// Copyright 2019 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at //
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package tcpip

import (
	"gvisor.dev/gvisor/pkg/tcpip/buffer"
)

// A PacketBuffer contains all the data of a network packet.
//
// As a PacketBuffer traverses up the stack, it may be necessary to pass it to
// multiple endpoints. Clone() should be called in such cases so that
// modifications to the Data field do not affect other copies.
//
// +stateify savable
type PacketBuffer struct {
	// Data holds the payload of the packet. For inbound packets, it also
	// holds the headers, which are consumed as the packet moves up the
	// stack. Headers are guaranteed not to be split across views.
	//
	// The bytes backing Data are immutable, but Data itself may be trimmed
	// or otherwise modified.
	Data buffer.VectorisedView

	// DataOffset is used for GSO output. It is the offset into the Data
	// field where the payload of this packet starts.
	DataOffset int

	// DataSize is used for GSO output. It is the size of this packet's
	// payload.
	DataSize int

	// Header holds the headers of outbound packets. As a packet is passed
	// down the stack, each layer adds to Header.
	Header buffer.Prependable

	// These fields are used by both inbound and outbound packets. They
	// typically overlap with the Data and Header fields.
	//
	// The bytes backing these views are immutable. Each field may be nil
	// if either it has not been set yet or no such header exists (e.g.
	// packets sent via loopback may not have a link header).
	//
	// These fields may be Views into other slices (either Data or Header).
	// SR dosen't support this, so deep copies are necessary in some cases.
	LinkHeader      buffer.View
	NetworkHeader   buffer.View
	TransportHeader buffer.View
}

// Clone makes a copy of pk. It clones the Data field, which creates a new
// VectorisedView but does not deep copy the underlying bytes.
//
// Clone also does not deep copy any of its other fields.
func (pk PacketBuffer) Clone() PacketBuffer {
	pk.Data = pk.Data.Clone(nil)
	return pk
}

//// TransportProtocol returns the transport protocol of pk.
////
//// Precondition: pk.NetworkHeader is set.
//func (pk PacketBuffer) TransportProtocolIPv4() uint16 {
//	if pk.NetworkHeader == nil {
//		panic("This should only be called when pk.NetworkHeader is set.")
//	}
//	return header.IPv4(pk.NetworkHeader).TransportProtocol()
//}

// func (pk Packet) findNetHeader() header.IPv4 {
// 	// Inbound:
// 	// Data holds everything, but may have had some headers shaved off.
// 	// Figure out whether it's set or still somewhere in data and return
// 	// appropriately.

// 	// Outbound:
// 	// NetworkHeader will be set if we've added one. Otherwise there's no
// 	// header.
// }