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// Copyright 2017-2018 New Vector Ltd
// Copyright 2019-2020 The Matrix.org Foundation C.I.C.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package postgres
import (
"context"
"database/sql"
"github.com/matrix-org/dendrite/internal"
"github.com/matrix-org/dendrite/roomserver/types"
)
const previousEventSchema = `
-- The previous events table stores the event_ids referenced by the events
-- stored in the events table.
-- This is used to tell if a new event is already referenced by an event in
-- the database.
CREATE TABLE IF NOT EXISTS roomserver_previous_events (
-- The string event ID taken from the prev_events key of an event.
previous_event_id TEXT NOT NULL,
-- The SHA256 reference hash taken from the prev_events key of an event.
previous_reference_sha256 BYTEA NOT NULL,
-- A list of numeric event IDs of events that reference this prev_event.
event_nids BIGINT[] NOT NULL,
CONSTRAINT roomserver_previous_event_id_unique UNIQUE (previous_event_id, previous_reference_sha256)
);
`
// Insert an entry into the previous_events table.
// If there is already an entry indicating that an event references that previous event then
// add the event NID to the list to indicate that this event references that previous event as well.
// This should only be modified while holding a "FOR UPDATE" lock on the row in the rooms table for this room.
// The lock is necessary to avoid data races when checking whether an event is already referenced by another event.
const insertPreviousEventSQL = "" +
"INSERT INTO roomserver_previous_events" +
" (previous_event_id, previous_reference_sha256, event_nids)" +
" VALUES ($1, $2, array_append('{}'::bigint[], $3))" +
" ON CONFLICT ON CONSTRAINT roomserver_previous_event_id_unique" +
" DO UPDATE SET event_nids = array_append(roomserver_previous_events.event_nids, $3)" +
" WHERE $3 != ALL(roomserver_previous_events.event_nids)"
// Check if the event is referenced by another event in the table.
// This should only be done while holding a "FOR UPDATE" lock on the row in the rooms table for this room.
const selectPreviousEventExistsSQL = "" +
"SELECT 1 FROM roomserver_previous_events" +
" WHERE previous_event_id = $1 AND previous_reference_sha256 = $2"
type previousEventStatements struct {
insertPreviousEventStmt *sql.Stmt
selectPreviousEventExistsStmt *sql.Stmt
}
func (s *previousEventStatements) prepare(db *sql.DB) (err error) {
_, err = db.Exec(previousEventSchema)
if err != nil {
return
}
return statementList{
{&s.insertPreviousEventStmt, insertPreviousEventSQL},
{&s.selectPreviousEventExistsStmt, selectPreviousEventExistsSQL},
}.prepare(db)
}
func (s *previousEventStatements) insertPreviousEvent(
ctx context.Context,
txn *sql.Tx,
previousEventID string,
previousEventReferenceSHA256 []byte,
eventNID types.EventNID,
) error {
stmt := internal.TxStmt(txn, s.insertPreviousEventStmt)
_, err := stmt.ExecContext(
ctx, previousEventID, previousEventReferenceSHA256, int64(eventNID),
)
return err
}
// Check if the event reference exists
// Returns sql.ErrNoRows if the event reference doesn't exist.
func (s *previousEventStatements) selectPreviousEventExists(
ctx context.Context, txn *sql.Tx, eventID string, eventReferenceSHA256 []byte,
) error {
var ok int64
stmt := internal.TxStmt(txn, s.selectPreviousEventExistsStmt)
return stmt.QueryRowContext(ctx, eventID, eventReferenceSHA256).Scan(&ok)
}
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