codec: move into tokio-util (#1675)

Related to #1318, Tokio APIs that are "less stable" are moved into a new
`tokio-util` crate. This crate will mirror `tokio` and provide
additional APIs that may require a greater rate of breaking changes.

As examples require `tokio-util`, they are moved into a separate
crate (`examples`). This has the added advantage of being able to avoid
example only dependencies in the `tokio` crate.

1 files changed, 299 insertions, 0 deletions

diff --git a/examples/tinyhttp.rs b/examples/tinyhttp.rs
new file mode 100644
index 00000000..65074018
--- /dev/null
+++ b/examples/tinyhttp.rs
@@ -0,0 +1,299 @@
+//! A "tiny" example of HTTP request/response handling using transports.
+//!
+//! This example is intended for *learning purposes* to see how various pieces
+//! hook up together and how HTTP can get up and running. Note that this example
+//! is written with the restriction that it *can't* use any "big" library other
+//! than Tokio, if you'd like a "real world" HTTP library you likely want a
+//! crate like Hyper.
+//!
+//! Code here is based on the `echo-threads` example and implements two paths,
+//! the `/plaintext` and `/json` routes to respond with some text and json,
+//! respectively. By default this will run I/O on all the cores your system has
+//! available, and it doesn't support HTTP request bodies.
+
+#![warn(rust_2018_idioms)]
+
+use bytes::BytesMut;
+use futures::{SinkExt, StreamExt};
+use http::{header::HeaderValue, Request, Response, StatusCode};
+use serde::Serialize;
+use std::{env, error::Error, fmt, io};
+use tokio::{
+    codec::{Decoder, Encoder, Framed},
+    net::{TcpListener, TcpStream},
+};
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn Error>> {
+    // Parse the arguments, bind the TCP socket we'll be listening to, spin up
+    // our worker threads, and start shipping sockets to those worker threads.
+    let addr = env::args().nth(1).unwrap_or("127.0.0.1:8080".to_string());
+
+    let mut incoming = TcpListener::bind(&addr).await?.incoming();
+    println!("Listening on: {}", addr);
+
+    while let Some(Ok(stream)) = incoming.next().await {
+        tokio::spawn(async move {
+            if let Err(e) = process(stream).await {
+                println!("failed to process connection; error = {}", e);
+            }
+        });
+    }
+
+    Ok(())
+}
+
+async fn process(stream: TcpStream) -> Result<(), Box<dyn Error>> {
+    let mut transport = Framed::new(stream, Http);
+
+    while let Some(request) = transport.next().await {
+        match request {
+            Ok(request) => {
+                let response = respond(request).await?;
+                transport.send(response).await?;
+            }
+            Err(e) => return Err(e.into()),
+        }
+    }
+
+    Ok(())
+}
+
+async fn respond(req: Request<()>) -> Result<Response<String>, Box<dyn Error>> {
+    let mut response = Response::builder();
+    let body = match req.uri().path() {
+        "/plaintext" => {
+            response.header("Content-Type", "text/plain");
+            "Hello, World!".to_string()
+        }
+        "/json" => {
+            response.header("Content-Type", "application/json");
+
+            #[derive(Serialize)]
+            struct Message {
+                message: &'static str,
+            }
+            serde_json::to_string(&Message {
+                message: "Hello, World!",
+            })?
+        }
+        _ => {
+            response.status(StatusCode::NOT_FOUND);
+            String::new()
+        }
+    };
+    let response = response
+        .body(body)
+        .map_err(|err| io::Error::new(io::ErrorKind::Other, err))?;
+
+    Ok(response)
+}
+
+struct Http;
+
+/// Implementation of encoding an HTTP response into a `BytesMut`, basically
+/// just writing out an HTTP/1.1 response.
+impl Encoder for Http {
+    type Item = Response<String>;
+    type Error = io::Error;
+
+    fn encode(&mut self, item: Response<String>, dst: &mut BytesMut) -> io::Result<()> {
+        use std::fmt::Write;
+
+        write!(
+            BytesWrite(dst),
+            "\
+             HTTP/1.1 {}\r\n\
+             Server: Example\r\n\
+             Content-Length: {}\r\n\
+             Date: {}\r\n\
+             ",
+            item.status(),
+            item.body().len(),
+            date::now()
+        )
+        .unwrap();
+
+        for (k, v) in item.headers() {
+            dst.extend_from_slice(k.as_str().as_bytes());
+            dst.extend_from_slice(b": ");
+            dst.extend_from_slice(v.as_bytes());
+            dst.extend_from_slice(b"\r\n");
+        }
+
+        dst.extend_from_slice(b"\r\n");
+        dst.extend_from_slice(item.body().as_bytes());
+
+        return Ok(());
+
+        // Right now `write!` on `Vec<u8>` goes through io::Write and is not
+        // super speedy, so inline a less-crufty implementation here which
+        // doesn't go through io::Error.
+        struct BytesWrite<'a>(&'a mut BytesMut);
+
+        impl fmt::Write for BytesWrite<'_> {
+            fn write_str(&mut self, s: &str) -> fmt::Result {
+                self.0.extend_from_slice(s.as_bytes());
+                Ok(())
+            }
+
+            fn write_fmt(&mut self, args: fmt::Arguments<'_>) -> fmt::Result {
+                fmt::write(self, args)
+            }
+        }
+    }
+}
+
+/// Implementation of decoding an HTTP request from the bytes we've read so far.
+/// This leverages the `httparse` crate to do the actual parsing and then we use
+/// that information to construct an instance of a `http::Request` object,
+/// trying to avoid allocations where possible.
+impl Decoder for Http {
+    type Item = Request<()>;
+    type Error = io::Error;
+
+    fn decode(&mut self, src: &mut BytesMut) -> io::Result<Option<Request<()>>> {
+        // TODO: we should grow this headers array if parsing fails and asks
+        //       for more headers
+        let mut headers = [None; 16];
+        let (method, path, version, amt) = {
+            let mut parsed_headers = [httparse::EMPTY_HEADER; 16];
+            let mut r = httparse::Request::new(&mut parsed_headers);
+            let status = r.parse(src).map_err(|e| {
+                let msg = format!("failed to parse http request: {:?}", e);
+                io::Error::new(io::ErrorKind::Other, msg)
+            })?;
+
+            let amt = match status {
+                httparse::Status::Complete(amt) => amt,
+                httparse::Status::Partial => return Ok(None),
+            };
+
+            let toslice = |a: &[u8]| {
+                let start = a.as_ptr() as usize - src.as_ptr() as usize;
+                assert!(start < src.len());
+                (start, start + a.len())
+            };
+
+            for (i, header) in r.headers.iter().enumerate() {
+                let k = toslice(header.name.as_bytes());
+                let v = toslice(header.value);
+                headers[i] = Some((k, v));
+            }
+
+            (
+                toslice(r.method.unwrap().as_bytes()),
+                toslice(r.path.unwrap().as_bytes()),
+                r.version.unwrap(),
+                amt,
+            )
+        };
+        if version != 1 {
+            return Err(io::Error::new(
+                io::ErrorKind::Other,
+                "only HTTP/1.1 accepted",
+            ));
+        }
+        let data = src.split_to(amt).freeze();
+        let mut ret = Request::builder();
+        ret.method(&data[method.0..method.1]);
+        ret.uri(data.slice(path.0, path.1));
+        ret.version(http::Version::HTTP_11);
+        for header in headers.iter() {
+            let (k, v) = match *header {
+                Some((ref k, ref v)) => (k, v),
+                None => break,
+            };
+            let value = unsafe { HeaderValue::from_shared_unchecked(data.slice(v.0, v.1)) };
+            ret.header(&data[k.0..k.1], value);
+        }
+
+        let req = ret
+            .body(())
+            .map_err(|e| io::Error::new(io::ErrorKind::Other, e))?;
+        Ok(Some(req))
+    }
+}
+
+mod date {
+    use std::cell::RefCell;
+    use std::fmt::{self, Write};
+    use std::str;
+
+    use time::{self, Duration};
+
+    pub struct Now(());
+
+    /// Returns a struct, which when formatted, renders an appropriate `Date`
+    /// header value.
+    pub fn now() -> Now {
+        Now(())
+    }
+
+    // Gee Alex, doesn't this seem like premature optimization. Well you see
+    // there Billy, you're absolutely correct! If your server is *bottlenecked*
+    // on rendering the `Date` header, well then boy do I have news for you, you
+    // don't need this optimization.
+    //
+    // In all seriousness, though, a simple "hello world" benchmark which just
+    // sends back literally "hello world" with standard headers actually is
+    // bottlenecked on rendering a date into a byte buffer. Since it was at the
+    // top of a profile, and this was done for some competitive benchmarks, this
+    // module was written.
+    //
+    // Just to be clear, though, I was not intending on doing this because it
+    // really does seem kinda absurd, but it was done by someone else [1], so I
+    // blame them!  :)
+    //
+    // [1]: https://github.com/rapidoid/rapidoid/blob/f1c55c0555007e986b5d069fe1086e6d09933f7b/rapidoid-commons/src/main/java/org/rapidoid/commons/Dates.java#L48-L66
+
+    struct LastRenderedNow {
+        bytes: [u8; 128],
+        amt: usize,
+        next_update: time::Timespec,
+    }
+
+    thread_local!(static LAST: RefCell<LastRenderedNow> = RefCell::new(LastRenderedNow {
+        bytes: [0; 128],
+        amt: 0,
+        next_update: time::Timespec::new(0, 0),
+    }));
+
+    impl fmt::Display for Now {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            LAST.with(|cache| {
+                let mut cache = cache.borrow_mut();
+                let now = time::get_time();
+                if now >= cache.next_update {
+                    cache.update(now);
+                }
+                f.write_str(cache.buffer())
+            })
+        }
+    }
+
+    impl LastRenderedNow {
+        fn buffer(&self) -> &str {
+            str::from_utf8(&self.bytes[..self.amt]).unwrap()
+        }
+
+        fn update(&mut self, now: time::Timespec) {
+            self.amt = 0;
+            write!(LocalBuffer(self), "{}", time::at(now).rfc822()).unwrap();
+            self.next_update = now + Duration::seconds(1);
+            self.next_update.nsec = 0;
+        }
+    }
+
+    struct LocalBuffer<'a>(&'a mut LastRenderedNow);
+
+    impl fmt::Write for LocalBuffer<'_> {
+        fn write_str(&mut self, s: &str) -> fmt::Result {
+            let start = self.0.amt;
+            let end = start + s.len();
+            self.0.bytes[start..end].copy_from_slice(s.as_bytes());
+            self.0.amt += s.len();
+            Ok(())
+        }
+    }
+}