Factor CloseNotifier use into a new function

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

docs/handlers/helpers.go

@@ -1,8 +1,12 @@
 package handlers
 
 import (
+	"errors"
 	"io"
 	"net/http"
+
+	ctxu "github.com/docker/distribution/context"
+	"github.com/docker/distribution/registry/api/errcode"
 )
 
 // closeResources closes all the provided resources after running the target
@@ -15,3 +19,38 @@ func closeResources(handler http.Handler, closers ...io.Closer) http.Handler {
 		handler.ServeHTTP(w, r)
 	})
 }
+
+// copyFullPayload copies the payload of a HTTP request to destWriter. If it
+// receives less content than expected, and the client disconnected during the
+// upload, it avoids sending a 400 error to keep the logs cleaner.
+func copyFullPayload(responseWriter http.ResponseWriter, r *http.Request, destWriter io.Writer, context ctxu.Context, action string, errSlice *errcode.Errors) error {
+	// Get a channel that tells us if the client disconnects
+	var clientClosed <-chan bool
+	if notifier, ok := responseWriter.(http.CloseNotifier); ok {
+		clientClosed = notifier.CloseNotify()
+	} else {
+		panic("the ResponseWriter does not implement CloseNotifier")
+	}
+
+	// Read in the data, if any.
+	copied, err := io.Copy(destWriter, r.Body)
+	if clientClosed != nil && (err != nil || (r.ContentLength > 0 && copied < r.ContentLength)) {
+		// Didn't recieve as much content as expected. Did the client
+		// disconnect during the request? If so, avoid returning a 400
+		// error to keep the logs cleaner.
+		select {
+		case <-clientClosed:
+			ctxu.GetLogger(context).Error("client disconnected during " + action)
+			return errors.New("client disconnected")
+		default:
+		}
+	}
+
+	if err != nil {
+		ctxu.GetLogger(context).Errorf("unknown error reading request payload: %v", err)
+		*errSlice = append(*errSlice, errcode.ErrorCodeUnknown.WithDetail(err))
+		return err
+	}
+
+	return nil
+}