Accessing assets of main application inside package

Question

i'm currently trying to develop a package for a Flutter App, with Kotlin. My issue is that I need to provide the package with a config file, which should only be defined inside the main App. Since the config differs for the Dev and Prod environment, the app should pass through the path of the File via the Method Channel. The problem is that the package isn't able to access the assets folder of the calling application. Path: "assets/config.json" (the root being the main application)

Steps I already tried:

Creating the file inside the res/raw & accessing the config file through a ressource id -> Kotlin gives me an "Unresolved reference" error, unless I create the file inside the packages res/raw
Instead of passing through the path, I tried passing through the content of the config & writing it into an empty temporary file. The code in Kotlin like this:
```
    val config = File(applicationContext.filesDir,"config.json")
    config.writeText(configContent)
```

-> This works, but it seems like a weird solution to the problem.

please let me know if I need to provide further information & thank you in advance!

edit:

The Java Method that is called during initialisation:

public static void createMultipleAccountPublicClientApplication(@NonNull final Context context,
                                                                @NonNull final File configFile,
                                                                @NonNull final IMultipleAccountApplicationCreatedListener listener)

As you've seen, you'll need to write the asset to a file, somewhere (if it really must be a file). You can do it the way you show, or have Dart write it to a temporary file you create with, say, `path_provider` and then pass the filename over the channel. That does raise the question of why your plugin needs a file. Can't it parse its config from a string in memory, for example? — Richard Heap, Dec 14 '21 at 18:36
Thank you for your answer! The Library I'm basing this plug in off of, requires the config to be parsed from a file during initialisation. (I'll add an example as an edit) Where should should the app create this file, so it can be accessed by the plugin? Is there an equivalent to the filesDir i've shown in my example in Dart? — Paul A., Dec 15 '21 at 12:53

score 1 · Accepted Answer · answered Dec 15 '21 at 14:01

Flutter assets aren't files - they are packaged up and only available through the rootBundle. So, if you want to make a file from a text asset, someone has to load the asset and write it to a file.

As your plugin user will be in charge of the asset, they will have to do the first part (and will end up with a String). The question arises of who should do the writing.

You could make the plugin user use path_provider to find the temporary directory and write it there and then pass you the file path. Eventually, down in the Java, you new File(theTempFilePath). Or they could pass the string to the Dart half of your plugin and you create the temp file in the same way.

It's probably more convenient if they pass your plugin the string, you pass that to the native side and have the native side create a temporary file and write the string there. (BTW, I assume we are talking about this config file: https://learn.microsoft.com/en-us/azure/active-directory/develop/msal-configuration#how-to-use-a-configuration-file )

See this answer for creating temporary files: Creating temporary files in Android

Note that there's actually no reason that your plugin user then needs to use an asset. They could, instead, just hard code the string in their code if the configuration never really changes.

There's an argument that as this is a JSON configuration file, you may not want to bother your user with the details of this JSON configuration file. You may want to default it in your Dart code (why not hard code it as a string, as above, if it never really changes) and then provide some methods to override particular values like the client id and the redirect uri, which may be the only things that users ever change in practice. So rather than making them supply a complete JSON file, they just give you those two strings and you plonk them into your default JSON. Maybe a version 2 feature :)

I wonder if you wouldn't find it easier to simply implement the parts of the MSAL library that you need in Dart. Why go to the effort of making a plugin to wrap the Android and iOS implementations - which are open source and you can read how they work. If all you need is authentication, check out https://pub.dev/packages/openid_client. We wrote out own OpenID connect client for Azure, so perfectly possible. — Richard Heap, Dec 15 '21 at 16:12
Wow, thank you so much for your detailed explanations! I'm curious how do you go about updating your implementation, if there are changes in the MSAL Library? Or is the method of authentication not something that is regularily updated? First of all I can't claim that it was my idea to wrap it through Kotlin, since im simply updating an outdated package. However it does seem easier to maintain, if all you have to do to get the newest security features is change the version number in the gradle, no? :) — Paul A., Dec 15 '21 at 17:10

Accessing assets of main application inside package

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