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// Copyright 2018 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.
// Package h2c implements the unencrypted "h2c" form of HTTP/2.
//
// The h2c protocol is the non-TLS version of HTTP/2 which is not available from
// net/http or golang.org/x/net/http2.
package h2c
import (
"bufio"
"bytes"
"encoding/base64"
"encoding/binary"
"errors"
"fmt"
"io"
"log"
"net"
"net/http"
"net/textproto"
"os"
"strings"
"golang.org/x/net/http/httpguts"
"golang.org/x/net/http2"
"golang.org/x/net/http2/hpack"
)
var (
http2VerboseLogs bool
)
func init() {
e := os.Getenv("GODEBUG")
if strings.Contains(e, "http2debug=1") || strings.Contains(e, "http2debug=2") {
http2VerboseLogs = true
}
}
// h2cHandler is a Handler which implements h2c by hijacking the HTTP/1 traffic
// that should be h2c traffic. There are two ways to begin a h2c connection
// (RFC 7540 Section 3.2 and 3.4): (1) Starting with Prior Knowledge - this
// works by starting an h2c connection with a string of bytes that is valid
// HTTP/1, but unlikely to occur in practice and (2) Upgrading from HTTP/1 to
// h2c - this works by using the HTTP/1 Upgrade header to request an upgrade to
// h2c. When either of those situations occur we hijack the HTTP/1 connection,
// convert it to a HTTP/2 connection and pass the net.Conn to http2.ServeConn.
type h2cHandler struct {
Handler http.Handler
s *http2.Server
}
// NewHandler returns an http.Handler that wraps h, intercepting any h2c
// traffic. If a request is an h2c connection, it's hijacked and redirected to
// s.ServeConn. Otherwise the returned Handler just forwards requests to h. This
// works because h2c is designed to be parseable as valid HTTP/1, but ignored by
// any HTTP server that does not handle h2c. Therefore we leverage the HTTP/1
// compatible parts of the Go http library to parse and recognize h2c requests.
// Once a request is recognized as h2c, we hijack the connection and convert it
// to an HTTP/2 connection which is understandable to s.ServeConn. (s.ServeConn
// understands HTTP/2 except for the h2c part of it.)
func NewHandler(h http.Handler, s *http2.Server) http.Handler {
return &h2cHandler{
Handler: h,
s: s,
}
}
// ServeHTTP implement the h2c support that is enabled by h2c.GetH2CHandler.
func (s h2cHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// Handle h2c with prior knowledge (RFC 7540 Section 3.4)
if r.Method == "PRI" && len(r.Header) == 0 && r.URL.Path == "*" && r.Proto == "HTTP/2.0" {
if http2VerboseLogs {
log.Print("h2c: attempting h2c with prior knowledge.")
}
conn, err := initH2CWithPriorKnowledge(w)
if err != nil {
if http2VerboseLogs {
log.Printf("h2c: error h2c with prior knowledge: %v", err)
}
return
}
defer conn.Close()
s.s.ServeConn(conn, &http2.ServeConnOpts{Handler: s.Handler})
return
}
// Handle Upgrade to h2c (RFC 7540 Section 3.2)
if conn, err := h2cUpgrade(w, r); err == nil {
defer conn.Close()
s.s.ServeConn(conn, &http2.ServeConnOpts{Handler: s.Handler})
return
}
s.Handler.ServeHTTP(w, r)
return
}
// initH2CWithPriorKnowledge implements creating a h2c connection with prior
// knowledge (Section 3.4) and creates a net.Conn suitable for http2.ServeConn.
// All we have to do is look for the client preface that is suppose to be part
// of the body, and reforward the client preface on the net.Conn this function
// creates.
func initH2CWithPriorKnowledge(w http.ResponseWriter) (net.Conn, error) {
hijacker, ok := w.(http.Hijacker)
if !ok {
panic("Hijack not supported.")
}
conn, rw, err := hijacker.Hijack()
if err != nil {
panic(fmt.Sprintf("Hijack failed: %v", err))
}
const expectedBody = "SM\r\n\r\n"
buf := make([]byte, len(expectedBody))
n, err := io.ReadFull(rw, buf)
if string(buf[:n]) == expectedBody {
c := &rwConn{
Conn: conn,
Reader: io.MultiReader(strings.NewReader(http2.ClientPreface), rw),
BufWriter: rw.Writer,
}
return c, nil
}
conn.Close()
if http2VerboseLogs {
log.Printf(
"h2c: missing the request body portion of the client preface. Wanted: %v Got: %v",
[]byte(expectedBody),
buf[0:n],
)
}
return nil, errors.New("invalid client preface")
}
// drainClientPreface reads a single instance of the HTTP/2 client preface from
// the supplied reader.
func drainClientPreface(r io.Reader) error {
var buf bytes.Buffer
prefaceLen := int64(len(http2.ClientPreface))
n, err := io.CopyN(&buf, r, prefaceLen)
if err != nil {
return err
}
if n != prefaceLen || buf.String() != http2.ClientPreface {
return fmt.Errorf("Client never sent: %s", http2.ClientPreface)
}
return nil
}
// h2cUpgrade establishes a h2c connection using the HTTP/1 upgrade (Section 3.2).
func h2cUpgrade(w http.ResponseWriter, r *http.Request) (net.Conn, error) {
if !isH2CUpgrade(r.Header) {
return nil, errors.New("non-conforming h2c headers")
}
// Initial bytes we put into conn to fool http2 server
initBytes, _, err := convertH1ReqToH2(r)
if err != nil {
return nil, err
}
hijacker, ok := w.(http.Hijacker)
if !ok {
return nil, errors.New("hijack not supported.")
}
conn, rw, err := hijacker.Hijack()
if err != nil {
return nil, fmt.Errorf("hijack failed: %v", err)
}
rw.Write([]byte("HTTP/1.1 101 Switching Protocols\r\n" +
"Connection: Upgrade\r\n" +
"Upgrade: h2c\r\n\r\n"))
rw.Flush()
// A conforming client will now send an H2 client preface which need to drain
// since we already sent this.
if err := drainClientPreface(rw); err != nil {
return nil, err
}
c := &rwConn{
Conn: conn,
Reader: io.MultiReader(initBytes, rw),
BufWriter: newSettingsAckSwallowWriter(rw.Writer),
}
return c, nil
}
// convert the data contained in the HTTP/1 upgrade request into the HTTP/2
// version in byte form.
func convertH1ReqToH2(r *http.Request) (*bytes.Buffer, []http2.Setting, error) {
h2Bytes := bytes.NewBuffer([]byte((http2.ClientPreface)))
framer := http2.NewFramer(h2Bytes, nil)
settings, err := getH2Settings(r.Header)
if err != nil {
return nil, nil, err
}
if err := framer.WriteSettings(settings...); err != nil {
return nil, nil, err
}
headerBytes, err := getH2HeaderBytes(r, getMaxHeaderTableSize(settings))
if err != nil {
return nil, nil, err
}
maxFrameSize := int(getMaxFrameSize(settings))
needOneHeader := len(headerBytes) < maxFrameSize
err = framer.WriteHeaders(http2.HeadersFrameParam{
StreamID: 1,
BlockFragment: headerBytes,
EndHeaders: needOneHeader,
})
if err != nil {
return nil, nil, err
}
for i := maxFrameSize; i < len(headerBytes); i += maxFrameSize {
if len(headerBytes)-i > maxFrameSize {
if err := framer.WriteContinuation(1,
false, // endHeaders
headerBytes[i:maxFrameSize]); err != nil {
return nil, nil, err
}
} else {
if err := framer.WriteContinuation(1,
true, // endHeaders
headerBytes[i:]); err != nil {
return nil, nil, err
}
}
}
return h2Bytes, settings, nil
}
// getMaxFrameSize returns the SETTINGS_MAX_FRAME_SIZE. If not present default
// value is 16384 as specified by RFC 7540 Section 6.5.2.
func getMaxFrameSize(settings []http2.Setting) uint32 {
for _, setting := range settings {
if setting.ID == http2.SettingMaxFrameSize {
return setting.Val
}
}
return 16384
}
// getMaxHeaderTableSize returns the SETTINGS_HEADER_TABLE_SIZE. If not present
// default value is 4096 as specified by RFC 7540 Section 6.5.2.
func getMaxHeaderTableSize(settings []http2.Setting) uint32 {
for _, setting := range settings {
if setting.ID == http2.SettingHeaderTableSize {
return setting.Val
}
}
return 4096
}
// bufWriter is a Writer interface that also has a Flush method.
type bufWriter interface {
io.Writer
Flush() error
}
// rwConn implements net.Conn but overrides Read and Write so that reads and
// writes are forwarded to the provided io.Reader and bufWriter.
type rwConn struct {
net.Conn
io.Reader
BufWriter bufWriter
}
// Read forwards reads to the underlying Reader.
func (c *rwConn) Read(p []byte) (int, error) {
return c.Reader.Read(p)
}
// Write forwards writes to the underlying bufWriter and immediately flushes.
func (c *rwConn) Write(p []byte) (int, error) {
n, err := c.BufWriter.Write(p)
if err := c.BufWriter.Flush(); err != nil {
return 0, err
}
return n, err
}
// settingsAckSwallowWriter is a writer that normally forwards bytes to it's
// underlying Writer, but swallows the first SettingsAck frame that it sees.
type settingsAckSwallowWriter struct {
Writer *bufio.Writer
buf []byte
didSwallow bool
}
// newSettingsAckSwallowWriter returns a new settingsAckSwallowWriter.
func newSettingsAckSwallowWriter(w *bufio.Writer) *settingsAckSwallowWriter {
return &settingsAckSwallowWriter{
Writer: w,
buf: make([]byte, 0),
didSwallow: false,
}
}
// Write implements io.Writer interface. Normally forwards bytes to w.Writer,
// except for the first Settings ACK frame that it sees.
func (w *settingsAckSwallowWriter) Write(p []byte) (int, error) {
if !w.didSwallow {
w.buf = append(w.buf, p...)
// Process all the frames we have collected into w.buf
for {
// Append until we get full frame header which is 9 bytes
if len(w.buf) < 9 {
break
}
// Check if we have collected a whole frame.
fh, err := http2.ReadFrameHeader(bytes.NewBuffer(w.buf))
if err != nil {
// Corrupted frame, fail current Write
return 0, err
}
fSize := fh.Length + 9
if uint32(len(w.buf)) < fSize {
// Have not collected whole frame. Stop processing buf, and withold on
// forward bytes to w.Writer until we get the full frame.
break
}
// We have now collected a whole frame.
if fh.Type == http2.FrameSettings && fh.Flags.Has(http2.FlagSettingsAck) {
// If Settings ACK frame, do not forward to underlying writer, remove
// bytes from w.buf, and record that we have swallowed Settings Ack
// frame.
w.didSwallow = true
w.buf = w.buf[fSize:]
continue
}
// Not settings ack frame. Forward bytes to w.Writer.
if _, err := w.Writer.Write(w.buf[:fSize]); err != nil {
// Couldn't forward bytes. Fail current Write.
return 0, err
}
w.buf = w.buf[fSize:]
}
return len(p), nil
}
return w.Writer.Write(p)
}
// Flush calls w.Writer.Flush.
func (w *settingsAckSwallowWriter) Flush() error {
return w.Writer.Flush()
}
// isH2CUpgrade returns true if the header properly request an upgrade to h2c
// as specified by Section 3.2.
func isH2CUpgrade(h http.Header) bool {
return httpguts.HeaderValuesContainsToken(h[textproto.CanonicalMIMEHeaderKey("Upgrade")], "h2c") &&
httpguts.HeaderValuesContainsToken(h[textproto.CanonicalMIMEHeaderKey("Connection")], "HTTP2-Settings")
}
// getH2Settings returns the []http2.Setting that are encoded in the
// HTTP2-Settings header.
func getH2Settings(h http.Header) ([]http2.Setting, error) {
vals, ok := h[textproto.CanonicalMIMEHeaderKey("HTTP2-Settings")]
if !ok {
return nil, errors.New("missing HTTP2-Settings header")
}
if len(vals) != 1 {
return nil, fmt.Errorf("expected 1 HTTP2-Settings. Got: %v", vals)
}
settings, err := decodeSettings(vals[0])
if err != nil {
return nil, fmt.Errorf("Invalid HTTP2-Settings: %q", vals[0])
}
return settings, nil
}
// decodeSettings decodes the base64url header value of the HTTP2-Settings
// header. RFC 7540 Section 3.2.1.
func decodeSettings(headerVal string) ([]http2.Setting, error) {
b, err := base64.RawURLEncoding.DecodeString(headerVal)
if err != nil {
return nil, err
}
if len(b)%6 != 0 {
return nil, err
}
settings := make([]http2.Setting, 0)
for i := 0; i < len(b)/6; i++ {
settings = append(settings, http2.Setting{
ID: http2.SettingID(binary.BigEndian.Uint16(b[i*6 : i*6+2])),
Val: binary.BigEndian.Uint32(b[i*6+2 : i*6+6]),
})
}
return settings, nil
}
// getH2HeaderBytes return the headers in r a []bytes encoded by HPACK.
func getH2HeaderBytes(r *http.Request, maxHeaderTableSize uint32) ([]byte, error) {
headerBytes := bytes.NewBuffer(nil)
hpackEnc := hpack.NewEncoder(headerBytes)
hpackEnc.SetMaxDynamicTableSize(maxHeaderTableSize)
// Section 8.1.2.3
err := hpackEnc.WriteField(hpack.HeaderField{
Name: ":method",
Value: r.Method,
})
if err != nil {
return nil, err
}
err = hpackEnc.WriteField(hpack.HeaderField{
Name: ":scheme",
Value: "http",
})
if err != nil {
return nil, err
}
err = hpackEnc.WriteField(hpack.HeaderField{
Name: ":authority",
Value: r.Host,
})
if err != nil {
return nil, err
}
path := r.URL.Path
if r.URL.RawQuery != "" {
path = strings.Join([]string{path, r.URL.RawQuery}, "?")
}
err = hpackEnc.WriteField(hpack.HeaderField{
Name: ":path",
Value: path,
})
if err != nil {
return nil, err
}
// TODO Implement Section 8.3
for header, values := range r.Header {
// Skip non h2 headers
if isNonH2Header(header) {
continue
}
for _, v := range values {
err := hpackEnc.WriteField(hpack.HeaderField{
Name: strings.ToLower(header),
Value: v,
})
if err != nil {
return nil, err
}
}
}
return headerBytes.Bytes(), nil
}
// Connection specific headers listed in RFC 7540 Section 8.1.2.2 that are not
// suppose to be transferred to HTTP/2. The Http2-Settings header is skipped
// since already use to create the HTTP/2 SETTINGS frame.
var nonH2Headers = []string{
"Connection",
"Keep-Alive",
"Proxy-Connection",
"Transfer-Encoding",
"Upgrade",
"Http2-Settings",
}
// isNonH2Header returns true if header should not be transferred to HTTP/2.
func isNonH2Header(header string) bool {
for _, nonH2h := range nonH2Headers {
if header == nonH2h {
return true
}
}
return false
}