Just discovered that it is possible to write edge ...

# supabase-kt

[Maanrifa Bacar Ali]

Just discovered that it is possible to write edge functions using kotlin and supabase-kt instead of typescript and supabase-js 👍

[Jan]

Via Kotlin/JS?

[Maanrifa Bacar Ali]

Yes

[Maanrifa Bacar Ali]

According to my observations, prerequisites are:

• Kotlin 2.0 (which bring ES modules support)
• JS IR with ES modules enabled (otherwise imports will not work as expected)
For now, to make it works I also have to set:

• Whole project JS IR output granularity (because of the way imports are done in generated kotlin code) but this can be fixed.
• NodeJs inside JS IR target
And for things to get simpler, I've created two gradle tasks (same task implementation) for development and production that depends respectively on jsNodeDevelopmentLibraryDistribution and jsNodeProductionLibraryDistribution tasks. The second one also invoke the supabase function deploy command.

The task generate two files:

• index.ts: contains the Deno serve function that will call and wait for the kotlin function to finish.
• import_map.json: contains all the dependencies from the package.json previously generated by the dependent kotlin task. This is necessary because of the way Deno works with imports even through Deno supports package.json.
For now this integration was experimental and can be greatly improved but it is sufficient to confirm that it is possible to write edge function using kotlin.

[Maanrifa Bacar Ali]

Below an exemple of a hello function written in kotlin:

index.ts (generated):

import { hello } from './build/dist/js/productionLibrary/hello.mjs';

Deno.serve(async (req) => {
   return await hello(req)
})

import_map.json (generated):

{
  "imports": {
    "format-util": "npm:format-util@^1.0.5",
    "node-fetch": "npm:node-fetch@2.6.7",
    "abort-controller": "npm:abort-controller@3.0.0",
    "ws": "npm:ws@8.5.0",
    "@js-joda/core": "npm:@js-joda/core@3.2.0"
  }
}

hello.kt (note that the body is suspending):

@Serializable
data class RequestBody(
    val name: String
)

@Serializable
data class ResponseBody(
    val message: String?
)

@OptIn(ExperimentalJsExport::class)
@JsExport
fun hello(request: Request) = serve {
    val requestBody = request.body<RequestBody>()

    val client = io.github.jan.supabase.createSupabaseClient(
        supabaseUrl = Deno.env[SupabaseSecrets.URL]!!,
        supabaseKey = Deno.env[SupabaseSecrets.ANON_KEY]!!
    ) {
        install(Auth) {
            codeVerifierCache = MemoryCodeVerifierCache()
            sessionManager = MemorySessionManager()
        }
    }

    jsonResponse(
        body = ResponseBody(
            message = "Hello ${requestBody.name} from ${client.supabaseUrl}",
        )
    )
}

serve.kt (from a shared module between functions, using composite build):

@OptIn(DelicateCoroutinesApi::class)
fun serve(action: suspend CoroutineScope.() -> Response): Promise<Response> {
    return GlobalScope
        .async(
            context = Dispatchers.Unconfined,
            start = CoroutineStart.UNDISPATCHED,
            block = action
        )
        .asPromise()
}

other things used (from different files in the same module as the serve function):

external interface Env {
    operator fun get(key: String): String?
}

external object Deno {
    val env: Env
}

object SupabaseSecrets {
    const val URL = "SUPABASE_URL"
    const val ANON_KEY = "SUPABASE_ANON_KEY"
    const val SERVICE_ROLE_KEY = "SUPABASE_SERVICE_ROLE_KEY"
    const val DB_URL = "SUPABASE_DB_URL"
}

// Gets the request body as instance of type T
suspend inline fun <reified T : Any> Request.body(): T {
    return Json.decodeFromString<T>(text().await())
}

inline fun <reified T : Any> jsonResponse(
    body: T,
    init: ResponseInit = ResponseInit(
        headers = Headers {
            jsonContentType()
        }
    )
): Response = Response(
    body = Json.encodeToString(body),
    init = init
)

[Maanrifa Bacar Ali]

Conjugated with gradle continuous build and gradle configuration cache, the development experience is more than satisfactory.

It requires less than 5 seconds in my machine (16" 2019 MBP) to compile that hello function and changing output granularity could improve things. During development, edge function invocation takes ≈400ms but once deployed in production it takes <100ms.

[Jan]

Nice work! We could transform this into a small experimental template/sample and steadily improve it. I'm sure a lot of people using Kotlin would prefer using Kotlin all the way.

[Maanrifa Bacar Ali]

I think so too. I’ll continue to play with that to find the limits and try to provide an experimental runtime lib accompanied by a gradle plugin.

[Thomas Valloo]

I also write edge functions in kt 👍
I am using FCM but couldn't find a way to get a FCM access token in pure Kotlin and had to use js.
If you also need to use your own js files :
in Kotlin :

@file:JsModule("./my-file.js")


import kotlin.js.Promise

@JsName("getFCMAccessToken")
external fun getFCMAccessToken(): Promise<String>

in src/jsMain/resources/my-file.js

import { JWT } from 'npm:google-auth-library@9'
import serviceAccount from '../service-account.json' with { type: 'json' }

//<https://supabase.com/docs/guides/functions/examples/push-notifications?queryGroups=platform&platform=fcm>

export function getFCMAccessToken() {
  return new Promise((resolve, reject) => {
    const jwtClient = new JWT({
      email: serviceAccount.client_email,
      key: serviceAccount.private_key,
      scopes: ['<https://www.googleapis.com/auth/firebase.messaging>'],
    })
    jwtClient.authorize((err, tokens) => {
      if (err) {
        reject(err)
        return
      }
      resolve(tokens.access_token)
    })
  })
}

And that way you can use it from Kotlin.

[Thomas Valloo]

I am currently trying to access postgres database directly, without using supabase.postgrest to execute multiple queries inside a transaction

[Maanrifa Bacar Ali]

Have you tried https://github.com/GitLiveApp/firebase-kotlin-sdk for getting an FCM access token in pure Kotlin ? (never tried it myself)

[Thomas Valloo]

I'll take a look, thanks

[blakelee]

@Maanrifa Bacar Ali I’m trying to follow your tips for creating my own edge functions with Kotlin.

How did you get that index.ts with the generated Deno?
What gradle task are you running to build
How do you test it locally? (localhost:8080?)

I’m just experimenting with it now but it would be really cool to have the edge function

[Maanrifa Bacar Ali]

Forget these tips, I’m working on something better, you’ll only have to focus on your business code. I plan to release something (experimental) by the end of the week or in the next 5 days

[blakelee]

Very cool. Thanks for the contribution. I don’t know anything about JS, but I know Kotlin very well so I’m trying to keep everything in house with my Kotlin Multiplatform app

[blakelee]

Any update to this? It would be cool to use Kotlin for an edge function.

[Maanrifa Bacar Ali]

Still on it, I was a little busy at work this week so I didn’t progress as planned. It’s about to be finished. I am currently working on composite build / projet dependency and js interoprability for sharing code between multiple projects with js sources. I ended up adding features that weren’t initially planned but that’s because I need them for my business. That’s why it took a little longer than expected.

[Maanrifa Bacar Ali]

I’ve finished writing source code and created an example repository. I’m currently writing the readme, generating documentation and dealing with maven for release. It will be ready for tomorrow and I’ll post the repository link here once available.

[blakelee]

Sweet thank you. Long live Kotlin

[Maanrifa Bacar Ali]

https://github.com/manriif/supabase-edge-functions-kt

Enjoy kodee loving

[blakelee]

Wow, this is much more than I was expecting. Great job! Thanks for your hard work.

[Maanrifa Bacar Ali]

It would be appreciated if someone could just confirm that they managed to compile the example, when they have time

[Thomas Valloo]

Did you have any luck with user auth for activating RLS policies ?

[Thomas Valloo]

In JS, it's possible to create the client like so :

const supabaseClient = createClient(
  Deno.env.get('SUPABASE_URL') ?? '',
  Deno.env.get('SUPABASE_ANON_KEY') ?? '',
  // Create client with Auth context of the user that called the function.
  // This way your row-level-security (RLS) policies are applied.
  {
    global: {
      headers: { Authorization: req.headers.get('Authorization')! },
    },
  }
)

Is there a way to do the same in kt ?

[Thomas Valloo]

@Jan maybe an idea ?

[Jan]

You can either just import the token into the Auth plugin or set the token per plugin.
1:

supabaseClient.auth.importAuthToken(tokenFromHeader)

2:

install(Postgrest) {
   jwtToken = tokenFromHeader
}

The 1. approach will assure that all other plugins use this token. Also, you should probably always use AuthConfig#minimalSettings when working with server-side code to avoid session saving somewhere you don't want

[Jan]

For creating a client, you can just have a look at the example

[Thomas Valloo]

thanks a lot for the detailed and quick answer !

[Thomas Valloo]

supabaseClient.auth.importAuthToken works like a charm ❤️