Adding logging and some common functions.

mwc/mwc.go

@@ -0,0 +1,42 @@
+// Package mwc implements MultiWriteClosers.
+package mwc
+
+import "io"
+
+type mwc struct {
+	wcs []io.WriteCloser
+}
+
+// Write implements the Writer interface.
+func (t *mwc) Write(p []byte) (n int, err error) {
+	for _, w := range t.wcs {
+		n, err = w.Write(p)
+		if err != nil {
+			return
+		}
+		if n != len(p) {
+			err = io.ErrShortWrite
+			return
+		}
+	}
+	return len(p), nil
+}
+
+// Close implements the Closer interface.
+func (t *mwc) Close() error {
+	for _, wc := range t.wcs {
+		err := wc.Close()
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// MultiWriteClose creates a WriteCloser that duplicates its writes to
+// all the provided writers, similar to the Unix tee(1) command.
+func MultiWriteCloser(wc ...io.WriteCloser) io.WriteCloser {
+	wcs := make([]io.WriteCloser, len(wc))
+	copy(wcs, wc)
+	return &mwc{wcs}
+}