replace non-ascii characters in filename

finstr.go

@@ -19,6 +19,7 @@ import (
 	"strings"
 	"text/template"
 	"time"
+	"unicode"
 )
 
 var dir string
@@ -130,8 +131,26 @@ func byModified(p []photo) func(int, int) bool {
 
 /*-------------------------*/
 
+func isASCII(r rune) bool {
+	return r <= 127
+}
+
+func convASCII(s string) string {
+	out := []rune(s)
+	for i, c := range out {
+		if (isASCII(c) && (unicode.IsLetter(c) || unicode.IsDigit(c))) || c == '.' {
+			// keep unchanged
+		} else if unicode.IsSpace(c) || unicode.IsPunct(c) {
+			out[i] = '-'
+		} else {
+			out[i] = 'x'
+		}
+	}
+	return string(out)
+}
+
 func filename(s string) string {
-	return url.QueryEscape(s)
+	return url.QueryEscape(convASCII(s))
 }
 
 func filenameDate(date calendarMonth) string {