payload almost done

payload/hash.go

@@ -0,0 +1,45 @@
+package payload
+
+import (
+	cryptoSHA512 "crypto/sha512"
+	"errors"
+	"fmt"
+	"hash"
+	"io"
+)
+
+type Hash string
+
+const SHA512 Hash = "sha512"
+
+func (this Hash) New() (hash.Hash, error) {
+	switch this {
+	case SHA512:
+		return cryptoSHA512.New(), nil
+	default:
+		msg := fmt.Sprintf("hash '%s' is not supported")
+		return nil, errors.New(msg)
+	}
+}
+
+func (this Hash) HashOnTheWay(data io.Reader, resultingHash chan []byte) (io.Reader, error) {
+	h, err := this.New()
+	pipeReader, pipeWriter := io.Pipe()
+	if err != nil {
+		return nil, err
+	}
+	go func(resultingHash chan []byte) {
+		ou1, ou2 := CopyToTwoWriters(h, pipeWriter, data)
+		if ou1.Err != nil {
+			panic(ou1.Err)
+		}
+		if ou2.Err != nil {
+			panic(ou2.Err)
+		}
+		if err := pipeWriter.Close(); err != nil {
+			panic(err)
+		}
+		resultingHash <- h.Sum(nil)
+	}(resultingHash)
+	return pipeReader, nil
+}