http3: add support for parsing and writing HTTP/3 capsules (#3607)

http3/capsule_test.go

@@ -0,0 +1,57 @@
+package http3
+
+import (
+	"bytes"
+	"io"
+
+	"github.com/lucas-clemente/quic-go/quicvarint"
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Capsule", func() {
+	It("parses Capsules", func() {
+		var buf bytes.Buffer
+		quicvarint.Write(&buf, 1337)
+		quicvarint.Write(&buf, 6)
+		buf.WriteString("foobar")
+
+		ct, r, err := ParseCapsule(&buf)
+		Expect(err).ToNot(HaveOccurred())
+		Expect(ct).To(BeEquivalentTo(1337))
+		val, err := io.ReadAll(r)
+		Expect(err).ToNot(HaveOccurred())
+		Expect(string(val)).To(Equal("foobar"))
+	})
+
+	It("writes capsules", func() {
+		var buf bytes.Buffer
+		WriteCapsule(&buf, 1337, []byte("foobar"))
+
+		ct, r, err := ParseCapsule(&buf)
+		Expect(err).ToNot(HaveOccurred())
+		Expect(ct).To(BeEquivalentTo(1337))
+		val, err := io.ReadAll(r)
+		Expect(err).ToNot(HaveOccurred())
+		Expect(string(val)).To(Equal("foobar"))
+	})
+
+	It("errors on EOF", func() {
+		var buf bytes.Buffer
+		quicvarint.Write(&buf, 1337)
+		quicvarint.Write(&buf, 6)
+		buf.WriteString("foobar")
+		data := buf.Bytes()
+
+		for i := range data {
+			ct, r, err := ParseCapsule(bytes.NewReader(data[:i]))
+			if err != nil {
+				Expect(err).To(MatchError(io.ErrUnexpectedEOF))
+				continue
+			}
+			Expect(ct).To(BeEquivalentTo(1337))
+			_, err = io.ReadAll(r)
+			Expect(err).To(Equal(io.ErrUnexpectedEOF))
+		}
+	})
+})