Add blobstore package.

pkg/blobstore/blobreader.go

@@ -0,0 +1,53 @@
+// Copyright (c) 2011 The Grumble Authors
+// The use of this source code is goverened by a BSD-style
+// license that can be found in the LICENSE-file.
+
+package blobstore
+
+import (
+	"bytes"
+	"crypto/sha1"
+	"encoding/hex"
+	"hash"
+	"io"
+	"os"
+)
+
+// blobReader is based on the principles of the checksumReader from the archive/zip
+// package of the Go standard library.
+
+// ErrHashMismatch is returned if a blobReader has read a file whose computed hash
+// did not match its key.
+var ErrHashMismatch = os.NewError("hash mismatch")
+
+// blobReader reads a blob from disk, hashing all incoming data. On EOF, it checks
+// whether the read data matches the key.
+type blobReader struct {
+	rc   io.ReadCloser
+	sum  []byte
+	hash hash.Hash
+}
+
+func newBlobReader(rc io.ReadCloser, key string) (br *blobReader, err os.Error) {
+	sum, err := hex.DecodeString(key)
+	if err != nil {
+		return
+	}
+	return &blobReader{rc, sum, sha1.New()}, nil
+}
+
+func (r *blobReader) Read(b []byte) (n int, err os.Error) {
+	n, err = r.rc.Read(b)
+	r.hash.Write(b[:n])
+	if err != os.EOF {
+		return
+	}
+	if !bytes.Equal(r.sum, r.hash.Sum()) {
+		err = ErrHashMismatch
+	}
+	return
+}
+
+func (r *blobReader) Close() os.Error {
+	return r.rc.Close()
+}