fix(mcp): split header value only on first colon in headerParser

[furkankoykiran]

Summary

Fix headerParser function in packages/playwright/src/mcp/browser/config.ts that silently truncates header values containing colons.

Problem

The headerParser function used arg.split(':') which splits on all colons in the string. JavaScript destructuring const [name, value] only captures the first two array elements, silently discarding any content after the second colon.

This caused header values containing colons to be silently truncated:

Input	Expected	Actual (before fix)
X-Custom: http://example.com	http://example.com	http ❌
X-Forwarded-Proto: value:with:colons	value:with:colons	value ❌

This affects:

• --cdp-header CLI flag
• PLAYWRIGHT_MCP_CDP_HEADERS environment variable
• Any header value containing URLs (http://, https://), port numbers (host:port), or Base64 strings with colons

Solution

Replace arg.split(':') with arg.indexOf(':') + arg.substring() to split only on the first colon, matching the HTTP header spec (RFC 7230 Section 3.2).

 export function headerParser(arg: string | undefined, previous?: Record<string, string>): Record<string, string> {
   if (!arg)
     return previous || {};
   const result: Record<string, string> = previous || {};
-  const [name, value] = arg.split(':').map(v => v.trim());
-  result[name] = value;
+  const colonIndex = arg.indexOf(':');
+  if (colonIndex === -1)
+    return result;
+  const name = arg.substring(0, colonIndex).trim();
+  const value = arg.substring(colonIndex + 1).trim();
+  result[name] = value;
   return result;
 }

Test Results

Added unit tests in tests/mcp/header-parser.spec.ts covering:

• ✅ Simple header parsing
• ✅ Header values containing URLs (colons in ://)
• ✅ Header values with multiple colons
• ✅ Undefined and empty input handling
• ✅ Headers without colons (malformed)
• ✅ Whitespace trimming
• ✅ Header accumulation with previous parameter

Local verification: 8/8 tests passed

Fixes microsoft/playwright-mcp#1417

[furkankoykiran]

@microsoft-github-policy-service agree

[yury-s]

This will lose support for headers with empty value.

[yury-s]

Let's instead add an integration test that validates the user-facing functionality. We normally don't write unit tests in playwright.