Add ReadByte to bytebuffer

R=rsc
APPROVED=rsc
DELTA=24  (24 added, 0 deleted, 0 changed)
OCL=30459
CL=30540

src/pkg/io/bytebuffer.go

@@ -102,6 +102,17 @@ func (b *ByteBuffer) Read(p []byte) (n int, err os.Error) {
 	return n, nil
 }
 
+// ReadByte reads and returns the next byte from the buffer.
+// If no byte is available, it returns error ErrEOF.
+func (b *ByteBuffer) ReadByte() (c byte, err os.Error) {
+	if b.off >= len(b.buf) {
+		return 0, ErrEOF;
+	}
+        c = b.buf[b.off];
+	b.off++;
+	return c, nil;
+}
+
 // NewByteBufferFromArray creates and initializes a new ByteBuffer
 // with buf as its initial contents.
 func NewByteBufferFromArray(buf []byte) *ByteBuffer {

src/pkg/io/bytebuffer_test.go

@@ -118,6 +118,19 @@ func TestBasicOperations(t *testing.T) {
 
 		empty(t, "TestBasicOperations (9)", &buf, string(data[0 : 20]), make([]byte, 5));
 		empty(t, "TestBasicOperations (10)", &buf, "", make([]byte, 100));
+
+		buf.WriteByte(data[1]);
+		c, err := buf.ReadByte();
+		if err != nil {
+			t.Errorf("ReadByte unexpected eof\n");
+		}
+		if c != data[1] {
+			t.Errorf("ReadByte wrong value c=%v\n", c);
+		}
+		c, err = buf.ReadByte();
+		if err == nil {
+			t.Errorf("ReadByte unexpected not eof\n");
+		}
 	}
 }