add streams chapter

Sascha Schulz

2024-07-22 e1ada75101952f5d94800334e64f3b452f18a89f

 index.html

@@ -4122,6 +4122,123 @@
                     </code>
                  </pre>
               </section>
               <section>
                  <h3>Buffer</h3>
                  <p>Array-artige Struktur für rohe Bytes</p>
                  <pre>
                     <code class="js" data-trim data-line-numbers>
                        const b1 = Buffer.from("abc"); // bevorzugt
                        const b2 = Buffer.alloc(100, 0); // Länge mit initialen Daten
                        const b3 = Buffer.allocUnsafe(100); // Länge ohne initiale Daten
                        const b4 = new Buffer("abc"); //  offiziell nicht empfohlen
								
                        console.log(b1); // => &lt;Buffer 61 62 63>
                        console.log(b1.toString("hex")); // => "616263"
                     </code>
                  </pre>
               </section>
               <section>
                  <p>Mit Buffern arbeiten:</p>
                  <pre>
                     <code class="js" data-trim data-line-numbers>
                        const a = Buffer.from("a") + Buffer.from("b");
                        const b = Buffer.concat([Buffer.from("a"), Buffer.from([98])]);
                        const c = b.toString()
								
                        console.log(a); // => ab
                        console.log(b); // => &lt;Buffer 61 62>
                        console.log(c); // => ab

                        for (const byte of a) {
                           console.log(byte); // => 97 98
                        }
                     </code>
                  </pre>
               </section>
               <section>
                  <p>Aufgabe</p>
                  <p>Implementiere eine XOR-Verschlüsselung (<code>^</code>-Operator), sodass jedes Byte einer Original-Nachricht der Reihe nach mit dem entsprechenden Byte eines Schlüsselwortes verschlüsselt wird und gebe die verschlüsselte Nachricht als Text aus.</p>
               </section>
               <section>
                  <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>