aws-lambda-runtime-proxy 0.3.0

use std::{
  env::{self, VarError},
  sync::LazyLock,
};

use anyhow::Result;
use http_body_util::{BodyExt, Full};
use hyper::{
  body::{Body, Bytes, Incoming},
  client::conn::http1::{self, SendRequest},
  Request, Response,
};
use hyper_util::rt::TokioIo;
use tokio::net::TcpStream;
use tracing::error;

/// An http client for the Lambda Runtime API.
/// A new-type wrapper around [`SendRequest<ReqBody>`].
/// # Examples
/// ```
/// # use hyper::{body::Incoming, Request};
/// use aws_lambda_runtime_proxy::LambdaRuntimeApiClient;
///
/// # async fn t1(req: Request<Incoming>) {
/// let mut client = LambdaRuntimeApiClient::new().await.unwrap();
/// // forward the original request to the runtime API
/// client.forward(req).await.unwrap();
/// # }
/// # async fn t2(req: Request<Incoming>) {
/// # let mut client = LambdaRuntimeApiClient::new().await.unwrap();
/// // construct a custom request and send it to the runtime API
/// client.as_mut().send_request(req).await.unwrap();
/// # }
/// ```
pub struct LambdaRuntimeApiClient<ReqBody>(SendRequest<ReqBody>);

impl<ReqBody> AsRef<SendRequest<ReqBody>> for LambdaRuntimeApiClient<ReqBody> {
  fn as_ref(&self) -> &SendRequest<ReqBody> {
    &self.0
  }
}
impl<ReqBody> AsMut<SendRequest<ReqBody>> for LambdaRuntimeApiClient<ReqBody> {
  fn as_mut(&mut self) -> &mut SendRequest<ReqBody> {
    &mut self.0
  }
}

impl<ReqBody: Body + Send + 'static> LambdaRuntimeApiClient<ReqBody> {
  /// Create a new client and connect to the runtime API.
  pub async fn new() -> Result<Self>
  where
    ReqBody::Data: Send,
    ReqBody::Error: Into<Box<dyn std::error::Error + Send + Sync>>,
  {
    static REAL_RUNTIME_API: LazyLock<Result<String, VarError>> =
      LazyLock::new(|| env::var("AWS_LAMBDA_RUNTIME_API"));

    let stream = TcpStream::connect(REAL_RUNTIME_API.as_ref()?).await?;
    let io = TokioIo::new(stream);
    let (sender, conn) = http1::handshake(io).await?;

    // Spawn a task to poll the connection, driving the HTTP state
    tokio::spawn(async move {
      if let Err(err) = conn.await {
        error!("Connection failed: {:?}", err);
      }
    });

    Ok(Self(sender))
  }
}

impl LambdaRuntimeApiClient<Incoming> {
  /// Send a request to the runtime API and return the response.
  pub async fn forward(&mut self, req: Request<Incoming>) -> Result<Response<Full<Bytes>>> {
    let res = self.as_mut().send_request(req).await?;
    let (parts, body) = res.into_parts();
    let bytes = body.collect().await?.to_bytes();
    Ok(Response::from_parts(parts, Full::new(bytes)))

    // TODO: why we can't just return `self.send_request(req).await`?
    // tested and it works but will add ~40ms latency when serving API GW event (maybe for all big event), why?
    // maybe because of the `Incoming` type? can we stream the body instead of buffering it?
  }
}