client: move content store client to containerd package

Signed-off-by: Jess Valarezo <valarezo.jessica@gmail.com>

content_reader.go

@@ -0,0 +1,49 @@
+package containerd
+
+import (
+	"context"
+
+	contentapi "github.com/containerd/containerd/api/services/content/v1"
+	digest "github.com/opencontainers/go-digest"
+)
+
+type remoteReaderAt struct {
+	ctx    context.Context
+	digest digest.Digest
+	size   int64
+	client contentapi.ContentClient
+}
+
+func (ra *remoteReaderAt) Size() int64 {
+	return ra.size
+}
+
+func (ra *remoteReaderAt) ReadAt(p []byte, off int64) (n int, err error) {
+	rr := &contentapi.ReadContentRequest{
+		Digest: ra.digest,
+		Offset: off,
+		Size_:  int64(len(p)),
+	}
+	rc, err := ra.client.Read(ra.ctx, rr)
+	if err != nil {
+		return 0, err
+	}
+
+	for len(p) > 0 {
+		var resp *contentapi.ReadContentResponse
+		// fill our buffer up until we can fill p.
+		resp, err = rc.Recv()
+		if err != nil {
+			return n, err
+		}
+
+		copied := copy(p, resp.Data)
+		n += copied
+		p = p[copied:]
+	}
+	return n, nil
+}
+
+func (ra *remoteReaderAt) Close() error {
+	return nil
+}