libnmdc: fix panic() on connection failure, owing to storing nil in an interface

src/libnmdc/libnmdc.go

@@ -3,9 +3,11 @@ package libnmdc
 
 import (
 	"crypto/tls"
+	"errors"
 	"fmt"
 	"net"
 	"net/url"
+	"reflect"
 	"regexp"
 	"strings"
 	"time"
@@ -65,6 +67,7 @@ const (
 var rx_protocolMessage *regexp.Regexp
 var rx_publicChat *regexp.Regexp
 var rx_incomingTo *regexp.Regexp
+var ErrNotConnected error = errors.New("Not connected")
 
 func init() {
 	rx_protocolMessage = regexp.MustCompile("(?ms)^[^|]*|")
@@ -92,10 +95,21 @@ type HubConnection struct {
 	OnEvent chan HubEvent
 
 	// Private state
-	conn         net.Conn
+	conn         net.Conn // this is an interface
 	sentOurHello bool
 }
 
+func isNil(a interface{}) bool {
+	// Workaround to catch the potential for storing nil in an interface.
+	// @ref http://stackoverflow.com/q/13476349
+	defer func() { recover() }()
+	return a == nil || reflect.ValueOf(a).IsNil()
+}
+
+func (this *HubConnection) isConnValid() bool {
+	return isNil(this.conn)
+}
+
 type HubEvent struct {
 	EventType   HubEventType
 	Nick        string
@@ -159,8 +173,12 @@ func (this *HubConnection) userJoined_Full(uinf *UserInfo) {
 // Note that protocol messages are transmitted on the caller thread, not from
 // any internal libnmdc thread.
 func (this *HubConnection) SayRaw(protocolCommand string) error {
+	if this.isConnValid() {
 		_, err := this.conn.Write([]byte(protocolCommand))
 		return err
+	} else {
+		return ErrNotConnected
+	}
 }
 
 func parseLock(lock []byte) string {
@@ -333,11 +351,12 @@ func (this *HubConnection) worker() {
 
 			if err == nil {
 				this.OnEvent <- HubEvent{EventType: EVENT_CONNECTION_STATE_CHANGED, StateChange: CONNECTIONSTATE_CONNECTING}
+				this.conn = nil // WARNING: storing nil in an interface(!)
 			}
 		}
 
 		// Read from socket into our local buffer (blocking)
-		if this.conn != nil {
+		if this.isConnValid() {
 			readBuff := make([]byte, 4096)
 			nbytes, err = this.conn.Read(readBuff)
 			if nbytes > 0 {

src/nmdc-log-service/main.go

@@ -15,6 +15,7 @@ var BaseDir string = "."
 var PMResponse string = ""
 var LogConnectionState bool
 var DebugMode bool
+var VerifyTLS bool
 var CharacterMatcher *regexp.Regexp
 
 func init() {
@@ -54,6 +55,7 @@ func HubWorker(addr, nick, password string) {
 
 	opts := libnmdc.HubConnectionOptions{
 		Address:       libnmdc.HubAddress(addr),
+		SkipVerifyTLS: !VerifyTLS,
 		Self:          libnmdc.UserInfo{Nick: nick},
 		NickPassword:  password,
 	}
@@ -104,6 +106,7 @@ func main() {
 	flag.BoolVar(&LogConnectionState, "LogConnectionState", true, "Include connection state changes in log")
 	flag.StringVar(&PMResponse, "PMResponse", "This is an automated service. For enquiries, please contact an administrator.", "Message to respond with on PM")
 	flag.BoolVar(&DebugMode, "Debug", false, "Print additional information on stdout")
+	flag.BoolVar(&VerifyTLS, "VerifyTLS", true, "Verify TLS certificates")
 	flag.Parse()
 
 	// Assert dir exists