Properly determine CSV delimiter (#17459)

* Fixes #16558 CSV delimiter determiner

* Fixes #16558 - properly determine CSV delmiiter

* Moves quoteString to a new function

* Adds big test with lots of commas for tab delimited csv

* Adds comments

* Shortens the text of the test

* Removes single quotes from regexp as only double quotes need to be searched

* Fixes spelling

* Fixes check of length as it probalby will only be 1e4, not greater

* Makes sample size a const, properly removes truncated line

* Makes sample size a const, properly removes truncated line

* Fixes comment

* Fixes comment

* tests for FormatError() function

* Adds logic to find the limiter before or after a quoted value

* Simplifies regex

* Error tests

* Error tests

* Update modules/csv/csv.go

Co-authored-by: delvh <dev.lh@web.de>

* Update modules/csv/csv.go

Co-authored-by: delvh <dev.lh@web.de>

* Adds comments

* Update modules/csv/csv.go

Co-authored-by: delvh <dev.lh@web.de>

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: delvh <dev.lh@web.de>

modules/csv/csv.go

@@ -7,16 +7,18 @@ package csv
 import (
 	"bytes"
 	stdcsv "encoding/csv"
-	"errors"
 	"io"
+	"path/filepath"
 	"regexp"
 	"strings"
 
+	"code.gitea.io/gitea/modules/markup"
 	"code.gitea.io/gitea/modules/translation"
 	"code.gitea.io/gitea/modules/util"
 )
 
-var quoteRegexp = regexp.MustCompile(`["'][\s\S]+?["']`)
+const maxLines = 10
+const guessSampleSize = 1e4 // 10k
 
 // CreateReader creates a csv.Reader with the given delimiter.
 func CreateReader(input io.Reader, delimiter rune) *stdcsv.Reader {
@@ -30,10 +32,10 @@ func CreateReader(input io.Reader, delimiter rune) *stdcsv.Reader {
 	return rd
 }
 
-// CreateReaderAndGuessDelimiter tries to guess the field delimiter from the content and creates a csv.Reader.
-// Reads at most 10k bytes.
-func CreateReaderAndGuessDelimiter(rd io.Reader) (*stdcsv.Reader, error) {
-	var data = make([]byte, 1e4)
+// CreateReaderAndDetermineDelimiter tries to guess the field delimiter from the content and creates a csv.Reader.
+// Reads at most guessSampleSize bytes.
+func CreateReaderAndDetermineDelimiter(ctx *markup.RenderContext, rd io.Reader) (*stdcsv.Reader, error) {
+	var data = make([]byte, guessSampleSize)
 	size, err := util.ReadAtMost(rd, data)
 	if err != nil {
 		return nil, err
@@ -41,59 +43,84 @@ func CreateReaderAndGuessDelimiter(rd io.Reader) (*stdcsv.Reader, error) {
 
 	return CreateReader(
 		io.MultiReader(bytes.NewReader(data[:size]), rd),
-		guessDelimiter(data[:size]),
+		determineDelimiter(ctx, data[:size]),
 	), nil
 }
 
-// guessDelimiter scores the input CSV data against delimiters, and returns the best match.
-func guessDelimiter(data []byte) rune {
-	maxLines := 10
-	text := quoteRegexp.ReplaceAllLiteralString(string(data), "")
-	lines := strings.SplitN(text, "\n", maxLines+1)
-	lines = lines[:util.Min(maxLines, len(lines))]
-
-	delimiters := []rune{',', ';', '\t', '|', '@'}
-	bestDelim := delimiters[0]
-	bestScore := 0.0
-	for _, delim := range delimiters {
-		score := scoreDelimiter(lines, delim)
-		if score > bestScore {
-			bestScore = score
-			bestDelim = delim
+// determineDelimiter takes a RenderContext and if it isn't nil and the Filename has an extension that specifies the delimiter,
+// it is used as the delimiter. Otherwise we call guessDelimiter with the data passed
+func determineDelimiter(ctx *markup.RenderContext, data []byte) rune {
+	extension := ".csv"
+	if ctx != nil {
+		extension = strings.ToLower(filepath.Ext(ctx.Filename))
 	}
+
+	var delimiter rune
+	switch extension {
+	case ".tsv":
+		delimiter = '\t'
+	case ".psv":
+		delimiter = '|'
+	default:
+		delimiter = guessDelimiter(data)
 	}
 
-	return bestDelim
+	return delimiter
 }
 
-// scoreDelimiter uses a count & regularity metric to evaluate a delimiter against lines of CSV.
-func scoreDelimiter(lines []string, delim rune) float64 {
-	countTotal := 0
-	countLineMax := 0
-	linesNotEqual := 0
+// quoteRegexp follows the RFC-4180 CSV standard for when double-quotes are used to enclose fields, then a double-quote appearing inside a
+// field must be escaped by preceding it with another double quote. https://www.ietf.org/rfc/rfc4180.txt
+// This finds all quoted strings that have escaped quotes.
+var quoteRegexp = regexp.MustCompile(`"[^"]*"`)
 
-	for _, line := range lines {
-		if len(line) == 0 {
-			continue
+// removeQuotedStrings uses the quoteRegexp to remove all quoted strings so that we can reliably have each row on one line
+// (quoted strings often have new lines within the string)
+func removeQuotedString(text string) string {
+	return quoteRegexp.ReplaceAllLiteralString(text, "")
+}
+
+// guessDelimiter takes up to maxLines of the CSV text, iterates through the possible delimiters, and sees if the CSV Reader reads it without throwing any errors.
+// If more than one delimiter passes, the delimiter that results in the most columns is returned.
+func guessDelimiter(data []byte) rune {
+	delimiter := guessFromBeforeAfterQuotes(data)
+	if delimiter != 0 {
+		return delimiter
 	}
 
-		countLine := strings.Count(line, string(delim))
-		countTotal += countLine
-		if countLine != countLineMax {
-			if countLineMax != 0 {
-				linesNotEqual++
+	// Removes quoted values so we don't have columns with new lines in them
+	text := removeQuotedString(string(data))
+
+	// Make the text just be maxLines or less, ignoring truncated lines
+	lines := strings.SplitN(text, "\n", maxLines+1) // Will contain at least one line, and if there are more than MaxLines, the last item holds the rest of the lines
+	if len(lines) > maxLines {
+		// If the length of lines is > maxLines we know we have the max number of lines, trim it to maxLines
+		lines = lines[:maxLines]
+	} else if len(lines) > 1 && len(data) >= guessSampleSize {
+		// Even with data >= guessSampleSize, we don't have maxLines + 1 (no extra lines, must have really long lines)
+		// thus the last line is probably have a truncated line. Drop the last line if len(lines) > 1
+		lines = lines[:len(lines)-1]
 	}
-			countLineMax = util.Max(countLine, countLineMax)
+
+	// Put lines back together as a string
+	text = strings.Join(lines, "\n")
+
+	delimiters := []rune{',', '\t', ';', '|', '@'}
+	validDelim := delimiters[0]
+	validDelimColCount := 0
+	for _, delim := range delimiters {
+		csvReader := stdcsv.NewReader(strings.NewReader(text))
+		csvReader.Comma = delim
+		if rows, err := csvReader.ReadAll(); err == nil && len(rows) > 0 && len(rows[0]) > validDelimColCount {
+			validDelim = delim
+			validDelimColCount = len(rows[0])
 		}
 	}
-
-	return float64(countTotal) * (1 - float64(linesNotEqual)/float64(len(lines)))
+	return validDelim
 }
 
 // FormatError converts csv errors into readable messages.
 func FormatError(err error, locale translation.Locale) (string, error) {
-	var perr *stdcsv.ParseError
-	if errors.As(err, &perr) {
+	if perr, ok := err.(*stdcsv.ParseError); ok {
 		if perr.Err == stdcsv.ErrFieldCount {
 			return locale.Tr("repo.error.csv.invalid_field_count", perr.Line), nil
 		}
@@ -102,3 +129,20 @@ func FormatError(err error, locale translation.Locale) (string, error) {
 
 	return "", err
 }
+
+// Looks for possible delimiters right before or after (with spaces after the former) double quotes with closing quotes
+var beforeAfterQuotes = regexp.MustCompile(`([,@\t;|]{0,1}) *(?:"[^"]*")+([,@\t;|]{0,1})`)
+
+// guessFromBeforeAfterQuotes guesses the limiter by finding a double quote that has a valid delimiter before it and a closing quote,
+// or a double quote with a closing quote and a valid delimiter after it
+func guessFromBeforeAfterQuotes(data []byte) rune {
+	rs := beforeAfterQuotes.FindStringSubmatch(string(data)) // returns first match, or nil if none
+	if rs != nil {
+		if rs[1] != "" {
+			return rune(rs[1][0]) // delimiter found left of quoted string
+		} else if rs[2] != "" {
+			return rune(rs[2][0]) // delimiter found right of quoted string
+		}
+	}
+	return 0 // no match found
+}

modules/csv/csv_test.go

@@ -6,9 +6,13 @@ package csv
 
 import (
 	"bytes"
+	"encoding/csv"
+	"io"
 	"strings"
 	"testing"
 
+	"code.gitea.io/gitea/modules/markup"
+
 	"github.com/stretchr/testify/assert"
 )
 
@@ -18,67 +22,566 @@ func TestCreateReader(t *testing.T) {
 }
 
 //nolint
-func TestCreateReaderAndGuessDelimiter(t *testing.T) {
-	var csvToRowsMap = map[string][][]string{
-		`a;b;c
+func TestCreateReaderAndDetermineDelimiter(t *testing.T) {
+	var cases = []struct {
+		csv               string
+		expectedRows      [][]string
+		expectedDelimiter rune
+	}{
+		// case 0 - semicolon delmited
+		{
+			csv: `a;b;c
 1;2;3
-4;5;6`: {{"a", "b", "c"}, {"1", "2", "3"}, {"4", "5", "6"}},
-		`col1	col2	col3
-a	b	c
+4;5;6`,
+			expectedRows: [][]string{
+				{"a", "b", "c"},
+				{"1", "2", "3"},
+				{"4", "5", "6"},
+			},
+			expectedDelimiter: ';',
+		},
+		// case 1 - tab delimited with empty fields
+		{
+			csv: `col1	col2	col3
+a,	b	c
 	e	f
 g	h	i
 j		l
-m	n	
+m	n,	
 p	q	r
 		u
 v	w	x
 y		
-		`: {{"col1", "col2", "col3"},
-			{"a", "b", "c"},
+		`,
+			expectedRows: [][]string{
+				{"col1", "col2", "col3"},
+				{"a,", "b", "c"},
 				{"", "e", "f"},
 				{"g", "h", "i"},
 				{"j", "", "l"},
-			{"m", "n", ""},
+				{"m", "n,", ""},
 				{"p", "q", "r"},
 				{"", "", "u"},
 				{"v", "w", "x"},
 				{"y", "", ""},
-			{"", "", ""}},
-		` col1,col2,col3
+				{"", "", ""},
+			},
+			expectedDelimiter: '\t',
+		},
+		// case 2 - comma delimited with leading spaces
+		{
+			csv: ` col1,col2,col3
  a, b, c
 d,e,f
  ,h, i
 j, , 
- , , `: {{"col1", "col2", "col3"},
+ , , `,
+			expectedRows: [][]string{
+				{"col1", "col2", "col3"},
 				{"a", "b", "c"},
 				{"d", "e", "f"},
 				{"", "h", "i"},
 				{"j", "", ""},
-			{"", "", ""}},
+				{"", "", ""},
+			},
+			expectedDelimiter: ',',
+		},
+	}
+
+	for n, c := range cases {
+		rd, err := CreateReaderAndDetermineDelimiter(nil, strings.NewReader(c.csv))
+		assert.NoError(t, err, "case %d: should not throw error: %v\n", n, err)
+		assert.EqualValues(t, c.expectedDelimiter, rd.Comma, "case %d: delimiter should be '%c', got '%c'", n, c.expectedDelimiter, rd.Comma)
+		rows, err := rd.ReadAll()
+		assert.NoError(t, err, "case %d: should not throw error: %v\n", n, err)
+		assert.EqualValues(t, c.expectedRows, rows, "case %d: rows should be equal", n)
 	}
+}
+
+type mockReader struct{}
+
+func (r *mockReader) Read(buf []byte) (int, error) {
+	return 0, io.ErrShortBuffer
+}
 
-	for csv, expectedRows := range csvToRowsMap {
-		rd, err := CreateReaderAndGuessDelimiter(strings.NewReader(csv))
-		assert.NoError(t, err)
+func TestDetermineDelimiterShortBufferError(t *testing.T) {
+	rd, err := CreateReaderAndDetermineDelimiter(nil, &mockReader{})
+	assert.Error(t, err, "CreateReaderAndDetermineDelimiter() should throw an error")
+	assert.ErrorIs(t, err, io.ErrShortBuffer)
+	assert.Nil(t, rd, "CSV reader should be mnil")
+}
+
+func TestDetermineDelimiterReadAllError(t *testing.T) {
+	rd, err := CreateReaderAndDetermineDelimiter(nil, strings.NewReader(`col1,col2
+	a;b
+	c@e
+	f	g
+	h|i
+	jkl`))
+	assert.NoError(t, err, "CreateReaderAndDetermineDelimiter() shouldn't throw error")
+	assert.NotNil(t, rd, "CSV reader should not be mnil")
 	rows, err := rd.ReadAll()
-		assert.NoError(t, err)
-		assert.EqualValues(t, rows, expectedRows)
+	assert.Error(t, err, "RaadAll() should throw error")
+	assert.ErrorIs(t, err, csv.ErrFieldCount)
+	assert.Empty(t, rows, "rows should be empty")
+}
+
+func TestDetermineDelimiter(t *testing.T) {
+	var cases = []struct {
+		csv               string
+		filename          string
+		expectedDelimiter rune
+	}{
+		// case 0 - semicolon delmited
+		{
+			csv:               "a",
+			filename:          "test.csv",
+			expectedDelimiter: ',',
+		},
+		// case 1 - single column/row CSV
+		{
+			csv:               "a",
+			filename:          "",
+			expectedDelimiter: ',',
+		},
+		// case 2 - single column, single row CSV w/ tsv file extension (so is tabbed delimited)
+		{
+			csv:               "1,2",
+			filename:          "test.tsv",
+			expectedDelimiter: '\t',
+		},
+		// case 3 - two column, single row CSV w/ no filename, so will guess comma as delimiter
+		{
+			csv:               "1,2",
+			filename:          "",
+			expectedDelimiter: ',',
+		},
+		// case 4 - semi-colon delimited with csv extension
+		{
+			csv:               "1;2",
+			filename:          "test.csv",
+			expectedDelimiter: ';',
+		},
+		// case 5 - tabbed delimited with tsv extension
+		{
+			csv:               "1\t2",
+			filename:          "test.tsv",
+			expectedDelimiter: '\t',
+		},
+		// case 6 - tabbed delimited without any filename
+		{
+			csv:               "1\t2",
+			filename:          "",
+			expectedDelimiter: '\t',
+		},
+		// case 7 - tabs won't work, only commas as every row has same amount of commas
+		{
+			csv:               "col1,col2\nfirst\tval,seconed\tval",
+			filename:          "",
+			expectedDelimiter: ',',
+		},
+		// case 8 - While looks like comma delimited, has psv extension
+		{
+			csv:               "1,2",
+			filename:          "test.psv",
+			expectedDelimiter: '|',
+		},
+		// case 9 - pipe delmiited with no extension
+		{
+			csv:               "1|2",
+			filename:          "",
+			expectedDelimiter: '|',
+		},
+		// case 10 - semi-colon delimited with commas in values
+		{
+			csv:               "1,2,3;4,5,6;7,8,9\na;b;c",
+			filename:          "",
+			expectedDelimiter: ';',
+		},
+		// case 11 - semi-colon delimited with newline in content
+		{
+			csv: `"1,2,3,4";"a
+b";%
+c;d;#`,
+			filename:          "",
+			expectedDelimiter: ';',
+		},
+		// case 12 - HTML as single value
+		{
+			csv:               "<br/>",
+			filename:          "",
+			expectedDelimiter: ',',
+		},
+		// case 13 - tab delimited with commas in values
+		{
+			csv: `name	email	note
+John Doe	john@doe.com	This,note,had,a,lot,of,commas,to,test,delimters`,
+			filename:          "",
+			expectedDelimiter: '\t',
+		},
+	}
+
+	for n, c := range cases {
+		delimiter := determineDelimiter(&markup.RenderContext{Filename: c.filename}, []byte(c.csv))
+		assert.EqualValues(t, c.expectedDelimiter, delimiter, "case %d: delimiter should be equal, expected '%c' got '%c'", n, c.expectedDelimiter, delimiter)
+	}
+}
+
+func TestRemoveQuotedString(t *testing.T) {
+	var cases = []struct {
+		text         string
+		expectedText string
+	}{
+		// case 0 - quoted text with escpaed quotes in 1st column
+		{
+			text: `col1,col2,col3
+"quoted ""text"" with
+new lines
+in first column",b,c`,
+			expectedText: `col1,col2,col3
+,b,c`,
+		},
+		// case 1 - quoted text with escpaed quotes in 2nd column
+		{
+			text: `col1,col2,col3
+a,"quoted ""text"" with
+new lines
+in second column",c`,
+			expectedText: `col1,col2,col3
+a,,c`,
+		},
+		// case 2 - quoted text with escpaed quotes in last column
+		{
+			text: `col1,col2,col3
+a,b,"quoted ""text"" with
+new lines
+in last column"`,
+			expectedText: `col1,col2,col3
+a,b,`,
+		},
+		// case 3 - csv with lots of quotes
+		{
+			text: `a,"b",c,d,"e
+e
+e",f
+a,bb,c,d,ee ,"f
+f"
+a,b,"c ""
+c",d,e,f`,
+			expectedText: `a,,c,d,,f
+a,bb,c,d,ee ,
+a,b,,d,e,f`,
+		},
+		// case 4 - csv with pipes and quotes
+		{
+			text: `Col1 | Col2 | Col3
+abc   | "Hello
+World"|123
+"de
+
+f" | 4.56 | 789`,
+			expectedText: `Col1 | Col2 | Col3
+abc   | |123
+ | 4.56 | 789`,
+		},
+	}
+
+	for n, c := range cases {
+		modifiedText := removeQuotedString(c.text)
+		assert.EqualValues(t, c.expectedText, modifiedText, "case %d: modified text should be equal", n)
 	}
 }
 
 func TestGuessDelimiter(t *testing.T) {
-	var csvToDelimiterMap = map[string]rune{
-		"a":                         ',',
-		"1,2":                       ',',
-		"1;2":                       ';',
-		"1\t2":                      '\t',
-		"1|2":                       '|',
-		"1,2,3;4,5,6;7,8,9\na;b;c":  ';',
-		"\"1,2,3,4\";\"a\nb\"\nc;d": ';',
-		"<br/>":                     ',',
+	var cases = []struct {
+		csv               string
+		expectedDelimiter rune
+	}{
+		// case 0 - single cell, comma delmited
+		{
+			csv:               "a",
+			expectedDelimiter: ',',
+		},
+		// case 1 - two cells, comma delimited
+		{
+			csv:               "1,2",
+			expectedDelimiter: ',',
+		},
+		// case 2 - semicolon delimited
+		{
+			csv:               "1;2",
+			expectedDelimiter: ';',
+		},
+		// case 3 - tab delimited
+		{
+			csv: "1	2",
+			expectedDelimiter: '\t',
+		},
+		// case 4 - pipe delimited
+		{
+			csv:               "1|2",
+			expectedDelimiter: '|',
+		},
+		// case 5 - semicolon delimited with commas in text
+		{
+			csv: `1,2,3;4,5,6;7,8,9
+a;b;c`,
+			expectedDelimiter: ';',
+		},
+		// case 6 - semicolon delmited with commas in quoted text
+		{
+			csv: `"1,2,3,4";"a
+b"
+c;d`,
+			expectedDelimiter: ';',
+		},
+		// case 7 - HTML
+		{
+			csv:               "<br/>",
+			expectedDelimiter: ',',
+		},
+		// case 8 - tab delimited with commas in value
+		{
+			csv: `name	email	note
+John Doe	john@doe.com	This,note,had,a,lot,of,commas,to,test,delimters`,
+			expectedDelimiter: '\t',
+		},
+		// case 9 - tab delimited with new lines in values, commas in values
+		{
+			csv: `1	"some,""more
+""
+	quoted,
+text,"	a
+2	"some,
+quoted,	
+	text,"	b
+3	"some,
+quoted,
+	text"	c
+4	"some,
+quoted,
+text,"	d`,
+			expectedDelimiter: '\t',
+		},
+		// case 10 - semicolon delmited with quotes and semicolon in value
+		{
+			csv: `col1;col2
+"this has a literal "" in the text";"and an ; in the text"`,
+			expectedDelimiter: ';',
+		},
+		// case 11 - pipe delimited with quotes
+		{
+			csv: `Col1 | Col2 | Col3
+abc   | "Hello
+World"|123
+"de
+|
+f" | 4.56 | 789`,
+			expectedDelimiter: '|',
+		},
+		// case 12 - a tab delimited 6 column CSV, but the values are not quoted and have lots of commas.
+		// In the previous bestScore algorithm, this would have picked comma as the delimiter, but now it should guess tab
+		{
+			csv: `c1	c2	c3	c4	c5	c6
+v,k,x,v	ym,f,oa,qn,uqijh,n,s,wvygpo	uj,kt,j,w,i,fvv,tm,f,ddt,b,mwt,e,t,teq,rd,p,a	e,wfuae,t,h,q,im,ix,y	h,mrlu,l,dz,ff,zi,af,emh	,gov,bmfelvb,axp,f,u,i,cni,x,z,v,sh,w,jo,,m,h
+k,ohf,pgr,tde,m,s	te,ek,,v,,ic,kqc,dv,w,oi,j,w,gojjr,ug,,l,j,zl	g,qziq,bcajx,zfow,ka,j,re,ohbc	k,nzm,qm,ts,auf	th,elb,lx,l,q,e,qf	asbr,z,k,y,tltobga
+g,m,bu,el	h,l,jwi,o,wge,fy,rure,c,g,lcxu,fxte,uns,cl,s,o,t,h,rsoy,f	bq,s,uov,z,ikkhgyg,,sabs,c,hzue	mc,b,,j,t,n	sp,mn,,m,t,dysi,eq,pigb,rfa,z	w,rfli,sg,,o,wjjjf,f,wxdzfk,x,t,p,zy,p,mg,r,l,h
+e,ewbkc,nugd,jj,sf,ih,i,n,jo,b,poem,kw,q,i,x,t,e,uug,k	j,xm,sch,ux,h,,fb,f,pq,,mh,,f,v,,oba,w,h,v,eiz,yzd,o,a,c,e,dhp,q	a,pbef,epc,k,rdpuw,cw	k,j,e,d	xf,dz,sviv,w,sqnzew,t,b	v,yg,f,cq,ti,g,m,ta,hm,ym,ii,hxy,p,z,r,e,ga,sfs,r,p,l,aar,w,kox,j
+l,d,v,pp,q,j,bxip,w,i,im,qa,o	e,o	h,w,a,a,qzj,nt,qfn,ut,fvhu,ts	hu,q,g,p,q,ofpje,fsqa,frp,p,vih,j,w,k,jx,	ln,th,ka,l,b,vgk,rv,hkx	rj,v,y,cwm,rao,e,l,wvr,ptc,lm,yg,u,k,i,b,zk,b,gv,fls
+velxtnhlyuysbnlchosqlhkozkdapjaueexjwrndwb	nglvnv	kqiv	pbshwlmcexdzipopxjyrxhvjalwp	pydvipwlkkpdvbtepahskwuornbsb	qwbacgq
+l,y,u,bf,y,m,eals,n,cop,h,g,vs,jga,opt	x,b,zwmn,hh,b,n,pdj,t,d	px	yn,vtd,u,y,b,ps,yo,qqnem,mxg,m,al,rd,c,k,d,q,f	ilxdxa,m,y,,p,p,y,prgmg,q,n,etj,k,ns	b,pl,z,jq,hk
+p,gc	jn,mzr,bw	sb,e,r,dy,ur,wzy,r,c,n,yglr,jbdu,r,pqk,k	q,d,,,p,l,euhl,dc,rwh,t,tq,z,h,p,s,t,x,fugr,h	wi,zxb,jcig,o,t,k	mfh,ym,h,e,p,cnvx,uv,zx,x,pq,blt,v,r,u,tr,g,g,xt
+nri,p,,t,if,,y,ptlqq	a,i	w,ovli,um,w,f,re,k,sb,w,jy,zf	i,g,p,q,mii,nr,jm,cc	i,szl,k,eg,l,d	,ah,w,b,vh
+,,sh,wx,mn,xm,u,d,yy,u,t,m,j,s,b	ogadq,g,y,y,i,h,ln,jda,g,cz,s,rv,r,s,s,le,r,	y,nu,f,nagj	o,h,,adfy,o,nf,ns,gvsvnub,k,b,xyz	v,h,g,ef,y,gb	c,x,cw,x,go,h,t,x,cu,u,qgrqzrcmn,kq,cd,g,rejp,zcq
+skxg,t,vay,d,wug,d,xg,sexc	rt	g,ag,mjq,fjnyji,iwa,m,ml,b,ua,b,qjxeoc	be,s,sh,n,jbzxs,g,n,i,h,y,r,be,mfo,u,p	cw,r,,u,zn,eg,r,yac,m,l,edkr,ha,x,g,b,c,tg,c	j,ye,u,ejd,maj,ea,bm,u,iy`,
+			expectedDelimiter: '\t',
+		},
+		// case 13 - a CSV with more than 10 lines and since we only use the first 10 lines, it should still get the delimiter as semicolon
+		{
+			csv: `col1;col2;col3
+1;1;1
+2;2;2
+3;3;3
+4;4;4
+5;5;5
+6;6;6
+7;7;7
+8;8;8
+9;9;9
+10;10;10
+11	11	11
+12|12|12`,
+			expectedDelimiter: ';',
+		},
+		// case 14 - a really long single line (over 10k) that will get truncated, but since it has commas and semicolons (but more semicolons) it will pick semicolon
+		{
+			csv:               strings.Repeat("a;b,c;", 1700),
+			expectedDelimiter: ';',
+		},
+		// case 15 - 2 lines that are well over 10k, but since the 2nd line is where this CSV will be truncated (10k sample), it will only use the first line, so semicolon will be picked
+		{
+			csv:               "col1@col2@col3\na@b@" + strings.Repeat("c", 6000) + "\nd,e," + strings.Repeat("f", 4000),
+			expectedDelimiter: '@',
+		},
+		// case 16 - has all delimters so should return comma
+		{
+			csv: `col1,col2;col3@col4|col5	col6
+a	b|c@d;e,f`,
+			expectedDelimiter: ',',
+		},
+		// case 16 - nothing works (bad csv) so returns comma by default
+		{
+			csv: `col1,col2
+a;b
+c@e
+f	g
+h|i
+jkl`,
+			expectedDelimiter: ',',
+		},
+	}
+
+	for n, c := range cases {
+		delimiter := guessDelimiter([]byte(c.csv))
+		assert.EqualValues(t, c.expectedDelimiter, delimiter, "case %d: delimiter should be equal, expected '%c' got '%c'", n, c.expectedDelimiter, delimiter)
+	}
+}
+
+func TestGuessFromBeforeAfterQuotes(t *testing.T) {
+	var cases = []struct {
+		csv               string
+		expectedDelimiter rune
+	}{
+		// case 0 - tab delimited with new lines in values, commas in values
+		{
+			csv: `1	"some,""more
+""
+	quoted,
+text,"	a
+2	"some,
+quoted,	
+	text,"	b
+3	"some,
+quoted,
+	text"	c
+4	"some,
+quoted,
+text,"	d`,
+			expectedDelimiter: '\t',
+		},
+		// case 1 - semicolon delmited with quotes and semicolon in value
+		{
+			csv: `col1;col2
+"this has a literal "" in the text";"and an ; in the text"`,
+			expectedDelimiter: ';',
+		},
+		// case 2 - pipe delimited with quotes
+		{
+			csv: `Col1 | Col2 | Col3
+abc   | "Hello
+World"|123
+"de
+|
+f" | 4.56 | 789`,
+			expectedDelimiter: '|',
+		},
+		// case 3 - a complicated quoted CSV that is semicolon delmiited
+		{
+			csv: `he; she
+"he said, ""hey!"""; "she said, ""hey back!"""
+but; "be"`,
+			expectedDelimiter: ';',
+		},
+		// case 4 - no delimiter should be found
+		{
+			csv:               `a,b`,
+			expectedDelimiter: 0,
+		},
+		// case 5 - no limiter should be found
+		{
+			csv: `col1
+"he said, ""here I am"""`,
+			expectedDelimiter: 0,
+		},
+		// case 6 - delimiter before double quoted string with space
+		{
+			csv: `col1|col2
+a| "he said, ""here I am"""`,
+			expectedDelimiter: '|',
+		},
+		// case 7 - delimiter before double quoted string without space
+		{
+			csv: `col1|col2
+a|"he said, ""here I am"""`,
+			expectedDelimiter: '|',
+		},
+		// case 8 - delimiter after double quoted string with space
+		{
+			csv: `col1, col2
+"abc\n
+
+", def`,
+			expectedDelimiter: ',',
+		},
+		// case 9 - delimiter after double quoted string without space
+		{
+			csv: `col1,col2
+"abc\n
+
+",def`,
+			expectedDelimiter: ',',
+		},
+	}
+
+	for n, c := range cases {
+		delimiter := guessFromBeforeAfterQuotes([]byte(c.csv))
+		assert.EqualValues(t, c.expectedDelimiter, delimiter, "case %d: delimiter should be equal, expected '%c' got '%c'", n, c.expectedDelimiter, delimiter)
+	}
+}
+
+type mockLocale struct{}
+
+func (l mockLocale) Language() string {
+	return "en"
+}
+
+func (l mockLocale) Tr(s string, _ ...interface{}) string {
+	return s
+}
+
+func TestFormatError(t *testing.T) {
+	var cases = []struct {
+		err             error
+		expectedMessage string
+		expectsError    bool
+	}{
+		{
+			err: &csv.ParseError{
+				Err: csv.ErrFieldCount,
+			},
+			expectedMessage: "repo.error.csv.invalid_field_count",
+			expectsError:    false,
+		},
+		{
+			err: &csv.ParseError{
+				Err: csv.ErrBareQuote,
+			},
+			expectedMessage: "repo.error.csv.unexpected",
+			expectsError:    false,
+		},
+		{
+			err:          bytes.ErrTooLarge,
+			expectsError: true,
+		},
 	}
 
-	for csv, expectedDelimiter := range csvToDelimiterMap {
-		assert.EqualValues(t, guessDelimiter([]byte(csv)), expectedDelimiter)
+	for n, c := range cases {
+		message, err := FormatError(c.err, mockLocale{})
+		if c.expectsError {
+			assert.Error(t, err, "case %d: expected an error to be returned", n)
+		} else {
+			assert.NoError(t, err, "case %d: no error was expected, got error: %v", n, err)
+			assert.EqualValues(t, c.expectedMessage, message, "case %d: messages should be equal, expected '%s' got '%s'", n, c.expectedMessage, message)
+		}
 	}
 }

modules/markup/csv/csv.go

@@ -102,7 +102,7 @@ func (Renderer) Render(ctx *markup.RenderContext, input io.Reader, output io.Wri
 		return err
 	}
 
-	rd, err := csv.CreateReaderAndGuessDelimiter(bytes.NewReader(rawBytes))
+	rd, err := csv.CreateReaderAndDetermineDelimiter(ctx, bytes.NewReader(rawBytes))
 	if err != nil {
 		return err
 	}

routers/web/repo/compare.go

@@ -23,6 +23,7 @@ import (
 	csv_module "code.gitea.io/gitea/modules/csv"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/markup"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/upload"
 	"code.gitea.io/gitea/modules/util"
@@ -106,7 +107,7 @@ func setCsvCompareContext(ctx *context.Context) {
 
 		errTooLarge := errors.New(ctx.Locale.Tr("repo.error.csv.too_large"))
 
-		csvReaderFromCommit := func(c *git.Commit) (*csv.Reader, io.Closer, error) {
+		csvReaderFromCommit := func(ctx *markup.RenderContext, c *git.Commit) (*csv.Reader, io.Closer, error) {
 			blob, err := c.GetBlobByPath(diffFile.Name)
 			if err != nil {
 				return nil, nil, err
@@ -121,18 +122,18 @@ func setCsvCompareContext(ctx *context.Context) {
 				return nil, nil, err
 			}
 
-			csvReader, err := csv_module.CreateReaderAndGuessDelimiter(charset.ToUTF8WithFallbackReader(reader))
+			csvReader, err := csv_module.CreateReaderAndDetermineDelimiter(ctx, charset.ToUTF8WithFallbackReader(reader))
 			return csvReader, reader, err
 		}
 
-		baseReader, baseBlobCloser, err := csvReaderFromCommit(baseCommit)
+		baseReader, baseBlobCloser, err := csvReaderFromCommit(&markup.RenderContext{Filename: diffFile.OldName}, baseCommit)
 		if baseBlobCloser != nil {
 			defer baseBlobCloser.Close()
 		}
 		if err == errTooLarge {
 			return CsvDiffResult{nil, err.Error()}
 		}
-		headReader, headBlobCloser, err := csvReaderFromCommit(headCommit)
+		headReader, headBlobCloser, err := csvReaderFromCommit(&markup.RenderContext{Filename: diffFile.Name}, headCommit)
 		if headBlobCloser != nil {
 			defer headBlobCloser.Close()
 		}

services/gitdiff/csv_test.go

@@ -194,16 +194,16 @@ c,d,e`,
 
 		var baseReader *csv.Reader
 		if len(c.base) > 0 {
-			baseReader, err = csv_module.CreateReaderAndGuessDelimiter(strings.NewReader(c.base))
+			baseReader, err = csv_module.CreateReaderAndDetermineDelimiter(nil, strings.NewReader(c.base))
 			if err != nil {
-				t.Errorf("CreateReaderAndGuessDelimiter failed: %s", err)
+				t.Errorf("CreateReaderAndDetermineDelimiter failed: %s", err)
 			}
 		}
 		var headReader *csv.Reader
 		if len(c.head) > 0 {
-			headReader, err = csv_module.CreateReaderAndGuessDelimiter(strings.NewReader(c.head))
+			headReader, err = csv_module.CreateReaderAndDetermineDelimiter(nil, strings.NewReader(c.head))
 			if err != nil {
-				t.Errorf("CreateReaderAndGuessDelimiter failed: %s", err)
+				t.Errorf("CreateReaderAndDetermineDelimiter failed: %s", err)
 			}
 		}