Implement tail for docker logs

Fixes #4330
Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Upstream-commit: 1dc0caf9c0170ab8e7f5a2f77f2dbdacff322eff
Component: engine

components/engine/api/client/commands.go

@@ -1693,6 +1693,7 @@ func (cli *DockerCli) CmdLogs(args ...string) error {
 		cmd    = cli.Subcmd("logs", "CONTAINER", "Fetch the logs of a container")
 		follow = cmd.Bool([]string{"f", "-follow"}, false, "Follow log output")
 		times  = cmd.Bool([]string{"t", "-timestamps"}, false, "Show timestamps")
+		tail   = cmd.String([]string{"-tail"}, "all", "Output the specified number of lines at the end of logs(all logs by default)")
 	)
 
 	if err := cmd.Parse(args); err != nil {
@@ -1726,6 +1727,7 @@ func (cli *DockerCli) CmdLogs(args ...string) error {
 	if *follow {
 		v.Set("follow", "1")
 	}
+	v.Set("tail", *tail)
 
 	return cli.streamHelper("GET", "/containers/"+name+"/logs?"+v.Encode(), env.GetSubEnv("Config").GetBool("Tty"), nil, cli.out, cli.err, nil)
 }

components/engine/api/server/server.go

@@ -378,6 +378,7 @@ func getContainersLogs(eng *engine.Engine, version version.Version, w http.Respo
 		return err
 	}
 	logsJob.Setenv("follow", r.Form.Get("follow"))
+	logsJob.Setenv("tail", r.Form.Get("tail"))
 	logsJob.Setenv("stdout", r.Form.Get("stdout"))
 	logsJob.Setenv("stderr", r.Form.Get("stderr"))
 	logsJob.Setenv("timestamps", r.Form.Get("timestamps"))