如何将GmailMessage.getAttachments获取的内嵌图片传递给MailApp.sendEmail

• 希望通过GmailMessage的getAttachments方法提取邮件内嵌图片，再通过MailApp类的sendEmail方法发送这些图片。
• 核心问题：前者返回Blob附件数组，而后者要求传入由字符串类型的图片键到图片数据Blob的映射构成的JavaScript对象，二者参数格式不匹配。

难点出在配置项中的{..., inlineImages: attachments, ...}部分：

function test() {
  var firstThread = GmailApp.getTrashThreads(0,1)[0];
  var message = firstThread.getMessages()[0];
  var from = message.getHeader('From');
  var attachments = message.getAttachments({includeAttachments: false});
  var obj = {htmlBody: message.getBody(), inlineImages: attachments, noReply: false, replyTo: message.getFrom(), name: from};
  MailApp.sendEmail("some@one.com", 'Testing', '', obj);
}

注意text/html部分的<img src="cid:key"用法，cid对应的键和附件的Content-ID一一匹配：

MIME-Version: 1.0
Date: Thu, 22 Jul 2021 23:06:23 +0300
Message-ID: <1234567890@mail.gmail.com>
Subject: Testing
From: Me <just@me.com>
To: Someone <some@one.com>
Content-Type: multipart/related; boundary="0000000000004aee5205c7bbd26b"

--0000000000004aee5205c7bbd26b
Content-Type: multipart/alternative; boundary="0000000000004aee5005c7bbd26a"

--0000000000004aee5005c7bbd26a
Content-Type: text/plain; charset="UTF-8"

This is an inline image:
[image: image.png]
And here's another:
[image: image.png]
Thanks!

--0000000000004aee5005c7bbd26a
Content-Type: text/html; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

<div dir="ltr">This is an inline image:<div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"></div></div></div><div><img src="cid:ii_krfchaks0" alt="image.png" width="117" height="118"><br></div><div>And here's another:</div><div><img src="cid:ii_krfchlll1" alt="image.png" width="41" height="47"><br></div><div>Thanks!</div></div>

--0000000000004aee5005c7bbd26a--
--0000000000004aee5205c7bbd26b
Content-Type: image/png; name="image.png"
Content-Disposition: attachment; filename="image.png"
Content-Transfer-Encoding: base64
X-Attachment-Id: ii_krfchaks0
Content-ID: <ii_krfchaks0>


--0000000000004aee5205c7bbd26b
Content-Type: image/png; name="image.png"
Content-Disposition: attachment; filename="image.png"
Content-Transfer-Encoding: base64
X-Attachment-Id: ii_krfchlll1
Content-ID: <ii_krfchlll1>


--0000000000004aee5205c7bbd26b--

核心逻辑是从每个内嵌附件中提取Content-ID（也就是HTML里cid:后面的字符串，去掉外层尖括号），构造键值对映射对象传入inlineImages即可。修改后的可用代码如下：

function test() {
  var firstThread = GmailApp.getTrashThreads(0,1)[0];
  var message = firstThread.getMessages()[0];
  var from = message.getHeader('From');
  // 只提取内嵌图片，排除普通附件
  var attachments = message.getAttachments({includeAttachments: false});
  var inlineImageMap = {};
  attachments.forEach(function(blob) {
    // 从blob的Content-ID元数据提取cid键，去掉前后的尖括号
    var cid = blob.getContentType()['Content-ID'].replace(/^<|>$/g, '');
    inlineImageMap[cid] = blob;
  });
  var obj = {
    htmlBody: message.getBody(), 
    inlineImages: inlineImageMap, 
    noReply: false, 
    replyTo: message.getFrom(), 
    name: from
  };
  MailApp.sendEmail("some@one.com", 'Testing', '', obj);
}

实现说明 #

• 每个内嵌图片的Blob对象都自带Content-ID元数据，和HTML代码中img标签的cid:xxx完全对应
• 处理时要注意Content-ID本身是用尖括号包裹的，需要去掉后才能作为inlineImages的键
• 构造完成的映射对象完全符合sendEmail方法的参数要求，内嵌图片可以正常显示不会丢失

内容的提问来源于stack exchange，提问作者LWC