drop support for Go 1.20, build on Go 1.22rc1 on CI (#4195)

* drop support for Go 1.20

* ci: udpate CircleCI to Go 1.21

* qtls: remove unnecessary type aliases

* ci: build using Go 1.22rc1

internal/qtls/qtls_test.go

@@ -0,0 +1,53 @@
+package qtls
+
+import (
+	"crypto/tls"
+
+	"github.com/quic-go/quic-go/internal/protocol"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Go 1.21", func() {
+	It("converts to tls.EncryptionLevel", func() {
+		Expect(ToTLSEncryptionLevel(protocol.EncryptionInitial)).To(Equal(tls.QUICEncryptionLevelInitial))
+		Expect(ToTLSEncryptionLevel(protocol.EncryptionHandshake)).To(Equal(tls.QUICEncryptionLevelHandshake))
+		Expect(ToTLSEncryptionLevel(protocol.Encryption1RTT)).To(Equal(tls.QUICEncryptionLevelApplication))
+		Expect(ToTLSEncryptionLevel(protocol.Encryption0RTT)).To(Equal(tls.QUICEncryptionLevelEarly))
+	})
+
+	It("converts from tls.EncryptionLevel", func() {
+		Expect(FromTLSEncryptionLevel(tls.QUICEncryptionLevelInitial)).To(Equal(protocol.EncryptionInitial))
+		Expect(FromTLSEncryptionLevel(tls.QUICEncryptionLevelHandshake)).To(Equal(protocol.EncryptionHandshake))
+		Expect(FromTLSEncryptionLevel(tls.QUICEncryptionLevelApplication)).To(Equal(protocol.Encryption1RTT))
+		Expect(FromTLSEncryptionLevel(tls.QUICEncryptionLevelEarly)).To(Equal(protocol.Encryption0RTT))
+	})
+
+	Context("setting up a tls.Config for the client", func() {
+		It("sets up a session cache if there's one present on the config", func() {
+			csc := tls.NewLRUClientSessionCache(1)
+			conf := &tls.QUICConfig{TLSConfig: &tls.Config{ClientSessionCache: csc}}
+			SetupConfigForClient(conf, nil, nil)
+			Expect(conf.TLSConfig.ClientSessionCache).ToNot(BeNil())
+			Expect(conf.TLSConfig.ClientSessionCache).ToNot(Equal(csc))
+		})
+
+		It("doesn't set up a session cache if there's none present on the config", func() {
+			conf := &tls.QUICConfig{TLSConfig: &tls.Config{}}
+			SetupConfigForClient(conf, nil, nil)
+			Expect(conf.TLSConfig.ClientSessionCache).To(BeNil())
+		})
+	})
+
+	Context("setting up a tls.Config for the server", func() {
+		It("sets the minimum TLS version to TLS 1.3", func() {
+			orig := &tls.Config{MinVersion: tls.VersionTLS12}
+			conf := &tls.QUICConfig{TLSConfig: orig}
+			SetupConfigForServer(conf, false, nil, nil)
+			Expect(conf.TLSConfig.MinVersion).To(BeEquivalentTo(tls.VersionTLS13))
+			// check that the original config wasn't modified
+			Expect(orig.MinVersion).To(BeEquivalentTo(tls.VersionTLS12))
+		})
+	})
+})