使用SwiftNIO和SwiftNIOHTTP2作为HTTP2客户端

Question

我目前正在使用SwiftNIO和SwiftNIOHTTP2 beta在Swift中使用简单的HTTP2客户端.我的实现看起来像这样:

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,连接始终失败并出现错误:

nghttp2错误:当我们期望SETTINGS帧时,远程对等体返回了意外数据.也许,peer不能正确支持HTTP/2.

但是,从命令行使用nghttp2连接和发出一个简单的请求可以正常工作.

$ 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

这是一个非常好的问题!让我们首先分析为什么这比发送HTTP/1.x请求更复杂.从广义上讲,这些问题分为两类:

1. NIO目前使它变得比必要的更复杂,因此我进一步写下来的很多东西有时候会不直观.我是NIO核心团队之一,甚至我有过相当多的代码来挖得到这个完全正常的,主要是因为我们还没有文档的一代swift-nio-ssl和swift-nio-http2上http://docs.swiftnio.io.
2. HTTP/2比HTTP/1复杂得多,而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来使其全部工作.

我将专注于必要的复杂性(2),并将为(1)提交错误/修复.让我们从NIO工具箱中检查我们需要哪些工具来实现这一点:

1. TLS.没有真实的HTTP/2服务器允许您通过纯文本说HTTP/2
2. ALPN.HTTP/1和HTTP/2共享相同的端口(通常443),因此我们需要告诉服务器我们想要说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(应用层协议协商)的机制来实现这一点,另一种选择是对HTTP2执行HTTP/1升级,但这更复杂,性能更低,所以我们不要在这里做
3. 一些HTTP/2工具:a)打开一个新的HTTP/2 b)HTTP/2到HTTP/1消息转换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规范中记录的HTTP/2.

好的,让我们sslContext在之前添加TLS :

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

我们告诉OpenSSLClientHandler服务器的主机名以便它可以正确验证证书也很重要.

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),这可以通过以下方式轻松完成ChannelHandler:

/// 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)
    }
}

好的,那是脚手架完成的.该SendAGETRequestHandler是这是将要尽快,我们之前打开新的HTTP/2流已经成功打开添加的处理程序的最后一部分.为了看到完整的响应,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渠道管道:

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 {

        }
}

为了看到一个完整的例子,我把一些东西放在一起PR swift-nio-examples/http2-client.

哦,NIO声称另一端没有正确说HTTP/2的原因是缺乏TLS.没有OpenSSLHandler那么NIO正在讲一个说明TLS的远程端的明文HTTP/2,然后这两个对等人彼此不理解:).