refactor: Convert from Gson to Moshi (#428)

Moshi is faster to decode JSON at runtime, is actively maintained, has a
smaller memory and method footprint, and a slightly smaller APK size.
Moshi also correctly creates default constructor arguments instead of
leaving them null, which was a source of `NullPointerExceptions` when
using Gson.

The conversion broadly consisted of:

- Adding `@JsonClass(generateAdapter = true)` to data classes that
marshall to/from JSON.

- Replacing `@SerializedName(value = ...)` with `@Json(name = ...)`.

- Replacing Gson instances with Moshi in Retrofit, Hilt, and tests.

- Using Moshi adapters to marshall to/from JSON instead of Gson `toJson`
/ `fromJson`.

- Deleting `Rfc3339DateJsonAdapter` and related code, and using the
equivalent adapter bundled with Moshi.

- Rewriting `GuardedBooleanAdapter` as a more generic `GuardedAdapter`.

- Deleting unused ProGuard rules; Moshi generates adapters using code
generation, not runtime reflection.

The conversion surfaced some bugs which have been fixed.

- Not all audio attachments have attachment size metadata. Don't show
the attachment preview if the metadata is missing.

- Some `throwable` were not being logged correctly.

- The wrong type was being used when parsing the response when sending a
scheduled status.

- Exceptions other than `HttpException` or `IoException` would also
cause a status to be resent. If there's a JSON error parsing a response
the status would be repeatedly sent.

- In tests strings containing error responses were not valid JSON.

- Workaround Mastodon a bug and ensure `filter.keywords` is populated,
mastodon/mastodon#29142

app/build.gradle.kts

@@ -143,7 +143,9 @@ dependencies {
 
     implementation(libs.android.material)
 
-    implementation(libs.gson)
+    implementation(libs.moshi)
+    implementation(libs.moshi.adapters)
+    ksp(libs.moshi.codegen)
 
     implementation(libs.bundles.retrofit)
 

app/proguard-rules.pro

@@ -57,19 +57,6 @@
 # error reports
 -keepnames class *
 
-# https://github.com/google/gson/blob/master/examples/android-proguard-example/proguard.cfg
-
-# Prevent proguard from stripping interface information from TypeAdapter, TypeAdapterFactory,
-# JsonSerializer, JsonDeserializer instances (so they can be used in @JsonAdapter)
--keep class * extends com.google.gson.TypeAdapter
--keep class * implements com.google.gson.TypeAdapterFactory
--keep class * implements com.google.gson.JsonSerializer
--keep class * implements com.google.gson.JsonDeserializer
-
-# Retain generic signatures of TypeToken and its subclasses with R8 version 3.0 and higher.
--keep,allowobfuscation,allowshrinking class com.google.gson.reflect.TypeToken
--keep,allowobfuscation,allowshrinking class * extends com.google.gson.reflect.TypeToken
-
 # Retain generic signatures of classes used in MastodonApi so Retrofit works
 -keep,allowobfuscation,allowshrinking class io.reactivex.rxjava3.core.Single
 -keep,allowobfuscation,allowshrinking class retrofit2.Response

app/src/fdroid/kotlin/app/pachli/di/UpdateCheckModule.kt

@@ -19,15 +19,14 @@ package app.pachli.di
 
 import app.pachli.updatecheck.FdroidService
 import at.connyduck.calladapter.networkresult.NetworkResultCallAdapterFactory
-import com.google.gson.Gson
 import dagger.Module
 import dagger.Provides
 import dagger.hilt.InstallIn
 import dagger.hilt.components.SingletonComponent
 import javax.inject.Singleton
 import okhttp3.OkHttpClient
 import retrofit2.Retrofit
-import retrofit2.converter.gson.GsonConverterFactory
+import retrofit2.converter.moshi.MoshiConverterFactory
 import retrofit2.create
 
 @InstallIn(SingletonComponent::class)
@@ -37,11 +36,10 @@ object UpdateCheckModule {
     @Singleton
     fun providesFdroidService(
         httpClient: OkHttpClient,
-        gson: Gson,
     ): FdroidService = Retrofit.Builder()
         .baseUrl("https://f-droid.org")
         .client(httpClient)
-        .addConverterFactory(GsonConverterFactory.create(gson))
+        .addConverterFactory(MoshiConverterFactory.create())
         .addCallAdapterFactory(NetworkResultCallAdapterFactory.create())
         .build()
         .create()

app/src/fdroid/kotlin/app/pachli/updatecheck/FdroidService.kt

@@ -19,16 +19,19 @@ package app.pachli.updatecheck
 
 import androidx.annotation.Keep
 import at.connyduck.calladapter.networkresult.NetworkResult
+import com.squareup.moshi.JsonClass
 import retrofit2.http.GET
 import retrofit2.http.Path
 
 @Keep
+@JsonClass(generateAdapter = true)
 data class FdroidPackageVersion(
     val versionName: String,
     val versionCode: Int,
 )
 
 @Keep
+@JsonClass(generateAdapter = true)
 data class FdroidPackage(
     val packageName: String,
     val suggestedVersionCode: Int,

app/src/github/kotlin/app/pachli/di/UpdateCheckModule.kt

@@ -19,15 +19,13 @@ package app.pachli.di
 
 import app.pachli.updatecheck.GitHubService
 import at.connyduck.calladapter.networkresult.NetworkResultCallAdapterFactory
-import com.google.gson.Gson
 import dagger.Module
 import dagger.Provides
 import dagger.hilt.InstallIn
 import dagger.hilt.components.SingletonComponent
 import javax.inject.Singleton
 import okhttp3.OkHttpClient
 import retrofit2.Retrofit
-import retrofit2.converter.gson.GsonConverterFactory
 import retrofit2.create
 
 @InstallIn(SingletonComponent::class)
@@ -37,11 +35,10 @@ object UpdateCheckModule {
     @Singleton
     fun providesGitHubService(
         httpClient: OkHttpClient,
-        gson: Gson,
     ): GitHubService = Retrofit.Builder()
         .baseUrl("https://api.github.com")
         .client(httpClient)
-        .addConverterFactory(GsonConverterFactory.create(gson))
+        .addConverterFactory(MoshiConverterFactory.create())
         .addCallAdapterFactory(NetworkResultCallAdapterFactory.create())
         .build()
         .create()

app/src/github/kotlin/app/pachli/updatecheck/GithubService.kt

@@ -19,23 +19,26 @@ package app.pachli.updatecheck
 
 import androidx.annotation.Keep
 import at.connyduck.calladapter.networkresult.NetworkResult
-import com.google.gson.annotations.SerializedName
+import com.squareup.moshi.Json
+import com.squareup.moshi.JsonClass
 import retrofit2.http.GET
 import retrofit2.http.Path
 
 @Keep
+@JsonClass(generateAdapter = true)
 data class GitHubReleaseAsset(
     /** File name for the asset, e.g., "113.apk" */
     val name: String,
 
     /** MIME content type for the asset, e.g., "application/vnd.android.package-archive" */
-    @SerializedName("content_type") val contentType: String,
+    @Json(name = "content_type") val contentType: String,
 )
 
 @Keep
+@JsonClass(generateAdapter = true)
 data class GitHubRelease(
     /** URL for the release's web page */
-    @SerializedName("html_url") val htmlUrl: String,
+    @Json(name = "html_url") val htmlUrl: String,
     val assets: List<GitHubReleaseAsset>,
 )
 

app/src/main/java/app/pachli/ViewMediaActivity.kt

@@ -37,10 +37,7 @@ import android.view.MenuItem
 import android.view.View
 import android.webkit.MimeTypeMap
 import android.widget.Toast
-import androidx.core.app.ActivityCompat.invalidateOptionsMenu
-import androidx.core.app.ActivityCompat.requestPermissions
 import androidx.core.app.ShareCompat
-import androidx.core.content.ContextCompat.getSystemService
 import androidx.core.content.FileProvider
 import androidx.fragment.app.FragmentActivity
 import androidx.lifecycle.Lifecycle
@@ -89,7 +86,7 @@ class ViewMediaActivity : BaseActivity(), ViewImageFragment.PhotoActionsListener
     var isToolbarVisible = true
         private set
 
-    private var attachments: ArrayList<AttachmentViewData>? = null
+    private var attachments: List<AttachmentViewData>? = null
     private val toolbarVisibilityListeners = mutableListOf<ToolbarVisibilityListener>()
     private var imageUrl: String? = null
 

app/src/main/java/app/pachli/adapter/ReportNotificationViewHolder.kt

@@ -91,7 +91,7 @@ class ReportNotificationViewHolder(
         binding.notificationSummary.text = itemView.context.getString(
             R.string.notification_summary_report_format,
             getRelativeTimeSpanString(itemView.context, report.createdAt.time, Date().time),
-            report.status_ids?.size ?: 0,
+            report.statusIds?.size ?: 0,
         )
         binding.notificationCategory.text = getTranslatedCategory(itemView.context, report.category)
 

app/src/main/java/app/pachli/adapter/StatusBaseViewHolder.kt

@@ -901,6 +901,8 @@ abstract class StatusBaseViewHolder<T : IStatusViewData> protected constructor(i
         protected fun hasPreviewableAttachment(attachments: List<Attachment>): Boolean {
             for (attachment in attachments) {
                 if (attachment.type == Attachment.Type.UNKNOWN) return false
+
+                if (attachment.meta?.original?.width == null && attachment.meta?.small?.width == null) return false
             }
             return true
         }

app/src/main/java/app/pachli/appstore/CacheUpdater.kt

@@ -2,19 +2,22 @@ package app.pachli.appstore
 
 import app.pachli.core.accounts.AccountManager
 import app.pachli.core.database.dao.TimelineDao
-import com.google.gson.Gson
+import app.pachli.core.network.model.Poll
+import com.squareup.moshi.Moshi
+import com.squareup.moshi.adapter
 import javax.inject.Inject
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.SupervisorJob
 import kotlinx.coroutines.cancel
 import kotlinx.coroutines.launch
 
+@OptIn(ExperimentalStdlibApi::class)
 class CacheUpdater @Inject constructor(
     eventHub: EventHub,
     accountManager: AccountManager,
     timelineDao: TimelineDao,
-    gson: Gson,
+    moshi: Moshi,
 ) {
     private val scope = CoroutineScope(Dispatchers.IO + SupervisorJob())
 
@@ -34,7 +37,7 @@ class CacheUpdater @Inject constructor(
                     is StatusDeletedEvent ->
                         timelineDao.delete(accountId, event.statusId)
                     is PollVoteEvent -> {
-                        val pollString = gson.toJson(event.poll)
+                        val pollString = moshi.adapter<Poll>().toJson(event.poll)
                         timelineDao.setVoted(accountId, event.statusId, pollString)
                     }
                     is PinEvent ->

app/src/main/java/app/pachli/appstore/Events.kt

@@ -18,7 +18,7 @@ data class StatusDeletedEvent(val statusId: String) : Event
 /** A status the user wrote was successfully sent */
 // TODO: Rename, calling it "Composed" does not imply anything about the sent state
 data class StatusComposedEvent(val status: Status) : Event
-data class StatusScheduledEvent(val status: Status) : Event
+data object StatusScheduledEvent : Event
 data class StatusEditedEvent(val originalId: String, val status: Status) : Event
 data class ProfileEditedEvent(val newProfileData: Account) : Event
 data class FilterChangedEvent(val filterKind: Filter.Kind) : Event

app/src/main/java/app/pachli/components/notifications/NotificationsPagingSource.kt

@@ -24,7 +24,8 @@ import app.pachli.core.network.model.Error
 import app.pachli.core.network.model.Links
 import app.pachli.core.network.model.Notification
 import app.pachli.core.network.retrofit.MastodonApi
-import com.google.gson.Gson
+import com.squareup.moshi.Moshi
+import com.squareup.moshi.adapter
 import javax.inject.Inject
 import kotlinx.coroutines.async
 import kotlinx.coroutines.coroutineScope
@@ -37,9 +38,10 @@ private val INVALID = LoadResult.Invalid<String, Notification>()
 /** [PagingSource] for Mastodon Notifications, identified by the Notification ID */
 class NotificationsPagingSource @Inject constructor(
     private val mastodonApi: MastodonApi,
-    private val gson: Gson,
+    private val moshi: Moshi,
     private val notificationFilter: Set<Notification.Type>,
 ) : PagingSource<String, Notification>() {
+    @OptIn(ExperimentalStdlibApi::class)
     override suspend fun load(params: LoadParams<String>): LoadResult<String, Notification> {
         Timber.d("load() with ${params.javaClass.simpleName} for key: ${params.key}")
 
@@ -67,12 +69,12 @@ class NotificationsPagingSource @Inject constructor(
                     if (errorBody.isBlank()) return@let "no reason given"
 
                     val error = try {
-                        gson.fromJson(errorBody, Error::class.java)
+                        moshi.adapter<Error>().fromJson(errorBody)!!
                     } catch (e: Exception) {
                         return@let "$errorBody ($e)"
                     }
 
-                    when (val desc = error.error_description) {
+                    when (val desc = error.errorDescription) {
                         null -> error.error
                         else -> "${error.error}: $desc"
                     }

app/src/main/java/app/pachli/components/notifications/NotificationsRepository.kt

@@ -25,7 +25,7 @@ import androidx.paging.PagingSource
 import app.pachli.core.common.di.ApplicationScope
 import app.pachli.core.network.model.Notification
 import app.pachli.core.network.retrofit.MastodonApi
-import com.google.gson.Gson
+import com.squareup.moshi.Moshi
 import javax.inject.Inject
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.async
@@ -36,7 +36,7 @@ import timber.log.Timber
 
 class NotificationsRepository @Inject constructor(
     private val mastodonApi: MastodonApi,
-    private val gson: Gson,
+    private val moshi: Moshi,
     @ApplicationScope private val externalScope: CoroutineScope,
 ) {
     private var factory: InvalidatingPagingSourceFactory<String, Notification>? = null
@@ -53,7 +53,7 @@ class NotificationsRepository @Inject constructor(
         Timber.d("getNotificationsStream(), filtering: $filter")
 
         factory = InvalidatingPagingSourceFactory {
-            NotificationsPagingSource(mastodonApi, gson, filter)
+            NotificationsPagingSource(mastodonApi, moshi, filter)
         }
 
         return Pager(

app/src/main/java/app/pachli/components/scheduled/ScheduledStatusViewModel.kt

@@ -51,7 +51,7 @@ class ScheduledStatusViewModel @Inject constructor(
                     pagingSourceFactory.remove(status)
                 },
                 { throwable ->
-                    Timber.w("Error deleting scheduled status", throwable)
+                    Timber.w("Error deleting scheduled status: $throwable")
                 },
             )
         }

app/src/main/java/app/pachli/components/search/adapter/SearchPagingSource.kt

@@ -22,6 +22,7 @@ import app.pachli.components.search.SearchType
 import app.pachli.core.network.model.SearchResult
 import app.pachli.core.network.retrofit.MastodonApi
 import at.connyduck.calladapter.networkresult.getOrElse
+import timber.log.Timber
 
 class SearchPagingSource<T : Any>(
     private val mastodonApi: MastodonApi,
@@ -61,7 +62,10 @@ class SearchPagingSource<T : Any>(
             limit = params.loadSize,
             offset = currentKey,
             following = false,
-        ).getOrElse { return LoadResult.Error(it) }
+        ).getOrElse {
+            Timber.w(it)
+            return LoadResult.Error(it)
+        }
 
         val res = parser(data)
 

app/src/main/java/app/pachli/components/search/fragments/SearchFragment.kt

@@ -79,7 +79,6 @@ abstract class SearchFragment<T : Any> :
         }
 
         adapter.addLoadStateListener { loadState ->
-
             if (loadState.refresh is LoadState.Error) {
                 showError()
             }

app/src/main/java/app/pachli/components/timeline/CachedTimelineRepository.kt

@@ -40,7 +40,7 @@ import app.pachli.util.EmptyPagingSource
 import app.pachli.viewdata.StatusViewData
 import at.connyduck.calladapter.networkresult.NetworkResult
 import at.connyduck.calladapter.networkresult.fold
-import com.google.gson.Gson
+import com.squareup.moshi.Moshi
 import javax.inject.Inject
 import javax.inject.Singleton
 import kotlinx.coroutines.CoroutineScope
@@ -66,7 +66,7 @@ class CachedTimelineRepository @Inject constructor(
     val timelineDao: TimelineDao,
     private val remoteKeyDao: RemoteKeyDao,
     private val translatedStatusDao: TranslatedStatusDao,
-    private val gson: Gson,
+    private val moshi: Moshi,
     @ApplicationScope private val externalScope: CoroutineScope,
 ) {
     private var factory: InvalidatingPagingSourceFactory<Int, TimelineStatusWithAccount>? = null
@@ -118,7 +118,7 @@ class CachedTimelineRepository @Inject constructor(
                     transactionProvider,
                     timelineDao,
                     remoteKeyDao,
-                    gson,
+                    moshi,
                 ),
                 pagingSourceFactory = factory!!,
             ).flow

app/src/main/java/app/pachli/components/timeline/viewmodel/CachedTimelineRemoteMediator.kt

@@ -36,7 +36,7 @@ import app.pachli.core.database.model.TimelineStatusWithAccount
 import app.pachli.core.network.model.Links
 import app.pachli.core.network.model.Status
 import app.pachli.core.network.retrofit.MastodonApi
-import com.google.gson.Gson
+import com.squareup.moshi.Moshi
 import java.io.IOException
 import kotlinx.coroutines.async
 import kotlinx.coroutines.coroutineScope
@@ -54,7 +54,7 @@ class CachedTimelineRemoteMediator(
     private val transactionProvider: TransactionProvider,
     private val timelineDao: TimelineDao,
     private val remoteKeyDao: RemoteKeyDao,
-    private val gson: Gson,
+    private val moshi: Moshi,
 ) : RemoteMediator<Int, TimelineStatusWithAccount>() {
     private val activeAccount = accountManager.activeAccount!!
 
@@ -254,17 +254,17 @@ class CachedTimelineRemoteMediator(
     @Transaction
     private suspend fun insertStatuses(statuses: List<Status>) {
         for (status in statuses) {
-            timelineDao.insertAccount(TimelineAccountEntity.from(status.account, activeAccount.id, gson))
+            timelineDao.insertAccount(TimelineAccountEntity.from(status.account, activeAccount.id, moshi))
             status.reblog?.account?.let {
-                val account = TimelineAccountEntity.from(it, activeAccount.id, gson)
+                val account = TimelineAccountEntity.from(it, activeAccount.id, moshi)
                 timelineDao.insertAccount(account)
             }
 
             timelineDao.insertStatus(
                 TimelineStatusEntity.from(
                     status,
                     timelineUserId = activeAccount.id,
-                    gson = gson,
+                    moshi = moshi,
                 ),
             )
         }