Throw meaningful exceptions for schema errors.

bramble-api/src/main/java/org/briarproject/bramble/api/db/DataTooNewException.java

@@ -0,0 +1,7 @@
+package org.briarproject.bramble.api.db;
+
+/**
+ * Thrown when the database uses a newer schema than the current code.
+ */
+public class DataTooNewException extends DbException {
+}

bramble-api/src/main/java/org/briarproject/bramble/api/db/DataTooOldException.java

@@ -0,0 +1,8 @@
+package org.briarproject.bramble.api.db;
+
+/**
+ * Thrown when the database uses an older schema than the current code and
+ * cannot be migrated.
+ */
+public class DataTooOldException extends DbException {
+}

bramble-api/src/main/java/org/briarproject/bramble/api/db/DatabaseComponent.java

@@ -37,6 +37,11 @@ public interface DatabaseComponent {
 
 	/**
 	 * Opens the database and returns true if the database already existed.
+	 *
+	 * @throws DataTooNewException if the data uses a newer schema than the
+	 * current code
+	 * @throws DataTooOldException if the data uses an older schema than the
+	 * current code and cannot be migrated
 	 */
 	boolean open() throws DbException;
 

bramble-core/src/main/java/org/briarproject/bramble/db/Database.java

@@ -2,6 +2,8 @@ package org.briarproject.bramble.db;
 
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DataTooNewException;
+import org.briarproject.bramble.api.db.DataTooOldException;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.Metadata;
 import org.briarproject.bramble.api.identity.Author;
@@ -37,6 +39,11 @@ interface Database<T> {
 
 	/**
 	 * Opens the database and returns true if the database already existed.
+	 *
+	 * @throws DataTooNewException if the data uses a newer schema than the
+	 * current code
+	 * @throws DataTooOldException if the data uses an older schema than the
+	 * current code and cannot be migrated
 	 */
 	boolean open() throws DbException;
 

bramble-core/src/main/java/org/briarproject/bramble/db/JdbcDatabase.java

@@ -3,6 +3,8 @@ package org.briarproject.bramble.db;
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.db.DataTooNewException;
+import org.briarproject.bramble.api.db.DataTooOldException;
 import org.briarproject.bramble.api.db.DbClosedException;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.Metadata;
@@ -295,7 +297,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 		Connection txn = startTransaction();
 		try {
 			if (reopen) {
-				if (!checkSchemaVersion(txn)) throw new DbException();
+				checkSchemaVersion(txn);
 			} else {
 				createTables(txn);
 				storeSchemaVersion(txn, CODE_SCHEMA_VERSION);
@@ -310,16 +312,21 @@ abstract class JdbcDatabase implements Database<Connection> {
 
 	/**
 	 * Compares the schema version stored in the database with the schema
-	 * version used by the current code, applies any suitable migrations to the
+	 * version used by the current code and applies any suitable migrations to
-	 * data if necessary, and returns true if the schema now matches the
+	 * the data if necessary.
-	 * current code.
+	 *
+	 * @throws DataTooNewException if the data uses a newer schema than the
+	 * current code
+	 * @throws DataTooOldException if the data uses an older schema than the
+	 * current code and cannot be migrated
 	 */
-	private boolean checkSchemaVersion(Connection txn) throws DbException {
+	private void checkSchemaVersion(Connection txn) throws DbException {
 		Settings s = getSettings(txn, DB_SETTINGS_NAMESPACE);
 		int dataSchemaVersion = s.getInt(SCHEMA_VERSION_KEY, -1);
-		if (dataSchemaVersion == -1) return false;
+		if (dataSchemaVersion == -1) throw new DbException();
-		if (dataSchemaVersion == CODE_SCHEMA_VERSION) return true;
+		if (dataSchemaVersion == CODE_SCHEMA_VERSION) return;
-		if (CODE_SCHEMA_VERSION < dataSchemaVersion) return false;
+		if (CODE_SCHEMA_VERSION < dataSchemaVersion)
+			throw new DataTooNewException();
 		// Apply any suitable migrations in order
 		for (Migration<Connection> m : getMigrations()) {
 			int start = m.getStartVersion(), end = m.getEndVersion();
@@ -333,7 +340,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 				dataSchemaVersion = end;
 			}
 		}
-		return dataSchemaVersion == CODE_SCHEMA_VERSION;
+		if (dataSchemaVersion != CODE_SCHEMA_VERSION)
+			throw new DataTooOldException();
 	}
 
 	// Package access for testing

bramble-core/src/test/java/org/briarproject/bramble/db/DatabaseMigrationTest.java

@@ -1,5 +1,7 @@
 package org.briarproject.bramble.db;
 
+import org.briarproject.bramble.api.db.DataTooNewException;
+import org.briarproject.bramble.api.db.DataTooOldException;
 import org.briarproject.bramble.api.db.DatabaseConfig;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
@@ -95,7 +97,7 @@ public abstract class DatabaseMigrationTest extends BrambleMockTestCase {
 		db.close();
 	}
 
-	@Test(expected = DbException.class)
+	@Test(expected = DataTooNewException.class)
 	public void testThrowsExceptionIfDataIsNewerThanCode() throws Exception {
 		// Open the DB for the first time
 		Database<Connection> db = createDatabase(asList(migration, migration1));
@@ -109,7 +111,7 @@ public abstract class DatabaseMigrationTest extends BrambleMockTestCase {
 		db.open();
 	}
 
-	@Test(expected = DbException.class)
+	@Test(expected = DataTooOldException.class)
 	public void testThrowsExceptionIfCodeIsNewerThanDataAndNoMigrations()
 			throws Exception {
 		// Open the DB for the first time
@@ -123,7 +125,7 @@ public abstract class DatabaseMigrationTest extends BrambleMockTestCase {
 		db.open();
 	}
 
-	@Test(expected = DbException.class)
+	@Test(expected = DataTooOldException.class)
 	public void testThrowsExceptionIfCodeIsNewerThanDataAndNoSuitableMigration()
 			throws Exception {
 		context.checking(new Expectations() {{