Add Tabular Diff for CSV files (#14661)

Implements request #14320 The rendering of CSV files does match the diff style. * Moved CSV logic into base package. * Added method to create a tabular diff. * Added CSV compare context. * Added CSV diff template. * Use new table style in CSV markup. * Added file size limit for CSV rendering. * Display CSV parser errors in diff. * Lazy read single file. * Lazy read rows for full diff. * Added unit tests for various CSV changes.
2025-11-03 20:36:07 +01:00 · 2021-03-29 22:44:28 +02:00
parent d3b8127ad3
commit 0c6137617f
20 changed files with 937 additions and 118 deletions
--- a/custom/conf/app.example.ini
+++ b/custom/conf/app.example.ini
@@ -248,6 +248,10 @@ EVENT_SOURCE_UPDATE_TIME = 10s
 ; Whether to render SVG files as images.  If SVG rendering is disabled, SVG files are displayed as text and cannot be embedded in markdown files as images.
 ENABLE_RENDER = true

+[ui.csv]
+; Maximum allowed file size in bytes to render CSV files as table. (Set to 0 for no limit).
+MAX_FILE_SIZE = 524288
+
 [markdown]
 ; Render soft line breaks as hard line breaks, which means a single newline character between
 ; paragraphs will cause a line break and adding trailing whitespace to paragraphs is not
--- a/docs/content/doc/advanced/config-cheat-sheet.en-us.md
+++ b/docs/content/doc/advanced/config-cheat-sheet.en-us.md
@@ -198,6 +198,10 @@ Values containing `#` or `;` must be quoted using `` ` `` or `"""`.

 - `ENABLE_RENDER`: **true**: Whether to render SVG files as images.  If SVG rendering is disabled, SVG files are displayed as text and cannot be embedded in markdown files as images.

+### UI - CSV Files (`ui.csv`)
+
+- `MAX_FILE_SIZE`: **524288** (512kb): Maximum allowed file size in bytes to render CSV files as table. (Set to 0 for no limit).
+
 ## Markdown (`markdown`)

 - `ENABLE_HARD_LINE_BREAK_IN_COMMENTS`: **true**: Render soft line breaks as hard line breaks in comments, which
--- a/modules/csv/csv.go
+++ b/modules/csv/csv.go
@@ -0,0 +1,93 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package csv
+
+import (
+	"bytes"
+	"encoding/csv"
+	"errors"
+	"regexp"
+	"strings"
+
+	"code.gitea.io/gitea/modules/translation"
+	"code.gitea.io/gitea/modules/util"
+)
+
+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))
+	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)
+}
+
+// guessDelimiter scores the input CSV data against delimiters, and returns the best match.
+// Reads at most 10k bytes & 10 lines.
+func guessDelimiter(data []byte) rune {
+	maxLines := 10
+	maxBytes := util.Min(len(data), 1e4)
+	text := string(data[:maxBytes])
+	text = quoteRegexp.ReplaceAllLiteralString(text, "")
+	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
+		}
+	}
+
+	return bestDelim
+}
+
+// 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
+
+	for _, line := range lines {
+		if len(line) == 0 {
+			continue
+		}
+
+		countLine := strings.Count(line, string(delim))
+		countTotal += countLine
+		if countLine != countLineMax {
+			if countLineMax != 0 {
+				linesNotEqual++
+			}
+			countLineMax = util.Max(countLine, countLineMax)
+		}
+	}
+
+	return float64(countTotal) * (1 - float64(linesNotEqual)/float64(len(lines)))
+}
+
+// FormatError converts csv errors into readable messages.
+func FormatError(err error, locale translation.Locale) (string, error) {
+	var perr *csv.ParseError
+	if errors.As(err, &perr) {
+		if perr.Err == csv.ErrFieldCount {
+			return locale.Tr("repo.error.csv.invalid_field_count", perr.Line), nil
+		}
+		return locale.Tr("repo.error.csv.unexpected", perr.Line, perr.Column), nil
+	}
+
+	return "", err
+}
--- a/modules/csv/csv_test.go
+++ b/modules/csv/csv_test.go
@@ -0,0 +1,40 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package csv
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCreateReader(t *testing.T) {
+	rd := CreateReader([]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))
+	assert.Equal(t, ';', rd.Comma)
+}
+
+func TestGuessDelimiter(t *testing.T) {
+	var kases = 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/>":                     ',',
+	}
+
+	for k, v := range kases {
+		assert.EqualValues(t, guessDelimiter([]byte(k)), v)
+	}
+}
--- a/modules/markup/csv/csv.go
+++ b/modules/markup/csv/csv.go
@@ -6,24 +6,20 @@ package markup

 import (
 	"bytes"
-	"encoding/csv"
 	"html"
 	"io"
-	"regexp"
-	"strings"
+	"strconv"

+	"code.gitea.io/gitea/modules/csv"
 	"code.gitea.io/gitea/modules/markup"
-	"code.gitea.io/gitea/modules/util"
+	"code.gitea.io/gitea/modules/setting"
 )

-var quoteRegexp = regexp.MustCompile(`["'][\s\S]+?["']`)
-
 func init() {
 	markup.RegisterParser(Parser{})
-
 }

-// Parser implements markup.Parser for orgmode
+// Parser implements markup.Parser for csv files
 type Parser struct {
 }

@@ -38,11 +34,35 @@ func (Parser) Extensions() []string {
 }

 // Render implements markup.Parser
-func (p Parser) Render(rawBytes []byte, urlPrefix string, metas map[string]string, isWiki bool) []byte {
-	rd := csv.NewReader(bytes.NewReader(rawBytes))
-	rd.Comma = p.bestDelimiter(rawBytes)
+func (Parser) Render(rawBytes []byte, urlPrefix string, metas map[string]string, isWiki bool) []byte {
 	var tmpBlock bytes.Buffer
-	tmpBlock.WriteString(`<table class="table">`)
+
+	if setting.UI.CSV.MaxFileSize != 0 && setting.UI.CSV.MaxFileSize < int64(len(rawBytes)) {
+		tmpBlock.WriteString("<pre>")
+		tmpBlock.WriteString(html.EscapeString(string(rawBytes)))
+		tmpBlock.WriteString("</pre>")
+		return tmpBlock.Bytes()
+	}
+
+	rd := csv.CreateReaderAndGuessDelimiter(rawBytes)
+
+	writeField := func(element, class, field string) {
+		tmpBlock.WriteString("<")
+		tmpBlock.WriteString(element)
+		if len(class) > 0 {
+			tmpBlock.WriteString(" class=\"")
+			tmpBlock.WriteString(class)
+			tmpBlock.WriteString("\"")
+		}
+		tmpBlock.WriteString(">")
+		tmpBlock.WriteString(html.EscapeString(field))
+		tmpBlock.WriteString("</")
+		tmpBlock.WriteString(element)
+		tmpBlock.WriteString(">")
+	}
+
+	tmpBlock.WriteString(`<table class="data-table">`)
+	row := 1
 	for {
 		fields, err := rd.Read()
 		if err == io.EOF {
@@ -52,62 +72,19 @@ func (p Parser) Render(rawBytes []byte, urlPrefix string, metas map[string]strin
 			continue
 		}
 		tmpBlock.WriteString("<tr>")
+		element := "td"
+		if row == 1 {
+			element = "th"
+		}
+		writeField(element, "line-num", strconv.Itoa(row))
 		for _, field := range fields {
-			tmpBlock.WriteString("<td>")
-			tmpBlock.WriteString(html.EscapeString(field))
-			tmpBlock.WriteString("</td>")
+			writeField(element, "", field)
 		}
 		tmpBlock.WriteString("</tr>")
+
+		row++
 	}
 	tmpBlock.WriteString("</table>")

 	return tmpBlock.Bytes()
 }
-
-// bestDelimiter scores the input CSV data against delimiters, and returns the best match.
-// Reads at most 10k bytes & 10 lines.
-func (p Parser) bestDelimiter(data []byte) rune {
-	maxLines := 10
-	maxBytes := util.Min(len(data), 1e4)
-	text := string(data[:maxBytes])
-	text = quoteRegexp.ReplaceAllLiteralString(text, "")
-	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 := p.scoreDelimiter(lines, delim)
-		if score > bestScore {
-			bestScore = score
-			bestDelim = delim
-		}
-	}
-
-	return bestDelim
-}
-
-// scoreDelimiter uses a count & regularity metric to evaluate a delimiter against lines of CSV
-func (Parser) scoreDelimiter(lines []string, delim rune) (score float64) {
-	countTotal := 0
-	countLineMax := 0
-	linesNotEqual := 0
-
-	for _, line := range lines {
-		if len(line) == 0 {
-			continue
-		}
-
-		countLine := strings.Count(line, string(delim))
-		countTotal += countLine
-		if countLine != countLineMax {
-			if countLineMax != 0 {
-				linesNotEqual++
-			}
-			countLineMax = util.Max(countLine, countLineMax)
-		}
-	}
-
-	return float64(countTotal) * (1 - float64(linesNotEqual)/float64(len(lines)))
-}
--- a/modules/markup/csv/csv_test.go
+++ b/modules/markup/csv/csv_test.go
@@ -13,14 +13,10 @@ import (
 func TestRenderCSV(t *testing.T) {
 	var parser Parser
 	var kases = map[string]string{
-		"a":                         "<table class=\"table\"><tr><td>a</td></tr></table>",
-		"1,2":                       "<table class=\"table\"><tr><td>1</td><td>2</td></tr></table>",
-		"1;2":                       "<table class=\"table\"><tr><td>1</td><td>2</td></tr></table>",
-		"1\t2":                      "<table class=\"table\"><tr><td>1</td><td>2</td></tr></table>",
-		"1|2":                       "<table class=\"table\"><tr><td>1</td><td>2</td></tr></table>",
-		"1,2,3;4,5,6;7,8,9\na;b;c":  "<table class=\"table\"><tr><td>1,2,3</td><td>4,5,6</td><td>7,8,9</td></tr><tr><td>a</td><td>b</td><td>c</td></tr></table>",
-		"\"1,2,3,4\";\"a\nb\"\nc;d": "<table class=\"table\"><tr><td>1,2,3,4</td><td>a\nb</td></tr><tr><td>c</td><td>d</td></tr></table>",
-		"<br/>":                     "<table class=\"table\"><tr><td>&lt;br/&gt;</td></tr></table>",
+		"a":        "<table class=\"data-table\"><tr><th class=\"line-num\">1</th><th>a</th></tr></table>",
+		"1,2":      "<table class=\"data-table\"><tr><th class=\"line-num\">1</th><th>1</th><th>2</th></tr></table>",
+		"1;2\n3;4": "<table class=\"data-table\"><tr><th class=\"line-num\">1</th><th>1</th><th>2</th></tr><tr><td class=\"line-num\">2</td><td>3</td><td>4</td></tr></table>",
+		"<br/>":    "<table class=\"data-table\"><tr><th class=\"line-num\">1</th><th>&lt;br/&gt;</th></tr></table>",
 	}

 	for k, v := range kases {
--- a/modules/markup/sanitizer.go
+++ b/modules/markup/sanitizer.go
@@ -69,6 +69,10 @@ func ReplaceSanitizer() {
 	// Allow icons, emojis, and chroma syntax on span
 	sanitizer.policy.AllowAttrs("class").Matching(regexp.MustCompile(`^((icon(\s+[\p{L}\p{N}_-]+)+)|(emoji))$|^([a-z][a-z0-9]{0,2})$`)).OnElements("span")

+	// Allow data tables
+	sanitizer.policy.AllowAttrs("class").Matching(regexp.MustCompile(`data-table`)).OnElements("table")
+	sanitizer.policy.AllowAttrs("class").Matching(regexp.MustCompile(`line-num`)).OnElements("th", "td")
+
 	// Allow generally safe attributes
 	generalSafeAttrs := []string{"abbr", "accept", "accept-charset",
 		"accesskey", "action", "align", "alt",
--- a/modules/setting/setting.go
+++ b/modules/setting/setting.go
@@ -213,6 +213,10 @@ var (
 			Enabled bool `ini:"ENABLE_RENDER"`
 		} `ini:"ui.svg"`

+		CSV struct {
+			MaxFileSize int64
+		} `ini:"ui.csv"`
+
 		Admin struct {
 			UserPagingNum   int
 			RepoPagingNum   int
@@ -258,6 +262,11 @@ var (
 		}{
 			Enabled: true,
 		},
+		CSV: struct {
+			MaxFileSize int64
+		}{
+			MaxFileSize: 524288,
+		},
 		Admin: struct {
 			UserPagingNum   int
 			RepoPagingNum   int
--- a/options/locale/locale_en-US.ini
+++ b/options/locale/locale_en-US.ini
@@ -1860,6 +1860,7 @@ diff.whitespace_ignore_at_eol = Ignore changes in whitespace at EOL
 diff.stats_desc = <strong> %d changed files</strong> with <strong>%d additions</strong> and <strong>%d deletions</strong>
 diff.stats_desc_file = %d changes: %d additions and %d deletions
 diff.bin = BIN
+diff.bin_not_shown = Binary file not shown.
 diff.view_file = View File
 diff.file_before = Before
 diff.file_after = After
@@ -1960,6 +1961,10 @@ topic.done = Done
 topic.count_prompt = You can not select more than 25 topics
 topic.format_prompt = Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.

+error.csv.too_large = Can't render this file because it is too large.
+error.csv.unexpected = Can't render this file because it contains an unexpected character in line %d and column %d.
+error.csv.invalid_field_count = Can't render this file because it has a wrong number of fields in line %d.
+
 [org]
 org_name_holder = Organization Name
 org_full_name_holder = Organization Full Name
--- a/routers/repo/commit.go
+++ b/routers/repo/commit.go
@@ -336,9 +336,8 @@ func Diff(ctx *context.Context) {
 			return
 		}
 	}
-	setImageCompareContext(ctx, parentCommit, commit)
 	headTarget := path.Join(userName, repoName)
-	setPathsCompareContext(ctx, parentCommit, commit, headTarget)
+	setCompareContext(ctx, parentCommit, commit, headTarget)
 	ctx.Data["Title"] = commit.Summary() + " · " + base.ShortSha(commitID)
 	ctx.Data["Commit"] = commit
 	verification := models.ParseCommitWithSignature(commit)
--- a/routers/repo/compare.go
+++ b/routers/repo/compare.go
@@ -6,14 +6,20 @@ package repo

 import (
 	"bufio"
+	"encoding/csv"
+	"errors"
 	"fmt"
 	"html"
+	"io/ioutil"
 	"path"
+	"path/filepath"
 	"strings"

 	"code.gitea.io/gitea/models"
 	"code.gitea.io/gitea/modules/base"
+	"code.gitea.io/gitea/modules/charset"
 	"code.gitea.io/gitea/modules/context"
+	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/setting"
@@ -26,6 +32,16 @@ const (
 	tplBlobExcerpt base.TplName = "repo/diff/blob_excerpt"
 )

+// setCompareContext sets context data.
+func setCompareContext(ctx *context.Context, base *git.Commit, head *git.Commit, headTarget string) {
+	ctx.Data["BaseCommit"] = base
+	ctx.Data["HeadCommit"] = head
+
+	setPathsCompareContext(ctx, base, head, headTarget)
+	setImageCompareContext(ctx, base, head)
+	setCsvCompareContext(ctx)
+}
+
 // setPathsCompareContext sets context data for source and raw paths
 func setPathsCompareContext(ctx *context.Context, base *git.Commit, head *git.Commit, headTarget string) {
 	sourcePath := setting.AppSubURL + "/%s/src/commit/%s"
@@ -65,6 +81,73 @@ func setImageCompareContext(ctx *context.Context, base *git.Commit, head *git.Co
 	}
 }

+// setCsvCompareContext sets context data that is required by the CSV compare template
+func setCsvCompareContext(ctx *context.Context) {
+	ctx.Data["IsCsvFile"] = func(diffFile *gitdiff.DiffFile) bool {
+		extension := strings.ToLower(filepath.Ext(diffFile.Name))
+		return extension == ".csv" || extension == ".tsv"
+	}
+
+	type CsvDiffResult struct {
+		Sections []*gitdiff.TableDiffSection
+		Error    string
+	}
+
+	ctx.Data["CreateCsvDiff"] = func(diffFile *gitdiff.DiffFile, baseCommit *git.Commit, headCommit *git.Commit) CsvDiffResult {
+		if diffFile == nil || baseCommit == nil || headCommit == nil {
+			return CsvDiffResult{nil, ""}
+		}
+
+		errTooLarge := errors.New(ctx.Locale.Tr("repo.error.csv.too_large"))
+
+		csvReaderFromCommit := func(c *git.Commit) (*csv.Reader, error) {
+			blob, err := c.GetBlobByPath(diffFile.Name)
+			if err != nil {
+				return nil, err
+			}
+
+			if setting.UI.CSV.MaxFileSize != 0 && setting.UI.CSV.MaxFileSize < blob.Size() {
+				return nil, errTooLarge
+			}
+
+			reader, err := blob.DataAsync()
+			if err != nil {
+				return nil, err
+			}
+			defer reader.Close()
+
+			b, err := ioutil.ReadAll(reader)
+			if err != nil {
+				return nil, err
+			}
+
+			b = charset.ToUTF8WithFallback(b)
+
+			return csv_module.CreateReaderAndGuessDelimiter(b), nil
+		}
+
+		baseReader, err := csvReaderFromCommit(baseCommit)
+		if err == errTooLarge {
+			return CsvDiffResult{nil, err.Error()}
+		}
+		headReader, err := csvReaderFromCommit(headCommit)
+		if err == errTooLarge {
+			return CsvDiffResult{nil, err.Error()}
+		}
+
+		sections, err := gitdiff.CreateCsvDiff(diffFile, baseReader, headReader)
+		if err != nil {
+			errMessage, err := csv_module.FormatError(err, ctx.Locale)
+			if err != nil {
+				log.Error("RenderCsvDiff failed: %v", err)
+				return CsvDiffResult{nil, ""}
+			}
+			return CsvDiffResult{nil, errMessage}
+		}
+		return CsvDiffResult{sections, ""}
+	}
+}
+
 // ParseCompareInfo parse compare info between two commit for preparing comparing references
 func ParseCompareInfo(ctx *context.Context) (*models.User, *models.Repository, *git.Repository, *git.CompareInfo, string, string) {
 	baseRepo := ctx.Repo.Repository
@@ -490,9 +573,8 @@ func PrepareCompareDiff(
 	ctx.Data["Username"] = headUser.Name
 	ctx.Data["Reponame"] = headRepo.Name

-	setImageCompareContext(ctx, baseCommit, headCommit)
 	headTarget := path.Join(headUser.Name, repo.Name)
-	setPathsCompareContext(ctx, baseCommit, headCommit, headTarget)
+	setCompareContext(ctx, baseCommit, headCommit, headTarget)

 	return false
 }
--- a/routers/repo/pull.go
+++ b/routers/repo/pull.go
@@ -591,7 +591,6 @@ func ViewPullFiles(ctx *context.Context) {
 		gitRepo       *git.Repository
 	)

-	var headTarget string
 	var prInfo *git.CompareInfo
 	if pull.HasMerged {
 		prInfo = PrepareMergedViewPullInfo(ctx, issue)
@@ -618,7 +617,6 @@ func ViewPullFiles(ctx *context.Context) {
 	startCommitID = prInfo.MergeBase
 	endCommitID = headCommitID

-	headTarget = path.Join(ctx.Repo.Owner.Name, ctx.Repo.Repository.Name)
 	ctx.Data["Username"] = ctx.Repo.Owner.Name
 	ctx.Data["Reponame"] = ctx.Repo.Repository.Name
 	ctx.Data["AfterCommitID"] = endCommitID
@@ -672,8 +670,8 @@ func ViewPullFiles(ctx *context.Context) {
 		}
 	}

-	setImageCompareContext(ctx, baseCommit, commit)
-	setPathsCompareContext(ctx, baseCommit, commit, headTarget)
+	headTarget := path.Join(ctx.Repo.Owner.Name, ctx.Repo.Repository.Name)
+	setCompareContext(ctx, baseCommit, commit, headTarget)

 	ctx.Data["RequireHighlightJS"] = true
 	ctx.Data["RequireSimpleMDE"] = true
--- a/services/gitdiff/csv.go
+++ b/services/gitdiff/csv.go
@@ -0,0 +1,379 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package gitdiff
+
+import (
+	"encoding/csv"
+	"errors"
+	"io"
+
+	"code.gitea.io/gitea/modules/util"
+)
+
+const unmappedColumn = -1
+const maxRowsToInspect int = 10
+const minRatioToMatch float32 = 0.8
+
+// TableDiffCellType represents the type of a TableDiffCell.
+type TableDiffCellType uint8
+
+// TableDiffCellType possible values.
+const (
+	TableDiffCellEqual TableDiffCellType = iota + 1
+	TableDiffCellChanged
+	TableDiffCellAdd
+	TableDiffCellDel
+)
+
+// TableDiffCell represents a cell of a TableDiffRow
+type TableDiffCell struct {
+	LeftCell  string
+	RightCell string
+	Type      TableDiffCellType
+}
+
+// TableDiffRow represents a row of a TableDiffSection.
+type TableDiffRow struct {
+	RowIdx int
+	Cells  []*TableDiffCell
+}
+
+// TableDiffSection represents a section of a DiffFile.
+type TableDiffSection struct {
+	Rows []*TableDiffRow
+}
+
+// csvReader wraps a csv.Reader which buffers the first rows.
+type csvReader struct {
+	reader *csv.Reader
+	buffer [][]string
+	line   int
+	eof    bool
+}
+
+// createCsvReader creates a csvReader and fills the buffer
+func createCsvReader(reader *csv.Reader, bufferRowCount int) (*csvReader, error) {
+	csv := &csvReader{reader: reader}
+	csv.buffer = make([][]string, bufferRowCount)
+	for i := 0; i < bufferRowCount && !csv.eof; i++ {
+		row, err := csv.readNextRow()
+		if err != nil {
+			return nil, err
+		}
+		csv.buffer[i] = row
+	}
+	csv.line = bufferRowCount
+	return csv, nil
+}
+
+// GetRow gets a row from the buffer if present or advances the reader to the requested row. On the end of the file only nil gets returned.
+func (csv *csvReader) GetRow(row int) ([]string, error) {
+	if row < len(csv.buffer) {
+		return csv.buffer[row], nil
+	}
+	if csv.eof {
+		return nil, nil
+	}
+	for {
+		fields, err := csv.readNextRow()
+		if err != nil {
+			return nil, err
+		}
+		if csv.eof {
+			return nil, nil
+		}
+		csv.line++
+		if csv.line-1 == row {
+			return fields, nil
+		}
+	}
+}
+
+func (csv *csvReader) readNextRow() ([]string, error) {
+	if csv.eof {
+		return nil, nil
+	}
+	row, err := csv.reader.Read()
+	if err != nil {
+		if err != io.EOF {
+			return nil, err
+		}
+		csv.eof = true
+	}
+	return row, nil
+}
+
+// CreateCsvDiff creates a tabular diff based on two CSV readers.
+func CreateCsvDiff(diffFile *DiffFile, baseReader *csv.Reader, headReader *csv.Reader) ([]*TableDiffSection, error) {
+	if baseReader != nil && headReader != nil {
+		return createCsvDiff(diffFile, baseReader, headReader)
+	}
+
+	if baseReader != nil {
+		return createCsvDiffSingle(baseReader, TableDiffCellDel)
+	}
+	return createCsvDiffSingle(headReader, TableDiffCellAdd)
+}
+
+// createCsvDiffSingle creates a tabular diff based on a single CSV reader. All cells are added or deleted.
+func createCsvDiffSingle(reader *csv.Reader, celltype TableDiffCellType) ([]*TableDiffSection, error) {
+	var rows []*TableDiffRow
+	i := 1
+	for {
+		row, err := reader.Read()
+		if err != nil {
+			if err == io.EOF {
+				break
+			}
+			return nil, err
+		}
+		cells := make([]*TableDiffCell, len(row))
+		for j := 0; j < len(row); j++ {
+			cells[j] = &TableDiffCell{LeftCell: row[j], Type: celltype}
+		}
+		rows = append(rows, &TableDiffRow{RowIdx: i, Cells: cells})
+		i++
+	}
+
+	return []*TableDiffSection{{Rows: rows}}, nil
+}
+
+func createCsvDiff(diffFile *DiffFile, baseReader *csv.Reader, headReader *csv.Reader) ([]*TableDiffSection, error) {
+	a, err := createCsvReader(baseReader, maxRowsToInspect)
+	if err != nil {
+		return nil, err
+	}
+
+	b, err := createCsvReader(headReader, maxRowsToInspect)
+	if err != nil {
+		return nil, err
+	}
+
+	a2b, b2a := getColumnMapping(a, b)
+
+	columns := len(a2b) + countUnmappedColumns(b2a)
+	if len(a2b) < len(b2a) {
+		columns = len(b2a) + countUnmappedColumns(a2b)
+	}
+
+	createDiffRow := func(aline int, bline int) (*TableDiffRow, error) {
+		cells := make([]*TableDiffCell, columns)
+
+		if aline == 0 || bline == 0 {
+			var (
+				row      []string
+				celltype TableDiffCellType
+				err      error
+			)
+			if bline == 0 {
+				row, err = a.GetRow(aline - 1)
+				celltype = TableDiffCellDel
+			} else {
+				row, err = b.GetRow(bline - 1)
+				celltype = TableDiffCellAdd
+			}
+			if err != nil {
+				return nil, err
+			}
+			if row == nil {
+				return nil, nil
+			}
+			for i := 0; i < len(row); i++ {
+				cells[i] = &TableDiffCell{LeftCell: row[i], Type: celltype}
+			}
+			return &TableDiffRow{RowIdx: bline, Cells: cells}, nil
+		}
+
+		arow, err := a.GetRow(aline - 1)
+		if err != nil {
+			return nil, err
+		}
+		brow, err := b.GetRow(bline - 1)
+		if err != nil {
+			return nil, err
+		}
+		if len(arow) == 0 && len(brow) == 0 {
+			return nil, nil
+		}
+
+		for i := 0; i < len(a2b); i++ {
+			acell, _ := getCell(arow, i)
+			if a2b[i] == unmappedColumn {
+				cells[i] = &TableDiffCell{LeftCell: acell, Type: TableDiffCellDel}
+			} else {
+				bcell, _ := getCell(brow, a2b[i])
+
+				celltype := TableDiffCellChanged
+				if acell == bcell {
+					celltype = TableDiffCellEqual
+				}
+
+				cells[i] = &TableDiffCell{LeftCell: acell, RightCell: bcell, Type: celltype}
+			}
+		}
+		for i := 0; i < len(b2a); i++ {
+			if b2a[i] == unmappedColumn {
+				bcell, _ := getCell(brow, i)
+				cells[i] = &TableDiffCell{LeftCell: bcell, Type: TableDiffCellAdd}
+			}
+		}
+
+		return &TableDiffRow{RowIdx: bline, Cells: cells}, nil
+	}
+
+	var sections []*TableDiffSection
+
+	for i, section := range diffFile.Sections {
+		var rows []*TableDiffRow
+		lines := tryMergeLines(section.Lines)
+		for j, line := range lines {
+			if i == 0 && j == 0 && (line[0] != 1 || line[1] != 1) {
+				diffRow, err := createDiffRow(1, 1)
+				if err != nil {
+					return nil, err
+				}
+				if diffRow != nil {
+					rows = append(rows, diffRow)
+				}
+			}
+			diffRow, err := createDiffRow(line[0], line[1])
+			if err != nil {
+				return nil, err
+			}
+			if diffRow != nil {
+				rows = append(rows, diffRow)
+			}
+		}
+
+		if len(rows) > 0 {
+			sections = append(sections, &TableDiffSection{Rows: rows})
+		}
+	}
+
+	return sections, nil
+}
+
+// getColumnMapping creates a mapping of columns between a and b
+func getColumnMapping(a *csvReader, b *csvReader) ([]int, []int) {
+	arow, _ := a.GetRow(0)
+	brow, _ := b.GetRow(0)
+
+	a2b := []int{}
+	b2a := []int{}
+
+	if arow != nil {
+		a2b = make([]int, len(arow))
+	}
+	if brow != nil {
+		b2a = make([]int, len(brow))
+	}
+
+	for i := 0; i < len(b2a); i++ {
+		b2a[i] = unmappedColumn
+	}
+
+	bcol := 0
+	for i := 0; i < len(a2b); i++ {
+		a2b[i] = unmappedColumn
+
+		acell, ea := getCell(arow, i)
+		if ea == nil {
+			for j := bcol; j < len(b2a); j++ {
+				bcell, eb := getCell(brow, j)
+				if eb == nil && acell == bcell {
+					a2b[i] = j
+					b2a[j] = i
+					bcol = j + 1
+					break
+				}
+			}
+		}
+	}
+
+	tryMapColumnsByContent(a, a2b, b, b2a)
+	tryMapColumnsByContent(b, b2a, a, a2b)
+
+	return a2b, b2a
+}
+
+// tryMapColumnsByContent tries to map missing columns by the content of the first lines.
+func tryMapColumnsByContent(a *csvReader, a2b []int, b *csvReader, b2a []int) {
+	start := 0
+	for i := 0; i < len(a2b); i++ {
+		if a2b[i] == unmappedColumn {
+			if b2a[start] == unmappedColumn {
+				rows := util.Min(maxRowsToInspect, util.Max(0, util.Min(len(a.buffer), len(b.buffer))-1))
+				same := 0
+				for j := 1; j <= rows; j++ {
+					acell, ea := getCell(a.buffer[j], i)
+					bcell, eb := getCell(b.buffer[j], start+1)
+					if ea == nil && eb == nil && acell == bcell {
+						same++
+					}
+				}
+				if (float32(same) / float32(rows)) > minRatioToMatch {
+					a2b[i] = start + 1
+					b2a[start+1] = i
+				}
+			}
+		}
+		start = a2b[i]
+	}
+}
+
+// getCell returns the specific cell or nil if not present.
+func getCell(row []string, column int) (string, error) {
+	if column < len(row) {
+		return row[column], nil
+	}
+	return "", errors.New("Undefined column")
+}
+
+// countUnmappedColumns returns the count of unmapped columns.
+func countUnmappedColumns(mapping []int) int {
+	count := 0
+	for i := 0; i < len(mapping); i++ {
+		if mapping[i] == unmappedColumn {
+			count++
+		}
+	}
+	return count
+}
+
+// tryMergeLines maps the separated line numbers of a git diff. The result is assumed to be ordered.
+func tryMergeLines(lines []*DiffLine) [][2]int {
+	ids := make([][2]int, len(lines))
+
+	i := 0
+	for _, line := range lines {
+		if line.Type != DiffLineSection {
+			ids[i][0] = line.LeftIdx
+			ids[i][1] = line.RightIdx
+			i++
+		}
+	}
+
+	ids = ids[:i]
+
+	result := make([][2]int, len(ids))
+
+	j := 0
+	for i = 0; i < len(ids); i++ {
+		if ids[i][0] == 0 {
+			if j > 0 && result[j-1][1] == 0 {
+				temp := j
+				for temp > 0 && result[temp-1][1] == 0 {
+					temp--
+				}
+				result[temp][1] = ids[i][1]
+				continue
+			}
+		}
+		result[j] = ids[i]
+		j++
+	}
+
+	return result[:j]
+}
--- a/services/gitdiff/csv_test.go
+++ b/services/gitdiff/csv_test.go
@@ -0,0 +1,119 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package gitdiff
+
+import (
+	"encoding/csv"
+	"strings"
+	"testing"
+
+	csv_module "code.gitea.io/gitea/modules/csv"
+	"code.gitea.io/gitea/modules/setting"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCSVDiff(t *testing.T) {
+	var cases = []struct {
+		diff  string
+		base  string
+		head  string
+		cells [][2]TableDiffCellType
+	}{
+		// case 0
+		{
+			diff: `diff --git a/unittest.csv b/unittest.csv
+--- a/unittest.csv
+++ b/unittest.csv
+@@ -0,0 +1,2 @@
+col1,col2
+a,a`,
+			base:  "",
+			head:  "col1,col2\na,a",
+			cells: [][2]TableDiffCellType{{TableDiffCellAdd, TableDiffCellAdd}, {TableDiffCellAdd, TableDiffCellAdd}},
+		},
+		// case 1
+		{
+			diff: `diff --git a/unittest.csv b/unittest.csv
+--- a/unittest.csv
+++ b/unittest.csv
+@@ -1,2 +1,3 @@
+ col1,col2
+-a,a
+a,a
+b,b`,
+			base:  "col1,col2\na,a",
+			head:  "col1,col2\na,a\nb,b",
+			cells: [][2]TableDiffCellType{{TableDiffCellEqual, TableDiffCellEqual}, {TableDiffCellEqual, TableDiffCellEqual}, {TableDiffCellAdd, TableDiffCellAdd}},
+		},
+		// case 2
+		{
+			diff: `diff --git a/unittest.csv b/unittest.csv
+--- a/unittest.csv
+++ b/unittest.csv
+@@ -1,3 +1,2 @@
+ col1,col2
+-a,a
+ b,b`,
+			base:  "col1,col2\na,a\nb,b",
+			head:  "col1,col2\nb,b",
+			cells: [][2]TableDiffCellType{{TableDiffCellEqual, TableDiffCellEqual}, {TableDiffCellDel, TableDiffCellDel}, {TableDiffCellEqual, TableDiffCellEqual}},
+		},
+		// case 3
+		{
+			diff: `diff --git a/unittest.csv b/unittest.csv
+--- a/unittest.csv
+++ b/unittest.csv
+@@ -1,2 +1,2 @@
+ col1,col2
+-b,b
+b,c`,
+			base:  "col1,col2\nb,b",
+			head:  "col1,col2\nb,c",
+			cells: [][2]TableDiffCellType{{TableDiffCellEqual, TableDiffCellEqual}, {TableDiffCellEqual, TableDiffCellChanged}},
+		},
+		// case 4
+		{
+			diff: `diff --git a/unittest.csv b/unittest.csv
+--- a/unittest.csv
+++ b/unittest.csv
+@@ -1,2 +0,0 @@
+-col1,col2
+-b,c`,
+			base:  "col1,col2\nb,c",
+			head:  "",
+			cells: [][2]TableDiffCellType{{TableDiffCellDel, TableDiffCellDel}, {TableDiffCellDel, TableDiffCellDel}},
+		},
+	}
+
+	for n, c := range cases {
+		diff, err := ParsePatch(setting.Git.MaxGitDiffLines, setting.Git.MaxGitDiffLineCharacters, setting.Git.MaxGitDiffFiles, strings.NewReader(c.diff))
+		if err != nil {
+			t.Errorf("ParsePatch failed: %s", err)
+		}
+
+		var baseReader *csv.Reader
+		if len(c.base) > 0 {
+			baseReader = csv_module.CreateReaderAndGuessDelimiter([]byte(c.base))
+		}
+		var headReader *csv.Reader
+		if len(c.head) > 0 {
+			headReader = csv_module.CreateReaderAndGuessDelimiter([]byte(c.head))
+		}
+
+		result, err := CreateCsvDiff(diff.Files[0], baseReader, headReader)
+		assert.NoError(t, err)
+		assert.Equal(t, 1, len(result), "case %d: should be one section", n)
+
+		section := result[0]
+		assert.Equal(t, len(c.cells), len(section.Rows), "case %d: should be %d rows", n, len(c.cells))
+
+		for i, row := range section.Rows {
+			assert.Equal(t, 2, len(row.Cells), "case %d: row %d should have two cells", n, i)
+			for j, cell := range row.Cells {
+				assert.Equal(t, c.cells[i][j], cell.Type, "case %d: row %d cell %d should be equal", n, i, j)
+			}
+		}
+	}
+}
--- a/templates/repo/diff/box.tmpl
+++ b/templates/repo/diff/box.tmpl
@@ -79,6 +79,8 @@
 							{{else}}
 								{{$isImage = (call $.IsImageFileInHead $file.Name)}}
 							{{end}}
+							{{$isCsv := (call $.IsCsvFile $file)}}
+							{{$showFileViewToggle := or $isImage $isCsv}}
 							<a role="button" class="fold-file muted mr-2">
 								{{svg "octicon-chevron-down" 18}}
 							</a>
@@ -92,6 +94,12 @@
 							<span class="file mono">{{if $file.IsRenamed}}{{$file.OldName}} &rarr; {{end}}{{$file.Name}}{{if .IsLFSFile}} ({{$.i18n.Tr "repo.stored_lfs"}}){{end}}</span>
 						</div>
 						<div class="diff-file-header-actions df ac">
+							{{if $showFileViewToggle}}
+								<div class="ui compact icon buttons">
+									<span class="ui tiny basic button poping up active file-view-toggle" data-toggle-selector="#diff-source-{{$i}}" data-content="{{$.i18n.Tr "repo.file_view_source"}}" data-position="bottom center" data-variation="tiny inverted">{{svg "octicon-code"}}</span>
+									<span class="ui tiny basic button poping up file-view-toggle" data-toggle-selector="#diff-rendered-{{$i}}" data-content="{{$.i18n.Tr "repo.file_view_rendered"}}" data-position="bottom center" data-variation="tiny inverted">{{svg "octicon-file"}}</span>
+								</div>
+							{{end}}
 							{{if $file.IsProtected}}
 								<span class="ui basic label">{{$.i18n.Tr "repo.diff.protected"}}</span>
 							{{end}}
@@ -106,21 +114,30 @@
 					</h4>
 					<div class="diff-file-body ui attached unstackable table segment">
 						{{if ne $file.Type 4}}
-							<div class="file-body file-code has-context-menu{{if not $isImage}} code-diff{{end}}{{if $.IsSplitStyle}} code-diff-split{{else}} code-diff-unified{{end}}{{if $isImage}} py-4{{end}}">
-								<table class="chroma{{if $isImage}} w-100{{end}}">
-									<tbody>
-										{{if $isImage}}
-											{{template "repo/diff/image_diff" dict "file" . "root" $}}
-										{{else}}
-											{{if $.IsSplitStyle}}
-												{{template "repo/diff/section_split" dict "file" . "root" $}}
-											{{else}}
-												{{template "repo/diff/section_unified" dict "file" . "root" $}}
-											{{end}}
-										{{end}}
-									</tbody>
+							<div id="diff-source-{{$i}}" class="file-body file-code has-context-menu code-diff{{if $.IsSplitStyle}} code-diff-split{{else}} code-diff-unified{{end}}">
+								{{if $file.IsBin}}
+								<div class="diff-file-body binary" style="padding: 5px 10px;">{{$.i18n.Tr "repo.diff.bin_not_shown"}}</div>
+								{{else}}
+								<table class="chroma">
+									{{if $.IsSplitStyle}}
+										{{template "repo/diff/section_split" dict "file" . "root" $}}
+									{{else}}
+										{{template "repo/diff/section_unified" dict "file" . "root" $}}
+									{{end}}
+								</table>
+								{{end}}
+							</div>
+							{{if or $isImage $isCsv}}
+							<div id="diff-rendered-{{$i}}" class="file-body file-code has-context-menu{{if $.IsSplitStyle}} code-diff-split{{else}} code-diff-unified{{end}} hide">
+								<table class="chroma w-100">
+									{{if $isImage}}
+										{{template "repo/diff/image_diff" dict "file" . "root" $}}
+									{{else}}
+										{{template "repo/diff/csv_diff" dict "file" . "root" $}}
+									{{end}}
 								</table>
 							</div>
+							{{end}}
 						{{end}}
 					</div>
 				</div>
--- a/templates/repo/diff/csv_diff.tmpl
+++ b/templates/repo/diff/csv_diff.tmpl
@@ -0,0 +1,46 @@
+<tr>
+	<td>
+		{{$result := call .root.CreateCsvDiff .file .root.BaseCommit .root.HeadCommit}}
+		{{if $result.Error}}
+			<div class="ui center">{{$result.Error}}</div>
+		{{else if $result.Sections}}
+			<table class="data-table">
+			{{range $i, $section := $result.Sections}}
+				<tbody {{if gt $i 0}}class="section"{{end}}>
+				{{range $j, $row := $section.Rows}}
+					<tr>
+						{{if and (eq $i 0) (eq $j 0)}}
+							<th class="line-num">{{.RowIdx}}</th>
+							{{range $j, $cell := $row.Cells}}
+								{{if eq $cell.Type 2}}
+									<th class="modified"><span class="removed-code">{{.LeftCell}}</span> <span class="added-code">{{.RightCell}}</span></th>
+								{{else if eq $cell.Type 3}}
+									<th class="added"><span class="added-code">{{.LeftCell}}</span></th>
+								{{else if eq $cell.Type 4}}
+									<th class="removed"><span class="removed-code">{{.LeftCell}}</span></th>
+								{{else}}
+									<th>{{.RightCell}}</th>
+								{{end}}
+							{{end}}
+						{{else}}
+							<td class="line-num">{{if .RowIdx}}{{.RowIdx}}{{end}}</td>
+							{{range $j, $cell := $row.Cells}}
+								{{if eq $cell.Type 2}}
+									<td class="modified"><span class="removed-code">{{.LeftCell}}</span> <span class="added-code">{{.RightCell}}</span></td>
+								{{else if eq $cell.Type 3}}
+									<td class="added"><span class="added-code">{{.LeftCell}}</span></td>
+								{{else if eq $cell.Type 4}}
+									<td class="removed"><span class="removed-code">{{.LeftCell}}</span></td>
+								{{else}}
+									<td>{{.RightCell}}</td>
+								{{end}}
+							{{end}}
+						{{end}}
+					</tr>
+				{{end}}
+				</tbody>
+			{{end}}
+			</table>
+		{{end}}
+	</td>
+</tr>
--- a/templates/repo/view_file.tmpl
+++ b/templates/repo/view_file.tmpl
@@ -64,7 +64,7 @@
 		{{end}}
 	</h4>
 	<div class="ui attached table unstackable segment">
-		<div class="file-view {{if .IsMarkup}}{{.MarkupType}} markdown{{else if .IsRenderedHTML}}plain-text{{else if .IsTextSource}}code-view{{end}}">
+		<div class="file-view {{if .IsMarkup}}{{.MarkupType}} {{if ne "csv" .MarkupType}}markdown{{end}}{{else if .IsRenderedHTML}}plain-text{{else if .IsTextSource}}code-view{{end}}">
 			{{if .IsMarkup}}
 				{{if .FileContent}}{{.FileContent | Safe}}{{end}}
 			{{else if .IsRenderedHTML}}
--- a/web_src/js/index.js
+++ b/web_src/js/index.js
@@ -2489,6 +2489,18 @@ function initIssueReferenceRepositorySearch() {
    });
 }

+function initFileViewToggle() {
+  $('.file-view-toggle').on('click', function() {
+    const $this = $(this);
+    $this.parent().children().removeClass('active');
+    $this.addClass('active');
+
+    const $target = $($this.data('toggle-selector'));
+    $target.parent().children().addClass('hide');
+    $target.removeClass('hide');
+  });
+}
+
 function initLinkAccountView() {
  const $lnkUserPage = $('.page-content.user.link-account');
  if ($lnkUserPage.length === 0) {
@@ -2756,6 +2768,7 @@ $(document).ready(async () => {
  initTableSort();
  initNotificationsTable();
  initPullRequestMergeInstruction();
+  initFileViewToggle();
  initReleaseEditor();
  initRelease();

--- a/web_src/less/_markdown.less
+++ b/web_src/less/_markdown.less
@@ -473,31 +473,6 @@
    box-shadow: inset 0 -1px 0 var(--color-secondary);
  }

-  .csv-data td,
-  .csv-data th {
-    padding: 5px;
-    overflow: hidden;
-    font-size: 12px;
-    line-height: 1;
-    text-align: left;
-    white-space: nowrap;
-  }
-
-  .csv-data .blob-num {
-    padding: 10px 8px 9px;
-    text-align: right;
-    border: 0;
-  }
-
-  .csv-data tr {
-    border-top: 0;
-  }
-
-  .csv-data th {
-    font-weight: 600;
-    border-top: 0;
-  }
-
  .ui.list .list,
  ol.ui.list ol,
  ul.ui.list ul {
--- a/web_src/less/_repository.less
+++ b/web_src/less/_repository.less
@@ -1455,6 +1455,65 @@
    }
  }

+  .data-table {
+    width: 100%;
+
+    tr {
+      border-top: 0;
+    }
+
+    td,
+    th {
+      padding: 5px !important;
+      overflow: hidden;
+      font-size: 12px;
+      text-align: left;
+      white-space: nowrap;
+      border: 1px solid var(--color-secondary);
+    }
+
+    td {
+      white-space: pre-line;
+    }
+
+    th {
+      font-weight: 600;
+      background: var(--color-box-header);
+      border-top: 0;
+    }
+
+    td.added,
+    th.added,
+    tr.added {
+      background-color: var(--color-diff-added-row-bg) !important;
+    }
+
+    td.removed,
+    th.removed,
+    tr.removed {
+      background-color: var(--color-diff-removed-row-bg) !important;
+    }
+
+    tbody.section {
+      border-top: 2px solid var(--color-secondary);
+    }
+
+    .line-num {
+      width: 1%;
+      min-width: 50px;
+      font-family: monospace;
+      line-height: 20px;
+      color: var(--color-secondary-dark-2);
+      white-space: nowrap;
+      vertical-align: top;
+      cursor: pointer;
+      user-select: none;
+      text-align: right;
+      background: var(--color-body);
+      border: 0;
+    }
+  }
+
  .diff-detail-box {
    padding: 7px 0;
    background: var(--color-body);