Response Date type is received as string

[dandeduck]

I have an endpoint which returns an object containing a Date field, eden displays the expected response correctly with Date so there are no TS errors. But during runtime, the field is actually a string.

Of course it makes sense because the JSON body can't contain Date fields, but if the intellisense is telling me that, I should receive a Date. It's still broken.

Ideally eden would have some process to fix this issue and convert the string to a Date, another solution would be for eden to interpret Dates as strings...

[mrctrifork]

Minimally reproducible example?

[dandeduck]

@mrctrifork Here you go

const app = new Elysia().get('/', () => ({ date: new Date() })).listen(3000)
const api = treaty<typeof app>('http://localhost:3000')

const res = await api.index.get()

console.log(res.data.date.getTime()) // Expected to work
// Actual result: Property 'getTime' does not exist, because date is a string

The intellisense shows the type of data as { date: Date }, but actual result is { date: string }

[mrctrifork]

You're right. I fixed a very similar bug some time ago in the websocktets part of eden. See this PR: #87
For some reason I thought that was fixed in eden too.

The fix should be simple but again; check this discussion to see why eden cannot differentiate when to parse a date from a string or to leave it as a string.

#92 (comment)

[dandeduck]

Thank you for looking into this. So the fix would involve adding the same check for ISO8601 strings, which isn't done currently in treaty correct?

If you ask me, I think it's worth adding to improve developer experience, even though we are limited by JSON structure. Perhaps one day Elysia could go the protobuf route and use a custom binary format for messaging to ensure 100% e2e type safety, which comes with its own downsides of course.

[mrctrifork]

Totally agree, I am not the author or the owner of this project; I just really like it :P; so it's not really my call

You could try submitting a similar PR to mine that checks for Date-shaped values as the values of a JSON response and attempt to parse them as dates.

[dandeduck]

I'll take a crack at it later today, looks pretty straight forward (never contributed to this project, so we'll see how it goes :P )

P.S. I Like this project a lot too :D

[dandeduck]

@mrctrifork Looking at the code I realized that in the case of application/json we just use the built in response.json(). Meaning to add this ability will require recursively looping over all properties of the parsed object and doing the date check, which might be pretty taxing performance wise on the client side... Do you think this should still be done?

P.S. while making the changes I realized there is a lot of duplicated code surrounding parsing (both in treaty2 and across other modules) I'm trying to combine everything into one parseUtils.ts file, what do you feel about it? Probably as part of this PR only treaty2 should be changed, in order to not make it as big.

[mrctrifork]

I agree that recursively traversing objects of unknown depth seeking for date-likes could take a hit on the performance.

I gave it some thought; and the approach with the least friction from the user" I believe is that this behavior could be toggled by a boolean flag; either when instantiating eden level or per-request level.

Another approach; perhaps Eden could ship an "onResponse" callback that people would import directly from the library and pass it along whenever they require dates to be parsed; making "enabling" such behavior explicit.

Regarding the dupped code; at least to me, it makes sense to extract common factor and reuse code whenever possible. Still, @SaltyAom might have reasons (of which, I am unaware of) on why this was done in such a way.

Since this is not my project I don't think I get to say how it should be done, hopefully @SaltyAom will share his opinion on the matter.

[dandeduck]

I thought about it some more, and I think that adding this step after calling response.json() isn't the right approach (even if it's configurable) Alternatively we could get the response as text (ignoring the json content header), and do the parsing manually, which probably has a performance cost as well.

There might be more creative solutions, but I don't have any easy ones off the top of my head. At least the docs should be updated to mention this known issue, since it may occur in many places where objects/arrays are sent with dates. Because the parsing code isn't centralized to one place, edge cases like that might reappear elsewhere. (Because of this we also sometimes check different standards to parse strings into Date for example)

I hope @SaltyAom can weigh in on this.

[mrctrifork]

True. The obvious approach sounds like it'd be to have the typebox schema also on the frontend do the parsing for each request but of course sometimes we don't even use it; like in your example.

[chneau]

Another solution to think about would be to use superjson?

[mrctrifork]

I don't see the usecase for superjson? that would fix the issue but introduces an (imho) unneeded level of complexity with extra metadata