implement client notify

chord/httpnode/client.go

@@ -48,7 +48,30 @@ func (cl *Client) FindSuccessor(ctx context.Context, s chord.Peer, id chord.ID)
 
 // Notify tells s we believe n to be its predecessor.
 func (cl *Client) Notify(ctx context.Context, n *chord.Node, s chord.Peer) error {
-	panic("not implemented") // TODO: Implement
+	_, addr := s.Values()
+	if !addr.IsValid() {
+		return errors.New("Notify with invalid peer")
+	}
+	_, self := n.Self().Values()
+	url := url.URL{
+		Scheme:   "http",
+		Host:     addr.String(),
+		Path:     path.Join("/", cl.APIBase, "pred"),
+		RawQuery: url.Values{"s": {self.String()}}.Encode(),
+	}
+	req, err := http.NewRequestWithContext(ctx, "POST", url.String(), nil)
+	if err != nil {
+		return err
+	}
+	resp, err := cl.HTTP.Do(req)
+	if err != nil {
+		return err
+	}
+	// We expect the server to only be capable of responding with No Content.
+	if resp.StatusCode != http.StatusNoContent {
+		return fmt.Errorf("strange response: %s", resp.Status)
+	}
+	return nil
 }
 
 // Neighbors requests a peer's beliefs about its own neighbors.

chord/topology.go

@@ -22,6 +22,10 @@ type Node struct {
 	fingers []Peer
 }
 
+func (n *Node) Self() Peer {
+	return n.self
+}
+
 func (n *Node) Successor() Peer {
 	return n.succ[0]
 }