Move content to core/content

Signed-off-by: Derek McGowan <derek@mcg.dev>

core/content/proxy/content_reader.go

@@ -0,0 +1,71 @@
+/*
+   Copyright The containerd 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 proxy
+
+import (
+	"context"
+
+	contentapi "github.com/containerd/containerd/v2/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.String(),
+		Offset: off,
+		Size:   int64(len(p)),
+	}
+	// we need a child context with cancel, or the eventually called
+	// grpc.NewStream will leak the goroutine until the whole thing is cleared.
+	// See comment at https://godoc.org/google.golang.org/grpc#ClientConn.NewStream
+	childCtx, cancel := context.WithCancel(ra.ctx)
+	// we MUST cancel the child context; see comment above
+	defer cancel()
+	rc, err := ra.client.Read(childCtx, 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
+}