mtc

Fork Notice

• This repository is a fork of github.com/mickamy/mtc.
• Module path has been changed to github.com/KiraboshiSys/mtc for long-term internal use.

mtc — Multi-Tenant Connector for Go (RLS + Context)

mtc is a lightweight Go library that automatically applies tenant-scoped context values (like app.tenant_id) to PostgreSQL connections using Row-Level Security (RLS).

Features

• Propagates tenant IDs from context.Context into PostgreSQL GUCs.
• Applies the tenant both for explicit transactions (BeginTx) and autocommit statements (QueryContext, ExecContext) by bracketing each query with set_config(..., false) / RESET.
• Works with any database/sql driver; pgx is supported out of the box.
• Validates tenant setting name to avoid SQL injection (reset setting safety).
• Keeps session state clean by resetting the tenant setting on pooled connections.

Installation

go get github.com/KiraboshiSys/mtc

Quick Start

package main

import (
	"context"
	"database/sql"
	"fmt"

	"github.com/jackc/pgx/v5/stdlib"
	"github.com/KiraboshiSys/mtc"
)

type tenantKey struct{}

func tenantFromContext(ctx context.Context) (string, error) {
	if v, ok := ctx.Value(tenantKey{}).(string); ok && v != "" {
		return v, nil
	}
	return "", nil
}

func main() {
	connector := mtc.New(
		stdlib.GetDefaultDriver(),
		"postgres://user:pass@localhost:5432/app?sslmode=disable",
		tenantFromContext,
		mtc.WithSettingName("app.tenant_id"),
	)

	db := sql.OpenDB(connector)
	defer db.Close()

	ctx := context.WithValue(context.Background(), tenantKey{}, "tenant-123")

	var tenant string
	if err := db.QueryRowContext(ctx, "select current_setting('app.tenant_id', true)").Scan(&tenant); err != nil {
		panic(err)
	}
	fmt.Println("tenant:", tenant)

	tx, err := db.BeginTx(ctx, nil)
	if err != nil {
		panic(err)
	}
	defer tx.Rollback()

	// Within this transaction the tenant is visible via current_setting as well.
}

mtc plays nicely with PostgreSQL RLS policies that depend on current_setting('app.tenant_id', true).

License

MIT