node.js - 一次讀取子進程stdout 100字節

Question

我生成一個產生大量數據的子（我在這裏使用'ls -lR /'作爲示例）。我想一次讀取孩子的標準輸出100字節。

所以我想做的事：get100（），然後（process100）。然後（get100）。然後（process100）。然後（...

出於某種原因，這個代碼僅循環。 3次，我停止獲取可讀的事件。我想不通爲什麼？

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，你可以從衍生的進程發出 100個字節的數據，只要有數據讀取（數據流是異步）：

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(); 
    }); 
});