Opal

A high-performance HTTP router and lightweight API framework for Crystal.

A high-performance HTTP router for Crystal with Trie-based route matching and URL parameter support.

Features

• ⚡ Fast Route Matching: O(k) complexity where k is the path length (not dependent on number of routes)
• 🎯 URL Parameters: Dynamic path segments using :param_name syntax
• 🔀 Multiple Parameters: Support for multiple params per route
• 🌐 HTTP Method Routing: GET, POST, PUT, DELETE, PATCH on the same path
• ✅ Automatic Status Codes: 404 Not Found, 405 Method Not Allowed
• 📊 Priority Matching: Exact paths take priority over parameter matches
• 🔧 Zero Dependencies: Uses only Crystal stdlib

Architecture

The router uses a Radix Tree (Trie) data structure for efficient route matching:

1. Trie Module: Core radix tree implementation

   • Node: Represents a URL segment in the tree
   • MatchResult: Contains matched node and extracted parameters
   • Handler: Proc that receives context and route parameters

2. LF Module: HTTP routing layer

   • Router: Main routing class with Trie-based matching
   • LFApi: HTTP::Handler wrapper for middleware integration
   • Convenience methods: get(), post(), put(), delete(), patch()

Installation

Add this to your application's shard.yml:

dependencies:
  ametist:
    github: your-username/opal

Usage

Basic Router

require "opal"

router = LF::Router.new

# Simple route
router.get("/") do |ctx, params|
  ctx.response.content_type = "text/plain"
  ctx.response.print "Welcome!"
end

# Route with parameter
router.get("/users/:id") do |ctx, params|
  user_id = params["id"]
  ctx.response.print "User ID: #{user_id}"
end

# Multiple parameters
router.get("/posts/:post_id/comments/:comment_id") do |ctx, params|
  ctx.response.print "Post: #{params["post_id"]}, Comment: #{params["comment_id"]}"
end

# Different HTTP methods
router.post("/users") do |ctx, params|
  ctx.response.status = HTTP::Status::CREATED
  ctx.response.print "User created"
end

router.delete("/users/:id") do |ctx, params|
  ctx.response.print "User #{params["id"]} deleted"
end

# Start server
server = HTTP::Server.new([router])
server.bind_tcp(8080)
server.listen

Using LFApi Wrapper

app = LF::LFApi.new do |router|
  router.get("/hello") do |ctx, params|
    ctx.response.print "Hello World!"
  end
  
  router.get("/hello/:name") do |ctx, params|
    ctx.response.print "Hello, #{params["name"]}!"
  end
end

# Use as HTTP::Handler
server = HTTP::Server.new([HTTP::LogHandler.new, app])
server.bind_tcp(8080)
server.listen

JSON Responses

class User
  include JSON::Serializable
  property id : Int32
  property name : String
end

router.get("/api/users/:id") do |ctx, params|
  user = User.new(
    id: params["id"].to_i,
    name: "John Doe"
  )
  
  ctx.response.content_type = "application/json"
  user.to_json(ctx.response)
end

All HTTP Methods

router.get("/resource/:id") { |ctx, params| ... }
router.post("/resource") { |ctx, params| ... }
router.put("/resource/:id") { |ctx, params| ... }
router.patch("/resource/:id") { |ctx, params| ... }
router.delete("/resource/:id") { |ctx, params| ... }

Route Matching Rules

1. Exact matches take priority over parameter matches:

   router.get("/users/list") { ... }  # Matches /users/list
   router.get("/users/:id") { ... }    # Matches /users/123, /users/456, etc.

2. Parameters must have values - empty segments won't match:

   # /users/:id matches /users/123
   # /users/:id does NOT match /users/ or /users

3. Multiple methods on same path are supported:

   router.get("/data") { ... }
   router.post("/data") { ... }
   # GET /data returns 200, POST /data returns 200
   # PUT /data returns 405 Method Not Allowed

Performance

The Trie-based approach provides O(k) lookup time where k is the path length:

• Not affected by the number of routes in your application
• Constant time for each path segment
• Memory efficient due to prefix compression
• Fast parameter extraction during traversal

Compared to linear scanning (O(n) where n = number of routes), this is significantly faster for applications with many routes.

HTTP Status Codes

The router automatically handles:

• 200 OK - Route found and handler executed
• 404 Not Found - No matching route
• 405 Method Not Allowed - Route exists but method not registered

Testing

crystal spec spec/opal_spec.cr

Example

See examples/router_example.cr for a complete working example.

crystal run examples/router_example.cr

API Reference

Trie::Node

# Add a route to the tree
add_route(path : String, handler : Handler, methods : Set(String) = Set{"GET"})

# Search for a matching route
search(path : String) : MatchResult

LF::Router

# HTTP method helpers
get(path : String, &handler : HTTP::Server::Context, Hash(String, String) -> Nil)
post(path : String, &handler : HTTP::Server::Context, Hash(String, String) -> Nil)
put(path : String, &handler : HTTP::Server::Context, Hash(String, String) -> Nil)
delete(path : String, &handler : HTTP::Server::Context, Hash(String, String) -> Nil)
patch(path : String, &handler : HTTP::Server::Context, Hash(String, String) -> Nil)

# Generic add method
add(path : String, methods : Set(String) = Set{"GET"}, &handler)

# Call method (implements HTTP::Handler)
call(context : HTTP::Server::Context)

LF::LFApi

# Initialize with block
LFApi.new(&block : Router -> Nil)

# Call method (implements HTTP::Handler)
call(context : HTTP::Server::Context)

Future Enhancements

Potential future features (not yet implemented):

• Wildcard routes (/files/*filepath)
• Route groups with prefixes
• Middleware support per route
• Query string parameter helpers
• Request body parsing helpers
• FastAPI-style automatic parameter injection (experimental)

License

See LICENSE file.

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Run tests (crystal spec)
4. Commit your changes (git commit -am 'Add some feature')
5. Push to the branch (git push origin my-new-feature)
6. Create a new Pull Request