Make CodedBufferWriter.writeRawByte argument type more accurate (#891)

`writeRawBytes` adds bytes to the output and it will only be fast when
the argument is `Uint8List`.

Since all the users already pass `Uint8List`, update the argument type.

This allows simplifyping `_copyInto`. Because it has only one call site,
we simplify it and inline it in the call site.

cl/576427817

protobuf/CHANGELOG.md

@@ -1,6 +1,6 @@
 ## 4.0.0-dev
 
-* The following types and members are now removed:
+* **Breaking:** The following types and members are now removed:
 
   - `PbEventMixin`
   - `PbFieldChange`
@@ -12,6 +12,9 @@
   surface small (to make it easier to change the library or migrate to another
   library) these types and members are removed. ([#738])
 
+* **Breaking:** `CodedBufferWriter.writeRawBytes` now takes a `Uint8List`
+  argument (instead of `TypedData`).
+
 [#738]: https://github.com/google/protobuf.dart/issues/738
 
 ## 3.1.0

protobuf/lib/protobuf.dart

@@ -17,7 +17,7 @@ import 'dart:convert'
         jsonDecode,
         jsonEncode;
 import 'dart:math' as math;
-import 'dart:typed_data' show ByteData, Endian, TypedData, Uint8List;
+import 'dart:typed_data' show ByteData, Endian, Uint8List;
 
 import 'package:fixnum/fixnum.dart' show Int64;
 import 'package:meta/meta.dart' show UseResult;

protobuf/lib/src/protobuf/coded_buffer_writer.dart

@@ -22,8 +22,8 @@ part of '../../protobuf.dart';
 class CodedBufferWriter {
   /// Array of splices representing the data written into the writer.
   /// Each element might be one of:
-  ///   * a TypedData object - represents a sequence of bytes that need to be
-  ///                          emitted into the result as-is;
+  ///   * a [Uint8List] object - represents a sequence of bytes that need to be
+  ///                            emitted into the result as-is;
   ///   * a positive integer - a number of bytes to copy from [_outputChunks]
   ///                          into resulting buffer;
   ///   * a non-positive integer - a positive number that needs to be emitted
@@ -166,9 +166,12 @@ class CodedBufferWriter {
           }
         }
       } else {
-        // action is a TypedData containing bytes to emit into the output
+        // action is a `Uint8List` containing bytes to emit into the output
         // buffer.
-        outPos = _copyInto(buffer, outPos, action);
+        final Uint8List value = action;
+        final end = outPos + value.length;
+        buffer.setRange(outPos, end, value);
+        outPos = end;
       }
     }
 
@@ -210,7 +213,7 @@ class CodedBufferWriter {
   /// Record number of bytes written into output chunks since last splice.
   ///
   /// This is used before reserving space for an unknown varint splice or
-  /// adding a TypedData array splice.
+  /// adding a [Uint8List] array splice.
   void _commitSplice() {
     final pos = _bytesInChunk + _outputChunksBytes;
     final bytes = pos - _lastSplicePos;
@@ -220,9 +223,9 @@ class CodedBufferWriter {
     _lastSplicePos = pos;
   }
 
-  /// Add TypedData splice - these bytes would be directly copied into the
-  /// output buffer by [writeTo].
-  void writeRawBytes(TypedData value) {
+  /// Add a [Uint8List] splice, without copying. These bytes will be directly
+  /// copied into the output buffer by [writeTo].
+  void writeRawBytes(Uint8List value) {
     _commitSplice();
     _splices.add(value);
     _bytesTotal += value.lengthInBytes;
@@ -419,24 +422,6 @@ class CodedBufferWriter {
     _writeVarint32(value & 0xFFFFFFFF);
   }
 
-  /// Copy bytes from the given typed data array into the output buffer.
-  ///
-  /// Has a specialization for [Uint8List] for performance.
-  int _copyInto(Uint8List buffer, int pos, TypedData value) {
-    if (value is Uint8List) {
-      final len = value.length;
-      final end = pos + len;
-      buffer.setRange(pos, end, value);
-      return end;
-    } else {
-      final len = value.lengthInBytes;
-      final end = pos + len;
-      final u8 = Uint8List.view(value.buffer, value.offsetInBytes, len);
-      buffer.setRange(pos, end, u8);
-      return end;
-    }
-  }
-
   /// This function maps a power-of-2 value (2^0 .. 2^31) to a unique value
   /// in the 0..31 range.
   ///