jdev - 2020-02-09


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  55. lovetox hm, if i lose internet connection, say disable wlan, my socket does not really care, i can still send endless data on it
  56. lovetox i thought that he would throw some error, but nothing
  57. lovetox now i read a bit about it and seems this works as intended
  58. lovetox so the only way to know if i lost connection is application layer pings
  59. lovetox can someone confirm this
  60. lovetox ?
  61. lovetox and there is some other functionality SO_KEEPALIVE, where the system tests if a socket is still connected
  62. lovetox but according to the internet the timeout is 2 hours on linux
  63. lovetox so not really useable as a client
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  67. MattJ Yes, this is all correct
  68. MattJ There are platform-specific ways to reduce the timeout
  69. lovetox damn, brilliant design
  70. defanor Well, the send buffer is finite. And according to tcp(7) (assuming it's about TCP), keep-alive probes would lead to timing out in about 11 minutes on Linux by default, while retransmission attempts would last 13 to 30 minutes. And then there's TCP_USER_TIMEOUT, and I think I've observed it timing out in just a few minutes (not sure why).
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  74. lovetox yeah i was looking for something in the range of seconds
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  86. jonas’ lovetox, anything in the range of seconds would make things fail on EDGE or GPRS type connections quickly
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  93. pulkomandy Or even wifi if you're a bit far from the router
  94. MattJ And consume battery/bandwidth
  95. pulkomandy Or ethernet if you just unplug the cable for a few seconds to untangle it :]
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  98. jonas’ in the case of EDGE/GPRS, you can easily get into a fun loop with packets from your closed connection cluttering the bandwidth, making your new connection choke right away.
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  103. lovetox hm, so what timeout would you suggest?
  104. lovetox i think its useful for the client to know if the connection broke down
  105. jonas’ timeouts are always wrong
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  107. lovetox problem is if the connection broke down, and client doesnt notice it, stuff stops working
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  109. jonas’ indeed
  110. jonas’ I suggest to have two timeouts
  111. lovetox for sending a message i can just show some icon that indicates the message didnt yet reach the server
  112. jonas’ one I call the `soft_timeout`, which is the maximum time you spend without receiving any data from the server
  113. jonas’ (be it whitespace or a stanza)
  114. jonas’ if the soft timeout elapses, you send a ping
  115. jonas’ and you wait for at most `round_trip_time` (the second timeout) to receive something (doesn’t have to be a reply to your ping, anything will do)
  116. jonas’ the good thing about this is that with high-delay links, you’ll still most of the time receive things and thus know that your stream is alive
  117. lovetox yeah i implemented this just now
  118. jonas’ you also save on sending pings when you get stanzas from the server (= saved energy)
  119. lovetox but what is the max roundtrip tie
  120. lovetox but what is the max roundtrip time
  121. lovetox is 10 seconds good?
  122. jonas’ in case of gajim, I’d probably set something like 5 minutes for the soft timeout, and auto-calibrate the round-trip time based on IQ round trips
  123. lovetox 60 seconds?
  124. jonas’ something between 60s and 120s is probably ok
  125. lovetox 5 minutes is way to high, as i said stuff stops working, if user opens his profile it just shows a endless loading screen, if he wants to join a MUC, shows a loading screen, etc etc
  126. jonas’ lovetox, you can make it more interactive on the application layet
  127. lovetox and at this time i want to give the user an indication, hey your connection may be broke down
  128. jonas’ e.g. if after 15s you have no reply, you could do othre things
  129. jonas’ such as pinging google or so
  130. lovetox but if i have a 5 minute soft timeout, i cant give the user any indication
  131. jonas’ and if you can’t ping google, suggest that the internte may be down
  132. jonas’ oh you can
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  134. jonas’ have an even softer 15s timeout on your requests (IQs, MUC joins etc.) which triggers some additional action to make the UX smooth
  135. jonas’ "This is taking longer than expected. Is your internet working?"
  136. jonas’ and also listen for OS events about connectivity changes
  137. lovetox so 15 seconds :)
  138. jonas’ if you get a "reconnected to network X" event from the OS, discard your stream and resume using '198
  139. lovetox thats the answer i wanted
  140. jonas’ but 15 seconds isn’t the time after which you should throw away the stream
  141. jonas’ that’s just when you start talking to your user
  142. jonas’ that’s also not the time after which you start sending pings
  143. jonas’ because you just sent a "ping"
  144. jonas’ (which is your request)
  145. lovetox yeah jonas’ i get it :)
  146. jonas’ uh, although, what could be fun is trying to establish a new stream
  147. lovetox i was always talking about the time i wait for the poing
  148. jonas’ in the background
  149. jonas’ and if you notice that this works very quickly, but your request is slow, you send a ping to the server. if you don’t get a reply within the time it took to get the new stream past TLS, you know that your stream is borked and you should '198 resume on the new stream and discard the old one
  150. jonas’ that’s neat actually
  151. jonas’ establishing a new TCP connection and doing TLS is not that expensive in number of packets and as good as a test as anything else
  152. jonas’ (it’ll also not clutter your own send buffers further, you can simply discard the new connection (along with its buffers) easily if it doesn’t work out)
  153. lovetox jonas’, sorry sounds way to complicated and over-engineered
  154. lovetox i wait X seconds, and throw the stream away, much easier
  155. lovetox thats what we have stream management for, for fast reconnects
  156. jonas’ lovetox, that’ll really hurt you
  157. jonas’ on a bad mobile link
  158. lovetox on bad mobile link, stuff will be bad, no suprise for the user :)
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  160. lovetox but the whole topic is a nightmare, we have many actions on xmpp that need a response
  161. lovetox so many action will look to the user like, he clicks something but nothing happens
  162. Zash Show a spinner if it takes more than a few seconds
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  164. lovetox for some things thats a fine approach
  165. lovetox for others its not so nice
  166. lovetox deleting a contact from your rosterfor example
  167. lovetox dont want to show a dialog with a spinner for that
  168. Zash Show it on the contact then. Like, replace the avatar or status icon or something
  169. lovetox you really have to design the whole application for this case
  170. lovetox what i think i will be doing, let the user send message when we lost connection
  171. lovetox but disable every other action
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  188. flow > lovetox> damn, brilliant design when is a connection "lost"? I don't think there is a better design without loosing some other (desirable) properties
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  191. Zash That's what you get when you emulate a circuit over a packet-switched network. All sorts of fun!
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  200. jonas’ lovetox, or just pretend that it has happened for things where you’re rather certain that you can enforce it to happen eventually
  201. jonas’ for example, contact deletion
  202. jonas’ queue the operation up and do it when you have connectivity and hide the element from the UI
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  211. pep. And then users get confused when they use another client that has connectivity :/
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  213. pep. I see the appeal in what you say but I'm not entirely sure I like it
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  270. lovetox jonas’, sounds easy, but reality is much harder
  271. lovetox you can invest thousands of lines of code into this, and it still will be buggy
  272. lovetox or you just tell the user, hey right now you cant delete, wait until you have a proper connection to the server
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  276. lovetox which is totally fine in my book, i dont think anyone expects to do server operations while offline
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  280. moparisthebest lovetox: you can change the SO_KEEPALIVE interval on Linux, it's settable if you are root
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  283. pep. yay gajim as root :P
  284. Zash Just run it in a container.
  285. pep. yay gajim as root in a container!
  286. jonas’ a.k.a. flatpak?
  287. jonas’ or was it snap?
  288. bhaveshsgupta has joined
  289. Zash why not both?
  290. pep. Is the process really root? Isn't bubblewrap used just to spawn the thing?
  291. jonas’ pep., I was making fun of those
  292. jonas’ probably not root ;)
  293. moparisthebest Well no gajim wouldn't change it, the machine administrator would
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  295. moparisthebest With sysctl
  296. Zash Isn't there a per-process/-socket option you can poke if your socket library doesn't hide it from you?
  297. moparisthebest Not for keepalive iirc
  298. moparisthebest Don't worry TCP's replacement is all in userspace not kernel so you can do whatever
  299. Zash :(
  300. Zash But I was excited about TLS in kernel space
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  327. Link Mauve I still want to play with that.
  328. Link Mauve I should have a look in rustls.
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  331. lovetox so if i do the xmpp pings, i guess i dont need the send every X seconds a whitespace
  332. lovetox or isthis useful for something else
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  334. Link Mauve The whitespace is a keepalive.
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  338. lovetox yeah though i just learned a socket does not break down, even if i cut the internet, so keeping it alive is not really the issue here
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  340. MattJ Heh
  341. MattJ Some (too many) routers like to silently terminate idle connections
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  343. lovetox ok but sending a xmpp ping on a idle connection every 15 seconds should keep it alive
  344. MattJ Sure
  345. lovetox im asking if i need both
  346. MattJ 15 seconds is kinda frequent :/
  347. MattJ You could at least use 198 <r>/<a> for pings, which are lighter
  348. Zash How about 14 minutes
  349. Link Mauve lovetox, that sounds like a battery drainer.
  350. Link Mauve Pidgin does that AFAIK, and it’s terrible.
  351. Link Mauve Don’t be like Pidgin.
  352. lovetox hm or i depend on a network manager, to tell me if the internet is down
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  354. Link Mauve Aren’t you already doing that with nm?
  355. Link Mauve But jonas’’s approach of using XEP-0198 stream resumption looks quite elegant to me.
  356. Link Mauve That’s what I’d do if I were to start something from scratch again.
  357. lovetox what approach is that?
  358. Link Mauve The one from 10:24:16 CET.
  359. Zash Just trying a new TCP connection to the server would at least tell you something about whether it's the existing connection that's broken or all connectivity
  360. Link Mauve or all connectivity to the server*
  361. lovetox but thats what a network manager is for
  362. lovetox ...
  363. Zash It won't detect if someone trips over a cable in the building switch room
  364. Link Mauve Seems like it would require running one though.
  365. Zash or the server suddenly explodes
  366. lovetox i think we are mixing 2 things here
  367. lovetox detecting if my remote is gone
  368. lovetox and detecting if my internet is gone
  369. lovetox or is this the same thing?
  370. lovetox i hope not
  371. Link Mauve What is your end goal?
  372. lovetox either way, network manager tells me when there is no route to the internet, reading the manual
  373. lovetox so this includes tripping over my cable
  374. lovetox Link Mauve, detecting when i have no connection to the server
  375. Link Mauve lovetox, why do you need to know about the Internet then?
  376. Link Mauve And also, what do you want to do in such a case?
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  380. Link Mauve What about if the kernel eventually flushes its buffers and messages you sent now got sent?
  381. lovetox i show the user that there is no connection and limit what he can do
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  384. Link Mauve That sounds like bad UX when you can instead remember what the user did and then figure out whether it got done or not on stream resumption.
  385. Link Mauve Meh, stupid Freenode sending me tons of presences from IRC…
  386. Zash There was just a notice about them doing some maintenence
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  388. Link Mauve poezio is still spending all of my CPU time handling those presences…
  389. lovetox so just a simple example
  390. lovetox its easy to just store the stanzas that are going out and on failed resumption replay them
  391. lovetox but if you think about that the user could close the application while not connected
  392. lovetox now you suddenly have to save your not acked stanza cache to harddisk, and on resume you have to judge which of them make sense to send
  393. MattJ Yes, it's hard
  394. lovetox you have to take into account how much time passed
  395. lovetox probably offer UI to ask the user etc etc
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  397. lovetox a lot of magic that can fail, and end in scenarios where the user just cant understand what and why something happend or didnt happen
  398. lovetox compare this with a very simple "You are not connected, so you cant do that right now"
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  400. lovetox but as it seems, i cant even determine if im connected :D
  401. pep. I agree with lovetox that it's a lot of magic that can go wrong, (buffering and resending when connectivity gets back) :/
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  403. lovetox for messages only i can imagine it, if i would have proper UI where i notify the user of messages that have not been sent last time, and he can choose to resend
  404. lovetox for everything else i would say not worth it
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  406. wurstsalat sending messages while being offline would also satisfy a feature request :)
  407. lovetox yeah not a problem, but we need UI first that shows that a message has not reached the server, and after X minutes, dont send it anymore instead user has to manually issue a command to resend them
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  409. wurstsalat we could use that info bar at the top of each chat control to inform + offer to try again (and mark unsent messages in the chat)
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  411. lovetox yeah that sentence is a week worth of work :D
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  415. wurstsalat sorry, just trying to point out a possible UI^^
  416. wurstsalat I always wanted to use that infobar for more :)
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