Allow NIOEchoClient to receive fragmented echo responses.

[SeJV]

Allow NIOEchoClient to receive fragmented echo responses.

Motivation:

While sending a message to NIOEchoServer and receiving the echoed response, it is not guaranteed that the sent message arrives inside one channelRead() call. This would fail in the current implementation.

Modifications:

On channelRead the data will be written to a buffer until all sendBytes got received.

Result:

The updated NIOEchoClient can now buffer split InboundIn data and prints the result, when all sendBytes got received.

Tests:

Tests for executables require swift-tools-version 5.5. To recreate the tests of the new NIOEchoClient receive message argument from constructor instead of the readLine(). Additionally context.writeAndFlush() the received buffer instead of printing it.

let expectedMessage = "Expected to read"
let expectedBuffer = ByteBuffer(string: expectedMessage)

let handler = EmbeddedChannel(handler: EchoHandler(message: expectedMessage))
try handler.connect(to: .init(ipAddress: "127.0.0.1", port: 80), promise: nil)
// empty outbound buffer
_ = try handler.readOutbound(as: ByteBuffer.self)

// Test case: EchoHandler receives split buffer
try handler.writeInbound(ByteBuffer(string: String(expectedMessage.prefix(5))))
try handler.writeInbound(ByteBuffer(string: String(expectedMessage.dropFirst(5))))
XCTAssertEqual(try handler.readOutbound(as: ByteBuffer.self), expectedBuffer)

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[Lukasa]

Nice change, thanks!

[Lukasa]

@swift-nio-bot test this please