Optimise docker stats to not require clearing the whole screen

Instead of clearing the whole screen and then writing the new stats,
we now write the new stats on top of the old text, and then clear
the remaining text.

This is a more efficient way to update the stats, as it avoids the
flickering that happens when the screen is cleared and rewritten.

Signed-off-by: Giedrius Jonikas <[email protected]>

cli/command/container/stats.go

@@ -287,16 +287,26 @@ func RunStats(ctx context.Context, dockerCLI command.Cli, options *StatsOptions)
 		cStats.mu.RUnlock()
 
 		if !options.NoStream {
-			// Start by clearing the screen and moving the cursor to the top-left
-			_, _ = fmt.Fprint(&statsTextBuffer, "\033[2J\033[H")
+			// Start by moving the cursor to the top-left
+			_, _ = fmt.Fprint(&statsTextBuffer, "\033[H")
 		}
 
 		if err = statsFormatWrite(statsCtx, ccStats, daemonOSType, !options.NoTrunc); err != nil {
 			break
 		}
 
-		_, _ = fmt.Fprint(dockerCLI.Out(), statsTextBuffer.String())
+		if !options.NoStream {
+			for _, line := range strings.Split(statsTextBuffer.String(), "\n") {
+				// In case the new text is shorter than the one we are writing over,
+				// we'll append the "erase line" escape sequence to clear the remaining text.
+				_, _ = fmt.Fprint(&statsTextBuffer, line, "\033[K\n")
+			}
 
+			// We might have fewer containers than before, so let's clear the remaining text
+			_, _ = fmt.Fprint(&statsTextBuffer, "\033[J")
+		}
+
+		_, _ = fmt.Fprint(dockerCLI.Out(), statsTextBuffer.String())
 		statsTextBuffer.Reset()
 
 		if len(cStats.cs) == 0 && !showAll {