A Swift NIO based MQTT v3.1.1 and v5.0 client supporting NIOTransportServices (required for iOS), WebSocket connections and TLS through both NIOSSL and NIOTransportServices.
MQTT (Message Queuing Telemetry Transport) is a lightweight messaging protocol that was developed by IBM and first released in 1999. It uses the pub/sub pattern and translates messages between devices, servers, and applications. It is commonly used in Internet of things (IoT) technologies.
Create a client and connect to the MQTT broker.
let client = MQTTClient(
host: "mqtt.eclipse.org",
port: 1883,
identifier: "My Client",
eventLoopGroupProvider: .createNew
)
client.connect().whenComplete { result in
switch result {
case .success:
print("Succesfully connected")
case .failure(let error):
print("Error while connecting \(error)")
}
}
Subscribe to a topic and add a publish listener to report publish messages sent from the server/broker.
let subscription = MQTTSubscribeInfo(topicFilter: "my-topics", qos: .atLeastOnce)
client.subscribe(to: [subscription]).whenComplete { result in
...
}
client.addPublishListener("My Listener") { result in
switch result {
case .success(let publish):
var buffer = publish.payload
let string = buffer.readString(length: buffer.readableBytes)
print(string)
case .failure(let error):
print("Error while receiving PUBLISH event")
}
}
Publish to a topic.
client.publish(
to: "my-topics",
payload: ByteBuffer(string: "This is the Test payload"),
qos: .atLeastOnce
).whenComplete { result in
...
}
Each MQTTClient function returns a Swift NIO EventLoopFuture
. In the examples above I just use whenComplete
to process the results, but you can use various methods to chain EventLoopFuture
together. You can find out more about Swift NIO here.
Alongside the EventLoopFuture
APIs MQTTNIO also includes async/await versions. So where with EventLoopFutures
you would write
client.connect()
.flatMap { _ -> EventLoopFuture<MQTTSuback> in
let subscription = MQTTSubscribeInfo(topicFilter: "my-topics", qos: .atLeastOnce)
return client.subscribe(to: [subscription])
}
.whenComplete { result in
doStuff()
}
you can now replace it with
_ = try await client.connect()
let subscription = MQTTSubscribeInfo(topicFilter: "my-topics", qos: .atLeastOnce)
_ = try await client.subscribe(to: [subscription])
doStuff()
If you don't want to parse incoming PUBLISH packets via a callback the Swift concurrency support also includes an AsyncSequence
for this purpose.
let listener = client.createPublishListener()
for await result in listener {
switch result {
case .success(let publish):
var buffer = publish.payload
let string = buffer.readString(length: buffer.readableBytes)
print(string)
case .failure(let error):
print("Error while receiving PUBLISH event")
}
}
MQTT NIO supports TLS connections. You can enable this through the Configuration
provided at initialization. SetConfiguration.useSSL
to true
and provide your SSL certificates via the Configuration.tlsConfiguration
struct. For example to connect to the mosquitto test server test.mosquitto.org
on port 8884 you need to provide their root certificate and your own certificate. They provide details on the website https://test.mosquitto.org/ on how to generate these.
let rootCertificate = try NIOSSLCertificate.fromPEMBytes([UInt8](mosquittoCertificateText.utf8))
let myCertificate = try NIOSSLCertificate.fromPEMBytes([UInt8](myCertificateText.utf8))
let myPrivateKey = try NIOSSLPrivateKey(bytes: [UInt8](myPrivateKeyText.utf8), format: .pem)
let tlsConfiguration: TLSConfiguration? = TLSConfiguration.forClient(
trustRoots: .certificates(rootCertificate),
certificateChain: myCertificate.map { .certificate($0) },
privateKey: .privateKey(myPrivateKey)
)
let client = MQTTClient(
host: "test.mosquitto.org",
port: 8884,
identifier: "MySSLClient",
eventLoopGroupProvider: .createNew,
configuration: .init(useSSL: true, tlsConfiguration: .niossl(tlsConfiguration)),
)
MQTT also supports Web Socket connections. Set Configuration.useWebSockets
to true
and set the URL path in Configuration.webSocketsURLPath
to enable these.
On macOS and iOS you can use the NIO Transport Services library (NIOTS) and Apple's Network.framework
for communication with the MQTT broker. If you don't provide an eventLoopGroup
or a TLSConfigurationType
then this is the default for both platforms. If you do provide either of these then the library will base it's decision on whether to use NIOTS or NIOSSL on what you provide. Provide a MultiThreadedEventLoopGroup
or NIOSSL.TLSConfiguration
and the client will use NIOSSL. Provide a NIOTSEventLoopGroup
or TSTLSConfiguration
and the client will use NIOTS. If you provide a MultiThreadedEventLoopGroup
and a TSTLSConfiguration
then the client will throw an error. If you are running on iOS you should always choose NIOTS.
The MQTT client can be used to connect to AWS IoT brokers. You can use both a WebSocket connection authenticated using AWS Signature V4 and a standard connection using a X.509 client certificate. If you are using a X.509 certificate make sure you update the attached role to allow your client id to connect and which topics you can subscribe, publish to.
If you are using an AWS Signature V4 authenticated WebSocket connection you can use the V4 signer from SotoCore to sign your initial request as follows
import SotoSignerV4
let host = "MY_AWS_IOT_ENDPOINT.iot.eu-west-1.amazonaws.com"
let headers = HTTPHeaders([("host", host)])
let signer = AWSSigner(
credentials: StaticCredential(accessKeyId: "MYACCESSKEY", secretAccessKey: "MYSECRETKEY"),
name: "iotdata",
region: "eu-west-1"
)
let signedURL = signer.signURL(
url: URL(string: "https://\(host)/mqtt")!,
method: .GET,
headers: headers,
body: .none,
expires: .minutes(30)
)
let requestURI = "/mqtt?\(signedURL.query!)"
let client = MQTTClient(
host: host,
identifier: "MyAWSClient",
eventLoopGroupProvider: .createNew,
configuration: .init(useSSL: true, useWebSockets: true, webSocketURLPath: requestUri)
)
You can find out more about connecting to AWS brokers here
Version 2.0 of MQTTNIO added support for MQTT v5.0. To create a client that will connect to a v5 MQTT broker you need to set the version in the configuration as follows
let client = MQTTClient(
host: host,
identifier: "MyAWSClient",
eventLoopGroupProvider: .createNew,
configuration: .init(version: .v5_0)
)
You can then use the same functions available to the v3.1.1 client but there are also v5.0 specific versions of connect
, publish
, subscribe
, unsubscribe
and disconnect
. These can be accessed via the variable MQTTClient.v5
. The v5.0 functions add support for MQTT properties in both function parameters and return types and the additional subscription parameters. For example here is a publish
call adding the contentType
property.
let futureResponse = client.v5.publish(
to: "JSONTest",
payload: payload,
qos: .atLeastOnce,
properties: [.contentType("application/json")]
)
Whoever subscribes to the "JSONTest" topic with a v5.0 client will also receive the .contentType
property along with the payload.
You can find reference documentation for MQTTNIO here. There is also a sample demonstrating using MQTTNIO within an iOS app found here