1 files changed, 122 insertions, 0 deletions
diff --git a/internal/verify/verify.go b/internal/verify/verify.go
new file mode 100644
index 0000000..463f7e4
--- /dev/null
+++ b/internal/verify/verify.go
@@ -0,0 +1,122 @@
+// Copyright 2020 Google LLC All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package verify provides a ReadCloser that verifies content matches the
+// expected hash values.
+package verify
+
+import (
+	"bytes"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"hash"
+	"io"
+
+	"github.com/google/go-containerregistry/internal/and"
+	v1 "github.com/google/go-containerregistry/pkg/v1"
+)
+
+// SizeUnknown is a sentinel value to indicate that the expected size is not known.
+const SizeUnknown = -1
+
+type verifyReader struct {
+	inner             io.Reader
+	hasher            hash.Hash
+	expected          v1.Hash
+	gotSize, wantSize int64
+}
+
+// Error provides information about the failed hash verification.
+type Error struct {
+	got     string
+	want    v1.Hash
+	gotSize int64
+}
+
+func (v Error) Error() string {
+	return fmt.Sprintf("error verifying %s checksum after reading %d bytes; got %q, want %q",
+		v.want.Algorithm, v.gotSize, v.got, v.want)
+}
+
+// Read implements io.Reader
+func (vc *verifyReader) Read(b []byte) (int, error) {
+	n, err := vc.inner.Read(b)
+	vc.gotSize += int64(n)
+	if err == io.EOF {
+		if vc.wantSize != SizeUnknown && vc.gotSize != vc.wantSize {
+			return n, fmt.Errorf("error verifying size; got %d, want %d", vc.gotSize, vc.wantSize)
+		}
+		got := hex.EncodeToString(vc.hasher.Sum(nil))
+		if want := vc.expected.Hex; got != want {
+			return n, Error{
+				got:     vc.expected.Algorithm + ":" + got,
+				want:    vc.expected,
+				gotSize: vc.gotSize,
+			}
+		}
+	}
+	return n, err
+}
+
+// ReadCloser wraps the given io.ReadCloser to verify that its contents match
+// the provided v1.Hash before io.EOF is returned.
+//
+// The reader will only be read up to size bytes, to prevent resource
+// exhaustion. If EOF is returned before size bytes are read, an error is
+// returned.
+//
+// A size of SizeUnknown (-1) indicates disables size verification when the size
+// is unknown ahead of time.
+func ReadCloser(r io.ReadCloser, size int64, h v1.Hash) (io.ReadCloser, error) {
+	w, err := v1.Hasher(h.Algorithm)
+	if err != nil {
+		return nil, err
+	}
+	r2 := io.TeeReader(r, w) // pass all writes to the hasher.
+	if size != SizeUnknown {
+		r2 = io.LimitReader(r2, size) // if we know the size, limit to that size.
+	}
+	return &and.ReadCloser{
+		Reader: &verifyReader{
+			inner:    r2,
+			hasher:   w,
+			expected: h,
+			wantSize: size,
+		},
+		CloseFunc: r.Close,
+	}, nil
+}
+
+// Descriptor verifies that the embedded Data field matches the Size and Digest
+// fields of the given v1.Descriptor, returning an error if the Data field is
+// missing or if it contains incorrect data.
+func Descriptor(d v1.Descriptor) error {
+	if d.Data == nil {
+		return errors.New("error verifying descriptor; Data == nil")
+	}
+
+	h, sz, err := v1.SHA256(bytes.NewReader(d.Data))
+	if err != nil {
+		return err
+	}
+	if h != d.Digest {
+		return fmt.Errorf("error verifying Digest; got %q, want %q", h, d.Digest)
+	}
+	if sz != d.Size {
+		return fmt.Errorf("error verifying Size; got %d, want %d", sz, d.Size)
+	}
+
+	return nil
+}