AsyncHTTPClientTransport.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the SwiftOpenAPIGenerator open source project
//
// Copyright (c) 2023 Apple Inc. and the SwiftOpenAPIGenerator project authors
// Licensed under Apache License v2.0
//
// See LICENSE.txt for license information
// See CONTRIBUTORS.txt for the list of SwiftOpenAPIGenerator project authors
//
// SPDX-License-Identifier: Apache-2.0
//
//===----------------------------------------------------------------------===//
import OpenAPIRuntime
import AsyncHTTPClient
import NIOCore
import NIOHTTP1
import NIOFoundationCompat
import HTTPTypes
#if canImport(Darwin)
import Foundation
#else
@preconcurrency import struct Foundation.URL
import struct Foundation.URLComponents
import struct Foundation.Data
import protocol Foundation.LocalizedError
#endif

/// A client transport that performs HTTP operations using the HTTPClient type
/// provided by the AsyncHTTPClient library.
///
/// ### Use the AsyncHTTPClient transport
///
/// Instantiate the transport:
///
///     let transport = AsyncHTTPClientTransport()
///
/// Create the base URL of the server to call using your client. If the server
/// URL was defined in the OpenAPI document, you find a generated method for it
/// on the `Servers` type, for example:
///
///     let serverURL = try Servers.server1()
///
/// Instantiate the `Client` type generated by the Swift OpenAPI Generator for
/// your provided OpenAPI document. For example:
///
///     let client = Client(
///         serverURL: serverURL,
///         transport: transport
///     )
///
/// Use the client to make HTTP calls defined in your OpenAPI document. For
/// example, if the OpenAPI document contains an HTTP operation with
/// the identifier `checkHealth`, call it from Swift with:
///
///     let response = try await client.checkHealth(.init())
///     // ...
///
/// ### Provide a custom Client
///
/// The ``AsyncHTTPClientTransport/Configuration-swift.struct`` type allows you
/// to provide a custom `HTTPClient` and tweak behaviors such as the default
/// timeout.
public struct AsyncHTTPClientTransport: ClientTransport {

    /// A set of configuration values for the AsyncHTTPClient transport.
    public struct Configuration: Sendable {

        /// The HTTP client used for performing HTTP calls.
        public var client: HTTPClient

        /// The default shared HTTP client.
        ///
        /// This is a workaround for the lack of a shared client
        /// in AsyncHTTPClient. Do not use this value directly, outside of
        /// the `Configuration.init(client:timeout:)` initializer, as it will
        /// likely be removed in the future.
        private static let sharedClient: HTTPClient = .init()

        /// The default request timeout.
        public var timeout: TimeAmount

        /// Creates a new configuration with the specified client and timeout.
        /// - Parameters:
        ///   - client: The underlying client used to perform HTTP operations.
        ///     Provide nil to use the shared internal client.
        ///   - timeout: The request timeout, defaults to 1 minute.
        public init(client: HTTPClient? = nil, timeout: TimeAmount = .minutes(1)) {
            self.client = client ?? Self.sharedClient
            self.timeout = timeout
        }
    }

    /// A request to be sent by the transport.
    internal typealias Request = HTTPClientRequest

    /// A response returned by the transport.
    internal typealias Response = HTTPClientResponse

    /// Specialized error thrown by the transport.
    internal enum Error: Swift.Error, CustomStringConvertible, LocalizedError {

        /// Invalid URL composed from base URL and received request.
        case invalidRequestURL(request: HTTPRequest, baseURL: URL)

        // MARK: CustomStringConvertible

        var description: String {
            switch self {
            case let .invalidRequestURL(request: request, baseURL: baseURL):
                return
                    "Invalid request URL from request path: \(request.path ?? "<nil>") relative to base URL: \(baseURL.absoluteString)"
            }
        }

        // MARK: LocalizedError

        var errorDescription: String? { description }
    }

    /// A set of configuration values used by the transport.
    public var configuration: Configuration

    /// Underlying request sender for the transport.
    internal let requestSender: any HTTPRequestSending

    /// Creates a new transport.
    /// - Parameters:
    ///   - configuration: A set of configuration values used by the transport.
    ///   - requestSender: The underlying request sender.
    internal init(configuration: Configuration, requestSender: any HTTPRequestSending) {
        self.configuration = configuration
        self.requestSender = requestSender
    }

    /// Creates a new transport.
    /// - Parameter configuration: A set of configuration values used by the transport.
    public init(configuration: Configuration = .init()) {
        self.init(configuration: configuration, requestSender: AsyncHTTPRequestSender())
    }

    // MARK: ClientTransport

    /// Sends an HTTP request and returns the corresponding HTTP response.
    ///
    /// - Parameters:
    ///   - request: The HTTP request to send.
    ///   - body: The HTTP body to include in the request (optional).
    ///   - baseURL: The base URL for the request.
    ///   - operationID: The identifier for the operation.
    ///
    /// - Returns: A tuple containing the HTTP response and an optional HTTP body in the response.
    /// - Throws: An error if the request or response handling encounters any issues.
    public func send(_ request: HTTPRequest, body: HTTPBody?, baseURL: URL, operationID: String) async throws -> (
        HTTPResponse, HTTPBody?
    ) {
        let httpRequest = try Self.convertRequest(request, body: body, baseURL: baseURL)
        let httpResponse = try await invokeSession(with: httpRequest)
        let response = try await Self.convertResponse(method: request.method, httpResponse: httpResponse)
        return response
    }

    // MARK: Internal

    /// Converts the shared Request type into URLRequest.
    internal static func convertRequest(_ request: HTTPRequest, body: HTTPBody?, baseURL: URL) throws
        -> HTTPClientRequest
    {
        guard var baseUrlComponents = URLComponents(string: baseURL.absoluteString),
            let requestUrlComponents = URLComponents(string: request.path ?? "")
        else { throw Error.invalidRequestURL(request: request, baseURL: baseURL) }
        baseUrlComponents.percentEncodedPath += requestUrlComponents.percentEncodedPath
        baseUrlComponents.percentEncodedQuery = requestUrlComponents.percentEncodedQuery
        guard let url = baseUrlComponents.url else { throw Error.invalidRequestURL(request: request, baseURL: baseURL) }
        var clientRequest = HTTPClientRequest(url: url.absoluteString)
        clientRequest.method = request.method.asHTTPMethod
        for header in request.headerFields {
            clientRequest.headers.add(name: header.name.canonicalName, value: header.value)
        }
        if let body {
            let length: HTTPClientRequest.Body.Length
            switch body.length {
            case .unknown: length = .unknown
            case .known(let count):
                if let intValue = Int(exactly: count) { length = .known(intValue) } else { length = .unknown }
            }
            clientRequest.body = .stream(body.map { .init(bytes: $0) }, length: length)
        }
        return clientRequest
    }

    /// Converts the received URLResponse into the shared Response.
    internal static func convertResponse(method: HTTPRequest.Method, httpResponse: HTTPClientResponse) async throws -> (
        HTTPResponse, HTTPBody?
    ) {

        var headerFields: HTTPFields = [:]
        for header in httpResponse.headers { headerFields[.init(header.name)!] = header.value }

        let length: HTTPBody.Length
        if let lengthHeaderString = headerFields[.contentLength], let lengthHeader = Int64(lengthHeaderString) {
            length = .known(lengthHeader)
        } else {
            length = .unknown
        }

        let body: HTTPBody?
        switch method {
        case .head, .connect, .trace: body = nil
        default:
            body = HTTPBody(httpResponse.body.map { $0.readableBytesView }, length: length, iterationBehavior: .single)
        }

        let response = HTTPResponse(status: .init(code: Int(httpResponse.status.code)), headerFields: headerFields)
        return (response, body)
    }

    // MARK: Private

    /// Makes the underlying HTTP call.
    private func invokeSession(with request: Request) async throws -> Response {
        try await requestSender.send(request: request, with: configuration.client, timeout: configuration.timeout)
    }
}

extension HTTPTypes.HTTPRequest.Method {
    var asHTTPMethod: NIOHTTP1.HTTPMethod {
        switch self {
        case .get: return .GET
        case .put: return .PUT
        case .post: return .POST
        case .delete: return .DELETE
        case .options: return .OPTIONS
        case .head: return .HEAD
        case .patch: return .PATCH
        case .trace: return .TRACE
        default: return .RAW(value: rawValue)
        }
    }
}

/// A type that performs HTTP operations using the HTTP client.
internal protocol HTTPRequestSending: Sendable {
    func send(request: AsyncHTTPClientTransport.Request, with client: HTTPClient, timeout: TimeAmount) async throws
        -> AsyncHTTPClientTransport.Response
}

/// Performs HTTP calls using AsyncHTTPClient
internal struct AsyncHTTPRequestSender: HTTPRequestSending {
    func send(request: AsyncHTTPClientTransport.Request, with client: AsyncHTTPClient.HTTPClient, timeout: TimeAmount)
        async throws -> AsyncHTTPClientTransport.Response
    { try await client.execute(request, timeout: timeout) }
}