New package: seekbuf (a seekable buffer).

seekbuf/seekbuf.go

@@ -0,0 +1,50 @@
+package seekbuf
+
+import "io"
+
+// Buffer is a ReadWriteCloser that supports seeking. It's intended to
+// replicate the functionality of bytes.Buffer that I use in my projects.
+//
+// Note that the seeking is limited to the read marker; all writes are
+// append-only.
+type Buffer struct {
+	data []byte
+	pos  int
+}
+
+func New(data []byte) *Buffer {
+	return &Buffer{
+		data: data,
+	}
+}
+
+func (b *Buffer) Read(p []byte) (int, error) {
+	if b.pos >= len(b.data) {
+		return 0, io.EOF
+	}
+
+	n := copy(p, b.data[b.pos:])
+	b.pos += n
+	return n, nil
+}
+
+func (b *Buffer) Write(p []byte) (int, error) {
+	b.data = append(b.data, p...)
+	return len(p), nil
+}
+
+// Seek sets the read pointer to pos.
+func (b *Buffer) Seek(pos int) {
+	b.pos = pos
+}
+
+// Rewind resets the read pointer to 0.
+func (b *Buffer) Rewind() {
+	b.pos = 0
+}
+
+// Close clears all the data out of the buffer and sets the read position to 0.
+func (b *Buffer) Close() error {
+	b.Clear()
+	return nil
+}