Merge keyserver & userapi (#2972)

As discussed yesterday, a first draft of merging the keyserver and the
userapi.

userapi/storage/postgres/deltas/2022012016470000_key_changes.go

@@ -0,0 +1,69 @@
+// Copyright 2022 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 deltas
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+)
+
+func UpRefactorKeyChanges(ctx context.Context, tx *sql.Tx) error {
+	// start counting from the last max offset, else 0. We need to do a count(*) first to see if there
+	// even are entries in this table to know if we can query for log_offset. Without the count then
+	// the query to SELECT the max log offset fails on new Dendrite instances as log_offset doesn't
+	// exist on that table. Even though we discard the error, the txn is tainted and gets aborted :/
+	var count int
+	_ = tx.QueryRowContext(ctx, `SELECT count(*) FROM keyserver_key_changes`).Scan(&count)
+	if count > 0 {
+		var maxOffset int64
+		_ = tx.QueryRowContext(ctx, `SELECT coalesce(MAX(log_offset), 0) AS offset FROM keyserver_key_changes`).Scan(&maxOffset)
+		if _, err := tx.ExecContext(ctx, fmt.Sprintf(`CREATE SEQUENCE IF NOT EXISTS keyserver_key_changes_seq START %d`, maxOffset)); err != nil {
+			return fmt.Errorf("failed to CREATE SEQUENCE for key changes, starting at %d: %s", maxOffset, err)
+		}
+	}
+
+	_, err := tx.ExecContext(ctx, `
+		-- make the new table
+		DROP TABLE IF EXISTS keyserver_key_changes;
+		CREATE TABLE IF NOT EXISTS keyserver_key_changes (
+			change_id BIGINT PRIMARY KEY DEFAULT nextval('keyserver_key_changes_seq'),
+			user_id TEXT NOT NULL,
+			CONSTRAINT keyserver_key_changes_unique_per_user UNIQUE (user_id)
+		);
+	`)
+	if err != nil {
+		return fmt.Errorf("failed to execute upgrade: %w", err)
+	}
+	return nil
+}
+
+func DownRefactorKeyChanges(ctx context.Context, tx *sql.Tx) error {
+	_, err := tx.ExecContext(ctx, `
+	-- Drop all data and revert back, we can't keep the data as Kafka offsets determine the numbers
+	DROP SEQUENCE IF EXISTS keyserver_key_changes_seq;
+	DROP TABLE IF EXISTS keyserver_key_changes;
+	CREATE TABLE IF NOT EXISTS keyserver_key_changes (
+		partition BIGINT NOT NULL,
+		log_offset BIGINT NOT NULL,
+		user_id TEXT NOT NULL,
+		CONSTRAINT keyserver_key_changes_unique UNIQUE (partition, log_offset)
+	);
+	`)
+	if err != nil {
+		return fmt.Errorf("failed to execute downgrade: %w", err)
+	}
+	return nil
+}