Fix CSV rendering (go-gitea#29663)

Fixes go-gitea#29663
Previously, when a CSV file was larger than the limit, the render function lost its function to render the code. There were also multiple reads to the file, in order to determine its size and render or pre-render.
This solution implements a new config variable MAX_ROWS, which corresponds to the “Maximum allowed rows to render CSV files. (0 for no limit)” and rewrites the Render function for CSV files in markup module. Now the render function only reads the file once, having MAX_FILE_SIZE+1 as a reader limit and MAX_ROWS as a row limit. When the file is larger than MAX_FILE_SIZE or has more rows than MAX_ROWS, it only renders until the limit, and displays a user-friendly warning informing that the rendered data is not complete, in the user's language.
The warning: ![image](https://s3.amazonaws.com/i.snag.gy/ieROGx.jpg)

custom/conf/app.example.ini

@@ -1333,6 +1333,9 @@ LEVEL = Info
 ;;
 ;; Maximum allowed file size in bytes to render CSV files as table. (Set to 0 for no limit).
 ;MAX_FILE_SIZE = 524288
+;;
+;; Maximum allowed rows to render CSV files. (Set to 0 for no limit)
+;MAX_ROWS = 2000
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

modules/markup/csv/csv.go

@@ -5,8 +5,6 @@ package markup
 
 import (
 	"bufio"
-	"bytes"
-	"fmt"
 	"html"
 	"io"
 	"regexp"
@@ -15,6 +13,7 @@ import (
 	"code.gitea.io/gitea/modules/csv"
 	"code.gitea.io/gitea/modules/markup"
 	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/translation"
 )
 
 func init() {
@@ -40,6 +39,8 @@ func (Renderer) SanitizerRules() []setting.MarkupSanitizerRule {
 		{Element: "table", AllowAttr: "class", Regexp: regexp.MustCompile(`data-table`)},
 		{Element: "th", AllowAttr: "class", Regexp: regexp.MustCompile(`line-num`)},
 		{Element: "td", AllowAttr: "class", Regexp: regexp.MustCompile(`line-num`)},
+		{Element: "div", AllowAttr: "class", Regexp: regexp.MustCompile(`ui top attached warning message`)},
+		{Element: "a", AllowAttr: "href", Regexp: regexp.MustCompile(`\?display=source`)},
 	}
 }
 
@@ -80,79 +81,32 @@ func writeField(w io.Writer, element, class, field string) error {
 // Render implements markup.Renderer
 func (r Renderer) Render(ctx *markup.RenderContext, input io.Reader, output io.Writer) error {
 	tmpBlock := bufio.NewWriter(output)
+	warnBlock := bufio.NewWriter(tmpBlock)
 	maxSize := setting.UI.CSV.MaxFileSize
+	maxRows := setting.UI.CSV.MaxRows
 
-	if maxSize == 0 {
-		return r.tableRender(ctx, input, tmpBlock)
+	if maxSize != 0 {
+		input = io.LimitReader(input, maxSize+1)
 	}
 
-	rawBytes, err := io.ReadAll(io.LimitReader(input, maxSize+1))
-	if err != nil {
-		return err
-	}
-
-	if int64(len(rawBytes)) <= maxSize {
-		return r.tableRender(ctx, bytes.NewReader(rawBytes), tmpBlock)
-	}
-	return r.fallbackRender(io.MultiReader(bytes.NewReader(rawBytes), input), tmpBlock)
-}
-
-func (Renderer) fallbackRender(input io.Reader, tmpBlock *bufio.Writer) error {
-	_, err := tmpBlock.WriteString("<pre>")
-	if err != nil {
-		return err
-	}
-
-	scan := bufio.NewScanner(input)
-	scan.Split(bufio.ScanRunes)
-	for scan.Scan() {
-		switch scan.Text() {
-		case `&`:
-			_, err = tmpBlock.WriteString("&amp;")
-		case `'`:
-			_, err = tmpBlock.WriteString("&#39;") // "&#39;" is shorter than "&apos;" and apos was not in HTML until HTML5.
-		case `<`:
-			_, err = tmpBlock.WriteString("&lt;")
-		case `>`:
-			_, err = tmpBlock.WriteString("&gt;")
-		case `"`:
-			_, err = tmpBlock.WriteString("&#34;") // "&#34;" is shorter than "&quot;".
-		default:
-			_, err = tmpBlock.Write(scan.Bytes())
-		}
-		if err != nil {
-			return err
-		}
-	}
-	if err = scan.Err(); err != nil {
-		return fmt.Errorf("fallbackRender scan: %w", err)
-	}
-
-	_, err = tmpBlock.WriteString("</pre>")
-	if err != nil {
-		return err
-	}
-	return tmpBlock.Flush()
-}
-
-func (Renderer) tableRender(ctx *markup.RenderContext, input io.Reader, tmpBlock *bufio.Writer) error {
 	rd, err := csv.CreateReaderAndDetermineDelimiter(ctx, input)
 	if err != nil {
 		return err
 	}
-
 	if _, err := tmpBlock.WriteString(`<table class="data-table">`); err != nil {
 		return err
 	}
+
 	row := 1
 	for {
 		fields, err := rd.Read()
-		if err == io.EOF {
+		if err == io.EOF || (row >= maxRows && maxRows != 0) {
 			break
 		}
 		if err != nil {
 			continue
 		}
+
 		if _, err := tmpBlock.WriteString("<tr>"); err != nil {
 			return err
 		}
@@ -174,6 +128,22 @@ func (Renderer) tableRender(ctx *markup.RenderContext, input io.Reader, tmpBlock
 
 		row++
 	}
+
+	// Check if maxRows or maxSize is reached, and if true, warn.
+	if (row >= maxRows && maxRows != 0) || (rd.InputOffset() >= maxSize && maxSize != 0) {
+		locale := ctx.Ctx.Value(translation.ContextKey).(translation.Locale)
+
+		// Construct the HTML string
+		warn := string(`<div class="ui top attached warning message" tabindex="0">` + locale.TrString("repo.file_too_large") + ` <b><a class="source" href="?display=source">` + locale.TrString("repo.file_view_source") + `</a></b></div>`)
+
+		// Write the HTML string to the output
+		if _, err := warnBlock.WriteString(warn); err != nil {
+			return err
+		}
+		if err = warnBlock.Flush(); err != nil {
+			return err
+		}
+	}
 	if _, err = tmpBlock.WriteString("</table>"); err != nil {
 		return err
 	}

modules/markup/csv/csv_test.go

@@ -4,8 +4,6 @@
 package markup
 
 import (
-	"bufio"
-	"bytes"
 	"strings"
 	"testing"
 
@@ -31,12 +29,4 @@ func TestRenderCSV(t *testing.T) {
 		assert.NoError(t, err)
 		assert.EqualValues(t, v, buf.String())
 	}
-
-	t.Run("fallbackRender", func(t *testing.T) {
-		var buf bytes.Buffer
-		err := render.fallbackRender(strings.NewReader("1,<a>\n2,<b>"), bufio.NewWriter(&buf))
-		assert.NoError(t, err)
-		want := "<pre>1,&lt;a&gt;\n2,&lt;b&gt;</pre>"
-		assert.Equal(t, want, buf.String())
-	})
 }

modules/setting/ui.go

@@ -52,6 +52,7 @@ var UI = struct {
 
 	CSV struct {
 		MaxFileSize int64
+		MaxRows     int
 	} `ini:"ui.csv"`
 
 	Admin struct {
@@ -108,8 +109,10 @@ var UI = struct {
 	},
 	CSV: struct {
 		MaxFileSize int64
+		MaxRows     int
 	}{
 		MaxFileSize: 524288,
+		MaxRows:     2000,
 	},
 	Admin: struct {
 		UserPagingNum   int