Refactor common email sending utility

The main thrust of this is to create a common POJO that contains email content in a simple way, then have one class that converts that to an email and sends it. Any class that uses email should only have to deal with creating that POJO.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=237883643

java/google/registry/util/BUILD

@@ -11,6 +11,7 @@ java_library(
         "//third_party/jaxb",
         "//third_party/objectify:objectify-v4_1",
         "@com_google_appengine_api_1_0_sdk",
+        "@com_google_auto_value",
         "@com_google_code_findbugs_jsr305",
         "@com_google_dagger",
         "@com_google_errorprone_error_prone_annotations",

java/google/registry/util/EmailMessage.java

@@ -0,0 +1,94 @@
+// Copyright 2019 The Nomulus Authors. All Rights Reserved.
+//
+// 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 google.registry.util;
+
+import com.google.auto.value.AutoValue;
+import com.google.common.collect.ImmutableList;
+import com.google.common.net.MediaType;
+import java.util.Collection;
+import java.util.Optional;
+import javax.mail.internet.InternetAddress;
+
+/** Value class representing the content and metadata of an email. */
+@AutoValue
+public abstract class EmailMessage {
+
+  public abstract String subject();
+  public abstract String body();
+  public abstract ImmutableList<InternetAddress> recipients();
+  public abstract InternetAddress from();
+  public abstract Optional<InternetAddress> bcc();
+  public abstract Optional<MediaType> contentType();
+  public abstract Optional<Attachment> attachment();
+
+  public static Builder newBuilder() {
+    return new AutoValue_EmailMessage.Builder();
+  }
+
+  public static EmailMessage create(
+      String subject, String body, InternetAddress recipient, InternetAddress from) {
+    return newBuilder()
+        .setSubject(subject)
+        .setBody(body)
+        .setRecipients(ImmutableList.of(recipient))
+        .setFrom(from)
+        .build();
+  }
+
+  /** Builder for {@link EmailMessage}. */
+  @AutoValue.Builder
+  public abstract static class Builder {
+
+    public abstract Builder setSubject(String subject);
+    public abstract Builder setBody(String body);
+    public abstract Builder setRecipients(Collection<InternetAddress> recipients);
+    public abstract Builder setFrom(InternetAddress from);
+    public abstract Builder setBcc(InternetAddress bcc);
+    public abstract Builder setContentType(MediaType contentType);
+    public abstract Builder setAttachment(Attachment attachment);
+
+    abstract ImmutableList.Builder<InternetAddress> recipientsBuilder();
+
+    public Builder addRecipient(InternetAddress value) {
+      recipientsBuilder().add(value);
+      return this;
+    }
+
+    public abstract EmailMessage build();
+  }
+
+  /** An attachment to the email, if one exists. */
+  @AutoValue
+  public abstract static class Attachment {
+
+    public abstract MediaType contentType();
+    public abstract String filename();
+    public abstract String content();
+
+    public static Builder newBuilder() {
+      return new AutoValue_EmailMessage_Attachment.Builder();
+    }
+
+    /** Builder for {@link Attachment}. */
+    @AutoValue.Builder
+    public abstract static class Builder {
+
+      public abstract Builder setContentType(MediaType contentType);
+      public abstract Builder setFilename(String filename);
+      public abstract Builder setContent(String content);
+      public abstract Attachment build();
+    }
+  }
+}

java/google/registry/util/SendEmailService.java

@@ -14,29 +14,78 @@
 
 package google.registry.util;
 
+import static com.google.common.collect.Iterables.toArray;
+
+import com.google.common.net.MediaType;
+import google.registry.util.EmailMessage.Attachment;
+import java.io.IOException;
 import java.util.Properties;
 import javax.inject.Inject;
 import javax.inject.Singleton;
+import javax.mail.BodyPart;
 import javax.mail.Message;
+import javax.mail.Message.RecipientType;
 import javax.mail.MessagingException;
+import javax.mail.Multipart;
 import javax.mail.Session;
-import javax.mail.Transport;
+import javax.mail.internet.InternetAddress;
+import javax.mail.internet.MimeBodyPart;
 import javax.mail.internet.MimeMessage;
+import javax.mail.internet.MimeMultipart;
 
-/** Wrapper around javax.mail's Transport.send that can be mocked for testing purposes. */
+/**
+ * Wrapper around javax.mail's email creation and sending functionality. Encompasses a retry policy
+ * as well.
+ */
 @Singleton
 public class SendEmailService {
 
-  @Inject
-  SendEmailService() {};
+  private final Retrier retrier;
+  private final TransportEmailSender transportEmailSender;
 
-  /** Returns a new MimeMessage using default App Engine transport settings. */
-  public Message createMessage() {
-    return new MimeMessage(Session.getDefaultInstance(new Properties(), null));
+  @Inject
+  SendEmailService(Retrier retrier, TransportEmailSender transportEmailSender) {
+    this.retrier = retrier;
+    this.transportEmailSender = transportEmailSender;
   }
 
-  /** Sends a message using default App Engine transport. */
-  public void sendMessage(Message msg) throws MessagingException {
-    Transport.send(msg);
+  /**
+   * Converts the provided message content into a {@link javax.mail.Message} and sends it with
+   * retry on transient failures.
+   */
+  public void sendEmail(EmailMessage emailMessage) {
+    retrier.callWithRetry(
+        () -> {
+          Message msg =
+              new MimeMessage(
+                  Session.getDefaultInstance(new Properties(), /* authenticator= */ null));
+          msg.setFrom(emailMessage.from());
+          msg.addRecipients(
+              RecipientType.TO, toArray(emailMessage.recipients(), InternetAddress.class));
+          msg.setSubject(emailMessage.subject());
+
+          Multipart multipart = new MimeMultipart();
+          BodyPart bodyPart = new MimeBodyPart();
+          bodyPart.setContent(
+              emailMessage.body(),
+              emailMessage.contentType().orElse(MediaType.PLAIN_TEXT_UTF_8).toString());
+          multipart.addBodyPart(bodyPart);
+
+          if (emailMessage.attachment().isPresent()) {
+            Attachment attachment = emailMessage.attachment().get();
+            BodyPart attachmentPart = new MimeBodyPart();
+            attachmentPart.setContent(attachment.content(), attachment.contentType().toString());
+            attachmentPart.setFileName(attachment.filename());
+            multipart.addBodyPart(attachmentPart);
+          }
+          if (emailMessage.bcc().isPresent()) {
+            msg.addRecipient(RecipientType.BCC, emailMessage.bcc().get());
+          }
+          msg.setContent(multipart);
+          msg.saveChanges();
+          transportEmailSender.sendMessage(msg);
+        },
+        IOException.class,
+        MessagingException.class);
   }
 }

java/google/registry/util/TransportEmailSender.java

@@ -0,0 +1,34 @@
+// Copyright 2019 The Nomulus Authors. All Rights Reserved.
+//
+// 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 google.registry.util;
+
+import javax.inject.Inject;
+import javax.inject.Singleton;
+import javax.mail.Message;
+import javax.mail.MessagingException;
+import javax.mail.Transport;
+
+/** Wrapper for sending email so that we can test {@link google.registry.util.SendEmailService}. */
+@Singleton
+class TransportEmailSender {
+
+  @Inject
+  TransportEmailSender() {}
+
+  /** Sends a message using default App Engine transport. */
+  void sendMessage(Message msg) throws MessagingException {
+    Transport.send(msg);
+  }
+}