1 files changed, 211 insertions, 0 deletions
diff --git a/modules/charset/charset.go b/modules/charset/charset.go
new file mode 100644
index 0000000..1855446
--- /dev/null
+++ b/modules/charset/charset.go
@@ -0,0 +1,211 @@
+// Copyright 2014 The Gogs Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package charset
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"strings"
+	"unicode/utf8"
+
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/util"
+
+	"github.com/gogs/chardet"
+	"golang.org/x/net/html/charset"
+	"golang.org/x/text/transform"
+)
+
+// UTF8BOM is the utf-8 byte-order marker
+var UTF8BOM = []byte{'\xef', '\xbb', '\xbf'}
+
+type ConvertOpts struct {
+	KeepBOM bool
+}
+
+// ToUTF8WithFallbackReader detects the encoding of content and converts to UTF-8 reader if possible
+func ToUTF8WithFallbackReader(rd io.Reader, opts ConvertOpts) io.Reader {
+	buf := make([]byte, 2048)
+	n, err := util.ReadAtMost(rd, buf)
+	if err != nil {
+		return io.MultiReader(bytes.NewReader(MaybeRemoveBOM(buf[:n], opts)), rd)
+	}
+
+	charsetLabel, err := DetectEncoding(buf[:n])
+	if err != nil || charsetLabel == "UTF-8" {
+		return io.MultiReader(bytes.NewReader(MaybeRemoveBOM(buf[:n], opts)), rd)
+	}
+
+	encoding, _ := charset.Lookup(charsetLabel)
+	if encoding == nil {
+		return io.MultiReader(bytes.NewReader(buf[:n]), rd)
+	}
+
+	return transform.NewReader(
+		io.MultiReader(
+			bytes.NewReader(MaybeRemoveBOM(buf[:n], opts)),
+			rd,
+		),
+		encoding.NewDecoder(),
+	)
+}
+
+// ToUTF8 converts content to UTF8 encoding
+func ToUTF8(content []byte, opts ConvertOpts) (string, error) {
+	charsetLabel, err := DetectEncoding(content)
+	if err != nil {
+		return "", err
+	} else if charsetLabel == "UTF-8" {
+		return string(MaybeRemoveBOM(content, opts)), nil
+	}
+
+	encoding, _ := charset.Lookup(charsetLabel)
+	if encoding == nil {
+		return string(content), fmt.Errorf("Unknown encoding: %s", charsetLabel)
+	}
+
+	// If there is an error, we concatenate the nicely decoded part and the
+	// original left over. This way we won't lose much data.
+	result, n, err := transform.Bytes(encoding.NewDecoder(), content)
+	if err != nil {
+		result = append(result, content[n:]...)
+	}
+
+	result = MaybeRemoveBOM(result, opts)
+
+	return string(result), err
+}
+
+// ToUTF8WithFallback detects the encoding of content and converts to UTF-8 if possible
+func ToUTF8WithFallback(content []byte, opts ConvertOpts) []byte {
+	bs, _ := io.ReadAll(ToUTF8WithFallbackReader(bytes.NewReader(content), opts))
+	return bs
+}
+
+// ToUTF8DropErrors makes sure the return string is valid utf-8; attempts conversion if possible
+func ToUTF8DropErrors(content []byte, opts ConvertOpts) []byte {
+	charsetLabel, err := DetectEncoding(content)
+	if err != nil || charsetLabel == "UTF-8" {
+		return MaybeRemoveBOM(content, opts)
+	}
+
+	encoding, _ := charset.Lookup(charsetLabel)
+	if encoding == nil {
+		return content
+	}
+
+	// We ignore any non-decodable parts from the file.
+	// Some parts might be lost
+	var decoded []byte
+	decoder := encoding.NewDecoder()
+	idx := 0
+	for {
+		result, n, err := transform.Bytes(decoder, content[idx:])
+		decoded = append(decoded, result...)
+		if err == nil {
+			break
+		}
+		decoded = append(decoded, ' ')
+		idx = idx + n + 1
+		if idx >= len(content) {
+			break
+		}
+	}
+
+	return MaybeRemoveBOM(decoded, opts)
+}
+
+// MaybeRemoveBOM removes a UTF-8 BOM from a []byte when opts.KeepBOM is false
+func MaybeRemoveBOM(content []byte, opts ConvertOpts) []byte {
+	if opts.KeepBOM {
+		return content
+	}
+	if len(content) > 2 && bytes.Equal(content[0:3], UTF8BOM) {
+		return content[3:]
+	}
+	return content
+}
+
+// DetectEncoding detect the encoding of content
+func DetectEncoding(content []byte) (string, error) {
+	// First we check if the content represents valid utf8 content excepting a truncated character at the end.
+
+	// Now we could decode all the runes in turn but this is not necessarily the cheapest thing to do
+	// instead we walk backwards from the end to trim off a the incomplete character
+	toValidate := content
+	end := len(toValidate) - 1
+
+	if end < 0 {
+		// no-op
+	} else if toValidate[end]>>5 == 0b110 {
+		// Incomplete 1 byte extension e.g. © <c2><a9> which has been truncated to <c2>
+		toValidate = toValidate[:end]
+	} else if end > 0 && toValidate[end]>>6 == 0b10 && toValidate[end-1]>>4 == 0b1110 {
+		// Incomplete 2 byte extension e.g. ⛔ <e2><9b><94> which has been truncated to <e2><9b>
+		toValidate = toValidate[:end-1]
+	} else if end > 1 && toValidate[end]>>6 == 0b10 && toValidate[end-1]>>6 == 0b10 && toValidate[end-2]>>3 == 0b11110 {
+		// Incomplete 3 byte extension e.g. 💩 <f0><9f><92><a9> which has been truncated to <f0><9f><92>
+		toValidate = toValidate[:end-2]
+	}
+	if utf8.Valid(toValidate) {
+		log.Debug("Detected encoding: utf-8 (fast)")
+		return "UTF-8", nil
+	}
+
+	textDetector := chardet.NewTextDetector()
+	var detectContent []byte
+	if len(content) < 1024 {
+		// Check if original content is valid
+		if _, err := textDetector.DetectBest(content); err != nil {
+			return "", err
+		}
+		times := 1024 / len(content)
+		detectContent = make([]byte, 0, times*len(content))
+		for i := 0; i < times; i++ {
+			detectContent = append(detectContent, content...)
+		}
+	} else {
+		detectContent = content
+	}
+
+	// Now we can't use DetectBest or just results[0] because the result isn't stable - so we need a tie break
+	results, err := textDetector.DetectAll(detectContent)
+	if err != nil {
+		if err == chardet.NotDetectedError && len(setting.Repository.AnsiCharset) > 0 {
+			log.Debug("Using default AnsiCharset: %s", setting.Repository.AnsiCharset)
+			return setting.Repository.AnsiCharset, nil
+		}
+		return "", err
+	}
+
+	topConfidence := results[0].Confidence
+	topResult := results[0]
+	priority, has := setting.Repository.DetectedCharsetScore[strings.ToLower(strings.TrimSpace(topResult.Charset))]
+	for _, result := range results {
+		// As results are sorted in confidence order - if we have a different confidence
+		// we know it's less than the current confidence and can break out of the loop early
+		if result.Confidence != topConfidence {
+			break
+		}
+
+		// Otherwise check if this results is earlier in the DetectedCharsetOrder than our current top guess
+		resultPriority, resultHas := setting.Repository.DetectedCharsetScore[strings.ToLower(strings.TrimSpace(result.Charset))]
+		if resultHas && (!has || resultPriority < priority) {
+			topResult = result
+			priority = resultPriority
+			has = true
+		}
+	}
+
+	// FIXME: to properly decouple this function the fallback ANSI charset should be passed as an argument
+	if topResult.Charset != "UTF-8" && len(setting.Repository.AnsiCharset) > 0 {
+		log.Debug("Using default AnsiCharset: %s", setting.Repository.AnsiCharset)
+		return setting.Repository.AnsiCharset, err
+	}
+
+	log.Debug("Detected encoding: %s", topResult.Charset)
+	return topResult.Charset, err
+}