client: Monitor fallback only on unsupported rpc

Falling back to a previous version of the monitor RPC should only happen
if we get a `unsupported rpc` error from ovsdb-server. Previously we
would fall back on `context deadline exceeded` which is not expected
behaviour

Signed-off-by: Dave Tucker <dave@dtucker.co.uk>

client/client.go

@@ -684,11 +684,7 @@ func (o *ovsdbClient) MonitorCancel(ctx context.Context, cookie MonitorCookie) e
 // RFC 7047 : monitor
 func (o *ovsdbClient) Monitor(ctx context.Context, monitor *Monitor) (MonitorCookie, error) {
  cookie := newMonitorCookie(o.primaryDBName)
- err := o.monitor(ctx, cookie, false, monitor)
- if err != nil && err == ErrUnsupportedRPC {
- return cookie, o.monitor(ctx, cookie, false, monitor)
- }
- return cookie, err
+ return cookie, o.monitor(ctx, cookie, false, monitor)
 }
 
 func (o *ovsdbClient) monitor(ctx context.Context, cookie MonitorCookie, reconnecting bool, monitor *Monitor) error {
@@ -769,17 +765,17 @@ func (o *ovsdbClient) monitor(ctx context.Context, cookie MonitorCookie, reconne
  if err == rpc2.ErrShutdown {
  return ErrNotConnected
  }
- // TODO: Match unsupported RPC method error
- if monitor.Method == ovsdb.ConditionalMonitorSinceRPC {
- log.Printf("libovsdb: method monitor_cond_since not supported, falling back to monitor_cond: %v", err.Error())
- monitor.Method = ovsdb.ConditionalMonitorRPC
- // return to ensure that we release any held mutexes, retry must happen from a calling function
- return ErrUnsupportedRPC
- } else if monitor.Method == ovsdb.ConditionalMonitorRPC {
- log.Printf("libovsdb: method monitor_cond not supported, falling back to monitor: %v", err.Error())
- monitor.Method = ovsdb.MonitorRPC
- // return to ensure that we release any held mutexes, retry must happen from a calling function
- return ErrUnsupportedRPC
+ if err.Error() == "unknown method" {
+  if monitor.Method == ovsdb.ConditionalMonitorSinceRPC {
+  log.Printf("libovsdb: method monitor_cond_since not supported, falling back to monitor_cond: %v", err.Error())
+  monitor.Method = ovsdb.ConditionalMonitorRPC
+  return o.monitor(ctx, cookie, reconnecting, monitor)
+ }
+  if monitor.Method == ovsdb.ConditionalMonitorRPC {
+  log.Printf("libovsdb: method monitor_cond not supported, falling back to monitor: %v", err.Error())
+  monitor.Method = ovsdb.MonitorRPC
+  return o.monitor(ctx, cookie, reconnecting, monitor)
+ }
  }
  return err
  }