Mangalord/backend/src/crawler/browser.rs

//! Chromium launcher and lifecycle.
//!
//! Uses `chromiumoxide`'s `fetcher` feature so we don't depend on a
//! system Chrome install — first call downloads a known-good revision
//! into a cache dir and reuses it forever after. `BrowserMode` toggles
//! headed vs headless; the headed path needs a display (real `$DISPLAY`
//! or `xvfb-run`).
//!
//! Extra Chromium command-line flags can be supplied through
//! [`LaunchOptions::extra_args`] in code, or via the
//! `CRAWLER_BROWSER_ARGS` env var (whitespace-separated) when going
//! through [`LaunchOptions::from_env`]. The launcher always also
//! injects `--no-sandbox` and `--disable-dev-shm-usage` because they're
//! near-mandatory for containerized Chromium; everything else is
//! caller-provided.

use std::path::PathBuf;
use std::sync::Arc;

use anyhow::Context;
use chromiumoxide::browser::{Browser, BrowserConfig};
use chromiumoxide::error::CdpError;
use chromiumoxide::fetcher::{BrowserFetcher, BrowserFetcherOptions};
use futures_util::StreamExt;
use tokio::task::JoinHandle;

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum BrowserMode {
    /// Real window. Needs `$DISPLAY` (or `xvfb-run` wrapping the
    /// binary). Opt-in via `CRAWLER_BROWSER_MODE=headed` — useful for
    /// debugging a flow visually or for sites that fingerprint
    /// headless Chrome. Not used in production.
    Headed,
    /// No window. Faster, lower resource use, runs without a display.
    /// This is the default for both `from_env()` and `Default`.
    Headless,
}

/// Configuration for a single browser launch.
///
/// Public fields rather than a builder — there are only two of them
/// and callers benefit from struct literal syntax for clarity.
#[derive(Clone, Debug)]
pub struct LaunchOptions {
    pub mode: BrowserMode,
    /// Extra Chromium flags, appended after the launcher's own
    /// defaults. Example: `vec!["--lang=de-DE".into(),
    /// "--window-size=1280,800".into()]`.
    pub extra_args: Vec<String>,
}

impl LaunchOptions {
    pub fn headed() -> Self {
        Self {
            mode: BrowserMode::Headed,
            extra_args: Vec::new(),
        }
    }

    pub fn headless() -> Self {
        Self {
            mode: BrowserMode::Headless,
            extra_args: Vec::new(),
        }
    }

    /// Reads `CRAWLER_BROWSER_MODE` (`headless`|`headed`, default
    /// `headless`) and `CRAWLER_BROWSER_ARGS` (whitespace-separated
    /// Chromium flags). Flags containing whitespace aren't supported
    /// through the env var — use the programmatic API for those.
    pub fn from_env() -> Self {
        let mode = match std::env::var("CRAWLER_BROWSER_MODE").as_deref() {
            Ok("headed") => BrowserMode::Headed,
            _ => BrowserMode::Headless,
        };
        let extra_args = std::env::var("CRAWLER_BROWSER_ARGS")
            .map(|s| parse_args(&s))
            .unwrap_or_default();
        Self { mode, extra_args }
    }
}

impl Default for LaunchOptions {
    fn default() -> Self {
        Self::headless()
    }
}

/// Whitespace-split a CRAWLER_BROWSER_ARGS-style string. Exposed
/// separately from `from_env` so it can be unit-tested without
/// touching process environment.
pub(crate) fn parse_args(s: &str) -> Vec<String> {
    s.split_whitespace().map(str::to_string).collect()
}

/// Owned browser plus the spawned task that drives its CDP event loop.
/// Dropping `Handle` without calling `close` leaks the Chromium process
/// — always call `close().await` in production paths.
///
/// The browser is stored behind an `Arc` so it can be shared across
/// worker tasks (via [`Handle::shared`]) without copying. `Browser::new_page`
/// only needs `&self`, so multiple workers can drive the same browser
/// concurrently as long as the manager keeps the `Arc` alive.
pub struct Handle {
    browser: Arc<Browser>,
    driver: JoinHandle<()>,
}

impl Handle {
    /// Borrow the browser. Equivalent to `&*handle.shared()`.
    pub fn browser(&self) -> &Browser {
        &self.browser
    }

    /// Clone the shared handle. Workers hold these to call `new_page`
    /// concurrently. The browser only exits when the last `Arc<Browser>`
    /// is dropped (kill-on-drop), or when `close()` is called on the
    /// originating `Handle` while it is the sole holder.
    pub fn shared(&self) -> Arc<Browser> {
        Arc::clone(&self.browser)
    }

    /// Closes the browser and awaits the driver task. If other Arcs to
    /// the browser are still alive we fall back to drop-kills-Chromium
    /// semantics and just join the driver — this is the rare case where
    /// shutdown raced an outstanding worker; the OS-level kill is the
    /// safety net.
    pub async fn close(self) -> anyhow::Result<()> {
        match Arc::try_unwrap(self.browser) {
            Ok(mut owned) => {
                let _ = owned.close().await;
                let _ = owned.wait().await;
            }
            Err(shared) => {
                tracing::warn!(
                    strong_count = Arc::strong_count(&shared),
                    "Handle::close while Arc<Browser> still shared — relying on kill-on-drop"
                );
                drop(shared);
            }
        }
        let _ = self.driver.await;
        Ok(())
    }
}

/// Launches Chromium. Downloads it on first run via the `fetcher`
/// feature; subsequent runs hit the cache. The cache dir is
/// `$CRAWLER_CHROMIUM_DIR` if set, else `$HOME/.cache/mangalord/chromium`,
/// else `./.chromium-cache` as a last-resort repo-local fallback.
pub async fn launch(options: LaunchOptions) -> anyhow::Result<Handle> {
    let cache = cache_dir()?;
    tokio::fs::create_dir_all(&cache)
        .await
        .with_context(|| format!("create cache dir {}", cache.display()))?;

    let fetcher = BrowserFetcher::new(
        BrowserFetcherOptions::builder()
            .with_path(&cache)
            .build()
            .map_err(|e| anyhow::anyhow!("fetcher options: {e}"))?,
    );
    tracing::info!(path = %cache.display(), "ensuring chromium revision is present");
    let info = fetcher
        .fetch()
        .await
        .context("download chromium via fetcher")?;
    tracing::info!(executable = %info.executable_path.display(), "chromium ready");

    let mut builder = BrowserConfig::builder()
        .chrome_executable(info.executable_path)
        // Linux containers / CI commonly lack the user namespaces
        // Chromium's sandbox wants. Disable it; the crawler runs in its
        // own container anyway.
        .arg("--no-sandbox")
        .arg("--disable-dev-shm-usage");
    for arg in &options.extra_args {
        builder = builder.arg(arg);
    }
    if matches!(options.mode, BrowserMode::Headed) {
        builder = builder.with_head();
    }
    tracing::info!(
        mode = ?options.mode,
        extra_args = ?options.extra_args,
        "building browser config"
    );
    let config = builder
        .build()
        .map_err(|e| anyhow::anyhow!("browser config: {e}"))?;

    let (browser, mut handler) = Browser::launch(config)
        .await
        .context("launch chromium")?;

    let driver = tokio::spawn(async move {
        while let Some(event) = handler.next().await {
            match event {
                Ok(_) => {}
                // chromiumoxide 0.7 ships fixed CDP type bindings, so any
                // CDP event Chrome added later fails to deserialize. The
                // connection is unaffected — these are noise. Suppress
                // them so real failures stay visible.
                Err(CdpError::Serde(_)) => {
                    tracing::trace!("chromium emitted an unrecognized CDP event");
                }
                Err(err) => tracing::warn!(?err, "chromium handler event error"),
            }
        }
    });

    Ok(Handle {
        browser: Arc::new(browser),
        driver,
    })
}

fn cache_dir() -> anyhow::Result<PathBuf> {
    if let Ok(dir) = std::env::var("CRAWLER_CHROMIUM_DIR") {
        return Ok(PathBuf::from(dir));
    }
    if let Ok(home) = std::env::var("HOME") {
        return Ok(PathBuf::from(home).join(".cache/mangalord/chromium"));
    }
    Ok(PathBuf::from("./.chromium-cache"))
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn parse_args_splits_on_whitespace() {
        assert_eq!(
            parse_args("--lang=de-DE --window-size=1280,800"),
            vec!["--lang=de-DE", "--window-size=1280,800"]
        );
    }

    #[test]
    fn parse_args_tolerates_irregular_whitespace() {
        // tabs, multiple spaces, leading/trailing — all collapsed.
        assert_eq!(
            parse_args("  --a\t--b   --c=1\n"),
            vec!["--a", "--b", "--c=1"]
        );
    }

    #[test]
    fn parse_args_empty_string_yields_empty_vec() {
        assert!(parse_args("").is_empty());
        assert!(parse_args("   \t\n").is_empty());
    }

    #[test]
    fn default_launch_options_are_headless() {
        // Headless is the production-safe default — no display required,
        // smaller resource footprint. `Headed` stays available as an
        // opt-in for debugging via CRAWLER_BROWSER_MODE=headed.
        assert_eq!(LaunchOptions::default().mode, BrowserMode::Headless);
        assert_eq!(LaunchOptions::headless().mode, BrowserMode::Headless);
        assert_eq!(LaunchOptions::headed().mode, BrowserMode::Headed);
    }
}