claviron-python 0.2.7

//! Streaming HTTP adaptation for an owned ASGI application handle.
//!
//! The host supplies routing and the lifecycle-managed handle cell. No
//! listener, runner registration or process supervisor is created here.

use std::convert::Infallible;
use std::future::Future;
use std::pin::Pin;
use std::sync::{Arc, RwLock};
use std::task::{Context, Poll};

use bytes::Bytes;
use http::{Request, Response, StatusCode};
use http_body_util::{BodyExt, Full};
use percent_encoding::percent_decode_str;
use tower_service::Service;

use crate::asgi::{HttpRequest, PythonApplicationHandle};

/// What the registered service answers with.
///
/// The body streams: an application's reply reaches the client as it is
/// produced — a server-sent event as it is sent — and one that is whole says
/// its exact size, which is how an ingress knows it can hand it over at once.
pub type AppResponse = http::Response<ResponseBody>;

/// A reply body: whatever the application produced, boxed so every ingress
/// takes one type.
pub type ResponseBody = claviron::http::RouteBody;

/// The error a reply body can end with.
pub type BoxError = claviron::http::RouteBodyError;

/// A whole body, as a [`ResponseBody`].
pub fn full_body(bytes: impl Into<Bytes>) -> ResponseBody {
    Full::new(bytes.into()).map_err(|never| match never {}).boxed_unsync()
}

type BoxFuture<T> = Pin<Box<dyn Future<Output = T> + Send>>;

/// The Python application, as a service to put behind your own routes.
///
/// It is generic over the request body, so it fits a framework's fallback slot
/// without this crate knowing that framework. The handle inside is filled when
/// the interpreter boots, which happens before any runnable is spawned. It
/// follows the current application generation; a stopped application returns 503.
#[derive(Clone)]
pub struct PythonService {
    handle: Arc<RwLock<Option<PythonApplicationHandle>>>,
}

impl PythonService {
    /// Adapt a shared application-generation handle without booting Python.
    /// The lifecycle owner publishes ready handles and clears the cell on stop.
    pub fn new(handle: Arc<RwLock<Option<PythonApplicationHandle>>>) -> Self {
        Self { handle }
    }

    /// Hand a request to the application and wait for its answer.
    ///
    /// The same thing the `Service` implementation does, as a plain method, so
    /// a closure can reach the interpreter without importing a trait.
    pub async fn handle<B>(
        &self,
        request: Request<B>,
    ) -> AppResponse
    where
        B: http_body::Body<Data = Bytes> + Send + 'static,
        B::Error: std::fmt::Display,
    {
        let handle = self.handle.read().expect("python handle lock").clone();
        dispatch(handle, request).await
    }
}

impl<B> Service<Request<B>> for PythonService
where
    B: http_body::Body<Data = Bytes> + Send + 'static,
    B::Error: std::fmt::Display,
{
    type Response = AppResponse;
    type Error = Infallible;
    type Future = BoxFuture<Result<AppResponse, Infallible>>;

    fn poll_ready(
        &mut self,
        _: &mut Context<'_>,
    ) -> Poll<Result<(), Self::Error>> {
        Poll::Ready(Ok(()))
    }

    fn call(
        &mut self,
        request: Request<B>,
    ) -> Self::Future {
        let handle = self.handle.read().expect("python handle lock").clone();
        Box::pin(async move { Ok(dispatch(handle, request).await) })
    }
}

async fn dispatch<B>(
    handle: Option<PythonApplicationHandle>,
    request: Request<B>,
) -> AppResponse
where
    B: http_body::Body<Data = Bytes> + Send + 'static,
    B::Error: std::fmt::Display,
{
    let Some(handle) = handle else {
        return text_response(
            StatusCode::SERVICE_UNAVAILABLE,
            "Python application is stopped".to_owned(),
        );
    };
    let (parts, body) = request.into_parts();
    let body = body.map_err(|error| BoxError::from(error.to_string()));
    let scope = request_scope(&parts);

    match handle.handle_http(scope, body).await {
        Ok(response) => response_from_asgi(
            response.status,
            response.headers,
            response.body.map_err(BoxError::from).boxed_unsync(),
        )
        .unwrap_or_else(internal_error),
        Err(crate::asgi::Error::ApplicationStopped) => text_response(
            StatusCode::SERVICE_UNAVAILABLE,
            "Python application is stopped".to_owned(),
        ),
        Err(error) => internal_error(error),
    }
}

fn internal_error(error: impl std::fmt::Display) -> AppResponse {
    tracing::error!(%error, "Python HTTP request failed");
    text_response(
        StatusCode::INTERNAL_SERVER_ERROR,
        "Internal Server Error".to_owned(),
    )
}

/// The ASGI scope of a request, HTTP or WebSocket alike. Where it came from is
/// read the way every owner reads it: a trusted hop's word first, the accepted
/// connection's otherwise.
pub fn request_scope(parts: &http::request::Parts) -> HttpRequest {
    let origin = claviron::http::trust::Origin::of(&parts.extensions);
    // A plain listener is `http`, which is what an unknown scheme reports.
    let scheme = origin
        .scheme
        .as_ref()
        .map(|scheme| scheme.as_str())
        .or(parts.uri.scheme_str())
        .unwrap_or("http")
        .to_owned();
    HttpRequest {
        method: parts.method.as_str().to_owned(),
        scheme,
        http_version: http_version(parts.version).to_owned(),
        path: percent_decode_str(parts.uri.path())
            .decode_utf8_lossy()
            .into_owned(),
        raw_path: parts.uri.path().as_bytes().to_vec(),
        query_string: parts.uri.query().unwrap_or_default().as_bytes().to_vec(),
        headers: scope_headers(parts),
        client: origin.client,
        server: origin.server,
    }
}

/// The request's headers as ASGI lists them. HTTP/2 and HTTP/3 name the host
/// in `:authority`, not in a `Host` header; ASGI puts the request's authority
/// first as `host`, in place of any `host` the client also sent, so an
/// application reads the name the client asked for on every version rather
/// than falling back to the server address. The authority is the one the
/// edge accepted: Claviron's own selection between the target and `Host`.
fn scope_headers(parts: &http::request::Parts) -> Vec<(Vec<u8>, Vec<u8>)> {
    let authority =
        claviron::http::authority::RequestAuthority::from_parts(parts)
            .ok()
            .flatten();
    let mut headers = Vec::with_capacity(parts.headers.len() + 1);
    if let Some(authority) = &authority {
        headers.push((
            b"host".to_vec(),
            authority.authority().as_str().as_bytes().to_vec(),
        ));
    }
    headers.extend(
        parts
            .headers
            .iter()
            .filter(|(name, _)| {
                authority.is_none() || *name != http::header::HOST
            })
            .map(|(name, value)| {
                (name.as_str().as_bytes().to_vec(), value.as_bytes().to_vec())
            }),
    );
    headers
}

fn response_from_asgi(
    status: u16,
    headers: Vec<(Vec<u8>, Vec<u8>)>,
    body: ResponseBody,
) -> Result<AppResponse, &'static str> {
    let status = StatusCode::from_u16(status)
        .map_err(|_| "invalid ASGI response status")?;
    let mut response = Response::new(body);
    *response.status_mut() = status;
    for (name, value) in headers {
        let name = http::HeaderName::from_bytes(&name)
            .map_err(|_| "invalid ASGI response header")?;
        // ASGI delegates transfer framing to the selected HTTP transport.
        if name == http::header::TRANSFER_ENCODING {
            continue;
        }
        let value = http::HeaderValue::from_bytes(&value)
            .map_err(|_| "invalid ASGI response header")?;
        response.headers_mut().append(name, value);
    }
    Ok(response)
}

pub(crate) fn text_response(
    status: StatusCode,
    message: String,
) -> AppResponse {
    let mut response = Response::new(full_body(message));
    *response.status_mut() = status;
    response
}

pub(crate) fn http_version(version: http::Version) -> &'static str {
    match version {
        http::Version::HTTP_09 => "0.9",
        http::Version::HTTP_10 => "1.0",
        http::Version::HTTP_11 => "1.1",
        http::Version::HTTP_2 => "2",
        http::Version::HTTP_3 => "3",
        _ => "1.1",
    }
}

#[cfg(test)]
#[path = "../tests/routing.rs"]
mod tests;