CSV previews are sometimes broken - refactoring of CSV previews controller

app/controllers/csv_preview_controller.rb

@@ -1,10 +1,8 @@
 require "csv"
 
 class CsvPreviewController < ApplicationController
-  MAXIMUM_COLUMNS = 50
-  MAXIMUM_ROWS = 1000
-
   rescue_from GdsApi::HTTPForbidden, with: :access_limited
+  rescue_from CSV::MalformedCSVError, with: :malformed_csv
 
   def show
     @asset = GdsApi.asset_manager.asset(params[:id]).to_hash
@@ -25,35 +23,20 @@ def show
       redirect_to(parent_document_uri, status: :see_other, allow_other_host: true) and return
     end
 
-    original_error = nil
-    row_sep = :auto
-
-    begin
-      csv_preview = CSV.parse(media_download_truncated, encoding: encoding(media_download_truncated), headers: true, row_sep:)
-    rescue CSV::MalformedCSVError => e
-      if original_error.nil?
-        original_error = e
-        row_sep = "\r\n"
-        retry
-      else
-        render :malformed_csv and return
-      end
-    end
-
-    @csv_rows = csv_preview.to_a.map do |row|
-      row.map { |column|
-        {
-          text: column&.encode("UTF-8"),
-        }
-      }.take(MAXIMUM_COLUMNS)
-    end
+    @csv_rows = CsvPreviewService
+      .new(GdsApi.asset_manager.media(params[:id], params[:filename]).body)
+      .csv_rows
   end
 
+private
+
   def access_limited
-    render :access_limited, status: :forbidden and return
+    render :access_limited, status: :forbidden
   end
 
-private
+  def malformed_csv
+    render :malformed_csv
+  end
 
   def asset_path
     request.path.sub("/preview", "").sub(/^\//, "")
@@ -63,48 +46,6 @@ def asset_filename
     asset_path.split("/").last
   end
 
-  def whitehall_media_download
-    GdsApi.asset_manager.whitehall_media(asset_path).body
-  end
-
-  def media_download_truncated
-    @media_download_truncated ||= truncate_to_maximum_number_of_lines(
-      GdsApi.asset_manager.media(params[:id], params[:filename]).body,
-      MAXIMUM_ROWS + 1,
-    )
-  end
-
-  def truncate_to_maximum_number_of_lines(string, maximum_number_of_lines)
-    string[0..newline_or_last_char_index(string, maximum_number_of_lines - 1)]
-  end
-
-  def newline_or_last_char_index(string, newline_index)
-    (0..newline_index).inject(-1) do |current_index|
-      next_index = string.index("\n", current_index + 1)
-      return string.length - 1 if next_index.nil?
-
-      next_index
-    end
-  end
-
-  def encoding(media)
-    @encoding ||= if utf_8_encoding?(media)
-                    "UTF-8"
-                  elsif windows_1252_encoding?(media)
-                    "windows-1252"
-                  else
-                    raise FileEncodingError, "File encoding not recognised"
-                  end
-  end
-
-  def utf_8_encoding?(media)
-    media.force_encoding("utf-8").valid_encoding?
-  end
-
-  def windows_1252_encoding?(media)
-    media.force_encoding("windows-1252").valid_encoding?
-  end
-
   def draft_asset?
     @asset["draft"] == true
   end

app/services/csv_preview_service.rb

@@ -0,0 +1,80 @@
+class CsvPreviewService
+  MAXIMUM_COLUMNS = 50
+  MAXIMUM_ROWS = 1000
+
+  def initialize(csv)
+    @csv = csv
+  end
+
+  def csv_rows
+    original_error = nil
+    row_sep = :auto
+
+    begin
+      parsed_csv = CSV.parse(
+        csv_truncated,
+        encoding: encoding(csv_truncated),
+        headers: true,
+        row_sep:,
+      )
+    rescue CSV::MalformedCSVError => e
+      if original_error.nil?
+        original_error = e
+        row_sep = "\r\n"
+        retry
+      else
+        raise
+      end
+    end
+    converted_and_restricted_csv(parsed_csv)
+  end
+
+private
+
+  attr_reader :id, :filename
+
+  def newline_or_last_char_index(string, newline_index)
+    (0..newline_index).inject(-1) do |current_index|
+      next_index = string.index("\n", current_index + 1)
+      return string.length - 1 if next_index.nil?
+
+      next_index
+    end
+  end
+
+  def truncate_to_maximum_number_of_lines(string, maximum_number_of_lines)
+    string[0..newline_or_last_char_index(string, maximum_number_of_lines - 1)]
+  end
+
+  def csv_truncated
+    @csv_truncated ||= truncate_to_maximum_number_of_lines(@csv, MAXIMUM_ROWS + 1)
+  end
+
+  def encoding(media)
+    @encoding ||= if utf_8_encoding?(media)
+                    "UTF-8"
+                  elsif windows_1252_encoding?(media)
+                    "windows-1252"
+                  else
+                    raise FileEncodingError, "File encoding not recognised"
+                  end
+  end
+
+  def utf_8_encoding?(media)
+    media.force_encoding("utf-8").valid_encoding?
+  end
+
+  def windows_1252_encoding?(media)
+    media.force_encoding("windows-1252").valid_encoding?
+  end
+
+  def converted_and_restricted_csv(parsed_csv)
+    @converted_and_restricted_csv ||= parsed_csv.to_a.map do |row|
+      row.map { |column|
+        {
+          text: column&.encode("UTF-8"),
+        }
+      }.take(MAXIMUM_COLUMNS)
+    end
+  end
+end

test/unit/services/csv_preview_service_test.rb

@@ -0,0 +1,114 @@
+require "test_helper"
+
+class CsvPreviewServiceTest < ActiveSupport::TestCase
+  setup do
+    @csv = <<~CSV
+      header 1,header 2,header 3
+      content 1,content 2,content 3
+    CSV
+
+    @long_csv = @csv.dup
+    (CsvPreviewService::MAXIMUM_ROWS + 10).times { @long_csv += "other content 1,other content 2,other content 3\n" }
+
+    @crlf_csv = @csv.gsub(/\n/, "\r\n")
+
+    @csv_with_many_columns = "column"
+    (CsvPreviewService::MAXIMUM_COLUMNS + 10).times { @csv_with_many_columns += ",column" }
+    @csv_with_many_columns << "\n"
+
+    @parsed_csv = [
+      [{ text: "header 1" }, { text: "header 2" }, { text: "header 3" }],
+      [{ text: "content 1" }, { text: "content 2" }, { text: "content 3" }],
+    ]
+  end
+
+  context "#csv_rows" do
+    context "with normal CSV" do
+      subject { CsvPreviewService.new(@csv).csv_rows }
+
+      should "parse the CSV correctly" do
+        assert_equal @parsed_csv, subject
+      end
+    end
+
+    context "with CSV containing CRLF line terminators" do
+      subject { CsvPreviewService.new(@crlf_csv).csv_rows }
+
+      should "parse the CSV correctly" do
+        assert_equal @parsed_csv, subject
+      end
+    end
+
+    context "with long CSV" do
+      subject { CsvPreviewService.new(@long_csv).csv_rows }
+
+      should "return only the header row and less or equal to the maximum number of normal rows" do
+        assert_operator subject.length, :<=, CsvPreviewService::MAXIMUM_ROWS + 1
+      end
+    end
+
+    context "with CSV containing many columns" do
+      subject { CsvPreviewService.new(@csv_with_many_columns).csv_rows }
+
+      should "return only less than or equal the maximum number of columns" do
+        assert_operator subject.first.length, :<=, CsvPreviewService::MAXIMUM_COLUMNS
+      end
+    end
+
+    context "with CSV in UTF-8" do
+      subject { CsvPreviewService.new("zażółć gęślą jaźń\n").csv_rows }
+
+      should "parse the CSV correctly" do
+        assert_equal [[{ text: "zażółć gęślą jaźń" }]], subject
+      end
+    end
+
+    context "with CSV in windows-1252" do
+      subject { CsvPreviewService.new("\xfe\xe6r he feoll his tw\xe6gen gebro\xf0ra\n").csv_rows }
+
+      should "parse the CSV and convert it to UTF-8" do
+        assert_equal [[{ text: "þær he feoll his twægen gebroðra" }]], subject
+      end
+    end
+  end
+
+  context "#newline_or_last_char_index" do
+    subject { CsvPreviewService.new("") }
+
+    context "when newline index is less than index of last newline" do
+      should "return correct index" do
+        assert_equal 8, subject.send(:newline_or_last_char_index, "a\nb\ncdef\ngh\nijk", 2)
+      end
+    end
+    context "when newline index is equal to index of last newline" do
+      should "return correct index" do
+        assert_equal 11, subject.send(:newline_or_last_char_index, "a\nb\ncdef\ngh\n", 3)
+      end
+    end
+    context "when newline index is greater than index of last newline" do
+      should "return correct index" do
+        assert_equal 14, subject.send(:newline_or_last_char_index, "a\nb\ncdef\ngh\nijk", 10)
+      end
+    end
+  end
+
+  context "#truncate_to_maximum_number_of_lines" do
+    subject { CsvPreviewService.new("") }
+
+    context "when requested number of lines is less than actual number of lines" do
+      should "return correct string" do
+        assert_equal "a\nb\ncdef\n", subject.send(:truncate_to_maximum_number_of_lines, "a\nb\ncdef\ngh\nijk", 3)
+      end
+    end
+    context "when requested number of lines is equal to actual number of lines" do
+      should "return correct string" do
+        assert_equal "a\nb\ncdef\ngh\n", subject.send(:truncate_to_maximum_number_of_lines, "a\nb\ncdef\ngh\n", 4)
+      end
+    end
+    context "when requested number of lines is greater than actual number of lines" do
+      should "return correct string" do
+        assert_equal "a\nb\ncdef\ngh\nijk", subject.send(:truncate_to_maximum_number_of_lines, "a\nb\ncdef\ngh\nijk", 10)
+      end
+    end
+  end
+end