I'm having trouble reading emails from Gmail using the Gmail API

Question

I am listing all messages from the inbox, being able to view the IDs of each email, but I cannot send them by parameter to search for each email using the function: gmail.users.messages.get Just return a message saying: undefined

Can anyone tell me why this is happening?

const fs = require('fs');
const readline = require('readline');
const {google} = require('googleapis');

// If modifying these scopes, delete token.json.
const SCOPES = ['https://www.googleapis.com/auth/gmail.readonly'];
// The file token.json stores the user's access and refresh tokens, and is
// created automatically when the authorization flow completes for the first
// time.
const TOKEN_PATH = 'token.json';

// Load client secrets from a local file.
fs.readFile('credentials.json', (err, content) => {
  if (err) return console.log('Error loading client secret file:', err);
  // Authorize a client with credentials, then call the Gmail API.
  authorize(JSON.parse(content), listLabels);
});

/**
 * Create an OAuth2 client with the given credentials, and then execute the
 * given callback function.
 * @param {Object} credentials The authorization client credentials.
 * @param {function} callback The callback to call with the authorized client.
 */
function authorize(credentials, callback) {
  const {client_secret, client_id, redirect_uris} = credentials.installed;
  const oAuth2Client = new google.auth.OAuth2(
      client_id, client_secret, redirect_uris[0]);

  // Check if we have previously stored a token.
  fs.readFile(TOKEN_PATH, (err, token) => {
    if (err) return getNewToken(oAuth2Client, callback);
    oAuth2Client.setCredentials(JSON.parse(token));
    callback(oAuth2Client);
  });
}

/**
 * Get and store new token after prompting for user authorization, and then
 * execute the given callback with the authorized OAuth2 client.
 * @param {google.auth.OAuth2} oAuth2Client The OAuth2 client to get token for.
 * @param {getEventsCallback} callback The callback for the authorized client.
 */
function getNewToken(oAuth2Client, callback) {
  const authUrl = oAuth2Client.generateAuthUrl({
    access_type: 'offline',
    scope: SCOPES,
  });
  console.log('Authorize this app by visiting this url:', authUrl);
  const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
  });
  rl.question('Enter the code from that page here: ', (code) => {
    rl.close();
    oAuth2Client.getToken(code, (err, token) => {
      if (err) return console.error('Error retrieving access token', err);
      oAuth2Client.setCredentials(token);
      // Store the token to disk for later program executions
      fs.writeFile(TOKEN_PATH, JSON.stringify(token), (err) => {
        if (err) return console.error(err);
        console.log('Token stored to', TOKEN_PATH);
      });
      callback(oAuth2Client);
    });
  });
}

/**
 * Lists the labels in the user's account.
 *
 * @param {google.auth.OAuth2} auth An authorized OAuth2 client.
 */
function listLabels(auth) {
  const gmail = google.gmail({version: 'v1', auth});
  gmail.users.labels.list({
    userId: 'me',
  }, (err, res) => {
    if (err) return console.log('The API returned an error: ' + err);
    const labels = res.data.labels;
    if (labels.length) {
      console.log('Labels:');
      labels.forEach((label) => {
        console.log(`- ${label.name}`);
      });
      listMessages(auth);
    } else {
      console.log('No labels found.');
    }
  });
}

/************************** My code is below *******************************/

function listMessages(auth){
    var gmail = google.gmail('v1');
    gmail.users.messages.list({
    auth: auth,
    userId: 'me',
    q : 'has:attachment',
    labelIds: 'INBOX',
  }, (err, res) => {
    if(err){
      console.log('Erro ao listar os emails');
    }
    var message = res;
    Object.keys(message).forEach(index => {
      console.log(res[index]);
      gmail.users.messages.get({
        userId: 'me',
        id: message[index].id,
        format: 'full',
      }, (err, res) => {
        console.log(res);
      })
    })
  })
}

Answer 1

• You want to retrieve the messages with gmail.users.messages.get using the values retrieved from gmail.users.messages.list.
• You want to achieve this using googleapis with Node.js.
• You have already been able to get the values from Gmail using Gmail API.

Modification points:

• The values from gmail.users.messages.list can be retrieved with res.data. In your script, how about modifying from var message = res is modified to var messages = res.data.messages?
• When you use auth: auth with gmail.users.messages.list, please also use it at gmail.users.messages.get.

I think that these points might be the reason of your issue. When above points are reflected to your script, it becomes as follows.

Modified script:

From:

var message = res;
Object.keys(message).forEach(index => {
  console.log(res[index]);
  gmail.users.messages.get({
    userId: 'me',
    id: message[index].id,
    format: 'full',
  }, (err, res) => {
    console.log(res);
  })
})

To:

var messages = res.data.messages;
messages.forEach((message) => {
  gmail.users.messages.get(
    {
      auth: auth,
      userId: "me",
      id: message.id,
      format: "full",
    },
    (err, res) => {
      if (err) {
        console.log(err);
        return;
      }
      console.log(res.data);
    }
  );
});

References:

• googleapis for Node.js
• Users.messages: get