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package extension
import "encoding/binary"
const (
useSRTPHeaderSize = 6
)
// UseSRTP allows a Client/Server to negotiate what SRTPProtectionProfiles
// they both support
//
// https://tools.ietf.org/html/rfc8422
type UseSRTP struct {
ProtectionProfiles []SRTPProtectionProfile
}
// TypeValue returns the extension TypeValue
func (u UseSRTP) TypeValue() TypeValue {
return UseSRTPTypeValue
}
// Marshal encodes the extension
func (u *UseSRTP) Marshal() ([]byte, error) {
out := make([]byte, useSRTPHeaderSize)
binary.BigEndian.PutUint16(out, uint16(u.TypeValue()))
binary.BigEndian.PutUint16(out[2:], uint16(2+(len(u.ProtectionProfiles)*2)+ /* MKI Length */ 1))
binary.BigEndian.PutUint16(out[4:], uint16(len(u.ProtectionProfiles)*2))
for _, v := range u.ProtectionProfiles {
out = append(out, []byte{0x00, 0x00}...)
binary.BigEndian.PutUint16(out[len(out)-2:], uint16(v))
}
out = append(out, 0x00) /* MKI Length */
return out, nil
}
// Unmarshal populates the extension from encoded data
func (u *UseSRTP) Unmarshal(data []byte) error {
if len(data) <= useSRTPHeaderSize {
return errBufferTooSmall
} else if TypeValue(binary.BigEndian.Uint16(data)) != u.TypeValue() {
return errInvalidExtensionType
}
profileCount := int(binary.BigEndian.Uint16(data[4:]) / 2)
if supportedGroupsHeaderSize+(profileCount*2) > len(data) {
return errLengthMismatch
}
for i := 0; i < profileCount; i++ {
supportedProfile := SRTPProtectionProfile(binary.BigEndian.Uint16(data[(useSRTPHeaderSize + (i * 2)):]))
if _, ok := srtpProtectionProfiles()[supportedProfile]; ok {
u.ProtectionProfiles = append(u.ProtectionProfiles, supportedProfile)
}
}
return nil
}
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