Add Base64 Encode Decode in TypeScript

archive/t/typescript/base64-encode-decode.ts

@@ -0,0 +1,83 @@
+function usageAndExit(): never {
+    console.log("Usage: please provide a mode and a string to encode/decode");
+    process.exit(1);
+}
+
+/**
+ * Validates if a string is valid base64 format
+ * @param str the string to validate
+ * @returns true if valid base64, false otherwise
+ */
+function isValidBase64(str: string): boolean {
+    // Check length is multiple of 4
+    if (str.length % 4 !== 0) {
+        return false;
+    }
+
+    // Only A-Z, a-z, 0-9, +, /, = allowed
+    if (!/^[A-Za-z0-9+/]*={0,2}$/.test(str)) {
+        return false;
+    }
+
+    // = only allowed at end, at most two
+    const idx = str.indexOf("=");
+    if (idx !== -1 && idx < str.length - 2) {
+        // e.g. "ab==cd" is invalid
+        return false;
+    }
+
+    return true;
+}
+
+/**
+ * Encodes a string to base64
+ * @param input the string to encode
+ * @returns base64 encoded string
+ */
+function encodeBase64(input: string): string {
+    // Use Buffer in Node.js
+    return Buffer.from(input, "ascii").toString("base64");
+}
+
+/**
+ * Decodes a base64 string
+ * @param input the base64 string to decode
+ * @returns decoded string
+ */
+function decodeBase64(input: string): string {
+    // Validate first
+    if (!isValidBase64(input)) {
+        usageAndExit();
+    }
+    // Buffer will decode the base64 string
+    return Buffer.from(input, "base64").toString("ascii");
+}
+
+/**
+ * Main function to process command line arguments
+ */
+function main(): void {
+    const args = process.argv.slice(2);
+
+    if (args.length < 2) {
+        usageAndExit();
+    }
+
+    const mode = args[0];
+    const text = args[1];
+
+    if (!text) {
+        usageAndExit();
+    }
+
+    if (mode === "encode") {
+        console.log(encodeBase64(text));
+    } else if (mode === "decode") {
+        console.log(decodeBase64(text));
+    } else {
+        usageAndExit();
+    }
+}
+
+// Execute main function
+main();