add streams chapter

Sascha Schulz

2024-07-22 e1ada75101952f5d94800334e64f3b452f18a89f

add streams chapter

 index.html

@@ -4163,6 +4163,82 @@
                        <p>Aufgabe</p>
                        <p>Implementiere zur vorherigen Verschlüsselung eine Entschlüsselung.</p>
                    </section>
                    <section>
                        <p>Lösung</p>
                        <pre>
                            <code class="js" data-trim data-line-numbers>
                                const word = Buffer.from("abcdef");
                                const key = Buffer.from("xyz");
                                const encrypted = Buffer.alloc(word.length, 0);
								
                                // encrypt
                                for (let i = 0; i &lt; word.length; i++) {
                                    encrypted[i] = word[i] ^ key[i % key.length];
                                }
								
                                // decrypt
                                for (let i = 0; i &lt; word.length; i++) {
                                    word[i] = encrypted[i] ^ key[i % key.length];
                                }
								
                                console.log(word.toString()); // => "abcdef"
                            </code>
                        </pre>
                    </section>
                    <section>
                        <h3>Streams</h3>
                        <p>Konstanter Fluss von (meist) großen Datenmengen in kleinen Paketen</p>
                    </section>
                    <section>
                        <p>Gängige Typen von Streams</p>
                        <ul>
                            <li>Standard In / Out</li>
                            <li>HTTP-Requests / -Responses</li>
                            <li>TCP-Sockets</li>
                            <li>Lese- und Schreib-Streams auf Dateien</li>
                            <li>Große Datenbank-Ergebnisse mittels Cursor</li>
                        </ul>
                    </section>
                    <section>
                        <pre>
                            <code class="js" data-trim data-line-numbers>
                                const readableStream = fs.createReadStream("./source.txt");
                                const writableStream = fs.createWriteStream("./target.txt");
								
                                readableStream.on("data", (data /* Buffer */) =&gt; {
                                    // process data here
                                    writableStream.write(data)
                                });
								
                                readableStream.on("end", (data) =&gt; {
                                    // stream has finished, e.g. EOF (end of file)
                                });
								
                                // alternatively pipe content
                                readableStream.pipe(writableStream);
                            </code>
                        </pre>
                    </section>
                    <section>
                        <p>Aufgabe</p>
                        <p>Lese eine beliebige Datei als Readable Stream, verschlüssele den Inhalt mit der XOR-Methode und schreibe die verschlüsselten Bytes in eine Zieldatei</p>
                    </section>
                    <section>
                        <p>Aufgabe</p>
                        <p>Ändere das Programm, sodass auf Konsolenebene ein Pipe (|) ermöglicht wird:</p>
                        <pre>
                            <code class="bash" data-trim data-line-numbers>
                                echo "Hello World!" | node index.js
                            </code>
                        </pre>
                        <p>Nutze dafür die implizit vorhandenen Streams von Standard In / Out:</p>
                        <pre>
                            <code class="js" data-trim data-line-numbers>
                                process.stdin; // Readable Stream
                                process.stdout; // Writable Stream
                            </code>
                        </pre>
                    </section>
                </section>
            </div>
        </div>