Add support for logging in SwiftWasm (via `WASILibc`) by helje5 · Pull Request #177 · apple/swift-log

helje5 · 2021-01-11T17:52:12Z

This is a port of Logging to the SwiftWasm WASILibc.

Motivation:

I'd like to log things in Wasm as well.

Modifications:

The library was using a lot of import Glibc as a fallback (you might want to consider to move to canImport). Added additional checks for WASILibc and emit an #error when no known runtime is available.
WASILibc (well, WASI) doesn't support threading and hence locks. #if guarded the Locks.swift file to not build the Lock classes w/ WASILibc. Then adjust the few invocations on the callsites to not use locks on WASILibc.
WASILibc doesn't have stdio, but it does have Foundation print. Defines a TextOutputStream using that when on WASILibc, and do not use the Stdio variant. (implies using the same stream for both stdout/err)
WASILibc doesn't have strftime, but it does have a working Foundation DateFormatter/Date. Use that instead of timestamp formatting.

Result:

swift-log can be used in Wasm environments.

Source:

import Logging
let logger = Logger(label: "zz.log")
logger.info("Hello World!")

helge@M1ni cowsa $ swift build --triple wasm32-unknown-wasi
[3/3] Linking cowsa.wasm
helge@M1ni cowsa $ wasmer .build/debug/cowsa.wasm 
2021-01-11 17:44:06.926 info zz.log : Hello World!

There is no threading on WASI (yet? ever?).

The WASILibc doesn't provide much C yet, apparently. Not even FILE.

WASILibc doesn't have stdio, e.g. no `FILE`. But it does have `print`, so let's just use that instead for both, regular and error logging.

WASILibc doesn't have `strftime`, but it does come w/ a working `DateFormatter`/`Date`. Use that instead.

Instead do not compile the locks on WASILibc and comment them out on the calling site.

swift-server-bot · 2021-01-11T17:52:15Z

Can one of the admins verify this patch?

swift-server-bot · 2021-01-11T17:52:15Z

Can one of the admins verify this patch?

swift-server-bot · 2021-01-11T17:52:15Z

Can one of the admins verify this patch?

swift-server-bot · 2021-01-11T17:52:15Z

Can one of the admins verify this patch?

swift-server-bot · 2021-01-11T17:52:15Z

Can one of the admins verify this patch?

swift-server-bot · 2021-01-11T17:52:15Z

Can one of the admins verify this patch?

ktoso · 2021-01-11T23:43:14Z

@swift-server-bot test this please

weissi

I'm mostly happy with this but it does seem to add a Foundation dependency.

helje5 · 2021-01-12T16:29:49Z

OK, lets put that on hold. Of course I tried w/ importing WASILibc first (obviously). As mentioned it didn't carry either FILE nor strftime. That was w/ the 5.3.1 release.

If those do work, 95% of my modifications do not make any sense.

Not sure what went wrong in my first try.

helje5 · 2021-01-12T17:18:42Z

FILE isn't available though, file'd: swiftwasm/swift#2480

For WASI the Lock is not used at all, drop the local modifications I had in place before.

As per swiftwasm/swift#2480 (comment) `FILE` is not available in SwiftWasm, but `stdio` is. FILE pointers are exposed as OpaquePointer's in that environment. Also import the whole libc, like it is done with the other runtimes.

helje5 · 2021-01-22T12:04:33Z

OK, I had another look at this, this is much simpler now:

no more PrintOutputStream, instead modified the StdioOutputStream to use an OpaquePointer on WASI (instead of a proper UnsafeMutablePointer<FILE>)
use strftime, it is available
also reverted the changes within Lock, for WASI we just don't use it at all

I didn't do the os(WASI) checks suggested (though I agree they are more correct), as I'm not sure whether those are available on Swift 5.0 and canImport(WASILibc) should be OK.

This should be worth another review, I tried it and it works w/ the SwiftWasm 5.3.1 toolchain.

weissi · 2021-01-22T17:27:57Z

@swift-server-bot test this please

weissi · 2021-01-22T17:28:04Z

@swift-server-bot add to allowlist

weissi · 2021-01-22T17:29:36Z

I didn't do the os(WASI) checks suggested (though I agree they are more correct), as I'm not sure whether those are available on Swift 5.0 and canImport(WASILibc) should be OK.

You can do

#if compiler(>=5.3)
#if os(WASIlibc)

helje5 · 2021-01-22T17:49:09Z

I didn't do the os(WASI) checks suggested (though I agree they are more correct), as I'm not sure whether those are available on Swift 5.0 and canImport(WASILibc) should be OK.

You can do
#if compiler(>=5.3)
#if os(WASIlibc)

Yes, but do you really want to add that much #if cruft everywhere? I think we better stick to the simpler #if canImport then?

weissi · 2021-01-22T18:33:56Z

Yes, but do you really want to add that much #if cruft everywhere? I think we better stick to the simpler #if canImport then?

fine by me

helje5 · 2021-01-25T12:48:41Z

@MaxDesiatov Is this good now from your perspective? (if so, please mark things as resolved so that the PR can be merged)

MaxDesiatov

Great stuff, thanks!

weissi

Looks good to me!

weissi · 2021-01-25T12:54:50Z

@ktoso / @tomerd want to have a look here or good to merge?

ktoso

Went through and it's looking good, thanks @helje5 -- let's merge.

ktoso · 2021-01-25T12:58:54Z

// Had some ancient review comment from the time of the initial commit still there; deleted, ignore that :)

helje5 added 5 commits January 11, 2021 18:15

Make the locks noops on WASI

44b8a3c

There is no threading on WASI (yet? ever?).

Attempt to adjust for WASI, but doesn't work yet

295109a

The WASILibc doesn't provide much C yet, apparently. Not even FILE.

Use a PrintOutputStream on WASILibc

947eaf2

WASILibc doesn't have stdio, e.g. no `FILE`. But it does have `print`, so let's just use that instead for both, regular and error logging.

Use DateFormatter for timestamps on WASILibc

2f7a37d

WASILibc doesn't have `strftime`, but it does come w/ a working `DateFormatter`/`Date`. Use that instead.

Do not fake Lock availability on WASILibc

fc654a9

Instead do not compile the locks on WASILibc and comment them out on the calling site.

weissi requested changes Jan 12, 2021

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