Fix Galaxy paging review findings

clients/go/mxgateway/galaxy.go

@@ -3,6 +3,7 @@ package mxgateway
 import (
 	"context"
 	"errors"
+	"fmt"
 	"io"
 	"time"
 
@@ -148,6 +149,7 @@ func (c *GalaxyClient) DiscoverHierarchy(ctx context.Context) ([]*GalaxyObject,
 	defer cancel()
 
 	var objects []*GalaxyObject
+	seenPageTokens := make(map[string]struct{})
 	pageToken := ""
 	for {
 		reply, err := c.raw.DiscoverHierarchy(callCtx, &pb.DiscoverHierarchyRequest{
@@ -162,6 +164,10 @@ func (c *GalaxyClient) DiscoverHierarchy(ctx context.Context) ([]*GalaxyObject,
 		if pageToken == "" {
 			break
 		}
+		if _, seen := seenPageTokens[pageToken]; seen {
+			return nil, fmt.Errorf("mxgateway: galaxy discover hierarchy returned repeated page token %q", pageToken)
+		}
+		seenPageTokens[pageToken] = struct{}{}
 	}
 	return objects, nil
 }

clients/go/mxgateway/galaxy_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"net"
+	"strings"
 	"testing"
 	"time"
 
@@ -159,6 +160,25 @@ func TestGalaxyDiscoverHierarchyReturnsObjects(t *testing.T) {
 	}
 }
 
+func TestGalaxyDiscoverHierarchyRejectsRepeatedPageToken(t *testing.T) {
+	fake := &fakeGalaxyServer{
+		discoverReplies: []*pb.DiscoverHierarchyReply{
+			{NextPageToken: "7:1"},
+			{NextPageToken: "7:1"},
+		},
+	}
+	client, cleanup := newGalaxyBufconnClient(t, fake)
+	defer cleanup()
+
+	_, err := client.DiscoverHierarchy(context.Background())
+	if err == nil {
+		t.Fatal("DiscoverHierarchy() error = nil, want repeated token error")
+	}
+	if !strings.Contains(err.Error(), "repeated page token") {
+		t.Fatalf("error = %v, want repeated page token", err)
+	}
+}
+
 func TestGalaxyDialReturnsGatewayErrorOnRpcFailure(t *testing.T) {
 	fake := &fakeGalaxyServer{failTest: true}
 	client, cleanup := newGalaxyBufconnClient(t, fake)