refactor: internal package

internal/engine/io.go

@@ -0,0 +1,31 @@
+package engine
+
+import "io"
+
+// A LimitedWriter writes to w but limits the amount
+// of data to only n bytes. After reaching the limit,
+// silently discards the rest of the data without errors.
+type LimitedWriter struct {
+	w io.Writer
+	n int64
+}
+
+// LimitWriter returns a writer that writes no more
+// than n bytes and silently discards the rest.
+func LimitWriter(w io.Writer, n int64) io.Writer {
+	return &LimitedWriter{w, n}
+}
+
+// Write implements the io.Writer interface.
+func (w *LimitedWriter) Write(p []byte) (int, error) {
+	lenp := len(p)
+	if w.n <= 0 {
+		return lenp, nil
+	}
+	if int64(lenp) > w.n {
+		p = p[:w.n]
+	}
+	n, err := w.w.Write(p)
+	w.n -= int64(n)
+	return lenp, err
+}