fix: pagination via ForEach does not progress past first page (#1)

Pagination was never progressing past the first page because the
itemsSeen was being set to the TotalCount, meaning that the loop would
always exit after the first page.

I've added some tests to cover this.

Signed-off-by: Rob Best <[email protected]>

go.mod

@@ -10,6 +10,7 @@ require (
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/google/go-cmp v0.5.9 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -1,6 +1,8 @@
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
+github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/google/uuid v1.3.0 h1:t6JiXgmwXMjEs8VusXIJk2BXHsn+wx8BZdTaoZ5fu7I=
 github.com/google/uuid v1.3.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/jarcoal/httpmock v1.2.0 h1:gSvTxxFR/MEMfsGrvRbdfpRUMBStovlSRLw0Ep1bwwc=

util.go

@@ -38,7 +38,7 @@ func ForEach[T any](pageFetchFunc func(po PageOptions) (Page[T], error), handler
 			}
 		}
 
-		itemsSeen += page.TotalCount
+		itemsSeen += len(page.Items)
 		if len(page.Items) == 0 || itemsSeen >= page.TotalCount {
 			break
 		}

util_test.go

@@ -0,0 +1,105 @@
+package dtrack
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func TestFetchAll(t *testing.T) {
+	var wantItems []int
+	for i := 0; i < 468; i++ {
+		wantItems = append(wantItems, i)
+	}
+	gotItems, err := FetchAll(func(po PageOptions) (p Page[int], err error) {
+		for i := 0; i < po.PageSize; i++ {
+			idx := (po.PageSize * (po.PageNumber - 1)) + i
+			if idx >= len(wantItems) {
+				break
+			}
+			p.Items = append(p.Items, wantItems[idx])
+		}
+		p.TotalCount = len(wantItems)
+		return p, nil
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %s", err)
+	}
+	if diff := cmp.Diff(wantItems, gotItems); diff != "" {
+		t.Errorf("unexpected items:\n%s", diff)
+	}
+}
+
+func TestFetchAll_PageFetchFuncErr(t *testing.T) {
+	var testErr = errors.New("test error")
+	if _, err := FetchAll(
+		func(po PageOptions) (p Page[int], err error) {
+			return p, testErr
+		},
+	); !errors.Is(err, testErr) {
+		t.Errorf("expected err but got nil")
+	}
+}
+
+func TestForEach(t *testing.T) {
+	var (
+		wantItems []int
+		gotItems  []int
+	)
+	for i := 0; i < 468; i++ {
+		wantItems = append(wantItems, i)
+	}
+	if err := ForEach(
+		func(po PageOptions) (p Page[int], err error) {
+			for i := 0; i < po.PageSize; i++ {
+				idx := (po.PageSize * (po.PageNumber - 1)) + i
+				if idx >= len(wantItems) {
+					break
+				}
+				p.Items = append(p.Items, wantItems[idx])
+			}
+			p.TotalCount = len(wantItems)
+			return p, nil
+		},
+		func(item int) error {
+			gotItems = append(gotItems, item)
+			return nil
+		},
+	); err != nil {
+		t.Errorf("unexpected error calling ForEach: %s", err)
+	}
+	if diff := cmp.Diff(wantItems, gotItems); diff != "" {
+		t.Errorf("unexpected items:\n%s", diff)
+	}
+}
+
+func TestForEach_PageFetchFuncErr(t *testing.T) {
+	var testErr = errors.New("test error")
+	if err := ForEach(
+		func(po PageOptions) (p Page[int], err error) {
+			return p, testErr
+		},
+		func(item int) error {
+			return nil
+		},
+	); !errors.Is(err, testErr) {
+		t.Errorf("expected error from pageFetchFunc but got nil")
+	}
+}
+
+func TestForEach_HandlerFuncErr(t *testing.T) {
+	var testErr = errors.New("test error")
+	if err := ForEach(
+		func(po PageOptions) (p Page[int], err error) {
+			p.Items = []int{0, 1, 2, 3}
+			p.TotalCount = len(p.Items)
+			return p, nil
+		},
+		func(item int) error {
+			return testErr
+		},
+	); !errors.Is(err, testErr) {
+		t.Errorf("expected error from handlerFunc but got nil")
+	}
+}