fix panic when close miner

lib/jsonrpc/client.go

@@ -137,6 +137,7 @@ func (c *client) makeOutChan(ctx context.Context, ftyp reflect.Type, valOut int)
 		// unpack chan type to make sure it's reflect.BothDir
 		ctyp := reflect.ChanOf(reflect.BothDir, ftyp.Out(valOut).Elem())
 		ch := reflect.MakeChan(ctyp, 0) // todo: buffer?
+		chCtx, chCancel := context.WithCancel(ctx)
 		retVal = ch.Convert(ftyp.Out(valOut))
 
 		buf := (&list.List{}).Init()
@@ -144,6 +145,7 @@ func (c *client) makeOutChan(ctx context.Context, ftyp reflect.Type, valOut int)
 
 		return ctx, func(result []byte, ok bool) {
 			if !ok {
+				chCancel()
 				// remote channel closed, close ours too
 				ch.Close()
 				return
@@ -172,15 +174,19 @@ func (c *client) makeOutChan(ctx context.Context, ftyp reflect.Type, valOut int)
 
 			go func() {
 				for buf.Len() > 0 {
+					select {
+					case <- chCtx.Done():
+						buf.Init()
+					default:
 						front := buf.Front()
-
 						bufLk.Unlock()
 
-					ch.Send(front.Value.(reflect.Value).Elem()) // todo: select on ctx is probably a good idea
+						ch.Send(front.Value.(reflect.Value).Elem())
 
 						bufLk.Lock()
 						buf.Remove(front)
 					}
+				}
 
 				bufLk.Unlock()
 			}()