Added an io pachage with a MultiWriter similar to the one included in…

… Go. The difference is this one will let you manage the Writers attached to it. This will be used by the log package.

io/multi.go

@@ -0,0 +1,57 @@
+package io
+
+import (
+	"io"
+)
+
+// MultiWriter enables you to have a writer that passes on the writing to one
+// of more Writers where the write is duplicated to each Writer. MultiWriter
+// is similar to the multiWriter that is part of Go. The difference is
+// this MultiWriter allows you to manager the Writers attached to it via CRUD
+// operations. To do this you will need to mock the type. For example,
+// mw := NewMultiWriter()
+// mw.(*MultiWriter).AddWriter("foo", foo)
+type MultiWriter struct {
+	writers map[string]io.Writer
+}
+
+func (t *MultiWriter) Write(p []byte) (n int, err error) {
+	for _, w := range t.writers {
+		n, err = w.Write(p)
+		if err != nil {
+			return
+		}
+		if n != len(p) {
+			err = io.ErrShortWrite
+			return
+		}
+	}
+	return len(p), nil
+}
+
+func (t *MultiWriter) Init() *MultiWriter {
+	t.writers = make(map[string]io.Writer)
+	return t
+}
+
+func (t *MultiWriter) Writer(name string) (io.Writer, bool) {
+	value, found := t.writers[name]
+	return value, found
+}
+
+func (t *MultiWriter) Writers() map[string]io.Writer {
+	return t.writers
+}
+
+func (t *MultiWriter) AddWriter(name string, writer io.Writer) {
+	t.writers[name] = writer
+}
+
+func (t *MultiWriter) RemoveWriter(name string) {
+	delete(t.writers, name)
+}
+
+func NewMultiWriter() io.Writer {
+	w := new(MultiWriter).Init()
+	return w
+}

io/multi_test.go

@@ -0,0 +1,62 @@
+package io
+
+import (
+	"bytes"
+	"crypto/sha1"
+	"fmt"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestMultiWrite(t *testing.T) {
+	sha1 := sha1.New()
+	sink := new(bytes.Buffer)
+	mw := NewMultiWriter()
+	mw.(*MultiWriter).AddWriter("sha1", sha1)
+	mw.(*MultiWriter).AddWriter("sink", sink)
+
+	sourceString := "My input text."
+	source := strings.NewReader(sourceString)
+	written, err := io.Copy(mw, source)
+
+	if written != int64(len(sourceString)) {
+		t.Errorf("short write of %d, not %d", written, len(sourceString))
+	}
+
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+
+	sha1hex := fmt.Sprintf("%x", sha1.Sum(nil))
+	if sha1hex != "01cb303fa8c30a64123067c5aa6284ba7ec2d31b" {
+		t.Error("incorrect sha1 value")
+	}
+
+	if sink.String() != sourceString {
+		t.Errorf("expected %q; got %q", sourceString, sink.String())
+	}
+}
+
+func TestMultiWriterCRUD(t *testing.T) {
+	sha1 := sha1.New()
+	mw := NewMultiWriter()
+	mw.(*MultiWriter).AddWriter("sha1", sha1)
+
+	sha1a, found := mw.(*MultiWriter).Writer("sha1")
+
+	if found == false {
+		t.Error("Did not find sha1 as expected.")
+	}
+	if sha1a != sha1 {
+		t.Error("Expected sha1 returned from MultiWriter to be what was set. They were different.")
+	}
+
+	mw.(*MultiWriter).RemoveWriter("sha1")
+	_, found = mw.(*MultiWriter).Writer("sha1")
+
+	if found == true {
+		t.Error("Expected sha1 to be removed from MultiWriter but it was not.")
+	}
+
+}