snapshot of https://github.com/ory/keto.git (master, 2026-09-16; blobs > 131072B omitted)

oryx/pagination/header.go

@@ -0,0 +1,96 @@
+// Copyright © 2023 Ory Corp
+// SPDX-License-Identifier: Apache-2.0
+
+package pagination
+
+import (
+	"fmt"
+	"math"
+	"net/http"
+	"net/url"
+	"strconv"
+	"strings"
+)
+
+func header(u *url.URL, rel string, limit, offset int64) string {
+	q := u.Query()
+	q.Set("limit", fmt.Sprintf("%d", limit))
+	q.Set("offset", fmt.Sprintf("%d", offset))
+	u.RawQuery = q.Encode()
+	return fmt.Sprintf("<%s>; rel=\"%s\"", u.String(), rel)
+}
+
+type formatter func(location *url.URL, rel string, itemsPerPage int64, offset int64) string
+
+// HeaderWithFormatter adds an HTTP header for pagination which uses a custom formatter for generating the URL links.
+func HeaderWithFormatter(w http.ResponseWriter, u *url.URL, total int64, page, itemsPerPage int, f formatter) {
+	if itemsPerPage <= 0 {
+		itemsPerPage = 1
+	}
+
+	itemsPerPage64 := int64(itemsPerPage)
+	offset := int64(page) * itemsPerPage64
+
+	// lastOffset will either equal the offset required to contain the remainder,
+	// or the limit.
+	var lastOffset int64
+	if total%itemsPerPage64 == 0 {
+		lastOffset = total - itemsPerPage64
+	} else {
+		lastOffset = (total / itemsPerPage64) * itemsPerPage64
+	}
+
+	w.Header().Set("X-Total-Count", strconv.FormatInt(total, 10))
+
+	// Check for last page
+	if offset >= lastOffset {
+		if total == 0 {
+			w.Header().Set("Link", strings.Join([]string{
+				f(u, "first", itemsPerPage64, 0),
+				f(u, "next", itemsPerPage64, ((offset/itemsPerPage64)+1)*itemsPerPage64),
+				f(u, "prev", itemsPerPage64, ((offset/itemsPerPage64)-1)*itemsPerPage64),
+			}, ","))
+			return
+		}
+
+		if total <= itemsPerPage64 {
+			w.Header().Set("link", f(u, "first", total, 0))
+			return
+		}
+
+		w.Header().Set("Link", strings.Join([]string{
+			f(u, "first", itemsPerPage64, 0),
+			f(u, "prev", itemsPerPage64, lastOffset-itemsPerPage64),
+		}, ","))
+		return
+	}
+
+	if offset < itemsPerPage64 {
+		w.Header().Set("Link", strings.Join([]string{
+			f(u, "next", itemsPerPage64, itemsPerPage64),
+			f(u, "last", itemsPerPage64, lastOffset),
+		}, ","))
+		return
+	}
+
+	w.Header().Set("Link", strings.Join([]string{
+		f(u, "first", itemsPerPage64, 0),
+		f(u, "next", itemsPerPage64, ((offset/itemsPerPage64)+1)*itemsPerPage64),
+		f(u, "prev", itemsPerPage64, ((offset/itemsPerPage64)-1)*itemsPerPage64),
+		f(u, "last", itemsPerPage64, lastOffset),
+	}, ","))
+}
+
+// Header adds an http header for pagination using a responsewriter where backwards compatibility is required.
+// The header will contain links any combination of the first, last, next, or previous (prev) pages in a paginated list (given a limit and an offset, and optionally a total).
+// If total is not set, then no "last" page will be calculated.
+// If no limit is provided, then it will default to 1.
+func Header(w http.ResponseWriter, u *url.URL, total int, limit, offset int) {
+	var page int
+	if limit == 0 {
+		limit = 1
+	}
+
+	page = int(math.Floor(float64(offset) / float64(limit)))
+	HeaderWithFormatter(w, u, int64(total), page, limit, header)
+}