Accurately determine transfer header size

[vcabbage]

Current implementation wastes several bytes on each transfer.

amqp/client.go

Lines 1545 to 1575 in ee6eb7e

	const maxTransferFrameHeader = 66 // determined by calcMaxTransferFrameHeader
	func calcMaxTransferFrameHeader() int {
	var buf buffer
	maxUint32 := uint32(math.MaxUint32)
	receiverSettleMode := ReceiverSettleMode(0)
	err := writeFrame(&buf, frame{
	type_: frameTypeAMQP,
	channel: math.MaxUint16,
	body: &performTransfer{
	Handle: maxUint32,
	DeliveryID: &maxUint32,
	DeliveryTag: bytes.Repeat([]byte{'a'}, 32),
	MessageFormat: &maxUint32,
	Settled: true,
	More: true,
	ReceiverSettleMode: &receiverSettleMode,
	State: nil, // TODO: determine whether state should be included in size
	Resume: true,
	Aborted: true,
	Batchable: true,
	// Payload omitted as it is appended directly without any header
	},
	})
	if err != nil {
	panic(err)
	}
	return buf.len()
	}