expose a VersionNegoationError

internal/qerr/quic_error.go

@@ -2,6 +2,8 @@ package qerr
 
 import (
 	"fmt"
+
+	"github.com/lucas-clemente/quic-go/internal/protocol"
 )
 
 var (
@@ -92,3 +94,18 @@ func (e *HandshakeTimeoutError) Is(target error) bool {
 	_, ok := target.(*HandshakeTimeoutError)
 	return ok
 }
+
+// A VersionNegotiationError occurs when the client and the server can't agree on a QUIC version.
+type VersionNegotiationError struct {
+	Ours   []protocol.VersionNumber
+	Theirs []protocol.VersionNumber
+}
+
+func (e *VersionNegotiationError) Error() string {
+	return fmt.Sprintf("no compatible QUIC version found (we support %s, server offered %s)", e.Ours, e.Theirs)
+}
+
+func (e *VersionNegotiationError) Is(target error) bool {
+	_, ok := target.(*VersionNegotiationError)
+	return ok
+}

internal/qerr/quic_error_test.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"net"
 
+	"github.com/lucas-clemente/quic-go/internal/protocol"
 	. "github.com/onsi/ginkgo"
 	. "github.com/onsi/gomega"
 )
@@ -101,4 +102,17 @@ var _ = Describe("QUIC Errors", func() {
 			Expect(errors.Is(err, &IdleTimeoutError{})).To(BeTrue())
 		})
 	})
+
+	Context("Version Negotiation errors", func() {
+		It("is a Version Negotiation error", func() {
+			Expect(errors.Is(&VersionNegotiationError{Ours: []protocol.VersionNumber{2, 3}}, &VersionNegotiationError{})).To(BeTrue())
+		})
+
+		It("has a string representation", func() {
+			Expect((&VersionNegotiationError{
+				Ours:   []protocol.VersionNumber{2, 3},
+				Theirs: []protocol.VersionNumber{4, 5, 6},
+			}).Error()).To(Equal("no compatible QUIC version found (we support [0x2 0x3], server offered [0x4 0x5 0x6])"))
+		})
+	})
 })