HTTPSock: extract IsValidHeaderField helper and add tests (#2010)

src/HTTPSock.cpp

@@ -762,14 +762,17 @@ void CHTTPSock::SetContentType(const CString& sContentType) {
     m_sContentType = sContentType;
 }
 
+bool CHTTPSock::IsValidHeaderField(const CString& s) {
+    return s.find_first_of("\r\n") == CString::npos;
+}
+
 void CHTTPSock::AddHeader(const CString& sName, const CString& sValue) {
     // Reject CR/LF in either half so we never emit a malformed header or
     // give a caller (e.g. a future module) a cheap response-splitting
     // primitive. No in-tree caller reaches this with attacker-controlled
     // bytes today; this is a defensive guard, not a fix for an existing
     // exploit.
-    if (sName.find_first_of("\r\n") != CString::npos) return;
-    if (sValue.find_first_of("\r\n") != CString::npos) return;
+    if (!IsValidHeaderField(sName) || !IsValidHeaderField(sValue)) return;
     m_msHeaders[sName] = sValue;
 }