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How To Download Files From a Remote Browser

The Problem​

In tip 2 we downloaded a file and checked it on disk. That works when the browser runs on our machine. But when it runs somewhere else, on a Selenium Grid node or at a cloud provider, the file lands on the disk of that machine. Our test can't open it there.

A Solution​

Ask the remote side to keep the downloaded files and to send them to us.

  • Selenium: Selenium Grid has "managed downloads". The test asks for a session with downloads enabled (the se:downloadsEnabled capability). The Grid then gives the session its own download folder, and the bindings can list the files in it and copy a file to our machine. Sauce Labs supports the same capability and commands, so the code is the same as with a Grid: only the address and the Sauce Labs options change. Selenide and WebdriverIO use the same feature.
  • Playwright: Playwright has its own remote mode. A Playwright server runs next to the browsers, and the test connects to it. When a download finishes, saveAs copies the file from the server to our machine.

Let's continue with an example.

Example​

Part 1: Start the Remote Browser​

The Selenium and WebdriverIO examples run on Sauce Labs. They read the credentials from the SAUCE_USERNAME and SAUCE_ACCESS_KEY environment variables (see tip 26 for more on running tests on Sauce Labs).

They work the same on a Selenium Grid started with managed downloads (it requires Java). Get the Selenium Server from the Selenium releases, start it, and use http://localhost:4444 as the address in the tests:

java -jar selenium-server-<version>.jar standalone --enable-managed-downloads true

The Selenide example uses this Grid: http://localhost:4444, or the address in the GRID_URL environment variable.

For the Playwright examples, start a Playwright server. Every Playwright package can start it. For example, with the one of the TypeScript example:

npx playwright run-server --port 3000 --host 127.0.0.1

The tests use ws://127.0.0.1:3000/, or the address in the PLAYWRIGHT_SERVER_URL environment variable. The server and the tests must use the same Playwright version. On a separate machine, use --host 0.0.0.0 so other machines can reach it.

Here the Grid and the Playwright server run on our machine to keep things simple, but the tests work the same when they run somewhere else.

Part 2: The Test​

If the Sauce Labs credentials are not set, or the Grid or the Playwright server is not running, the tests are skipped.

Expected Behavior​

  • Start a browser on Sauce Labs (or the Grid, or the Playwright server) with downloads enabled
  • Visit the page and click the first download link
  • The browser downloads the file on the remote machine
  • Wait until the file is there
  • Copy the file to a temp folder on our machine and check it is not empty
  • Close the browser

Summary​

With the files on our machine, we can check them as in tip 2: the name, the size, or the content.

The remote machine keeps the files only while the session lives. So copy the files you need before quitting the browser.

Happy Testing!

Authors​

Diego Molina
Diego Molina
Elemental Selenium maintainer