Send trace to a browser incrementally when build is running

We send a state of ansi2html to client, client needs to send this state back.
The state describes the configuration of generator and position within trace.

app/controllers/projects/builds_controller.rb

@@ -38,6 +38,14 @@ class Projects::BuildsController < Projects::ApplicationController
     end
   end
 
+  def trace
+    respond_to do |format|
+      format.json do
+        render json: @build.trace_with_state(params_state).merge!(id: @build.id, status: @build.status)
+      end
+    end
+  end
+
   def retry
     unless @build.retryable?
       return render_404
@@ -72,6 +80,13 @@ class Projects::BuildsController < Projects::ApplicationController
 
   private
 
+  def params_state
+    begin
+      JSON.parse(params[:state], symbolize_names: true)
+    rescue
+    end
+  end
+
   def build
     @build ||= project.builds.unscoped.find_by!(id: params[:id])
   end

app/models/ci/build.rb

@@ -132,8 +132,12 @@ module Ci
     end
 
     def trace_html
-      html = Ci::Ansi2html::convert(trace) if trace.present?
-      html || ''
+      trace_with_state[:html]
+    end
+
+    def trace_with_state(state = nil)
+      trace_with_state = Ci::Ansi2html::convert(trace, state) if trace.present?
+      trace_with_state || {}
     end
 
     def timeout

app/views/projects/builds/show.html.haml

 - page_title "#{@build.name} (##{@build.id})", "Builds"
 = render "header_title"
+- trace = build.trace_for_state
 
 .build-page
   .row-content-block.top-block
@@ -85,7 +86,9 @@
         %pre.trace#build-trace
           %code.bash
             = preserve do
-              = raw @build.trace_html
+              = raw trace[:html]
+              - if @build.active?
+                %i{:class => "fa fa-refresh fa-spin"}
 
       %div#down-build-trace
 
@@ -216,4 +219,4 @@
 
 
   :javascript
-    new CiBuild("#{namespace_project_build_url(@project.namespace, @project, @build)}", "#{@build.status}")
+    new CiBuild("#{namespace_project_build_url(@project.namespace, @project, @build)}", "#{@build.status}", "#{trace[:state]}")

config/routes.rb

@@ -672,6 +672,7 @@ Rails.application.routes.draw do
             post :cancel
             post :retry
             post :erase
+            get :trace
             get :raw
           end
 

lib/ci/ansi2html.rb

@@ -23,8 +23,8 @@ module Ci
       cross:      0x10,
     }
 
-    def self.convert(ansi)
-      Converter.new().convert(ansi)
+    def self.convert(ansi, state = nil)
+      Converter.new.convert(ansi, state)
     end
 
     class Converter
@@ -84,22 +84,36 @@ module Ci
       def on_107(s) set_bg_color(7, 'l') end
       def on_109(s) set_bg_color(9, 'l') end
 
-      def convert(ansi)
-        @out = ""
-        @n_open_tags = 0
-        reset()
+      attr_accessor :offset, :n_open_tags, :fg_color, :bg_color, :style_mask
+
+      STATE_PARAMS = [:offset, :n_open_tags, :fg_color, :bg_color, :style_mask]
+
+      def convert(raw, new_state)
+        reset_state
+        restore_state(new_state) if new_state && new_state[:offset].to_i < raw.length
+
+        start = @offset
+        ansi = raw[@offset..-1]
+
+        open_new_tag
 
-        s = StringScanner.new(ansi.gsub("<", "&lt;"))
+        s = StringScanner.new(ansi)
         while(!s.eos?)
           if s.scan(/\e([@-_])(.*?)([@-~])/)
             handle_sequence(s)
+          elsif s.scan(/\e(([@-_])(.*?)?)?$/)
+            break
+          elsif s.scan(/</)
+            @out << '&lt;'
           else
             @out << s.scan(/./m)
           end
+          @offset += s.matched_size
         end
 
         close_open_tags()
-        @out
+
+        { state: state, html: @out, text: ansi[0, @offset - start], append: start > 0 }
       end
 
       def handle_sequence(s)
@@ -121,6 +135,20 @@ module Ci
 
         evaluate_command_stack(commands)
 
+        open_new_tag
+      end
+
+      def evaluate_command_stack(stack)
+        return unless command = stack.shift()
+
+        if self.respond_to?("on_#{command}", true)
+          self.send("on_#{command}", stack)
+        end
+
+        evaluate_command_stack(stack)
+      end
+
+      def open_new_tag
         css_classes = []
 
         unless @fg_color.nil?
@@ -138,20 +166,8 @@ module Ci
           css_classes << "term-#{css_class}" if @style_mask & flag != 0
         end
 
-        open_new_tag(css_classes) if css_classes.length > 0
-      end
-
-      def evaluate_command_stack(stack)
-        return unless command = stack.shift()
-
-        if self.respond_to?("on_#{command}", true)
-          self.send("on_#{command}", stack)
-        end
-
-        evaluate_command_stack(stack)
-      end
+        return if css_classes.empty?
 
-      def open_new_tag(css_classes)
         @out << %{<span class="#{css_classes.join(' ')}">}
         @n_open_tags += 1
       end
@@ -163,6 +179,26 @@ module Ci
         end
       end
 
+      def reset_state
+        @offset = 0
+        @n_open_tags = 0
+        @out = ''
+        reset
+      end
+
+      def state
+        STATE_PARAMS.inject({}) do |h, param|
+          h[param] = send(param)
+          h
+        end
+      end
+
+      def restore_state(new_state)
+        STATE_PARAMS.each do |param|
+          send("#{param}=".to_sym, new_state[param])
+        end
+      end
+
       def reset
         @fg_color = nil
         @bg_color = nil