带有 while 循环的 NodeJS 结束事件

Question

我尝试使用 sax 迭代这个大 xml 文件，代码如下：

'use strict';
const fs = require('fs');
const sax = require('sax');

let rowsAdded = 0;
let rows = [];
let options = {
    encoding: 'utf8',
    mode: 0o444
};
let strict = true,
feedFile = 'Comments.xml',
saxStream = sax.createStream(strict);
saxStream.on('opentag', node => {
    if(rowsAdded === 5) {
        return saxStream.end();
    }
    // I only need nodes named 'row'
    if(node.name === 'row') {
        rowsAdded++;
        // If the name is 'row' and `attribute` prop exists, push it. 
        if(node.attributes) rows.push(node.attributes);
    }
})
.on('error', () => {
})
.on('end', () => {
    console.log('Done reading:', rowsAdded);
    // If you remove this while loop the above console will called only once
    while(rowsAdded--) {

    }
});
fs.createReadStream(feedFile, options).pipe(saxStream);

console.log 将记录 Done reading: 5 大约 43 次，如果我注释掉 while 循环，它只会控制台 Done reading: 5 once!,我做错了什么吗？是bug吗？

Answer 1

所以你想在需要继续数据管道的时候暂停一个可读流。这就是 shutdown 函数应该在管道范围之外的原因，您可以在 done 函数内将其作为 readable.pause 简单地暂停。

'use strict';
const fs = require('fs');
const sax = require('sax');

let rowsAdded = 0;
let rows = [];
let options = {
    encoding: 'utf8',
    mode: 0o444
};
let strict = true,
feedFile = 'Comments.xml',
saxStream = sax.createStream(strict);
saxStream.on('opentag', node => {
    // I only need nodes named 'row'
    if(node.name === 'row' && rowsAdded < 5) {
        rowsAdded++;
        // If the name is 'row' and `attribute` prop exists, push it. 
        if(node.attributes) rows.push(node.attributes);
    }
    if(rowsAdded === 5)
        done();
})
.on('error', () => {
})
.on('end', () => {
    console.log('Done reading:', rowsAdded);
});

var readable = fs.createReadStream(feedFile, options)
readable.pipe(saxStream);

function done(){
    // this should stop reading part.
    readable.pause();
    while(rowsAdded--) {
        // do you processing here
    }
}

Answer 2

当您从 saxStream.on('opentag') return 时，这意味着您已完成该标记的处理，但解析器会继续，直到完成整个 xml。

带有 while 循环的 NodeJS 结束事件

NodeJS end event with while loop

javascript

sax

node.js