http3: introduce an HTTP/3 error type (#4039)

* http3: introduce an HTTP/3 error type

* http3: use a pointer receiver for the Error

http3/error_test.go

@@ -0,0 +1,41 @@
+package http3
+
+import (
+	"errors"
+
+	"github.com/quic-go/quic-go"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("HTTP/3 errors", func() {
+	It("converts", func() {
+		Expect(maybeReplaceError(nil)).To(BeNil())
+		Expect(maybeReplaceError(errors.New("foobar"))).To(MatchError("foobar"))
+		Expect(maybeReplaceError(&quic.StreamError{
+			ErrorCode: 1337,
+			Remote:    true,
+		})).To(Equal(&Error{
+			Remote:    true,
+			ErrorCode: 1337,
+		}))
+		Expect(maybeReplaceError(&quic.ApplicationError{
+			ErrorCode:    42,
+			Remote:       true,
+			ErrorMessage: "foobar",
+		})).To(Equal(&Error{
+			Remote:       true,
+			ErrorCode:    42,
+			ErrorMessage: "foobar",
+		}))
+	})
+
+	It("has a string representation", func() {
+		Expect((&Error{ErrorCode: 0x10c, Remote: true}).Error()).To(Equal("H3_REQUEST_CANCELLED"))
+		Expect((&Error{ErrorCode: 0x10c, Remote: true, ErrorMessage: "foobar"}).Error()).To(Equal("H3_REQUEST_CANCELLED: foobar"))
+		Expect((&Error{ErrorCode: 0x10c, Remote: false}).Error()).To(Equal("H3_REQUEST_CANCELLED (local)"))
+		Expect((&Error{ErrorCode: 0x10c, Remote: false, ErrorMessage: "foobar"}).Error()).To(Equal("H3_REQUEST_CANCELLED (local): foobar"))
+		Expect((&Error{ErrorCode: 0x1337, Remote: true}).Error()).To(Equal("H3 error (0x1337)"))
+	})
+})