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// Package extension implements the extension values in the ClientHello/ServerHello
package extension
import "encoding/binary"
// TypeValue is the 2 byte value for a TLS Extension as registered in the IANA
//
// https://www.iana.org/assignments/tls-extensiontype-values/tls-extensiontype-values.xhtml
type TypeValue uint16
// TypeValue constants
const (
ServerNameTypeValue TypeValue = 0
SupportedEllipticCurvesTypeValue TypeValue = 10
SupportedPointFormatsTypeValue TypeValue = 11
SupportedSignatureAlgorithmsTypeValue TypeValue = 13
UseSRTPTypeValue TypeValue = 14
UseExtendedMasterSecretTypeValue TypeValue = 23
RenegotiationInfoTypeValue TypeValue = 65281
)
// Extension represents a single TLS extension
type Extension interface {
Marshal() ([]byte, error)
Unmarshal(data []byte) error
TypeValue() TypeValue
}
// Unmarshal many extensions at once
func Unmarshal(buf []byte) ([]Extension, error) {
switch {
case len(buf) == 0:
return []Extension{}, nil
case len(buf) < 2:
return nil, errBufferTooSmall
}
declaredLen := binary.BigEndian.Uint16(buf)
if len(buf)-2 != int(declaredLen) {
return nil, errLengthMismatch
}
extensions := []Extension{}
unmarshalAndAppend := func(data []byte, e Extension) error {
err := e.Unmarshal(data)
if err != nil {
return err
}
extensions = append(extensions, e)
return nil
}
for offset := 2; offset < len(buf); {
if len(buf) < (offset + 2) {
return nil, errBufferTooSmall
}
var err error
switch TypeValue(binary.BigEndian.Uint16(buf[offset:])) {
case ServerNameTypeValue:
err = unmarshalAndAppend(buf[offset:], &ServerName{})
case SupportedEllipticCurvesTypeValue:
err = unmarshalAndAppend(buf[offset:], &SupportedEllipticCurves{})
case UseSRTPTypeValue:
err = unmarshalAndAppend(buf[offset:], &UseSRTP{})
case UseExtendedMasterSecretTypeValue:
err = unmarshalAndAppend(buf[offset:], &UseExtendedMasterSecret{})
case RenegotiationInfoTypeValue:
err = unmarshalAndAppend(buf[offset:], &RenegotiationInfo{})
default:
}
if err != nil {
return nil, err
}
if len(buf) < (offset + 4) {
return nil, errBufferTooSmall
}
extensionLength := binary.BigEndian.Uint16(buf[offset+2:])
offset += (4 + int(extensionLength))
}
return extensions, nil
}
// Marshal many extensions at once
func Marshal(e []Extension) ([]byte, error) {
extensions := []byte{}
for _, e := range e {
raw, err := e.Marshal()
if err != nil {
return nil, err
}
extensions = append(extensions, raw...)
}
out := []byte{0x00, 0x00}
binary.BigEndian.PutUint16(out, uint16(len(extensions)))
return append(out, extensions...), nil
}
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