feat(unicode): ensure 140 char text limit is unicode aware

Author: missinglink

helper/unicode.js

@@ -1,6 +1,11 @@
 const _ = require('lodash');
 const regenerate = require('regenerate');
 
+// shared grapheme segmenter (UAX-29)
+// note: locale 'en' only affects word/sentence granularity; grapheme rules are script-agnostic.
+const graphemeSegmenter = new Intl.Segmenter('en', { granularity: 'grapheme' });
+const toGraphemes = (str) => Array.from(graphemeSegmenter.segment(str), ({ segment }) => segment);
+
 // non-printable control characters
 // ref: https://en.wikipedia.org/wiki/List_of_Unicode_characters
 const CONTROL_CODES = regenerate()
@@ -96,3 +101,26 @@ function normalize(str) {
 }
 
 module.exports.normalize = normalize;
+
+// unicode aware truncation function
+// counts user-perceived characters (UAX-29 grapheme clusters) via Intl.Segmenter.
+module.exports.truncate = (input, len) => {
+
+  // sanity checking
+  if (!_.isString(input)) { throw new Error('invalid string'); }
+
+  // short-circuit common case of short strings
+  // if input.length <= len, grapheme count must also be <= len
+  if (input.length > len) {
+    // truncate to len graphemes
+    const graphemes = toGraphemes(input);
+    if (graphemes.length > len) {
+      return {
+        truncated: graphemes.slice(0, len).join(''),
+        isTruncated: true
+      };
+    }
+  }
+
+  return { truncated: input, isTruncated: false };
+};

sanitizer/_text.js

@@ -21,11 +21,13 @@ function _sanitize( raw, clean ){
   if( !_.isString(text) || _.isEmpty(text) ){
     messages.errors.push(`invalid param 'text': text length, must be >0`);
   } else {
-    if( text.length > MAX_TEXT_LENGTH ){
+    clean.text = text;
+
+    const { truncated, isTruncated } = unicode.truncate(text, MAX_TEXT_LENGTH);
+    if( isTruncated ){
       messages.warnings.push(`param 'text' truncated to ${MAX_TEXT_LENGTH} characters`);
-      text = text.substring(0, MAX_TEXT_LENGTH);
+      clean.text = truncated;
     }
-    clean.text = text;
   }
 
   return messages;

sanitizer/_text_pelias_parser.js

@@ -40,9 +40,10 @@ function _sanitize (raw, clean, req) {
   else {
 
     // truncate text to $MAX_TEXT_LENGTH chars
-    if (text.length > MAX_TEXT_LENGTH) {
+    const { truncated, isTruncated } = unicode.truncate(text, MAX_TEXT_LENGTH);
+    if( isTruncated ){
       messages.warnings.push(`param 'text' truncated to ${MAX_TEXT_LENGTH} characters`);
-      text = text.substring(0, MAX_TEXT_LENGTH);
+      text = truncated;
     }
 
     // tokenize text

test/unit/sanitizer/_text.js

@@ -1,4 +1,5 @@
 const sanitizer = require('../../../sanitizer/_text')();
+const unicode = require('../../../helper/unicode');
 
 module.exports.tests = {};
 
@@ -155,14 +156,25 @@ it again and again until we reach our destination.` };
     t.end();
   });
 
-  test('strips emoji', (t) => {
-    const raw = { text: 'abc' + '👩‍❤️‍👩'.repeat(200) };
+  test('truncate should be unicode aware', (t) => {
+    const grapheme = '\uD842\uDFB7';
+    const raw = { text: grapheme.repeat(200) };
     const clean = {};
     const messages = sanitizer.sanitize(raw, clean);
 
-    t.equals(clean.text, 'abc');
+    // sanity: fixture genuinely distinguishes code units from graphemes
+    t.equals(grapheme.length, 2, 'fixture is a surrogate pair (2 code units)');
+    t.equals([...grapheme].length, 1, 'fixture is one code point');
+    t.equals(grapheme.normalize('NFC'), grapheme, 'fixture is NFC-stable');
+
+    // t.equals(unicode.length(clean.text), 140, 'length counts characters, not code units');
+    t.equals(clean.text, grapheme.repeat(140), 'truncated correctly');
+
+    // text.length on the truncated result is 280 (140 × 2 code units),
+    t.equals(clean.text.length, 280, 'truncated string is 280 UTF-16 code units');
+
     t.deepEquals(messages.errors, [], 'no errors');
-    t.deepEquals(messages.warnings, []);
+    t.deepEquals(messages.warnings, [`param 'text' truncated to 140 characters`]);
     t.end();
   });
 };