fix(ui): unresponsive agent pool page (#701)

Fixes #698
Fixes #661

internal/agent/web.go

@@ -243,6 +243,7 @@ func (h *webHandlers) getAgentPool(w http.ResponseWriter, r *http.Request) {
 	// sets documented above.
 	allWorkspaces, err := resource.ListAll(func(opts resource.PageOptions) (*resource.Page[*workspacepkg.Workspace], error) {
 		return h.workspaces.List(r.Context(), workspacepkg.ListOptions{
+			PageOptions:  opts,
 			Organization: &pool.Organization,
 		})
 	})

internal/resource/pagination.go

@@ -1,6 +1,7 @@
 package resource
 
 import (
+	"errors"
 	"math"
 
 	"github.com/jackc/pgx/v5/pgtype"
@@ -71,12 +72,16 @@ func NewPage[T any](resources []T, opts PageOptions, count *int64) *Page[T] {
 	}
 }
 
+var ErrInfinitePaginationDetected = errors.New("infinite pagination detected")
+
 // ListAll is a helper for retrieving all pages. The provided fn should perform
 // an operation that retrieves a page at a time.
 func ListAll[T any](fn func(PageOptions) (*Page[T], error)) ([]T, error) {
 	var (
 		opts PageOptions
 		all  []T
+		// keep track of the last NextPage to prevent an infinite loop.
+		lastNextPage int
 	)
 	for {
 		page, err := fn(opts)
@@ -91,7 +96,11 @@ func ListAll[T any](fn func(PageOptions) (*Page[T], error)) ([]T, error) {
 		if page.NextPage == nil {
 			break
 		}
+		if *page.NextPage == lastNextPage {
+			return nil, ErrInfinitePaginationDetected
+		}
 		opts.PageNumber = *page.NextPage
+		lastNextPage = *page.NextPage
 	}
 	return all, nil
 }

internal/resource/pagination_test.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/leg100/otf/internal"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestPagination(t *testing.T) {
@@ -154,3 +155,41 @@ func TestNewPage(t *testing.T) {
 		})
 	}
 }
+
+func TestListAll(t *testing.T) {
+	type foo int
+
+	var page int
+	got, err := ListAll(func(opts PageOptions) (*Page[foo], error) {
+		if opts.PageNumber == 10 {
+			return &Page[foo]{
+				Pagination: &Pagination{},
+			}, nil
+		}
+		page++
+		return &Page[foo]{
+			Items: []foo{foo(page)},
+			Pagination: &Pagination{
+				NextPage: internal.Int(page),
+			},
+		}, nil
+	})
+	require.NoError(t, err)
+	assert.Equal(t, []foo{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, got)
+}
+
+func TestListAll_infinite_pagination(t *testing.T) {
+	type foo int
+
+	// This demonstrates an incorrectly implemented func being passed to
+	// ListAll, which retrieves the same page ad infinitum.
+	_, err := ListAll(func(opts PageOptions) (*Page[foo], error) {
+		return &Page[foo]{
+			Items: []foo{0},
+			Pagination: &Pagination{
+				NextPage: internal.Int(1),
+			},
+		}, nil
+	})
+	assert.Equal(t, ErrInfinitePaginationDetected, err)
+}