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// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
// SPDX-License-Identifier: MIT
package extension
import (
"golang.org/x/crypto/cryptobyte"
)
// ALPN is a TLS extension for application-layer protocol negotiation within
// the TLS handshake.
//
// https://tools.ietf.org/html/rfc7301
type ALPN struct {
ProtocolNameList []string
}
// TypeValue returns the extension TypeValue.
func (a ALPN) TypeValue() TypeValue {
return ALPNTypeValue
}
// Marshal encodes the extension.
func (a *ALPN) Marshal() ([]byte, error) {
var builder cryptobyte.Builder
builder.AddUint16(uint16(a.TypeValue()))
builder.AddUint16LengthPrefixed(func(b *cryptobyte.Builder) {
b.AddUint16LengthPrefixed(func(b *cryptobyte.Builder) {
for _, proto := range a.ProtocolNameList {
p := proto // Satisfy range scope lint
b.AddUint8LengthPrefixed(func(b *cryptobyte.Builder) {
b.AddBytes([]byte(p))
})
}
})
})
return builder.Bytes()
}
// Unmarshal populates the extension from encoded data.
func (a *ALPN) Unmarshal(data []byte) error {
val := cryptobyte.String(data)
var extension uint16
val.ReadUint16(&extension)
if TypeValue(extension) != a.TypeValue() {
return errInvalidExtensionType
}
var extData cryptobyte.String
val.ReadUint16LengthPrefixed(&extData)
var protoList cryptobyte.String
if !extData.ReadUint16LengthPrefixed(&protoList) || protoList.Empty() {
return ErrALPNInvalidFormat
}
for !protoList.Empty() {
var proto cryptobyte.String
if !protoList.ReadUint8LengthPrefixed(&proto) || proto.Empty() {
return ErrALPNInvalidFormat
}
a.ProtocolNameList = append(a.ProtocolNameList, string(proto))
}
return nil
}
// ALPNProtocolSelection negotiates a shared protocol according to #3.2 of rfc7301.
func ALPNProtocolSelection(supportedProtocols, peerSupportedProtocols []string) (string, error) {
if len(supportedProtocols) == 0 || len(peerSupportedProtocols) == 0 {
return "", nil
}
for _, s := range supportedProtocols {
for _, c := range peerSupportedProtocols {
if s == c {
return s, nil
}
}
}
return "", errALPNNoAppProto
}
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