feat: add token pagination link header parser (#722)

go.mod

@@ -58,6 +58,7 @@ require (
 	github.com/ory/herodot v0.9.13
 	github.com/ory/jsonschema/v3 v3.0.7
 	github.com/pelletier/go-toml v1.9.5
+	github.com/peterhellberg/link v1.2.0
 	github.com/pkg/errors v0.9.1
 	github.com/pkg/profile v1.7.0
 	github.com/prometheus/client_golang v1.13.0

go.sum

@@ -752,6 +752,8 @@ github.com/pelletier/go-toml v1.9.5 h1:4yBQzkHv+7BHq2PQUZF3Mx0IYxG7LsP222s7Agd3v
 github.com/pelletier/go-toml v1.9.5/go.mod h1:u1nR/EPcESfeI/szUZKdtJ0xRNbUoANCkoOuaOx1Y+c=
 github.com/pelletier/go-toml/v2 v2.0.6 h1:nrzqCb7j9cDFj2coyLNLaZuJTLjWjlaz6nvTvIwycIU=
 github.com/pelletier/go-toml/v2 v2.0.6/go.mod h1:eumQOmlWiOPt5WriQQqoM5y18pDHwha2N+QD+EUNTek=
+github.com/peterhellberg/link v1.2.0 h1:UA5pg3Gp/E0F2WdX7GERiNrPQrM1K6CVJUUWfHa4t6c=
+github.com/peterhellberg/link v1.2.0/go.mod h1:gYfAh+oJgQu2SrZHg5hROVRQe1ICoK0/HHJTcE0edxc=
 github.com/phayes/freeport v0.0.0-20180830031419-95f893ade6f2 h1:JhzVVoYvbOACxoUmOs6V/G4D5nPVUW73rKvXxP4XUJc=
 github.com/phayes/freeport v0.0.0-20180830031419-95f893ade6f2/go.mod h1:iIss55rKnNBTvrwdmkUpLnDpZoAHvWaiq5+iMmen4AE=
 github.com/phpdave11/gofpdf v1.4.2/go.mod h1:zpO6xFn9yxo3YLyMvW8HcKWVdbNqgIfOOp2dXMnm1mY=

pagination/keysetpagination/parse_header.go

@@ -0,0 +1,44 @@
+// Copyright © 2023 Ory Corp
+// SPDX-License-Identifier: Apache-2.0
+
+package keysetpagination
+
+import (
+	"net/http"
+	"net/url"
+
+	"github.com/peterhellberg/link"
+)
+
+// PaginationResult represents a parsed result of the link HTTP header.
+type PaginationResult struct {
+	// NextToken is the next page token. If it's empty, there is no next page.
+	NextToken string
+
+	// FirstToken is the first page token.
+	FirstToken string
+}
+
+// ParseHeader parses the response header's Link.
+func ParseHeader(r *http.Response) *PaginationResult {
+	links := link.ParseResponse(r)
+	return &PaginationResult{
+		NextToken:  findRel(links, "next"),
+		FirstToken: findRel(links, "first"),
+	}
+}
+
+func findRel(links link.Group, rel string) string {
+	for idx, l := range links {
+		if idx == rel {
+			parsed, err := url.Parse(l.URI)
+			if err != nil {
+				continue
+			}
+
+			return parsed.Query().Get("page_token")
+		}
+	}
+
+	return ""
+}

pagination/keysetpagination/parse_header_test.go

@@ -0,0 +1,49 @@
+// Copyright © 2023 Ory Corp
+// SPDX-License-Identifier: Apache-2.0
+
+package keysetpagination
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestParseHeader(t *testing.T) {
+	u, err := url.Parse("https://www.ory.sh/")
+	require.NoError(t, err)
+
+	t.Run("has next page", func(t *testing.T) {
+		p := &Paginator{
+			defaultToken: StringPageToken("default"),
+			token:        StringPageToken("next"),
+			size:         2,
+		}
+
+		r := httptest.NewRecorder()
+		Header(r, u, p)
+
+		result := ParseHeader(&http.Response{Header: r.Header()})
+		assert.Equal(t, "next", result.NextToken, r.Header())
+		assert.Equal(t, "default", result.FirstToken, r.Header())
+	})
+
+	t.Run("is last page", func(t *testing.T) {
+		p := &Paginator{
+			defaultToken: StringPageToken("default"),
+			size:         1,
+			isLast:       true,
+		}
+
+		r := httptest.NewRecorder()
+		Header(r, u, p)
+
+		result := ParseHeader(&http.Response{Header: r.Header()})
+		assert.Equal(t, "", result.NextToken, r.Header())
+		assert.Equal(t, "default", result.FirstToken, r.Header())
+	})
+}