implement client neighbors

chord/httpnode/client.go

@@ -76,5 +76,34 @@ func (cl *Client) Notify(ctx context.Context, n *chord.Node, s chord.Peer) error
 
 // Neighbors requests a peer's beliefs about its own neighbors.
 func (cl *Client) Neighbors(ctx context.Context, p chord.Peer) (pred chord.Peer, succ []chord.Peer, err error) {
-	panic("not implemented") // TODO: Implement
+	_, addr := p.Values()
+	if !addr.IsValid() {
+		return chord.Peer{}, nil, errors.New("Neighbors with invalid peer")
+	}
+	url := url.URL{
+		Scheme: "http",
+		Host:   addr.String(),
+		Path:   path.Join("/", cl.APIBase, "neighbors"),
+	}
+	req, err := http.NewRequestWithContext(ctx, "GET", url.String(), nil)
+	if err != nil {
+		return chord.Peer{}, nil, err
+	}
+	resp, err := cl.HTTP.Do(req)
+	if err != nil {
+		return chord.Peer{}, nil, err
+	}
+	n, err := readResponse[neighbors](resp)
+	if err != nil {
+		return chord.Peer{}, nil, fmt.Errorf("%w (%s)", err, resp.Status)
+	}
+	pred = chord.Address(n.Pred)
+	succ = make([]chord.Peer, 0, len(n.Succ))
+	for _, addr := range n.Succ {
+		p := chord.Address(addr)
+		if p.IsValid() {
+			succ = append(succ, p)
+		}
+	}
+	return pred, succ, nil
 }