Issues CSV attachment can be truncated by target size

app/mailers/emails/issues.rb

@@ -49,11 +49,12 @@ module Emails
       mail_answer_thread(issue, issue_thread_options(updated_by_user.id, recipient.id))
     end
 
-    def issues_csv_email(user, project, content, issues_count)
+    def issues_csv_email(user, project, csv_data, issues_count, truncated = false)
       @project = project
       @issues_count = issues_count
+      @truncated = truncated
 
-      attachments['issues.csv'] = { content: content, mime_type: 'text/csv' }
+      attachments['issues.csv'] = { content: csv_data, mime_type: 'text/csv' }
       mail(to: user.notification_email, subject: subject("Issues exported as CSV"))
     end
 

app/services/issues/export_csv_service.rb

 module Issues
   class ExportCsvService
+    # Target attachment size before base64 encoding
+    TARGET_FILESIZE = 15000000
+
     def initialize(issues_relation)
       @issues = issues_relation
       @labels = @issues.labels_hash
     end
 
     def csv_data
-      csv_builder.render
+      csv_builder.render(TARGET_FILESIZE)
     end
 
     def email(user, project)
-      Notify.issues_csv_email(user, project, csv_data, @issues.count).deliver_now
+      Notify.issues_csv_email(user, project, csv_data, @issues.count, csv_builder.truncated?).deliver_now
+    end
+
+    def csv_builder
+      @csv_builder ||=
+        CsvBuilder.new(@issues.includes(:author, :assignee), header_to_value_hash)
     end
 
     private
 
-    def csv_builder
-      @csv_builder ||= CsvBuilder.new(@issues.includes(:author, :assignee),
-                                       'Issue ID' => 'iid',
-                                       'Title' => 'title',
-                                       'State' => 'state',
-                                       'Description' => 'description',
-                                       'Author' => 'author_name',
-                                       'Assignee' => 'assignee_name',
-                                       'Confidential' => 'confidential',
-                                       'Due Date' => -> (issue) { issue.due_date&.to_s(:csv) },
-                                       'Created At (UTC)' => -> (issue) { issue.created_at&.to_s(:csv) },
-                                       'Updated At (UTC)' => -> (issue) { issue.updated_at&.to_s(:csv) },
-                                       'Milestone' => -> (issue) { issue.milestone&.title },
-                                       'Labels' => -> (issue) { @labels[issue.id].sort.join(',').presence }
-                                     )
+    def header_to_value_hash
+      {
+       'Issue ID' => 'iid',
+       'Title' => 'title',
+       'State' => 'state',
+       'Description' => 'description',
+       'Author' => 'author_name',
+       'Assignee' => 'assignee_name',
+       'Confidential' => 'confidential',
+       'Due Date' => -> (issue) { issue.due_date&.to_s(:csv) },
+       'Created At (UTC)' => -> (issue) { issue.created_at&.to_s(:csv) },
+       'Updated At (UTC)' => -> (issue) { issue.updated_at&.to_s(:csv) },
+       'Milestone' => -> (issue) { issue.milestone&.title },
+       'Labels' => -> (issue) { @labels[issue.id].sort.join(',').presence }
+      }
     end
   end
 end

app/views/notify/issues_csv_email.html.haml

@@ -59,6 +59,10 @@
                     %a{ href: project_url(@project), style: "color:#3777b0;text-decoration:none;" }
                       = @project.name
                     has been added to this email as an attachment.
+                    -if @truncated
+                      %br
+                      %br
+                      This attachment has been truncated due to exceeding the maximum attachment size. Consider re-exporting with a narrower selection of issues.
         %tr.footer
           %td{ style: "font-family:'Helvetica Neue',Helvetica,Arial,sans-serif;padding:25px 0;font-size:13px;line-height:1.6;color:#5c5c5c;" }
             %img{ alt: "GitLab", height: "33", src: image_url('mailers/ci_pipeline_notif_v1/gitlab-logo-full-horizontal.gif'), style: "display:block;margin:0 auto 1em;", width: "90" }/

app/views/notify/issues_csv_email.text.erb

-Your .csv export of <%= @issues_count %> issues from project <%= @project.name %> ( <%= project_url(@project) %> ) has been added to this email as an attachment.
\ No newline at end of file
+Your .csv export of <%= @issues_count %> issues from project <%= @project.name %> ( <%= project_url(@project) %> ) has been added to this email as an attachment.
+
+<% if @truncated %>
+This attachment has been truncated due to exceeding the maximum attachment size. Consider re-exporting with a narrower selection of issues.
+<% end %>
\ No newline at end of file

lib/csv_builder.rb

@@ -22,17 +22,27 @@ class CsvBuilder
   def initialize(collection, header_to_value_hash)
     @header_to_value_hash = header_to_value_hash
     @collection = collection
+    @truncated = false
   end
 
   # Renders the csv to a string
-  def render
-    generate_csv_with_tempfile do |csv|
-      csv << headers
+  def render(truncate_after_bytes = nil)
+    tempfile = Tempfile.new('issues_csv')
+    csv = CSV.new(tempfile)
 
-      @collection.find_each do |object|
-        csv << row(object)
-      end
+    write_csv(csv) do
+      truncate_after_bytes && tempfile.size > truncate_after_bytes
     end
+
+    tempfile.rewind
+    tempfile.read
+  ensure
+    tempfile.close
+    tempfile.unlink
+  end
+
+  def truncated?
+    @truncated
   end
 
   private
@@ -55,16 +65,16 @@ class CsvBuilder
     end
   end
 
-  def generate_csv_with_tempfile
-    tempfile = Tempfile.new('issues_csv')
-    csv = CSV.new(tempfile)
+  def write_csv(csv, &until_block)
+    csv << headers
 
-    yield(csv)
+    @collection.find_each do |object|
+      csv << row(object)
 
-    tempfile.rewind
-    tempfile.read
-  ensure
-    tempfile.close
-    tempfile.unlink
+      if until_block.call
+        @truncated = true
+        break
+      end
+    end
   end
 end

spec/lib/csv_builder_spec.rb

@@ -20,6 +20,26 @@ describe CsvBuilder, lib: true do
     subject.render
   end
 
+  describe 'truncation' do
+    let(:big_object) { double(question: 'Long' * 1024) }
+    let(:row_size) { big_object.question.length * 2 }
+
+    before do
+      allow(fake_relation).to receive(:find_each).and_yield(big_object)
+                                                 .and_yield(big_object)
+                                                 .and_yield(big_object)
+    end
+
+    it 'after given number of bytes' do
+      expect(subject.render(row_size * 2).length).to be_between(row_size * 2, row_size * 3)
+      expect(subject).to be_truncated
+    end
+
+    it 'is ignored by default' do
+      expect(subject.render.length).to be > row_size * 3
+    end
+  end
+
   it 'avoids loading all data in a single query' do
     expect(fake_relation).to receive(:find_each)
 

spec/mailers/emails/issues_spec.rb

@@ -8,7 +8,8 @@ describe Notify do
   describe 'csv export email' do
     let(:user) { create(:user) }
     let(:empty_project) { create(:empty_project) }
-    subject { Notify.issues_csv_email(user, empty_project, "dummy content", 3) }
+    let(:truncated) { false }
+    subject { Notify.issues_csv_email(user, empty_project, "dummy content", 3, truncated) }
 
     it 'attachment has csv mime type' do
       attachment = subject.attachments.first
@@ -19,5 +20,17 @@ describe Notify do
       expect(subject).to have_content '3'
       expect(subject).to have_content empty_project.name
     end
+
+    it "doesn't need to mention truncation by default" do
+      expect(subject).not_to have_content 'truncated'
+    end
+
+    context 'when truncated' do
+      let(:truncated) { true }
+
+      it 'mentions that the csv has been truncated' do
+        expect(subject).to have_content 'truncated'
+      end
+    end
   end
 end

spec/mailers/previews/issues_csv_mailer_preview.rb

@@ -4,6 +4,6 @@ class IssuesCsvMailerPreview < ActionMailer::Preview
     project = Project.unscoped.first
     issues_count = 891
 
-    Notify.issues_csv_email(user, project, "Dummy,Csv\n0,1", issues_count)
+    Notify.issues_csv_email(user, project, "Dummy,Csv\n0,1", issues_count, [true, false].sample)
   end
 end

spec/services/issues/export_csv_service_spec.rb

@@ -14,6 +14,12 @@ describe Issues::ExportCsvService, services: true do
     it 'emails csv' do
       expect{ subject.email(user, project) }.to change(ActionMailer::Base.deliveries, :count)
     end
+
+    it 'renders with a target filesize' do
+      expect(subject.csv_builder).to receive(:render).with(described_class::TARGET_FILESIZE)
+
+      subject.email(user, project)
+    end
   end
 
   def csv