Refactor renders (#15175)

* Refactor renders

* Some performance optimization

* Fix comment

* Transform reader

* Fix csv test

* Fix test

* Fix tests

* Improve optimaziation

* Fix test

* Fix test

* Detect file encoding with reader

* Improve optimaziation

* reduce memory usage

* improve code

* fix build

* Fix test

* Fix for go1.15

* Fix render

* Fix comment

* Fix lint

* Fix test

* Don't use NormalEOF when unnecessary

* revert change on util.go

* Apply suggestions from code review

Co-authored-by: zeripath <art27@cantab.net>

* rename function

* Take NormalEOF back

Co-authored-by: zeripath <art27@cantab.net>

2 files changed, 26 insertions, 7 deletions

diff --git a/modules/csv/csv.go b/modules/csv/csv.go
index 1aa78fdeec..bf433f77d2 100644
--- a/modules/csv/csv.go
+++ b/modules/csv/csv.go
@@ -7,7 +7,9 @@ package csv
 import (
 	"bytes"
 	"encoding/csv"
+	stdcsv "encoding/csv"
 	"errors"
+	"io"
 	"regexp"
 	"strings"
 
@@ -18,17 +20,31 @@ import (
 var quoteRegexp = regexp.MustCompile(`["'][\s\S]+?["']`)
 
 // CreateReader creates a csv.Reader with the given delimiter.
-func CreateReader(rawBytes []byte, delimiter rune) *csv.Reader {
-	rd := csv.NewReader(bytes.NewReader(rawBytes))
+func CreateReader(input io.Reader, delimiter rune) *stdcsv.Reader {
+	rd := stdcsv.NewReader(input)
 	rd.Comma = delimiter
 	rd.TrimLeadingSpace = true
 	return rd
 }
 
 // CreateReaderAndGuessDelimiter tries to guess the field delimiter from the content and creates a csv.Reader.
-func CreateReaderAndGuessDelimiter(rawBytes []byte) *csv.Reader {
-	delimiter := guessDelimiter(rawBytes)
-	return CreateReader(rawBytes, delimiter)
+func CreateReaderAndGuessDelimiter(rd io.Reader) (*stdcsv.Reader, error) {
+	var data = make([]byte, 1e4)
+	size, err := rd.Read(data)
+	if err != nil {
+		return nil, err
+	}
+
+	delimiter := guessDelimiter(data[:size])
+
+	var newInput io.Reader
+	if size < 1e4 {
+		newInput = bytes.NewReader(data[:size])
+	} else {
+		newInput = io.MultiReader(bytes.NewReader(data), rd)
+	}
+
+	return CreateReader(newInput, delimiter), nil
 }
 
 // guessDelimiter scores the input CSV data against delimiters, and returns the best match.
diff --git a/modules/csv/csv_test.go b/modules/csv/csv_test.go
index 3a7584e21d..3cc09c40aa 100644
--- a/modules/csv/csv_test.go
+++ b/modules/csv/csv_test.go
@@ -5,20 +5,23 @@
 package csv
 
 import (
+	"bytes"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 )
 
 func TestCreateReader(t *testing.T) {
-	rd := CreateReader([]byte{}, ',')
+	rd := CreateReader(bytes.NewReader([]byte{}), ',')
 	assert.Equal(t, ',', rd.Comma)
 }
 
 func TestCreateReaderAndGuessDelimiter(t *testing.T) {
 	input := "a;b;c\n1;2;3\n4;5;6"
 
-	rd := CreateReaderAndGuessDelimiter([]byte(input))
+	rd, err := CreateReaderAndGuessDelimiter(strings.NewReader(input))
+	assert.NoError(t, err)
 	assert.Equal(t, ';', rd.Comma)
 }