Unable to export a google slide as pdf format on server side

问题

Here is my code for testing exporting files from google drive on server side.

import logging

from flask import Flask, render_template, request

from googleapiclient.discovery import build
from googleapiclient.http import MediaIoBaseDownload
from oauth2client.client import AccessTokenCredentials

import httplib2
import io


app = Flask(__name__)


@app.route('/gdrive/selectcallback')
def userselectioncallback():
    print "In user selection callback... "

    code = request.args.get('user_token')
    fileId = request.args.get('fileId')

    credentials = AccessTokenCredentials(code,
                                         'my-user-agent/1.0')


    http = httplib2.Http()
    http_auth = credentials.authorize(http)

    drive_service = build('drive', 'v3', http=http_auth)

    drive_request = drive_service.files().export(
        fileId=fileId,
        mimeType='application/pdf')
    fh = io.FileIO('test.pdf', 'wb')
    downloader = MediaIoBaseDownload(fh, drive_request)
    done = False
    while done is False:
        status, done = downloader.next_chunk()
        print "Download %d%%." % int(status.progress() * 100)

    return code


if __name__ == '__main__':
    # This is used when running locally. Gunicorn is used to run the
    # application on Google App Engine. See entrypoint in app.yaml.
    app.run(host='127.0.0.1', port=8090, debug=True)

On the web client side, once a user selects a file from the file picker, the javascript front end will call the /gdrive/selectcallback in the above python code with the token and file id.

As an example, the token looks something like this: ya29.Glu5BG-LQJFqZ-e4uImMSxz-14iS41jVLfXk6rVKvAPjylCwhUh98ZJk1iIC5Eb49pTfflGnU6qE7uzK44AYr0Wn79QMUkF368WFaYrhidrvpVjcsJSZ9P1M8VU6 and file id looks something like this 1ON9kGyb02TFCygy8jeIYyo2BKj5SzKgAP0xi5Rm08D4

Here is the relevant front end code (in coffeescript):

  pickerCallback = () ->
    view   = new google.picker.View(google.picker.ViewId.PRESENTATIONS)
    picker = new google.picker.PickerBuilder()
      .enableFeature(google.picker.Feature.NAV_HIDDEN)
      .setAppId('zeetings')
      .setOAuthToken(oauthToken)
      .addView(view)
      .setDeveloperKey(env['googleapi-client'].apiKey)
      .setCallback(selectCallback)  # The callback calls the python backend
      .build()
    picker.setVisible true

  selectCallback = (data) ->
    if data.action is google.picker.Action.PICKED
      fileId = data.docs[0].id
      fileSelectedCallback(fileId, oauthToken) if fileSelectedCallback

Based on the debug information, my python code emits these two https calls:

2017-09-01 11:32:38,810 pid 260 tid 140546358265600 INFO
discovery URL being requested: GET https://www.googleapis.com/discovery/v1/apis/drive/v3/rest

2017-09-01 11:32:39,009 pid 260 tid 140546358265600 INFO discovery URL being requested: GET https://www.googleapis.com/drive/v3/files/1ON9kGyb02TFCygy8jeIYyo2BKj5SzKgAP0xi4Rm08D4/export?mimeType=application%2Fpdf

If I use the second url directly in a browser, I get the following error:

{
 "error": {
  "errors": [
   {
    "domain": "usageLimits",
    "reason": "dailyLimitExceededUnreg",
    "message": "Daily Limit for Unauthenticated Use Exceeded. Continued use requires signup.",
    "extendedHelp": "https://code.google.com/apis/console"
   }
  ],
  "code": 403,
  "message": "Daily Limit for Unauthenticated Use Exceeded. Continued use requires signup."
 }
}

(I don't think the above error message actually reflects the root cause. It is more likely due to the fact that the call is not authenticated in my browser.)

I suspect I have to use the google-auth library (https://google-auth.readthedocs.io/en/latest/user-guide.html#making-authenticated-requests), but I am not sure how to marry google-auth to the python code I have above. I suppose I can obtain a credential via

from google.oauth2 import service_account

credentials = service_account.Credentials.from_service_account_file(
    '/path/to/key.json')

But what should I do with the credentials after this? Do I use it to replace credentials = AccessTokenCredentials(code,'my-user-agent/1.0') entirely?

P.S.

As per @Tanaike's suggestion, I tried to use the API url directly. It is the result I got:

{
 "error": {
  "errors": [
   {
    "domain": "global",
    "reason": "fileNotDownloadable",
    "message": "Only files with binary content can be downloaded. Use Export with Google Docs files.",
    "locationType": "parameter",
    "location": "alt"
   }
  ],
  "code": 403,
  "message": "Only files with binary content can be downloaded. Use Export with Google Docs files."
 }
}

It seems to be a v3 API problem. If I switch to v2 and use a downloadUrl link, I can download the file in pdf format.

回答1:

User @Tanaike has given me many good advise to debug this problem. I were able to test the REST API directly to verify that 1) I have the correct access code and, 2) the drive v3 file export API works as expected

Turns out the issue is with the MediaIoBaseDownload class. If I remove it from the code and just receive the data directly:

data = drive_service.files().export(
        fileId=fileId,
        mimeType='application/pdf').execute()
f = open('test.pdf)
f.write(data)
f.close()

then it works as expected

来源：https://stackoverflow.com/questions/45429618/unable-to-export-a-google-slide-as-pdf-format-on-server-side