Tighten up header validation to match Node

In future, if we successfully ship Node lenient mode, this could be
relaxed in turn, but for now this is what stops us forwarding content
Node will reject, so we do need to handle it identically.

Author: pimterry

src/util/header-utils.ts

@@ -286,11 +286,15 @@ export function dropDefaultHeaders(response: OngoingResponse) {
 // RFC 7230 token char set — anything outside this in a name is invalid.
 const VALID_TOKEN_CHARS = /^[!#$%&'*+\-.^_`|~0-9A-Za-z]+$/;
 
+// RFC 7230 field-value chars: HTAB / SP / VCHAR / obs-text. I.e. tab, plus
+// 0x20–0x7E, plus 0x80–0xFF. Matches Node's checkInvalidHeaderChar.
+const INVALID_VALUE_CHAR = /[^\t\x20-\x7E\x80-\xFF]/;
+
 export function validateHeader(name: string, value: string | string[]): boolean {
     if (typeof name !== 'string' || !VALID_TOKEN_CHARS.test(name)) return false;
     const values = Array.isArray(value) ? value : [value];
     for (const v of values) {
-        if (typeof v !== 'string' || /[\r\n]/.test(v)) return false;
+        if (typeof v !== 'string' || INVALID_VALUE_CHAR.test(v)) return false;
     }
     return true;
 }