From ce331a7d67fb26a09a4c3a15ec02fc75a2935c76 Mon Sep 17 00:00:00 2001
From: Scott Kay <noreply@syntaxnode.com>
Date: Thu, 8 Aug 2024 14:28:25 -0400
Subject: [PATCH] Fix: Aliases Of Bidders With UserSync Supports Declared Only
 (#3850)

---
 config/bidderinfo.go       |  17 ++++++-
 config/bidderinfo_test.go  | 101 +++++++++++++++++++++++++++++++++++++
 usersync/syncersbuilder.go |   6 +--
 3 files changed, 118 insertions(+), 6 deletions(-)

diff --git a/config/bidderinfo.go b/config/bidderinfo.go
index 6e38fc0c1db..6352728de5c 100644
--- a/config/bidderinfo.go
+++ b/config/bidderinfo.go
@@ -201,6 +201,21 @@ func (bi BidderInfo) IsEnabled() bool {
 	return !bi.Disabled
 }
 
+// Defined returns true if at least one field exists, except for the supports field.
+func (s *Syncer) Defined() bool {
+	if s == nil {
+		return false
+	}
+
+	return s.Key != "" ||
+		s.IFrame != nil ||
+		s.Redirect != nil ||
+		s.ExternalURL != "" ||
+		s.SupportCORS != nil ||
+		s.FormatOverride != "" ||
+		s.SkipWhen != nil
+}
+
 type InfoReader interface {
 	Read() (map[string][]byte, error)
 }
@@ -335,7 +350,7 @@ func processBidderAliases(aliasNillableFieldsByBidder map[string]aliasNillableFi
 		if aliasBidderInfo.PlatformID == "" {
 			aliasBidderInfo.PlatformID = parentBidderInfo.PlatformID
 		}
-		if aliasBidderInfo.Syncer == nil && parentBidderInfo.Syncer != nil {
+		if aliasBidderInfo.Syncer == nil && parentBidderInfo.Syncer.Defined() {
 			syncerKey := aliasBidderInfo.AliasOf
 			if parentBidderInfo.Syncer.Key != "" {
 				syncerKey = parentBidderInfo.Syncer.Key
diff --git a/config/bidderinfo_test.go b/config/bidderinfo_test.go
index 3305e34e88a..3837cfed815 100644
--- a/config/bidderinfo_test.go
+++ b/config/bidderinfo_test.go
@@ -8,6 +8,7 @@ import (
 	"gopkg.in/yaml.v3"
 
 	"github.com/prebid/prebid-server/v2/openrtb_ext"
+	"github.com/prebid/prebid-server/v2/util/ptrutil"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -401,6 +402,15 @@ func TestProcessAliasBidderInfo(t *testing.T) {
 		Key: "bidderA",
 	}
 
+	parentWithSyncerSupports := parentWithoutSyncerKey
+	parentWithSyncerSupports.Syncer = &Syncer{
+		Supports: []string{"iframe"},
+	}
+
+	aliasWithoutSyncer := parentWithoutSyncerKey
+	aliasWithoutSyncer.AliasOf = "bidderA"
+	aliasWithoutSyncer.Syncer = nil
+
 	testCases := []struct {
 		description         string
 		aliasInfos          map[string]aliasNillableFields
@@ -428,6 +438,26 @@ func TestProcessAliasBidderInfo(t *testing.T) {
 			expectedErr:         nil,
 			expectedBidderInfos: BidderInfos{"bidderA": parentWithSyncerKey, "bidderB": bidderB},
 		},
+		{
+			description: "inherit all parent info in alias bidder, except for syncer is parent only defines supports",
+			aliasInfos: map[string]aliasNillableFields{
+				"bidderB": {
+					Disabled:                nil,
+					ModifyingVastXmlAllowed: nil,
+					Experiment:              nil,
+					XAPI:                    nil,
+				},
+			},
+			bidderInfos: BidderInfos{
+				"bidderA": parentWithSyncerSupports,
+				"bidderB": BidderInfo{
+					AliasOf: "bidderA",
+					// all other fields should be inherited from parent bidder, except for syncer
+				},
+			},
+			expectedErr:         nil,
+			expectedBidderInfos: BidderInfos{"bidderA": parentWithSyncerSupports, "bidderB": aliasWithoutSyncer},
+		},
 		{
 			description: "inherit all parent info in alias bidder, use parent name as syncer alias key",
 			aliasInfos: map[string]aliasNillableFields{
@@ -1522,6 +1552,77 @@ func TestSyncerEndpointOverride(t *testing.T) {
 	}
 }
 
+func TestSyncerDefined(t *testing.T) {
+	testCases := []struct {
+		name        string
+		givenSyncer *Syncer
+		expected    bool
+	}{
+		{
+			name:        "nil",
+			givenSyncer: nil,
+			expected:    false,
+		},
+		{
+			name:        "empty",
+			givenSyncer: &Syncer{},
+			expected:    false,
+		},
+		{
+			name:        "key-only",
+			givenSyncer: &Syncer{Key: "anyKey"},
+			expected:    true,
+		},
+		{
+			name:        "iframe-only",
+			givenSyncer: &Syncer{IFrame: &SyncerEndpoint{}},
+			expected:    true,
+		},
+		{
+			name:        "redirect-only",
+			givenSyncer: &Syncer{Redirect: &SyncerEndpoint{}},
+			expected:    true,
+		},
+		{
+			name:        "externalurl-only",
+			givenSyncer: &Syncer{ExternalURL: "anyURL"},
+			expected:    true,
+		},
+		{
+			name:        "supportscors-only",
+			givenSyncer: &Syncer{SupportCORS: ptrutil.ToPtr(false)},
+			expected:    true,
+		},
+		{
+			name:        "formatoverride-only",
+			givenSyncer: &Syncer{FormatOverride: "anyFormat"},
+			expected:    true,
+		},
+		{
+			name:        "skipwhen-only",
+			givenSyncer: &Syncer{SkipWhen: &SkipWhen{}},
+			expected:    true,
+		},
+		{
+			name:        "supports-only",
+			givenSyncer: &Syncer{Supports: []string{"anySupports"}},
+			expected:    false,
+		},
+		{
+			name:        "supports-with-other",
+			givenSyncer: &Syncer{Key: "anyKey", Supports: []string{"anySupports"}},
+			expected:    true,
+		},
+	}
+
+	for _, test := range testCases {
+		t.Run(test.name, func(t *testing.T) {
+			result := test.givenSyncer.Defined()
+			assert.Equal(t, test.expected, result)
+		})
+	}
+}
+
 func TestApplyBidderInfoConfigSyncerOverrides(t *testing.T) {
 	var (
 		givenFileSystem = BidderInfos{"a": {Syncer: &Syncer{Key: "original"}}}
diff --git a/usersync/syncersbuilder.go b/usersync/syncersbuilder.go
index 9c916b821b4..ed86ef02efd 100644
--- a/usersync/syncersbuilder.go
+++ b/usersync/syncersbuilder.go
@@ -84,13 +84,9 @@ func shouldCreateSyncer(cfg config.BidderInfo) bool {
 		return false
 	}
 
-	if cfg.Syncer == nil {
-		return false
-	}
-
 	// a syncer may provide just a Supports field to provide hints to the host. we should only try to create a syncer
 	// if there is at least one non-Supports value populated.
-	return cfg.Syncer.Key != "" || cfg.Syncer.IFrame != nil || cfg.Syncer.Redirect != nil || cfg.Syncer.SupportCORS != nil
+	return cfg.Syncer.Defined()
 }
 
 func chooseSyncerConfig(biddersSyncerConfig []namedSyncerConfig) (namedSyncerConfig, error) {