HTTPClient.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the AsyncHTTPClient open source project
//
// Copyright (c) 2018-2019 Swift Server Working Group and the AsyncHTTPClient project authors
// Licensed under Apache License v2.0
//
// See LICENSE.txt for license information
// See CONTRIBUTORS.txt for the list of AsyncHTTPClient project authors
//
// SPDX-License-Identifier: Apache-2.0
//
//===----------------------------------------------------------------------===//

import Foundation
import NIO
import NIOConcurrencyHelpers
import NIOHTTP1
import NIOSSL

/// HTTPClient class provides API for request execution.
///
/// Example:
///
/// ```swift
///     let client = HTTPClient(eventLoopGroupProvider = .createNew)
///     client.get(url: "https://swift.org", deadline: .now() + .seconds(1)).whenComplete { result in
///         switch result {
///         case .failure(let error):
///             // process error
///         case .success(let response):
///             if let response.status == .ok {
///                 // handle response
///             } else {
///                 // handle remote error
///             }
///         }
///     }
/// ```
///
/// It is important to close the client instance, for example in a defer statement, after use to cleanly shutdown the underlying NIO `EventLoopGroup`:
///
/// ```swift
///     try client.syncShutdown()
/// ```
public class HTTPClient {
    public let eventLoopGroup: EventLoopGroup
    let eventLoopGroupProvider: EventLoopGroupProvider
    let configuration: Configuration
    let isShutdown = Atomic<Bool>(value: false)

    /// Create an `HTTPClient` with specified `EventLoopGroup` provider and configuration.
    ///
    /// - parameters:
    ///     - eventLoopGroupProvider: Specify how `EventLoopGroup` will be created.
    ///     - configuration: Client configuration.
    public init(eventLoopGroupProvider: EventLoopGroupProvider, configuration: Configuration = Configuration()) {
        self.eventLoopGroupProvider = eventLoopGroupProvider
        switch self.eventLoopGroupProvider {
        case .shared(let group):
            self.eventLoopGroup = group
        case .createNew:
            self.eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: 1)
        }
        self.configuration = configuration
    }

    deinit {
        assert(self.isShutdown.load(), "Client not shut down before the deinit. Please call client.syncShutdown() when no longer needed.")
    }

    /// Shuts down the client and `EventLoopGroup` if it was created by the client.
    public func syncShutdown() throws {
        switch self.eventLoopGroupProvider {
        case .shared:
            self.isShutdown.store(true)
            return
        case .createNew:
            if self.isShutdown.compareAndExchange(expected: false, desired: true) {
                try self.eventLoopGroup.syncShutdownGracefully()
            } else {
                throw HTTPClientError.alreadyShutdown
            }
        }
    }

    /// Execute `GET` request using specified URL.
    ///
    /// - parameters:
    ///     - url: Remote URL.
    ///     - deadline: Point in time by which the request must complete.
    public func get(url: String, deadline: NIODeadline? = nil) -> EventLoopFuture<Response> {
        do {
            let request = try Request(url: url, method: .GET)
            return self.execute(request: request, deadline: deadline)
        } catch {
            return self.eventLoopGroup.next().makeFailedFuture(error)
        }
    }

    /// Execute `POST` request using specified URL.
    ///
    /// - parameters:
    ///     - url: Remote URL.
    ///     - body: Request body.
    ///     - deadline: Point in time by which the request must complete.
    public func post(url: String, body: Body? = nil, deadline: NIODeadline? = nil) -> EventLoopFuture<Response> {
        do {
            let request = try HTTPClient.Request(url: url, method: .POST, body: body)
            return self.execute(request: request, deadline: deadline)
        } catch {
            return self.eventLoopGroup.next().makeFailedFuture(error)
        }
    }

    /// Execute `PATCH` request using specified URL.
    ///
    /// - parameters:
    ///     - url: Remote URL.
    ///     - body: Request body.
    ///     - deadline: Point in time by which the request must complete.
    public func patch(url: String, body: Body? = nil, deadline: NIODeadline? = nil) -> EventLoopFuture<Response> {
        do {
            let request = try HTTPClient.Request(url: url, method: .PATCH, body: body)
            return self.execute(request: request, deadline: deadline)
        } catch {
            return self.eventLoopGroup.next().makeFailedFuture(error)
        }
    }

    /// Execute `PUT` request using specified URL.
    ///
    /// - parameters:
    ///     - url: Remote URL.
    ///     - body: Request body.
    ///     - deadline: Point in time by which the request must complete.
    public func put(url: String, body: Body? = nil, deadline: NIODeadline? = nil) -> EventLoopFuture<Response> {
        do {
            let request = try HTTPClient.Request(url: url, method: .PUT, body: body)
            return self.execute(request: request, deadline: deadline)
        } catch {
            return self.eventLoopGroup.next().makeFailedFuture(error)
        }
    }

    /// Execute `DELETE` request using specified URL.
    ///
    /// - parameters:
    ///     - url: Remote URL.
    ///     - deadline: The time when the request must have been completed by.
    public func delete(url: String, deadline: NIODeadline? = nil) -> EventLoopFuture<Response> {
        do {
            let request = try Request(url: url, method: .DELETE)
            return self.execute(request: request, deadline: deadline)
        } catch {
            return self.eventLoopGroup.next().makeFailedFuture(error)
        }
    }

    /// Execute arbitrary HTTP request using specified URL.
    ///
    /// - parameters:
    ///     - request: HTTP request to execute.
    ///     - deadline: Point in time by which the request must complete.
    public func execute(request: Request, deadline: NIODeadline? = nil) -> EventLoopFuture<Response> {
        let accumulator = ResponseAccumulator(request: request)
        return self.execute(request: request, delegate: accumulator, deadline: deadline).futureResult
    }

    /// Execute arbitrary HTTP request using specified URL.
    ///
    /// - parameters:
    ///     - request: HTTP request to execute.
    ///     - eventLoop: NIO Event Loop preference.
    ///     - deadline: Point in time by which the request must complete.
    public func execute(request: Request, eventLoop: EventLoopPreference, deadline: NIODeadline? = nil) -> EventLoopFuture<Response> {
        let accumulator = ResponseAccumulator(request: request)
        return self.execute(request: request, delegate: accumulator, eventLoop: eventLoop, deadline: deadline).futureResult
    }

    /// Execute arbitrary HTTP request and handle response processing using provided delegate.
    ///
    /// - parameters:
    ///     - request: HTTP request to execute.
    ///     - delegate: Delegate to process response parts.
    ///     - deadline: Point in time by which the request must complete.
    public func execute<Delegate: HTTPClientResponseDelegate>(request: Request,
                                                              delegate: Delegate,
                                                              deadline: NIODeadline? = nil) -> Task<Delegate.Response> {
        let eventLoop = self.eventLoopGroup.next()
        return self.execute(request: request, delegate: delegate, eventLoop: eventLoop, deadline: deadline)
    }

    /// Execute arbitrary HTTP request and handle response processing using provided delegate.
    ///
    /// - parameters:
    ///     - request: HTTP request to execute.
    ///     - delegate: Delegate to process response parts.
    ///     - eventLoop: NIO Event Loop preference.
    ///     - deadline: Point in time by which the request must complete.
    public func execute<Delegate: HTTPClientResponseDelegate>(request: Request,
                                                              delegate: Delegate,
                                                              eventLoop: EventLoopPreference,
                                                              deadline: NIODeadline? = nil) -> Task<Delegate.Response> {
        switch eventLoop.preference {
        case .indifferent:
            return self.execute(request: request, delegate: delegate, eventLoop: self.eventLoopGroup.next(), deadline: deadline)
        case .prefers(let preferred):
            precondition(self.eventLoopGroup.makeIterator().contains { $0 === preferred }, "Provided EventLoop must be part of clients EventLoopGroup.")
            return self.execute(request: request, delegate: delegate, eventLoop: preferred, deadline: deadline)
        }
    }

    private func execute<Delegate: HTTPClientResponseDelegate>(request: Request,
                                                               delegate: Delegate,
                                                               eventLoop: EventLoop,
                                                               deadline: NIODeadline? = nil) -> Task<Delegate.Response> {
        let redirectHandler: RedirectHandler<Delegate.Response>?
        if self.configuration.followRedirects {
            redirectHandler = RedirectHandler<Delegate.Response>(request: request) { newRequest in
                self.execute(request: newRequest, delegate: delegate, eventLoop: eventLoop, deadline: deadline)
            }
        } else {
            redirectHandler = nil
        }

        let task = Task<Delegate.Response>(eventLoop: eventLoop)

        var bootstrap = ClientBootstrap(group: eventLoop)
            .channelOption(ChannelOptions.socket(SocketOptionLevel(IPPROTO_TCP), TCP_NODELAY), value: 1)
            .channelInitializer { channel in
                let encoder = HTTPRequestEncoder()
                let decoder = ByteToMessageHandler(HTTPResponseDecoder(leftOverBytesStrategy: .forwardBytes))
                return channel.pipeline.addHandlers([encoder, decoder], position: .first).flatMap {
                    switch self.configuration.proxy {
                    case .none:
                        return channel.pipeline.addSSLHandlerIfNeeded(for: request, tlsConfiguration: self.configuration.tlsConfiguration)
                    case .some(let proxy):
                        return channel.pipeline.addProxyHandler(for: request, decoder: decoder, encoder: encoder, tlsConfiguration: self.configuration.tlsConfiguration, proxy: proxy)
                    }
                }.flatMap {
                    switch self.configuration.decompression {
                    case .disabled:
                        return channel.eventLoop.makeSucceededFuture(())
                    case .enabled(let limit):
                        return channel.pipeline.addHandler(HTTPResponseDecompressor(limit: limit))
                    }
                }.flatMap {
                    if let timeout = self.resolve(timeout: self.configuration.timeout.read, deadline: deadline) {
                        return channel.pipeline.addHandler(IdleStateHandler(readTimeout: timeout))
                    } else {
                        return channel.eventLoop.makeSucceededFuture(())
                    }
                }.flatMap {
                    let taskHandler = TaskHandler(task: task, delegate: delegate, redirectHandler: redirectHandler, ignoreUncleanSSLShutdown: self.configuration.ignoreUncleanSSLShutdown)
                    return channel.pipeline.addHandler(taskHandler)
                }
            }

        if let timeout = self.resolve(timeout: self.configuration.timeout.connect, deadline: deadline) {
            bootstrap = bootstrap.connectTimeout(timeout)
        }

        let address = self.resolveAddress(request: request, proxy: self.configuration.proxy)
        bootstrap.connect(host: address.host, port: address.port)
            .map { channel in
                task.setChannel(channel)
            }
            .flatMap { channel in
                channel.writeAndFlush(request)
            }
            .whenFailure { error in
                task.fail(error)
            }

        return task
    }

    private func resolve(timeout: TimeAmount?, deadline: NIODeadline?) -> TimeAmount? {
        switch (timeout, deadline) {
        case (.some(let timeout), .some(let deadline)):
            return min(timeout, deadline - .now())
        case (.some(let timeout), .none):
            return timeout
        case (.none, .some(let deadline)):
            return deadline - .now()
        case (.none, .none):
            return nil
        }
    }

    private func resolveAddress(request: Request, proxy: Configuration.Proxy?) -> (host: String, port: Int) {
        switch self.configuration.proxy {
        case .none:
            return (request.host, request.port)
        case .some(let proxy):
            return (proxy.host, proxy.port)
        }
    }

    /// `HTTPClient` configuration.
    public struct Configuration {
        /// TLS configuration, defaults to `TLSConfiguration.forClient()`.
        public var tlsConfiguration: TLSConfiguration?
        /// Enables following 3xx redirects automatically, defaults to `false`.
        ///
        /// Following redirects are supported:
        ///  - `301: Moved Permanently`
        ///  - `302: Found`
        ///  - `303: See Other`
        ///  - `304: Not Modified`
        ///  - `305: Use Proxy`
        ///  - `307: Temporary Redirect`
        ///  - `308: Permanent Redirect`
        public var followRedirects: Bool
        /// Default client timeout, defaults to no timeouts.
        public var timeout: Timeout
        /// Upstream proxy, defaults to no proxy.
        public var proxy: Proxy?
        /// Enables automatic body decompression. Supported algorithms are gzip and deflate.
        public var decompression: Decompression
        /// Ignore TLS unclean shutdown error, defaults to `false`.
        public var ignoreUncleanSSLShutdown: Bool

        public init(tlsConfiguration: TLSConfiguration? = nil,
                    followRedirects: Bool = false,
                    timeout: Timeout = Timeout(),
                    proxy: Proxy? = nil,
                    ignoreUncleanSSLShutdown: Bool = false,
                    decompression: Decompression = .disabled) {
            self.tlsConfiguration = tlsConfiguration
            self.followRedirects = followRedirects
            self.timeout = timeout
            self.proxy = proxy
            self.ignoreUncleanSSLShutdown = ignoreUncleanSSLShutdown
            self.decompression = decompression
        }

        public init(certificateVerification: CertificateVerification,
                    followRedirects: Bool = false,
                    timeout: Timeout = Timeout(),
                    proxy: Proxy? = nil,
                    ignoreUncleanSSLShutdown: Bool = false,
                    decompression: Decompression = .disabled) {
            self.tlsConfiguration = TLSConfiguration.forClient(certificateVerification: certificateVerification)
            self.followRedirects = followRedirects
            self.timeout = timeout
            self.proxy = proxy
            self.ignoreUncleanSSLShutdown = ignoreUncleanSSLShutdown
            self.decompression = decompression
        }
    }

    /// Specifies how `EventLoopGroup` will be created and establishes lifecycle ownership.
    public enum EventLoopGroupProvider {
        /// `EventLoopGroup` will be provided by the user. Owner of this group is responsible for its lifecycle.
        case shared(EventLoopGroup)
        /// `EventLoopGroup` will be created by the client. When `syncShutdown` is called, created `EventLoopGroup` will be shut down as well.
        case createNew
    }

    /// Specifies how the library will treat event loop passed by the user.
    public struct EventLoopPreference {
        enum Preference {
            /// Event Loop will be selected by the library.
            case indifferent
            /// Library will try to use provided event loop if possible.
            case prefers(EventLoop)
        }

        var preference: Preference

        init(_ preference: Preference) {
            self.preference = preference
        }

        /// Event Loop will be selected by the library.
        public static let indifferent = EventLoopPreference(.indifferent)
        /// Library will try to use provided event loop if possible.
        public static func prefers(_ eventLoop: EventLoop) -> EventLoopPreference {
            return EventLoopPreference(.prefers(eventLoop))
        }
    }

    /// Specifies decompression settings.
    public enum Decompression {
        /// Decompression is disabled.
        case disabled
        /// Decompression is enabled.
        case enabled(limit: DecompressionLimit)
    }

    /// Specifies how to limit decompression inflation.
    public enum DecompressionLimit {
        /// No limit will be set.
        case none
        /// Limit will be set on the request body size.
        case size(Int)
        /// Limit will be set on a ratio between compressed body size and decompressed result.
        case ratio(Int)

        func exceeded(compressed: Int, decompressed: Int) -> Bool {
            switch self {
            case .none:
                return false
            case .size(let allowed):
                return compressed > allowed
            case .ratio(let ratio):
                return decompressed > compressed * ratio
            }
        }
    }
}

extension HTTPClient.Configuration {
    /// Timeout configuration
    public struct Timeout {
        /// Specifies connect timeout.
        public var connect: TimeAmount?
        /// Specifies read timeout.
        public var read: TimeAmount?

        /// Create timeout.
        ///
        /// - parameters:
        ///     - connect: `connect` timeout.
        ///     - read: `read` timeout.
        public init(connect: TimeAmount? = nil, read: TimeAmount? = nil) {
            self.connect = connect
            self.read = read
        }
    }
}

private extension ChannelPipeline {
    func addProxyHandler(for request: HTTPClient.Request, decoder: ByteToMessageHandler<HTTPResponseDecoder>, encoder: HTTPRequestEncoder, tlsConfiguration: TLSConfiguration?, proxy: HTTPClient.Configuration.Proxy?) -> EventLoopFuture<Void> {
        let handler = HTTPClientProxyHandler(host: request.host, port: request.port, authorization: proxy?.authorization, onConnect: { channel in
            channel.pipeline.removeHandler(decoder).flatMap {
                return channel.pipeline.addHandler(
                    ByteToMessageHandler(HTTPResponseDecoder(leftOverBytesStrategy: .forwardBytes)),
                    position: .after(encoder)
                )
            }.flatMap {
                return channel.pipeline.addSSLHandlerIfNeeded(for: request, tlsConfiguration: tlsConfiguration)
            }
        })
        return self.addHandler(handler)
    }

    func addSSLHandlerIfNeeded(for request: HTTPClient.Request, tlsConfiguration: TLSConfiguration?) -> EventLoopFuture<Void> {
        guard request.useTLS else {
            return self.eventLoop.makeSucceededFuture(())
        }

        do {
            let tlsConfiguration = tlsConfiguration ?? TLSConfiguration.forClient()
            let context = try NIOSSLContext(configuration: tlsConfiguration)
            return self.addHandler(try NIOSSLClientHandler(context: context, serverHostname: request.host),
                                   position: .first)
        } catch {
            return self.eventLoop.makeFailedFuture(error)
        }
    }
}

/// Possible client errors.
public struct HTTPClientError: Error, Equatable, CustomStringConvertible {
    private enum Code: Equatable {
        case invalidURL
        case emptyHost
        case alreadyShutdown
        case emptyScheme
        case unsupportedScheme(String)
        case readTimeout
        case remoteConnectionClosed
        case cancelled
        case identityCodingIncorrectlyPresent
        case chunkedSpecifiedMultipleTimes
        case invalidProxyResponse
        case contentLengthMissing
        case proxyAuthenticationRequired
        case decompressionLimit
        case decompressionInitialization(Int32)
        case decompression(Int32)
    }

    private var code: Code

    private init(code: Code) {
        self.code = code
    }

    public var description: String {
        return "HTTPClientError.\(String(describing: self.code))"
    }

    /// URL provided is invalid.
    public static let invalidURL = HTTPClientError(code: .invalidURL)
    /// URL does not contain host.
    public static let emptyHost = HTTPClientError(code: .emptyHost)
    /// Client is shutdown and cannot be used for new requests.
    public static let alreadyShutdown = HTTPClientError(code: .alreadyShutdown)
    /// URL does not contain scheme.
    public static let emptyScheme = HTTPClientError(code: .emptyScheme)
    /// Provided URL scheme is not supported, supported schemes are: `http` and `https`
    public static func unsupportedScheme(_ scheme: String) -> HTTPClientError { return HTTPClientError(code: .unsupportedScheme(scheme)) }
    /// Request timed out.
    public static let readTimeout = HTTPClientError(code: .readTimeout)
    /// Remote connection was closed unexpectedly.
    public static let remoteConnectionClosed = HTTPClientError(code: .remoteConnectionClosed)
    /// Request was cancelled.
    public static let cancelled = HTTPClientError(code: .cancelled)
    /// Request contains invalid identity encoding.
    public static let identityCodingIncorrectlyPresent = HTTPClientError(code: .identityCodingIncorrectlyPresent)
    /// Request contains multiple chunks definitions.
    public static let chunkedSpecifiedMultipleTimes = HTTPClientError(code: .chunkedSpecifiedMultipleTimes)
    /// Proxy response was invalid.
    public static let invalidProxyResponse = HTTPClientError(code: .invalidProxyResponse)
    /// Request does not contain `Content-Length` header.
    public static let contentLengthMissing = HTTPClientError(code: .contentLengthMissing)
    /// Proxy Authentication Required.
    public static let proxyAuthenticationRequired = HTTPClientError(code: .proxyAuthenticationRequired)
    /// Decompression limit reached.
    public static let decompressionLimit = HTTPClientError(code: .decompressionLimit)
    /// Decompression initialization failed.
    public static func decompressionInitialization(_ code: Int32) -> HTTPClientError { return HTTPClientError(code: .decompressionInitialization(code)) }
    /// Decompression failed.
    public static func decompression(_ code: Int32) -> HTTPClientError { return HTTPClientError(code: .decompression(code)) }
}