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// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
// SPDX-License-Identifier: MIT
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
MasterKeyIdentifier []byte
}
// 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()))
//nolint:gosec // G115
binary.BigEndian.PutUint16(
out[2:],
uint16(2+(len(u.ProtectionProfiles)*2)+ /* MKI Length */ 1+len(u.MasterKeyIdentifier)),
)
binary.BigEndian.PutUint16(out[4:], uint16(len(u.ProtectionProfiles)*2)) //nolint:gosec // G115
for _, v := range u.ProtectionProfiles {
out = append(out, []byte{0x00, 0x00}...) //nolint:makezero // todo: fix
binary.BigEndian.PutUint16(out[len(out)-2:], uint16(v))
}
if len(u.MasterKeyIdentifier) > 255 {
return nil, errMasterKeyIdentifierTooLarge
}
out = append(out, byte(len(u.MasterKeyIdentifier))) //nolint:makezero // todo: fix
out = append(out, u.MasterKeyIdentifier...) //nolint:makezero // todo: fix
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)
masterKeyIdentifierIndex := supportedGroupsHeaderSize + (profileCount * 2)
if masterKeyIdentifierIndex+1 > 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)
}
}
masterKeyIdentifierLen := int(data[masterKeyIdentifierIndex])
if masterKeyIdentifierIndex+masterKeyIdentifierLen >= len(data) {
return errLengthMismatch
}
u.MasterKeyIdentifier = append(
[]byte{},
data[masterKeyIdentifierIndex+1:masterKeyIdentifierIndex+1+masterKeyIdentifierLen]...,
)
return nil
}
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