payload almost done

payload/copy.go

@@ -0,0 +1,56 @@
+package payload
+
+import (
+	"io"
+)
+
+type CopyOutput struct {
+	Err     error
+	Written int64
+}
+
+func copyAndUpdate(dst io.Writer, data []byte, copyOutput *CopyOutput) {
+	if copyOutput.Err != nil {
+		return
+	}
+	nw, ew := dst.Write(data)
+	if nw > 0 {
+		copyOutput.Written += int64(nw)
+	}
+	if ew != nil {
+		copyOutput.Err = ew
+		return
+	}
+	if len(data) != nw {
+		copyOutput.Err = io.ErrShortWrite
+	}
+}
+
+func CopyToTwoWriters(dst1 io.Writer, dst2 io.Writer, src io.Reader) (copyOutput1 *CopyOutput, copyOutput2 *CopyOutput) {
+	// TODO: if necessary, implements the speedup methods if src implements *WriterTo*
+	//       or if both dst implement ReaderFrom.  See
+	//       http://golang.org/src/pkg/io/io.go for example
+	copyOutput1, copyOutput2 = new(CopyOutput), new(CopyOutput)
+	var nr int
+	var er error
+	buf := make([]byte, 32*1024)
+	for {
+		nr, er = src.Read(buf)
+		if nr > 0 {
+			copyAndUpdate(dst1, buf[0:nr], copyOutput1)
+			copyAndUpdate(dst2, buf[0:nr], copyOutput2)
+		}
+		if copyOutput1.Err != nil && copyOutput2.Err != nil {
+			break
+		}
+		if er == io.EOF {
+			break
+		}
+		if er != nil {
+			copyOutput1.Err = er
+			copyOutput2.Err = er
+			break
+		}
+	}
+	return
+}