fichier: 1fichier support - fixes #2908

This was started by Fionera, finished off by Laura with fixes and more
docs from Nick.

Co-authored-by: Fionera <fionera@fionera.de>
Co-authored-by: Nick Craig-Wood <nick@craig-wood.com>

backend/fichier/replace.go

@@ -0,0 +1,71 @@
+/*
+Translate file names for 1fichier
+
+1Fichier reserved characters
+
+The following characters are 1Fichier reserved characters, and can't
+be used in 1Fichier  folder and file names.
+
+*/
+
+package fichier
+
+import (
+	"regexp"
+	"strings"
+)
+
+// charMap holds replacements for characters
+//
+// 1Fichier has a restricted set of characters compared to other cloud
+// storage systems, so we to map these to the FULLWIDTH unicode
+// equivalents
+//
+// http://unicode-search.net/unicode-namesearch.pl?term=SOLIDUS
+var (
+	charMap = map[rune]rune{
+		'\\': '＼', // FULLWIDTH REVERSE SOLIDUS
+		'<':  '＜', // FULLWIDTH LESS-THAN SIGN
+		'>':  '＞', // FULLWIDTH GREATER-THAN SIGN
+		'"':  '＂', // FULLWIDTH QUOTATION MARK - not on the list but seems to be reserved
+		'\'': '＇', // FULLWIDTH APOSTROPHE
+		'$':  '＄', // FULLWIDTH DOLLAR SIGN
+		'`':  '｀', // FULLWIDTH GRAVE ACCENT
+		' ':  '␠', // SYMBOL FOR SPACE
+	}
+	invCharMap           map[rune]rune
+	fixStartingWithSpace = regexp.MustCompile(`(/|^) `)
+)
+
+func init() {
+	// Create inverse charMap
+	invCharMap = make(map[rune]rune, len(charMap))
+	for k, v := range charMap {
+		invCharMap[v] = k
+	}
+}
+
+// replaceReservedChars takes a path and substitutes any reserved
+// characters in it
+func replaceReservedChars(in string) string {
+	// file names can't start with space either
+	in = fixStartingWithSpace.ReplaceAllString(in, "$1"+string(charMap[' ']))
+	// Replace reserved characters
+	return strings.Map(func(c rune) rune {
+		if replacement, ok := charMap[c]; ok && c != ' ' {
+			return replacement
+		}
+		return c
+	}, in)
+}
+
+// restoreReservedChars takes a path and undoes any substitutions
+// made by replaceReservedChars
+func restoreReservedChars(in string) string {
+	return strings.Map(func(c rune) rune {
+		if replacement, ok := invCharMap[c]; ok {
+			return replacement
+		}
+		return c
+	}, in)
+}