ChromeDriver --print-to-pdf after page load

Question

According to the docs, Chrome can be started in headless mode with --print-to-pdf in order to export a PDF of a web page. This works well for pages accessible with a GET request.

Trying to find a print-to-pdf solution that would allow me to export a PDF after executing multiple navigation request from within Chrome. Example: open google.com, input a search query, click the first result link, export to PDF.

Looking at the [very limited amount of available] docs and samples, I failed to find a way to instruct Chrome to export a PDF, after a page loads. I'm using the Java chrome-driver.

One possible solution not involving Chrome, is by using a tool like wkhtmltopdf. Going on this path would force me to - before sending the HTML to the tool - do the following:

• save the HTML in a local file
• traverse the DOM, and download all file links (images, js, css, etc)

Don't prefer this path as it would require a lot of tinkering [I assume] on my part to get downloads' file paths correct for wkhtmltopdf to read correctly.

Is there a way to instruct Chrome to print to PDF, but only after a page loads?

Answer 1

This is indeed possible to do through Selenium Chromedriver, by means of the ExecuteChromeCommandWithResult method. When executing the command Page.printToPDF, a base-64-encoded PDF document is returned in the "data" item of the result dictionary.

A C# example, which should be easy to translate into Java, is available in this answer:

https://stackoverflow.com/a/58698226/2416627

Here is another C# example, which illustrates some useful options:

public static void Main(string[] args)
{
    var driverOptions = new ChromeOptions();
    // In headless mode, PDF writing is enabled by default (tested with driver major version 85)
    driverOptions.AddArgument("headless");
    using (var driver = new ChromeDriver(driverOptions))
    {
        driver.Navigate().GoToUrl("https://stackoverflow.com/questions");
        new WebDriverWait(driver, TimeSpan.FromSeconds(10)).Until(d => d.FindElements(By.CssSelector("#questions")).Count == 1);
        // Output a PDF of the first page in A4 size at 90% scale
        var printOptions = new Dictionary<string, object>
        {
            { "paperWidth", 210 / 25.4 },
            { "paperHeight", 297 / 25.4 },
            { "scale", 0.9 },
            { "pageRanges", "1" }
        };
        var printOutput = driver.ExecuteChromeCommandWithResult("Page.printToPDF", printOptions) as Dictionary<string, object>;
        var pdf = Convert.FromBase64String(printOutput["data"] as string);
        File.WriteAllBytes("stackoverflow-page-1.pdf", pdf);
    }
}

The options available for the Page.printToPDF call are documented here:

https://chromedevtools.github.io/devtools-protocol/tot/Page/#method-printToPDF