我写了一些可能起作用的代码，但我认为readable.destroy()（例如，在我的示例中为src.destroy()）应该发出close和error事件...
下面是一个最小的例子来说明我的困惑：
const fs = require('fs');
const src = fs.createReadStream('streaming-example.js');
const dst = fs.createWriteStream('streaming-example.txt');
src.pipe(dst);
src.on('readable', () => {
let chunk;
while (null !== (chunk = src.read())) {
/**
* This should cause 'error' and 'close' events to emit
* @see https://nodejs.org/dist/latest-v11.x/docs/api/stream.html#stream_readable_destroy_error
*/
src.destroy();
}
});
src.on('close', () => console.log(`'close' event emitted`));
src.on('end', () => console.log(`'end' event emitted`));
src.on('error', (err) => console.log(`'error' event emitted`));
这是该程序的示例运行：
$ node streaming-example.js
'close' event emitted
$
（而且恰好还完成了写入名为streaming-example.txt的新文件的操作）
如果不清楚，我希望发出close和error事件，并依次触发相应的回调。但是，似乎仅发出了close事件。
error事件发生了什么？
答案 0 :(得分：1)
事实证明，深入研究node.js代码库可以消除这种混淆。
看看node/lib/_stream_readable.js，我们看到destroy函数是在node/lib/internal/streams/destroy.js中定义的。在这里，我们直接通过纯JavaScript得知，error事件仅在将一个真实值传递给destroy函数时才发出（从语义上讲，这是在同一客户端代码中生成的错误） destroy被调用。）
例如，如果我们只是通过更改来修改上面的示例代码
readable.destroy();
成为
readable.destroy(true); // or, more semantically correct, some Error value
我们得到以下输出：
$ node streaming-example.js
'error' event emitted with err: true
$
但是，现在我们丢失了close事件。所以...发生了什么事？
再次查看node/lib/internal/streams/destroy.js，我们注意到以下特殊情况的逻辑：
const readableDestroyed = this._readableState &&
this._readableState.destroyed;
const writableDestroyed = this._writableState &&
this._writableState.destroyed;
if (readableDestroyed || writableDestroyed) {
if (cb) {
cb(err);
} else if (err &&
(!this._writableState || !this._writableState.errorEmitted)) {
process.nextTick(emitErrorNT, this, err);
}
return this;
}
// We set destroyed to true before firing error callbacks in order
// to make it re-entrance safe in case destroy() is called within callbacks
if (this._readableState) {
this._readableState.destroyed = true;
}
// If this is a duplex stream mark the writable part as destroyed as well
if (this._writableState) {
this._writableState.destroyed = true;
}
error被正确发出，但close却没有被发出的事实提示我们正在处理双工流。我们可以只是查找一下内容，但为了让操作更简单，请坚持使用计算机告诉我们的内容。用此while循环替换原始的while循环
while (null !== (chunk = src.read())) {
console.log('before-destroy, src:', JSON.stringify(src));
src.destroy(true); // should cause 'close' and 'error' events to emit
console.log('after-destroy, src:', JSON.stringify(src));
}
我们得到以下输出：
$ node streaming-example.js
before-destroy, src: {"_readableState":{"objectMode":false,"highWaterMark":65536,"buffer":{"head":null,"tail":null,"length":0},"length":0,"pipes":{"_writableState":{"objectMode":false,"highWaterMark":16384,"finalCalled":false,"needDrain":false,"ending":false,"ended":false,"finished":false,"destroyed":false,"decodeStrings":true,"defaultEncoding":"utf8","length":633,"writing":true,"corked":0,"sync":false,"bufferProcessing":false,"writelen":633,"bufferedRequest":null,"lastBufferedRequest":null,"pendingcb":1,"prefinished":false,"errorEmitted":false,"emitClose":false,"autoDestroy":false,"bufferedRequestCount":0,"corkedRequestsFree":{"next":null,"entry":null}},"writable":true,"_events":{},"_eventsCount":5,"path":"streaming-example.txt","fd":24,"flags":"w","mode":438,"autoClose":true,"bytesWritten":0,"closed":false},"pipesCount":1,"flowing":false,"ended":false,"endEmitted":false,"reading":true,"sync":false,"needReadable":true,"emittedReadable":false,"readableListening":true,"resumeScheduled":false,"paused":false,"emitClose":false,"autoDestroy":false,"destroyed":false,"defaultEncoding":"utf8","awaitDrain":0,"readingMore":true,"decoder":null,"encoding":null},"readable":true,"_events":{"end":[null,null,null]},"_eventsCount":5,"path":"streaming-example.js","fd":23,"flags":"r","mode":438,"end":null,"autoClose":true,"bytesRead":633,"closed":false}
after-destroy, src: {"_readableState":{"objectMode":false,"highWaterMark":65536,"buffer":{"head":null,"tail":null,"length":0},"length":0,"pipes":{"_writableState":{"objectMode":false,"highWaterMark":16384,"finalCalled":false,"needDrain":false,"ending":false,"ended":false,"finished":false,"destroyed":false,"decodeStrings":true,"defaultEncoding":"utf8","length":633,"writing":true,"corked":0,"sync":false,"bufferProcessing":false,"writelen":633,"bufferedRequest":null,"lastBufferedRequest":null,"pendingcb":1,"prefinished":false,"errorEmitted":false,"emitClose":false,"autoDestroy":false,"bufferedRequestCount":0,"corkedRequestsFree":{"next":null,"entry":null}},"writable":true,"_events":{},"_eventsCount":5,"path":"streaming-example.txt","fd":24,"flags":"w","mode":438,"autoClose":true,"bytesWritten":0,"closed":false},"pipesCount":1,"flowing":false,"ended":false,"endEmitted":false,"reading":true,"sync":false,"needReadable":true,"emittedReadable":false,"readableListening":true,"resumeScheduled":false,"paused":false,"emitClose":false,"autoDestroy":false,"destroyed":true,"defaultEncoding":"utf8","awaitDrain":0,"readingMore":true,"decoder":null,"encoding":null},"readable":true,"_events":{"end":[null,null,null]},"_eventsCount":5,"path":"streaming-example.js","fd":null,"flags":"r","mode":438,"end":null,"autoClose":true,"bytesRead":633,"closed":false}
'error' event emitted
$
这表明我们可能正在处理双工流，或者至少这向我们确切解释了为什么仅发出error事件的原因（因为，特别是仅查看after-destroy输出，this._readableState和this._writeableState都是真实的，因此destroy函数将局部变量readableDestroyed和writeableDestroyed设置为true，我们从{{ 1}} console.log是this._writableState.errorEmitted，因此false在退出process.nextTick(emitErrorNT, this, err);函数之前就被执行了。）
问题已经得到足够的答案。
另外，最好知道destroy流与某种其他流之间的区别。为此，请快速参考this portion of the node.js documentation。
那么，当同时发生duplex和close事件时（例如，当我们不处理error流时）如何处理呢？下面的代码和执行如下所示：
duplex执行此脚本以及一些I / O（键入const readable = process.stdin;
const writable = process.stdout;
readable.setEncoding('utf8');
readable.on('readable', () => {
let chunk;
while ((chunk = readable.read()) !== null) {
writable.write(`data: ${chunk}`);
}
readable.destroy(true);
});
readable.on('close', () => console.log(`'close' event emitted`));
readable.on('error', (err) => console.log(`'error' event emitted with err:`, err));
，然后按回车/确认键）将提供以下输出：
asdf