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use std::{convert::Infallible, error::Error as StdError, io::Write as _, sync::LazyLock};
use actix_web::{
HttpResponse, Responder,
body::{BodyStream, MessageBody},
};
use bytes::{Bytes, BytesMut};
use futures_core::Stream;
use futures_util::TryStreamExt as _;
use mime::Mime;
use pin_project_lite::pin_project;
use serde::Serialize;
use crate::util::{InfallibleStream, MutWriter};
static NDJSON_MIME: LazyLock<Mime> = LazyLock::new(|| "application/x-ndjson".parse().unwrap());
pin_project! {
/// A buffered [NDJSON] serializing body stream.
///
/// This has significant memory efficiency advantages over returning an array of JSON objects
/// when the data set is very large because it avoids buffering the entire response.
///
/// # Examples
/// ```
/// # use actix_web::Responder;
/// # use actix_web_lab::respond::NdJson;
/// # use futures_core::Stream;
/// fn streaming_data_source() -> impl Stream<Item = serde_json::Value> {
/// // get item stream from source
/// # futures_util::stream::empty()
/// }
///
/// async fn handler() -> impl Responder {
/// let data_stream = streaming_data_source();
///
/// NdJson::new_infallible(data_stream)
/// .into_responder()
/// }
/// ```
///
/// [NDJSON]: https://github.com/ndjson/ndjson-spec
pub struct NdJson<S> {
// The wrapped item stream.
#[pin]
stream: S,
}
}
impl<S> NdJson<S> {
/// Constructs a new `NdJson` from a stream of items.
pub fn new(stream: S) -> Self {
Self { stream }
}
}
impl<S> NdJson<S> {
/// Constructs a new `NdJson` from an infallible stream of items.
pub fn new_infallible(stream: S) -> NdJson<InfallibleStream<S>> {
NdJson::new(InfallibleStream::new(stream))
}
}
impl<S, T, E> NdJson<S>
where
S: Stream<Item = Result<T, E>>,
T: Serialize,
E: Into<Box<dyn StdError>> + 'static,
{
/// Creates a chunked body stream that serializes as NDJSON on-the-fly.
pub fn into_body_stream(self) -> impl MessageBody {
BodyStream::new(self.into_chunk_stream())
}
/// Creates a `Responder` type with a serializing stream and correct Content-Type header.
pub fn into_responder(self) -> impl Responder
where
S: 'static,
T: 'static,
E: 'static,
{
HttpResponse::Ok()
.content_type(NDJSON_MIME.clone())
.message_body(self.into_body_stream())
.unwrap()
}
/// Creates a stream of serialized chunks.
pub fn into_chunk_stream(self) -> impl Stream<Item = Result<Bytes, E>> {
self.stream.map_ok(serialize_json_line)
}
}
impl NdJson<Infallible> {
/// Returns the NDJSON MIME type (`application/x-ndjson`).
pub fn mime() -> Mime {
NDJSON_MIME.clone()
}
}
fn serialize_json_line(item: impl Serialize) -> Bytes {
let mut buf = BytesMut::new();
let mut wrt = MutWriter(&mut buf);
// serialize JSON line to buffer
serde_json::to_writer(&mut wrt, &item).unwrap();
// add line break to buffer
wrt.write_all(b"\n").unwrap();
buf.freeze()
}
#[cfg(test)]
mod tests {
use std::error::Error as StdError;
use actix_web::body;
use futures_util::stream;
use serde_json::json;
use super::*;
#[actix_web::test]
async fn serializes_into_body() {
let ndjson_body = NdJson::new_infallible(stream::iter(vec![
json!(null),
json!(1u32),
json!("123"),
json!({ "abc": "123" }),
json!(["abc", 123u32]),
]))
.into_body_stream();
let body_bytes = body::to_bytes(ndjson_body)
.await
.map_err(Into::<Box<dyn StdError>>::into)
.unwrap();
const EXP_BYTES: &str = "null\n\
1\n\
\"123\"\n\
{\"abc\":\"123\"}\n\
[\"abc\",123]\n";
assert_eq!(body_bytes, EXP_BYTES);
}
}