feat: load model from oci image

vendor/oras.land/oras-go/v2/internal/ioutil/io.go

@@ -0,0 +1,58 @@
+/*
+Copyright The ORAS Authors.
+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 ioutil
+
+import (
+	"fmt"
+	"io"
+	"reflect"
+
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"oras.land/oras-go/v2/content"
+)
+
+// CloserFunc is the basic Close method defined in io.Closer.
+type CloserFunc func() error
+
+// Close performs close operation by the CloserFunc.
+func (fn CloserFunc) Close() error {
+	return fn()
+}
+
+// CopyBuffer copies from src to dst through the provided buffer
+// until either EOF is reached on src, or an error occurs.
+// The copied content is verified against the size and the digest.
+func CopyBuffer(dst io.Writer, src io.Reader, buf []byte, desc ocispec.Descriptor) error {
+	// verify while copying
+	vr := content.NewVerifyReader(src, desc)
+	if _, err := io.CopyBuffer(dst, vr, buf); err != nil {
+		return fmt.Errorf("copy failed: %w", err)
+	}
+	return vr.Verify()
+}
+
+// nopCloserType is the type of `io.NopCloser()`.
+var nopCloserType = reflect.TypeOf(io.NopCloser(nil))
+
+// UnwrapNopCloser unwraps the reader wrapped by `io.NopCloser()`.
+// Similar implementation can be found in the built-in package `net/http`.
+// Reference: https://github.com/golang/go/blob/go1.17.6/src/net/http/transfer.go#L423-L425
+func UnwrapNopCloser(rc io.Reader) io.Reader {
+	if reflect.TypeOf(rc) == nopCloserType {
+		return reflect.ValueOf(rc).Field(0).Interface().(io.Reader)
+	}
+	return rc
+}