spider_lib/

builder.rs

//! Builder for constructing and configuring the `Crawler` instance.
//!
//! This module provides the `CrawlerBuilder`, a fluent API for
//! setting up and customizing a web crawler. It simplifies the process of
//! assembling various `spider-lib` components, including:
//! - Defining concurrency settings for downloads, parsing, and pipelines.
//! - Attaching custom `Downloader` implementations.
//! - Registering `Middleware`s to process requests and responses.
//! - Adding `Pipeline`s to process scraped items.
//! - Configuring checkpointing for persistence and fault tolerance.
//!
//! The builder handles default configurations (e.g., adding a default User-Agent
//! middleware if none is specified) and loading existing checkpoints.

use crate::ConsoleWriterPipeline;
#[cfg(feature = "checkpoint")]
use crate::checkpoint::Checkpoint;
use crate::downloader::Downloader;
use crate::downloaders::reqwest_client::ReqwestClientDownloader;
use crate::error::SpiderError;
use crate::middleware::Middleware;
use crate::middlewares::user_agent::{UserAgentMiddleware, UserAgentSource};
use crate::pipeline::Pipeline;
use crate::scheduler::Scheduler;
use crate::spider::Spider;
use num_cpus;
#[cfg(feature = "checkpoint")]
use std::fs;
use std::marker::PhantomData;
#[cfg(feature = "checkpoint")]
use std::path::{Path, PathBuf};
use std::sync::Arc;
#[cfg(feature = "checkpoint")]
use std::time::Duration;
#[cfg(feature = "checkpoint")]
use tracing::{debug, warn};

use super::Crawler;

/// Configuration for the crawler's concurrency settings.
pub struct CrawlerConfig {
    /// The maximum number of concurrent downloads.
    pub max_concurrent_downloads: usize,
    /// The number of workers dedicated to parsing responses.
    pub parser_workers: usize,
    /// The maximum number of concurrent item processing pipelines.
    pub max_concurrent_pipelines: usize,
}

impl Default for CrawlerConfig {
    fn default() -> Self {
        CrawlerConfig {
            max_concurrent_downloads: 5,
            parser_workers: num_cpus::get(),
            max_concurrent_pipelines: 5,
        }
    }
}

pub struct CrawlerBuilder<S: Spider, D = ReqwestClientDownloader>
where
    D: Downloader,
{
    crawler_config: CrawlerConfig,
    downloader: D,
    spider: Option<S>,
    middlewares: Vec<Box<dyn Middleware<D::Client> + Send + Sync>>,
    item_pipelines: Vec<Box<dyn Pipeline<S::Item>>>,
    #[cfg(feature = "checkpoint")]
    checkpoint_path: Option<PathBuf>,
    #[cfg(feature = "checkpoint")]
    checkpoint_interval: Option<Duration>,
    _phantom: PhantomData<S>,
}

impl<S: Spider, D: Default + Downloader> Default for CrawlerBuilder<S, D> {
    fn default() -> Self {
        Self {
            crawler_config: CrawlerConfig::default(),
            downloader: D::default(),
            spider: None,
            middlewares: Vec::new(),
            item_pipelines: Vec::new(),
            #[cfg(feature = "checkpoint")]
            checkpoint_path: None,
            #[cfg(feature = "checkpoint")]
            checkpoint_interval: None,
            _phantom: PhantomData,
        }
    }
}

impl<S: Spider, D: Downloader> CrawlerBuilder<S, D> {
    /// Creates a new `CrawlerBuilder` for a given spider.
    pub fn new(spider: S) -> Self
    where
        D: Default,
    {
        Self {
            spider: Some(spider),
            ..Default::default()
        }
    }

    /// Sets the maximum number of concurrent downloads.
    pub fn max_concurrent_downloads(mut self, limit: usize) -> Self {
        self.crawler_config.max_concurrent_downloads = limit;
        self
    }

    /// Sets the maximum number of concurrent parser workers.
    pub fn max_parser_workers(mut self, limit: usize) -> Self {
        self.crawler_config.parser_workers = limit;
        self
    }

    /// Sets the maximum number of concurrent pipelines.
    pub fn max_concurrent_pipelines(mut self, limit: usize) -> Self {
        self.crawler_config.max_concurrent_pipelines = limit;
        self
    }

    /// Sets a custom downloader for the crawler.
    pub fn downloader(mut self, downloader: D) -> Self {
        self.downloader = downloader;
        self
    }

    /// Adds a middleware to the crawler.
    pub fn add_middleware<M>(mut self, middleware: M) -> Self
    where
        D: Downloader,
        M: Middleware<D::Client> + Send + Sync + 'static,
    {
        self.middlewares.push(Box::new(middleware));
        self
    }

    /// Adds an item pipeline to the crawler.
    pub fn add_pipeline<P>(mut self, pipeline: P) -> Self
    where
        P: Pipeline<S::Item> + 'static,
    {
        self.item_pipelines.push(Box::new(pipeline));
        self
    }

    /// Enables checkpointing and sets the path for the checkpoint file.
    #[cfg(feature = "checkpoint")]
    pub fn with_checkpoint_path<P: AsRef<Path>>(mut self, path: P) -> Self {
        self.checkpoint_path = Some(path.as_ref().to_path_buf());
        self
    }

    /// Sets the interval for periodic checkpointing.
    #[cfg(feature = "checkpoint")]
    pub fn with_checkpoint_interval(mut self, interval: Duration) -> Self {
        self.checkpoint_interval = Some(interval);
        self
    }

    /// Builds the `Crawler` instance.
    pub async fn build(mut self) -> Result<Crawler<S, D::Client>, SpiderError>
    where
        D: Downloader + Send + Sync + 'static,
        D::Client: Send + Sync,
    {
        if self.item_pipelines.is_empty() {
            self = self.add_pipeline(ConsoleWriterPipeline::new());
        }

        let spider = self.spider.take().ok_or_else(|| {
            SpiderError::ConfigurationError("Crawler must have a spider.".to_string())
        })?;

        if self.crawler_config.max_concurrent_downloads == 0 {
            return Err(SpiderError::ConfigurationError(
                "max_concurrent_downloads must be greater than 0.".to_string(),
            ));
        }
        if self.crawler_config.parser_workers == 0 {
            return Err(SpiderError::ConfigurationError(
                "parser_workers must be greater than 0.".to_string(),
            ));
        }

        #[cfg(feature = "checkpoint")]
        let mut initial_scheduler_state = None;
        #[cfg(not(feature = "checkpoint"))]
        let initial_scheduler_state = None;
        #[cfg(feature = "checkpoint")]
        let mut loaded_pipelines_state = None;

        #[cfg(feature = "checkpoint")]
        if let Some(path) = &self.checkpoint_path {
            debug!("Attempting to load checkpoint from {:?}", path);
            match fs::read(path) {
                Ok(bytes) => match rmp_serde::from_slice::<Checkpoint>(&bytes) {
                    Ok(checkpoint) => {
                        initial_scheduler_state = Some(checkpoint.scheduler);
                        loaded_pipelines_state = Some(checkpoint.pipelines);
                    }
                    Err(e) => warn!("Failed to deserialize checkpoint from {:?}: {}", path, e),
                },
                Err(e) => warn!("Failed to read checkpoint file {:?}: {}", path, e),
            }
        }

        #[cfg(feature = "checkpoint")]
        // Restore pipeline states now that pipelines are built
        if let Some(pipeline_states) = loaded_pipelines_state {
            for (name, state) in pipeline_states {
                if let Some(pipeline) = self.item_pipelines.iter().find(|p| p.name() == name) {
                    pipeline.restore_state(state).await?;
                } else {
                    warn!("Checkpoint contains state for unknown pipeline: {}", name);
                }
            }
        }

        let (scheduler_arc, req_rx) = Scheduler::new(initial_scheduler_state);

        let has_user_agent_middleware = self
            .middlewares
            .iter()
            .any(|m| m.name() == "UserAgentMiddleware");

        if !has_user_agent_middleware {
            let pkg_name = env!("CARGO_PKG_NAME");
            let pkg_version = env!("CARGO_PKG_VERSION");
            let default_user_agent = format!("{}/{}", pkg_name, pkg_version);

            let default_user_agent_mw = UserAgentMiddleware::builder()
                .source(UserAgentSource::List(vec![default_user_agent.clone()]))
                .fallback_user_agent(default_user_agent)
                .build()?;
            self.middlewares.insert(0, Box::new(default_user_agent_mw));
        }

        let downloader_arc = Arc::new(self.downloader);

        let crawler = Crawler::new(
            scheduler_arc,
            req_rx,
            downloader_arc,
            self.middlewares,
            spider,
            self.item_pipelines,
            self.crawler_config.max_concurrent_downloads,
            self.crawler_config.parser_workers,
            self.crawler_config.max_concurrent_pipelines,
            #[cfg(feature = "checkpoint")]
            self.checkpoint_path.take(),
            #[cfg(feature = "checkpoint")]
            self.checkpoint_interval,
        );

        Ok(crawler)
    }
}