metadataHeaders option failing with multiple headers

Question

Here is my code snippet:

    if messages['messages']:
        for message in messages['messages']:
            batch.add(gmail_client.users().messages().get(userId='me', id=message['id'], format='metadata', fields="payload,threadId,id", metadataHeaders="from,to,date,subject"), callback=messageCallback)

    batch.execute()

This works fine with just one option in metadataHeaders, but with multiple headers listed it's not returning any headers at all. Any ideas?

Answer 1

Just figured it out. The documentation is incorrect, the correct format for this parameter is an array of strings rather than a single string. You can see the error on this page:

https://developers.google.com/gmail/api/v1/reference/users/messages/get

Answer 2

You can do like following:

message2 =gmail_service.users().messages().get(userId='me', id=thread['id'], format='metadata', metadataHeaders=['subject','from','to','date']).execute()
for num in range(0,4):
  if message2['payload']['headers'][num]['name'].lower() == "subject":
    subject=message2['payload']['headers'][num]['value']
  elif  message2['payload']['headers'][num]['name'].lower() == "from": 
    From=message2['payload']['headers'][num]['value']
  elif  message2['payload']['headers'][num]['name'].lower() == "to": 
    to=message2['payload']['headers'][num]['value']
  elif  message2['payload']['headers'][num]['name'].lower() == "date": 
    date=message2['payload']['headers'][num]['value']

f.write("Date : %s "  % date.encode('utf8')+'\n')
f.write("Subject : %s "  % subject.encode('utf8')+'\n')
f.write("From : %s "  % From.encode('utf8')+'\n')
f.write("To : %s "  % to.encode('utf8')+'\n')