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package extension
import (
"encoding/binary"
"github.com/pion/dtls/v2/pkg/crypto/elliptic"
)
const (
supportedGroupsHeaderSize = 6
)
// SupportedEllipticCurves allows a Client/Server to communicate
// what curves they both support
//
// https://tools.ietf.org/html/rfc8422#section-5.1.1
type SupportedEllipticCurves struct {
EllipticCurves []elliptic.Curve
}
// TypeValue returns the extension TypeValue
func (s SupportedEllipticCurves) TypeValue() TypeValue {
return SupportedEllipticCurvesTypeValue
}
// Marshal encodes the extension
func (s *SupportedEllipticCurves) Marshal() ([]byte, error) {
out := make([]byte, supportedGroupsHeaderSize)
binary.BigEndian.PutUint16(out, uint16(s.TypeValue()))
binary.BigEndian.PutUint16(out[2:], uint16(2+(len(s.EllipticCurves)*2)))
binary.BigEndian.PutUint16(out[4:], uint16(len(s.EllipticCurves)*2))
for _, v := range s.EllipticCurves {
out = append(out, []byte{0x00, 0x00}...)
binary.BigEndian.PutUint16(out[len(out)-2:], uint16(v))
}
return out, nil
}
// Unmarshal populates the extension from encoded data
func (s *SupportedEllipticCurves) Unmarshal(data []byte) error {
if len(data) <= supportedGroupsHeaderSize {
return errBufferTooSmall
} else if TypeValue(binary.BigEndian.Uint16(data)) != s.TypeValue() {
return errInvalidExtensionType
}
groupCount := int(binary.BigEndian.Uint16(data[4:]) / 2)
if supportedGroupsHeaderSize+(groupCount*2) > len(data) {
return errLengthMismatch
}
for i := 0; i < groupCount; i++ {
supportedGroupID := elliptic.Curve(binary.BigEndian.Uint16(data[(supportedGroupsHeaderSize + (i * 2)):]))
if _, ok := elliptic.Curves()[supportedGroupID]; ok {
s.EllipticCurves = append(s.EllipticCurves, supportedGroupID)
}
}
return nil
}
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