dep: qtls now points to utls in all cases

Since uTLS essentially is a fork of the latest crypto/tls, it would work for any Go version if no compilation error.

internal/qtls/cipher_suite.go

@@ -0,0 +1,65 @@
+package qtls
+
+import (
+	"crypto"
+	"crypto/cipher"
+	"fmt"
+	"unsafe"
+
+	tls "github.com/refraction-networking/utls"
+)
+
+type cipherSuiteTLS13 struct {
+	ID     uint16
+	KeyLen int
+	AEAD   func(key, fixedNonce []byte) cipher.AEAD
+	Hash   crypto.Hash
+}
+
+//go:linkname cipherSuiteTLS13ByID crypto/tls.cipherSuiteTLS13ByID
+func cipherSuiteTLS13ByID(id uint16) *cipherSuiteTLS13
+
+//go:linkname cipherSuitesTLS13 crypto/tls.cipherSuitesTLS13
+var cipherSuitesTLS13 []unsafe.Pointer
+
+//go:linkname defaultCipherSuitesTLS13 crypto/tls.defaultCipherSuitesTLS13
+var defaultCipherSuitesTLS13 []uint16
+
+//go:linkname defaultCipherSuitesTLS13NoAES crypto/tls.defaultCipherSuitesTLS13NoAES
+var defaultCipherSuitesTLS13NoAES []uint16
+
+var cipherSuitesModified bool
+
+// SetCipherSuite modifies the cipherSuiteTLS13 slice of cipher suites inside qtls
+// such that it only contains the cipher suite with the chosen id.
+// The reset function returned resets them back to the original value.
+func SetCipherSuite(id uint16) (reset func()) {
+	if cipherSuitesModified {
+		panic("cipher suites modified multiple times without resetting")
+	}
+	cipherSuitesModified = true
+
+	origCipherSuitesTLS13 := append([]unsafe.Pointer{}, cipherSuitesTLS13...)
+	origDefaultCipherSuitesTLS13 := append([]uint16{}, defaultCipherSuitesTLS13...)
+	origDefaultCipherSuitesTLS13NoAES := append([]uint16{}, defaultCipherSuitesTLS13NoAES...)
+	// The order is given by the order of the slice elements in cipherSuitesTLS13 in qtls.
+	switch id {
+	case tls.TLS_AES_128_GCM_SHA256:
+		cipherSuitesTLS13 = cipherSuitesTLS13[:1]
+	case tls.TLS_CHACHA20_POLY1305_SHA256:
+		cipherSuitesTLS13 = cipherSuitesTLS13[1:2]
+	case tls.TLS_AES_256_GCM_SHA384:
+		cipherSuitesTLS13 = cipherSuitesTLS13[2:]
+	default:
+		panic(fmt.Sprintf("unexpected cipher suite: %d", id))
+	}
+	defaultCipherSuitesTLS13 = []uint16{id}
+	defaultCipherSuitesTLS13NoAES = []uint16{id}
+
+	return func() {
+		cipherSuitesTLS13 = origCipherSuitesTLS13
+		defaultCipherSuitesTLS13 = origDefaultCipherSuitesTLS13
+		defaultCipherSuitesTLS13NoAES = origDefaultCipherSuitesTLS13NoAES
+		cipherSuitesModified = false
+	}
+}