Issues with Rendering Pages via localhost vs. Remote Web Sites

[thiscantbetaken]

OS: Ubuntu 17.10

Selenium Version: 3.8.1

Browser: Chrome

Browser Version: 63.0.3239.132

Expected Behavior -
For JavaScript libraries such as a JavaScript PDF viewer to exhibit the same behavior if served from a localhost web server vs. remote web sites using a FQDN.

Actual Behavior -
Using a JavaScript library, PDFs on remote websites can be viewed with snapshots taken using the Xvfb virtual framebuffer. However, when running that exact same JavaScript library on localhost:8888 to view and then snapshot locally stored PDFs, no PDF content is rendered using either Xvfb or Headless Chrome.

Steps to reproduce -

This works as expected:

import time
from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
from selenium.common.exceptions import TimeoutException
from pyvirtualdisplay import Display

display = Display(visible=0, size=(800, 600))
display.start()

chromeOptions = webdriver.ChromeOptions()
#chromeOptions.add_argument("headless")

driver = webdriver.Chrome(chrome_options=chromeOptions)
driver.get("https://mozilla.github.io/pdf.js/web/viewer.html")

timeout = 5

try:
    element_present = EC.presence_of_element_located((By.CLASS_NAME, 'dropdownToolbarButton'))
    WebDriverWait(driver, timeout).until(element_present)
except TimeoutException:
    print "Timed out waiting for page to load"

time.sleep(5)
driver.get_screenshot_as_file('screenshot.png')
driver.quit()

This does not, even though the only difference is a web server running on localhost:

import time
from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
from selenium.common.exceptions import TimeoutException
from pyvirtualdisplay import Display

display = Display(visible=0, size=(800, 600))
display.start()

chromeOptions = webdriver.ChromeOptions()
#chromeOptions.add_argument("headless")

driver = webdriver.Chrome(chrome_options=chromeOptions)
driver.get("http://localhost:8888/web/viewer.html?file=%2Ftest%2Fpdfs%2F1.pdf#search=JavaScript")

timeout = 5

try:
    element_present = EC.presence_of_element_located((By.CLASS_NAME, 'dropdownToolbarButton'))
    WebDriverWait(driver, timeout).until(element_present)
except TimeoutException:
    print "Timed out waiting for page to load"

time.sleep(5)
driver.get_screenshot_as_file('screenshot.png')
driver.quit()

There is a five second delay loop right above the screenshot to make sure there is enough time for the PDF to be rendered in both contexts, but nothing is rendered via localhost for some reason.

Are there any debugging options I can enable to trace through what's happening?

[barancev]

This is a question rather than an issue. Please send questions to the selenium user group

[thiscantbetaken]

How is this a "question rather than an issue"? Selenium renders properly a web endpoint when the address is remote, but does not render the endpoint when the address is localhost. This is not complex.

[barancev]

Selenium does not render anything. A browser does. Open the same local/remote URLs manually, without Selenium, in a browser -- are they rendered properly?

[thiscantbetaken]

Yes, they are rendered properly. The POC code above is exactly the same between the two instances, the only difference is a localhost endpoint vs. remote FQDN.

[barancev]

Please provide two screenshots for the same page http://localhost:8888/web/viewer.html?file=%2Ftest%2Fpdfs%2F1.pdf#search=JavaScript:

1. in a browser opened manually
2. in a browser opened by Selenium

[thiscantbetaken]

In a browser opened manually, here is http://localhost:8888/web/viewer.html?file=%2Ftest%2Fpdfs%2F1.pdf#search=JavaScript:

Here is that exact same URL via the Selenium code above:

And, the same JavaScript library viewing a PDF via a FQDN URL opened with Selenium Webdriver (code above):

[barancev]

Wait longer :)

pdf.js is rather slow, I've deployed it locally, opened a page from the localhost, and took several screenshots with 5 sec interval between them, and the third one (that was taken after 15 sec) shown properly rendered page.

[thiscantbetaken]

Hmm, yeah it renders after 15 seconds. That's pretty strange, I wonder if it's some type of DNS resolver issue.

Thanks for taking the time to look into this.