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use crate::callback::{Callback, Indeterminate};
use crate::handler::Handler;
use futures::{
stream::StreamExt,
Stream,
};
use reqwest::{Client, Request};
use std::fmt::Debug;
use std::num::NonZeroUsize;
use thiserror::Error;
use tokio::{
spawn,
sync::mpsc::{channel, error::SendError, unbounded_channel, Sender, UnboundedSender},
};
use tracing::{debug, error, info, instrument, Instrument};
#[derive(Error, Debug)]
pub(crate) enum Error<I, C>
where
I: Debug,
C: Debug,
{
#[error("a task was not able to be added to the task queue: {0:?}")]
TaskQueue(SendError<PendingCallback<I, C>>),
#[error("was not able to add the item (given: {0:?}) to the item queue")]
ItemQueue(SendError<I>),
#[error("an error occured executing the callback: {0}")]
Callback(reqwest::Error),
}
#[derive(Clone)]
pub struct Spider {
client: Client,
}
impl Spider {
pub fn new(client: Client) -> Self {
Self { client }
}
pub fn web<H, I, C>(&self) -> WebBuilder<H, C>
where
H: Handler<I, C> + 'static,
I: Debug + Send + Unpin + 'static,
C: Debug + Send + Unpin + 'static,
{
WebBuilder {
client: self.client.clone(),
start: None,
handler: None,
context: None,
concurrent_requests: None,
task_queue_size_bytes: None,
}
}
}
pub struct WebBuilder<H, C> {
client: Client,
start: Option<Request>,
handler: Option<H>,
context: Option<C>,
concurrent_requests: Option<NonZeroUsize>,
task_queue_size_bytes: Option<NonZeroUsize>,
}
impl<H, C> WebBuilder<H, C>
where
C: Debug + Send + Unpin + 'static,
{
pub fn start(mut self, start: Request) -> Self {
self.start = Some(start);
self
}
pub fn handler(mut self, handler: H) -> Self {
self.handler = Some(handler);
self
}
pub fn context(mut self, context: C) -> Self {
self.context = Some(context);
self
}
pub fn concurrent_requests(mut self, concurrent_requests: NonZeroUsize) -> Self {
self.concurrent_requests = Some(concurrent_requests);
self
}
pub fn task_queue_size_bytes(mut self, task_queue_size_bytes: NonZeroUsize) -> Self {
self.task_queue_size_bytes = Some(task_queue_size_bytes);
self
}
pub fn build<I>(self) -> Web<I, C>
where
I: Debug + Send + Unpin + 'static,
H: Handler<I, C> + 'static,
{
let callback = Callback::new(
self.handler.expect("initial request handler"),
self.start.expect("initial request"),
self.context.expect("initial context"),
);
Web {
client: self.client,
start: callback,
concurrent_requests: self
.concurrent_requests
.unwrap_or_else(|| NonZeroUsize::new(20).unwrap()),
task_queue_size_bytes: self
.task_queue_size_bytes
.unwrap_or_else(|| NonZeroUsize::new(10_000_000).unwrap()),
}
}
}
#[derive(Debug)]
pub struct Web<I, C> {
client: Client,
start: Callback<I, C>,
concurrent_requests: NonZeroUsize,
task_queue_size_bytes: NonZeroUsize,
}
impl<I, C> Web<I, C>
where
I: Debug + Send + Unpin + 'static,
C: Debug + Send + Unpin + 'static,
{
#[instrument]
pub async fn crawl(self) -> impl Stream<Item = I> {
let concurrent_requests = self.concurrent_requests.into();
let task_queue_size =
self.task_queue_size_bytes.get() / std::mem::size_of::<PendingCallback<I, C>>();
info!(
task_queue_size = task_queue_size,
concurrent_requests = concurrent_requests
);
info!("Starting traversal");
let (item_sender, mut item_reciever) = unbounded_channel();
let (task_sender, mut task_reciever) = channel(task_queue_size);
let pending_start = PendingCallback {
inner: self.start,
task_sender: task_sender.clone(),
item_sender,
};
let client = self.client;
task_sender
.send(pending_start)
.await
.expect("active task channel");
spawn(
async move {
let task_stream = async_stream::stream! {
while let Some(callback) = task_reciever.recv().await {
let client = client.clone();
let callback_name = format!("{}", callback.inner);
yield spawn(async move {
if let Err(err) = callback.run(
client,
)
.await
{
error!(
error = %err, callback = %callback_name,
"Error occurred while executing the callback",
);
}
});
}
};
task_stream
.buffer_unordered(concurrent_requests)
.for_each(move |join_handle| async move {
if let Err(join_err) = join_handle {
error!(error = %join_err, "Error joining the task");
}
})
.instrument(tracing::info_span!("task_stream"))
.await;
}
.instrument(tracing::info_span!("manager_task")),
);
let stream = async_stream::stream! {
while let Some(item) = item_reciever.recv().await {
yield item;
}
};
stream
}
}
#[derive(Debug)]
pub(crate) struct PendingCallback<I, C> {
inner: Callback<I, C>,
task_sender: Sender<Self>,
item_sender: UnboundedSender<I>,
}
impl<I, C> PendingCallback<I, C>
where
I: Debug,
C: Debug,
{
#[instrument]
pub(crate) async fn run(self, client: Client) -> Result<(), Error<I, C>> {
let callback_name = format!("{}", &self.inner);
info!(callback = %callback_name, "Runnning callback");
let output = match self.inner.run(client).await {
Ok(mut stream) => {
while let Some(indeterminate) = stream.recv().await {
match indeterminate {
Indeterminate::Item(item) => {
if let Err(err) = self.item_sender.send(item) {
error!(
error = %err,
"Got an error sending an item");
return Err(Error::ItemQueue(err));
}
}
Indeterminate::Callback(next) => {
let next_name = format!("{}", next);
let pending_next = Self {
inner: next,
task_sender: self.task_sender.clone(),
item_sender: self.item_sender.clone(),
};
if let Err(err) = self.task_sender.send(pending_next).await {
error!(error = %err, next = %next_name,
"Got an error queuing the next task");
return Err(Error::TaskQueue(err));
}
}
}
}
Ok(())
}
Err(err) => Err(Error::Callback(err)),
};
debug!(callback = %callback_name, "Finishing callback");
output
}
}