[MM-141]: Made access to KV store atomically safe when saving/removing subscriptions (#840)

Author: Kshitij-Katiyar

server/plugin/plugin.go

@@ -68,6 +68,7 @@ type kvStore interface {
 	ListKeys(page int, count int, options ...pluginapi.ListKeysOption) ([]string, error)
 	Get(key string, o any) error
 	Delete(key string) error
+	SetAtomicWithRetries(key string, valueFunc func(oldValue []byte) (newValue interface{}, err error)) error
 }
 
 type Plugin struct {
@@ -169,7 +170,7 @@ func (p *Plugin) GetGitHubClient(ctx context.Context, userID string) (*github.Cl
 	return p.githubConnectUser(ctx, userInfo), nil
 }
 
-func (p *Plugin) githubConnectUser(ctx context.Context, info *GitHubUserInfo) *github.Client {
+func (p *Plugin) githubConnectUser(_ context.Context, info *GitHubUserInfo) *github.Client {
 	tok := *info.Token
 	return p.githubConnectToken(tok)
 }

server/plugin/subscriptions.go

@@ -2,6 +2,7 @@ package plugin
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"sort"
 	"strconv"
@@ -311,11 +312,14 @@ func (p *Plugin) GetSubscriptions() (*Subscriptions, error) {
 }
 
 func (p *Plugin) StoreSubscriptions(s *Subscriptions) error {
-	if _, err := p.store.Set(SubscriptionsKey, s); err != nil {
-		return errors.Wrap(err, "could not store subscriptions in KV store")
-	}
+	return p.store.SetAtomicWithRetries(SubscriptionsKey, func(_ []byte) (interface{}, error) {
+		modifiedBytes, err := json.Marshal(s)
+		if err != nil {
+			return nil, errors.Wrap(err, "could not store subscriptions in KV store")
+		}
 
-	return nil
+		return modifiedBytes, nil
+	})
 }
 
 func (p *Plugin) GetSubscribedChannelsForRepository(repo *github.Repository) []*Subscription {