Unable to retrieve message content after Google Pub/Sub webhook call to server

Question

I've subscribed to Google Cloud Pub/Sub, created a topic and created a subscription with a webhook that points to a URL at my server. I've then used the Gmail API to call watch on a particular label that I've created in my Gmail account and associated it with the topic I created.

When I messages arrive into the label in my Gmail account, the webhook is triggered a POST request to the URL at my server. But no matter what the content of the email is, the POST body is always something like this:

{
    "message": {
        "attributes": {},
        "data": "eyJlbWFpbEFkZHJlc3MiOiJteWVtYWlsQG15ZG9tYWluLmNvbSIsImhpc3RvcnlJZCI6MTIzNDU2N30K",
        "messageId": "12345678900000", # only relevant to Pub/Sub
        "message_id": "12345678900000",
        "publishTime": "2017-04-16T15:42:08.968Z",
        "publish_time": "2017-04-16T15:42:08.968Z"
    },
    "subscription": "projects/proj-name/subscriptions/sub-name"
}

The data field is Base64 encoded, which in this case is:

{"emailAddress":"[email protected]","historyId":1234567}

That's what I get, every time, no matter what the email content is. However, if run a publish test from the google developer console, the base64 encoded value in the data field is the actual message string that I specified.

I've tried making a subsequent call to history.list with the Gmail API using the historyId from the base64 decoded data value, but all I get back is a response like this:

{"historyId": "1234567"}

How am I suppose to get the email content?

It seems like that somehow, the request sent is using metadata/minimal format as default. I haven't delved much into Google Pub/Sub, but it might be you're just missing a parameter. — AL.
If that's true, I wonder how you're supposed to specify the format for the push request. The watch request itself doesn't provide a parameter for that, and I don't see any configuration for that for the push request from the console. — RTF

jboga jboga · Accepted Answer · 2017-04-26T22:26:25

A bit late but others might be interested. The answer is here. Basically you get an historyId from the watch call. Store it. Then when you get a notification from Gmail:

keep track of the historyId
fetch the history list (gmail.users.history.list) using the stored historyId (from the watch call)
import all the desired messages from the history
once you're done, replace the current historyId by the one from the notification.

Hope it helps.

Unable to retrieve message content after Google Pub/Sub webhook call to server

1 Answers