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