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dialer_proxy.go
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/
dialer_proxy.go
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// Copyright (c) 2023 Proton AG
//
// This file is part of Proton Mail Bridge.Bridge.
//
// Proton Mail Bridge is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Proton Mail Bridge is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Proton Mail Bridge. If not, see <https://www.gnu.org/licenses/>.
package dialer
import (
"context"
"net"
"net/url"
"sync"
"time"
"github.com/ProtonMail/gluon/async"
"github.com/pkg/errors"
"github.com/sirupsen/logrus"
)
var ErrNoConnection = errors.New("no connection")
// ProxyTLSDialer wraps a TLSDialer to switch to a proxy if the initial dial fails.
type ProxyTLSDialer struct {
dialer TLSDialer
locker sync.RWMutex
directAddress string
proxyAddress string
allowProxy bool
proxyProvider *proxyProvider
proxyUseDuration time.Duration
panicHandler async.PanicHandler
}
// NewProxyTLSDialer constructs a dialer which provides a proxy-managing layer on top of an underlying dialer.
func NewProxyTLSDialer(dialer TLSDialer, hostURL string, panicHandler async.PanicHandler) *ProxyTLSDialer {
return &ProxyTLSDialer{
dialer: dialer,
locker: sync.RWMutex{},
directAddress: formatAsAddress(hostURL),
proxyAddress: formatAsAddress(hostURL),
proxyProvider: newProxyProvider(dialer, hostURL, DoHProviders, panicHandler),
proxyUseDuration: proxyUseDuration,
panicHandler: panicHandler,
}
}
// formatAsAddress returns URL as `host:port` for easy comparison in DialTLS.
func formatAsAddress(rawURL string) string {
url, err := url.Parse(rawURL)
if err != nil {
// This means wrong configuration.
// Developer should get feedback right away.
panic(err)
}
host := url.Host
if host == "" {
host = url.Path
}
port := "443"
if url.Scheme == "http" {
port = "80"
}
return net.JoinHostPort(host, port)
}
// DialTLSContext dials the given network/address. If it fails, it retries using a proxy.
func (d *ProxyTLSDialer) DialTLSContext(ctx context.Context, network, address string) (net.Conn, error) {
d.locker.RLock()
if address == d.directAddress {
address = d.proxyAddress
}
d.locker.RUnlock()
conn, err := d.dialer.DialTLSContext(ctx, network, address)
if err == nil || !d.allowProxy {
return conn, err
} else if errors.Is(err, context.Canceled) {
return nil, err
}
logrus.WithError(err).Debug("DialTLS failed, trying proxy")
if err := d.switchToReachableServer(); err != nil {
return nil, err
}
d.locker.RLock()
defer d.locker.RUnlock()
return d.dialer.DialTLSContext(ctx, network, d.proxyAddress)
}
// switchToReachableServer switches to using a reachable server (either proxy or standard API).
func (d *ProxyTLSDialer) switchToReachableServer() error {
d.locker.Lock()
defer d.locker.Unlock()
logrus.Info("Attempting to switch to a proxy")
proxy, err := d.proxyProvider.findReachableServer()
if err != nil {
return errors.Wrap(err, "failed to find a usable proxy")
}
proxyAddress := formatAsAddress(proxy)
// If the chosen proxy is the standard API, we want to use it but still show the troubleshooting screen.
if proxyAddress == d.directAddress {
logrus.Info("The standard API is reachable again; connection drop was only intermittent")
d.proxyAddress = proxyAddress
return ErrNoConnection
}
logrus.WithField("proxy", proxyAddress).Info("Switching to a proxy")
// If the host is currently the rootURL, it's the first time we are enabling a proxy.
// This means we want to disable it again in 24 hours.
if d.proxyAddress == d.directAddress {
go func() {
defer async.HandlePanic(d.panicHandler)
<-time.After(d.proxyUseDuration)
d.locker.Lock()
defer d.locker.Unlock()
d.proxyAddress = d.directAddress
}()
}
d.proxyAddress = proxyAddress
return nil
}
// AllowProxy allows the dialer to switch to a proxy if need be.
func (d *ProxyTLSDialer) AllowProxy() {
d.locker.Lock()
defer d.locker.Unlock()
d.allowProxy = true
}
// DisallowProxy prevents the dialer from switching to a proxy if need be.
func (d *ProxyTLSDialer) DisallowProxy() {
d.locker.Lock()
defer d.locker.Unlock()
d.allowProxy = false
d.proxyAddress = d.directAddress
}