🐘 Non-blocking, event-driven Swift client for PostgreSQL.

What's New

Support parameter status messages in query / simpleQuery

This patch was authored and released by @tanner0101.

Adds support for parameter status (S) messages in query and simpleQuery calls (#116, fixes #115).


Documentation Team Chat MIT License Continuous Integration Swift 5.2

🐘 Non-blocking, event-driven Swift client for PostgreSQL built on SwiftNIO.

Major Releases

The table below shows a list of PostgresNIO major releases alongside their compatible NIO and Swift versions.

Version NIO Swift SPM
1.0 2.0+ 5.2+ from: "1.0.0"

Use the SPM string to easily include the dependendency in your Package.swift file.

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

Supported Platforms

PostgresNIO supports the following platforms:

  • Ubuntu 16.04+
  • macOS 10.15+


PostgresNIO is a client package for connecting to, authorizing, and querying a PostgreSQL server. At the heart of this module are NIO channel handlers for parsing and serializing messages in PostgreSQL'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 (binary) querying is provided out of the box alongside a PostgresData type that handles conversion between PostgreSQL's wire format and native Swift types.


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


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

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

  • Connection pooling
  • Swift Codable integration
  • Query building

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


This package has four dependencies:

This package has no additional system dependencies.

API Docs

Check out the PostgresNIO 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 PostgresNIO.

Creating a Connection

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

import PostgresNIO

let eventLoop: EventLoop = ...
let conn = try PostgresConnection.connect(
    to: .makeAddressResolvingHost("my.psql.server", port: 5432),
    on: eventLoop

Note: These examples will make use of wait() for simplicity. This is appropriate if you are using PostgresNIO 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. If supplied, the PostgreSQL connection will be upgraded to use SSL.
  • serverHostname An optional String to use in conjunction with tlsConfiguration to specify the server's hostname.

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

Client Protocol

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

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

import PostgresNIO

let client: PostgresClient = ...
// now we can use client to do queries

Simple Query

Simple (or text) queries allow you to execute a SQL string on the connected PostgreSQL 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 client.simpleQuery("SELECT version()").wait()
print(rows) // [["version": "11.0.0"]]

try client.simpleQuery("SELECT version()") { row in
    print(row) // ["version": "11.0.0"]

Parameterized Query

Parameterized (or binary) queries allow you to execute a SQL string on the connected PostgreSQL server. These queries support passing bound parameters as a separate argument. Each parameter is represented in the SQL string using incrementing placeholders, starting at $1.

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 client.query("SELECT * FROM planets WHERE name = $1", ["Earth"]).wait()
print(rows) // [["id": 42, "name": "Earth"]]

try client.query("SELECT * FROM planets WHERE name = $1", ["Earth"]) { row in
    print(row) // ["id": 42, "name": "Earth"]

Rows and Data

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

let row: PostgresRow = ...
let version = row.column("version")
print(version) // PostgresData?

PostgresRow columns are stored as PostgresData. This struct contains the raw bytes returned by PostgreSQL as well as some information for parsing them, such as:

  • Postgres column type
  • Wire format: binary or text
  • Value as array of bytes

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

let data: PostgresData= ...

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?

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

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

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

print(data.numeric) // PostgresNumeric?

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

Library development

If you want to contribute to the library development, here is how to get started.


To run the test, you need to start a local PostgreSQL database using Docker.

If you have Docker installed and running, you can use Docker Compose to start PostgreSQL:

The following command will download the required containers to run the test and start them:

$ docker-compose up -d psql-11

You can choose to run one of the following PostgreSQL version: psql-11, psql-10, psql-9, psql-ssl.

From another console or from Xcode, you can then run the test:

$ swift test

You can check that the test are passing, before adding your own to the test suite.

Finally, you can shut down and clean up Docker test environment with:

$ docker-compose down --volumes


  • Swift Tools 5.2.0


Last updated: Sun Aug 09 2020 15:25:07 GMT-0500 (GMT-05:00)