How to retrieve email attachments with Gmail API

Other Questions Gmail
1

I’m working on a project where I need to fetch email attachments through the Gmail API. I wrote some code but I’m running into issues with authentication and the gapi library. Here’s what I have so far:

const emailData = request.body;
const messageParts = emailData.payload.parts;

for (let index = 0; index < messageParts.length; index++) {
  const currentPart = messageParts[index];
  if (currentPart.filename && currentPart.filename.length > 0) {
    const attachmentId = currentPart.body.attachmentId;
    const apiRequest = gapi.client.gmail.users.messages.attachments.get({
      'id': attachmentId,
      'messageId': emailMessage.id,
      'userId': currentUserId
    });
    apiRequest.execute(function(attachmentData) {
      handleResponse(currentPart.filename, currentPart.mimeType, attachmentData);
    });
  }
}

The main problem is that I’m getting a “Gmail is not defined” error. I installed the gapi package and imported it like this:

const coffeeScript = require("coffee-script/register");
const gapi = require('gapi');

I’m also confused about the authentication part. Do I need to pass things like refresh tokens, client secrets, client IDs, and access tokens? If so, how should I handle that in my code? Any help would be appreciated.

2

You’re using the wrong library. gapi is for browsers, not Node.js servers. Switch to the official googleapis library instead - it handles server-side auth properly. You’ll need OAuth2 credentials: client ID, client secret, and access tokens. Set up a service account in Google Cloud Console or use OAuth2 flow depending on what you need. Don’t forget to include the https://www.googleapis.com/auth/gmail.readonly scope when requesting permissions. One heads up - attachment data comes back base64-encoded, so you’ll need to decode it before saving or processing files.

3

u might be mixing browser and server code. the gapi library is for client-side usage. try using the googleapis package instead: npm install googleapis. for server-side, consider service account credentials or OAuth2 with the proper scopes like gmail.readonly.

4

Your auth error happens because you’re mixing client-side gapi with Node.js. I hit this same problem last year on a similar email project. Switch to the googleapis npm package and set up OAuth2 credentials properly. Create your credentials in Google Cloud Console, then initialize the client with your creds and request the right scopes. You’ll need gmail.readonly scope at minimum for attachments. Your attachment logic looks good, but double-check you’re handling the base64 data correctly when it comes back. Large attachments can timeout, so add some error handling and retry logic.