gtsocial-umbx

h2c.go (7201B)

---

 // 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"
 	"errors"
 	"fmt"
 	"io"
 	"log"
 	"net"
 	"net/http"
 	"net/textproto"
 	"os"
 	"strings"
 
 	"golang.org/x/net/http/httpguts"
 	"golang.org/x/net/http2"
 )
 
 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 an 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.)
 //
 // The first request on an h2c connection is read entirely into memory before
 // the Handler is called. To limit the memory consumed by this request, wrap
 // the result of NewHandler in an http.MaxBytesHandler.
 func NewHandler(h http.Handler, s *http2.Server) http.Handler {
 	return &h2cHandler{
 		Handler: h,
 		s:       s,
 	}
 }
 
 // extractServer extracts existing http.Server instance from http.Request or create an empty http.Server
 func extractServer(r *http.Request) *http.Server {
 	server, ok := r.Context().Value(http.ServerContextKey).(*http.Server)
 	if ok {
 		return server
 	}
 	return new(http.Server)
 }
 
 // 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{
 			Context:          r.Context(),
 			BaseConfig:       extractServer(r),
 			Handler:          s.Handler,
 			SawClientPreface: true,
 		})
 		return
 	}
 	// Handle Upgrade to h2c (RFC 7540 Section 3.2)
 	if isH2CUpgrade(r.Header) {
 		conn, settings, err := h2cUpgrade(w, r)
 		if err != nil {
 			if http2VerboseLogs {
 				log.Printf("h2c: error h2c upgrade: %v", err)
 			}
 			w.WriteHeader(http.StatusInternalServerError)
 			return
 		}
 		defer conn.Close()
 		s.s.ServeConn(conn, &http2.ServeConnOpts{
 			Context:        r.Context(),
 			BaseConfig:     extractServer(r),
 			Handler:        s.Handler,
 			UpgradeRequest: r,
 			Settings:       settings,
 		})
 		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 {
 		return nil, errors.New("h2c: connection does not support Hijack")
 	}
 	conn, rw, err := hijacker.Hijack()
 	if err != nil {
 		return nil, err
 	}
 
 	const expectedBody = "SM\r\n\r\n"
 
 	buf := make([]byte, len(expectedBody))
 	n, err := io.ReadFull(rw, buf)
 	if err != nil {
 		return nil, fmt.Errorf("h2c: error reading client preface: %s", err)
 	}
 
 	if string(buf[:n]) == expectedBody {
 		return newBufConn(conn, rw), nil
 	}
 
 	conn.Close()
 	return nil, errors.New("h2c: invalid client preface")
 }
 
 // h2cUpgrade establishes a h2c connection using the HTTP/1 upgrade (Section 3.2).
 func h2cUpgrade(w http.ResponseWriter, r *http.Request) (_ net.Conn, settings []byte, err error) {
 	settings, err = getH2Settings(r.Header)
 	if err != nil {
 		return nil, nil, err
 	}
 	hijacker, ok := w.(http.Hijacker)
 	if !ok {
 		return nil, nil, errors.New("h2c: connection does not support Hijack")
 	}
 
 	body, err := io.ReadAll(r.Body)
 	if err != nil {
 		return nil, nil, err
 	}
 	r.Body = io.NopCloser(bytes.NewBuffer(body))
 
 	conn, rw, err := hijacker.Hijack()
 	if err != nil {
 		return nil, nil, err
 	}
 
 	rw.Write([]byte("HTTP/1.1 101 Switching Protocols\r\n" +
 		"Connection: Upgrade\r\n" +
 		"Upgrade: h2c\r\n\r\n"))
 	return newBufConn(conn, rw), settings, nil
 }
 
 // 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 settings in the HTTP2-Settings header.
 func getH2Settings(h http.Header) ([]byte, 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 := base64.RawURLEncoding.DecodeString(vals[0])
 	if err != nil {
 		return nil, err
 	}
 	return settings, nil
 }
 
 func newBufConn(conn net.Conn, rw *bufio.ReadWriter) net.Conn {
 	rw.Flush()
 	if rw.Reader.Buffered() == 0 {
 		// If there's no buffered data to be read,
 		// we can just discard the bufio.ReadWriter.
 		return conn
 	}
 	return &bufConn{conn, rw.Reader}
 }
 
 // bufConn wraps a net.Conn, but reads drain the bufio.Reader first.
 type bufConn struct {
 	net.Conn
 	*bufio.Reader
 }
 
 func (c *bufConn) Read(p []byte) (int, error) {
 	if c.Reader == nil {
 		return c.Conn.Read(p)
 	}
 	n := c.Reader.Buffered()
 	if n == 0 {
 		c.Reader = nil
 		return c.Conn.Read(p)
 	}
 	if n < len(p) {
 		p = p[:n]
 	}
 	return c.Reader.Read(p)
 }