bigtable/bttest: allow no Rows to be specified in ReadRows

This results in all rows being read. It is supported by the protocol but
not by the Go client.

Change-Id: I7e5f1bef78906151664afadea0ab4bc3637b8e0b
Reviewed-on: https://code-review.googlesource.com/7411
Reviewed-by: Jonathan Amsterdam <jba@google.com>

bigtable/bttest/inmem.go

@@ -228,29 +228,34 @@ func (s *server) ReadRows(req *btpb.ReadRowsRequest, stream btpb.Bigtable_ReadRo
 	tbl.mu.RLock()
 
 	rowSet := make(map[string]*row)
-	// Add the explicitly given keys
-	for _, key := range req.Rows.RowKeys {
-		start := string(key)
-		addRows(start, start+"\x00", tbl, rowSet)
-	}
+	if req.Rows != nil {
+		// Add the explicitly given keys
+		for _, key := range req.Rows.RowKeys {
+			start := string(key)
+			addRows(start, start + "\x00", tbl, rowSet)
+		}
+
+		// Add keys from row ranges
+		for _, rr := range req.Rows.RowRanges {
+			var start, end string
+			switch sk := rr.StartKey.(type) {
+			case *btpb.RowRange_StartKeyClosed:
+				start = string(sk.StartKeyClosed)
+			case *btpb.RowRange_StartKeyOpen:
+				start = string(sk.StartKeyOpen) + "\x00"
+			}
+			switch ek := rr.EndKey.(type) {
+			case *btpb.RowRange_EndKeyClosed:
+				end = string(ek.EndKeyClosed) + "\x00"
+			case *btpb.RowRange_EndKeyOpen:
+				end = string(ek.EndKeyOpen)
+			}
 
-	// Add keys from row ranges
-	for _, rr := range req.Rows.RowRanges {
-		var start, end string
-		switch sk := rr.StartKey.(type) {
-		case *btpb.RowRange_StartKeyClosed:
-			start = string(sk.StartKeyClosed)
-		case *btpb.RowRange_StartKeyOpen:
-			start = string(sk.StartKeyOpen) + "\x00"
+			addRows(start, end, tbl, rowSet)
 		}
-		switch ek := rr.EndKey.(type) {
-		case *btpb.RowRange_EndKeyClosed:
-			end = string(ek.EndKeyClosed) + "\x00"
-		case *btpb.RowRange_EndKeyOpen:
-			end = string(ek.EndKeyOpen)
-		}
-
-		addRows(start, end, tbl, rowSet)
+	} else {
+		// Read all rows
+		addRows("", "", tbl, rowSet)
 	}
 	tbl.mu.RUnlock()