strings: add ReadRune to Reader

R=rsc
CC=golang-dev
https://golang.org/cl/940041

diff --git a/src/pkg/strings/reader.go b/src/pkg/strings/reader.go
index 7cefbd24bbe36cf2f323629f3125fe04cbc5bfa1..914faa00359916b1250852712babebdbb2850e1b 100644 (file)
--- a/src/pkg/strings/reader.go
+++ b/src/pkg/strings/reader.go
@@ -4,9 +4,12 @@
 
 package strings
 
-import "os"
+import (
+       "os"
+       "utf8"
+)
 
-// A Reader satisfies calls to Read and ReadByte by
+// A Reader satisfies calls to Read, ReadByte, and ReadRune by
 // reading from a string.
 type Reader string
 
@@ -33,6 +36,26 @@ func (r *Reader) ReadByte() (b byte, err os.Error) {
        return
 }
 
+// ReadRune reads and returns the next UTF-8-encoded
+// Unicode code point from the buffer.
+// If no bytes are available, the error returned is os.EOF.
+// If the bytes are an erroneous UTF-8 encoding, it
+// consumes one byte and returns U+FFFD, 1.
+func (r *Reader) ReadRune() (rune int, size int, err os.Error) {
+       s := *r
+       if len(s) == 0 {
+               return 0, 0, os.EOF
+       }
+       c := s[0]
+       if c < utf8.RuneSelf {
+               *r = s[1:]
+               return int(c), 1, nil
+       }
+       rune, size = utf8.DecodeRuneInString(string(s))
+       *r = s[size:]
+       return
+}
+
 // NewReader returns a new Reader reading from s.
 // It is similar to bytes.NewBufferString but more efficient and read-only.
 func NewReader(s string) *Reader { return (*Reader)(&s) }

diff --git a/src/pkg/strings/strings_test.go b/src/pkg/strings/strings_test.go
index 3c9dc5847a70ac4b8c78fbadd8a8a22227fbde6b..2c99a6ec360083ccbe687c884ca104d4671f6448 100644 (file)
--- a/src/pkg/strings/strings_test.go
+++ b/src/pkg/strings/strings_test.go
@@ -5,6 +5,7 @@
 package strings_test
 
 import (
+       "os"
        . "strings"
        "testing"
        "unicode"
@@ -576,3 +577,25 @@ func TestRunes(t *testing.T) {
                }
        }
 }
+
+func TestReadRune(t *testing.T) {
+       testStrings := []string{"", abcd, faces, commas}
+       for _, s := range testStrings {
+               reader := NewReader(s)
+               res := ""
+               for {
+                       r, _, e := reader.ReadRune()
+                       if e == os.EOF {
+                               break
+                       }
+                       if e != nil {
+                               t.Errorf("Reading %q: %s", s, e)
+                               break
+                       }
+                       res += string(r)
+               }
+               if res != s {
+                       t.Errorf("Reader(%q).ReadRune() produced %q", s, res)
+               }
+       }
+}