在 Android 中使用 Gmail API 发送带附件的电子邮件(execute() 挂起)

public MimeMessage toMimeMessage(String from, Context context) throws MessagingException {
    Properties props = new Properties();
    Session session = Session.getDefaultInstance(props, null);

    MimeMessage mimeMessage = new MimeMessage(session);

    mimeMessage.setFrom(new InternetAddress(from));
    mimeMessage.addRecipient(javax.mail.Message.RecipientType.TO, new InternetAddress(recipient));
    mimeMessage.setSubject(subject);

    MimeBodyPart mimeBodyText = new MimeBodyPart();
    mimeBodyText.setContent(body,"text/html");
    mimeBodyText.setHeader("Content-Type","text/plain; charset="UTF-8"");

    Multipart mp = new MimeMultipart();
    mp.addBodyPart(mimeBodyText);

    if (attachments != null && attachments.size() > 0) {
        MimeBodyPart mimeBodyAttachments = new MimeBodyPart();
        for (Uri uri : attachments) {
            String fileName = UriUtils.getFileName(uri, context);
            String mimeType = UriUtils.getMimeType(uri, context);
            Log.d(TAG,"Generating file info, uri=" + uri.getPath() +", mimeType=" + mimeType);
            FileInputStream is = UriUtils.generateFileInfo(context, uri, mimeType);
            if (is == null) {
                throw new MessagingException("Failed to get file for uri=" + uri.getPath());
            }
            try
            {
                DataSource source = new ByteArrayDataSource(is, mimeType);
                mimeBodyAttachments.setDataHandler(new DataHandler(source));
                mimeBodyAttachments.setFileName(fileName);
                mimeBodyAttachments.setHeader("Content-Type", mimeType +"; name="" + fileName +""");
            } catch (IOException e) {
                throw new MessagingException(e.getMessage());
            }
        }
        mimeBodyAttachments.setHeader("Content-Transfer-Encoding","base64");
        mimeBodyAttachments.setDisposition(MimeBodyPart.ATTACHMENT);
        mp.addBodyPart(mimeBodyAttachments);
    }

    mimeMessage.setContent(mp);

    return mimeMessage;
}

Message createMessageWithEmail(MimeMessage mimeMessage) throws MessagingException, IOException {
        ByteArrayOutputStream bytes = new ByteArrayOutputStream();
        mimeMessage.writeTo(bytes);
        String encodedEmail = Base64.encodeBase64URLSafeString(bytes.toByteArray());
        Message message = new Message();
        message.setRaw(encodedEmail);
        return message;
    }

MimeMessage mimeMessage = email.toMimeMessage(userId, context);
Message message = createMessageWithEmail(mimeMessage);
Gmail.Users.Messages messages = service.users().messages();
Gmail.Users.Messages.Send send = messages.send(userId, message);
send.execute(); // method hangs when using large attachment

POST https://www.googleapis.com/gmail/v1/users/{USER_ID}/messages/send
Content-Type: application/json
Authorization: Bearer {ACCESS_TOKEN}

{
 "raw":"{MESSAGE_URL_SAFE_BASE64_ENCODED}"
}

POST https://www.googleapis.com/upload/gmail/v1/users/{USER_ID}/messages/send?uploadType=multipart
Content-Type: message/rfc822
Authorization: Bearer {ACCESS_TOKEN}

"{MESSAGE_IN_RFC822_FORMAT}"