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我在测试 NodeJS 流时遇到了问题。在运行 stream.pipeline 后,我似乎无法让我的项目等待 Duplex 和 Transform 流的输出,即使它返回了一个承诺。也许我遗漏了一些东西,但我相信脚本应该等待函数返回,然后再继续。我正在尝试的项目中最重要的部分是:

// Message system is a duplex (read/write) stream
export class MessageSystem extends Duplex {
    constructor() {
        super({highWaterMark: 100, readableObjectMode: true, writableObjectMode: true});
    }
    public _read(size: number): void {
        var chunk = this.read();
        console.log(`Recieved ${chunk}`);
        this.push(chunk);
    }
    public _write(chunk: Message, encoding: string, 
        callback: (error?: Error | null | undefined, chunk?: Message) => any): void {
        if (chunk.data === null) {
            callback(new Error("Message.Data is null"));
        } else {
            callback();
        }
    }
}

export class SystemStream extends Transform {
    public type: MessageType = MessageType.Global;
    public data: Array<Message> = new Array<Message>();
    constructor() {
        super({highWaterMark: 100, readableObjectMode: true, writableObjectMode: true});
    }
    public _transform(chunk: Message, encoding: string, 
        callback: TransformCallback): void {
        if (chunk.single && (chunk.type === this.type || chunk.type === MessageType.Global)) {
            console.log(`Adding ${chunk}`);
            this.data.push(chunk);
            chunk = new Message(chunk.data, MessageType.Removed, true);
            callback(undefined, chunk); // TODO: Is this correct?
        } else if (chunk.type === this.type || chunk.type === MessageType.Global) { // Ours and global
            this.data.push(chunk);
            callback(undefined, chunk);
        } else { // Not ours
            callback(undefined, chunk);
        }
    }
}

export class EngineStream extends SystemStream {
    public type: MessageType = MessageType.Engine;
}

export class IOStream extends SystemStream {
    public type: MessageType = MessageType.IO;
}

let ms = new MessageSystem();
let es = new EngineStream();
let io = new IOStream();

let pipeline = promisify(Stream.pipeline);

async function start() {
    console.log("Running Message System");
    console.log("Writing new messages");
    ms.write(new Message("Hello"));
    ms.write(new Message("world!"));
    ms.write(new Message("Engine data", MessageType.Engine));
    ms.write(new Message("IO data", MessageType.IO));
    ms.write(new Message("Order matters in the pipe, even if Global", MessageType.Global, true));
    ms.end(new Message("Final message in the stream"));
    console.log("Piping data");
    await pipeline(
        ms,
        es,
        io
    );
}

Promise.all([start()]).then(() => {
    console.log(`Engine Messages to parse: ${es.data.toString()}`);
    console.log(`IO Messages to parse: ${io.data.toString()}`);
});

输出应类似于:

Running message system
Writing new messages
Hello
world!
Engine Data
IO Data
Order Matters in the pipe, even if Global
Engine messages to parse: Engine Data
IO messages to parse: IO Data

任何帮助将不胜感激。谢谢!

注意:我用我的另一个帐户发布了这个,而不是这个是我的实际帐户。为重复道歉。

编辑:我最初将回购私有化,但已将其公开以帮助澄清答案。更多用法可以在feature/inital_system 分支上找到。它可以npm start在签出时运行。

编辑:我把我的自定义流放在这里是为了冗长。我认为我比以前走得更好,但现在得到了一个“空”对象。

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2 回答 2

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正如文档所述,stream.pipeline是基于回调的不返回承诺。

它具有自定义承诺版本,可以通过以下方式访问util.promisify

const pipeline = util.promisify(stream.pipeline);

...

await pipeline(...);
于 2019-02-06T07:46:54.267 回答
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经过过去几天的一些工作,我找到了答案。问题是我对双工流的实现。从那以后,我将其更改MessageSystem为转换流,以便更易于管理和使用。

这是产品:

export class MessageSystem extends Transform {
    constructor() {
        super({highWaterMark: 100, readableObjectMode: true, writableObjectMode: true});
    }
    public _transform(chunk: Message, encoding: string,
        callback: TransformCallback): void {
            try {
                let output: string = chunk.toString();
                callback(undefined, output);
            } catch (err) {
                callback(err);
            }
        }
}

感谢@estus 的快速回复和检查。同样,我一直在 API 中找到我的答案!

我的发现的存档存储库可以在这个存储库中找到。

于 2019-02-13T00:50:13.863 回答