code review 111780045: strconv: fix CanBackquote for invalud UTF-8

src/pkg/strconv/quote.go

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 package strconv
 
 import (
         "unicode/utf8"
 )
 
@@ skipping 125 matching lines @@
 // AppendQuoteRuneToASCII appends a single-quoted Go character literal representing the rune,
 // as generated by QuoteRuneToASCII, to dst and returns the extended buffer.
 func AppendQuoteRuneToASCII(dst []byte, r rune) []byte {
         return append(dst, QuoteRuneToASCII(r)...)
 }
 
 // CanBackquote reports whether the string s can be represented
 // unchanged as a single-line backquoted string without control
 // characters other than space and tab.
 func CanBackquote(s string) bool {
-        i := 0
-        for i < len(s) {
-                c := s[i]
-                if c < utf8.RuneSelf {
-                        if (c < ' ' && c != '\t') || c == '`' || c == '\u007F' {
-                                return false
-                        }
-                        i++
-                } else {
-                        _, size := utf8.DecodeRuneInString(s[i:])
-                        if size == 1 {
-                                // A RuneError as all runes of size 1 have
-                                // been handled above.
-                                return false
-                        }
-                        i += size
+        for len(s) > 0 {
+                r, wid := utf8.DecodeRuneInString(s)
+                s = s[wid:]
+                if wid > 1 {
+                        continue // All multibyte runes are correctly encoded and assumed printable.
+                }
+                if r == utf8.RuneError {
+                        return false
+                }
+                if (r < ' ' && r != '\t') || r == '`' || r == '\u007F' {
+                        return false
                 }
         }
         return true
 }
 
 func unhex(b byte) (v rune, ok bool) {
         c := rune(b)
         switch {
         case '0' <= c && c <= '9':
                 return c - '0', true
@@ skipping 274 matching lines @@
         if i >= len(isPrint) || rr < isPrint[i&^1] || isPrint[i|1] < rr {
                 return false
         }
         if r >= 0x20000 {
                 return true
         }
         r -= 0x10000
         j := bsearch16(isNotPrint, uint16(r))
         return j >= len(isNotPrint) || isNotPrint[j] != uint16(r)
 }