Is it possible to control the viewport size in headless_chrome (Rust)?

Yes, it's possible to control the viewport size in headless Chrome, even when using Rust. To do this, you typically need to use a Rust library that provides bindings to the Selenium WebDriver or the Chrome DevTools Protocol (CDP). One of the widely-used Rust libraries for controlling Chrome in both headless and headed mode is fantoccini.

Here is how you can control the viewport size with fantoccini, which under the hood uses the WebDriver protocol:

First, add fantoccini and tokio to your Cargo.toml:

[dependencies]
fantoccini = "0.23"
tokio = { version = "1", features = ["full"] }

Then, you can write an async function to launch a headless Chrome browser and set the viewport size:

use fantoccini::{Client, ClientBuilder};

#[tokio::main]
async fn main() -> Result<(), fantoccini::error::NewSessionError> {
    // Connect to the WebDriver (make sure chromedriver is running and accessible)
    let mut client = ClientBuilder::native()
        .connect("http://localhost:9515")
        .await?;

    // Navigate to the desired web page
    client.goto("https://www.example.com").await?;

    // Set the window size using WebDriver commands
    client.set_window_size(1920, 1080).await?;

    // Do your web scraping tasks here...

    // Clean up the session
    client.close().await?;

    Ok(())
}

Please note that you need to have the Chrome WebDriver (chromedriver) running and listening on the specified port (default 9515) for this to work. You can start chromedriver with the following command (make sure chromedriver is installed and in your PATH):

chromedriver --port=9515

Alternatively, if you want to use the CDP directly, you can use the chrome-devtools-rs library, which requires a bit more setup but gives you more control and access to the Chrome DevTools Protocol features.

Here's how you could potentially use chrome-devtools-rs to control the viewport size:

First, add chrome-devtools as a dependency in your Cargo.toml:

[dependencies]
chrome-devtools = "0.1"

Then, write your code:

use chrome_devtools as protocol;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Assumes that Chrome is running with --remote-debugging-port=9222
    let browser = protocol::Browser::connect("http://localhost:9222")?;

    // Create a new page/tab
    let tab = browser.new_tab().await?;

    // Navigate to the page
    tab.navigate_to("https://www.example.com").await?;

    // Resize viewport using CDP commands
    let emulation_cmd = protocol::emulation::SetDeviceMetricsOverride {
        width: 1920,
        height: 1080,
        device_scale_factor: 1.0,
        mobile: false,
        fit_window: false,
        ... // Other necessary fields
    };
    tab.execute(&emulation_cmd).await?;

    // Do your web scraping tasks here...

    // Close the browser tab
    tab.close().await?;

    Ok(())
}

Please be aware that the APIs of these libraries may evolve, and you should always refer to the latest documentation for the most up-to-date usage instructions.