AsyncHTTPClient

This package provides simple HTTP Client library built on top of SwiftNIO.

This library provides the following:

Asynchronous and non-blocking request methods
Simple follow-redirects (cookie headers are dropped)
Streaming body download
TLS support
Automatic HTTP/2 over HTTPS (since version 1.7.0)
Cookie parsing (but not storage)

NOTE: You will need Xcode 11.4 or Swift 5.2 to try out AsyncHTTPClient.

Getting Started

Adding the dependency

Add the following entry in your Package.swift to start using HTTPClient:

.package(url: "https://github.com/swift-server/async-http-client.git", from: "1.0.0")

and AsyncHTTPClient dependency to your target:

.target(name: "MyApp", dependencies: [.product(name: "AsyncHTTPClient", package: "async-http-client")]),

Request-Response API

The code snippet below illustrates how to make a simple GET request to a remote server.

Please note that the example will spawn a new EventLoopGroup which will create fresh threads which is a very costly operation. In a real-world application that uses SwiftNIO for other parts of your application (for example a web server), please prefer eventLoopGroupProvider: .shared(myExistingEventLoopGroup) to share the EventLoopGroup used by AsyncHTTPClient with other parts of your application.

If your application does not use SwiftNIO yet, it is acceptable to use eventLoopGroupProvider: .createNew but please make sure to share the returned HTTPClient instance throughout your whole application. Do not create a large number of HTTPClient instances with eventLoopGroupProvider: .createNew, this is very wasteful and might exhaust the resources of your program.

import AsyncHTTPClient

let httpClient = HTTPClient(eventLoopGroupProvider: .createNew)
httpClient.get(url: "https://swift.org").whenComplete { result in
    switch result {
    case .failure(let error):
        // process error
    case .success(let response):
        if response.status == .ok {
            // handle response
        } else {
            // handle remote error
        }
    }
}

You should always shut down HTTPClient instances you created using try httpClient.syncShutdown(). Please note that you must not call httpClient.syncShutdown before all requests of the HTTP client have finished, or else the in-flight requests will likely fail because their network connections are interrupted.

Usage guide

Most common HTTP methods are supported out of the box. In case you need to have more control over the method, or you want to add headers or body, use the HTTPRequest struct:

import AsyncHTTPClient

let httpClient = HTTPClient(eventLoopGroupProvider: .createNew)
defer {
    try? httpClient.syncShutdown()
}

var request = try HTTPClient.Request(url: "https://swift.org", method: .POST)
request.headers.add(name: "User-Agent", value: "Swift HTTPClient")
request.body = .string("some-body")

httpClient.execute(request: request).whenComplete { result in
    switch result {
    case .failure(let error):
        // process error
    case .success(let response):
        if response.status == .ok {
            // handle response
        } else {
            // handle remote error
        }
    }
}

Redirects following

Enable follow-redirects behavior using the client configuration:

let httpClient = HTTPClient(eventLoopGroupProvider: .createNew,
                            configuration: HTTPClient.Configuration(followRedirects: true))

Timeouts

Timeouts (connect and read) can also be set using the client configuration:

let timeout = HTTPClient.Configuration.Timeout(connect: .seconds(1), read: .seconds(1))
let httpClient = HTTPClient(eventLoopGroupProvider: .createNew,
                            configuration: HTTPClient.Configuration(timeout: timeout))

or on a per-request basis:

httpClient.execute(request: request, deadline: .now() + .milliseconds(1))

Streaming

When dealing with larger amount of data, it's critical to stream the response body instead of aggregating in-memory. Handling a response stream is done using a delegate protocol. The following example demonstrates how to count the number of bytes in a streaming response body:

import NIOCore
import NIOHTTP1

class CountingDelegate: HTTPClientResponseDelegate {
    typealias Response = Int

    var count = 0

    func didSendRequestHead(task: HTTPClient.Task<Response>, _ head: HTTPRequestHead) {
        // this is executed right after request head was sent, called once
    }

    func didSendRequestPart(task: HTTPClient.Task<Response>, _ part: IOData) {
        // this is executed when request body part is sent, could be called zero or more times
    }

    func didSendRequest(task: HTTPClient.Task<Response>) {
        // this is executed when request is fully sent, called once
    }

    func didReceiveHead(
        task: HTTPClient.Task<Response>, 
        _ head: HTTPResponseHead
    ) -> EventLoopFuture<Void> {
        // this is executed when we receive HTTP response head part of the request 
        // (it contains response code and headers), called once in case backpressure 
        // is needed, all reads will be paused until returned future is resolved
        return task.eventLoop.makeSucceededFuture(())
    }

    func didReceiveBodyPart(
        task: HTTPClient.Task<Response>, 
        _ buffer: ByteBuffer
    ) -> EventLoopFuture<Void> {
        // this is executed when we receive parts of the response body, could be called zero or more times
        count += buffer.readableBytes
        // in case backpressure is needed, all reads will be paused until returned future is resolved
        return task.eventLoop.makeSucceededFuture(())
    }

    func didFinishRequest(task: HTTPClient.Task<Response>) throws -> Int {
        // this is called when the request is fully read, called once
        // this is where you return a result or throw any errors you require to propagate to the client
        return count
    }

    func didReceiveError(task: HTTPClient.Task<Response>, _ error: Error) {
        // this is called when we receive any network-related error, called once
    }
}

let request = try HTTPClient.Request(url: "https://swift.org")
let delegate = CountingDelegate()

httpClient.execute(request: request, delegate: delegate).futureResult.whenSuccess { count in
    print(count)
}

File downloads

Based on the HTTPClientResponseDelegate example above you can build more complex delegates, the built-in FileDownloadDelegate is one of them. It allows streaming the downloaded data asynchronously, while reporting the download progress at the same time, like in the following example:

let client = HTTPClient(eventLoopGroupProvider: .createNew)
let request = try HTTPClient.Request(
    url: "https://swift.org/builds/development/ubuntu1804/latest-build.yml"
)

let delegate = try FileDownloadDelegate(path: "/tmp/latest-build.yml", reportProgress: {
    if let totalBytes = $0.totalBytes {
        print("Total bytes count: \(totalBytes)")
    }
    print("Downloaded \($0.receivedBytes) bytes so far")
})

client.execute(request: request, delegate: delegate).futureResult
    .whenSuccess { progress in
        if let totalBytes = progress.totalBytes {
            print("Final total bytes count: \(totalBytes)")
        }
        print("Downloaded finished with \(progress.receivedBytes) bytes downloaded")
    }

Unix Domain Socket Paths

Connecting to servers bound to socket paths is easy:

let httpClient = HTTPClient(eventLoopGroupProvider: .createNew)
httpClient.execute(
    .GET, 
    socketPath: "/tmp/myServer.socket", 
    urlPath: "/path/to/resource"
).whenComplete (...)

Connecting over TLS to a unix domain socket path is possible as well:

let httpClient = HTTPClient(eventLoopGroupProvider: .createNew)
httpClient.execute(
    .POST, 
    secureSocketPath: "/tmp/myServer.socket", 
    urlPath: "/path/to/resource", 
    body: .string("hello")
).whenComplete (...)

Direct URLs can easily be constructed to be executed in other scenarios:

let socketPathBasedURL = URL(
    httpURLWithSocketPath: "/tmp/myServer.socket", 
    uri: "/path/to/resource"
)
let secureSocketPathBasedURL = URL(
    httpsURLWithSocketPath: "/tmp/myServer.socket", 
    uri: "/path/to/resource"
)

Disabling HTTP/2

The exclusive use of HTTP/1 is possible by setting httpVersion to .http1Only on HTTPClient.Configuration:

var configuration = HTTPClient.Configuration()
configuration.httpVersion = .http1Only
let client = HTTPClient(
    eventLoopGroupProvider: .createNew,
    configuration: configuration
)

Security

Please have a look at SECURITY.md for AsyncHTTPClient's security process.

vlm/async-http-client