change message Encoding/Decoding method

src/core/format/Convert.ts

@@ -165,12 +165,7 @@ export class Convert {
      * @return {string}
      */
     public static utf8ToHex = (input: string): string => {
-        const rawString = Convert.rstr2utf8(input);
-        let result = '';
-        for (let i = 0; i < rawString.length; i++) {
-            result += rawString.charCodeAt(i).toString(16).padStart(2, '0');
-        }
-        return result.toUpperCase();
+        return Buffer.from(input, 'utf-8').toString('hex').toUpperCase();
     };
 
     /**

src/model/message/Message.ts

@@ -26,15 +26,7 @@ export abstract class Message {
      * @returns {string}
      */
     public static decodeHex(hex: string): string {
-        let str = '';
-        for (let i = 0; i < hex.length; i += 2) {
-            str += String.fromCharCode(parseInt(hex.substr(i, 2), 16));
-        }
-        try {
-            return decode(str);
-        } catch (e) {
-            return str;
-        }
+        return Buffer.from(hex, 'hex').toString();
     }
 
     /**

test/core/format/Convert.spec.ts

@@ -272,6 +272,14 @@ describe('convert', () => {
             expect(actual).to.equal('E58588E7A7A6E585A9E6BCA2');
         });
 
+        it('utf8 text containing emoji to hex', () => {
+            // Act:
+            const actual = convert.utf8ToHex('😀こんにちは😀');
+
+            // Assert:
+            expect(actual).to.equal('F09F9880E38193E38293E381ABE381A1E381AFF09F9880');
+        });
+
         it('utf8 text to hex with control char', () => {
             // Act:
             const actual = convert.utf8ToHex(String.fromCodePoint(0x0f) + ' Hello World!');

test/model/message/Message.spec.ts

@@ -50,4 +50,9 @@ describe('Message', () => {
         const hex = '746573742D6D657373616765';
         expect(Message.decodeHex(hex)).to.be.equal('test-message');
     });
+
+    it('should decode hex string (emoji)', () => {
+        const hex = 'F09F9880E38193E38293E381ABE381A1E381AFF09F9880';
+        expect(Message.decodeHex(hex)).to.be.equal('😀こんにちは😀');
+    });
 });