[Internal] Swift Lock Improvements

CHANGELOG.md

@@ -6,6 +6,7 @@
   to upload multiple transactions in a batch.
 * Fix modifying severity of the global Kermit logger
 * Add `PowerSync` tag for the logs
+* [INTERNAL] Added helpers for Swift read and write lock exception handling.
 
 ## 1.4.0
 

PowerSyncKotlin/src/appleMain/kotlin/com/powersync/Locks.kt

@@ -0,0 +1,57 @@
+package com.powersync
+
+import com.powersync.db.ThrowableLockCallback
+import com.powersync.db.ThrowableTransactionCallback
+import com.powersync.db.internal.ConnectionContext
+import com.powersync.db.internal.PowerSyncTransaction
+
+/**
+ * The Kotlin [Result] type is an inline class which cannot be used on the Swift side.
+ * This declares something similar which will help to bridge exceptions to Kotlin.
+ * SKIEE doesn't handle generics well.
+ * Making the Result type generic will cause the return type to be casted to "Any", but
+ * also add restrictions that the generic should extend an object - which causes issues when returning
+ * primitive types like `Int` or `String`.
+ */
+public sealed class PowerSyncResult {
+    public data class Success(
+        val value: Any,
+    ) : PowerSyncResult()
+
+    public data class Failure(
+        val exception: PowerSyncException,
+    ) : PowerSyncResult()
+}
+
+// Throws the [PowerSyncException] if the result is a failure, or returns the value if it is a success.
+// We throw the exception on behalf of the Swift SDK.
+@Throws(PowerSyncException::class)
+private fun handleLockResult(result: PowerSyncResult): Any {
+    when (result) {
+        is PowerSyncResult.Failure -> {
+            throw result.exception
+        }
+
+        is PowerSyncResult.Success -> {
+            return result.value
+        }
+    }
+}
+
+public class LockContextWrapper(
+    private val handler: (context: ConnectionContext) -> PowerSyncResult,
+) : ThrowableLockCallback<Any> {
+    override fun execute(context: ConnectionContext): Any = handleLockResult(handler(context))
+}
+
+public class TransactionContextWrapper(
+    private val handler: (context: PowerSyncTransaction) -> PowerSyncResult,
+) : ThrowableTransactionCallback<Any> {
+    override fun execute(transaction: PowerSyncTransaction): Any = handleLockResult(handler(transaction))
+}
+
+public fun wrapContextHandler(handler: (context: ConnectionContext) -> PowerSyncResult): ThrowableLockCallback<Any> =
+    LockContextWrapper(handler)
+
+public fun wrapTransactionContextHandler(handler: (context: PowerSyncTransaction) -> PowerSyncResult): ThrowableTransactionCallback<Any> =
+    TransactionContextWrapper(handler)

core/src/commonMain/kotlin/com/powersync/db/internal/InternalDatabaseImpl.kt

@@ -2,7 +2,6 @@ package com.powersync.db.internal
 
 import app.cash.sqldelight.db.SqlPreparedStatement
 import com.powersync.DatabaseDriverFactory
-import com.powersync.PowerSyncException
 import com.powersync.db.SqlCursor
 import com.powersync.db.ThrowableLockCallback
 import com.powersync.db.ThrowableTransactionCallback
@@ -181,9 +180,7 @@ internal class InternalDatabaseImpl(
         withContext(dbContext) {
             runWrapped {
                 readPool.withConnection {
-                    catchSwiftExceptions {
-                        callback(it)
-                    }
+                    callback(it)
                 }
             }
         }
@@ -196,23 +193,19 @@ internal class InternalDatabaseImpl(
     override suspend fun <R> readTransaction(callback: ThrowableTransactionCallback<R>): R =
         internalReadLock {
             it.transactor.transactionWithResult(noEnclosing = true) {
-                catchSwiftExceptions {
-                    callback.execute(
-                        PowerSyncTransactionImpl(
-                            it.driver,
-                        ),
-                    )
-                }
+                callback.execute(
+                    PowerSyncTransactionImpl(
+                        it.driver,
+                    ),
+                )
             }
         }
 
     private suspend fun <R> internalWriteLock(callback: (TransactorDriver) -> R): R =
         withContext(dbContext) {
             writeLockMutex.withLock {
                 runWrapped {
-                    catchSwiftExceptions {
-                        callback(writeConnection)
-                    }
+                    callback(writeConnection)
                 }.also {
                     // Trigger watched queries
                     // Fire updates inside the write lock
@@ -229,31 +222,17 @@ internal class InternalDatabaseImpl(
     override suspend fun <R> writeTransaction(callback: ThrowableTransactionCallback<R>): R =
         internalWriteLock {
             it.transactor.transactionWithResult(noEnclosing = true) {
-                // Need to catch Swift exceptions here for Rollback
-                catchSwiftExceptions {
-                    callback.execute(
-                        PowerSyncTransactionImpl(
-                            it.driver,
-                        ),
-                    )
-                }
+                callback.execute(
+                    PowerSyncTransactionImpl(
+                        it.driver,
+                    ),
+                )
             }
         }
 
     // Register callback for table updates on a specific table
     override fun updatesOnTables(): SharedFlow<Set<String>> = writeConnection.driver.updatesOnTables()
 
-    // Unfortunately Errors can't be thrown from Swift SDK callbacks.
-    // These are currently returned and should be thrown here.
-    private fun <R> catchSwiftExceptions(action: () -> R): R {
-        val result = action()
-
-        if (result is PowerSyncException) {
-            throw result
-        }
-        return result
-    }
-
     private suspend fun getSourceTables(
         sql: String,
         parameters: List<Any?>?,