tauri-plugins-workspace/plugins/fs/android/src/main/java/FsPlugin.kt

// Copyright 2019-2023 Tauri Programme within The Commons Conservancy
// SPDX-License-Identifier: Apache-2.0
// SPDX-License-Identifier: MIT

package com.plugin.fs

import android.annotation.SuppressLint
import android.app.Activity
import android.content.res.AssetManager.ACCESS_BUFFER
import android.net.Uri
import android.os.ParcelFileDescriptor
import app.tauri.annotation.Command
import app.tauri.annotation.InvokeArg
import app.tauri.annotation.TauriPlugin
import app.tauri.plugin.Invoke
import app.tauri.plugin.JSObject
import app.tauri.plugin.Plugin
import java.io.File
import java.io.FileOutputStream
import java.io.IOException
import java.io.InputStream
import java.io.OutputStream

@InvokeArg
class WriteTextFileArgs {
  val uri: String = ""
  val content: String = ""
}

@InvokeArg
class GetFileDescriptorArgs {
    lateinit var uri: String
    lateinit var mode: String
}

@TauriPlugin
class FsPlugin(private val activity: Activity): Plugin(activity) {
    @SuppressLint("Recycle")
    @Command
    fun getFileDescriptor(invoke: Invoke) {
        val args = invoke.parseArgs(GetFileDescriptorArgs::class.java)

        val res = JSObject()

        if (args.uri.startsWith(app.tauri.TAURI_ASSETS_DIRECTORY_URI)) {
            val path = args.uri.substring(app.tauri.TAURI_ASSETS_DIRECTORY_URI.length)
            try {
                val fd = activity.assets.openFd(path).parcelFileDescriptor?.detachFd()
                res.put("fd", fd)
            } catch (e: IOException) {
                // if the asset is compressed, we cannot open a file descriptor directly
                // so we copy it to the cache and get a fd from there
                // this is a lot faster than serializing the file and sending it as invoke response
                // because on the Rust side we can leverage the custom protocol IPC and read the file directly
                val cacheFile = File(activity.cacheDir, "_assets/$path")
                cacheFile.parentFile?.mkdirs()
                copyAsset(path, cacheFile)

                val fd = ParcelFileDescriptor.open(cacheFile, ParcelFileDescriptor.parseMode(args.mode)).detachFd()
                res.put("fd", fd)
            }
        } else {
            val fd = activity.contentResolver.openAssetFileDescriptor(
                Uri.parse(args.uri),
                args.mode
            )?.parcelFileDescriptor?.detachFd()
            res.put("fd", fd)
        }

        invoke.resolve(res)
    }

    @Throws(IOException::class)
    private fun copy(input: InputStream, output: OutputStream) {
        val buf = ByteArray(1024)
        var len: Int
        while ((input.read(buf).also { len = it }) > 0) {
            output.write(buf, 0, len)
        }
    }

    @Throws(IOException::class)
    private fun copyAsset(assetPath: String, cacheFile: File) {
        val input = activity.assets.open(assetPath, ACCESS_BUFFER)
        input.use { i ->
            val output = FileOutputStream(cacheFile, false)
            output.use { o ->
                copy(i, o)
            }
        }
    }
}