text/scanner: guard against installed IsIdentRune that accepts EOF

IsIdentRune may be installed by a client of the scanner. If the installed function accepts EOF as a valid identifier rune, Scan calls may not terminate. Check for EOF when a user-defined IsIdentRune is used. Fixes #50909. Change-Id: Ib104b03ee59e2d58faa71f227c3b51ba424f7f61 Reviewed-on: https://go-review.googlesource.com/c/go/+/393254 Trust: Robert Griesemer <[email protected]> Run-TryBot: Robert Griesemer <[email protected]> TryBot-Result: Gopher Robot <[email protected]> Reviewed-by: Ian Lance Taylor <[email protected]>
cloudflare · Mar 17, 2022 · 9956a54 · 9956a54
1 parent 8427429
commit 9956a54
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diff --git a/src/text/scanner/scanner.go b/src/text/scanner/scanner.go
@@ -346,7 +346,7 @@ func (s *Scanner) errorf(format string, args ...any) {
 
 func (s *Scanner) isIdentRune(ch rune, i int) bool {
  if s.IsIdentRune != nil {
- return s.IsIdentRune(ch, i)
+ return ch != EOF && s.IsIdentRune(ch, i)
  }
  return ch == '_' || unicode.IsLetter(ch) || unicode.IsDigit(ch) && i > 0
 }

diff --git a/src/text/scanner/scanner_test.go b/src/text/scanner/scanner_test.go
@@ -913,3 +913,22 @@ func extractInts(t string, mode uint) (res string) {
  }
  }
 }
+
+func TestIssue50909(t *testing.T) {
+ var s Scanner
+ s.Init(strings.NewReader("hello \n\nworld\n!\n"))
+ s.IsIdentRune = func(ch rune, _ int) bool { return ch != '\n' }
+
+ r := ""
+ n := 0
+ for s.Scan() != EOF && n < 10 {
+ r += s.TokenText()
+ n++
+ }
+
+ const R = "hello world!"
+ const N = 3
+ if r != R || n != N {
+ t.Errorf("got %q (n = %d); want %q (n = %d)", r, n, R, N)
+ }
+}