tailscale/derp/derphttp/derphttp_server.go

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// Copyright (c) 2020 Tailscale Inc & 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 derphttp
import (
"fmt"
"log"
"net/http"
"strings"
"tailscale.com/derp"
)
// fastStartHeader is the header (with value "1") that signals to the HTTP
// server that the DERP HTTP client does not want the HTTP 101 response
// headers and it will begin writing & reading the DERP protocol immediately
// following its HTTP request.
const fastStartHeader = "Derp-Fast-Start"
func Handler(s *derp.Server) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
up := strings.ToLower(r.Header.Get("Upgrade"))
if up != "websocket" && up != "derp" {
if up != "" {
log.Printf("Weird upgrade: %q", up)
}
http.Error(w, "DERP requires connection upgrade", http.StatusUpgradeRequired)
return
}
fastStart := r.Header.Get(fastStartHeader) == "1"
h, ok := w.(http.Hijacker)
if !ok {
http.Error(w, "HTTP does not support general TCP support", 500)
return
}
netConn, conn, err := h.Hijack()
if err != nil {
log.Printf("Hijack failed: %v", err)
http.Error(w, "HTTP does not support general TCP support", 500)
return
}
if !fastStart {
pubKey := s.PublicKey()
fmt.Fprintf(conn, "HTTP/1.1 101 Switching Protocols\r\n"+
"Upgrade: DERP\r\n"+
"Connection: Upgrade\r\n"+
"Derp-Version: %v\r\n"+
"Derp-Public-Key: %s\r\n\r\n",
derp.ProtocolVersion,
pubKey.UntypedHexString())
}
s.Accept(netConn, conn, netConn.RemoteAddr().String())
})
}