node.js - 一次读取子进程标准输出 100 个字节

Question

我正在生成一个产生大量数据的孩子（我在这里使用“ls -lR /”作为示例）。我想一次异步读取孩子的标准输出 100 个字节。

所以我想做：get100().then(process100).then(get100).then(process100).then(...

由于某种原因，这段代码只循环了 3 次，并且我停止接收 Readable 事件。我想不通为什么？

var Promise = require('bluebird');
var spawn   = require("child_process").spawn;

var exec = spawn( "ls", [ "-lR", "/"] );  

var get100 = function () {
     return new Promise(function(resolve, reject) {
       var tryTransfer = function() {
          var block = exec.stdout.read(100);
          if (block) {
            console.log("Got 100 Bytes");
            exec.stdout.removeAllListeners('readable');  
            resolve();
          } else console.log("Read Failed - not enough bytes?");
        };
        exec.stdout.on('readable', tryTransfer);
    });
};

var forEver = Promise.method(function(action) {
    return action().then(forEver.bind(null, action));
});

forEver(
    function() { return get100(); }
)

Answer 1

使用event-stream，只要有数据要读取（流是异步的），您就可以发出 100 字节数据从衍生进程中读取（流是异步的）：

var es = require('event-stream');
var spawn = require("child_process").spawn;

var exec = spawn("ls", ["-lR", "/"]);

var stream = es.readable(function (count, next) {
    // read 100 bytes
    while (block = exec.stdout.read(100)) {
        // if you have tons of data, it's not a good idea to log here
        // console.log("Got 100 Bytes");
        // emit the block
        this.emit('data', block.toString()); // block is a buffer (bytes array), you may need toString() or not
    }

    // no more data left to read
    this.emit('end');
    next();
}).on('data', function(data) {
    // data is the 100 bytes block, do what you want here

    // the stream is pausable and resumable at will
    stream.pause();
    doStuff(data, function() {
        stream.resume();
    });
});