Send emails from Appengine with inline attachments through Mailgun

CloudStorageManager.java

package com.alejandrogr.gists.mailgun;

import static com.alejandrogr.gists.mailgun.CloudStorageManager.JSON_FACTORY;
import static com.alejandrogr.gists.mailgun.CloudStorageManager.TRANSPORT;
import com.google.api.client.extensions.appengine.http.UrlFetchTransport;
import com.google.api.client.googleapis.auth.oauth2.GoogleCredential;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.json.JsonFactory;
import com.google.api.client.json.gson.GsonFactory;
import com.google.api.services.storage.Storage;
import com.google.appengine.api.appidentity.AppIdentityService;
import com.google.appengine.api.appidentity.AppIdentityServiceFactory;
import java.io.IOException;
import java.util.Arrays;

public class CloudStorageManager {

    public static final JsonFactory JSON_FACTORY = new GsonFactory();
    public static final HttpTransport TRANSPORT = new UrlFetchTransport();
    
    public Storage getStorageManager() throws IOException{
        AppIdentityService appIdentity = AppIdentityServiceFactory.getAppIdentityService();
        AppIdentityService.GetAccessTokenResult accessToken = appIdentity.getAccessToken(Arrays.asList("https://www.googleapis.com/auth/devstorage.read_write"));
        GoogleCredential credential = new GoogleCredential().setAccessToken(accessToken.getAccessToken());
        Storage storage = new Storage.Builder(TRANSPORT, JSON_FACTORY, credential).setApplicationName( "APP_NAME" ).build();
        return storage;
    }
    
    public Storage.Objects.Get getFileStorage( String p_bucket, String p_name ) throws IOException{
        Storage storage = getStorageManager();
        Storage.Objects.Get fileStorage = storage.objects().get(p_bucket, p_name);
        fileStorage.getMediaHttpDownloader().setDirectDownloadEnabled(false);
        return fileStorage;
    }
    
}

GCSFile.java

package com.alejandrogr.gists.mailgun;

public class GCSFile {
    public String bucket;
    public String name;
}

MailgunManager.java

package com.alejandrogr.gists.mailgun;

import com.google.api.services.storage.Storage;
import com.google.gson.Gson;
import com.google.gson.JsonObject;
import com.igzcode.java.util.Trace;
import com.sun.jersey.api.client.Client;
import com.sun.jersey.api.client.ClientResponse;
import com.sun.jersey.api.client.WebResource;
import com.sun.jersey.api.client.filter.HTTPBasicAuthFilter;
import com.sun.jersey.core.util.MultivaluedMapImpl;
import com.sun.jersey.multipart.FormDataMultiPart;
import com.sun.jersey.multipart.file.StreamDataBodyPart;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import java.util.logging.Logger;

import javax.ws.rs.core.MediaType;

public class MailgunManager {

    protected static final Logger LOGGER = Logger.getLogger(MailgunManager.class.getName());
    
    private static final String API_ENDPOINT = "API_ENDPOINT";
    private static final String API_KEY = "API_KEY";
    private static final String FROM_EMAIL = "[email protected]";

    
    public static ClientResponse sendMailToUsers(List<MailgunRecipient> p_recipients, String p_content, String p_subject) {
        return sendMail(p_recipients, p_content, p_subject);
    }
    
    public static ClientResponse sendMailToUsers(List<MailgunRecipient> p_recipients, String p_content, String p_subject, List<GCSFile> p_attachments) throws IOException {
        return sendMailWithAttachments(p_recipients, p_content, p_subject, p_attachments);
    }
    
    private static ClientResponse sendMail(List<MailgunRecipient> p_to, String p_content, String p_subject) {
        Client client = Client.create();
        client.addFilter(new HTTPBasicAuthFilter("api", API_KEY));

        WebResource webResource = client.resource(API_ENDPOINT + "/messages");

        MultivaluedMapImpl formData = new MultivaluedMapImpl();
        formData.add("from", FROM_EMAIL);
        formData.add("subject", p_subject);
        formData.add("html", p_content);

        JsonObject recipients = new JsonObject();
        for (MailgunRecipient mailgunRecipient : p_to) {
            formData.add("to", mailgunRecipient.email);
            recipients.add(mailgunRecipient.email, new Gson().toJsonTree(mailgunRecipient));
        }

        String recipientsString = new Gson().toJson(recipients);
        LOGGER.info(("SEND RECIPIENTS " + recipientsString));
        formData.add("recipient-variables", recipientsString);

        return webResource.type(MediaType.APPLICATION_FORM_URLENCODED).post(ClientResponse.class, formData);
    }
    
    private static ClientResponse sendMailWithAttachments(List<MailgunRecipient> p_to, String p_content, String p_subject, List<GCSFile> p_attachments) throws IOException {
        CloudStorageManager cloudSM = new CloudStorageManager();
        Client client = Client.create();
        
        client.addFilter(new HTTPBasicAuthFilter("api", API_KEY));

        WebResource webResource = client.resource(API_ENDPOINT + "/messages");

        FormDataMultiPart formData = new FormDataMultiPart();
        formData.field("from", FROM_EMAIL);
        formData.field("subject", p_subject);
        formData.field("html", p_content);

        JsonObject recipients = new JsonObject();
        for (MailgunRecipient mailgunRecipient : p_to) {
            formData.field("to", mailgunRecipient.email);
            recipients.add(mailgunRecipient.email, new Gson().toJsonTree(mailgunRecipient));
        }

        String recipientsString = new Gson().toJson(recipients);
        LOGGER.info(("SEND RECIPIENTS " + recipientsString));

        formData.field("recipient-variables", recipientsString);
        
        for (GCSFile gCSFile : p_attachments) {
            
            String filename = gCSFile.name;
            String filebucket = gCSFile.bucket;
            
            Storage.Objects.Get fileStorage = cloudSM.getFileStorage(filebucket, filename);
            InputStream imageStream = fileStorage.setAlt("media").executeAsInputStream();
            
            StreamDataBodyPart bodyPart = new StreamDataBodyPart("inline",imageStream,filename,MediaType.APPLICATION_OCTET_STREAM_TYPE);
            formData.bodyPart(bodyPart);
            
            try {
                imageStream.close();
            } catch (IOException ex) {
                LOGGER.warning( Trace.error(ex));
            }
        }

        return webResource.type(MediaType.MULTIPART_FORM_DATA_TYPE).post(ClientResponse.class, formData);
    }

}

MailgunManagerTest.java

package com.alejandrogr.gists.mailgun;

import junit.framework.TestCase;

import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import com.google.appengine.tools.development.testing.LocalServiceTestHelper;
import com.sun.jersey.api.client.ClientResponse;
import java.io.IOException;
import java.util.Arrays;
import java.util.logging.Logger;
import static junit.framework.Assert.assertTrue;


public class MailgunManagerTest extends TestCase{

    private final LocalServiceTestHelper helper = new LocalServiceTestHelper();
    protected static final Logger LOGGER = Logger.getLogger(MailgunManagerTest.class.getName());

    @Override
    @Before
    public void setUp() {
        this.helper.setUp();
    }

    @Override
    @After
    public void tearDown() {
        this.helper.tearDown();
    }

    @Test
    public void testSendEmail(){

        MailgunRecipient recipient = new MailgunRecipient();
        recipient.name = "Recipient Name";
        recipient.email = "[email protected]";
        
        ClientResponse response = MailgunManager.sendMailToUsers(Arrays.asList(recipient), "mail content", "mail subject");
        String responseEntity = response.getEntity(String.class);
        
        assertTrue(responseEntity.contains("Queued. Thank you."));
    }
    
    
    @Test
    public void testSendEmailInlineAttachments() throws IOException{

        MailgunRecipient recipient = new MailgunRecipient();
        recipient.name = "Recipient Name";
        recipient.email = "[email protected]";
        
        GCSFile file = new GCSFile();
        file.bucket = "valid_bucket";
        file.name = "valid_filename";
        
        String content = "inline image attached <img src=\"cid:"+file.name+"\">";
        
        ClientResponse response = MailgunManager.sendMailToUsers(Arrays.asList(recipient), content, "mail subject", Arrays.asList(file));
        String responseEntity = response.getEntity(String.class);
        
        assertTrue(responseEntity.contains("Queued. Thank you."));
    }
    

}

MailgunRecipient.java

package com.alejandrogr.gists.mailgun;

public class MailgunRecipient {
    public String name;
    public String email;
}