Composing draft messages

In a Google Workspace add-on you can create widgets that have linked actions. You can use an action to compose new email drafts, optionally filling them using information entered into the add-on UI or information from an open message. For example, you can have a button in your add-on's message UI that creates a reply to the currently opened message prepopulated with information from the add-on.

When an action that builds messages is triggered, Gmail executes a callback function to build and return the draft. Gmail then displays that draft in its UI in a standard email compose window, which the user can then edit and send as needed.

Configuring an action to build a draft message

To configure a widget to start a draft-building action when selected, you must do the following:

1. Make sure your manifest includes the action.compose scope:

   https://www.googleapis.com/auth/gmail.addons.current.action.compose

   You can use more a permissive scope instead, but should only do so if that scope is absolutely necessary.

2. Create an Action object and associate it with a callback function you define.

3. Call the widget's setComposeAction() widget handler function, providing it the Action object and specifying the ComposeEmailType.

4. Implement the callback function that executes the draft-building action. This function is given an event object as an argument. The callback function must do the following:

   1. Create a GmailDraft object.
   2. Build a ComposeActionResponse object using the ComposeActionResponseBuilder class and the GmailDraft object.
   3. Return the built ComposeActionResponse.

You can prefill the GmailDraft you create in the callback function with recipients, a subject, a message body, and attachments. To fill in the draft, data can come from any source, but typically it derives from information provided to the add-on itself, information in the open message, or information gathered from a third-party service. The event object passed to the callback function contains the open message ID and other add-on information you can use to prefill the draft.

You can create the draft as a new standalone message or a reply to an existing message. This is controlled by the ComposeEmailType enum given to the setComposeAction(). You can create reply drafts as single replies or 'reply-all' messages.

Standalone drafts

A standalone draft starts a new thread and isn't a reply to any existing message. You can create a standalone draft with one of the following Gmail service functions:

• GmailApp.createDraft(recipient, subject, body)
• GmailApp.createDraft(recipient, subject, body, options)

Reply drafts

A reply draft is part of an existing message thread. Reply drafts are either single replies that only get sent to the sender of a message or "reply all" drafts that get sent to everyone who received that message. You can create a reply draft with one of these Gmail service functions:

• GmailMessage.createDraftReply(body)
• GmailMessage.createDraftReply(body, options)
• GmailMessage.createDraftReplyAll(body)
• GmailMessage.createDraftReplyAll(body, options)
• GmailThread.createDraftReply(body)
• GmailThread.createDraftReply(body, options)
• GmailThread.createDraftReplyAll(body)
• GmailThread.createDraftReplyAll(body, options)

Example

The following code snippet shows how to assign an action that builds a reply draft to a button.

varcomposeAction=CardService.newAction()
.setFunctionName('createReplyDraft');
varcomposeButton=CardService.newTextButton()
.setText('Compose Reply')
.setComposeAction(
composeAction,
CardService.ComposedEmailType.REPLY_AS_DRAFT);
//...
/**
*Createsadraftemail(withanattachmentandinlineimage)
*asareplytoanexistingmessage.
*@param{Object}eAneventobjectpassedbytheaction.
*@return{ComposeActionResponse}
*/
functioncreateReplyDraft(e){
//ActivatetemporaryGmailscopes,inthiscasetoallow
//areplytobedrafted.
varaccessToken=e.gmail.accessToken;
GmailApp.setCurrentMessageAccessToken(accessToken);
//Createsadraftreply.
varmessageId=e.gmail.messageId;
varmessage=GmailApp.getMessageById(messageId);
vardraft=message.createDraftReply('',
{
htmlBody:"Kitten! <img src='cid:kitten'/>",
attachments:[
UrlFetchApp.fetch('https://example.com/images/myDog.jpg')
.getBlob()
],
inlineImages:{
"kitten":UrlFetchApp.fetch('https://example.com/images/myKitten.jpg')
.getBlob()
}
}
);
//Returnabuiltdraftresponse.ThiscausesGmailtopresenta
//composewindowtotheuser,pre-filledwiththecontentspecified
//above.
returnCardService.newComposeActionResponseBuilder()
.setGmailDraft(draft).build();
}