From 2604b0b8ecacf776b348a85a7221cb95ae60fef8 Mon Sep 17 00:00:00 2001
From: Neil Alexander <neilalexander@users.noreply.github.com>
Date: Mon, 21 Sep 2020 13:24:29 +0100
Subject: [PATCH] Update SQLite InsertPreviousEvent properly

---
 .../storage/sqlite3/previous_events_table.go  | 29 +++++++++++++++----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/roomserver/storage/sqlite3/previous_events_table.go b/roomserver/storage/sqlite3/previous_events_table.go
index 887c625c0..1b672912c 100644
--- a/roomserver/storage/sqlite3/previous_events_table.go
+++ b/roomserver/storage/sqlite3/previous_events_table.go
@@ -18,6 +18,8 @@ package sqlite3
 import (
 	"context"
 	"database/sql"
+	"fmt"
+	"strings"
 
 	"github.com/matrix-org/dendrite/internal/sqlutil"
 	"github.com/matrix-org/dendrite/roomserver/storage/shared"
@@ -43,8 +45,11 @@ const insertPreviousEventSQL = `
 	INSERT OR REPLACE INTO roomserver_previous_events
 	  (previous_event_id, previous_reference_sha256, event_nids)
 	  VALUES ($1, $2, $3)
-	  ON CONFLICT DO UPDATE
-	  SET event_nids = event_nids || ',' || $3
+`
+
+const selectPreviousEventNIDsSQL = `
+	SELECT event_nids FROM roomserver_previous_events
+	  WHERE previous_event_id = $1 AND previous_reference_sha256 = $2
 `
 
 // Check if the event is referenced by another event in the table.
@@ -57,6 +62,7 @@ const selectPreviousEventExistsSQL = `
 type previousEventStatements struct {
 	db                            *sql.DB
 	insertPreviousEventStmt       *sql.Stmt
+	selectPreviousEventNIDsStmt   *sql.Stmt
 	selectPreviousEventExistsStmt *sql.Stmt
 }
 
@@ -71,6 +77,7 @@ func NewSqlitePrevEventsTable(db *sql.DB) (tables.PreviousEvents, error) {
 
 	return s, shared.StatementList{
 		{&s.insertPreviousEventStmt, insertPreviousEventSQL},
+		{&s.selectPreviousEventNIDsStmt, selectPreviousEventNIDsSQL},
 		{&s.selectPreviousEventExistsStmt, selectPreviousEventExistsSQL},
 	}.Prepare(db)
 }
@@ -82,9 +89,21 @@ func (s *previousEventStatements) InsertPreviousEvent(
 	previousEventReferenceSHA256 []byte,
 	eventNID types.EventNID,
 ) error {
-	stmt := sqlutil.TxStmt(txn, s.insertPreviousEventStmt)
-	_, err := stmt.ExecContext(
-		ctx, previousEventID, previousEventReferenceSHA256, int64(eventNID),
+	var eventNIDs string
+	selectStmt := sqlutil.TxStmt(txn, s.selectPreviousEventExistsStmt)
+	err := selectStmt.QueryRowContext(ctx, previousEventID, previousEventReferenceSHA256).Scan(&eventNIDs)
+	if err != sql.ErrNoRows {
+		return fmt.Errorf("selectStmt.QueryRowContext.Scan: %w", err)
+	}
+	for _, nid := range strings.Split(eventNIDs, ",") {
+		if nid == fmt.Sprintf("%d", eventNID) {
+			return nil
+		}
+	}
+	eventNIDs = fmt.Sprintf("%s,%d", eventNIDs, eventNID)
+	insertStmt := sqlutil.TxStmt(txn, s.insertPreviousEventStmt)
+	_, err = insertStmt.ExecContext(
+		ctx, previousEventID, previousEventReferenceSHA256, eventNIDs,
 	)
 	return err
 }