add a http3.HTTPStreamer, allowing users to take over the HTTP/3 stream

integrationtests/self/http_test.go

@@ -311,6 +311,41 @@ var _ = Describe("HTTP tests", func() {
 				Expect(req.Body.Close()).To(Succeed())
 				Eventually(done).Should(BeClosed())
 			})
+
+			It("allows taking over the stream", func() {
+				mux.HandleFunc("/httpstreamer", func(w http.ResponseWriter, r *http.Request) {
+					defer GinkgoRecover()
+					w.WriteHeader(200)
+					w.(http.Flusher).Flush()
+
+					str := r.Body.(http3.HTTPStreamer).HTTPStream()
+					str.Write([]byte("foobar"))
+
+					_, err := io.Copy(str, str)
+					Expect(err).ToNot(HaveOccurred())
+					Expect(str.Close()).To(Succeed())
+				})
+
+				req, err := http.NewRequest(http.MethodGet, "https://localhost:"+port+"/httpstreamer", nil)
+				Expect(err).ToNot(HaveOccurred())
+				rsp, err := client.Transport.(*http3.RoundTripper).RoundTripOpt(req, http3.RoundTripOpt{DontCloseRequestStream: true})
+				Expect(err).ToNot(HaveOccurred())
+				Expect(rsp.StatusCode).To(Equal(200))
+
+				str := rsp.Body.(http3.HTTPStreamer).HTTPStream()
+				b := make([]byte, 6)
+				_, err = io.ReadFull(str, b)
+				Expect(err).ToNot(HaveOccurred())
+				Expect(b).To(Equal([]byte("foobar")))
+
+				data := GeneratePRData(8 * 1024)
+				_, err = str.Write(data)
+				Expect(err).ToNot(HaveOccurred())
+				Expect(str.Close()).To(Succeed())
+				repl, err := io.ReadAll(str)
+				Expect(err).ToNot(HaveOccurred())
+				Expect(repl).To(Equal(data))
+			})
 		})
 	}
 })