add commands support

Signed-off-by: Casey Lee <cplee@nektos.com>

pkg/common/line_writer.go

@@ -0,0 +1,47 @@
+package common
+
+import (
+	"bytes"
+	"io"
+)
+
+// LineHandler is a callback function for handling a line
+type LineHandler func(line string)
+
+type lineWriter struct {
+	buffer   bytes.Buffer
+	handlers []LineHandler
+}
+
+// NewLineWriter creates a new instance of a line writer
+func NewLineWriter(handlers ...LineHandler) io.Writer {
+	w := new(lineWriter)
+	w.handlers = handlers
+	return w
+}
+
+func (lw *lineWriter) Write(p []byte) (n int, err error) {
+	pBuf := bytes.NewBuffer(p)
+	written := 0
+	for {
+		line, err := pBuf.ReadString('\n')
+		w, _ := lw.buffer.WriteString(line)
+		written += w
+		if err == nil {
+			lw.handleLine(lw.buffer.String())
+			lw.buffer.Reset()
+		} else if err == io.EOF {
+			break
+		} else {
+			return written, err
+		}
+	}
+
+	return written, nil
+}
+
+func (lw *lineWriter) handleLine(line string) {
+	for _, h := range lw.handlers {
+		h(line)
+	}
+}