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client_hello.go
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/
client_hello.go
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package quicsni
import (
"bytes"
"crypto"
"crypto/tls"
"errors"
"fmt"
"github.com/quic-go/quic-go/quicvarint"
"golang.org/x/crypto/hkdf"
"src.agwa.name/tlshacks"
)
// ReadClientHello parses the packet and return *tls.ClientHelloInfo if found.
func ReadClientHello(packet []byte) (*tls.ClientHelloInfo, error) {
hdr, offset, err := ParseInitialHeader(packet)
if err != nil {
return nil, err
}
initialSecret := hkdf.Extract(crypto.SHA256.New, hdr.DestConnectionID, getSalt(hdr.Version))
clientSecret := hkdfExpandLabel(crypto.SHA256.New, initialSecret, "client in", []byte{}, crypto.SHA256.Size())
key, err := NewInitialProtectionKey(clientSecret, hdr.Version)
if err != nil {
return nil, fmt.Errorf("NewInitialProtectionKey: %w", err)
}
pp := NewPacketProtector(key)
// https://datatracker.ietf.org/doc/html/draft-ietf-quic-tls-32#name-client-initial
//
// "The unprotected header includes the connection ID and a 4-byte packet number encoding for a packet number of 2"
unProtectedPayload, err := pp.UnProtect(packet[:offset+hdr.Length], offset, 2)
if err != nil {
return nil, err
}
cr, err := findCryptoFrame(bytes.NewReader(unProtectedPayload))
if err != nil {
return nil, err
}
ch := tlshacks.UnmarshalClientHello(cr.Data)
if ch != nil && ch.Info.ServerName != nil {
return &tls.ClientHelloInfo{ServerName: *ch.Info.ServerName}, nil
}
return nil, errors.New("no client hello found")
}
func findCryptoFrame(br *bytes.Reader) (*CryptoFrame, error) {
for br.Len() != 0 {
typ, err := quicvarint.Read(br)
if err != nil {
return nil, err
}
// Skip padding frames.
if typ == PaddingFrameType {
continue
}
if typ != CryptoFrameType {
return nil, errors.New("not CRYPTO FRAME")
}
return readCryptoFrame(br)
}
return nil, errors.New("no CRYPTO FRAME found")
}