1 files changed, 149 insertions, 0 deletions
diff --git a/modules/csv/csv.go b/modules/csv/csv.go
new file mode 100644
index 00000000..35c5d6ab
--- /dev/null
+++ b/modules/csv/csv.go
@@ -0,0 +1,149 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package csv
+
+import (
+	"bytes"
+	stdcsv "encoding/csv"
+	"io"
+	"path/filepath"
+	"regexp"
+	"strings"
+
+	"code.gitea.io/gitea/modules/markup"
+	"code.gitea.io/gitea/modules/translation"
+	"code.gitea.io/gitea/modules/util"
+)
+
+const (
+	maxLines        = 10
+	guessSampleSize = 1e4 // 10k
+)
+
+// CreateReader creates a csv.Reader with the given delimiter.
+func CreateReader(input io.Reader, delimiter rune) *stdcsv.Reader {
+	rd := stdcsv.NewReader(input)
+	rd.Comma = delimiter
+	if delimiter != '\t' && delimiter != ' ' {
+		// TrimLeadingSpace can't be true when delimiter is a tab or a space as the value for a column might be empty,
+		// thus would change `\t\t` to just `\t` or `  ` (two spaces) to just ` ` (single space)
+		rd.TrimLeadingSpace = true
+	}
+	return rd
+}
+
+// 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) {
+	data := make([]byte, guessSampleSize)
+	size, err := util.ReadAtMost(rd, data)
+	if err != nil {
+		return nil, err
+	}
+
+	return CreateReader(
+		io.MultiReader(bytes.NewReader(data[:size]), rd),
+		determineDelimiter(ctx, data[:size]),
+	), nil
+}
+
+// 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.RelativePath))
+	}
+
+	var delimiter rune
+	switch extension {
+	case ".tsv":
+		delimiter = '\t'
+	case ".psv":
+		delimiter = '|'
+	default:
+		delimiter = guessDelimiter(data)
+	}
+
+	return delimiter
+}
+
+// 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(`"[^"]*"`)
+
+// 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
+	}
+
+	// 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]
+	}
+
+	// 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 validDelim
+}
+
+// FormatError converts csv errors into readable messages.
+func FormatError(err error, locale translation.Locale) (string, error) {
+	if perr, ok := err.(*stdcsv.ParseError); ok {
+		if perr.Err == stdcsv.ErrFieldCount {
+			return locale.TrString("repo.error.csv.invalid_field_count", perr.Line), nil
+		}
+		return locale.TrString("repo.error.csv.unexpected", perr.Line, perr.Column), nil
+	}
+
+	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
+}