Add optional endian argument for WriteBuffer/ReadBuffer

[Sunbreak]

Signed-off-by: sunbreak sunbreak.wang@gmail.com

Description

This PR add an optional endian to WriteBuffer/ReadBuffer class for convenience

I'm a IoT developer, writing applications via BLE protocol as below
https://github.com/woodemi/notepad-core-flutter/blob/develop/lib/woodemi/WoodemiClient.dart#L455-L465

var imageId = fileInfo.item1;
var byteData = ByteData(imageId.length + 4 + 4 + 2 + 1 + 2);
var position = 0;
for (var b in imageId)
  byteData.setInt8(position++, b);
byteData.setUint32(position, currentPos, Endian.little);
byteData.setUint32(position += 4, blockSize, Endian.little);
byteData.setUint16(position += 4, maxChunkSize, Endian.little);
byteData.setUint8(position += 2, transferMethod);
byteData.setUint16(position += 1, l2capChannelOrPsm, Endian.little);
var request = Uint8List.fromList([0x04] + byteData.buffer.asUint8List());

I find WriteBuffer/ReadBuffer in package:flutter/foundation with similiar methods, except for the endians

With this PR merged

var writeBuffer = WriteBuffer();
writeBuffer.putUint8List(imageId);
writeBuffer.putUint32(currentPos, Endian.little);
writeBuffer.putUint32(blockSize, Endian.little);
writeBuffer.putUint16(maxChunkSize, Endian.little);
writeBuffer.putUint8(transferMethod);
writeBuffer.putUint16(l2capChannelOrPsm, Endian.little);
var request = Uint8List.fromList([0x04] + writeBuffer.done().buffer.asUint8List());

Related Issues

• Make ByteBuffer an active object with a useful interface, not an opaque capability. dart-lang/sdk#16130
• https://stackoverflow.com/questions/51801051/how-to-use-bytedata-and-bytebuffer-in-flutter-without-mirror-package

Tests

I added the following tests:

• of 32-bit integer in big endian
• of 64-bit integer in big endian
• of double in big endian

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[Sunbreak]

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[goderbauer]

If you already have a way of doing this, why do you need this change in the framework?

[Sunbreak]

If you already have a way of doing this, why do you need this change in the framework?

WriteBuffer/ReadBuffer are introduced for some byte operations in the framework from the beginning, I suppose. A little improvement may help others as well.

[Sunbreak]

Update the PR with an appended commit.
@chunhtai should I rebase into one commit, and/or rebase onto branch master commit?

[goderbauer]

LGTM

[chunhtai]

LGTM