Merge pull request #38 from lyft/conn-nil

Capture when mongoSocket.conn is nil to prevent panics

Author: Chris Roche

server.go

@@ -28,6 +28,7 @@ package mgo
 
 import (
 	"errors"
+	"fmt"
 	"net"
 	"sort"
 	"sync"
@@ -198,6 +199,14 @@ func (server *mongoServer) Connect(timeout time.Duration, socket *mongoSocket) e
 		logf("Connection to %s failed: %v", server.Addr, err.Error())
 		return err
 	}
+
+	if conn == nil {
+		// if a dialer is incorrectly implemented, it may return (nil, nil)
+		// which will cause a panic downstream
+		logf("Received nil connection to %s", server.Addr)
+		return fmt.Errorf("received nil connection to %s", server.Addr)
+	}
+
 	logf("Connection to %s established.", server.Addr)
 
 	stats.conn(+1, master)

socket.go

@@ -350,7 +350,9 @@ func (socket *mongoSocket) kill(err error, abend bool) {
 
 	logf("Socket %p to %s: closing: %s (abend=%v)", socket, socket.addr, err.Error(), abend)
 	socket.dead = err
-	socket.conn.Close()
+	if socket.conn != nil {
+		socket.conn.Close()
+	}
 	stats.socketsAlive(-1)
 	replyFuncs := socket.replyFuncs
 	socket.replyFuncs = make(map[uint32]replyFunc)