Bundle sapling params in APK instead of downloading from remote servers

- Add sapling-spend.params and sapling-output.params to sdk-lib assets
- Rewrite SaplingParamTool to copy params from bundled assets instead of HTTP download
- Remove OkHttp dependency from SaplingParamTool
- Initialize SaplingParamTool with app context from Initializer

sdk-lib/src/main/java/cash/z/ecc/android/sdk/Initializer.kt

@@ -3,6 +3,7 @@ package cash.z.ecc.android.sdk
 import android.content.Context
 import cash.z.ecc.android.sdk.exception.InitializerException
 import cash.z.ecc.android.sdk.ext.ZcashSdk
+import cash.z.ecc.android.sdk.internal.SaplingParamTool
 import cash.z.ecc.android.sdk.internal.SdkDispatchers
 import cash.z.ecc.android.sdk.internal.ext.getCacheDirSuspend
 import cash.z.ecc.android.sdk.internal.ext.getDatabasePathSuspend
@@ -319,6 +320,7 @@ class Initializer private constructor(
             config: Config
         ): Initializer {
             config.validate()
+            SaplingParamTool.init(context)
 
             val loadedCheckpoint = run {
                 val height = config.birthdayHeight

sdk-lib/src/main/java/cash/z/ecc/android/sdk/internal/SaplingParamTool.kt

@@ -1,21 +1,28 @@
 package cash.z.ecc.android.sdk.internal
 
+import android.content.Context
 import cash.z.ecc.android.sdk.exception.TransactionEncoderException
 import cash.z.ecc.android.sdk.ext.ZcashSdk
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
-import okhttp3.OkHttpClient
-import okhttp3.Request
-import okio.buffer
-import okio.sink
 import java.io.File
 
 class SaplingParamTool {
 
     companion object {
+
+        private var appContext: Context? = null
+
         /**
-         * Checks the given directory for the output and spending params and calls [fetchParams] if
-         * they're missing.
+         * Initialize with application context so params can be copied from bundled assets.
+         */
+        fun init(context: Context) {
+            appContext = context.applicationContext
+        }
+
+        /**
+         * Checks the given directory for the output and spending params and copies them from
+         * bundled assets if they're missing.
          *
          * @param destinationDir the directory where the params should be stored.
          */
@@ -32,64 +39,44 @@ class SaplingParamTool {
             }
             if (hadError) {
                 try {
-                    Bush.trunk.twigTask("attempting to download missing params") {
-                        fetchParams(destinationDir)
+                    Bush.trunk.twigTask("copying bundled sapling params") {
+                        copyBundledParams(destinationDir)
                     }
                 } catch (e: Throwable) {
-                    twig("failed to fetch params due to: $e")
+                    twig("failed to copy bundled params due to: $e")
                     throw TransactionEncoderException.MissingParamsException
                 }
             }
         }
 
         /**
-         * Download and store the params into the given directory.
+         * Copy the sapling params from bundled assets into the given directory.
          *
-         * @param destinationDir the directory where the params will be stored. It's assumed that we
-         * have write access to this directory. Typically, this should be the app's cache directory
-         * because it is not harmful if these files are cleared by the user since they are downloaded
-         * on-demand.
+         * @param destinationDir the directory where the params will be stored.
          */
-        suspend fun fetchParams(destinationDir: String) {
-            val client = createHttpClient()
-            var failureMessage = ""
+        private suspend fun copyBundledParams(destinationDir: String) {
+            val context = appContext
+                ?: throw IllegalStateException("SaplingParamTool not initialized. Call init(context) first.")
+
             arrayOf(
                 ZcashSdk.SPEND_PARAM_FILE_NAME,
                 ZcashSdk.OUTPUT_PARAM_FILE_NAME
             ).forEach { paramFileName ->
-                val url = "${ZcashSdk.CLOUD_PARAM_DIR_URL.random()}/$paramFileName"
-                twig("Downloading Sapling params from ${url}...")
-                val request = Request.Builder().url(url).build()
-                val response = withContext(Dispatchers.IO) { client.newCall(request).execute() }
-                if (response.isSuccessful) {
-                    twig("fetch succeeded", -1)
-                    val file = File(destinationDir, paramFileName)
-                    if (file.parentFile?.existsSuspend() == true) {
-                        twig("directory exists!", -1)
-                    } else {
-                        twig("directory did not exist attempting to make it")
-                        file.parentFile?.mkdirsSuspend()
+                val destFile = File(destinationDir, paramFileName)
+                if (!destFile.existsSuspend()) {
+                    if (destFile.parentFile?.existsSuspend() != true) {
+                        destFile.parentFile?.mkdirsSuspend()
                     }
                     withContext(Dispatchers.IO) {
-                        response.body?.let { body ->
-                            body.source().use { source ->
-                                file.sink().buffer().use { sink ->
-                                    twig("writing to $file")
-                                    sink.writeAll(source)
-                                }
+                        context.assets.open("params/$paramFileName").use { input ->
+                            destFile.outputStream().use { output ->
+                                twig("copying bundled $paramFileName to $destFile")
+                                input.copyTo(output)
                             }
                         }
                     }
-                } else {
-                    failureMessage += "Error while fetching $paramFileName : $response\n"
-                    twig(failureMessage)
                 }
-
-                twig("fetch succeeded, done writing $paramFileName")
             }
-            if (failureMessage.isNotEmpty()) throw TransactionEncoderException.FetchParamsException(
-                failureMessage
-            )
         }
 
         suspend fun clear(destinationDir: String) {
@@ -119,19 +106,6 @@ class SaplingParamTool {
             }
         }
 
-        //
-        // Helpers
-        //
-        /**
-         * Http client is only used for downloading sapling spend and output params data, which are
-         * necessary for the wallet to scan blocks.
-         *
-         * @return an http client suitable for downloading params data.
-         */
-        private fun createHttpClient(): OkHttpClient {
-            // TODO: add logging and timeouts
-            return OkHttpClient()
-        }
     }
 }