Fixes #103

_test/extra.txt

@@ -93,4 +93,15 @@ correctly</a></p>
 []()
 //- - - - - - - - -//
 <p><a href=""></a></p>
-//= = = = = = = = = = = = = = = = = = = = = = = =//
+//= = = = = = = = = = = = = = = = = = = = = = = =//
+
+
+
+9
+//- - - - - - - - -//
+[daß] is the old german spelling of [dass]
+
+[daß]: www.das-dass.de
+//- - - - - - - - -//
+<p><a href="www.das-dass.de">daß</a> is the old german spelling of <a href="www.das-dass.de">dass</a></p>
+//= = = = = = = = = = = = = = = = = = = = = = = =//

_tools/gen-unicode-case-folding-map.go

@@ -0,0 +1,73 @@
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"os"
+	"strconv"
+	"strings"
+)
+
+const outPath = "../util/unicode_case_folding.go"
+
+type caseFolding struct {
+	Class byte
+	From  rune
+	To    []rune
+}
+
+func main() {
+	url := "http://www.unicode.org/Public/12.1.0/ucd/CaseFolding.txt"
+
+	resp, err := http.Get(url)
+	if err != nil {
+		fmt.Printf("Failed to get CaseFolding.txt: %v\n", err)
+		os.Exit(1)
+	}
+	defer resp.Body.Close()
+
+	bs, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		fmt.Printf("Failed to get CaseFolding.txt: %v\n", err)
+		os.Exit(1)
+	}
+
+	buf := bytes.NewBuffer(bs)
+	scanner := bufio.NewScanner(buf)
+	f, err := os.Create(outPath)
+	if err != nil {
+		fmt.Printf("Failed to open %s: %v\n", outPath, err)
+		os.Exit(1)
+	}
+	defer f.Close()
+	_, _ = f.WriteString("package util\n\n")
+	_, _ = f.WriteString("var unicodeCaseFoldings = map[rune][]rune {\n")
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		if strings.HasPrefix(line, "#") || len(strings.TrimSpace(line)) == 0 {
+			continue
+		}
+		line = strings.Split(line, "#")[0]
+		parts := strings.Split(line, ";")
+		for i, p := range parts {
+			parts[i] = strings.TrimSpace(p)
+		}
+		cf := caseFolding{}
+		v, _ := strconv.ParseInt(parts[0], 16, 32)
+		cf.From = rune(int32(v))
+		cf.Class = parts[1][0]
+		for _, v := range strings.Split(parts[2], " ") {
+			c, _ := strconv.ParseInt(v, 16, 32)
+			cf.To = append(cf.To, rune(int32(c)))
+		}
+		if cf.Class != 'C' && cf.Class != 'F' {
+			continue
+		}
+		fmt.Fprintf(f, "  %#x : %#v,\n", cf.From, cf.To)
+	}
+	fmt.Fprintf(f, "}\n")
+}

util/util.go

@@ -8,7 +8,6 @@ import (
 	"regexp"
 	"sort"
 	"strconv"
-	"strings"
 	"unicode/utf8"
 )
 
@@ -387,6 +386,52 @@ func TrimRightSpace(source []byte) []byte {
 	return TrimRight(source, spaces)
 }
 
+// DoFullUnicodeCaseFolding performs full unicode case folding to given bytes.
+func DoFullUnicodeCaseFolding(v []byte) []byte {
+	var rbuf []byte
+	cob := NewCopyOnWriteBuffer(v)
+	n := 0
+	for i := 0; i < len(v); i++ {
+		c := v[i]
+		if c < 0xb5 {
+			if c >= 0x41 && c <= 0x5a {
+				// A-Z to a-z
+				cob.Write(v[n:i])
+				cob.WriteByte(c + 32)
+				n = i + 1
+			}
+			continue
+		}
+
+		if !utf8.RuneStart(c) {
+			continue
+		}
+		r, length := utf8.DecodeRune(v[i:])
+		if r == utf8.RuneError {
+			continue
+		}
+		folded, ok := unicodeCaseFoldings[r]
+		if !ok {
+			continue
+		}
+
+		cob.Write(v[n:i])
+		if rbuf == nil {
+			rbuf = make([]byte, 4)
+		}
+		for _, f := range folded {
+			l := utf8.EncodeRune(rbuf, f)
+			cob.Write(rbuf[:l])
+		}
+		i += length - 1
+		n = i + 1
+	}
+	if cob.IsCopied() {
+		cob.Write(v[n:])
+	}
+	return cob.Bytes()
+}
+
 // ReplaceSpaces replaces sequence of spaces with the given repl.
 func ReplaceSpaces(source []byte, repl byte) []byte {
 	var ret []byte
@@ -439,13 +484,14 @@ func ToValidRune(v rune) rune {
 	return v
 }
 
-// ToLinkReference convert given bytes into a valid link reference string.
+// ToLinkReference converts given bytes into a valid link reference string.
-// ToLinkReference trims leading and trailing spaces and convert into lower
+// ToLinkReference performs unicode case folding, trims leading and trailing spaces,  converts into lower
 // case and replace spaces with a single space character.
 func ToLinkReference(v []byte) string {
 	v = TrimLeftSpace(v)
 	v = TrimRightSpace(v)
-	return strings.ToLower(string(ReplaceSpaces(v, ' ')))
+	v = DoFullUnicodeCaseFolding(v)
+	return string(ReplaceSpaces(v, ' '))
 }
 
 var htmlEscapeTable = [256][]byte{nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, []byte("&quot;"), nil, nil, nil, []byte("&amp;"), nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, []byte("&lt;"), nil, []byte("&gt;"), nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil}