Add rack middleware (#3)

Co-authored-by: Sebastian Ohm <[email protected]>

Gemfile

@@ -2,3 +2,5 @@ source "https://rubygems.org"
 
 gem "rspec"
 gem "timecop"
+gem "rack"
+gem "webmock"

Gemfile.lock

@@ -1,7 +1,15 @@
 GEM
   remote: https://rubygems.org/
   specs:
+    addressable (2.8.0)
+      public_suffix (>= 2.0.2, < 5.0)
+    crack (0.4.5)
+      rexml
     diff-lcs (1.4.4)
+    hashdiff (1.0.1)
+    public_suffix (4.0.6)
+    rack (2.2.3)
+    rexml (3.2.5)
     rspec (3.10.0)
       rspec-core (~> 3.10.0)
       rspec-expectations (~> 3.10.0)
@@ -16,13 +24,19 @@ GEM
       rspec-support (~> 3.10.0)
     rspec-support (3.10.2)
     timecop (0.9.4)
+    webmock (3.14.0)
+      addressable (>= 2.8.0)
+      crack (>= 0.3.2)
+      hashdiff (>= 0.4.0, < 2.0.0)
 
 PLATFORMS
   ruby
 
 DEPENDENCIES
+  rack
   rspec
   timecop
+  webmock
 
 BUNDLED WITH
    2.1.4

README.md

@@ -53,7 +53,17 @@ end
 puts(exporter.export)
 ```
 
-### Run tests
+## Use a Rack middleware
+
+You can use this library as a [Rack](https://github.com/rack/rack) middleware, that allow us you to capture any error happening during the life of a request. You need to use it with an instance of a [pushgateway](https://github.com/soundcloud/periskop-pushgateway/).
+
+```ruby
+require 'periskop/rack/middleware'
+
+use Periskop::Rack::Middleware, {pushgateway_address: "http://localhost:7878"}
+```
+
+## Run tests
 
 1. `make prepare`
 2. `make test`

lib/periskop/client/collector.rb

@@ -39,7 +39,7 @@ def add_exception(exception, context)
           exception.class.name,
           exception.message,
           exception.backtrace,
-          exception.cause
+          get_cause(exception)
         )
         exception_with_context = ExceptionWithContext.new(
           exception_instance,
@@ -58,6 +58,14 @@ def add_exception(exception, context)
         aggregated_exception = @aggregated_exceptions_dict[aggregation_key]
         aggregated_exception.add_exception(exception_with_context)
       end
+
+      def get_cause(exception)
+        if RUBY_VERSION > '2.0'
+          return exception.cause
+        end
+
+        nil
+      end
     end
   end
 end

lib/periskop/client/exporter.rb

@@ -1,3 +1,6 @@
+require 'net/http'
+require 'uri'
+
 module Periskop
   module Client
     # Exporter exposes in json format all collected exceptions from the specified `collector`
@@ -9,6 +12,14 @@ def initialize(collector)
       def export
         @collector.aggregated_exceptions.to_json
       end
+
+      def push_to_gateway(addr)
+        uri = URI.parse("#{addr}/errors")
+        http = Net::HTTP.new(uri.host, uri.port)
+        request = Net::HTTP::Post.new(uri.request_uri, 'Content-Type' => 'application/json')
+        request.body = export
+        http.request(request)
+      end
     end
   end
 end

lib/periskop/rack/middleware.rb

@@ -0,0 +1,87 @@
+require 'periskop/client/collector'
+require 'periskop/client/exporter'
+require 'periskop/client/models'
+
+module Periskop
+  module Rack
+    class Middleware
+      attr_accessor :collector
+
+      def initialize(app, options = {})
+        @app = app
+        @pushgateway_address = options.fetch(:pushgateway_address)
+        @collector = Periskop::Client::ExceptionCollector.new
+        @exporter = Periskop::Client::Exporter.new(@collector)
+      end
+
+      def call(env)
+        begin
+          response = @app.call(env)
+        rescue Exception => ex
+          report_push(env, ex)
+          raise(ex)
+        end
+
+        maybe_ex = framework_exception(env)
+        report_push(env, maybe_ex) if maybe_ex
+
+        response
+      end
+
+      private
+
+      # Web framework middlewares often store rescued exceptions inside the
+      # Rack env, but Rack doesn't have a standard key for it:
+      #
+      # - Rails uses action_dispatch.exception: https://goo.gl/Kd694n
+      # - Sinatra uses sinatra.error: https://goo.gl/LLkVL9
+      # - Goliath uses rack.exception: https://goo.gl/i7e1nA
+      def framework_exception(env)
+        env['rack.exception'] ||
+          env['sinatra.error'] ||
+          env['action_dispatch.exception']
+      end
+
+      def find_request(env)
+        if defined?(ActionDispatch::Request)
+          ActionDispatch::Request.new(env)
+        elsif defined?(Sinatra::Request)
+          Sinatra::Request.new(env)
+        else
+          ::Rack::Request.new(env)
+        end
+      end
+
+      def get_http_headers(request_env)
+        header_prefixes = %w[
+          HTTP_
+          CONTENT_TYPE
+          CONTENT_LENGTH
+        ].freeze
+
+        request_env.map.with_object({}) do |(key, value), headers|
+          if header_prefixes.any? { |prefix| key.to_s.start_with?(prefix) }
+            headers[key] = value
+          end
+          headers
+        end
+      end
+
+      def get_http_context(env)
+        request = find_request(env)
+        Periskop::Client::HTTPContext.new(request.request_method, request.url, get_http_headers(request.env), nil)
+      end
+
+      def report_push(env, maybe_ex)
+        ex =
+          if maybe_ex.is_a?(Exception)
+            maybe_ex
+          else
+            RuntimeError.new(maybe_ex.to_s)
+          end
+        @collector.report_with_context(ex, get_http_context(env))
+        @exporter.push_to_gateway(@pushgateway_address)
+      end
+    end
+  end
+end

spec/periskop/client/exporter_spec.rb

@@ -20,13 +20,21 @@
       end
     end
 
+    def get_aggregation_hash()
+      if RUBY_VERSION < '3.0'
+        'cfbf9f17'
+      else
+        '138b8e97'
+      end
+    end
+
     it 'exports to the expected format' do
       expected_json = <<HEREDOC
       {
         "target_uuid": "5d9893c6-51d6-11ea-8aad-f894c260afe5",
         "aggregated_errors": [
           {
-            "aggregation_key": "StandardError@cfbf9f17",
+            "aggregation_key": "StandardError@#{get_aggregation_hash()}",
             "total_count": 1,
             "severity": "error",
             "created_at": "2019-10-11T12:47:25Z",

spec/periskop/rack/middleware_spec.rb

@@ -0,0 +1,28 @@
+require 'rack'
+require 'periskop/rack/middleware'
+require 'webmock/rspec'
+
+describe Periskop::Rack::Middleware do
+  class App
+    def call(_)
+      raise StandardError
+    end
+  end
+
+  let :middleware do
+    stub_request(:post, 'http://localhost:7878/errors')
+    Periskop::Rack::Middleware.new(App.new, pushgateway_address: 'http://localhost:7878')
+  end
+
+  it 'captures exception on error' do
+    begin
+      middleware.call env_for('http://example.com?q=s', {})
+    rescue StandardError
+      expect(middleware.collector.aggregated_exceptions_dict.size).to eq(1)
+    end
+  end
+
+  def env_for(url, opts = {})
+    Rack::MockRequest.env_for(url, opts)
+  end
+end