Implement an offline mode

Fixes #528

dnscrypt-proxy/config.go

@@ -70,6 +70,7 @@ type Config struct {
 	TLSCipherSuite           []uint16                   `toml:"tls_cipher_suite"`
 	NetprobeAddress          string                     `toml:"netprobe_address"`
 	NetprobeTimeout          int                        `toml:"netprobe_timeout"`
+	OfflineMode              bool                       `toml:"offline_mode"`
 }
 
 func newConfig() Config {
@@ -104,6 +105,7 @@ func newConfig() Config {
 		TLSCipherSuite:           nil,
 		NetprobeAddress:          "9.9.9.9:53",
 		NetprobeTimeout:          30,
+		OfflineMode:              false,
 	}
 }
 
@@ -397,12 +399,13 @@ func ConfigLoad(proxy *Proxy, svcFlag *string) error {
 	}
 
 	netProbe(config.NetprobeAddress, config.NetprobeTimeout)
-
-	if err := config.loadSources(proxy); err != nil {
-		return err
-	}
-	if len(proxy.registeredServers) == 0 {
-		return errors.New("No servers configured")
+	if !config.OfflineMode {
+		if err := config.loadSources(proxy); err != nil {
+			return err
+		}
+		if len(proxy.registeredServers) == 0 {
+			return errors.New("No servers configured")
+		}
 	}
 	if *list || *listAll {
 		config.printRegisteredServers(proxy, *jsonOutput)

dnscrypt-proxy/example-dnscrypt-proxy.toml

@@ -186,6 +186,13 @@ ignore_system_dns = false
 netprobe_timeout = 30
 
 
+## Offline mode - Do not use any remote encrypted servers.
+## The proxy will remain fully functional to respond to queries that
+## plugins can handle directly (forwarding, cloaking, ...)
+
+# offline_mode = false
+
+
 ## Automatic log files rotation
 
 # Maximum log files size in MB

dnscrypt-proxy/proxy.go

@@ -3,9 +3,9 @@ package main
 import (
 	"io"
 	"io/ioutil"
-	"os"
 	"math/rand"
 	"net"
+	"os"
 	"sync/atomic"
 	"time"
 
@@ -119,7 +119,7 @@ func (proxy *Proxy) StartProxy() {
 				FileDescriptors = append(FileDescriptors, fdUDP)
 				FileDescriptors = append(FileDescriptors, fdTCP)
 
-			// if 'username' is set and we are the child process
+				// if 'username' is set and we are the child process
 			} else {
 				// child
 				listenerUDP, err := net.FilePacketConn(os.NewFile(uintptr(3+FileDescriptorNum), "listenerUDP"))
@@ -159,16 +159,18 @@ func (proxy *Proxy) StartProxy() {
 		dlog.Notice("dnscrypt-proxy is waiting for at least one server to be reachable")
 	}
 	proxy.prefetcher(&proxy.urlsToPrefetch)
-	go func() {
-		for {
-			delay := proxy.certRefreshDelay
-			if proxy.serversInfo.liveServers() == 0 {
-				delay = proxy.certRefreshDelayAfterFailure
+	if len(proxy.serversInfo.registeredServers) > 0 {
+		go func() {
+			for {
+				delay := proxy.certRefreshDelay
+				if proxy.serversInfo.liveServers() == 0 {
+					delay = proxy.certRefreshDelayAfterFailure
+				}
+				clocksmith.Sleep(delay)
+				proxy.serversInfo.refresh(proxy)
 			}
-			clocksmith.Sleep(delay)
-			proxy.serversInfo.refresh(proxy)
-		}
-	}()
+		}()
+	}
 }
 
 func (proxy *Proxy) prefetcher(urlsToPrefetch *[]URLToPrefetch) {
@@ -318,7 +320,7 @@ func (proxy *Proxy) clientsCountDec() {
 }
 
 func (proxy *Proxy) processIncomingQuery(serverInfo *ServerInfo, clientProto string, serverProto string, query []byte, clientAddr *net.Addr, clientPc net.Conn) {
-	if len(query) < MinDNSPacketSize || serverInfo == nil {
+	if len(query) < MinDNSPacketSize {
 		return
 	}
 	pluginsState := NewPluginsState(proxy, clientProto, clientAddr)
@@ -342,7 +344,7 @@ func (proxy *Proxy) processIncomingQuery(serverInfo *ServerInfo, clientProto str
 	} else {
 		pluginsState.returnCode = PluginsReturnCodeForward
 	}
-	if len(response) == 0 {
+	if len(response) == 0 && serverInfo != nil {
 		var ttl *uint32
 		if serverInfo.Proto == stamps.StampProtoTypeDNSCrypt {
 			sharedKey, encryptedQuery, clientNonce, err := proxy.Encrypt(serverInfo, query, serverProto)
@@ -408,6 +410,14 @@ func (proxy *Proxy) processIncomingQuery(serverInfo *ServerInfo, clientProto str
 			serverInfo.noticeSuccess(proxy)
 		}
 	}
+	if len(response) < MinDNSPacketSize || len(response) > MaxDNSPacketSize {
+		pluginsState.returnCode = PluginsReturnCodeParseError
+		pluginsState.ApplyLoggingPlugins(&proxy.pluginsGlobals)
+		if serverInfo != nil {
+			serverInfo.noticeFailure(proxy)
+		}
+		return
+	}
 	if clientProto == "udp" {
 		if len(response) > MaxDNSUDPPacketSize {
 			response, err = TruncatedResponse(response)
@@ -428,7 +438,9 @@ func (proxy *Proxy) processIncomingQuery(serverInfo *ServerInfo, clientProto str
 		if err != nil {
 			pluginsState.returnCode = PluginsReturnCodeParseError
 			pluginsState.ApplyLoggingPlugins(&proxy.pluginsGlobals)
-			serverInfo.noticeFailure(proxy)
+			if serverInfo != nil {
+				serverInfo.noticeFailure(proxy)
+			}
 			return
 		}
 		clientPc.Write(response)