Lamby Proxy Server for Local Development.

Author: metaskills

Gemfile.lock

@@ -170,6 +170,7 @@ GEM
     timeout (0.3.2)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
+    webrick (1.8.1)
     websocket-driver (0.7.5)
       websocket-extensions (>= 0.1.0)
     websocket-extensions (0.1.5)
@@ -189,6 +190,7 @@ DEPENDENCIES
   pry
   rails
   rake
+  webrick
 
 BUNDLED WITH
    2.3.26

Rakefile

@@ -5,7 +5,13 @@ require "rake/testtask"
 Rake::TestTask.new(:test) do |t|
   t.libs << "test"
   t.libs << "lib"
-  t.test_files = FileList["test/**/*_test.rb"]
+  t.test_files = begin
+    if ENV['TEST_FILE']
+      [ENV['TEST_FILE']]
+    else
+      FileList["test/**/*_test.rb"]
+    end
+  end
   t.verbose = false
   t.warning = false
 end

lamby.gemspec

@@ -26,4 +26,5 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'minitest-focus'
   spec.add_development_dependency 'mocha'
   spec.add_development_dependency 'pry'
+  spec.add_development_dependency 'webrick'
 end

lib/lamby.rb

@@ -35,5 +35,7 @@ def config
   end
 
   autoload :SsmParameterStore, 'lamby/ssm_parameter_store'
+  autoload :ProxyContext, 'lamby/proxy_context'
+  autoload :ProxyServer, 'lamby/proxy_server'
 
 end

lib/lamby/proxy_context.rb

@@ -0,0 +1,25 @@
+module Lamby
+  # This class is used by the `lamby:proxy_server` Rake task to run a
+  # Rack server for local development proxy. Specifically, this class 
+  # accepts a JSON respresentation of a Lambda context object converted 
+  # to a Hash as the single arugment.
+  # 
+  class ProxyContext
+    def initialize(data)
+      @data = data
+    end
+
+    def method_missing(method_name, *args, &block)
+      key = method_name.to_s
+      if @data.key?(key)
+        @data[key]
+      else
+        super
+      end
+    end
+
+    def respond_to_missing?(method_name, include_private = false)
+      @data.key?(method_name.to_s) || super
+    end
+  end
+end

lib/lamby/proxy_server.rb

@@ -0,0 +1,34 @@
+module Lamby
+  class ProxyServer
+    
+    METHOD_NOT_ALLOWED = <<-HEREDOC.strip
+      <h1>Method Not Allowed</h1>
+      <p>Please POST to this endpoint with an application/json content type and JSON payload of your Lambda's event and context.<p>
+      <p>Example: <code>{ "event": event, "context": context }</code></p>
+    HEREDOC
+    
+    def call(env)
+      return method_not_allowed unless method_allowed?(env)
+      event, context = event_and_context(env)
+      Lamby.cmd event: event, context: context
+    end
+
+    private
+
+    def event_and_context(env)
+      data = env['rack.input'].dup.read
+      json = JSON.parse(data)
+      [ json['event'], Lamby::ProxyContext.new(json['context']) ]
+    end
+
+    def method_allowed?(env)
+      env['REQUEST_METHOD'] == 'POST' && env['CONTENT_TYPE'] == 'application/json'
+    end
+
+    def method_not_allowed
+      { statusCode: 405,
+        headers: {"Content-Type" => "text/html"},
+        body: METHOD_NOT_ALLOWED.dup }
+    end
+  end
+end

lib/lamby/railtie.rb

@@ -1,5 +1,9 @@
 module Lamby
   class Railtie < ::Rails::Railtie
     config.lamby = Lamby::Config.config
+
+    rake_tasks do
+      load 'lamby/tasks.rake'
+    end
   end
 end

lib/lamby/tasks.rake

@@ -0,0 +1,7 @@
+namespace :lamby do
+  task :proxy_server => [:environment] do
+    require 'webrick'
+    port = ENV['LAMBY_PROXY_PORT'] || 3000
+    Rack::Handler::WEBrick.run Lamby::ProxyServer.new, Port: port
+  end
+end

test/proxy_context_test.rb

@@ -0,0 +1,29 @@
+require 'test_helper'
+
+class ProxyContextTest < LambySpec
+  
+  let(:context_data) { TestHelpers::LambdaContext.raw_data }
+  let(:proxy_context) { Lamby::ProxyContext.new(context_data) }
+
+  it 'should respond to all context methods' do
+    context_data.keys.each do |key|
+      response = proxy_context.respond_to?(key.to_sym)
+      expect(response).must_equal true, "Expected context to respond to #{key.inspect}"
+    end
+  end
+
+  it 'should return the correct value for each context method' do
+    expect(proxy_context.clock_diff).must_equal 1681486457423
+    expect(proxy_context.deadline_ms).must_equal 1681492072985
+    expect(proxy_context.aws_request_id).must_equal "d6f5961b-5034-4db5-b3a9-fa378133b0f0"
+  end
+
+  it 'should raise an error for unknown methods' do
+    expect { proxy_context.foo }.must_raise NoMethodError
+  end
+
+  it 'should return false for respond_to? for a unknown method' do
+    expect(proxy_context.respond_to?(:foo)).must_equal false
+  end
+
+end

test/proxy_server_test.rb

@@ -0,0 +1,47 @@
+require 'net/http'
+require 'test_helper'
+
+class ProxyServerTest < LambySpec
+  let(:event)    { TestHelpers::Events::HttpV2.create }
+  let(:context)  { TestHelpers::LambdaContext.raw_data }
+  let(:rack_app) { Rack::Builder.new { run lambda { |env| [200, {}, StringIO.new('{"statusCode": 200}')] } }.to_app }
+  let(:proxy)    { Lamby::ProxyServer.new }
+
+  before { Lamby.config.rack_app = rack_app }
+  
+  it 'should return a 405 helpful message on GET' do
+    response = proxy.call(env("REQUEST_METHOD" => 'GET'))
+    expect(response[:statusCode]).must_equal 405
+    expect(response[:headers]).must_equal({"Content-Type" => "text/html"})
+    expect(response[:body]).must_include 'Method Not Allowed'
+  end
+  
+  it 'should call Lamby.cmd on POST' do
+    response = proxy.call(env)
+    expect(response[:statusCode]).must_equal 200
+    expect(response[:headers]).must_equal({})
+    expect(response[:body]).must_equal '{"statusCode": 200}'
+  end
+
+  private
+
+  def env(options={})
+    json = {"event": event, "context": context}.to_json
+    { 'REQUEST_METHOD' => 'POST',
+      'PATH_INFO' => '/',
+      'QUERY_STRING' => '',
+      'SERVER_NAME' => 'localhost',
+      'SERVER_PORT' => '3000',
+      'HTTP_VERSION' => 'HTTP/1.1',
+      'rack.version' => Rack::VERSION,
+      'rack.input' => StringIO.new(json),
+      'rack.url_scheme' => 'http',
+      'rack.errors' => $stderr,
+      'rack.multithread' => true,
+      'rack.multiprocess' => false,
+      'rack.run_once' => false,
+      'CONTENT_TYPE' => 'application/json',
+      'CONTENT_LENGTH' => json.bytesize.to_s
+    }.merge(options)
+  end
+end

test/test_helper/lambda_context.rb

@@ -1,6 +1,22 @@
 module TestHelpers
   class LambdaContext
 
+    RAW_DATA ={
+      "clock_diff" => 1681486457423,
+      "deadline_ms" => 1681492072985,
+      "aws_request_id" => "d6f5961b-5034-4db5-b3a9-fa378133b0f0",
+      "invoked_function_arn" => "arn:aws:lambda:us-east-1:576043675419:function:lamby-ws-production-WSConnectLambda-5in18cNskwz6",
+      "log_group_name" => "/aws/lambda/lamby-ws-production-WSConnectLambda-5in18cNskwz6",
+      "log_stream_name" => "2023/04/14/[$LATEST]55a1d458479a4546b64acca17af3a69f",
+      "function_name" => "lamby-ws-production-WSConnectLambda-5in18cNskwz6",
+      "memory_limit_in_mb" => "1792",
+      "function_version" => "$LATEST"
+    }.freeze 
+
+    def self.raw_data
+      RAW_DATA.dup
+    end
+
     def clock_diff
       1585237646907
     end