[CDAP-20711] Fix RFC 5322 multiple To headers issue for multiple recipients in EmailAction

core-plugins/src/main/java/io/cdap/plugin/batch/action/EmailAction.java

@@ -124,9 +124,8 @@ public PasswordAuthentication getPasswordAuthentication() {
     try {
       Message msg = new MimeMessage(session);
       msg.setFrom(new InternetAddress(config.sender));
-      for (InternetAddress internetAddress : InternetAddress.parse(config.recipients)) {
-        msg.addRecipient(Message.RecipientType.TO, internetAddress);
-      }
+      msg.setRecipients(Message.RecipientType.TO,
+                        InternetAddress.parse(config.recipients));
       msg.setSubject(config.subject);
       WorkflowToken token = context.getToken();
       String message = config.includeWorkflowToken ?

core-plugins/src/test/java/io/cdap/plugin/batch/action/EmailActionTestRun.java

@@ -19,9 +19,12 @@
 import com.dumbster.smtp.SimpleSmtpServer;
 import com.dumbster.smtp.SmtpMessage;
 import com.google.common.collect.ImmutableMap;
+import io.cdap.cdap.common.utils.Networks;
+import io.cdap.cdap.etl.api.batch.BatchActionContext;
 import io.cdap.cdap.etl.api.batch.BatchSink;
 import io.cdap.cdap.etl.api.batch.BatchSource;
 import io.cdap.cdap.etl.api.batch.PostAction;
+import io.cdap.cdap.etl.mock.validation.MockFailureCollector;
 import io.cdap.cdap.etl.proto.v2.ETLBatchConfig;
 import io.cdap.cdap.etl.proto.v2.ETLPlugin;
 import io.cdap.cdap.etl.proto.v2.ETLStage;
@@ -30,7 +33,9 @@
 import org.junit.Assert;
 import org.junit.Ignore;
 import org.junit.Test;
+import org.mockito.Mockito;
 
+import java.lang.reflect.Field;
 import java.util.Iterator;
 
 /**
@@ -87,4 +92,41 @@ public void testEmailAction() throws Exception {
     Assert.assertTrue(email.getBody().startsWith("Run for 1970-01-01 completed."));
     Assert.assertFalse(emailIter.hasNext());
   }
+
+  @Test
+  public void testMultipleRecipientsSingleToHeader() throws Exception {
+    int smtpPort = Networks.getRandomPort();
+    SimpleSmtpServer smtpServer = SimpleSmtpServer.start(smtpPort);
+    try {
+      EmailAction.Config config = new EmailAction.Config();
+      setField(config, "sender", "from@test.com");
+      setField(config, "recipients", "to1@test.com, to2@test.com");
+      setField(config, "subject", "Test Multiple Recipients");
+      setField(config, "message", "Test message body.");
+      setField(config, "port", smtpPort);
+
+      BatchActionContext context = Mockito.mock(BatchActionContext.class);
+      Mockito.when(context.getFailureCollector()).thenReturn(new MockFailureCollector());
+
+      EmailAction emailAction = new EmailAction(config);
+      emailAction.run(context);
+
+      Assert.assertEquals(1, smtpServer.getReceivedEmailSize());
+      Iterator<?> emailIter = smtpServer.getReceivedEmail();
+      SmtpMessage email = (SmtpMessage) emailIter.next();
+      Assert.assertEquals("Test Multiple Recipients", email.getHeaderValue("Subject"));
+      String[] toHeaders = email.getHeaderValues("To");
+      Assert.assertEquals(1, toHeaders.length);
+      Assert.assertEquals("to1@test.com, to2@test.com", toHeaders[0]);
+      Assert.assertFalse(emailIter.hasNext());
+    } finally {
+      smtpServer.stop();
+    }
+  }
+
+  private static void setField(Object target, String fieldName, Object value) throws Exception {
+    Field field = target.getClass().getDeclaredField(fieldName);
+    field.setAccessible(true);
+    field.set(target, value);
+  }
 }