49 lines
1.5 KiB
Go
49 lines
1.5 KiB
Go
// Copyright 2026 LiveKit, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package packettrailer
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var Magic = [4]byte{'L', 'K', 'T', 'S'}
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const (
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xorByte = 0xFF
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envelopeSize = 5 // 1B trailer_len + 4B magic
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)
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// StripTrailer returns the number of bytes to strip from the end of an RTP
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// payload if it contains an LKTS trailer. The trailer is located by checking
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// for the "LKTS" magic suffix and then reading the XORed trailer_len byte
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// immediately before it. isEndOfFrame must be set only for packets ending an
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// encoded frame, i. e. where a trailer could have been appended. Returns 0 if
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// absent or ineligible.
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func StripTrailer(payload []byte, isEndOfFrame bool) int {
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if !isEndOfFrame || len(payload) < envelopeSize {
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return 0
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}
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tail := payload[len(payload)-4:]
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if tail[0] != Magic[0] || tail[1] != Magic[1] ||
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tail[2] != Magic[2] || tail[3] != Magic[3] {
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return 0
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}
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trailerLen := int(payload[len(payload)-5] ^ xorByte)
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if trailerLen < envelopeSize || trailerLen > len(payload) {
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return 0
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}
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return trailerLen
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}
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