Crate webmachine_rust

webmachine-rust

Port of Webmachine-Ruby (https://github.com/webmachine/webmachine-ruby) to Rust.

webmachine-rust is a port of the Ruby version of webmachine. It implements a finite state machine for the HTTP protocol that provides semantic HTTP handling (based on the diagram from the webmachine project). It is basically a HTTP toolkit for building HTTP-friendly applications using the Hyper rust crate.

Webmachine-rust works with Hyper and sits between the Hyper Handler and your application code. It provides a resource struct with callbacks to handle the decisions required as the state machine is executed against the request with the following sequence.

REQUEST -> Hyper Handler -> WebmachineDispatcher -> Resource -> Your application code -> WebmachineResponse -> Hyper -> RESPONSE

Features

• Handles the hard parts of content negotiation, conditional requests, and response codes for you.
• Provides a resource trait and struct with points of extension to let you describe what is relevant about your particular resource.

Missing Features

Currently, the following features from webmachine-ruby have not been implemented:

• Visual debugger
• Streaming response bodies

Implementation Deficiencies:

This implementation has the following deficiencies:

• Automatically decoding request bodies and encoding response bodies.
• No easy mechanism to generate bodies with different content types (e.g. JSON vs. XML).
• Dynamically determining the methods allowed on the resource.

Getting started with Hyper

Follow the getting started documentation from the Hyper crate to setup a Hyper service for your server.

There are two ways of using this crate. You can either use the WebmachineResource struct and add callbacks for the state you need to modify, or you can create your own resource structs and implement the Resource trait.

You need to define a WebmachineDispatcher that maps resource paths to your webmachine resources (WebmachineResource or structs that implement Resource). WebmachineResource defines all the callbacks (via Closures) and values required to implement a resource.

Note: This example uses the maplit crate to provide the btreemap macro and the log crate for the logging macros.

use std::convert::Infallible;
use std::future::ready;
use std::io::Read;
use std::net::SocketAddr;
use std::sync::Arc;

use webmachine_rust::*;
use webmachine_rust::context::*;
use webmachine_rust::headers::*;

use bytes::Bytes;
use futures_util::future::FutureExt;
use hyper::{body, Request};
use hyper::server::conn::http1;
use hyper::service::service_fn;
use hyper_util::rt::TokioIo;
use maplit::btreemap;
use serde_json::{Value, json};
use tracing::error;
use tokio::net::TcpListener;


async fn start_server() -> anyhow::Result<()> {
  // setup the dispatcher, which maps paths to resources. We wrap it in an Arc so we can
  // use it in the loop below.
  let dispatcher = Arc::new(WebmachineDispatcher {
      routes: btreemap!{
         "/myresource" => WebmachineDispatcher::box_resource(WebmachineResource {
           // Methods allowed on this resource
           allowed_methods: owned_vec(&["OPTIONS", "GET", "HEAD", "POST"]),
           // if the resource exists callback
           resource_exists: callback(|_, _| true),
           // callback to render the response for the resource, it has to be async
           render_response: async_callback(|_, _| {
               let json_response = json!({
                  "data": [1, 2, 3, 4]
               });
               ready(Ok(Some(Bytes::from(json_response.to_string())))).boxed()
           }),
           // callback to process the post for the resource
           process_post: async_callback(|_, _|  /* Handle the post here */ ready(Ok(true)).boxed() ),
           // default everything else
           .. WebmachineResource::default()
         })
     }
  });

  // Create a Hyper server that delegates to the dispatcher. See https://hyper.rs/guides/1/server/hello-world/
  let addr: SocketAddr = "0.0.0.0:8080".parse()?;
  let listener = TcpListener::bind(addr).await?;
  loop {
       let dispatcher = dispatcher.clone();
       let (stream, _) = listener.accept().await?;
       let io = TokioIo::new(stream);
       tokio::task::spawn(async move {
           if let Err(err) = http1::Builder::new()
               .serve_connection(io, service_fn(|req: Request<body::Incoming>| dispatcher.dispatch(req)))
               .await
           {
               error!("Error serving connection: {:?}", err);
           }
       });
  }
  Ok(())
}

Example implementations

For an example of a project using this crate, have a look at the Pact Mock Server from the Pact reference implementation.

Modules

content_negotiation

The content_negotiation module deals with handling media types, languages, charsets and encodings as per https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html.

context

The context module encapsulates the context of the environment that the webmachine is executing in. Basically wraps the request and response.

headers

The headers deals with parsing and formatting request and response headers

paths

Utilities for matching URI paths

Macros

h

Simple macro to convert a string to a HeaderValue struct.

Structs

WebmachineDispatcher

The main hyper dispatcher

WebmachineResource

Struct to represent a resource in webmachine

Traits

Resource

All webmachine resources implement this trait

Functions

async_callback

Wrap a callback in a structure that is safe to call between threads

callback

Wrap a callback in a structure that is safe to call between threads

owned_vec

Convenience function to create a vector of string structs from a slice of strings

Type Aliases

AsyncWebmachineCallback

Wrap an async callback in a structure that is safe to call between threads

WebmachineCallback

Type of a Webmachine resource callback