From 97e6e104b5eef4d36499754a28d595ff6a5dc372 Mon Sep 17 00:00:00 2001
From: Ben Brooks <ben.brooks@couchbase.com>
Date: Thu, 2 Nov 2023 13:27:35 +0000
Subject: [PATCH] Move currentRevChannels logic down into SyncData type

---
 db/document.go            | 48 ++++++++++++++++++++++++++++-----------
 db/revision_cache_test.go |  8 ++++++-
 2 files changed, 42 insertions(+), 14 deletions(-)

diff --git a/db/document.go b/db/document.go
index 161ff851e4..89b626d320 100644
--- a/db/document.go
+++ b/db/document.go
@@ -94,6 +94,41 @@ type SyncData struct {
 
 	addedRevisionBodies     []string          // revIDs of non-winning revision bodies that have been added (and so require persistence)
 	removedRevisionBodyKeys map[string]string // keys of non-winning revisions that have been removed (and so may require deletion), indexed by revID
+
+	currentRevChannels base.Set // A base.Set of the current revision's channels (determined by SyncData.Channels at UnmarshalJSON time)
+}
+
+func (sd *SyncData) UnmarshalJSON(b []byte) error {
+
+	// type alias avoids UnmarshalJSON stack overflow (forces fallback to standard JSON unmarshal instead of this one)
+	type stdSyncData SyncData
+	var tmp stdSyncData
+
+	err := base.JSONUnmarshal(b, &tmp)
+	if err != nil {
+		return err
+	}
+
+	*sd = SyncData(tmp)
+
+	// determine current revision's channels and store in-memory (avoids Channels iteration at access-check time)
+	sd.currentRevChannels = sd.getCurrentChannels()
+
+	return nil
+}
+
+// determine set of current channels based on removal entries.
+func (sd *SyncData) getCurrentChannels() base.Set {
+	if len(sd.Channels) > 0 {
+		ch := base.SetOf()
+		for channelName, channelRemoval := range sd.Channels {
+			if channelRemoval == nil || channelRemoval.Seq == 0 {
+				ch.Add(channelName)
+			}
+		}
+		return ch
+	}
+	return nil
 }
 
 func (sd *SyncData) HashRedact(salt string) SyncData {
@@ -180,8 +215,6 @@ type Document struct {
 	RevID          string
 	DocAttachments AttachmentsMeta
 	inlineSyncData bool
-
-	currentRevChannels base.Set // A base.Set of the current revision's channels (determined by SyncData.Channels at UnmarshalJSON time)
 }
 
 type historyOnlySyncData struct {
@@ -1075,17 +1108,6 @@ func (doc *Document) UnmarshalJSON(data []byte) error {
 		doc.SyncData = *syncData.SyncData
 	}
 
-	// determine current revision's channels and store in-memory (avoids doc.Channels iteration at access-check time)
-	if len(doc.Channels) > 0 {
-		ch := base.SetOf()
-		for channelName, channelRemoval := range doc.Channels {
-			if channelRemoval == nil || channelRemoval.Seq == 0 {
-				ch.Add(channelName)
-			}
-		}
-		doc.currentRevChannels = ch
-	}
-
 	// Unmarshal the rest of the doc body as map[string]interface{}
 	if err := doc._body.Unmarshal(data); err != nil {
 		return pkgerrors.WithStack(base.RedactErrorf("Failed to UnmarshalJSON() doc with id: %s.  Error: %v", base.UD(doc.ID), err))
diff --git a/db/revision_cache_test.go b/db/revision_cache_test.go
index 3bae02b261..9a6d38d56c 100644
--- a/db/revision_cache_test.go
+++ b/db/revision_cache_test.go
@@ -19,6 +19,7 @@ import (
 	"testing"
 
 	"github.com/couchbase/sync_gateway/base"
+	"github.com/couchbase/sync_gateway/channels"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -47,9 +48,14 @@ func (t *testBackingStore) GetDocument(ctx context.Context, docid string, unmars
 	doc.CurrentRev = "1-abc"
 	doc.History = RevTree{
 		doc.CurrentRev: {
-			Channels: base.SetOf("*"),
+			ID: doc.CurrentRev,
 		},
 	}
+	doc.Channels = channels.ChannelMap{
+		"*": &channels.ChannelRemoval{RevID: doc.CurrentRev},
+	}
+	// currentRevChannels usually populated on JSON unmarshal
+	doc.currentRevChannels = doc.getCurrentRevChannels()
 	return doc, nil
 }