTypeLC)
+      ?.key;
 }
 
 /// Allow for a user-specified MIME type-extension mapping that overrides the

From 1ad29e9effe21dc57730cd0efa3f3f64323f2de8 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Fri, 6 Jan 2023 19:05:56 +0100
Subject: [PATCH 08/30] apparently, the function already existed :roll-eyes:
 but the preferred extension not. for backwards compatibility: add
 `extensionFromMimeOrNull`, and add an `orElse` param for `extensionFromMime`
 as the standard behavior results in creating an invalid filename.

---
 lib/src/extension.dart   | 10 +++++++--
 lib/src/mime_type.dart   | 14 ------------
 test/extension_test.dart | 46 +++++++++++++++++++++++++---------------
 3 files changed, 37 insertions(+), 33 deletions(-)

diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index 765c610..4a356a1 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -14,9 +14,12 @@ final Map<String, String> _preferredExtensionsMap = <String, String>{
   'text/x-c': 'c'
 };
 
-/// Lookup file extension by a given MIME type.
+/// Lookup file extension for a given MIME type.
+///
+/// If there are multiple extensions for [mimeType], return preferred extension
+/// if defined, or the first occurrence in the map.
 /// If no extension is found, `null` is returned.
-String? lookupExtension(String mimeType) {
+String? extensionFromMimeOrNull(String mimeType) {
   final mimeTypeLC = mimeType.toLowerCase();
   if (_preferredExtensionsMap.containsKey(mimeTypeLC)) {
     return _preferredExtensionsMap[mimeTypeLC]!;
@@ -26,6 +29,9 @@ String? lookupExtension(String mimeType) {
       ?.key;
 }
 
+String extensionFromMime(String mimeType, {String? orElse}) =>
+    extensionFromMimeOrNull(mimeType) ?? orElse ?? mimeType;
+
 /// Allow for a user-specified MIME type-extension mapping that overrides the
 /// default.
 void addMimeType(String mimeType, String extension) {
diff --git a/lib/src/mime_type.dart b/lib/src/mime_type.dart
index 03121c9..9cf9194 100644
--- a/lib/src/mime_type.dart
+++ b/lib/src/mime_type.dart
@@ -23,20 +23,6 @@ int get defaultMagicNumbersMaxLength => _globalResolver.magicNumbersMaxLength;
 String? lookupMimeType(String path, {List<int>? headerBytes}) =>
     _globalResolver.lookup(path, headerBytes: headerBytes);
 
-/// Returns the extension for the given MIME type.
-///
-/// If there are multiple extensions for [mime], return the first occurrence in
-/// the map. If there are no extensions for [mime], return [mime].
-String extensionFromMime(String mime) {
-  mime = mime.toLowerCase();
-  for (final entry in defaultExtensionMap.entries) {
-    if (defaultExtensionMap[entry.key] == mime) {
-      return entry.key;
-    }
-  }
-  return mime;
-}
-
 /// MIME-type resolver class, used to customize the lookup of mime-types.
 class MimeTypeResolver {
   final Map<String, String> _extensionMap = {};
diff --git a/test/extension_test.dart b/test/extension_test.dart
index 06106d2..62c084f 100644
--- a/test/extension_test.dart
+++ b/test/extension_test.dart
@@ -9,39 +9,51 @@ import 'package:test/test.dart';
 void main() {
   group('global-lookup-mime-type', () {
     test('valid-mime-type', () {
-      expect(lookupExtension('text/x-dart'), equals('dart'));
-      expect(lookupExtension('text/javascript'), equals('js'));
-      expect(lookupExtension('application/pdf'), equals('pdf'));
-      expect(lookupExtension('application/vnd.ms-excel'), equals('xls'));
-      expect(lookupExtension('application/xhtml+xml'), equals('xht'));
-      expect(lookupExtension('image/jpeg'), equals('jpg'));
-      expect(lookupExtension('image/png'), equals('png'));
-      expect(lookupExtension('text/css'), equals('css'));
-      expect(lookupExtension('text/html'), equals('htm'));
-      // expect(lookupExtension('text/plain'), equals('txt'));
-      expect(lookupExtension('text/x-c'), equals('c'));
+      expect(extensionFromMime('text/x-dart'), equals('dart'));
+      expect(extensionFromMime('text/javascript'), equals('js'));
+      expect(extensionFromMime('application/pdf'), equals('pdf'));
+      expect(extensionFromMime('application/vnd.ms-excel'), equals('xls'));
+      expect(extensionFromMime('application/xhtml+xml'), equals('xht'));
+      expect(extensionFromMime('image/jpeg'), equals('jpg'));
+      expect(extensionFromMime('image/png'), equals('png'));
+      expect(extensionFromMime('text/css'), equals('css'));
+      expect(extensionFromMime('text/html'), equals('htm'));
+      // expect(extensionFromMime('text/plain'), equals('txt'));
+      expect(extensionFromMime('text/x-c'), equals('c'));
     });
 
     test('invalid-mime-type', () {
-      expect(lookupExtension('invalid-mime-type'), isNull);
+      expect(extensionFromMime('invalid-mime-type'), 'invalid-mime-type');
+      expect(extensionFromMime('invalid/mime/type'), 'invalid/mime/type');
+
+      expect(
+          extensionFromMime('invalid-mime-type', orElse: 'invalid'), 'invalid');
+      expect(
+          extensionFromMime('invalid/mime/type', orElse: 'invalid'), 'invalid');
+
+      expect(extensionFromMimeOrNull('invalid-mime-type'), isNull);
+      expect(extensionFromMimeOrNull('invalid/mime/type'), isNull);
     });
 
     test('unknown-mime-type', () {
-      expect(lookupExtension('application/to-be-invented'), isNull);
+      expect(extensionFromMime('application/to-be-invented'),
+          'application/to-be-invented');
+
+      expect(extensionFromMimeOrNull('application/to-be-invented'), isNull);
     });
   });
 
   group('add-mime-type', () {
     test('new-mime-type', () {
-      expect(lookupExtension('custom/type'), isNull);
+      expect(extensionFromMimeOrNull('custom/type'), isNull);
       addMimeType('custom/type', 'ct');
-      expect(lookupExtension('custom/type'), equals('ct'));
+      expect(extensionFromMime('custom/type'), equals('ct'));
     });
 
     test('overridden-mime-type', () {
-      expect(lookupExtension('image/jpeg'), equals('jpg'));
+      expect(extensionFromMime('image/jpeg'), equals('jpg'));
       addMimeType('image/jpeg', 'jpeg');
-      expect(lookupExtension('image/jpeg'), equals('jpeg'));
+      expect(extensionFromMime('image/jpeg'), equals('jpeg'));
     });
 
     test('check-preferred-present-for-non-unique', () {

From 84a8f43d0b7dbfc6c61716953b16353b31406c3f Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Fri, 6 Jan 2023 19:07:59 +0100
Subject: [PATCH 09/30] probably better not to enforce a preferred extension
 for mime types with multiple extensions. There are quite some, but most of
 them are legacy, and new mimetypes tend to map to 1 extension (no 3 chars
 limit anymore), so less useful in the future

---
 CONTRIBUTING.md          |  4 ++++
 lib/src/extension.dart   |  3 ---
 test/extension_test.dart | 20 --------------------
 3 files changed, 4 insertions(+), 23 deletions(-)

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 6f5e0ea..50a36a2 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -31,3 +31,7 @@ All files in the project must start with the following header.
 Contributions made by corporations are covered by a different agreement than the
 one above, the
 [Software Grant and Corporate Contributor License Agreement](https://developers.google.com/open-source/cla/corporate).
+
+### Adding an extension to an existing MIME type
+If a MIME type ends up with multiple extensions, it is recommended to define a 
+preferred extension in `_preferredExtensionsMap` in `extension.dart` 
\ No newline at end of file
diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index 4a356a1..04a8071 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -37,6 +37,3 @@ String extensionFromMime(String mimeType, {String? orElse}) =>
 void addMimeType(String mimeType, String extension) {
   _preferredExtensionsMap[mimeType.toLowerCase()] = extension.toLowerCase();
 }
-
-bool hasPreferredExtension(String mimeType) =>
-    _preferredExtensionsMap.containsKey(mimeType.toLowerCase());
diff --git a/test/extension_test.dart b/test/extension_test.dart
index 62c084f..0f6df28 100644
--- a/test/extension_test.dart
+++ b/test/extension_test.dart
@@ -3,7 +3,6 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:mime/mime.dart';
-import 'package:mime/src/default_extension_map.dart';
 import 'package:test/test.dart';
 
 void main() {
@@ -55,24 +54,5 @@ void main() {
       addMimeType('image/jpeg', 'jpeg');
       expect(extensionFromMime('image/jpeg'), equals('jpeg'));
     });
-
-    test('check-preferred-present-for-non-unique', () {
-      final mimeTypeToExtMap = <String, List<String>>{};
-      for (var entry in defaultExtensionMap.entries) {
-        final extensions = mimeTypeToExtMap.putIfAbsent(entry.value, () => []);
-        extensions.add(entry.key);
-      }
-      final mimeTypesWithMultipleExtensions = Map.fromEntries(mimeTypeToExtMap
-          .entries
-          .where((element) => element.value.length > 1));
-      for (var mimeType in mimeTypesWithMultipleExtensions.keys) {
-        expect(
-          hasPreferredExtension(mimeType),
-          isTrue,
-          reason: 'mimeType $mimeType with multiple extension, '
-              'does not have preferred extension defined',
-        );
-      }
-    });
   });
 }

From 1f2ab54da7c69d99f84669b0656a9d137bbca0a4 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Fri, 6 Jan 2023 19:08:49 +0100
Subject: [PATCH 10/30] added some preferred extensions for common file formats

---
 lib/src/extension.dart | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index 04a8071..c70afb1 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -10,8 +10,19 @@ import 'default_extension_map.dart';
 /// to the same MIME type.
 final Map<String, String> _preferredExtensionsMap = <String, String>{
   'application/vnd.ms-excel': 'xls',
+  'application/vnd.ms-powerpoint': 'ppt',
   'image/jpeg': 'jpg',
-  'text/x-c': 'c'
+  'image/tiff': 'tif',
+  'image/svg+xml': 'svg',
+  'text/calendar': 'ics',
+  'text/javascript': 'js',
+  'text/plain': 'txt',
+  'text/sgml': 'sgml',
+  'text/x-pascal': 'pas',
+  'video/mp4': 'mp4',
+  'video/mpeg': 'mpg',
+  'video/quicktime': 'mov',
+  'video/x-matroska': 'mkv',
 };
 
 /// Lookup file extension for a given MIME type.

From fbf8f685cc963c019a828d2915af222434f3a6e0 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Fri, 6 Jan 2023 19:16:54 +0100
Subject: [PATCH 11/30] cleanup old tests

---
 test/extension_test.dart |  2 ++
 test/mime_type_test.dart | 17 -----------------
 2 files changed, 2 insertions(+), 17 deletions(-)

diff --git a/test/extension_test.dart b/test/extension_test.dart
index 0f6df28..a3d7f98 100644
--- a/test/extension_test.dart
+++ b/test/extension_test.dart
@@ -10,6 +10,8 @@ void main() {
     test('valid-mime-type', () {
       expect(extensionFromMime('text/x-dart'), equals('dart'));
       expect(extensionFromMime('text/javascript'), equals('js'));
+      expect(extensionFromMime('application/java-archive'), equals('jar'));
+      expect(extensionFromMime('application/json'), equals('json'));
       expect(extensionFromMime('application/pdf'), equals('pdf'));
       expect(extensionFromMime('application/vnd.ms-excel'), equals('xls'));
       expect(extensionFromMime('application/xhtml+xml'), equals('xht'));
diff --git a/test/mime_type_test.dart b/test/mime_type_test.dart
index 5e444e2..2aec6e3 100644
--- a/test/mime_type_test.dart
+++ b/test/mime_type_test.dart
@@ -184,21 +184,4 @@ void main() {
     expect(initialMagicNumbersMaxLength, actualMaxBytes);
   });
 
-  group('extensionFromMime', () {
-    test('returns match for mime with single extension', () {
-      expect(extensionFromMime('application/json'), equals('json'));
-      expect(extensionFromMime('application/java-archive'), equals('jar'));
-    });
-
-    test('returns first match for mime with multiple extensions', () {
-      expect(extensionFromMime('text/html'), equals('htm'));
-      expect(extensionFromMime('application/x-cbr'), equals('cb7'));
-    });
-
-    test('returns inputted string for unrecognized mime', () {
-      expect(
-          extensionFromMime('unrecognized_mime'), equals('unrecognized_mime'));
-      expect(extensionFromMime('i/am/not/a/mime'), equals('i/am/not/a/mime'));
-    });
-  });
 }

From 6600a3fefeb96430c2dd01e6d6f2dd150fac2144 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Mon, 16 Jan 2023 15:16:02 +0100
Subject: [PATCH 12/30] test orElse param for unknown mime type

---
 test/extension_test.dart | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/test/extension_test.dart b/test/extension_test.dart
index a3d7f98..bed63b4 100644
--- a/test/extension_test.dart
+++ b/test/extension_test.dart
@@ -40,6 +40,9 @@ void main() {
       expect(extensionFromMime('application/to-be-invented'),
           'application/to-be-invented');
 
+      expect(extensionFromMime('application/to-be-invented', orElse: 'unknown'),
+          'unknown');
+
       expect(extensionFromMimeOrNull('application/to-be-invented'), isNull);
     });
   });

From 6fe7ecbd3b0ebd79dca2d8dc05219dacf4250950 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Mon, 16 Jan 2023 15:22:24 +0100
Subject: [PATCH 13/30] link to file

---
 CONTRIBUTING.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 50a36a2..cd7d82f 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -34,4 +34,4 @@ one above, the
 
 ### Adding an extension to an existing MIME type
 If a MIME type ends up with multiple extensions, it is recommended to define a 
-preferred extension in `_preferredExtensionsMap` in `extension.dart` 
\ No newline at end of file
+preferred extension in `_preferredExtensionsMap` in [extension.dart](lib/src/extension.dart). 
\ No newline at end of file

From d57b9fc66dd5cfbb636e16bdc3dc4007cbf942e3 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Mon, 16 Jan 2023 15:26:38 +0100
Subject: [PATCH 14/30] fix title to be more accurate

---
 CONTRIBUTING.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index cd7d82f..bd079dd 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -32,6 +32,6 @@ Contributions made by corporations are covered by a different agreement than the
 one above, the
 [Software Grant and Corporate Contributor License Agreement](https://developers.google.com/open-source/cla/corporate).
 
-### Adding an extension to an existing MIME type
+### Adding an extension / MIME type mapping
 If a MIME type ends up with multiple extensions, it is recommended to define a 
 preferred extension in `_preferredExtensionsMap` in [extension.dart](lib/src/extension.dart). 
\ No newline at end of file

From 0d6c519db9a0f94bc86e0d11b96a07195a193d2b Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Mon, 16 Jan 2023 15:32:15 +0100
Subject: [PATCH 15/30] rename to existing function

---
 README.md | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index c83d567..7688822 100644
--- a/README.md
+++ b/README.md
@@ -64,9 +64,9 @@ The top level function `lookupExtension` can be used to determine the
 file extension of a given MIME type.
 
 ```dart
-print(lookupExtension('text/html'));  // Will print html
-print(lookupExtension('image/jpeg'));  // Will print jpg
-print(lookupExtension('application/pdf'));  // Will print pdf
+print(extensionFromMime('text/html'));  // Will print html
+print(extensionFromMime('image/jpeg'));  // Will print jpg
+print(extensionFromMime('application/pdf'));  // Will print pdf
 ```
 
 You can override the default MIME type-extension mapping using
@@ -74,5 +74,5 @@ You can override the default MIME type-extension mapping using
 
 ```dart
 addMimeType('image/jpeg', 'jpeg');
-print(lookupExtension('image/jpeg'));  // Will print jpeg
+print(extensionFromMime('image/jpeg'));  // Will print jpeg
 ```

From bb9fc15fd067dbe72827fdd7af06bc0c56acb7ef Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Mon, 16 Jan 2023 15:32:41 +0100
Subject: [PATCH 16/30] add standard behavior to make example more clear

---
 README.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/README.md b/README.md
index 7688822..4fdd85e 100644
--- a/README.md
+++ b/README.md
@@ -73,6 +73,7 @@ You can override the default MIME type-extension mapping using
 `addMimeType`:
 
 ```dart
+print(extensionFromMime('image/jpeg'));  // Will print jpg
 addMimeType('image/jpeg', 'jpeg');
 print(extensionFromMime('image/jpeg'));  // Will print jpeg
 ```

From 72806150b5d53c562134724e95ee78bf628cf629 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Mon, 16 Jan 2023 15:34:31 +0100
Subject: [PATCH 17/30] include text/plain mapping again

---
 test/extension_test.dart | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/extension_test.dart b/test/extension_test.dart
index bed63b4..7a22f02 100644
--- a/test/extension_test.dart
+++ b/test/extension_test.dart
@@ -19,7 +19,7 @@ void main() {
       expect(extensionFromMime('image/png'), equals('png'));
       expect(extensionFromMime('text/css'), equals('css'));
       expect(extensionFromMime('text/html'), equals('htm'));
-      // expect(extensionFromMime('text/plain'), equals('txt'));
+      expect(extensionFromMime('text/plain'), equals('txt'));
       expect(extensionFromMime('text/x-c'), equals('c'));
     });
 

From 40107ff862062814374b76ab4d3a0b4e976df06a Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Tue, 17 Jan 2023 10:31:44 +0100
Subject: [PATCH 18/30] remove collection dependency

---
 lib/src/extension.dart | 12 ++++++++++--
 pubspec.yaml           |  3 ---
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index c70afb1..94e3f7d 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:collection/collection.dart';
-
 import 'default_extension_map.dart';
 
 /// Add an override for common extensions since different extensions may map
@@ -48,3 +46,13 @@ String extensionFromMime(String mimeType, {String? orElse}) =>
 void addMimeType(String mimeType, String extension) {
   _preferredExtensionsMap[mimeType.toLowerCase()] = extension.toLowerCase();
 }
+
+extension _IterableExtension<T> on Iterable<T> {
+  /// The first element satisfying [test], or `null` if there are none.
+  T? firstWhereOrNull(bool Function(T element) test) {
+    for (var element in this) {
+      if (test(element)) return element;
+    }
+    return null;
+  }
+}
\ No newline at end of file
diff --git a/pubspec.yaml b/pubspec.yaml
index 3620028..186f288 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -8,9 +8,6 @@ repository: https://github.com/dart-lang/mime
 environment:
   sdk: '>=2.18.0 <3.0.0'
 
-dependencies:
-  collection: ^1.17.0
-
 dev_dependencies:
   lints: ^2.0.0
   test: ^1.16.0

From c384ef347353368c414a7c66143e12bd91d5a8c2 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <178714+mx1up@users.noreply.github.com>
Date: Fri, 27 Jan 2023 14:08:23 +0100
Subject: [PATCH 19/30] lookupExtension has been renamed to existing
 extensionFromMime

---
 README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 4fdd85e..20670f1 100644
--- a/README.md
+++ b/README.md
@@ -60,7 +60,7 @@ request
 
 ## Determining file extension by MIME type
 
-The top level function `lookupExtension` can be used to determine the
+The top level function `extensionFromMime` can be used to determine the
 file extension of a given MIME type.
 
 ```dart

From 76f80f6e39c272b4b7f68e5fdb1ae72f74a8f897 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <121732-mx1up@users.noreply.gitlab.com>
Date: Wed, 13 Dec 2023 19:13:13 +0100
Subject: [PATCH 20/30] drop non-nullable extensionFromMime variant per review
 suggestion

---
 lib/src/extension.dart   |  5 +----
 test/extension_test.dart | 22 ++++------------------
 2 files changed, 5 insertions(+), 22 deletions(-)

diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index 94e3f7d..69a1bdc 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -28,7 +28,7 @@ final Map<String, String> _preferredExtensionsMap = <String, String>{
 /// If there are multiple extensions for [mimeType], return preferred extension
 /// if defined, or the first occurrence in the map.
 /// If no extension is found, `null` is returned.
-String? extensionFromMimeOrNull(String mimeType) {
+String? extensionFromMime(String mimeType) {
   final mimeTypeLC = mimeType.toLowerCase();
   if (_preferredExtensionsMap.containsKey(mimeTypeLC)) {
     return _preferredExtensionsMap[mimeTypeLC]!;
@@ -38,9 +38,6 @@ String? extensionFromMimeOrNull(String mimeType) {
       ?.key;
 }
 
-String extensionFromMime(String mimeType, {String? orElse}) =>
-    extensionFromMimeOrNull(mimeType) ?? orElse ?? mimeType;
-
 /// Allow for a user-specified MIME type-extension mapping that overrides the
 /// default.
 void addMimeType(String mimeType, String extension) {
diff --git a/test/extension_test.dart b/test/extension_test.dart
index 7a22f02..a57e9c6 100644
--- a/test/extension_test.dart
+++ b/test/extension_test.dart
@@ -24,32 +24,18 @@ void main() {
     });
 
     test('invalid-mime-type', () {
-      expect(extensionFromMime('invalid-mime-type'), 'invalid-mime-type');
-      expect(extensionFromMime('invalid/mime/type'), 'invalid/mime/type');
-
-      expect(
-          extensionFromMime('invalid-mime-type', orElse: 'invalid'), 'invalid');
-      expect(
-          extensionFromMime('invalid/mime/type', orElse: 'invalid'), 'invalid');
-
-      expect(extensionFromMimeOrNull('invalid-mime-type'), isNull);
-      expect(extensionFromMimeOrNull('invalid/mime/type'), isNull);
+      expect(extensionFromMime('invalid-mime-type'), isNull);
+      expect(extensionFromMime('invalid/mime/type'), isNull);
     });
 
     test('unknown-mime-type', () {
-      expect(extensionFromMime('application/to-be-invented'),
-          'application/to-be-invented');
-
-      expect(extensionFromMime('application/to-be-invented', orElse: 'unknown'),
-          'unknown');
-
-      expect(extensionFromMimeOrNull('application/to-be-invented'), isNull);
+      expect(extensionFromMime('application/to-be-invented'), isNull);
     });
   });
 
   group('add-mime-type', () {
     test('new-mime-type', () {
-      expect(extensionFromMimeOrNull('custom/type'), isNull);
+      expect(extensionFromMime('custom/type'), isNull);
       addMimeType('custom/type', 'ct');
       expect(extensionFromMime('custom/type'), equals('ct'));
     });

From 7b2804f1f0e66c2f3bbd79a0fc0851d362352fa6 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <121732-mx1up@users.noreply.gitlab.com>
Date: Wed, 13 Dec 2023 19:34:09 +0100
Subject: [PATCH 21/30] doc update: try using noun phrase; don't refer to
 implementation details

---
 lib/src/extension.dart | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index 69a1bdc..4344be9 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -23,10 +23,10 @@ final Map<String, String> _preferredExtensionsMap = <String, String>{
   'video/x-matroska': 'mkv',
 };
 
-/// Lookup file extension for a given MIME type.
+/// The extension for a given MIME type.
 ///
 /// If there are multiple extensions for [mimeType], return preferred extension
-/// if defined, or the first occurrence in the map.
+/// if defined, otherwise an extension chosen by the library.
 /// If no extension is found, `null` is returned.
 String? extensionFromMime(String mimeType) {
   final mimeTypeLC = mimeType.toLowerCase();

From 65c70168fe3abaca19a3b4a597fe5e60ccc4f554 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <121732-mx1up@users.noreply.gitlab.com>
Date: Wed, 13 Dec 2023 19:37:19 +0100
Subject: [PATCH 22/30] don't use extension method

---
 lib/src/extension.dart | 18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index 4344be9..b9160ed 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -33,9 +33,11 @@ String? extensionFromMime(String mimeType) {
   if (_preferredExtensionsMap.containsKey(mimeTypeLC)) {
     return _preferredExtensionsMap[mimeTypeLC]!;
   }
-  return defaultExtensionMap.entries
-      .firstWhereOrNull((entry) => entry.value == mimeTypeLC)
-      ?.key;
+
+  for (final entry in defaultExtensionMap.entries) {
+    if (entry.value == mimeTypeLC) return entry.key;
+  }
+  return null;
 }
 
 /// Allow for a user-specified MIME type-extension mapping that overrides the
@@ -43,13 +45,3 @@ String? extensionFromMime(String mimeType) {
 void addMimeType(String mimeType, String extension) {
   _preferredExtensionsMap[mimeType.toLowerCase()] = extension.toLowerCase();
 }
-
-extension _IterableExtension<T> on Iterable<T> {
-  /// The first element satisfying [test], or `null` if there are none.
-  T? firstWhereOrNull(bool Function(T element) test) {
-    for (var element in this) {
-      if (test(element)) return element;
-    }
-    return null;
-  }
-}
\ No newline at end of file

From e8a6ed56c5f68b4c920092bc9a5b7fa49fb0240d Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <121732-mx1up@users.noreply.gitlab.com>
Date: Wed, 13 Dec 2023 19:44:13 +0100
Subject: [PATCH 23/30] remove addMimeType and leave it for another time..

---
 lib/src/extension.dart   |  6 ------
 test/extension_test.dart | 14 --------------
 2 files changed, 20 deletions(-)

diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index b9160ed..22b3e07 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -39,9 +39,3 @@ String? extensionFromMime(String mimeType) {
   }
   return null;
 }
-
-/// Allow for a user-specified MIME type-extension mapping that overrides the
-/// default.
-void addMimeType(String mimeType, String extension) {
-  _preferredExtensionsMap[mimeType.toLowerCase()] = extension.toLowerCase();
-}
diff --git a/test/extension_test.dart b/test/extension_test.dart
index a57e9c6..0a3db0f 100644
--- a/test/extension_test.dart
+++ b/test/extension_test.dart
@@ -32,18 +32,4 @@ void main() {
       expect(extensionFromMime('application/to-be-invented'), isNull);
     });
   });
-
-  group('add-mime-type', () {
-    test('new-mime-type', () {
-      expect(extensionFromMime('custom/type'), isNull);
-      addMimeType('custom/type', 'ct');
-      expect(extensionFromMime('custom/type'), equals('ct'));
-    });
-
-    test('overridden-mime-type', () {
-      expect(extensionFromMime('image/jpeg'), equals('jpg'));
-      addMimeType('image/jpeg', 'jpeg');
-      expect(extensionFromMime('image/jpeg'), equals('jpeg'));
-    });
-  });
 }

From f8642bd66a694ec522b83f2becd85b5da88fc32a Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <121732-mx1up@users.noreply.gitlab.com>
Date: Wed, 13 Dec 2023 20:53:17 +0100
Subject: [PATCH 24/30] remove addMimeType documentation

---
 README.md | 9 ---------
 1 file changed, 9 deletions(-)

diff --git a/README.md b/README.md
index 20670f1..7ea762c 100644
--- a/README.md
+++ b/README.md
@@ -68,12 +68,3 @@ print(extensionFromMime('text/html'));  // Will print html
 print(extensionFromMime('image/jpeg'));  // Will print jpg
 print(extensionFromMime('application/pdf'));  // Will print pdf
 ```
-
-You can override the default MIME type-extension mapping using
-`addMimeType`:
-
-```dart
-print(extensionFromMime('image/jpeg'));  // Will print jpg
-addMimeType('image/jpeg', 'jpeg');
-print(extensionFromMime('image/jpeg'));  // Will print jpeg
-```

From 8acfbe4a5a946882f1cbde5816a230cb9be47506 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <121732-mx1up@users.noreply.gitlab.com>
Date: Mon, 19 Feb 2024 19:00:11 +0100
Subject: [PATCH 25/30] be more specific about extension

---
 lib/src/extension.dart | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index 22b3e07..871ee55 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -23,7 +23,7 @@ final Map<String, String> _preferredExtensionsMap = <String, String>{
   'video/x-matroska': 'mkv',
 };
 
-/// The extension for a given MIME type.
+/// The file extension for a given MIME type.
 ///
 /// If there are multiple extensions for [mimeType], return preferred extension
 /// if defined, otherwise an extension chosen by the library.

From f20c40f30baa21070fd218368630e033dc8a7443 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <121732-mx1up@users.noreply.gitlab.com>
Date: Mon, 19 Feb 2024 19:07:41 +0100
Subject: [PATCH 26/30] review feedback: avoid abbreviations, just overwrite
 function param

---
 lib/src/extension.dart | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index 871ee55..e77b038 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -29,13 +29,13 @@ final Map<String, String> _preferredExtensionsMap = <String, String>{
 /// if defined, otherwise an extension chosen by the library.
 /// If no extension is found, `null` is returned.
 String? extensionFromMime(String mimeType) {
-  final mimeTypeLC = mimeType.toLowerCase();
-  if (_preferredExtensionsMap.containsKey(mimeTypeLC)) {
-    return _preferredExtensionsMap[mimeTypeLC]!;
+  mimeType = mimeType.toLowerCase();
+  if (_preferredExtensionsMap.containsKey(mimeType)) {
+    return _preferredExtensionsMap[mimeType]!;
   }
 
   for (final entry in defaultExtensionMap.entries) {
-    if (entry.value == mimeTypeLC) return entry.key;
+    if (entry.value == mimeType) return entry.key;
   }
   return null;
 }

From 2be331fae754c5c6ba0ff56e0ccf13d14f137cf4 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <121732-mx1up@users.noreply.gitlab.com>
Date: Mon, 19 Feb 2024 19:25:01 +0100
Subject: [PATCH 27/30] since extensions can no longer by added at runtime, we
 can optimize and avoid the linear search

---
 lib/src/extension.dart | 43 +++++++++++++++++++-----------------------
 1 file changed, 19 insertions(+), 24 deletions(-)

diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index e77b038..5b223a3 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -6,22 +6,24 @@ import 'default_extension_map.dart';
 
 /// Add an override for common extensions since different extensions may map
 /// to the same MIME type.
-final Map<String, String> _preferredExtensionsMap = <String, String>{
-  'application/vnd.ms-excel': 'xls',
-  'application/vnd.ms-powerpoint': 'ppt',
-  'image/jpeg': 'jpg',
-  'image/tiff': 'tif',
-  'image/svg+xml': 'svg',
-  'text/calendar': 'ics',
-  'text/javascript': 'js',
-  'text/plain': 'txt',
-  'text/sgml': 'sgml',
-  'text/x-pascal': 'pas',
-  'video/mp4': 'mp4',
-  'video/mpeg': 'mpg',
-  'video/quicktime': 'mov',
-  'video/x-matroska': 'mkv',
-};
+final Map<String, String> _defaultMimeTypeMap = {
+  for (var entry in defaultExtensionMap.entries) entry.value: entry.key,
+}..addAll({
+    'application/vnd.ms-excel': 'xls',
+    'application/vnd.ms-powerpoint': 'ppt',
+    'image/jpeg': 'jpg',
+    'image/tiff': 'tif',
+    'image/svg+xml': 'svg',
+    'text/calendar': 'ics',
+    'text/javascript': 'js',
+    'text/plain': 'txt',
+    'text/sgml': 'sgml',
+    'text/x-pascal': 'pas',
+    'video/mp4': 'mp4',
+    'video/mpeg': 'mpg',
+    'video/quicktime': 'mov',
+    'video/x-matroska': 'mkv',
+  });
 
 /// The file extension for a given MIME type.
 ///
@@ -30,12 +32,5 @@ final Map<String, String> _preferredExtensionsMap = <String, String>{
 /// If no extension is found, `null` is returned.
 String? extensionFromMime(String mimeType) {
   mimeType = mimeType.toLowerCase();
-  if (_preferredExtensionsMap.containsKey(mimeType)) {
-    return _preferredExtensionsMap[mimeType]!;
-  }
-
-  for (final entry in defaultExtensionMap.entries) {
-    if (entry.value == mimeType) return entry.key;
-  }
-  return null;
+  return _defaultMimeTypeMap[mimeType];
 }

From 60e9a7be55c15dc2556540836ff061ba626dbd99 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <121732-mx1up@users.noreply.gitlab.com>
Date: Mon, 19 Feb 2024 19:27:23 +0100
Subject: [PATCH 28/30] local var no longer needed

---
 lib/src/extension.dart | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index 5b223a3..1edaca2 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -30,7 +30,5 @@ final Map<String, String> _defaultMimeTypeMap = {
 /// If there are multiple extensions for [mimeType], return preferred extension
 /// if defined, otherwise an extension chosen by the library.
 /// If no extension is found, `null` is returned.
-String? extensionFromMime(String mimeType) {
-  mimeType = mimeType.toLowerCase();
-  return _defaultMimeTypeMap[mimeType];
-}
+String? extensionFromMime(String mimeType) =>
+    _defaultMimeTypeMap[mimeType.toLowerCase()];

From 54da123451038f524bde787d4b8c506968ed0d1f Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <121732-mx1up@users.noreply.gitlab.com>
Date: Mon, 19 Feb 2024 19:34:51 +0100
Subject: [PATCH 29/30] update docs

---
 CONTRIBUTING.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index bd079dd..463063a 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -34,4 +34,4 @@ one above, the
 
 ### Adding an extension / MIME type mapping
 If a MIME type ends up with multiple extensions, it is recommended to define a 
-preferred extension in `_preferredExtensionsMap` in [extension.dart](lib/src/extension.dart). 
\ No newline at end of file
+preferred extension in `_defaultMimeTypeMap` in [extension.dart](lib/src/extension.dart). 
\ No newline at end of file

From d1909147a838601970351f536cb731b80a382a08 Mon Sep 17 00:00:00 2001
From: matthias sweertvaegher <121732-mx1up@users.noreply.gitlab.com>
Date: Mon, 19 Feb 2024 19:38:56 +0100
Subject: [PATCH 30/30] update docs

---
 lib/src/extension.dart | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/src/extension.dart b/lib/src/extension.dart
index 1edaca2..35a860f 100644
--- a/lib/src/extension.dart
+++ b/lib/src/extension.dart
@@ -4,8 +4,8 @@
 
 import 'default_extension_map.dart';
 
-/// Add an override for common extensions since different extensions may map
-/// to the same MIME type.
+/// Reverse map of [defaultExtensionMap] with overrides for common extensions
+/// since different extensions may map to the same MIME type.
 final Map<String, String> _defaultMimeTypeMap = {
   for (var entry in defaultExtensionMap.entries) entry.value: entry.key,
 }..addAll({
@@ -28,7 +28,9 @@ final Map<String, String> _defaultMimeTypeMap = {
 /// The file extension for a given MIME type.
 ///
 /// If there are multiple extensions for [mimeType], return preferred extension
-/// if defined, otherwise an extension chosen by the library.
+/// if defined in [_defaultMimeTypeMap], otherwise an extension chosen by the
+/// library.
+///
 /// If no extension is found, `null` is returned.
 String? extensionFromMime(String mimeType) =>
     _defaultMimeTypeMap[mimeType.toLowerCase()];