FLW-8555

modules/flowable-engine/src/test/java/org/flowable/engine/test/bpmn/mail/EmailServiceTaskTest.java

@@ -502,6 +502,58 @@ public void testTextMailWithDataSourceAttachment() throws Exception {
         assertThat(attachmentFileName).isEqualTo(fileName);
     }
 
+    @Test
+    @Deployment(resources = "org/flowable/engine/test/bpmn/mail/EmailServiceTaskTest.testTextMailWithDataSourceAttachment.bpmn20.xml")
+    public void testTextMailWithDataSourceAttachmentLongNonAsciiFileName() throws Exception {
+        String fileName = "Précis of Evidence VA23-5-1034 Lorge Chocolatier PN 1136882 Retail Henry Street Kenmare Co.pdf";
+        String fileContent = "This is the file content";
+        HashMap<String, Object> vars = new HashMap<>();
+        vars.put("attachmentsBean", new AttachmentsBean());
+        vars.put("fileContent", fileContent);
+        vars.put("fileName", fileName);
+        runtimeService.startProcessInstanceByKey("textMailWithDataSourceAttachment", vars);
+
+        List<WiserMessage> messages = wiser.getMessages();
+        assertThat(messages).hasSize(1);
+        WiserMessage message = messages.get(0);
+        MimeMultipart mm = (MimeMultipart) message.getMimeMessage().getContent();
+        assertThat(mm.getCount()).isEqualTo(2);
+        String attachmentFileName = mm.getBodyPart(1).getDataHandler().getName();
+        assertThat(attachmentFileName).isEqualTo(fileName);
+    }
+
+    @Test
+    @Deployment(resources = "org/flowable/engine/test/bpmn/mail/EmailServiceTaskTest.testTextMailWithDataSourceAttachment.bpmn20.xml")
+    public void testTextMailWithDataSourceAttachmentUsesConfiguredCharset() throws Exception {
+        Charset originalCharset = processEngineConfiguration.getMailServerDefaultCharset();
+
+        try {
+            processEngineConfiguration.setMailServerDefaultCharset(StandardCharsets.ISO_8859_1);
+            reinitilizeMailClients();
+
+            String fileName = "café.pdf";
+            String fileContent = "This is the file content";
+            HashMap<String, Object> vars = new HashMap<>();
+            vars.put("attachmentsBean", new AttachmentsBean());
+            vars.put("fileContent", fileContent);
+            vars.put("fileName", fileName);
+            runtimeService.startProcessInstanceByKey("textMailWithDataSourceAttachment", vars);
+
+            List<WiserMessage> messages = wiser.getMessages();
+            assertThat(messages).hasSize(1);
+            WiserMessage message = messages.get(0);
+            MimeMultipart mm = (MimeMultipart) message.getMimeMessage().getContent();
+            String contentDisposition = mm.getBodyPart(1).getHeader("Content-Disposition")[0];
+
+            // 'é' is a single byte (0xE9) in ISO-8859-1 but two bytes (0xC3 0xA9) in UTF-8: this string can only
+            // appear if the configured ISO-8859-1 charset was actually used to encode the attachment file name.
+            assertThat(contentDisposition).contains("ISO-8859-1''caf%E9.pdf");
+            assertThat(mm.getBodyPart(1).getDataHandler().getName()).isEqualTo(fileName);
+        } finally {
+            processEngineConfiguration.setMailServerDefaultCharset(originalCharset);
+        }
+    }
+
     @Test
     @Deployment
     public void testTextMailWithNotExistingFileAttachment() throws Exception {

modules/flowable-mail/src/main/java/org/flowable/mail/common/impl/jakarta/mail/JakartaMailFlowableMailClient.java

@@ -36,11 +36,13 @@
 import jakarta.mail.Session;
 import jakarta.mail.Transport;
 import jakarta.mail.internet.AddressException;
+import jakarta.mail.internet.ContentDisposition;
 import jakarta.mail.internet.InternetAddress;
 import jakarta.mail.internet.MimeBodyPart;
 import jakarta.mail.internet.MimeMessage;
 import jakarta.mail.internet.MimeMultipart;
 import jakarta.mail.internet.MimeUtility;
+import jakarta.mail.internet.ParameterList;
 
 import org.apache.commons.lang3.StringUtils;
 import org.flowable.common.engine.api.FlowableException;
@@ -323,12 +325,7 @@ protected MimeMultipart createMultiPartContent(String text, String html, String
         if (attachmentsExists) {
             for (DataSource attachment : attachments) {
                 BodyPart bodyPart = new MimeBodyPart();
-                bodyPart.setDisposition(Part.ATTACHMENT);
-                try {
-                    bodyPart.setFileName(MimeUtility.encodeText(attachment.getName(), charset, null));
-                } catch (UnsupportedEncodingException e) {
-                    throw new FlowableMailException("Could not encode attachment file name", e);
-                }
+                setAttachmentFileName(bodyPart, attachment.getName(), charset);
                 bodyPart.setDataHandler(new DataHandler(attachment));
                 rootContainer.addBodyPart(bodyPart);
             }
@@ -337,6 +334,21 @@ protected MimeMultipart createMultiPartContent(String text, String html, String
         return rootContainer;
     }
 
+    protected void setAttachmentFileName(BodyPart bodyPart, String fileName, String charset) throws MessagingException {
+        // Build the Content-Disposition header ourselves instead of using BodyPart.setFileName(): that method
+        // ignores the charset argument entirely and RFC 2231 encodes with MimeUtility.getDefaultMIMECharset()
+        // (the JVM's file.encoding, unless mail.mime.charset is set), so it silently diverges from the charset
+        // used for the rest of the message. ParameterList.set(name, value, charset) does the same RFC 2231
+        // encoding and continuation folding, but with the charset we actually pass it, and leaves ASCII names
+        // untouched. When no charset is configured, fall back to the same default MimeBodyPart.setText() falls
+        // back to for the message body, so the file name and body stay consistent with each other.
+        String mimeCharset = charset != null ? charset : MimeUtility.mimeCharset(MimeUtility.getDefaultJavaCharset());
+        ParameterList parameters = new ParameterList();
+        parameters.set("filename", fileName, mimeCharset);
+        ContentDisposition disposition = new ContentDisposition(Part.ATTACHMENT, parameters);
+        bodyPart.setHeader("Content-Disposition", disposition.toString());
+    }
+
     protected Session createSession() {
         if (serverConfiguration instanceof MailJndiServerConfiguration jndiServerConfiguration) {
             return createSession(jndiServerConfiguration);

modules/flowable-mail/src/test/java/org/flowable/mail/common/impl/jakarta/mail/JakartaMailFlowableMailClientTest.java

@@ -0,0 +1,73 @@
+/* Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.flowable.mail.common.impl.jakarta.mail;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.List;
+
+import jakarta.mail.BodyPart;
+import jakarta.mail.MessagingException;
+import jakarta.mail.internet.MimeMultipart;
+import jakarta.mail.util.ByteArrayDataSource;
+
+import org.junit.jupiter.api.Test;
+
+class JakartaMailFlowableMailClientTest {
+
+    protected final JakartaMailFlowableMailClient client = new JakartaMailFlowableMailClient(null, null);
+
+    @Test
+    void attachmentFileNameThatIsLongAndNonAsciiIsNotCorrupted() throws MessagingException {
+        String fileName = "Précis of Evidence VA23-5-1034 Lorge Chocolatier PN 1136882 Retail Henry Street Kenmare Co.pdf";
+
+        ByteArrayDataSource attachment = new ByteArrayDataSource("attachment content".getBytes(), "application/pdf");
+        attachment.setName(fileName);
+
+        MimeMultipart multipart = client.createMultiPartContent(null, null, "UTF-8", List.of(attachment));
+
+        BodyPart attachmentPart = multipart.getBodyPart(0);
+        assertThat(attachmentPart.getFileName()).isEqualTo(fileName);
+    }
+
+    @Test
+    void attachmentFileNameThatIsShortAndAsciiIsUnaffected() throws MessagingException {
+        String fileName = "invoice.pdf";
+        ByteArrayDataSource attachment = new ByteArrayDataSource("attachment content".getBytes(), "application/pdf");
+        attachment.setName(fileName);
+
+        MimeMultipart multipart = client.createMultiPartContent(null, null, "UTF-8", List.of(attachment));
+
+        BodyPart attachmentPart = multipart.getBodyPart(0);
+        assertThat(attachmentPart.getFileName()).isEqualTo(fileName);
+    }
+
+    @Test
+    void attachmentFileNameIsEncodedWithTheGivenCharsetRatherThanThePlatformDefault() throws MessagingException {
+        String fileName = "café.pdf";
+        ByteArrayDataSource attachment = new ByteArrayDataSource("attachment content".getBytes(), "application/pdf");
+        attachment.setName(fileName);
+
+        MimeMultipart multipart = client.createMultiPartContent(null, null, "ISO-8859-1", List.of(attachment));
+
+        BodyPart attachmentPart = multipart.getBodyPart(0);
+        String contentDisposition = attachmentPart.getHeader("Content-Disposition")[0];
+
+        // 'é' is a single byte (0xE9) in ISO-8859-1 but two bytes (0xC3 0xA9) in UTF-8: this string can only
+        // appear if the ISO-8859-1 charset passed to createMultiPartContent() was actually used to encode it,
+        // rather than UTF-8 or the JVM's platform default charset.
+        assertThat(contentDisposition).contains("ISO-8859-1''caf%E9.pdf");
+        assertThat(attachmentPart.getFileName()).isEqualTo(fileName);
+    }
+
+}