Fix Set Name Buffer reference for browser

Replace Node-only Buffer.byteLength with a TextEncoder-based UTF-8 byte
length helper so the Set Name page and byte counter work in the browser.

By specifier.

src/components/app-body/set-name/index.js

@@ -12,6 +12,7 @@ import { useNavigate } from 'react-router-dom'
 // Local libraries
 import MemoSetName from '../../../services/memo-set-name'
 import SetNamePage from '../../../services/set-name-page'
+import { byteLength } from '../../../services/utf8'
 
 function SetName (props) {
   const { appData } = props
@@ -22,7 +23,7 @@ function SetName (props) {
   const [err, setErr] = useState('')
   const [settingName, setSettingName] = useState(false)
 
-  const remaining = maxBytes - Buffer.byteLength(input, 'utf8')
+  const remaining = maxBytes - byteLength(input)
 
   async function handleSubmit (event) {
     event.preventDefault()

src/services/memo-set-name.js

@@ -17,6 +17,7 @@
 */
 
 const MemoAction = require('./memo-action')
+const { byteLength } = require('./utf8')
 
 const MEMO_SET_NAME_PREFIX = '6d01'
 const MAX_NAME_BYTES = 77
@@ -38,7 +39,7 @@ class MemoSetName extends MemoAction {
 
   // A name is over-length when it exceeds the byte limit.
   isTooLong (name) {
-    return Buffer.byteLength(name, 'utf8') > MAX_NAME_BYTES
+    return byteLength(name) > MAX_NAME_BYTES
   }
 
   // Compose and broadcast a Memo set-name transaction for the given name.

src/services/set-name-page.js

@@ -15,6 +15,7 @@
 
 const PageController = require('./page-controller')
 const MemoSetName = require('./memo-set-name')
+const { byteLength } = require('./utf8')
 
 const SET_NAME_PATH = '/memo/set-name'
 const ACCOUNT_PATH = '/account'
@@ -30,7 +31,7 @@ class SetNamePage extends PageController {
 
   // Bytes remaining before the name limit is reached.
   remainingCount () {
-    return MemoSetName.MAX_NAME_BYTES - Buffer.byteLength(this.input, 'utf8')
+    return MemoSetName.MAX_NAME_BYTES - byteLength(this.input)
   }
 
   // Set the in-flight setting-name flag.

src/services/utf8.js

@@ -0,0 +1,15 @@
+/*
+  UTF-8 byte-length helper for browser and Node.
+
+  The Node global `Buffer` is not available in the browser, so byte counting
+  (used by the Memo set-name byte counter and length check) must not depend on
+  it. TextEncoder is available in both environments and reports the UTF-8 byte
+  length of a string.
+*/
+
+// Return the number of UTF-8 bytes in a string.
+function byteLength (str) {
+  return new TextEncoder().encode(String(str)).length
+}
+
+module.exports = { byteLength }

test/unit/utf8.test.js

@@ -0,0 +1,38 @@
+/*
+  Unit tests for the UTF-8 byte-length helper (src/services/utf8.js).
+
+  The helper must report the same UTF-8 byte length as Node's Buffer without
+  depending on the Node-only `Buffer` global, so the browser build (which has
+  no Buffer) can count bytes for the Memo set-name counter and length check.
+*/
+
+'use strict'
+
+const test = require('node:test')
+const assert = require('node:assert/strict')
+
+const { byteLength } = require('../../src/services/utf8')
+
+test('byteLength matches Buffer.byteLength for ASCII text', () => {
+  for (const s of ['', 'trout', 'a longer name with spaces', 'x'.repeat(77)]) {
+    assert.equal(byteLength(s), Buffer.byteLength(s, 'utf8'))
+  }
+})
+
+test('byteLength matches Buffer.byteLength for multi-byte characters', () => {
+  for (const s of ['é', 'é'.repeat(38), '😀', '😀'.repeat(20), '日本語']) {
+    assert.equal(byteLength(s), Buffer.byteLength(s, 'utf8'))
+  }
+})
+
+test('byteLength counts UTF-8 bytes, not characters', () => {
+  // 'é' is 1 character but 2 UTF-8 bytes; an emoji is 1 character but 4 bytes.
+  assert.equal(byteLength('é'), 2)
+  assert.equal(byteLength('😀'), 4)
+  assert.equal(byteLength('a'), 1)
+})
+
+test('byteLength coerces non-string input to a string', () => {
+  assert.equal(byteLength(42), 2)
+  assert.equal(byteLength(null), 4) // String(null) === 'null'
+})