Fix the PUT-existing bug in writable gateway API

See on https://discuss.ipfs.io/t/writeable-http-gateways/210

Previously, a PUT to a filename that already exists would return the hash
of the newly-inserted file instead of the hash of the new tree. This is not
useful, and it makes much more sense for the API to be consistent.

Furthermore, anybody who knows about the bug is already DELETE-ing the filename
before PUT-ing the new content, so the fix doesn't trample over that behaviour
either.

With this fix, every conceivable usage of the API is either unaffected or
improved.

It could do with a unit test.

License: MIT
Signed-off-by: James Stanley <james@incoherency.co.uk>

core/corehttp/gateway_handler.go

@@ -421,74 +421,39 @@ func (i *gatewayHandler) putHandler(w http.ResponseWriter, r *http.Request) {
 		newPath = path.Join(rsegs[2:])
 	}
 
-	var newcid cid.Cid
-	rnode, err := core.Resolve(ctx, i.node.Namesys, i.node.Resolver, rootPath)
-	switch ev := err.(type) {
-	case resolver.ErrNoLink:
-		// ev.Node < node where resolve failed
-		// ev.Name < new link
-		// but we need to patch from the root
-		c, err := cid.Decode(rsegs[1])
-		if err != nil {
-			webError(w, "putHandler: bad input path", err, http.StatusBadRequest)
-			return
-		}
-
-		rnode, err := i.node.DAG.Get(ctx, c)
-		if err != nil {
-			webError(w, "putHandler: Could not create DAG from request", err, http.StatusInternalServerError)
-			return
-		}
-
-		pbnd, ok := rnode.(*dag.ProtoNode)
-		if !ok {
-			webError(w, "Cannot read non protobuf nodes through gateway", dag.ErrNotProtobuf, http.StatusBadRequest)
-			return
-		}
-
-		e := dagutils.NewDagEditor(pbnd, i.node.DAG)
-		err = e.InsertNodeAtPath(ctx, newPath, newnode, ft.EmptyDirNode)
-		if err != nil {
-			webError(w, "putHandler: InsertNodeAtPath failed", err, http.StatusInternalServerError)
-			return
-		}
-
-		nnode, err := e.Finalize(ctx, i.node.DAG)
-		if err != nil {
-			webError(w, "putHandler: could not get node", err, http.StatusInternalServerError)
-			return
-		}
-
-		newcid = nnode.Cid()
+	c, err := cid.Decode(rsegs[1])
+	if err != nil {
+		webError(w, "putHandler: bad input path", err, http.StatusBadRequest)
+		return
+	}
 
-	case nil:
-		pbnd, ok := rnode.(*dag.ProtoNode)
-		if !ok {
-			webError(w, "Cannot read non protobuf nodes through gateway", dag.ErrNotProtobuf, http.StatusBadRequest)
-			return
-		}
+	rnode, err := i.node.DAG.Get(ctx, c)
+	if err != nil {
+		webError(w, "putHandler: Could not create DAG from request", err, http.StatusInternalServerError)
+		return
+	}
 
-		pbnewnode, ok := newnode.(*dag.ProtoNode)
-		if !ok {
-			webError(w, "Cannot read non protobuf nodes through gateway", dag.ErrNotProtobuf, http.StatusBadRequest)
-			return
-		}
+	pbnd, ok := rnode.(*dag.ProtoNode)
+	if !ok {
+		webError(w, "Cannot read non protobuf nodes through gateway", dag.ErrNotProtobuf, http.StatusBadRequest)
+		return
+	}
 
-		// object set-data case
-		pbnd.SetData(pbnewnode.Data())
+	e := dagutils.NewDagEditor(pbnd, i.node.DAG)
+	err = e.InsertNodeAtPath(ctx, newPath, newnode, ft.EmptyDirNode)
+	if err != nil {
+		webError(w, "putHandler: InsertNodeAtPath failed", err, http.StatusInternalServerError)
+		return
+	}
 
-		newcid = pbnd.Cid()
-		err = i.node.DAG.Add(ctx, pbnd)
-		if err != nil {
-			nnk := newnode.Cid()
-			webError(w, fmt.Sprintf("putHandler: Could not add newnode(%q) to root(%q)", nnk.String(), newcid.String()), err, http.StatusInternalServerError)
-			return
-		}
-	default:
-		webError(w, "could not resolve root DAG", ev, http.StatusInternalServerError)
+	nnode, err := e.Finalize(ctx, i.node.DAG)
+	if err != nil {
+		webError(w, "putHandler: could not get node", err, http.StatusInternalServerError)
 		return
 	}
 
+	newcid := nnode.Cid()
+
 	i.addUserHeaders(w) // ok, _now_ write user's headers.
 	w.Header().Set("IPFS-Hash", newcid.String())
 	http.Redirect(w, r, gopath.Join(ipfsPathPrefix, newcid.String(), newPath), http.StatusCreated)