Comment by krackers

Comment by krackers 3 days ago

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>so presumably there's some other low-level non-blocking call

Correct, CFNetwork is open source so you can check implementation but last I remember it used some variant like `getaddrinfo_async`. But Apple really doesn't want you (the end-user) to use getaddrinfo (or the async variant CF exposes) to resolve an IP and then directly connect() via that ip, everything is geared towards connect-by-hostname since then Apple's can internally handle the implementation of happy-eyeballs.

Edit: You can read https://www.ietf.org/proceedings/72/slides/plenaryw-6.pdf for their thoughts on why they don't like the getaddrinfo() model [there are speaker notes at the bottom of each slide]

conradev 3 days ago

If you do need the lower-level control, Apple does still recommend `getaddrinfo`. It handles NAT64 translation for IPv6-only carrier networks:

https://developer.apple.com/library/archive/documentation/Ne...

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  • simscitizen 2 days ago

    That’s not the current documentation, as evidenced by the “archive” in the URL.

    If you want to stay at a lower level the recommendation these days is to use Network.framework. If you want something higher level then use CFNetwork (probably through the classes exported by Foundation like NSURLSession).

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    • conradev 2 days ago

      I actually found it linked from here, which seems current: https://developer.apple.com/support/ipv6/

      It is not best practice to use `getaddrinfo` for DNS resolution, for sure. But it is best practice to use it before connecting to an IP address directly because that address may need to be translated.

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  • krackers 3 days ago

    I'm actually surprised they suggest getaddrinfo() directly over the async CF wrapper.

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Terretta 2 days ago

TL;DR:

Applications should not use getaddrinfo(). Because for the connect by name, the OS or app SDK can parallelize the entire multi-step lookup and connection process, not just step by step:

“Now, I’m not saying that all implementations of these APIs [Java, Apple Foundation, etc., doing connect by name] necessarily do the right thing today, but if applications are using these APIs, then the implementations can be improved over time.”

“The difference with getaddrinfo() and similar APIs is that they fundamentally can’t be improved over time. The API definition is that they return you a full list of addresses, so they have to wait until they have that full list to give you. There’s no way getaddrinfo can return you a partial list and then later give you some more.”

The deck's position on implementation of happy-eyeballs (which could sound dismissive here but is treated as "you had one job" important by the deck), is finding a way to avoid waiting 5 seconds for either side of IPv4 vs. IPv5 stack to timeout before finishing connection setup and serving the user a web page.

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matheusmoreira 2 days ago

Thanks for that link, it's a very convincing presentation that very clearly explains the shortcomings of getaddrinfo.

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  • SOLAR_FIELDS 2 days ago

    Yeah, I went in thinking that it was going to be some case of Apple wanting to bend the Unix philosophy to their will for their own desires and steer implementations in their direction, but no - they are simply pointing out a clear flaw in the design of the function in question for a usecase that does not apply only to Apple. Basically all OS vendors need to be doing something like this usecase to support IPv6 adoption.

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    • marxisttemp 2 days ago

      I often find this is the case with Apple on a technical level.

      For instance, their recent Spatial (stereographic) Video features uses a format that has basically zero current support outside of Apple—which is in fact just standard MV-HEVC [0] (with some extra optional metadata [1]), which is just the H.265 evolution of the standard H.264 MVC that 3D Blu-rays have used for a long time. (AFAIK no 4K 3D Blu-rays have been released, presumably due to space constraints, explaining the lack of usage of MV-HEVC outside Apple).

      In piracy world, most re-encoded 3D movies just use objectively inferior composited 2D formats like half-side-by-side or over/under. And without diving in you’d just assume Apple was using some bespoke format to be evil, when in fact they are popularizing what should be the canonical, standardized format for 3D video.

      [0] http://hevc.info/mvhevc [1] https://developer.apple.com/av-foundation/HEVC-Stereo-Video-...

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