使用 SwiftNIO 和 SwiftNIOHTTP2 作为 HTTP2 客户端

Question

我目前正在 Swift 使用 SwiftNIO 和 SwiftNIOHTTP2 beta 开发一个简单的 HTTP2 客户端。我的实现如下所示：

let group = MultiThreadedEventLoopGroup(numberOfThreads: 1)
let bootstrap = ClientBootstrap(group: group)
    .channelOption(ChannelOptions.socket(SocketOptionLevel(SOL_SOCKET), SO_REUSEADDR), value: 1)
    .channelInitializer { channel in
        channel.pipeline.add(handler: HTTP2Parser(mode: .client)).then {
            let multiplexer = HTTP2StreamMultiplexer { (channel, streamID) -> EventLoopFuture<Void> in
                return channel.pipeline.add(handler: HTTP2ToHTTP1ClientCodec(streamID: streamID, httpProtocol: .https))
            }
            return channel.pipeline.add(handler: multiplexer)
        }
}

defer {
    try! group.syncShutdownGracefully()
}

let url = URL(string: "https://strnmn.me")!

_ = try bootstrap.connect(host: url.host!, port: url.port ?? 443)
    .wait()

不幸的是，连接总是因错误而失败：

nghttp2 error: Remote peer returned unexpected data while we expected SETTINGS frame. Perhaps, peer does not support HTTP/2 properly.

但是，从命令行使用 nghttp2 连接和发出一个简单的请求工作正常。

$ nghttp -vn https://strnmn.me
[  0.048] Connected
The negotiated protocol: h2
[  0.110] recv SETTINGS frame <length=18, flags=0x00, stream_id=0>
          (niv=3)
          [SETTINGS_MAX_CONCURRENT_STREAMS(0x03):128]
          [SETTINGS_INITIAL_WINDOW_SIZE(0x04):65536]
          [SETTINGS_MAX_FRAME_SIZE(0x05):16777215]
[  0.110] recv WINDOW_UPDATE frame <length=4, flags=0x00, stream_id=0>
          (window_size_increment=2147418112)
[  0.110] send SETTINGS frame <length=12, flags=0x00, stream_id=0>
          (niv=2)
          [SETTINGS_MAX_CONCURRENT_STREAMS(0x03):100]
          [SETTINGS_INITIAL_WINDOW_SIZE(0x04):65535]
[  0.110] send SETTINGS frame <length=0, flags=0x01, stream_id=0>
          ; ACK
          (niv=0)
[  0.110] send PRIORITY frame <length=5, flags=0x00, stream_id=3>
          (dep_stream_id=0, weight=201, exclusive=0)
[  0.110] send PRIORITY frame <length=5, flags=0x00, stream_id=5>
          (dep_stream_id=0, weight=101, exclusive=0)
[  0.110] send PRIORITY frame <length=5, flags=0x00, stream_id=7>
          (dep_stream_id=0, weight=1, exclusive=0)
[  0.110] send PRIORITY frame <length=5, flags=0x00, stream_id=9>
          (dep_stream_id=7, weight=1, exclusive=0)
[  0.110] send PRIORITY frame <length=5, flags=0x00, stream_id=11>
          (dep_stream_id=3, weight=1, exclusive=0)
[  0.111] send HEADERS frame <length=35, flags=0x25, stream_id=13>
          ; END_STREAM | END_HEADERS | PRIORITY
          (padlen=0, dep_stream_id=11, weight=16, exclusive=0)
          ; Open new stream
          :method: GET
          :path: /
          :scheme: https
          :authority: strnmn.me
          accept: */*
          accept-encoding: gzip, deflate
          user-agent: nghttp2/1.34.0
[  0.141] recv SETTINGS frame <length=0, flags=0x01, stream_id=0>
          ; ACK
          (niv=0)
[  0.141] recv (stream_id=13) :status: 200
[  0.141] recv (stream_id=13) server: nginx
[  0.141] recv (stream_id=13) date: Sat, 24 Nov 2018 16:29:13 GMT
[  0.141] recv (stream_id=13) content-type: text/html
[  0.141] recv (stream_id=13) last-modified: Sat, 01 Jul 2017 20:23:11 GMT
[  0.141] recv (stream_id=13) vary: Accept-Encoding
[  0.141] recv (stream_id=13) etag: W/"595804af-8a"
[  0.141] recv (stream_id=13) expires: Sat, 24 Nov 2018 16:39:13 GMT
[  0.141] recv (stream_id=13) cache-control: max-age=600
[  0.141] recv (stream_id=13) x-frame-options: SAMEORIGIN
[  0.141] recv (stream_id=13) content-encoding: gzip
[  0.141] recv HEADERS frame <length=185, flags=0x04, stream_id=13>
          ; END_HEADERS
          (padlen=0)
          ; First response header
[  0.142] recv DATA frame <length=114, flags=0x01, stream_id=13>
          ; END_STREAM
[  0.142] send GOAWAY frame <length=8, flags=0x00, stream_id=0>
          (last_stream_id=0, error_code=NO_ERROR(0x00), opaque_data(0)=[])

如何使用 SwiftNIOHTTP2 建立会话并发出 GET 请求？

Answer 1

这是个很好的问题！我们先分析一下为什么这比发送HTTP/1.x请求要复杂。从广义上讲，这些问题分为两类：

NIO 目前使它变得比必要的更复杂，因此我接下来要写的很多内容有时可能不直观。我是 NIO 核心团队的一员，我什至不得不挖掘相当多的代码才能使其完全正常工作，主要是因为我们仍然没有 swift-nio-ssl and swift-nio-http2 on http://docs.swiftnio.io 的文档生成。
HTTP/2 只是比 HTTP/1 复杂得多，NIO 更像是一个可用于构建 HTTP 客户端的工具箱，因此我们需要一起使用一堆工具才能使其正常工作.

我将在此处重点介绍必要的复杂性 (2)，并将针对 (1) 提交 bugs/fixes。让我们检查一下我们需要 NIO 工具箱中的哪些工具来实现此功能：

TLS。没有真实世界的 HTTP/2 服务器会允许您通过明文 HTTP/2 说话
ALPN。 HTTP/1 和 HTTP/2 共享同一个端口（通常是 443）所以我们需要告诉服务器我们想说话 HTTP/2 因为为了向后兼容，默认值仍然是 HTTP/1.我们可以使用一种称为 ALPN (Application-layer Protocol Negotiation) 的机制来做到这一点，另一种选择是执行 HTTP/1 升级到 HTTP2，但这既复杂又性能低下，所以我们不要在这里这样做
一些HTTP/2工具：a) 打开一个新的HTTP/2 b) HTTP/2 到HTTP/1 消息翻译c) HTTP/2 多路复用

您问题中的代码包含最重要的位，即上面列表中的 3b 和 3c。但是我们需要添加 1、2 和 3a，所以让我们这样做:)

让我们从 2) ALPN 开始：

let tlsConfig = TLSConfiguration.forClient(applicationProtocols: ["h2"])
let sslContext = try SSLContext(configuration: tlsConfig)

这是一个带有 "h2" ALPN 协议标识符的 SSL 配置，它将告诉服务器我们想要说 HTTP/2，如 HTTP/2 spec 中所述。

好的，让我们添加之前设置的 sslContext 的 TLS：

let sslHandler = try! OpenSSLClientHandler(context: sslContext, serverHostname: hostname)

我们告诉 OpenSSLClientHandler 服务器的主机名也很重要，这样它才能正确验证证书。

最后我们需要做 3a（创建一个新的 HTTP/2 流来发出我们的请求）这可以使用 ChannelHandler:

轻松完成

/// Creates a new HTTP/2 stream when our channel is active and adds the `SendAGETRequestHandler` so a request is sent.
final class CreateRequestStreamHandler: ChannelInboundHandler {
    typealias InboundIn = Never

    private let multiplexer: HTTP2StreamMultiplexer
    private let responseReceivedPromise: EventLoopPromise<[HTTPClientResponsePart]>

    init(multiplexer: HTTP2StreamMultiplexer, responseReceivedPromise: EventLoopPromise<[HTTPClientResponsePart]>) {
        self.multiplexer = multiplexer
        self.responseReceivedPromise = responseReceivedPromise
    }

    func channelActive(ctx: ChannelHandlerContext) {
        func requestStreamInitializer(channel: Channel, streamID: HTTP2StreamID) -> EventLoopFuture<Void> {
            return channel.pipeline.addHandlers([HTTP2ToHTTP1ClientCodec(streamID: streamID, httpProtocol: .https),
                                                 SendAGETRequestHandler(responseReceivedPromise: self.responseReceivedPromise)],
                                                first: false)
        }

        // this is the most important line: When the channel is active we add the `HTTP2ToHTTP1ClientCodec` to deal in HTTP/1 messages as well as the `SendAGETRequestHandler` which will send a request.
        self.multiplexer.createStreamChannel(promise: nil, requestStreamInitializer)
    }
}

好了，脚手架搭建完成。 SendAGETRequestHandler 是最后一部分，它是将在我们之前打开的新 HTTP/2 流成功打开后立即添加的处理程序。为了查看完整的响应，我还实现了将响应的所有位累加到一个承诺中：

/// Fires off a GET request when our stream is active and collects all response parts into a promise.
///
/// - warning: This will read the whole response into memory and delivers it into a promise.
final class SendAGETRequestHandler: ChannelInboundHandler {
    typealias InboundIn = HTTPClientResponsePart
    typealias OutboundOut = HTTPClientRequestPart

    private let responseReceivedPromise: EventLoopPromise<[HTTPClientResponsePart]>
    private var responsePartAccumulator: [HTTPClientResponsePart] = []

    init(responseReceivedPromise: EventLoopPromise<[HTTPClientResponsePart]>) {
        self.responseReceivedPromise = responseReceivedPromise
    }

    func channelActive(ctx: ChannelHandlerContext) {
        assert(ctx.channel.parent!.isActive)
        var reqHead = HTTPRequestHead(version: .init(major: 2, minor: 0), method: .GET, uri: "/")
        reqHead.headers.add(name: "Host", value: hostname)
        ctx.write(self.wrapOutboundOut(.head(reqHead)), promise: nil)
        ctx.writeAndFlush(self.wrapOutboundOut(.end(nil)), promise: nil)
    }

    func channelRead(ctx: ChannelHandlerContext, data: NIOAny) {
        let resPart = self.unwrapInboundIn(data)
        self.responsePartAccumulator.append(resPart)
        if case .end = resPart {
            self.responseReceivedPromise.succeed(result: self.responsePartAccumulator)
        }
    }
}

为了完成它，让我们设置客户端的通道管道：

let bootstrap = ClientBootstrap(group: group)
    .channelInitializer { channel in
        let myEventLoop = channel.eventLoop
        let sslHandler = try! OpenSSLClientHandler(context: sslContext, serverHostname: hostname)
        let http2Parser = HTTP2Parser(mode: .client)
        let http2Multiplexer = HTTP2StreamMultiplexer { (channel, streamID) -> EventLoopFuture<Void> in
            return myEventLoop.newSucceededFuture(result: ())
        }
        return channel.pipeline.addHandlers([sslHandler,
                                             http2Parser,
                                             http2Multiplexer,
                                             CreateRequestStreamHandler(multiplexer: http2Multiplexer,
                                                                        responseReceivedPromise: responseReceivedPromise),
                                             CollectErrorsAndCloseStreamHandler(responseReceivedPromise: responseReceivedPromise)],
                                            first: false).map {

        }
}

为了查看完整的示例，我为 swift-nio-examples/http2-client.

整理了一些 PR

哦，NIO 声称另一端没有正常说话的原因 HTTP/2 是缺乏 TLS。没有 OpenSSLHandler，所以 NIO 向使用 TLS 的远程终端发送明文 HTTP/2，然后两个对等点无法相互理解:)。

使用 SwiftNIO 和 SwiftNIOHTTP2 作为 HTTP2 客户端

Using SwiftNIO and SwiftNIOHTTP2 as an HTTP2 client

http2

swift

nghttp2

swift-nio