Question

因此，我正在使用Node的child_process模块来生成弹性搜索的实例。我需要检查服务何时启动，resolve()承诺何时启动。这就是我现在正在做的事情：

const { join } = require('path');
const { spawn } = require('child_process');
const { createWriteStream } = require('fs');
const { Transform } = require('stream');

function start() {
  return new Promise(resolve => {
    const outStream = new Transform({
      transform(chunk, encoding, callback) {
        if (chunk.toString().includes('started')) resolve();
        this.push(chunk);
        callback();
      }
    });

    const logFile = createWriteStream(join(LOG_DIR, 'es.log'), 'w');
    const errorFile = createWriteStream(join(LOG_DIR, 'es.error.log'), 'w');

    outStream.pipe(logFile);

    child = spawn(
      ES_BAT_PATH,
      [],
      { cwd: process.cwd(), stdio: ['ignore', outStream, errorFile] }
    );
  });
}

这是最好的方法吗？（可能不是），如果没有，我该怎么做？

Answer 1

总的来说，我会说这是一种合理的方法，但是我在这里看到了一些问题：

这些块可能未包含您要查找的整个单词，但可能介于两者之间（一个块以'sta'结尾，下一个以'rted'开头。
最初发现之后，您仍然有不再需要的转换流
还有unicode字符的问题，但是由于您正在寻找' started '，因此可以省略。

通过将最后一部分保留在空格后，可以轻松缓解第一个问题。对于第二个，您需要解压转换-这样您将得到如下结果：

const { join } = require('path');
const { spawn } = require('child_process');
const { createWriteStream } = require('fs');
const { Readable, PassThrough } = require('stream');

function start() {

    return new Promise(resolve => {
        const outStream = new PassThrough();
        let last;
        const lookupStream = new Readable({
            read(chunk, encoding, callback) {
                const ref = chunk.toString();
                if ((last + ref).includes('started')) {
                    outStream.unpipe(lookupStream);
                    resolve();
                }
                last = ref.replace(/^.* /, '');
                callback();
            }
        });

        const logFile = createWriteStream(join(LOG_DIR, 'es.log'), 'w');
        const errorFile = createWriteStream(join(LOG_DIR, 'es.error.log'), 'w');

        outStream.pipe(logFile);
        outStream.pipe(lookupStream);

        child = spawn(
            ES_BAT_PATH,
            [],
            { cwd: process.cwd(), stdio: ['ignore', outStream, errorFile] }
        );
    });
}

另一种选择是使用on('data'侦听器，并在找到正确的块后将其删除。

最后，我的框架scramjet会让这变得容易一些

const { join } = require('path');
const { spawn } = require('child_process');
const { createWriteStream } = require('fs');
const { StringStream } = require('scramjet');

function start() {

    const outStream = new PassThrough();
    const lookupStream = new StringStream();
    const logFile = createWriteStream(join(LOG_DIR, 'es.log'), 'w');
    const errorFile = createWriteStream(join(LOG_DIR, 'es.error.log'), 'w');

    outStream.pipe(logFile);
    outStream.pipe(lookupStream);

    child = spawn(
        ES_BAT_PATH,
        [],
        { cwd: process.cwd(), stdio: ['ignore', outStream, errorFile] }
    );

    return lookupStream
        .split('\n')                                    // split line by line
        .filter(x => x.includes('started'))             // check if line contains "started"
        .until(x => outStream.unpipe(lookupStream))     // end stream on first occurence
        .run();                                         // run and resolve on stream end
}

Node.js-监视生成的孩子的输出以获取特定文本

1 个答案: