mono_wasm_timezone_get_local_name() throws an unhandled exception

[liorbalmas]

mono_wasm_timezone_get_local_name throws an unhandled exception when failing to resolve timezone from OS

To Reproduce

Not able to do so now ,as fixed the running server's timezone and didn't notice what it was before.
Point is Intl.DateTimeFormat().resolvedOptions().timeZone might return undefined in some cases and code should expect that.

Exceptions (if any)

unhandled exception

Further technical details

netstandard2.1

[Dotnet-GitSync-Bot]

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[mkArtakMSFT]

@lewing FYI

[lewing]

@liorbalmas what version of blazor are you using?

The net5.0 version wraps that code in a try/catch

https://github.com/dotnet/aspnetcore/blob/628ce6114bd426c80e57f637234fe94cf9b37c7d/src/Components/Web.JS/src/Platform/Mono/MonoPlatform.ts#L425

[campersau]

timeZone could return undefined:

timeZone
The value provided for this property in the options argument; undefined (representing the runtime's default time zone) if none was provided. Warning: Applications should not rely on undefined being returned, as future versions may return a String value > identifying the runtime’s default time zone instead.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DateTimeFormat/resolvedOptions

So the code should look like this:

    let timeZone;
    try {
      timeZone = Intl.DateTimeFormat().resolvedOptions().timeZone;
    } catch { }
    MONO.mono_wasm_setenv("TZ", timeZone || "UTC");

[lewing]

@campersau ah good point I just read the exception bit. I imagine this mostly impacts CI?

[campersau]

@lewing I think it just depends if the timezone is defined or not (see OP), not sure how CI servers are setup up. Does this also need to be fixed here?

runtime/src/mono/wasm/runtime/driver.c

Lines 930 to 941 in ee74ce2

	// Returns the local timezone default is UTC.
	EM_JS(size_t, mono_wasm_timezone_get_local_name, (),
	{
	var res = "UTC";
	try {
	res = Intl.DateTimeFormat().resolvedOptions().timeZone;
	} catch(e) {}
	var buff = Module._malloc((res.length + 1) * 2);
	stringToUTF16 (res, buff, (res.length + 1) * 2);
	return buff;
	})

[lewing]

@campersau that code needs a different fix, it isn't used in the blazor case though. I meant it is typically CI that doesn't have a timezone set, that isn't a common scenario for a browser in use. The initial issue mentioned the server's timezone which sounded like CI.