feedback: error check

Author: andrewkmin

auth/index.html

@@ -218,10 +218,15 @@ <h2>Message log</h2>
         if (!hexString || hexString.length % 2 != 0 || !hexRegex.test(hexString)) {
           throw new Error('cannot create uint8array from invalid hex string');
         }
+
         var buffer = new Uint8Array(hexString.match(/../g).map((h) => parseInt(h, 16)));
         if (!length) {
             return buffer;
         }
+        if ((hexString.length) / 2 > length) {
+          throw new Error("hex value cannot fit in a buffer of " + length + " byte(s)");
+        }
+
         var paddedBuffer = new Uint8Array(length);
         paddedBuffer.set(buffer, length - buffer.length);
         return paddedBuffer;
@@ -503,7 +508,7 @@ <h2>Message log</h2>
       /**
        * Converts a `BigInt` into a base64url encoded string
        * @param {BigInt} num
-       * @param {number} length: optional number of bytes contained in the resulting string
+       * @param {number} length: optional number of bytes contained in the intermediary buffer before encoding as base64url
        * @return {string}
        */
       var bigIntToBase64Url = function(num, length) {

auth/index.test.js

@@ -262,6 +262,10 @@ describe("TKHQ", () => {
     expect(TKHQ.uint8arrayFromHexString("01", 2).toString()).toEqual("0,1");
     // Happy path: if length parameter is omitted, do not pad the resulting buffer
     expect(TKHQ.uint8arrayFromHexString("01").toString()).toEqual("1");
+    // Error case: hex value cannot fit in desired length
+    expect(() => {
+      TKHQ.uint8arrayFromHexString("0100", 1).toString(); // the number 256 cannot fit into 1 byte
+    }).toThrow("hex value cannot fit in a buffer of 1 byte(s)")
   });
 
   it("contains bigIntToHex", () => {
@@ -282,6 +286,11 @@ describe("TKHQ", () => {
     // extrapolate to larger numbers
     expect(TKHQ.bigIntToBase64Url(BigInt(255))).toEqual("_w"); // max 1 byte
     expect(TKHQ.bigIntToBase64Url(BigInt(255), 2)).toEqual("AP8"); // max 1 byte expressed in 2 bytes
+
+    // error case
+    expect(() => {
+      TKHQ.bigIntToBase64Url(BigInt(256), 1);
+    }).toThrow("hex value cannot fit in a buffer of 1 byte(s)");
   });
 
   it("logs messages and sends messages up", async () => {