[garganzol]

Wrong direction. WASI should be simple and stable. Initially, it was revolving around a simple Unix-like API model and it was close to perfect. Now, there is an opinionated component model which is an unneeded overcomplication that should have never been considered as part of WebAssembly spec IMHO.

A real component model is a separate development and cannot be blindly tied to a particular ecosystem. Otherwise, its main purpose of providing easy interoperability between different ecosystems is totally lost.

I do not know why WebAssembly committee thinks that shoving-in CORBA-like monstrosity is even an acceptable idea. Let's keep WebAssembly lean and fast! Anything extra can (and should) be implemented by other technologies.

[spankalee]

The component model is what unlocks relatively type-safe interop between modules written in different languages. Given that Wasm is a runtime target for many languages, this is an entirely appropriate and useful goal.

If you have a host system where you want to expose APIs in an language-agnostic way, IDLs are the best way to do that.

You're also conflating the core WebAssembly work with the WASI work. There is some overlap in people, but WASI is developed separately.

[lenkite]

Why was the component model not expressed in LISP syntax like the way WAT is ? Why have yet another custom IDL language with bespoke parsing rules ?

[phickey]

There is a wat (s expression) syntax for the component model. The problem with the wat syntax for both Wasm and the component model is they’re a reflection of a binary format, and therefore are terrible for writing by hand. They’re designed to be written by tools, and the text format is just to help you understand the binary format.

I’ve written Wasm and component model wat extensively over the last decade to develop tests for Wasmtime, and even for an expert it’s a bad experience.

Wit syntax is easy to read and write by hand. There are high quality parsers that can transform it to and from the binary or wat format as needed, and code generators for a wide range of languages. It’s a way, way better experience in every way to deal with wit compared to the wat format.

[yoshuaw]

Seconding this. Writing .wast files by hand is kind of fun as a novelty, but it's in no way something I'd want to maintain interfaces in.

Declarative interfaces via the WIT format are so much more readable in comparison; I'm really happy that's the direction we took for the component model.

[pie_flavor]

The present component model is "simple and stable". It is presently providing "interoperability between different ecosystems" and has been for years. It has basically nothing in common with CORBA. All the major problems with the Unix design they ran into that caused them to switch to a component model haven't vanished; the component model is still the best way of solving WASM's major complications that traditional C-based designs don't have. C-based designs, in general, are not better just because they came first; if you were designing systems programming from scratch, you'd want something like WIT (proof: Microsoft has done this twice now).

[garganzol]

WASM component model is internal to the WASM project, isn't it? As such, it provides interoperability for one and only ecosystem (WASM), and thus has no chances to be perceived worthy and universal enough for people to care, that's the point.

[pie_flavor]

What are you talking about? The point of WASI is to stabilize WASM's access to OS APIs. It uses the component model to do this, which is bound to by languages that compile to WASM and by runtimes that run WASM. That is the only kind of interoperability that is required for this WASM system for WASM components to do WASM things.

[tete]

I agree. This is saddening. It seems to often happen in "standard first" scenarios for some reason. I was very happy when CloudABI and POSIX were picked as prior art inspiration.

Now it feels like it moved from "what would we need to get things done and achieve our goals?" to "what could be done and which goals could we achieve?"

Maybe I am missing something, but are the recent changes something that people requested?

[0x457]

Yes, you missed people asking for years: away to do interop between languages in WASM, a way to interact with browser APIs without JavaScript from WASM.

Component model enable both using one thing.

[garganzol]

> way to do interop between languages

This problem stems from the lack of a standardized component model. WASM is merely another casualty of that deficiency - one among hundreds of affected technologies.

The alliance is attempting to solve the problem at the wrong level and only for WASM, rather than addressing the root cause in a way that would benefit everyone.

[0x457]

Why WASM folks need to solve for not WASM?

[tete]

Fair enough. Isn't that another topic more tied to WASM compare to what initially claimed to be a "System Interface" and not a language interface or a browser interface?

[0x457]

Do you know see how components model solves all three?

If WASI decided to keep bespoke runtime capabilities, then you would have whole zoo of:

  - this runtime does support WASI

  - this runtime does NOT support WASI

  - this one supports WASI, but only older spec

  - this claims to support WASI, but X/Y/Z capabilities are bugged

I think WASI switching to components was the right move. Sure, tooling right now maybe meh outside of rust (and even rust is still meh), but once things stabilize good tooling is to follow.

[azakai]

> Let's keep WebAssembly lean and fast!

Note that wasm is still lean and fast - WASI is not part of core wasm, but layered on top.

That is, it is possible to implement wasm without WASI. That is also true for other wasm proposals like WasmGC. It is very possible that parts of the ecosystem will not implement certain proposals if they don't make sense there (e.g. parts of the embedded ecosystem may never add GC, etc.).

[lifthrasiir]

I have seriously attempted to write my own WebAssembly 3.0 implementation recently, and while I did finish the whole thing [1] that left me a bitter taste about WasmGC which turned out to be very annoying to implement. In fact, I originally wanted to avoid GC but spectest assumed that GC is always available and I had no other option but implementing one in order to make use of spectest in the first place.

[1] https://github.com/lifthrasiir/wah/

[panick21_]

Interfacing with GC is usually hard, how should have it been done?

[lifthrasiir]

Of course, but I'm talking about "annoyance". GC type system is especially annoying if you are not writing the full compiler.

[zozbot234]

AIUI, the underlying motivation for the WASM component model is the same as for the early interface types proposal, which has been a planned part of WASM since the very beginning - namely to allow modules written in high-level languages to expose "native" interfaces, without requiring a completely bespoke translation into WASM's lower level facilities. That's a sensible goal, even if achieving this may ultimately involve something that's at least loosely reminiscent of CORBA.

[throawayonthe]

i don't think people calling it CORBA-like are doing it in good faith, but regardless, no we should not do unix apis everywhere for the rest of time please

[fragmede]

what would you have it look like?

[IshKebab]

I disagree. We shouldn't just be copying Unix until the end of time.

[tete]

I think there is a difference between "just copying" and "building upon understood systems and standards".

Also to be fair "just copying" works really really well, especially for standards. The primary goal of standardization is not to invent something new, but to have a target that isn't constantly moving.

If you want to build something new and better do that, and if you are ready to build a standard based of it which is very valid. You can also build them together, and CloudABI which they mention as inspiration in their readme for example did it that way. All valid paths.

But you want to start out simple and something common so that people that make use of the standard have an easy time to implement it. After all having more than one implementation is why you need a standard. Otherwise it's maybe a specification, which again, fair enough.

I can stand behind not copying Unix until the end of time, but "Unix" is a common target that people know how to implement and use. And while not even the authors of Unix claim it's great or even good it is something that people already implement (often enough even when not targeting anything unixy at all) so if your goal is to create a standard that those people can target then abandoning that does seem like a wrong move.

[iqihs]

less copying and more keeping in the spirit of, as it has clearly shown it is a model that is built to last

[wbl]

Unix is completely inapplicable to this environment which is inherently managed and intraprocess. Why not send an object saying what you want instead of a plain C struct, or worse a bunch of ints? How do we handle ownership across these boundaries? Why should two high level components be forced to squeeze into a primitive bottleneck between them?

Don't get me wrong: I think C is cute and fills a niche decently well. But that niche is not the one we have here.

The reasons why Unix displaced a bunch of more elegant systems were downward scalability, free distribution, and positioning to take advantage of network effects. Quality was secondary, especially with multiprocessing and networking where a lot had to change, and the designs were not always good.

[Ericson2314]

That's like saying "the US Constitution has clearly shown it's a model that is built to last"

Sometimes bad designs stick around due to pure inertia

[tete]

Even if something lasts due to pure inertia it lasts. And something that lasts is pretty nice if you want a standard to last, or be implemented. The standard usually isn't the thing that you use to proof you can do something better, by being different. Because then everyone will have a harder time adapting it. People implement interfaces they dislike.

Since this is related to Webassembly, Browsers, the Web. The web has a lot of historically baggage, that one might have to work around at times, sometimes more sometimes less. There are good bits and not so good bits and in the end a lot of the time more modern web applications (whether you think they are good or bad) as well as web browsers jump through hoops to do things. For many applications there would be better protocols. But it became the dominant standard, a standard that is actually being used a lot and that is why it has become a success story. It wasn't a hundred times better than everything else. It simply was something that people managed to implement successfully and something where they were willing to deal with shortcomings, because there are great benefits in implementing the same standard as everyone else.

Don't know much about the US constitution, but it seems that it was largely good enough to make people work together that otherwise might have ended up fighting each other. That's what you'd get if everyone had a different idea about what a good constitution is. Maybe things are unclear, and maybe there are uproars because of things, but it doesn't even get to that if people don't agree on a standard or a constitution in first place.

And while over the years I often imagined how great it would be if everyone just used that better standard that has been there for a long time and nobody uses and is completely forgotten, if it ever had any popularity, then everything would be so much better and greater and I wouldn't have to do that senseless thing I am doing now. But if that standard doesn't allow for people to agree with it by implementing it it's essentially worthless (outside of maybe "prior art" consideration).

And like it or not we currently live in a world where designs persist due to pure inertia. But we know that obviously people are willing to implement these which means when a standard comes along that is similar to what already is there then having many people adapting it is realistic. Otherwise it's that super interesting university project that never makes it into anything in the real world.

[IshKebab]

It clearly hasn't, if you've been paying any attention to security. The Unix security model is that all code that a user runs is 100% trusted. That's absurd in today's world.

[derefr]

> WASI should be ... stable.

The WASI standard is not at 1.0 yet! The people designing WASI are still trying to figure out what people want WASI to be at this point.

This is very likely to involve a lot of major reworking before 1.0, in response to feedback from orgs actually trying to implement WASI-based WebAssembly embeddings into their systems and runtimes. 0.1.x -> 0.2.x was one reworking; 0.2.x -> 0.3.x is another. There may be more of these before an approach is finally settled upon / "locked in" for 1.x.

---

> Let's keep WebAssembly lean and fast!

AFAICT, the entire point of the changes (incl. the more detailed component model) in WASI 0.3 is performance. Not performance of WebAssembly as a black box, though; but rather, performance of the running system as a whole, when a lot of FFI traffic is flowing across the WASI boundary. The richer component model enables lower impedance mismatches and "thinner" FFI-layer implementations.

For example, from the OP:

> WASI 0.2 handed you an output-stream that you wrote into imperatively. WASI 0.3 has you pass in a stream<u8> and get back a future that resolves when the write completes.

For some host languages/runtimes, "imperative blocking write calls" is already how writes against IO descriptors are exposed to the programmer. For those languages, WASI 0.2 made sense.

But in other host languages/runtimes, writes against IO descriptors are inherently non-blocking, returning promises or yielding. For those languages, WASI 0.2 "left performance on the table." WASI 0.2 required such languages to implement a blocking IO write abstraction on top of their non-blocking IO write semantics, in order to pass that blocking-IO-write primitive into the WebAssembly componennt... even if the WebAssembly component was internally concurrent (e.g. compiled from a language like Golang) and so would highly benefit from a non-blocking-IO-write primitive!

Meanwhile, if you require that the host expose a non-blocking-IO-write primitive (as WASI 0.3 does), then for hosts with native non-blocking IO, doing so is free; while for hosts with only blocking IO, non-blocking IO can be "faked" basically for free (i.e. with a global or per-resource linearized write queue on the host side.) And likewise, non-blocking-IO-aware WebAssembly components can freely take advantage of NIO; while WebAssembly components that expect blocking IO only need the tiniest added bit of a codegen shim (`blocking_write(x) => await nonblocking_write(x);`) to fit into a WASI 0.3 world.

In other words, implementing nonblocking IO abstractions on top of blocking IO abstractions costs FFI performance, but implementing blocking IO abstractions on top of nonblocking IO abstractions is "free" (in FFI terms.) Nonblocking IO should therefore be considered the more "primitive" of the two; and so, if you have to choose only BIO or NIO to expose as a capability across a boundary to an unknown peer, NIO should be the one you choose.

---

That being said...

The WASI devs were likely aware of the "FFI optimization opportunities being left on the floor" in WASI 0.2. They likely already wanted to take things in this direction from the beginning. But in WASI 0.2, without async, it was impossible to express the concept of nonblocking IO (i.e. of IO operations returning a promise/future.) They needed to introduce this more "opinionated" (i.e. richer) component model in order to get here.

AFAICT, WASI 0.2 was never intended to be a Release Candidate of the WASI spec. (And WASI 0.3 likely isn't either!)

Rather, WASI 0.2 had areas (like IO) that were purposefully left "under-baked". The WASI team knew people needed some version of these primitives in order for WebAssembly components to usefully integrate into systems at all. But they hadn't yet put in the work on designing how certain aspects of WASI (e.g. async) would work. So they designed WASI 0.2 as a prototype design, based on the limited toolbag of primitives they had already fully agreed upon. Some aspects of WASI turned out to only "want" that limited toolbag of primitives, and so didn't change at all under WASI 0.3 (and might even be in their final shapes.) Other aspects "wanted" things that weren't there, and so experienced over-constrained designs under WASI 0.2, replaced with less-constrained designs under WASI 0.3.

I fully expect there will be more such changes under WASI 0.4. If you don't want to be a guinea pig for major WASI changes, you might want to wait for WASI 1.0. (However long that takes.)