Add examples

hashing/impl.go

@@ -0,0 +1,109 @@
+// Copyright (c) 2014, Alexander Neumann <alexander@bumpern.de>
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this
+// list of conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice,
+// this list of conditions and the following disclaimer in the documentation
+// and/or other materials provided with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Packgae hashing provides hashing readers and writers.
+package hashing
+
+import (
+	"hash"
+	"io"
+)
+
+// Reader is the interfaces that wraps a normal reader. When Hash() is called,
+// it returns the hash for all data that has been read so far.
+type Reader interface {
+	io.Reader
+	Hash() []byte
+}
+
+// Writer is the interfaces that wraps a normal writer. When Hash() is called,
+// it returns the hash for all data that has been written so far.
+type Writer interface {
+	io.Writer
+	Hash() []byte
+}
+
+type reader struct {
+	reader io.Reader
+	hash   hash.Hash
+}
+
+// NewReader wraps an io.Reader and in addition feeds all data read through the
+// given hash.
+func NewReader(r io.Reader, h func() hash.Hash) *reader {
+	return &reader{
+		reader: r,
+		hash:   h(),
+	}
+}
+
+func (h *reader) Read(p []byte) (int, error) {
+	// call original reader
+	n, err := h.reader.Read(p)
+
+	// hash bytes
+	if n > 0 {
+		// hash
+		h.hash.Write(p[0:n])
+	}
+
+	// return result
+	return n, err
+}
+
+func (h *reader) Hash() []byte {
+	return h.hash.Sum([]byte{})
+}
+
+type writer struct {
+	writer io.Writer
+	hash   hash.Hash
+}
+
+// NewWriter wraps an io.Reader and in addition feeds all data written through
+// the given hash.
+func NewWriter(w io.Writer, h func() hash.Hash) *writer {
+	return &writer{
+		writer: w,
+		hash:   h(),
+	}
+}
+
+func (h *writer) Write(p []byte) (int, error) {
+	// call original writer
+	n, err := h.writer.Write(p)
+
+	// hash bytes
+	if n > 0 {
+		// hash
+		h.hash.Write(p[0:n])
+	}
+
+	// return result
+	return n, err
+}
+
+func (h *writer) Hash() []byte {
+	return h.hash.Sum([]byte{})
+}