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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 tshttpproxy
import (
"context"
"encoding/base64"
"fmt"
"log"
"net/http"
"net/url"
"runtime"
"strings"
"sync"
"syscall"
"time"
"unsafe"
"github.com/alexbrainman/sspi/negotiate"
"golang.org/x/sys/windows"
"tailscale.com/types/logger"
)
var (
winHTTP = windows.NewLazySystemDLL("winhttp.dll")
httpOpenProc = winHTTP.NewProc("WinHttpOpen")
closeHandleProc = winHTTP.NewProc("WinHttpCloseHandle")
getProxyForUrlProc = winHTTP.NewProc("WinHttpGetProxyForUrl")
)
func init() {
sysProxyFromEnv = proxyFromWinHTTPOrCache
sysAuthHeader = sysAuthHeaderWindows
}
var cachedProxy struct {
sync.Mutex
val *url.URL
}
// proxyErrorf is a rate-limited logger specifically for errors asking
// WinHTTP for the proxy information. We don't want to log about
// errors often, otherwise the log message itself will generate a new
// HTTP request which ultimately will call back into us to log again,
// forever. So for errors, we only log a bit.
var proxyErrorf = logger.RateLimitedFn(log.Printf, 10*time.Minute, 2 /* burst*/, 10 /* maxCache */)
func proxyFromWinHTTPOrCache(req *http.Request) (*url.URL, error) {
if req.URL == nil {
return nil, nil
}
urlStr := req.URL.String()
ctx, cancel := context.WithTimeout(req.Context(), 5*time.Second)
defer cancel()
type result struct {
proxy *url.URL
err error
}
resc := make(chan result, 1)
go func() {
proxy, err := proxyFromWinHTTP(ctx, urlStr)
resc <- result{proxy, err}
}()
select {
case res := <-resc:
err := res.err
if err == nil {
cachedProxy.Lock()
defer cachedProxy.Unlock()
if was, now := fmt.Sprint(cachedProxy.val), fmt.Sprint(res.proxy); was != now {
log.Printf("tshttpproxy: winhttp: updating cached proxy setting from %v to %v", was, now)
}
cachedProxy.val = res.proxy
return res.proxy, nil
}
// See https://docs.microsoft.com/en-us/windows/win32/winhttp/error-messages
const (
ERROR_WINHTTP_AUTODETECTION_FAILED = 12180
ERROR_WINHTTP_UNABLE_TO_DOWNLOAD_SCRIPT = 12167
)
if err == syscall.Errno(ERROR_WINHTTP_AUTODETECTION_FAILED) {
setNoProxyUntil(10 * time.Second)
return nil, nil
}
if err == windows.ERROR_INVALID_PARAMETER {
// Seen on Windows 8.1. (https://github.com/tailscale/tailscale/issues/879)
// TODO(bradfitz): figure this out.
setNoProxyUntil(time.Hour)
proxyErrorf("tshttpproxy: winhttp: GetProxyForURL(%q): ERROR_INVALID_PARAMETER [unexpected]", urlStr)
return nil, nil
}
proxyErrorf("tshttpproxy: winhttp: GetProxyForURL(%q): %v/%#v", urlStr, err, err)
if err == syscall.Errno(ERROR_WINHTTP_UNABLE_TO_DOWNLOAD_SCRIPT) {
setNoProxyUntil(10 * time.Second)
return nil, nil
}
return nil, err
case <-ctx.Done():
cachedProxy.Lock()
defer cachedProxy.Unlock()
proxyErrorf("tshttpproxy: winhttp: GetProxyForURL(%q): timeout; using cached proxy %v", urlStr, cachedProxy.val)
return cachedProxy.val, nil
}
}
func proxyFromWinHTTP(ctx context.Context, urlStr string) (proxy *url.URL, err error) {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
whi, err := winHTTPOpen()
if err != nil {
proxyErrorf("winhttp: Open: %v", err)
return nil, err
}
defer whi.Close()
t0 := time.Now()
v, err := whi.GetProxyForURL(urlStr)
td := time.Since(t0).Round(time.Millisecond)
if err := ctx.Err(); err != nil {
log.Printf("tshttpproxy: winhttp: context canceled, ignoring GetProxyForURL(%q) after %v", urlStr, td)
return nil, err
}
if err != nil {
return nil, err
}
if v == "" {
return nil, nil
}
// Discard all but first proxy value for now.
if i := strings.Index(v, ";"); i != -1 {
v = v[:i]
}
if !strings.HasPrefix(v, "https://") {
v = "http://" + v
}
return url.Parse(v)
}
var userAgent = windows.StringToUTF16Ptr("Tailscale")
const (
winHTTP_ACCESS_TYPE_AUTOMATIC_PROXY = 4
winHTTP_AUTOPROXY_ALLOW_AUTOCONFIG = 0x00000100
winHTTP_AUTOPROXY_AUTO_DETECT = 1
winHTTP_AUTO_DETECT_TYPE_DHCP = 0x00000001
winHTTP_AUTO_DETECT_TYPE_DNS_A = 0x00000002
)
func winHTTPOpen() (winHTTPInternet, error) {
if err := httpOpenProc.Find(); err != nil {
return 0, err
}
r, _, err := httpOpenProc.Call(
uintptr(unsafe.Pointer(userAgent)),
winHTTP_ACCESS_TYPE_AUTOMATIC_PROXY,
0, /* WINHTTP_NO_PROXY_NAME */
0, /* WINHTTP_NO_PROXY_BYPASS */
0)
if r == 0 {
return 0, err
}
return winHTTPInternet(r), nil
}
type winHTTPInternet windows.Handle
func (hi winHTTPInternet) Close() error {
if err := closeHandleProc.Find(); err != nil {
return err
}
r, _, err := closeHandleProc.Call(uintptr(hi))
if r == 1 {
return nil
}
return err
}
// WINHTTP_AUTOPROXY_OPTIONS
// https://docs.microsoft.com/en-us/windows/win32/api/winhttp/ns-winhttp-winhttp_autoproxy_options
type autoProxyOptions struct {
DwFlags uint32
DwAutoDetectFlags uint32
AutoConfigUrl *uint16
_ uintptr
_ uint32
FAutoLogonIfChallenged bool
}
// WINHTTP_PROXY_INFO
// https://docs.microsoft.com/en-us/windows/win32/api/winhttp/ns-winhttp-winhttp_proxy_info
type winHTTPProxyInfo struct {
AccessType uint16
Proxy *uint16
ProxyBypass *uint16
}
var proxyForURLOpts = &autoProxyOptions{
DwFlags: winHTTP_AUTOPROXY_ALLOW_AUTOCONFIG | winHTTP_AUTOPROXY_AUTO_DETECT,
DwAutoDetectFlags: winHTTP_AUTO_DETECT_TYPE_DHCP, // | winHTTP_AUTO_DETECT_TYPE_DNS_A,
}
func (hi winHTTPInternet) GetProxyForURL(urlStr string) (string, error) {
if err := getProxyForUrlProc.Find(); err != nil {
return "", err
}
var out winHTTPProxyInfo
r, _, err := getProxyForUrlProc.Call(
uintptr(hi),
uintptr(unsafe.Pointer(windows.StringToUTF16Ptr(urlStr))),
uintptr(unsafe.Pointer(proxyForURLOpts)),
uintptr(unsafe.Pointer(&out)))
if r == 1 {
return windows.UTF16PtrToString(out.Proxy), nil
}
return "", err
}
func sysAuthHeaderWindows(u *url.URL) (string, error) {
spn := "HTTP/" + u.Hostname()
creds, err := negotiate.AcquireCurrentUserCredentials()
if err != nil {
return "", fmt.Errorf("negotiate.AcquireCurrentUserCredentials: %w", err)
}
defer creds.Release()
secCtx, token, err := negotiate.NewClientContext(creds, spn)
if err != nil {
return "", fmt.Errorf("negotiate.NewClientContext: %w", err)
}
defer secCtx.Release()
return "Negotiate " + base64.StdEncoding.EncodeToString(token), nil
}
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