🐬 Non-blocking, event-driven Swift client for MySQL.

What's New

1.7.2 - Avoid double-logging queries


What's Changed

Avoid double-logging queries by @gwynne in #110

This logging is handled in MySQLKit and should not be present at the MySQLNIO layer.


Thanks to the reviewers for their help:

This patch was released by @gwynne

Full Changelog: 1.7.1...1.7.2


Documentation Team Chat MIT License Continuous Integration Swift 5.7+

🐬 Non-blocking, event-driven Swift client for MySQL built on SwiftNIO.


Use standard SwiftPM syntax to include MySQLNIO as a dependency in your Package.swift file.

.package(url: "", from: "1.0.0")

Supported Platforms

MySQLNIO supports the following platforms:

  • Ubuntu 20.04+
  • macOS 10.15+
  • iOS 13+
  • tvOS 13+ and watchOS 7+ (experimental)


MySQLNIO is a client package for connecting to, authorizing, and querying a MySQL server. At the heart of this module are NIO channel handlers for parsing and serializing messages in MySQL's proprietary wire protocol. These channel handlers are combined in a request / response style connection type that provides a convenient, client-like interface for performing queries.

Support for both simple (text) and parameterized (prepared statement) querying is provided out of the box alongside a MySQLData type that handles conversion between MySQL's wire format and native Swift types.


Most Swift implementations of MySQL clients are based on the libmysqlclient C library which handles transport internally. Building a library directly on top of MySQL's wire protocol using SwiftNIO should yield a more reliable, maintainable, and performant interface for MySQL databases.


This package is meant to be a low-level, unopinionated MySQL wire-protocol implementation for Swift. The hope is that higher level packages can share MySQLNIO as a foundation for interacting with MySQL servers without needing to duplicate complex logic.

Because of this, MySQLNIO excludes some important concepts for the sake of simplicity, such as:

  • Connection pooling
  • Swift Codable integration
  • Query building

If you are looking for a MySQL client package to use in your project, take a look at these higher-level packages built on top of MySQLNIO:


This package has four dependencies:

This package has no additional system dependencies.

API Docs

Check out the MySQLNIO API docs for a detailed look at all of the classes, structs, protocols, and more.

Getting Started

This section will provide a quick look at using MySQLNIO.

Creating a Connection

The first step to making a query is creating a new MySQLConnection. The minimum requirements to create one are a SocketAddress, EventLoop, and credentials.

import MySQLNIO

let eventLoop: any EventLoop = ...
let conn = try await MySQLConnection(
    to: .makeAddressResolvingHost("my.mysql.server", port: 3306),
    username: "test_username",
    database: "test_database",
    password: "test_password",
    on: eventLoop

Note: These examples will make use of wait() for simplicity. This is appropriate if you are using MySQLNIO on the main thread, like for a CLI tool or in tests. However, you should never use wait() on an event loop.

There are a few ways to create a SocketAddress:

  • init(ipAddress: String, port: Int)
  • init(unixDomainSocketPath: String)
  • makeAddressResolvingHost(_ host: String, port: Int)

There are also some additional arguments you can supply to connect.

  • tlsConfiguration An optional TLSConfiguration struct. This will be used if the MySQL server supports TLS. Pass nil to opt-out of TLS.
  • serverHostname An optional String to use in conjunction with tlsConfiguration to specify the server's hostname.

connect will return a future MySQLConnection, or an error if it could not connect.

Database Protocol

Interaction with a server revolves around the MySQLDatabase protocol. This protocol includes methods like query(_:) for executing SQL queries and reading the resulting rows.

MySQLConnection is the default implementation of MySQLDatabase provided by this package. Assume the client here is the connection from the previous example.

import MySQLNIO

let db: any MySQLDatabase = ...
// now we can use client to do queries

Simple Query

Simple (text) queries allow you to execute a SQL string on the connected MySQL server. These queries do not support binding parameters, so any values sent must be escaped manually.

These queries are most useful for schema or transactional queries, or simple selects. Note that values returned by simple queries will be transferred in the less efficient text format.

simpleQuery has two overloads, one that returns an array of rows, and one that accepts a closure for handling each row as it is returned.

let rows = try await db.simpleQuery("SELECT @@version").get()
print(rows) // [["@@version": "8.x.x"]]

try await db.simpleQuery("SELECT @@version") { row in
    print(row) // ["@@version": "8.x.x"]

Parameterized Query

Parameterized (prepared statement) queries allow you to execute a SQL string on the connected MySQL server. These queries support passing bound parameters as a separate argument. Each parameter is represented in the SQL string using placeholders (?).

These queries are most useful for selecting, inserting, and updating data. Data for these queries is transferred using the highly efficient binary format.

Just like simpleQuery, query also offers two overloads. One that returns an array of rows, and one that accepts a closure for handling each row as it is returned.

let rows = try await db.query("SELECT * FROM planets WHERE name = ?", ["Earth"]).get()
print(rows) // [["id": 42, "name": "Earth"]]

try await db.query("SELECT * FROM planets WHERE name = ?", ["Earth"]) { row in
    print(row) // ["id": 42, "name": "Earth"]

Rows and Data

Both simpleQuery and query return the same MySQLRow type. Columns can be fetched from the row using the column(_:table:) method.

let row: any MySQLRow = ...
let version = row.column("name")
print(version) // MySQLData?

MySQLRow columns are stored as MySQLData. This struct contains the raw bytes returned by MySQL as well as some information for parsing them, such as:

  • MySQL data type
  • Wire format: binary or text
  • Value as array of bytes

MySQLData has a variety of convenience methods for converting column data to usable Swift types.

let data: MySQLData = ...

print(data.string) // String?

print( // Int?
print(data.int8) // Int8?
print(data.int16) // Int16?
print(data.int32) // Int32?
print(data.int64) // Int64?

print(data.uint) // UInt?
print(data.uint8) // UInt8?
print(data.uint16) // UInt16?
print(data.uint32) // UInt32?
print(data.uint64) // UInt64?

print(data.bool) // Bool?

try print(data.json(as: Foo.self)) // Foo?

print(data.float) // Float?
print(data.double) // Double?

print( // Date?
print(data.uuid) // UUID?
print(data.decimal) // Decimal?

print(data.time) // MySQLTime?

MySQLData is also used for sending data to the server via parameterized values. To create MySQLData from a Swift type, use the available intializer methods.


  • Swift Tools 5.7.0
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Last updated: Wed Jun 05 2024 18:33:52 GMT-0900 (Hawaii-Aleutian Daylight Time)