Implement core redaction logic (#1185)

* Implement core redaction logic

- Add a new `redactions_table.go` which tracks the mapping of
  the redaction event ID and the redacted event ID
- Mark redactions as 'validated' when we have both events.
- When redactions are validated, add `unsigned.redacted_because`
  and modify the `eventJSON` accordingly.

Note: We currently do NOT redact the event content - it's gated
behind a feature flag - until we have tested redactions a bit more.

* Linting

3 files changed, 126 insertions, 2 deletions

diff --git a/roomserver/storage/sqlite3/event_json_table.go b/roomserver/storage/sqlite3/event_json_table.go
index da0c448d..6368675b 100644
--- a/roomserver/storage/sqlite3/event_json_table.go
+++ b/roomserver/storage/sqlite3/event_json_table.go
@@ -35,8 +35,7 @@ const eventJSONSchema = `
 `
 
 const insertEventJSONSQL = `
-	INSERT INTO roomserver_event_json (event_nid, event_json) VALUES ($1, $2)
-	  ON CONFLICT DO NOTHING
+	INSERT OR REPLACE INTO roomserver_event_json (event_nid, event_json) VALUES ($1, $2)
 `
 
 // Bulk event JSON lookup by numeric event ID.
diff --git a/roomserver/storage/sqlite3/redactions_table.go b/roomserver/storage/sqlite3/redactions_table.go
new file mode 100644
index 00000000..9910892c
--- /dev/null
+++ b/roomserver/storage/sqlite3/redactions_table.go
@@ -0,0 +1,120 @@
+// Copyright 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 sqlite3
+
+import (
+	"context"
+	"database/sql"
+
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/roomserver/storage/shared"
+	"github.com/matrix-org/dendrite/roomserver/storage/tables"
+)
+
+const redactionsSchema = `
+-- Stores information about the redacted state of events.
+-- We need to track redactions rather than blindly updating the event JSON table on receipt of a redaction
+-- because we might receive the redaction BEFORE we receive the event which it redacts (think backfill).
+CREATE TABLE IF NOT EXISTS roomserver_redactions (
+    redaction_event_id TEXT PRIMARY KEY,
+	redacts_event_id TEXT NOT NULL,
+	-- Initially FALSE, set to TRUE when the redaction has been validated according to rooms v3+ spec
+	-- https://matrix.org/docs/spec/rooms/v3#authorization-rules-for-events
+	validated BOOLEAN NOT NULL
+);
+`
+
+const insertRedactionSQL = "" +
+	"INSERT INTO roomserver_redactions (redaction_event_id, redacts_event_id, validated)" +
+	" VALUES ($1, $2, $3)"
+
+const selectRedactedEventSQL = "" +
+	"SELECT redaction_event_id, redacts_event_id, validated FROM roomserver_redactions" +
+	" WHERE redaction_event_id = $1"
+
+const selectRedactionEventSQL = "" +
+	"SELECT redaction_event_id, redacts_event_id, validated FROM roomserver_redactions" +
+	" WHERE redacts_event_id = $1"
+
+const markRedactionValidatedSQL = "" +
+	" UPDATE roomserver_redactions SET validated = $2 WHERE redaction_event_id = $1"
+
+type redactionStatements struct {
+	insertRedactionStmt        *sql.Stmt
+	selectRedactedEventStmt    *sql.Stmt
+	selectRedactionEventStmt   *sql.Stmt
+	markRedactionValidatedStmt *sql.Stmt
+}
+
+func NewSqliteRedactionsTable(db *sql.DB) (tables.Redactions, error) {
+	s := &redactionStatements{}
+	_, err := db.Exec(redactionsSchema)
+	if err != nil {
+		return nil, err
+	}
+
+	return s, shared.StatementList{
+		{&s.insertRedactionStmt, insertRedactionSQL},
+		{&s.selectRedactedEventStmt, selectRedactedEventSQL},
+		{&s.selectRedactionEventStmt, selectRedactionEventSQL},
+		{&s.markRedactionValidatedStmt, markRedactionValidatedSQL},
+	}.Prepare(db)
+}
+
+func (s *redactionStatements) InsertRedaction(
+	ctx context.Context, txn *sql.Tx, info tables.RedactionInfo,
+) error {
+	stmt := sqlutil.TxStmt(txn, s.insertRedactionStmt)
+	_, err := stmt.ExecContext(ctx, info.RedactionEventID, info.RedactsEventID, info.Validated)
+	return err
+}
+
+func (s *redactionStatements) SelectRedactedEvent(
+	ctx context.Context, txn *sql.Tx, redactionEventID string,
+) (info *tables.RedactionInfo, err error) {
+	info = &tables.RedactionInfo{}
+	stmt := sqlutil.TxStmt(txn, s.selectRedactedEventStmt)
+	err = stmt.QueryRowContext(ctx, redactionEventID).Scan(
+		&info.RedactionEventID, &info.RedactsEventID, &info.Validated,
+	)
+	if err == sql.ErrNoRows {
+		info = nil
+		err = nil
+	}
+	return
+}
+
+func (s *redactionStatements) SelectRedactionEvent(
+	ctx context.Context, txn *sql.Tx, redactedEventID string,
+) (info *tables.RedactionInfo, err error) {
+	info = &tables.RedactionInfo{}
+	stmt := sqlutil.TxStmt(txn, s.selectRedactionEventStmt)
+	err = stmt.QueryRowContext(ctx, redactedEventID).Scan(
+		&info.RedactionEventID, &info.RedactsEventID, &info.Validated,
+	)
+	if err == sql.ErrNoRows {
+		info = nil
+		err = nil
+	}
+	return
+}
+
+func (s *redactionStatements) MarkRedactionValidated(
+	ctx context.Context, txn *sql.Tx, redactionEventID string, validated bool,
+) error {
+	stmt := sqlutil.TxStmt(txn, s.markRedactionValidatedStmt)
+	_, err := stmt.ExecContext(ctx, redactionEventID, validated)
+	return err
+}
diff --git a/roomserver/storage/sqlite3/storage.go b/roomserver/storage/sqlite3/storage.go
index 767b13ce..11781ce0 100644
--- a/roomserver/storage/sqlite3/storage.go
+++ b/roomserver/storage/sqlite3/storage.go
@@ -114,6 +114,10 @@ func Open(dataSourceName string) (*Database, error) {
 	if err != nil {
 		return nil, err
 	}
+	redactions, err := NewSqliteRedactionsTable(d.db)
+	if err != nil {
+		return nil, err
+	}
 	d.Database = shared.Database{
 		DB:                  d.db,
 		EventsTable:         d.events,
@@ -129,6 +133,7 @@ func Open(dataSourceName string) (*Database, error) {
 		InvitesTable:        d.invites,
 		MembershipTable:     d.membership,
 		PublishedTable:      published,
+		RedactionsTable:     redactions,
 	}
 	return &d, nil
 }