internal/http3: add RoundTrip

Send request headers, receive response headers.

For golang/go#70914

Change-Id: I78d4dcc69c253ed7ad1543dfc3c5d8f1c321ced9
Reviewed-on: https://go-review.googlesource.com/c/net/+/644118
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Jonathan Amsterdam <[email protected]>
Auto-Submit: Damien Neil <[email protected]>

internal/http3/roundtrip.go

@@ -0,0 +1,226 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.24
+
+package http3
+
+import (
+	"io"
+	"net/http"
+	"strconv"
+
+	"golang.org/x/net/internal/httpcommon"
+)
+
+// RoundTrip sends a request on the connection.
+func (cc *ClientConn) RoundTrip(req *http.Request) (_ *http.Response, err error) {
+	// Each request gets its own QUIC stream.
+	st, err := newConnStream(req.Context(), cc.qconn, streamTypeRequest)
+	if err != nil {
+		return nil, err
+	}
+	defer func() {
+		switch e := err.(type) {
+		case nil:
+		case *connectionError:
+			cc.abort(e)
+		case *streamError:
+			st.stream.CloseRead()
+			st.stream.Reset(uint64(e.code))
+		default:
+			st.stream.CloseRead()
+			st.stream.Reset(uint64(errH3NoError))
+		}
+	}()
+
+	// Cancel reads/writes on the stream when the request expires.
+	st.stream.SetReadContext(req.Context())
+	st.stream.SetWriteContext(req.Context())
+
+	var encr httpcommon.EncodeHeadersResult
+	headers := cc.enc.encode(func(yield func(itype indexType, name, value string)) {
+		encr, err = httpcommon.EncodeHeaders(httpcommon.EncodeHeadersParam{
+			Request:               req,
+			AddGzipHeader:         false, // TODO: add when appropriate
+			PeerMaxHeaderListSize: 0,
+			DefaultUserAgent:      "Go-http-client/3",
+		}, func(name, value string) {
+			// Issue #71374: Consider supporting never-indexed fields.
+			yield(mayIndex, name, value)
+		})
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	// Write the HEADERS frame.
+	st.writeVarint(int64(frameTypeHeaders))
+	st.writeVarint(int64(len(headers)))
+	st.Write(headers)
+	if err := st.Flush(); err != nil {
+		return nil, err
+	}
+
+	if encr.HasBody {
+		// TODO: Send the request body.
+	}
+
+	// Read the response headers.
+	for {
+		ftype, err := st.readFrameHeader()
+		if err != nil {
+			return nil, err
+		}
+		switch ftype {
+		case frameTypeHeaders:
+			statusCode, h, err := cc.handleHeaders(st)
+			if err != nil {
+				return nil, err
+			}
+
+			if statusCode >= 100 && statusCode < 199 {
+				// TODO: Handle 1xx responses.
+				continue
+			}
+
+			// We have the response headers.
+			// Set up the response and return it to the caller.
+			contentLength, err := parseResponseContentLength(req.Method, statusCode, h)
+			if err != nil {
+				return nil, err
+			}
+			resp := &http.Response{
+				Proto:         "HTTP/3.0",
+				ProtoMajor:    3,
+				Header:        h,
+				StatusCode:    statusCode,
+				Status:        strconv.Itoa(statusCode) + " " + http.StatusText(statusCode),
+				ContentLength: contentLength,
+				Body:          io.NopCloser(nil), // TODO: read the response body
+			}
+			// TODO: Automatic Content-Type: gzip decoding.
+			return resp, nil
+		case frameTypePushPromise:
+			if err := cc.handlePushPromise(st); err != nil {
+				return nil, err
+			}
+		default:
+			if err := st.discardUnknownFrame(ftype); err != nil {
+				return nil, err
+			}
+		}
+	}
+}
+
+func parseResponseContentLength(method string, statusCode int, h http.Header) (int64, error) {
+	clens := h["Content-Length"]
+	if len(clens) == 0 {
+		return -1, nil
+	}
+
+	// We allow duplicate Content-Length headers,
+	// but only if they all have the same value.
+	for _, v := range clens[1:] {
+		if clens[0] != v {
+			return -1, &streamError{errH3MessageError, "mismatching Content-Length headers"}
+		}
+	}
+
+	// "A server MUST NOT send a Content-Length header field in any response
+	// with a status code of 1xx (Informational) or 204 (No Content).
+	// A server MUST NOT send a Content-Length header field in any 2xx (Successful)
+	// response to a CONNECT request [...]"
+	// https://www.rfc-editor.org/rfc/rfc9110#section-8.6-8
+	if (statusCode >= 100 && statusCode < 200) ||
+		statusCode == 204 ||
+		(method == "CONNECT" && statusCode >= 200 && statusCode < 300) {
+		// This is a protocol violation, but a fairly harmless one.
+		// Just ignore the header.
+		return -1, nil
+	}
+
+	contentLen, err := strconv.ParseUint(clens[0], 10, 63)
+	if err != nil {
+		return -1, &streamError{errH3MessageError, "invalid Content-Length header"}
+	}
+	return int64(contentLen), nil
+}
+
+func (cc *ClientConn) handleHeaders(st *stream) (statusCode int, h http.Header, err error) {
+	haveStatus := false
+	cookie := ""
+	// Issue #71374: Consider tracking the never-indexed status of headers
+	// with the N bit set in their QPACK encoding.
+	err = cc.dec.decode(st, func(_ indexType, name, value string) error {
+		switch {
+		case name == ":status":
+			if haveStatus {
+				return &streamError{errH3MessageError, "duplicate :status"}
+			}
+			haveStatus = true
+			statusCode, err = strconv.Atoi(value)
+			if err != nil {
+				return &streamError{errH3MessageError, "invalid :status"}
+			}
+		case name[0] == ':':
+			// "Endpoints MUST treat a request or response
+			// that contains undefined or invalid
+			// pseudo-header fields as malformed."
+			// https://www.rfc-editor.org/rfc/rfc9114.html#section-4.3-3
+			return &streamError{errH3MessageError, "undefined pseudo-header"}
+		case name == "cookie":
+			// "If a decompressed field section contains multiple cookie field lines,
+			// these MUST be concatenated into a single byte string [...]"
+			// using the two-byte delimiter of "; "''
+			// https://www.rfc-editor.org/rfc/rfc9114.html#section-4.2.1-2
+			if cookie == "" {
+				cookie = value
+			} else {
+				cookie += "; " + value
+			}
+		default:
+			if h == nil {
+				h = make(http.Header)
+			}
+			// TODO: Use a per-connection canonicalization cache as we do in HTTP/2.
+			// Maybe we could put this in the QPACK decoder and have it deliver
+			// pre-canonicalized headers to us here?
+			cname := httpcommon.CanonicalHeader(name)
+			// TODO: Consider using a single []string slice for all headers,
+			// as we do in the HTTP/1 and HTTP/2 cases.
+			// This is a bit tricky, since we don't know the number of headers
+			// at the start of decoding. Perhaps it's worth doing a two-pass decode,
+			// or perhaps we should just allocate header value slices in
+			// reasonably-sized chunks.
+			h[cname] = append(h[cname], value)
+		}
+		return nil
+	})
+	if !haveStatus {
+		// "[The :status] pseudo-header field MUST be included in all responses [...]"
+		// https://www.rfc-editor.org/rfc/rfc9114.html#section-4.3.2-1
+		err = errH3MessageError
+	}
+	if cookie != "" {
+		if h == nil {
+			h = make(http.Header)
+		}
+		h["Cookie"] = []string{cookie}
+	}
+	if err := st.endFrame(); err != nil {
+		return 0, nil, err
+	}
+	return statusCode, h, err
+}
+
+func (cc *ClientConn) handlePushPromise(st *stream) error {
+	// "A client MUST treat receipt of a PUSH_PROMISE frame that contains a
+	// larger push ID than the client has advertised as a connection error of H3_ID_ERROR."
+	// https://www.rfc-editor.org/rfc/rfc9114.html#section-7.2.5-5
+	return &connectionError{
+		code:    errH3IDError,
+		message: "PUSH_PROMISE received when no MAX_PUSH_ID has been sent",
+	}
+}