有没有办法让 `readline` 正确响应 `pause` 事件？答案

【问题标题】：Is there a way to have `readline` respond to `pause` events properly?有没有办法让 `readline` 正确响应 `pause` 事件？
【发布时间】：2019-10-26 15:51:39
【问题描述】：

我正在尝试编写一个可以在输出中包含其他文件的降价预处理器。

不幸的是，我发现了"the pause method does not stop queued up line events"。

我写的解决方案是完成对原始文件的读写，然后在最后附加其他文件：

import { createInterface } from "readline";
import * as fs from "fs";
import * as path from "path";
import minimist from "minimist";

const argv = minimist(process.argv.slice(2));

const inputFile = path.resolve(argv._[0]);
const outputFile = path.resolve(argv._[1]);

const inputFileReadStream = createInterface({
    "input": fs.createReadStream(inputFile)
});

const writeStream = fs.createWriteStream(outputFile);

readStream.on("line", function readLine(line) {
    if (line.startsWith("@import") === true) {
        inputFileReadStream.pause();

        console.log(line.substring(line.indexOf("\"") + 1, line.lastIndexOf("\"")));

        const readStream = createInterface({
            "input": fs.createReadStream(path.resolve(path.dirname(inputFile), line.substring(line.indexOf("\"") + 1, line.lastIndexOf("\""))))
        });

        readStream.on("line", function(line) {
            readLine(line);
        });

        readStream.on("end", function() {
            inputFileReadStream.resume();
        });
    } else {
        writeStream.write(line + "\n");
    }
});

所以我尝试修改它以使用我链接的帖子中提到的line-by-line 库，看看是否可行：

let readStream = new (require("line-by-line"))(fs.createReadStream(inputFile));

const writeStream = fs.createWriteStream(outputFile);

readStream.on("line", function readLine(line) {
    if (line.startsWith("@import") === true) {
        const tempStream = readStream;

        tempStream.pause();

        console.log(line.substring(line.indexOf("\"") + 1, line.lastIndexOf("\"")));

        readStream = new (require("line-by-line"))(fs.createReadStream(path.resolve(path.dirname(inputFile), line.substring(line.indexOf("\"") + 1, line.lastIndexOf("\"")))));

        readStream.on("line", function(line) {
            readLine(line);
        });

        readStream.on("end", function() {
            tempStream.resume();
        });
    } else {
        writeStream.write(line + "\n");
    }
});

但这产生了一个文件，该文件逐渐将导入文件中的行散布到主文件中。

我的问题是：有没有办法让readline 正确响应pause 事件？

这可以用Transform 解决吗？

如果有帮助，这里是存储库的链接：https://github.com/brianjenkins94/Rosettas-Node

【问题讨论】：

标签： node.js readline

【解决方案1】：

这可能会对性能产生负面影响，但我通过将 highWaterMark 值设置为 1 得到了我想要的。

import { createInterface } from "readline";
import * as fs from "fs";
import * as path from "path";
import minimist from "minimist";

const argv = minimist(process.argv.slice(2));

const inputFile = path.resolve(argv._[0]);
const outputFile = path.resolve(argv._[1]);

const inputFileReadStream = createInterface({
    "input": fs.createReadStream(inputFile, { "highWaterMark": 1 })
});

const writeStream = fs.createWriteStream(outputFile);

inputFileReadStream.on("line", function readLine(line, readStream = inputFileReadStream) {
    if (line.startsWith("@import") === true) {
        readStream.pause();

        const childReadStream = createInterface({
            "input": fs.createReadStream(path.resolve(path.dirname(inputFile), line.substring(line.indexOf("\"") + 1, line.lastIndexOf("\""))), { "highWaterMark": 1 })
        });

        childReadStream.on("line", function(line) {
            readLine(line, childReadStream);
        });

        childReadStream.on("close", function() {
            readStream.resume();
        });
    } else {
        writeStream.write(line + "\n");
    }
});

【讨论】：