TLS Support for SwiftNIO, based on BoringSSL.

What's New

SwiftNIO SSL 2.26.0


SemVer Minor

  • Add support for shrinking massive ByteBufferBIOs (#443)
  • Bump minimum Swift version to 5.7 (#445)

SemVer Patch

  • fclose fix for linux-glibc 2.38 (#448, patch credit to @Saljooq)
  • Android: update Bionic declarations for nullability annotations added in NDK 26 (#449, patch credit to @finagolfin)
  • Changes to support building with Musl. (#450, patch credit to @al45tair)
  • Define _DARWIN_C_SOURCE on Darwin to fix the build in Xcode. (#451, patch credit to @al45tair)
  • Update BoringSSL to 3309ca66385ecb0c37f1ac1be9f88712e25aa8ec (#446)

Other Changes

  • Update Apple.com cert (#447)
  • Add cxx interop build pipeline (#454)
  • Update expired apple.com certificates (#455)


SwiftNIO SSL is a Swift package that contains an implementation of TLS based on BoringSSL. This package allows users of SwiftNIO to write protocol clients and servers that use TLS to secure data in flight.

The name is inspired primarily by the names of the library this package uses (BoringSSL), and not because we don't know the name of the protocol. We know the protocol is TLS!

To get started, check out the API docs.

Using SwiftNIO SSL

SwiftNIO SSL provides two ChannelHandlers to use to secure a data stream: the NIOSSLClientHandler and the NIOSSLServerHandler. Each of these can be added to a Channel to secure the communications on that channel.

Additionally, we provide a number of low-level primitives for configuring your TLS connections. These will be shown below.

To secure a server connection, you will need a X.509 certificate chain in a file (either PEM or DER, but PEM is far easier), and the associated private key for the leaf certificate. These objects can then be wrapped up in a TLSConfiguration object that is used to initialize the ChannelHandler.

For example:

let configuration = TLSConfiguration.makeServerConfiguration(
    certificateChain: try NIOSSLCertificate.fromPEMFile("cert.pem").map { .certificate($0) },
    privateKey: .file("key.pem")
let sslContext = try NIOSSLContext(configuration: configuration)

let server = ServerBootstrap(group: group)
    .childChannelInitializer { channel in
        // important: The handler must be initialized _inside_ the `childChannelInitializer`
        let handler = NIOSSLServerHandler(context: sslContext)


For clients, it is a bit simpler as there is no need to have a certificate chain or private key (though clients may have these things). Setup for clients may be done like this:

let configuration = TLSConfiguration.makeClientConfiguration()
let sslContext = try NIOSSLContext(configuration: configuration)

let client = ClientBootstrap(group: group)
    .channelInitializer { channel in
        // important: The handler must be initialized _inside_ the `channelInitializer`
        let handler = try NIOSSLClientHandler(context: sslContext)


The most recent versions of SwiftNIO SSL support Swift 5.7 and newer. The minimum Swift version supported by SwiftNIO SSL releases are detailed below:

SwiftNIO SSL Minimum Swift Version
2.0.0 ..< 2.14.0 5.0
2.14.0 ..< 2.19.0 5.2
2.19.0 ..< 2.23.0 5.4
2.23.0 ..< 2.23.2 5.5.2
2.23.2 ..< 2.26.0 5.6
2.26.0 ... 5.7


  • Swift Tools 5.7.0
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Last updated: Tue Apr 16 2024 10:15:56 GMT-0900 (Hawaii-Aleutian Daylight Time)