Michael Mahemoff, on Google Plus, points out an idea from the Rails people to slow down your network connection to your local machine in order to simulate the experience of using the web, where slow connections are common (especially on mobile).
The commands they mention are for OS X, though. To do this in Ubuntu you want the following:
Slow down your network connection to localhost by adding a 500ms delay:
sudo tc qdisc add dev lo root handle 1:0 netem delay 500msec
If you do this, then ping localhost, you’ll see that packets now take a second to return (because the 500ms delay applies on the way out and the way back).
To remove this delay:
sudo tc qdisc del dev lo root
Since those commands are pretty alarmingly impenetrable, I put together a tiny little app to do it for you instead. Grab the Python code below and run it, and then you can enable throttling by just ticking a box, and drag the sliders to set the amount you want to slow down your connection. Try it next time you’re building an app which talks to the network — you may find it enlightening (although depressing) how badly your app (or the framework you’re using) deals with slow connections… and half your users will have those slow connections. So we need to get better at dealing with them.
fromgi.repositoryimportGtk,GLibimportsocket,fcntl,struct,array,sys,osdefwhich(program):importosdefis_exe(fpath):returnos.path.isfile(fpath)andos.access(fpath,os.X_OK)fpath,fname=os.path.split(program)iffpath:ifis_exe(program):returnprogramelse:forpathinos.environ["PATH"].split(os.pathsep):path=path.strip('"')exe_file=os.path.join(path,program)ifis_exe(exe_file):returnexe_filereturnNonedefall_interfaces():max_possible=128# arbitrary. raise if needed.bytes=max_possible*32s=socket.socket(socket.AF_INET,socket.SOCK_DGRAM)names=array.array('B','\0'*bytes)outbytes=struct.unpack('iL',fcntl.ioctl(s.fileno(),0x8912,# SIOCGIFCONFstruct.pack('iL',bytes,names.buffer_info()[0])))[0]namestr=names.tostring()lst={}foriinrange(0,outbytes,40):name=namestr[i:i+16].split('\0',1)[0]ip=namestr[i+20:i+24]friendly=""ifname=="lo":friendly="localhost"ifname.startswith("eth"):friendly="Wired connection %s"%(name.replace("eth",""))ifname.startswith("wlan"):friendly="Wifi connection %s"%(name.replace("eth",""))lst[name]=({"friendly":friendly,"action_timer":None,"current_real_value":0,"toggled_by_code":False})returnlstclassApp(object):def__init__(self):win=Gtk.Window()win.set_size_request(300,200)win.connect("destroy",Gtk.main_quit)win.set_title("Network Throttle")self.ifs=all_interfaces()tbl=Gtk.Table(rows=len(self.ifs.keys())+1,columns=4)tbl.set_row_spacings(3)tbl.set_col_spacings(10)tbl.attach(Gtk.Label("Throttled"),2,3,0,1)delay_label=Gtk.Label("Delay")delay_label.set_size_request(150,40)tbl.attach(delay_label,3,4,0,1)row=1fork,vinself.ifs.items():tbl.attach(Gtk.Label(k),0,1,row,row+1)tbl.attach(Gtk.Label(v["friendly"]),1,2,row,row+1)tb=Gtk.CheckButton()tbl.attach(tb,2,3,row,row+1)tb.connect("toggled",self.toggle_button,k)self.ifs[k]["checkbox"]=tbsl=Gtk.HScale()sl.set_draw_value(True)sl.set_increments(20,100)sl.set_range(20,980)sl.connect("value_changed",self.value_changed,k)sl.set_sensitive(False)tbl.attach(sl,3,4,row,row+1)self.ifs[k]["slider"]=slrow+=1box=Gtk.Box(spacing=6)box.pack_start(tbl,True,True,6)win.add(box)win.show_all()self.get_tc()deftoggle_button(self,button,interface):self.ifs[interface]["slider"].set_sensitive(button.get_active())ifself.ifs[interface]["toggled_by_code"]:print"ignoring toggle button because it was toggled by code, not user"self.ifs[interface]["toggled_by_code"]=Falsereturnprint"toggled to",button.get_active()ifbutton.get_active():self.turn_on_throttling(interface)else:self.turn_off_throttling(interface)defvalue_changed(self,slider,interface):print"value_changed",slider.get_value()ifslider.get_value()==self.ifs[interface]["current_real_value"]:print"Not setting if because it already is that value"returnself.turn_on_throttling(interface)defget_tc(self):print"getting tc"self.throttled_ifs={}defget_tc_output(io,condition):print"got tc output",conditionline=io.readline()print"got tc line",lineparts=line.split()iflen(parts)>2andparts[0]=="qdisc"andparts[1]=="netem":iflen(parts)==12:self.throttled_ifs[parts[4]]={"delay":parts[11].replace("ms","")}ifcondition==GLib.IO_IN:returnTrueelifcondition==GLib.IO_HUP|GLib.IO_IN:GLib.source_remove(self.source_id)print"throttled IFs are",self.throttled_ifsself.update_throttled_list(self.throttled_ifs)returnFalsepid,stdin,stdout,stderr=GLib.spawn_async(["tc","qdisc"],flags=GLib.SpawnFlags.SEARCH_PATH,standard_output=True)io=GLib.IOChannel(stdout)self.source_id=io.add_watch(GLib.IO_IN|GLib.IO_HUP,get_tc_output,priority=GLib.PRIORITY_HIGH)pid.close()defactually_turn_on_throttling(self,interface,value):print"actually throttling",interface,"to",valueself.ifs[interface]["action_timer"]=Nonecmd="pkexec tc qdisc replace dev %s root handle 1:0 netem delay %smsec"%(interface,int(value),)printcmdos.system(cmd)defturn_on_throttling(self,interface):val=self.ifs[interface]["slider"].get_value()ifself.ifs[interface]["action_timer"]isnotNone:print"aborting previous throttle request for",interfaceGLib.source_remove(self.ifs[interface]["action_timer"])print"throttling",interface,"to",valsource_id=GLib.timeout_add_seconds(1,self.actually_turn_on_throttling,interface,val)self.ifs[interface]["action_timer"]=source_iddefactually_turn_off_throttling(self,interface):print"actually unthrottling",interfaceself.ifs[interface]["action_timer"]=Nonecmd="pkexec tc qdisc del dev %s root"%(interface,)printcmdos.system(cmd)defturn_off_throttling(self,interface):ifself.ifs[interface]["action_timer"]isnotNone:print"aborting previous throttle request for",interfaceGLib.source_remove(self.ifs[interface]["action_timer"])print"unthrottling",interfacesource_id=GLib.timeout_add_seconds(1,self.actually_turn_off_throttling,interface)self.ifs[interface]["action_timer"]=source_iddefupdate_throttled_list(self,throttled_ifs):fork,vinself.ifs.items():ifkinthrottled_ifs:current=v["checkbox"].get_active()ifnotcurrent:self.ifs[k]["toggled_by_code"]=Truev["checkbox"].set_active(True)delay=float(throttled_ifs[k]["delay"])self.ifs[k]["current_real_value"]=delayv["slider"].set_value(delay)else:current=v["checkbox"].get_active()ifcurrent:v["checkbox"].set_active(False)if__name__=="__main__":ifnotwhich("pkexec"):print"You need pkexec installed."sys.exit(1)app=App()Gtk.main()