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net/packet: documentation cleanups.

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Signed-off-by: David Anderson <danderson@tailscale.com>
This commit is contained in:
David Anderson 2020-11-10 21:12:46 -08:00
parent 9ef39af2f2
commit d7ee3096dd
2 changed files with 21 additions and 15 deletions
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25
net/packet/header.go
View File

@ -16,27 +16,34 @@
const maxPacketLength = math.MaxUint16
var (
// errSmallBuffer is returned when Marshal receives a buffer
// too small to contain the header to marshal.
errSmallBuffer = errors.New("buffer too small")
// errLargePacket is returned when Marshal receives a payload
// larger than the maximum representable size in header
// fields.
errLargePacket = errors.New("packet too large")
)
// Header is a packet header capable of marshaling itself into a byte buffer.
// Header is a packet header capable of marshaling itself into a byte
// buffer.
type Header interface {
// Len returns the length of the header after marshaling.
// Len returns the length of the marshaled packet.
Len() int
// Marshal serializes the header into buf in wire format.
// It clobbers the header region, which is the first h.Length() bytes of buf.
// It explicitly initializes every byte of the header region,
// so pre-zeroing it on reuse is not required. It does not allocate memory.
// It fails if and only if len(buf) < Length().
// Marshal serializes the header into buf, which must be at
// least Len() bytes long. Implementations of Marshal assume
// that bytes after the first Len() are payload bytes for the
// purpose of computing length and checksum fields. Marshal
// implementations must not allocate memory.
Marshal(buf []byte) error
// ToResponse transforms the header into one for a response packet.
// For instance, this swaps the source and destination IPs.
ToResponse()
}
// Generate generates a new packet with the given header and payload.
// Unlike Header.Marshal, this does allocate memory.
// Generate generates a new packet with the given Header and
// payload. This function allocates memory, see Header.Marshal for an
// allocation-free option.
func Generate(h Header, payload []byte) []byte {
hlen := h.Len()
buf := make([]byte, hlen+len(payload))

11
net/packet/udp4.go
View File

@ -14,17 +14,17 @@ type UDP4Header struct {
}
const (
// udpHeaderLength is the size of the UDP packet header, not
// including the outer IP header.
udpHeaderLength = 8
// udpTotalHeaderLength is the length of all headers in a UDP packet.
udpTotalHeaderLength = ip4HeaderLength + udpHeaderLength
)
func (UDP4Header) Len() int {
return udpTotalHeaderLength
return ip4HeaderLength + udpHeaderLength
}
func (h UDP4Header) Marshal(buf []byte) error {
if len(buf) < udpTotalHeaderLength {
if len(buf) < h.Len() {
return errSmallBuffer
}
if len(buf) > maxPacketLength {
@ -39,9 +39,8 @@ func (h UDP4Header) Marshal(buf []byte) error {
binary.BigEndian.PutUint16(buf[24:26], uint16(length))
binary.BigEndian.PutUint16(buf[26:28], 0) // blank checksum
h.IP4Header.MarshalPseudo(buf)
// UDP checksum with IP pseudo header.
h.IP4Header.MarshalPseudo(buf)
binary.BigEndian.PutUint16(buf[26:28], ipChecksum(buf[8:]))
h.IP4Header.Marshal(buf)