spire-reqwest 0.8.0

use std::future::{Future, ready};
use std::sync::Arc;

use spire_core::backend::{Backend, Session, StatusPolicy};
use spire_core::http::{Request, Response};
use spire_core::identity::Identity;
use spire_core::{Error, ErrorKind, Result};

use crate::clients::Clients;
use crate::conversion::{head_from_reqwest, request_to_reqwest};

/// An HTTP [`Backend`] built on [`reqwest::Client`].
///
/// Every request of a crawl gets a [`ReqwestSession`], and all of them share
/// one reqwest client: its connection pool, cookie store and
/// configuration. Error statuses are turned into errors according to the
/// [`StatusPolicy`].
///
/// It is built from a function that makes the reqwest configuration, see
/// [`from_builder`](Self::from_builder), because a crawl with
/// [identities](spire_core::identity) gets a client per identity from it,
/// with the identity's proxy and, with the `cookies` feature, a cookie store
/// of its own. An identity's client is dropped once the identity is gone.
///
/// # Examples
///
/// ```
/// use std::time::Duration;
///
/// use spire_reqwest::{ReqwestBackend, StatusPolicy};
///
/// let backend = ReqwestBackend::from_builder(|| {
///     reqwest::Client::builder()
///         .timeout(Duration::from_secs(30))
///         .user_agent("MyBot/1.0")
/// })?
/// .with_status_policy(StatusPolicy::Accept);
/// # Ok::<_, spire_core::Error>(())
/// ```
#[derive(Debug, Clone, Default)]
pub struct ReqwestBackend {
    clients: Clients,
    status_policy: StatusPolicy,
}

impl ReqwestBackend {
    /// Creates a client with reqwest's default configuration.
    #[must_use]
    pub fn new() -> Self {
        Self::default()
    }

    /// Creates a client from the configuration `builder` makes, which
    /// identities' clients are built from too.
    ///
    /// ```
    /// use std::time::Duration;
    ///
    /// use spire_reqwest::ReqwestBackend;
    ///
    /// let backend = ReqwestBackend::from_builder(|| {
    ///     reqwest::Client::builder().timeout(Duration::from_secs(30))
    /// })?;
    /// # Ok::<_, spire_core::Error>(())
    /// ```
    ///
    /// # Errors
    ///
    /// Returns a [`Backend`](ErrorKind::Backend) error if reqwest cannot
    /// build the client, e.g. when TLS fails to initialize.
    pub fn from_builder<F>(builder: F) -> Result<Self>
    where
        F: Fn() -> reqwest::ClientBuilder + Send + Sync + 'static,
    {
        Ok(Self {
            clients: Clients::new(Arc::new(builder))?,
            status_policy: StatusPolicy::default(),
        })
    }

    /// Sets how error statuses are treated.
    #[must_use]
    pub const fn with_status_policy(mut self, policy: StatusPolicy) -> Self {
        self.status_policy = policy;
        self
    }

    /// Returns the [`reqwest::Client`] requests without an identity use.
    #[must_use]
    pub const fn as_reqwest(&self) -> &reqwest::Client {
        self.clients.direct()
    }

    /// Returns the [`StatusPolicy`].
    #[must_use]
    pub const fn status_policy(&self) -> StatusPolicy {
        self.status_policy
    }
}

impl Backend for ReqwestBackend {
    type Session = ReqwestSession;

    fn connect(&self) -> impl Future<Output = Result<Self::Session>> + Send {
        ready(Ok(self.session(self.clients.direct().clone())))
    }

    /// Sends the identity's requests with a reqwest client of its own, with
    /// its proxy and cookies.
    fn connect_as(
        &self,
        identity: &Identity,
    ) -> impl Future<Output = Result<Self::Session>> + Send {
        ready(self.clients.of(identity).map(|client| self.session(client)))
    }
}

impl ReqwestBackend {
    fn session(&self, client: reqwest::Client) -> ReqwestSession {
        ReqwestSession {
            http: self.clone(),
            client,
        }
    }
}

/// The [`Session`] a [`ReqwestBackend`] hands out for one request: it sends the
/// request and returns the complete response.
#[derive(Debug)]
pub struct ReqwestSession {
    http: ReqwestBackend,
    /// The reqwest client it sends with: the crawl's, or its identity's.
    client: reqwest::Client,
}

impl ReqwestSession {
    /// Returns the [`ReqwestBackend`] the session belongs to.
    #[must_use]
    pub const fn http(&self) -> &ReqwestBackend {
        &self.http
    }
}

impl Session for ReqwestSession {
    async fn fetch(&self, request: &Request) -> Result<Response> {
        let uri = request.uri().clone();
        let failed = |error: Error| error.with_uri(uri.clone());
        let converted = request_to_reqwest(request).map_err(failed)?;
        let response = self
            .client
            .execute(converted)
            .await
            .map_err(|error| failed(classify(error)))?;

        // An error status is rejected before its body is downloaded.
        let head = self
            .http
            .status_policy
            .check(head_from_reqwest(&response))?;
        let body = response
            .bytes()
            .await
            .map_err(|error| failed(classify(error)))?;
        Ok(head.map(|()| body))
    }
}

/// Classifies a failed transfer, so the crawler only retries what may
/// succeed on another attempt.
fn classify(error: reqwest::Error) -> Error {
    let kind = if error.is_timeout() {
        ErrorKind::Timeout
    } else if error.is_builder() {
        ErrorKind::Invalid
    } else if error.is_redirect() {
        // Too many redirects or a redirect loop; retrying loops again.
        ErrorKind::Rejected
    } else {
        // Connection, DNS, protocol and body errors are usually transient.
        ErrorKind::Http
    };
    Error::new(kind).with_source(error)
}

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

    #[tokio::test]
    async fn invalid_request_is_rejected_before_sending() {
        let session = ReqwestBackend::new().connect().await.unwrap();
        let error = session.fetch(&Request::default()).await.unwrap_err();
        assert_eq!(error.kind(), ErrorKind::Invalid);
    }

    #[tokio::test]
    async fn sessions_share_the_client() {
        let backend = ReqwestBackend::new().with_status_policy(StatusPolicy::Accept);
        let session = backend.connect().await.unwrap();
        assert_eq!(session.http().status_policy(), StatusPolicy::Accept);
    }
}