Fix chardet test and add ordering option (#11621)

* Fix chardet test and add ordering option

Signed-off-by: Andrew Thornton <art27@cantab.net>

* minor fixes

Signed-off-by: Andrew Thornton <art27@cantab.net>

* remove log

Signed-off-by: Andrew Thornton <art27@cantab.net>

* remove log2

Signed-off-by: Andrew Thornton <art27@cantab.net>

* only iterate through top results

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Update docs/content/doc/advanced/config-cheat-sheet.en-us.md

* slight restructure of for loop

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

5 files changed, 117 insertions, 6 deletions

diff --git a/custom/conf/app.ini.sample b/custom/conf/app.ini.sample
index 5e150172d5..4f5529edfa 100644
--- a/custom/conf/app.ini.sample
+++ b/custom/conf/app.ini.sample
@@ -14,7 +14,12 @@ RUN_MODE = dev
 [repository]
 ROOT =
 SCRIPT_TYPE = bash
-; Default ANSI charset
+; DETECTED_CHARSETS_ORDER tie-break order for detected charsets.
+; If the charsets have equal confidence, tie-breaking will be done by order in this list
+; with charsets earlier in the list chosen in preference to those later.
+; Adding "defaults" will place the unused charsets at that position. 
+DETECTED_CHARSETS_ORDER=UTF-8, UTF-16BE, UTF-16LE, UTF-32BE, UTF-32LE, ISO-8859, windows-1252, ISO-8859, windows-1250, ISO-8859, ISO-8859, ISO-8859, windows-1253, ISO-8859, windows-1255, ISO-8859, windows-1251, windows-1256, KOI8-R, ISO-8859, windows-1254, Shift_JIS, GB18030, EUC-JP, EUC-KR, Big5, ISO-2022, ISO-2022, ISO-2022, IBM424_rtl, IBM424_ltr, IBM420_rtl, IBM420_ltr
+; Default ANSI charset to override non-UTF-8 charsets to
 ANSI_CHARSET =
 ; Force every new repository to be private
 FORCE_PRIVATE = false
diff --git a/docs/content/doc/advanced/config-cheat-sheet.en-us.md b/docs/content/doc/advanced/config-cheat-sheet.en-us.md
index f0908c22a3..c29151f648 100644
--- a/docs/content/doc/advanced/config-cheat-sheet.en-us.md
+++ b/docs/content/doc/advanced/config-cheat-sheet.en-us.md
@@ -46,7 +46,8 @@ Values containing `#` or `;` must be quoted using `` ` `` or `"""`.
    an absolute path.
 - `SCRIPT_TYPE`: **bash**: The script type this server supports. Usually this is `bash`,
    but some users report that only `sh` is available.
-- `ANSI_CHARSET`: **\<empty\>**: The default charset for an unrecognized charset.
+- `DETECTED_CHARSETS_ORDER`: **UTF-8, UTF-16BE, UTF-16LE, UTF-32BE, UTF-32LE, ISO-8859, windows-1252, ISO-8859, windows-1250, ISO-8859, ISO-8859, ISO-8859, windows-1253, ISO-8859, windows-1255, ISO-8859, windows-1251, windows-1256, KOI8-R, ISO-8859, windows-1254, Shift_JIS, GB18030, EUC-JP, EUC-KR, Big5, ISO-2022, ISO-2022, ISO-2022, IBM424_rtl, IBM424_ltr, IBM420_rtl, IBM420_ltr**: Tie-break order of detected charsets - if the detected charsets have equal confidence, charsets earlier in the list will be chosen in preference to those later. Adding `defaults` will place the unnamed charsets at that point.
+- `ANSI_CHARSET`: **\<empty\>**: Default ANSI charset to override non-UTF-8 charsets to.
 - `FORCE_PRIVATE`: **false**: Force every new repository to be private.
 - `DEFAULT_PRIVATE`: **last**: Default private when creating a new repository.
    \[last, private, public\]
diff --git a/modules/charset/charset.go b/modules/charset/charset.go
index 3d3d1664f9..a7e427db99 100644
--- a/modules/charset/charset.go
+++ b/modules/charset/charset.go
@@ -7,6 +7,7 @@ package charset
 import (
 	"bytes"
 	"fmt"
+	"strings"
 	"unicode/utf8"
 
 	"code.gitea.io/gitea/modules/log"
@@ -137,16 +138,42 @@ func DetectEncoding(content []byte) (string, error) {
 	} else {
 		detectContent = content
 	}
-	result, err := textDetector.DetectBest(detectContent)
+
+	// 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 guesss
+		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 result.Charset != "UTF-8" && len(setting.Repository.AnsiCharset) > 0 {
+	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", result.Charset)
-	return result.Charset, err
+	log.Debug("Detected encoding: %s", topResult.Charset)
+	return topResult.Charset, err
 }
diff --git a/modules/charset/charset_test.go b/modules/charset/charset_test.go
index a81a6e03ee..394a42c71f 100644
--- a/modules/charset/charset_test.go
+++ b/modules/charset/charset_test.go
@@ -230,7 +230,11 @@ func TestDetectEncoding(t *testing.T) {
 	// we accept either.
 	assert.Contains(t, encoding, "ISO-8859")
 
+	old := setting.Repository.AnsiCharset
 	setting.Repository.AnsiCharset = "placeholder"
+	defer func() {
+		setting.Repository.AnsiCharset = old
+	}()
 	testSuccess(b, "placeholder")
 
 	// invalid bytes
diff --git a/modules/setting/repository.go b/modules/setting/repository.go
index 8af3eaaf46..1796a8d6b5 100644
--- a/modules/setting/repository.go
+++ b/modules/setting/repository.go
@@ -24,6 +24,8 @@ const (
 // Repository settings
 var (
 	Repository = struct {
+		DetectedCharsetsOrder                   []string
+		DetectedCharsetScore                    map[string]int `ini:"-"`
 		AnsiCharset                             string
 		ForcePrivate                            bool
 		DefaultPrivate                          string
@@ -88,6 +90,42 @@ var (
 			Wiki          []string
 		} `ini:"repository.signing"`
 	}{
+		DetectedCharsetsOrder: []string{
+			"UTF-8",
+			"UTF-16BE",
+			"UTF-16LE",
+			"UTF-32BE",
+			"UTF-32LE",
+			"ISO-8859-1",
+			"windows-1252",
+			"ISO-8859-2",
+			"windows-1250",
+			"ISO-8859-5",
+			"ISO-8859-6",
+			"ISO-8859-7",
+			"windows-1253",
+			"ISO-8859-8-I",
+			"windows-1255",
+			"ISO-8859-8",
+			"windows-1251",
+			"windows-1256",
+			"KOI8-R",
+			"ISO-8859-9",
+			"windows-1254",
+			"Shift_JIS",
+			"GB18030",
+			"EUC-JP",
+			"EUC-KR",
+			"Big5",
+			"ISO-2022-JP",
+			"ISO-2022-KR",
+			"ISO-2022-CN",
+			"IBM424_rtl",
+			"IBM424_ltr",
+			"IBM420_rtl",
+			"IBM420_ltr",
+		},
+		DetectedCharsetScore:                    map[string]int{},
 		AnsiCharset:                             "",
 		ForcePrivate:                            false,
 		DefaultPrivate:                          RepoCreatingLastUserVisibility,
@@ -208,6 +246,10 @@ func newRepository() {
 	} else {
 		RepoRootPath = filepath.Clean(RepoRootPath)
 	}
+	defaultDetectedCharsetsOrder := make([]string, 0, len(Repository.DetectedCharsetsOrder))
+	for _, charset := range Repository.DetectedCharsetsOrder {
+		defaultDetectedCharsetsOrder = append(defaultDetectedCharsetsOrder, strings.ToLower(strings.TrimSpace(charset)))
+	}
 	ScriptType = sec.Key("SCRIPT_TYPE").MustString("bash")
 
 	if err = Cfg.Section("repository").MapTo(&Repository); err != nil {
@@ -222,6 +264,38 @@ func newRepository() {
 		log.Fatal("Failed to map Repository.PullRequest settings: %v", err)
 	}
 
+	preferred := make([]string, 0, len(Repository.DetectedCharsetsOrder))
+	for _, charset := range Repository.DetectedCharsetsOrder {
+		canonicalCharset := strings.ToLower(strings.TrimSpace(charset))
+		preferred = append(preferred, canonicalCharset)
+		// remove it from the defaults
+		for i, charset := range defaultDetectedCharsetsOrder {
+			if charset == canonicalCharset {
+				defaultDetectedCharsetsOrder = append(defaultDetectedCharsetsOrder[:i], defaultDetectedCharsetsOrder[i+1:]...)
+				break
+			}
+		}
+	}
+
+	i := 0
+	for _, charset := range preferred {
+		// Add the defaults
+		if charset == "defaults" {
+			for _, charset := range defaultDetectedCharsetsOrder {
+				canonicalCharset := strings.ToLower(strings.TrimSpace(charset))
+				if _, has := Repository.DetectedCharsetScore[canonicalCharset]; !has {
+					Repository.DetectedCharsetScore[canonicalCharset] = i
+					i++
+				}
+			}
+			continue
+		}
+		if _, has := Repository.DetectedCharsetScore[charset]; !has {
+			Repository.DetectedCharsetScore[charset] = i
+			i++
+		}
+	}
+
 	if !filepath.IsAbs(Repository.Upload.TempPath) {
 		Repository.Upload.TempPath = path.Join(AppWorkPath, Repository.Upload.TempPath)
 	}