Improve based on testing

Author: WilliamBergamin

packages/web-api/src/instrument.test.ts

@@ -60,15 +60,24 @@ describe('instrument', () => {
       assert.ok(isLatin1Safe(ua));
     });
 
-    it('should return a Latin-1 safe user agent when process.title contains non-ASCII characters', () => {
-      const notLatin1SafeTitle = '管理者'
+    it('should return a Latin-1 safe user agent when process.title contains non-Latin-1 characters', () => {
+      const notLatin1SafeTitle = '管理者: Windows PowerShell'
       assert.strictEqual(isLatin1Safe(notLatin1SafeTitle), false);
 
       mockProcessTitle(notLatin1SafeTitle);
       const { getUserAgent } = freshImport();
       const ua = getUserAgent();
       assert.ok(isLatin1Safe(ua), `User-Agent contains non-Latin-1 characters: ${ua}`);
       assert.ok(!ua.includes(notLatin1SafeTitle), 'User-Agent should not contain raw non-ASCII characters');
+      assert.ok(ua.includes('%E7%AE%A1%E7%90%86%E8%80%85: Windows PowerShell'), 'User-Agent should percent-encode only non-Latin-1 characters');
+    });
+
+    it('should preserve Latin-1 characters in process.title', () => {
+      mockProcessTitle('café');
+      const { getUserAgent } = freshImport();
+      const ua = getUserAgent();
+      assert.ok(ua.includes('café/'), `User-Agent should preserve Latin-1 characters: ${ua}`);
+      assert.ok(isLatin1Safe(ua));
     });
   });
 });

packages/web-api/src/instrument.ts

@@ -10,6 +10,20 @@ function replaceSlashes(s: string): string {
   return s.replace('/', ':');
 }
 
+const MAX_LATIN1_CODE = 0xFF;
+
+/**
+ * Ensures a string is safe for use in HTTP headers by URI-encoding characters outside the Latin-1 (ISO-8859-1) range.
+ * Latin-1 characters (code points 0x00–0xFF) are preserved as-is; all others are percent-encoded via encodeURIComponent.
+ */
+function toLatin1Safe(s: string): string {
+  let result = '';
+  for (const char of s) {
+    result += char.charCodeAt(0) <= MAX_LATIN1_CODE ? char : encodeURIComponent(char);
+  }
+  return result;
+}
+
 // TODO: for the deno build (see the `npm run build:deno` npm run script), we could replace the `os-browserify` npm
 // module shim with our own shim leveraging the deno beta compatibility layer for node's `os` module (for more info
 // see https://deno.land/std@0.116.0/node/os.ts). At the time of writing this TODO (2021/11/25), this required deno
@@ -18,7 +32,7 @@ function replaceSlashes(s: string): string {
 // based code will report "browser/undefined" from a deno runtime.
 const baseUserAgent =
   `${replaceSlashes(packageJson.name)}/${packageJson.version} ` +
-  `${encodeURI(basename(process.title))}/${process.version.replace('v', '')} ` +
+  `${toLatin1Safe(basename(process.title))}/${process.version.replace('v', '')} ` +
   `${os.platform()}/${os.release()}`;
 
 const appMetadata: { [key: string]: string } = {};