问题(可从 nodeschool.io/#stream-adventure 下载)
Write a program that exports a function that spawns a process from a
cmd
string and anargs
array and returns a single duplex stream joining together the stdin and stdout of the spawned process. There is a very handy module you can use here: duplexer. The duplexer module exports a single functionduplexer(writable, readable)
that joins together a writable stream and readable stream into a single, readable/writable duplex stream.
官方解决方案
var spawn = require('child_process').spawn;
var duplexer = require('duplexer');
module.exports = function (cmd, args) {
var ps = spawn(cmd, args);
return duplexer(ps.stdin, ps.stdout);
};
此代码主要执行以下操作:
var spawn = require("child_process").spawn,
Stream = require("stream");
module.exports = function (cmd, args) {
var ps = spawn(cmd, args),
stream = new Stream();
stream.write = function (chunk, enc, cb) { ps.stdin.write(chunk, enc, cb); }
stream.end = function (chunk, enc, cb) { ps.stdin.end(chunk, enc, cb); }
ps.stdout.on("data", function (chunk) { stream.emit("data", chunk); });
ps.stdout.on("end", function () { stream.emit("end"); });
return stream;
};
没有双工器包的解决方案
我试图通过继承 Duplex
来解决问题类:
var spawn = require("child_process").spawn,
Stream = require("stream");
require("util").inherits(Dx, Stream.Duplex);
function Dx(stdin, stdout) {
Stream.Duplex.call(this);
this.stdin = stdin;
this.stdout = stdout;
}
Dx.prototype._write = function (chunk, enc, cb) { this.stdin.write(chunk, enc, cb); };
Dx.prototype._read = function (size) { return this.stdout.read(size); };
module.exports = function (cmd, args) {
var ps = spawn(cmd, args),
stream = new Dx(ps.stdin, ps.stdout);
return stream;
};
当我测试这个 (stream-adventure verify program.js
) 时,测试程序打印出 ACTUAL vs. EXPECTED
表(看起来正确),但在那之后它被卡住了。我的代码有什么问题?感谢您的帮助。
更新
添加这一行解决了问题:
Dx.prototype.end = function (chunk, enc, cb) { this.stdin.end(chunk, enc, cb); }
那么问题来了,为什么实现_read
和_write
方法还不够呢?
最佳答案
process.stdin
在完成所有其他操作后仍然存在,这就是该过程不会结束的原因。要让进程结束,通常是方法process.stdin.pause()
已使用,因为您可以在此之后恢复它。
您可以尝试覆盖 .end()
方法,但这不是一个好的做法,更好的做法是:
#1 如果您知道要为此流写入的结束消息,您应该添加 .resume()
._write()
中的方法实现:
dstream._write = function (chunk, encoding, callback) {
this.stdin.write(chunk, encoding, callback);
if (someConditionToEnd) {
this.stdin.pause();
}
};
#2 收听结束事件:
/*
inside the stream prototype constructor
*/
this.on('end', function () {
this.stdin.pause();
});
关于javascript - 如何在没有 Duplexer 包的情况下解决 NodeSchool 的 Duplexer 挑战,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/23387960/