factor rendering into trait

Fixes #21.

benches/benches.rs

@@ -2,6 +2,7 @@ use criterion::BenchmarkId;
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
 use tokio::runtime;
 
+use aurelius::render::MarkdownRenderer;
 use aurelius::Server;
 
 fn from_elem(c: &mut Criterion) {
@@ -15,7 +16,8 @@ fn from_elem(c: &mut Criterion) {
 
         let addr = "127.0.0.1:0".parse().unwrap();
 
-        let server = runtime.block_on(async { Server::bind(&addr).await.unwrap() });
+        let server =
+            runtime.block_on(async { Server::bind(&addr, MarkdownRenderer::new()).await.unwrap() });
 
         b.to_async(&runtime).iter(|| async {
             server.send(black_box("Hello, world!")).await.unwrap();
@@ -30,7 +32,8 @@ fn from_elem(c: &mut Criterion) {
 
         let addr = "127.0.0.1:0".parse().unwrap();
 
-        let server = runtime.block_on(async { Server::bind(&addr).await.unwrap() });
+        let server =
+            runtime.block_on(async { Server::bind(&addr, MarkdownRenderer::new()).await.unwrap() });
 
         let markdown = "a ".repeat(100_000);
 

src/lib.rs

@@ -1,24 +1,26 @@
 //! [aurelius](https://github.com/euclio/aurelius) is a complete solution for live-previewing
-//! markdown as HTML.
+//! markdown (and more!) as HTML.
 //!
-//! This crate provides a server that can render and update an HTML preview of markdown without a
+//! This crate provides a [`Server`] that can render and update an HTML preview of input without a
 //! client-side refresh. Upon receiving an HTTP request, the server responds with an HTML page
-//! containing a rendering of supplied markdown. Client-side JavaScript then initiates a WebSocket
+//! containing a rendering of the input. Client-side JavaScript then initiates a WebSocket
 //! connection which allows the server to push changes to the client.
 //!
 //! This crate was designed to power [vim-markdown-composer], a markdown preview plugin for
-//! [Neovim](http://neovim.io), but it may be used to implement similar plugins for any editor.
+//! [Neovim](http://neovim.io), but it may be used to implement similar plugins for any editor. It
+//! also supports arbitrary renderers through the [`Renderer`] trait.
 //! See [vim-markdown-composer] for a real-world usage example.
 //!
 //! # Example
 //!
 //! ```no_run
 //! use std::net::SocketAddr;
 //! use aurelius::Server;
+//! use aurelius::render::MarkdownRenderer;
 //!
 //! # tokio_test::block_on(async {
 //! let addr = "127.0.0.1:1337".parse::<SocketAddr>()?;
-//! let mut server = Server::bind(&addr).await?;
+//! let mut server = Server::bind(&addr, MarkdownRenderer::new()).await?;
 //!
 //! server.open_browser()?;
 //!
@@ -52,23 +54,23 @@ use std::process::Stdio;
 use std::sync::{Arc, RwLock};
 
 use axum::{extract::Extension, http::Uri, routing::get, Router};
-use pulldown_cmark::{Options, Parser};
-use tokio::io::{AsyncReadExt, AsyncWriteExt};
 use tokio::process::Command;
 use tokio::sync::oneshot;
 use tokio::sync::watch::{self, Sender};
 use tower_http::trace::TraceLayer;
 use tracing::log::*;
 
-mod render;
+pub mod render;
 mod service;
 
-pub use render::*;
+use crate::render::Renderer;
 
-/// Markdown preview server.
+/// Live preview server.
 ///
-/// Listens for HTTP connections and serves a page containing a live markdown preview. The page
+/// Listens for HTTP connections and serves a page containing a live rendered preview. The page
 /// contains JavaScript to open a websocket connection back to the server for rendering updates.
+///
+/// The server is asynchronous, and assumes that a `tokio` runtime is in use.
 #[derive(Debug)]
 pub struct Server<R> {
     addr: SocketAddr,
@@ -79,14 +81,17 @@ pub struct Server<R> {
     _shutdown_tx: oneshot::Sender<()>,
 }
 
-impl<R> Server<R> where R: Renderer {
-    /// Binds the server to a specified address.
+impl<R> Server<R>
+where
+    R: Renderer,
+{
+    /// Binds the server to a specified address `addr` using the provided `renderer`.
     ///
     /// Binding to port 0 will request a port assignment from the OS. Use [`addr()`][Self::addr]
     /// to determine what port was assigned.
     ///
     /// The server must be bound using a Tokio runtime.
-    pub async fn bind(addr: &SocketAddr) -> io::Result<Self> {
+    pub async fn bind(addr: &SocketAddr, renderer: R) -> io::Result<Server<R>> {
         let (tx, rx) = watch::channel(String::new());
         let (shutdown_tx, shutdown_rx) = oneshot::channel();
 
@@ -114,7 +119,7 @@ impl<R> Server<R> where R: Renderer {
         Ok(Server {
             addr,
             config,
-            external_renderer: None,
+            renderer,
             tx,
             output: RefCell::new(String::new()),
             _shutdown_tx: shutdown_tx,
@@ -126,22 +131,17 @@ impl<R> Server<R> where R: Renderer {
         self.addr
     }
 
-    /// Publish new markdown to be rendered by the server.
+    /// Publish new input to be rendered by the server.
     ///
     /// The new HTML will be sent to all connected websocket clients.
-    ///
-    /// # Errors
-    ///
-    /// This method forwards errors from an external renderer, if set. Otherwise, the method is
-    /// infallible.
-    pub async fn send(&self, markdown: &str) -> Result<(), R::Error> {
+    pub async fn send(&self, input: &str) -> Result<(), R::Error> {
         let mut output = self.output.take();
         output.clear();
 
         // Heuristic taken from rustdoc
-        output.reserve(markdown.len() * 3 / 2);
+        output.reserve(input.len() * 3 / 2);
 
-        self.renderer.render(markdown, &mut output)?;
+        self.renderer.render(input, &mut output)?;
 
         self.output.replace(self.tx.send_replace(output));
 
@@ -152,7 +152,7 @@ impl<R> Server<R> where R: Renderer {
     ///
     /// This can be thought of as the "working directory" of the server. Any HTTP requests with
     /// non-root paths will be joined to this folder and used to serve files from the filesystem.
-    /// Typically this is used to serve image links relative to the markdown file.
+    /// Typically this is used to serve image links relative to the input file.
     ///
     /// By default, the server will not serve static files.
     pub fn set_static_root(&mut self, root: impl Into<PathBuf>) {
@@ -265,11 +265,12 @@ mod tests {
     use tokio::net::lookup_host;
     use tokio::time::{timeout, Duration};
 
-    use super::Server;
+    use crate::render::MarkdownRenderer;
+    use crate::Server;
 
-    async fn new_server() -> anyhow::Result<Server> {
+    async fn new_server() -> anyhow::Result<Server<MarkdownRenderer>> {
         let addr = lookup_host("localhost:0").await?.next().unwrap();
-        Ok(Server::bind(&addr).await?)
+        Ok(Server::bind(&addr, MarkdownRenderer::new()).await?)
     }
 
     async fn assert_websocket_closed<S: AsyncRead + AsyncWrite + Unpin>(

src/render.rs

@@ -1,26 +1,32 @@
-mod external;
+//! HTML rendering.
+
+mod command;
 mod markdown;
 
-pub use external::ExternalCommand;
-pub use markdown::Markdown;
+pub use command::CommandRenderer;
+pub use markdown::MarkdownRenderer;
 
-/// Markdown renderer implementation.
+/// HTML renderer implementation.
 ///
-/// Implementors of this trait convert markdown into HTML.
+/// Implementors of this trait convert input into HTML.
 pub trait Renderer {
-    /// Potential errors returned by rendering. If rendering is infallible (markdown can always
-    /// produce HTML from its input), this type can be set to [`std::convert::Infallible`].
+    /// Potential errors returned by the rendering. If rendering is infallible (for example,
+    /// markdown can always produce HTML from its input), this type can be set to
+    /// [`std::convert::Infallible`].
     type Error;
 
-    /// Renders markdown as HTML.
+    /// Renders input as HTML.
     ///
-    /// The HTML should be written directly into the `html` buffer.
+    /// The HTML should be written directly into the `html` buffer. The buffer will be reused
+    /// between multiple calls to this method, with its capacity already reserved, so this function
+    /// only needs to write the HTML.
     fn render(&self, input: &str, html: &mut String) -> Result<(), Self::Error>;
 
     /// A hint for how many bytes the output will be.
     ///
     /// This hint should be cheap to compute and is not required to be accurate. However, accurate
-    /// hints may improve performance by saving intermediate allocations.
+    /// hints may improve performance by saving intermediate allocations when reserving capacity
+    /// for the output buffer.
     fn size_hint(&self, input: &str) -> usize {
         input.len()
     }

src/render/external.rs → src/render/command.rs

@@ -4,53 +4,53 @@ use std::process::{Command, Stdio};
 
 use super::Renderer;
 
-/// Markdown renderer that uses an external command as a backend.
+/// Renderer that uses an external command to render input.
 ///
-/// The [`Markdown`] renderer uses an extremely fast, in-memory parser that is sufficient for most
-/// use-cases. However, this renderer may be useful if your markdown requires features unsupported
-/// by [`pulldown_cmark`].
+/// [`MarkdownRenderer`](crate::render::MarkdownRenderer) uses an extremely fast, in-memory parser
+/// that is sufficient for most use-cases. However, this renderer may be useful if your markdown
+/// requires features unsupported by [`pulldown_cmark`].
 ///
 /// # Example
 ///
-/// Creating an external renderer that uses [pandoc](https://pandoc.org/):
+/// Creating an external renderer that uses [pandoc](https://pandoc.org/) to render markdown:
 ///
 /// ```no_run
 /// use std::process::Command;
-/// use aurelius::ExternalCommand;
+/// use aurelius::render::CommandRenderer;
 ///
 /// let mut pandoc = Command::new("pandoc");
 /// pandoc.args(&["-f", "markdown", "-t", "html"]);
 ///
-/// ExternalCommand::new(pandoc);
+/// CommandRenderer::new(pandoc);
 /// ```
 #[derive(Debug)]
-pub struct ExternalCommand {
+pub struct CommandRenderer {
     command: RefCell<Command>,
 }
 
-impl ExternalCommand {
+impl CommandRenderer {
     /// Create a new external command renderer that will spawn processes using the given `command`.
     ///
     /// The provided [`Command`] should expect markdown input on stdin and print HTML on stdout.
-    pub fn new(mut command: Command) -> ExternalCommand {
+    pub fn new(mut command: Command) -> CommandRenderer {
         command
             .stdin(Stdio::piped())
             .stdout(Stdio::piped())
             .stderr(Stdio::null());
 
-        ExternalCommand {
+        CommandRenderer {
             command: RefCell::new(command),
         }
     }
 }
 
-impl Renderer for ExternalCommand {
+impl Renderer for CommandRenderer {
     type Error = io::Error;
 
-    fn render(&self, markdown: &str, html: &mut String) -> Result<(), Self::Error> {
+    fn render(&self, input: &str, html: &mut String) -> Result<(), Self::Error> {
         let child = self.command.borrow_mut().spawn()?;
 
-        child.stdin.unwrap().write_all(markdown.as_bytes())?;
+        child.stdin.unwrap().write_all(input.as_bytes())?;
 
         child.stdout.unwrap().read_to_string(html)?;
 

src/render/markdown.rs

@@ -6,14 +6,14 @@ use super::Renderer;
 
 /// Markdown renderer that uses [`pulldown_cmark`] as the backend.
 #[derive(Debug)]
-pub struct Markdown {
+pub struct MarkdownRenderer {
     options: Options,
 }
 
-impl Markdown {
+impl MarkdownRenderer {
     /// Create a new instance of the renderer.
-    pub fn new() -> Markdown {
-        Markdown {
+    pub fn new() -> MarkdownRenderer {
+        MarkdownRenderer {
             options: Options::ENABLE_FOOTNOTES
                 | Options::ENABLE_TABLES
                 | Options::ENABLE_STRIKETHROUGH
@@ -22,13 +22,13 @@ impl Markdown {
     }
 }
 
-impl Default for Markdown {
+impl Default for MarkdownRenderer {
     fn default() -> Self {
         Self::new()
     }
 }
 
-impl Renderer for Markdown {
+impl Renderer for MarkdownRenderer {
     type Error = Infallible;
 
     fn render(&self, markdown: &str, html: &mut String) -> Result<(), Self::Error> {

tests/it/main.rs

@@ -1,11 +1,12 @@
 use tokio::net::lookup_host;
 
+use aurelius::render::MarkdownRenderer;
 use aurelius::Server;
 
 mod files;
 mod options;
 
-async fn new_server() -> anyhow::Result<Server> {
+async fn new_server() -> anyhow::Result<Server<MarkdownRenderer>> {
     let addr = lookup_host("localhost:0").await?.next().unwrap();
-    Ok(Server::bind(&addr).await?)
+    Ok(Server::bind(&addr, MarkdownRenderer::new()).await?)
 }

tests/it/options.rs

@@ -93,11 +93,15 @@ async fn highlight_theme() -> Result<(), Box<dyn Error>> {
 #[cfg(not(windows))]
 #[tokio::test]
 async fn external_renderer() -> Result<(), Box<dyn Error>> {
-    use tokio::process::Command;
+    use aurelius::render::CommandRenderer;
+    use aurelius::Server;
+    use std::process::Command;
 
-    let mut server = new_server().await?;
-
-    server.set_external_renderer(Command::new("cat"));
+    let addr = tokio::net::lookup_host("localhost:0")
+        .await?
+        .next()
+        .unwrap();
+    let server = Server::bind(&addr, CommandRenderer::new(Command::new("cat"))).await?;
 
     let (mut websocket, _) =
         async_tungstenite::tokio::connect_async(format!("ws://{}", server.addr())).await?;