Übung 07 - Node

7.1 File Generatoren

Number File Generator

                        
    import * as process from "process";
    import fs from 'fs';

    const number = process.argv[process.argv.length -1]
    let text = "";

    for (let i = 1; i <= number; i++) {
        text += i + " .\n";
    }
    text = text.substring(0, text.length-1);

    fs.writeFile('testfile.txt', text, function (err) {
        if (err) throw err;
        console.log('Saved!');
    });

Alpha File Generator

                        
    import process from 'process'
    import fs from 'fs'
    const number = process.argv[process.argv.length -1]
    let text = "";

    for (let i = 1; i <= number; i++) {
        text += numbersToLetters(i) + "\n"
    }
    text = text.substring(0, text.length-1);

    fs.writeFile('alphafile.txt', text, function (err) {
        if (err) throw err;
        console.log('Saved!');
    });

    // function numbersToLetters from Flambino on Stackexchange
    // https://codereview.stackexchange.com/a/16129
    function numbersToLetters(number) {
        let baseChar = ("A").charCodeAt(0),
            letters = "";
        do {
            number -= 1;
            letters = String.fromCharCode(baseChar + (number % 26)) + letters;
            number = (number / 26) >> 0; // quick `floor`
        } while(number > 0);
        return letters;
    }

7.2 Performance Merge

Merge Files

                        
    import fs from 'fs/promises'
    import * as process from "process";

    const file1 = process.argv[process.argv.length - 1];
    const file2 = process.argv[process.argv.length - 2];

    console.time("merge");
    (async _=> {
        const [text1, text2] = await Promise.all([fs.readFile(file1, 'utf8'), fs.readFile(file2, 'utf8')])
        let arr1 = text1.split("\n");
        let arr2 = text2.split("\n");
        const text = interleave(arr1, arr2);
        const output = text.join('\n')
        fs.writeFile('mergeFileRes.txt', output, function (err) {
            if (err) throw err;
            console.log('Saved!');
        });
        console.timeEnd("merge");
    })();

    // interleave function taken from Mulan on stackoverflow
    // https://stackoverflow.com/a/47061616/15212696
    const interleave = ([x, ...xs], ys = []) =>
        x === undefined
            ? ys                             // base: no x
            : [x, ...interleave(ys, xs)]     // inductive: some x

Merge Streams

                        
    const fs = require("fs");

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

    console.time("merge")

    const stream1 = fs.createReadStream(files[0], "utf8");
    const stream2 = fs.createReadStream(files[1], "utf8");

    const lines1 = [], lines2 = [];

    stream1.on("data", process_chunk(lines1));
    stream2.on("data", process_chunk(lines2));
    stream1.on("end", output);
    stream2.on("end", output);

    let result = "";
    let count = 0;

    function output() {
        count += 1;
        if (count === 2) {
            lines1.forEach((line, i) => result += line + "\n" + lines2[i] + "\n")
        }
        fs.writeFile('mergeStreamsRes.txt', result.substring(0, result.length - 1), function (err) {
            if (err) throw err;
        });
        console.timeEnd("merge")
    }

    function process_chunk(lines) {
        return function (chunk) {
            let i = 0;
            chunk.split("\n").forEach(function (line) {
                if (!lines[i]) {
                    lines[i] = '';
                }
                lines[i++] += line;
            });
        }
    }

Performanzmessung:

Merge Files: 1.716ms

Merge Streams: 7.352ms

7.3 Express Server


    const express = require('express');
    const fs = require('fs');
    const fileUpload = require('express-fileupload')
    const app = express();
    const port = 3000;

    app.use(fileUpload());

    app.get('/', (req, res) => {
        res.writeHead(200, {"Content-Type": "text/html"});
        res.end('<!DOCTYPE html>\n' +
            '<html lang="en">\n' +
            '<head>\n' +
            '    <meta charset="UTF-8">\n' +
            '    <title>Merge Files</title>\n' +
            '</head>\n' +
            '<body style="font-family: Calibri">\n' +
            '<h2>Wählen Sie zwei Dateien zum Mergen aus.</h2>\n' +
            '<form enctype="multipart/form-data" method="POST" action="/upload">\n' +
            '    <input name="first" type="file">\n' +
            '    <input name="second" type="file">\n' +
            '    <input type="submit">\n' +
            '</form>\n' +
            '</body>\n' +
            '</html>')
    })

    app.post('/upload', function (req, res) {
        let first = req.files.first.data.toString('utf8').split("\n");
        let second = req.files.second.data.toString('utf8').split("\n");
        const text = interleave(first, second).join('\n');
       fs.writeFile('mergedResult.txt', text, function (err) {
            if (err) throw err;
        });
        res.send(`<h2 style="font-family: Calibri">Die Ergebnisdatei kann
        <a href="/download" target="_blank">hier</a> heruntergeladen werden und hat folgenden Inhalt:</h2>` + text);
    })

    app.get('/download', function(req, res){
        const file = "mergedResult.txt";
        res.download(file)
    })


    // interleave function taken from Mulan on stackoverflow
    // https://stackoverflow.com/a/47061616/15212696
    const interleave = ([x, ...xs], ys = []) =>
        x === undefined
            ? ys                             // base: no x
            : [x, ...interleave(ys, xs)]     // inductive: some x

    app.listen(port, () => {
        console.log(`Example app listening at http://localhost:${port}`)
    })