document main crawler elements

Author: mikkeldenker

crates/core/src/crawler/mod.rs

@@ -14,6 +14,15 @@
 // You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
+//! # Crawler
+//!
+//! The crawler is responsible for fetching webpages and storing them in WARC files
+//! for later processing.
+//!
+//! Before starting a crawl, a plan needs to be created. This plan is then used by
+//! the crawler coordinator to assign sites to crawl to different workers.
+//! A site is only assigned to one worker at a time for politeness.
+
 use std::{collections::VecDeque, future::Future, net::SocketAddr, sync::Arc};
 
 type HashMap<K, V> = std::collections::HashMap<K, V, ahash::RandomState>;
@@ -35,7 +44,7 @@ pub use router::Router;
 mod file_queue;
 pub mod planner;
 pub mod robot_client;
-mod wander_prirotiser;
+mod wander_prioritiser;
 mod warc_writer;
 mod worker;
 
@@ -304,7 +313,7 @@ impl Crawler {
     }
 }
 
-pub trait DatumStream: Send + Sync {
+pub trait DatumSink: Send + Sync {
     fn write(&self, crawl_datum: CrawlDatum) -> impl Future<Output = Result<()>> + Send;
     fn finish(&self) -> impl Future<Output = Result<()>> + Send;
 }

crates/core/src/crawler/planner.rs

@@ -13,6 +13,7 @@
 //
 // You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
 use anyhow::{anyhow, Result};
 use futures::stream::FuturesOrdered;
 use futures::StreamExt;
@@ -71,6 +72,7 @@ impl From<StoredUrl> for Url {
     }
 }
 
+/// Store urls in groups on disk based on their harmonic rank.
 struct UrlGrouper {
     groups: Vec<speedy_kv::Db<StoredUrl, ()>>,
     folder: std::path::PathBuf,
@@ -169,6 +171,7 @@ struct Budget {
     remaining_schedulable: u64,
 }
 
+/// Create a crawl plan based on the harmonic rank of the hosts.
 pub struct CrawlPlanner {
     host_centrality: Arc<speedy_kv::Db<NodeID, f64>>,
     host_centrality_rank: Arc<speedy_kv::Db<NodeID, u64>>,

crates/core/src/crawler/robot_client.rs

@@ -45,6 +45,7 @@ pub(super) fn reqwest_client(config: &CrawlerConfig) -> Result<reqwest::Client>
         .map_err(|e| Error::from(anyhow!(e)))
 }
 
+/// Reqwest client that respects robots.txt for each request.
 #[derive(Clone)]
 pub struct RobotClient {
     robots_txt_manager: RobotsTxtManager,

crates/core/src/crawler/wander_prirotiser.rs renamed to crates/core/src/crawler/wander_prioritiser.rs

@@ -21,7 +21,7 @@ use crate::{
     warc,
 };
 
-use super::{CrawlDatum, DatumStream, Error, Result};
+use super::{CrawlDatum, DatumSink, Error, Result};
 use anyhow::anyhow;
 
 /// The WarcWriter is responsible for storing the crawl datums
@@ -30,7 +30,7 @@ pub struct WarcWriter {
     tx: tokio::sync::mpsc::Sender<WarcWriterMessage>,
 }
 
-impl DatumStream for WarcWriter {
+impl DatumSink for WarcWriter {
     async fn write(&self, crawl_datum: CrawlDatum) -> Result<()> {
         self.tx
             .send(WarcWriterMessage::Crawl(crawl_datum))

crates/core/src/crawler/warc_writer.rs

@@ -39,8 +39,8 @@ use crate::{
 };
 
 use super::{
-    encoded_body, robot_client::RobotClient, wander_prirotiser::WanderPrioritiser, CrawlDatum,
-    DatumStream, Domain, Error, Result, RetrieableUrl, Site, WarcWriter, WeightedUrl, WorkerJob,
+    encoded_body, robot_client::RobotClient, wander_prioritiser::WanderPrioritiser, CrawlDatum,
+    DatumSink, Domain, Error, Result, RetrieableUrl, Site, WarcWriter, WeightedUrl, WorkerJob,
     MAX_CONTENT_LENGTH, MAX_OUTGOING_URLS_PER_PAGE,
 };
 
@@ -126,7 +126,8 @@ impl WorkerThread {
     }
 }
 
-pub struct JobExecutor<S: DatumStream> {
+/// JobExecutor receives a job from the coordinator and crawls the urls in the job.
+pub struct JobExecutor<S: DatumSink> {
     writer: Arc<S>,
     client: RobotClient,
     has_gotten_429_response: bool,
@@ -144,7 +145,7 @@ pub struct JobExecutor<S: DatumStream> {
     job: WorkerJob,
 }
 
-impl<S: DatumStream> JobExecutor<S> {
+impl<S: DatumSink> JobExecutor<S> {
     pub fn new(
         job: WorkerJob,
         config: Arc<CrawlerConfig>,

crates/core/src/crawler/worker.rs

@@ -136,7 +136,7 @@ impl CrawlableSite {
     }
 }
 
-impl crawler::DatumStream for tokio::sync::Mutex<Vec<crawler::CrawlDatum>> {
+impl crawler::DatumSink for tokio::sync::Mutex<Vec<crawler::CrawlDatum>> {
     async fn write(&self, crawl_datum: crawler::CrawlDatum) -> Result<(), crawler::Error> {
         self.lock().await.push(crawl_datum);
         Ok(())