prepare for public link thumbnails

- Implement a CS3 image source handler
 - Use checksum instead of etag for unique check
 - Simplify storage layout

thumbnails/pkg/thumbnail/imgsource/cs3.go

@@ -0,0 +1,78 @@
+package imgsource
+
+import (
+	"context"
+	"crypto/tls"
+	"fmt"
+	gateway "github.com/cs3org/go-cs3apis/cs3/gateway/v1beta1"
+	rpc "github.com/cs3org/go-cs3apis/cs3/rpc/v1beta1"
+	provider "github.com/cs3org/go-cs3apis/cs3/storage/provider/v1beta1"
+	"github.com/cs3org/reva/pkg/rhttp"
+	"github.com/cs3org/reva/pkg/token"
+	"github.com/pkg/errors"
+	"google.golang.org/grpc/metadata"
+	"image"
+	"net/http"
+)
+
+type CS3 struct {
+		client gateway.GatewayAPIClient
+}
+
+func NewCS3Source(c gateway.GatewayAPIClient) CS3 {
+	return CS3{
+		client: c,
+	}
+}
+
+func (s CS3) Get(ctx context.Context, path string) (image.Image, error) {
+	auth, _ := ContextGetAuthorization(ctx)
+	ctx = metadata.AppendToOutgoingContext(context.Background(), token.TokenHeader, auth)
+	rsp, err := s.client.InitiateFileDownload(ctx, &provider.InitiateFileDownloadRequest{
+		Ref: &provider.Reference{
+			Spec: &provider.Reference_Path{
+				Path: path,
+			},
+		} ,
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	if rsp.Status.Code != rpc.Code_CODE_OK {
+		return nil, fmt.Errorf("could not load image: %s", rsp.Status.Message)
+	}
+	var ep, tk string
+	for _, p := range rsp.Protocols {
+		if p.Protocol == "simple" {
+			ep, tk = p.DownloadEndpoint, p.Token
+		}
+	}
+
+	httpReq, err := rhttp.NewRequest(ctx, "GET", ep, nil)
+	if err != nil {
+		return nil, err
+	}
+	httpReq.Header.Set(token.TokenHeader, auth)
+	httpReq.Header.Set("X-REVA-TRANSFER", tk)
+
+	http.DefaultTransport.(*http.Transport).TLSClientConfig = &tls.Config{InsecureSkipVerify: true} //nolint:gosec
+	client := &http.Client{}
+
+	resp, err := client.Do(httpReq)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close() //nolint:errcheck
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("could not get the image \"%s\". Request returned with statuscode %d ", path, resp.StatusCode)
+	}
+
+	img, _, err := image.Decode(resp.Body)
+	if err != nil {
+		return nil, errors.Wrapf(err, `could not decode the image "%s"`, path)
+	}
+	return img, nil
+}