Truncate trailing zeros from AOF at startup

This commit addresses issue #230, where an AOF file will sometimes
not load due to the file being padded with trailing zeros. It's
uncertain what is causing this corruption, but it appears to be
coming from outside of the tile38-server process. I suspect it's
due to some block store layer in Kubernetes/Docker cloud
environments.

This fix allows for Tile38 to start up by discovering the trailing
zeros while loading the AOF and safely truncating the file as to
not include the zeros in the future.

internal/server/aof.go

@@ -32,7 +32,7 @@ func (err errAOFHook) Error() string {
 
 var errInvalidAOF = errors.New("invalid aof file")
 
-func (s *Server) loadAOF() error {
+func (s *Server) loadAOF() (err error) {
 	fi, err := s.aof.Stat()
 	if err != nil {
 		return err
@@ -58,6 +58,7 @@ func (s *Server) loadAOF() error {
 	var buf []byte
 	var args [][]byte
 	var packet [0xFFFF]byte
+	var zeros int
 	for {
 		n, err := s.aof.Read(packet[:])
 		if err != nil {
@@ -65,6 +66,18 @@ func (s *Server) loadAOF() error {
 				if len(buf) > 0 {
 					return io.ErrUnexpectedEOF
 				}
+				if zeros > 0 {
+					// Trailing zeros in AOF. Truncate the file so it's sane.
+					// See issue #230 for more information. Force a warning.
+					log.Infof("Truncating %d zeros from AOF (issue #230)", zeros)
+					s.aofsz -= zeros
+					if err := s.aof.Truncate(int64(s.aofsz)); err != nil {
+						return err
+					}
+					if _, err := s.aof.Seek(int64(s.aofsz), 0); err != nil {
+						return err
+					}
+				}
 				return nil
 			}
 			return err
@@ -76,6 +89,16 @@ func (s *Server) loadAOF() error {
 		}
 		var complete bool
 		for {
+			if len(data) > 0 {
+				if data[0] == 0 {
+					zeros++
+					data = data[1:]
+					continue
+				}
+				if zeros > 0 {
+					return errors.New("Zeros found in AOF file (issue #230)")
+				}
+			}
 			complete, args, _, data, err = redcon.ReadNextCommand(data, args[:0])
 			if err != nil {
 				return err