ControlPlaneRequestEncoder.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the SwiftAWSLambdaRuntime open source project
//
// Copyright (c) 2021 Apple Inc. and the SwiftAWSLambdaRuntime project authors
// Licensed under Apache License v2.0
//
// See LICENSE.txt for license information
// See CONTRIBUTORS.txt for the list of SwiftAWSLambdaRuntime project authors
//
// SPDX-License-Identifier: Apache-2.0
//
//===----------------------------------------------------------------------===//

import NIOCore

struct ControlPlaneRequestEncoder: _EmittingChannelHandler {
    typealias OutboundOut = ByteBuffer

    private var host: String
    private var byteBuffer: ByteBuffer!

    init(host: String) {
        self.host = host
    }

    mutating func writeRequest(
        _ request: ControlPlaneRequest,
        context: ChannelHandlerContext,
        promise: EventLoopPromise<Void>?
    ) {
        self.byteBuffer.clear(minimumCapacity: self.byteBuffer.storageCapacity)

        switch request {
        case .next:
            self.byteBuffer.writeString(.nextInvocationRequestLine)
            self.byteBuffer.writeHostHeader(host: self.host)
            self.byteBuffer.writeString(.userAgentHeader)
            self.byteBuffer.writeString(.CRLF)  // end of head
            context.write(self.wrapOutboundOut(self.byteBuffer), promise: promise)
            context.flush()

        case .invocationResponse(let requestID, let payload):
            let contentLength = payload?.readableBytes ?? 0
            self.byteBuffer.writeInvocationResultRequestLine(requestID)
            self.byteBuffer.writeHostHeader(host: self.host)
            self.byteBuffer.writeString(.userAgentHeader)
            self.byteBuffer.writeContentLengthHeader(length: contentLength)
            self.byteBuffer.writeString(.CRLF)  // end of head
            if let payload = payload, contentLength > 0 {
                context.write(self.wrapOutboundOut(self.byteBuffer), promise: nil)
                context.write(self.wrapOutboundOut(payload), promise: promise)
            } else {
                context.write(self.wrapOutboundOut(self.byteBuffer), promise: promise)
            }
            context.flush()

        case .invocationError(let requestID, let errorMessage):
            let payload = errorMessage.toJSONBytes()
            self.byteBuffer.writeInvocationErrorRequestLine(requestID)
            self.byteBuffer.writeContentLengthHeader(length: payload.count)
            self.byteBuffer.writeHostHeader(host: self.host)
            self.byteBuffer.writeString(.userAgentHeader)
            self.byteBuffer.writeString(.unhandledErrorHeader)
            self.byteBuffer.writeString(.CRLF)  // end of head
            self.byteBuffer.writeBytes(payload)
            context.write(self.wrapOutboundOut(self.byteBuffer), promise: promise)
            context.flush()

        case .initializationError(let errorMessage):
            let payload = errorMessage.toJSONBytes()
            self.byteBuffer.writeString(.runtimeInitErrorRequestLine)
            self.byteBuffer.writeContentLengthHeader(length: payload.count)
            self.byteBuffer.writeHostHeader(host: self.host)
            self.byteBuffer.writeString(.userAgentHeader)
            self.byteBuffer.writeString(.unhandledErrorHeader)
            self.byteBuffer.writeString(.CRLF)  // end of head
            self.byteBuffer.writeBytes(payload)
            context.write(self.wrapOutboundOut(self.byteBuffer), promise: promise)
            context.flush()
        }
    }

    mutating func writerAdded(context: ChannelHandlerContext) {
        self.byteBuffer = context.channel.allocator.buffer(capacity: 256)
    }

    mutating func writerRemoved(context: ChannelHandlerContext) {
        self.byteBuffer = nil
    }
}

extension String {
    static let CRLF: String = "\r\n"

    static let userAgentHeader: String = "user-agent: Swift-Lambda/Unknown\r\n"
    static let unhandledErrorHeader: String = "lambda-runtime-function-error-type: Unhandled\r\n"

    static let nextInvocationRequestLine: String =
        "GET /2018-06-01/runtime/invocation/next HTTP/1.1\r\n"

    static let runtimeInitErrorRequestLine: String =
        "POST /2018-06-01/runtime/init/error HTTP/1.1\r\n"
}

extension ByteBuffer {
    fileprivate mutating func writeInvocationResultRequestLine(_ requestID: String) {
        self.writeString("POST /2018-06-01/runtime/invocation/")
        self.writeString(requestID)
        self.writeString("/response HTTP/1.1\r\n")
    }

    fileprivate mutating func writeInvocationErrorRequestLine(_ requestID: String) {
        self.writeString("POST /2018-06-01/runtime/invocation/")
        self.writeString(requestID)
        self.writeString("/error HTTP/1.1\r\n")
    }

    fileprivate mutating func writeHostHeader(host: String) {
        self.writeString("host: ")
        self.writeString(host)
        self.writeString(.CRLF)
    }

    fileprivate mutating func writeContentLengthHeader(length: Int) {
        self.writeString("content-length: ")
        self.writeString("\(length)")
        self.writeString(.CRLF)
    }
}