add support for removing binaries.

lib/src/kdbx_entry.dart

@@ -198,6 +198,7 @@ class KdbxEntry extends KdbxObject {
 
   set label(String label) => setString(KdbxKey('Title'), PlainValue(label));
 
+  /// Creates a new binary and adds it to this entry.
   KdbxBinary createBinary({
     @required bool isProtected,
     @required String name,
@@ -219,6 +220,17 @@ class KdbxEntry extends KdbxObject {
     return binary;
   }
 
+  void removeBinary(KdbxKey binaryKey) {
+    final binary = _binaries.remove(binaryKey);
+    if (binary == null) {
+      throw StateError(
+          'Trying to remove binary key $binaryKey does not exist.');
+    }
+    if (!binary.isInline) {
+      file.ctx.removeBinary(binary);
+    }
+  }
+
   KdbxKey _uniqueBinaryName(String fileName) {
     final lastIndex = fileName.lastIndexOf('.');
     final baseName =

lib/src/kdbx_format.dart

@@ -118,6 +118,15 @@ class KdbxReadWriteContext {
     }
     return id;
   }
+
+  /// removes the given binary. Does not check if it is still referenced
+  /// in any [KdbxEntry]!!
+  void removeBinary(KdbxBinary binary) {
+    if (!_binaries.remove(binary)) {
+      throw KdbxCorruptedFileException(
+          'Tried to remove binary which is not in this file.');
+    }
+  }
 }
 
 abstract class CredentialsPart {

test/kdbx_binaries_test.dart

@@ -88,6 +88,23 @@ void main() {
     test('Add new attachment', () async {
       await _testAddNewAttachment('test/keepass2binaries.kdbx');
     });
+    test('Remove attachment', () async {
+      final saved = await (() async {
+        final file = await TestUtil.readKdbxFile('test/keepass2binaries.kdbx');
+        final entry = file.body.rootGroup.entries.first;
+        expectKeepass2binariesContents(entry);
+        expect(file.ctx.binariesIterable, hasLength(3));
+        entry.removeBinary(KdbxKey('example1.txt'));
+        expect(file.ctx.binariesIterable, hasLength(2));
+        return await file.save();
+      })();
+      final file = await TestUtil.readKdbxFileBytes(saved);
+      final entry = file.body.rootGroup.entries.first;
+      expect(entry.binaryEntries, hasLength(2));
+      expect(entry.binaryEntries.map((e) => (e.key.key)),
+          ['example2.txt', 'keepasslogo.jpeg']);
+      expect(file.ctx.binariesIterable, hasLength(2));
+    });
   });
   group('kdbx4 attachment', () {
     test('read binary', () async {
@@ -111,6 +128,27 @@ void main() {
       expectBinary(file.body.rootGroup.entries.last, 'keepasslogo.jpeg',
           hasLength(7092));
     });
+    test('remove attachment kdbx4', () async {
+      final saved = await (() async {
+        final file =
+            await TestUtil.readKdbxFile('test/keepass2kdbx4binaries.kdbx');
+        final entry = file.body.rootGroup.entries.first;
+        expectBinary(file.body.rootGroup.entries.first, 'example2.txt',
+            IsUtf8String('content2 example\n\n'));
+        expectBinary(file.body.rootGroup.entries.last, 'keepasslogo.jpeg',
+            hasLength(7092));
+        expect(file.ctx.binariesIterable, hasLength(2));
+        entry.removeBinary(KdbxKey('example2.txt'));
+        expect(file.ctx.binariesIterable, hasLength(1));
+        return await file.save();
+      })();
+      final file = await TestUtil.readKdbxFileBytes(saved);
+      final entry = file.body.rootGroup.entries.first;
+      expect(entry.binaryEntries, hasLength(0));
+      expectBinary(file.body.rootGroup.entries.last, 'keepasslogo.jpeg',
+          hasLength(7092));
+      expect(file.ctx.binariesIterable, hasLength(1));
+    });
     test('Add new attachment kdbx4', () async {
       await _testAddNewAttachment('test/keepass2kdbx4binaries.kdbx');
     });