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

Question

只要附件很小，一切似乎都可以工作。
但是，当我尝试附加一个更大的文件（例如 7MB）时，Send execute()方法只是挂起。
我尝试浏览文档，如果我理解正确，我应该使用实际执行upload的 send API，但是，我没有弄清楚应该在哪里提供这些参数。
这是电子邮件生成方法：

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;
    }

其次：

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

Answer 1

正如您提到的，我认为您正在达到允许的消息大小的上限。我不认为（如果我错了，有人请纠正我）Java Gmail API 客户端对超过此大小的邮件有任何内置支持，因此由您来实现它。

在后台，messages.send -方法会产生常规的 http POST 请求：

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}"
}

正如您发现的那样，这最多只能工作~5 mb的总大小。如果要使用 35 MB 的最大限制，则需要执行以下操作：

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}"

请注意，upload URL 中的

uploadType=multipart URL 参数message/rfc822请求正文中的Content-Type和message non-encoded。这个答案可能会给人一些启发。

因此，您可能需要绕过（再次，如果我错了，有人纠正我）Java客户端并使用其他库自己发出常规的http请求。