frp/vendor/golang.org/x/net/ipv4/packet.go

// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package ipv4

import (
	"net"
	"syscall"

	"golang.org/x/net/internal/socket"
)

// BUG(mikio): On Windows, the ReadFrom and WriteTo methods of RawConn
// are not implemented.

// A packetHandler represents the IPv4 datagram handler.
type packetHandler struct {
	*net.IPConn
	*socket.Conn
	rawOpt
}

func (c *packetHandler) ok() bool { return c != nil && c.IPConn != nil && c.Conn != nil }

// ReadFrom reads an IPv4 datagram from the endpoint c, copying the
// datagram into b. It returns the received datagram as the IPv4
// header h, the payload p and the control message cm.
func (c *packetHandler) ReadFrom(b []byte) (h *Header, p []byte, cm *ControlMessage, err error) {
	if !c.ok() {
		return nil, nil, nil, syscall.EINVAL
	}
	return c.readFrom(b)
}

func slicePacket(b []byte) (h, p []byte, err error) {
	if len(b) < HeaderLen {
		return nil, nil, errHeaderTooShort
	}
	hdrlen := int(b[0]&0x0f) << 2
	return b[:hdrlen], b[hdrlen:], nil
}

// WriteTo writes an IPv4 datagram through the endpoint c, copying the
// datagram from the IPv4 header h and the payload p. The control
// message cm allows the datagram path and the outgoing interface to be
// specified.  Currently only Darwin and Linux support this. The cm
// may be nil if control of the outgoing datagram is not required.
//
// The IPv4 header h must contain appropriate fields that include:
//
//	Version       = <must be specified>
//	Len           = <must be specified>
//	TOS           = <must be specified>
//	TotalLen      = <must be specified>
//	ID            = platform sets an appropriate value if ID is zero
//	FragOff       = <must be specified>
//	TTL           = <must be specified>
//	Protocol      = <must be specified>
//	Checksum      = platform sets an appropriate value if Checksum is zero
//	Src           = platform sets an appropriate value if Src is nil
//	Dst           = <must be specified>
//	Options       = optional
func (c *packetHandler) WriteTo(h *Header, p []byte, cm *ControlMessage) error {
	if !c.ok() {
		return syscall.EINVAL
	}
	return c.writeTo(h, p, cm)
}