Crystal's metaprogramming macros to build a Sinatra-like DSL for the Crystal language.

The DSL doesn't stock blocks to be invoked later on, but rather produces actual methods using macros (match and the sugar get, post, etc.) where special chars like /, ., ( and ) are replaced as _SLASH_, _DOT_, _LPAREN_ and _RPAREN_. Also, :param segments are replaced to _PARAM_.

Eventually methods look like:

get "/posts"        |    def match_GET__SLASH_posts
get "/posts.xml"    |    def match_GET__SLASH_posts_DOT_xml

Please read dsl.cr for more details.

Eventually a call method is generated. It iterates over the class methods, selects the generated match_* methods and generates a big case statement, transforming the method names back to regular expressions, and eventually calling the method with matched data (if any).

Please read application.cr for more details.

require "http/server"
require "artanis"

class App < Artanis::Application
  get "/" do
    "ROOT"
  end

  get "/forbidden" do
    403
  end

  get "/posts/:id.:format" do
    p params["id"]
    p params["format"]
    "post"
  end

  get "/posts/:post_id/comments/:id(.:format)" do |post_id, id, format|
    p params["format"]?
    200
  end
end

server = HTTP::Server.new(9292) do |context|
  App.call(context)
end

puts "Listening on http://0.0.0.0:9292"
server.listen

Running wrk against the above example (pointless hello world) gives the following results (TL;DR 12µs per request):

$ wrk -c 1000 -t 2 -d 5 http://localhost:9292/fast
Running 5s test @ http://localhost:9292/fast
  2 threads and 1000 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency    12.26ms   14.48ms 423.28ms   99.05%
    Req/Sec    41.17k     2.93k   48.65k    76.00%
  409663 requests in 5.01s, 25.79MB read
Requests/sec:  81722.08
Transfer/sec:      5.14MB

A better benchmark is available in test/dsl_bench.cr which monitors some limits of the generated Crystal code, like going over all routes to find nothing takes an awful lot of time, since it must build/execute a regular expression against EVERY routes to eventually... find nothing.

$ crystal run --release test/dsl_bench.cr
get root: 0.84 µs
get param: 1.51 µs
get params (block args): 2.18 µs
get many params: 3.75 µs
get many params (block args): 2.59 µs
not found (method): 0.73 µs
not found (path): 15.93 µs

Keep in mind these numbers tell nothing about reality. They only measure how fast the generated Application.call(request) method is in predefined cases.

Licensed under the MIT License