From 4da2712b527a170d15ed4c6e7bd63c3d47ff3cf3 Mon Sep 17 00:00:00 2001
From: eyjhb <eyjhbb@gmail.com>
Date: Tue, 30 Jun 2020 08:45:56 +0200
Subject: [PATCH] added pagination to `v2/<name>/tags/list` endpoint

Signed-off-by: eyjhb <eyjhbb@gmail.com>
---
 registry/handlers/tags.go    | 47 ++++++++++++++++++++++++++++++++++++
 registry/storage/tagstore.go |  5 ++++
 2 files changed, 52 insertions(+)

diff --git a/registry/handlers/tags.go b/registry/handlers/tags.go
index 72d1dc8ff..0cc38102f 100644
--- a/registry/handlers/tags.go
+++ b/registry/handlers/tags.go
@@ -3,6 +3,8 @@ package handlers
 import (
 	"encoding/json"
 	"net/http"
+	"sort"
+	"strconv"
 
 	"github.com/distribution/distribution/v3"
 	"github.com/distribution/distribution/v3/registry/api/errcode"
@@ -49,6 +51,51 @@ func (th *tagsHandler) GetTags(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// do pagination if requested
+	q := r.URL.Query()
+	// get entries after latest, if any specified
+	if lastEntry := q.Get("last"); lastEntry != "" {
+		lastEntryIndex := sort.SearchStrings(tags, lastEntry)
+
+		// as`sort.SearchStrings` can return len(tags), if the
+		// specified `lastEntry` is not found, we need to
+		// ensure it does not panic when slicing.
+		if lastEntryIndex == len(tags) {
+			tags = []string{}
+		} else {
+			tags = tags[lastEntryIndex+1:]
+		}
+	}
+
+	// if no error, means that the user requested `n` entries
+	if n := q.Get("n"); n != "" {
+		maxEntries, err := strconv.Atoi(n)
+		if err != nil || maxEntries < 0 {
+			th.Errors = append(th.Errors, v2.ErrorCodePaginationNumberInvalid.WithDetail(map[string]string{"n": n}))
+			return
+		}
+
+		// if there is requested more than or
+		// equal to the amount of tags we have,
+		// then set the request to equal `len(tags)`.
+		// the reason for the `=`, is so the else
+		// clause will only activate if there
+		// are tags left the user needs.
+		if maxEntries >= len(tags) {
+			maxEntries = len(tags)
+		} else if maxEntries > 0 {
+			// defined in `catalog.go`
+			urlStr, err := createLinkEntry(r.URL.String(), maxEntries, tags[maxEntries-1])
+			if err != nil {
+				th.Errors = append(th.Errors, errcode.ErrorCodeUnknown.WithDetail(err))
+				return
+			}
+			w.Header().Set("Link", urlStr)
+		}
+
+		tags = tags[:maxEntries]
+	}
+
 	w.Header().Set("Content-Type", "application/json")
 
 	enc := json.NewEncoder(w)
diff --git a/registry/storage/tagstore.go b/registry/storage/tagstore.go
index e33bf9da7..7bbb2f01f 100644
--- a/registry/storage/tagstore.go
+++ b/registry/storage/tagstore.go
@@ -3,6 +3,7 @@ package storage
 import (
 	"context"
 	"path"
+	"sort"
 
 	"github.com/distribution/distribution/v3"
 	storagedriver "github.com/distribution/distribution/v3/registry/storage/driver"
@@ -47,6 +48,10 @@ func (ts *tagStore) All(ctx context.Context) ([]string, error) {
 		tags = append(tags, filename)
 	}
 
+	// there is no guarantee for the order,
+	// therefore sort before return.
+	sort.Strings(tags)
+
 	return tags, nil
 }