Return ArbitraryTransactionData instead of a byte array, as it is more useful if the bytes are transformed separately.

src/main/java/org/qortal/api/resource/ArbitraryResource.java

@@ -262,10 +262,10 @@ public class ArbitraryResource {
 					publicKey58, Paths.get(path), name, Method.valueOf(methodString), Service.ARBITRARY_DATA
 			);
 
-			byte[] bytes = transactionBuilder.build();
-			return Base58.encode(bytes);
+			ArbitraryTransactionData transactionData = transactionBuilder.build();
+			return Base58.encode(ArbitraryTransactionTransformer.toBytes(transactionData));
 
-		} catch (DataException e) {
+		} catch (DataException | TransformationException e) {
 			throw ApiExceptionFactory.INSTANCE.createCustomException(request, ApiError.INVALID_DATA, e.getMessage());
 		}
 	}

src/main/java/org/qortal/api/resource/WebsiteResource.java

@@ -31,6 +31,7 @@ import org.qortal.api.ApiExceptionFactory;
 import org.qortal.api.HTMLParser;
 import org.qortal.api.Security;
 import org.qortal.arbitrary.ArbitraryDataTransactionBuilder;
+import org.qortal.data.transaction.ArbitraryTransactionData;
 import org.qortal.data.transaction.ArbitraryTransactionData.*;
 import org.qortal.repository.DataException;
 import org.qortal.settings.Settings;
@@ -38,6 +39,8 @@ import org.qortal.arbitrary.ArbitraryDataFile;
 import org.qortal.arbitrary.ArbitraryDataFile.*;
 import org.qortal.arbitrary.ArbitraryDataReader;
 import org.qortal.arbitrary.ArbitraryDataWriter;
+import org.qortal.transform.TransformationException;
+import org.qortal.transform.transaction.ArbitraryTransactionTransformer;
 import org.qortal.utils.Base58;
 
 
@@ -93,10 +96,10 @@ public class WebsiteResource {
                     publicKey58, Paths.get(path), name, Method.valueOf(methodString), Service.WEBSITE
             );
 
-            byte[] bytes = transactionBuilder.build();
-            return Base58.encode(bytes);
+            ArbitraryTransactionData transactionData = transactionBuilder.build();
+            return Base58.encode(ArbitraryTransactionTransformer.toBytes(transactionData));
 
-        } catch (DataException e) {
+        } catch (DataException | TransformationException e) {
             throw ApiExceptionFactory.INSTANCE.createCustomException(request, ApiError.INVALID_DATA, e.getMessage());
         }
     }

src/main/java/org/qortal/arbitrary/ArbitraryDataTransactionBuilder.java

@@ -44,7 +44,7 @@ public class ArbitraryDataTransactionBuilder {
         this.service = service;
     }
 
-    public byte[] build() throws DataException {
+    public ArbitraryTransactionData build() throws DataException {
         ArbitraryDataFile arbitraryDataFile = null;
         try (final Repository repository = RepositoryManager.getRepository()) {
 
@@ -109,11 +109,11 @@ public class ArbitraryDataTransactionBuilder {
                 throw new DataException(String.format("Arbitrary transaction invalid: %s", result));
             }
 
-            return ArbitraryTransactionTransformer.toBytes(transactionData);
+            return transactionData;
 
-        } catch (TransformationException | DataException e) {
+        } catch (DataException e) {
             arbitraryDataFile.deleteAll();
-            throw new DataException(String.format("Unable to build ARBITRARY transaction: %s", e.getMessage()));
+            throw(e);
         }
 
     }