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

test/HTTPSockTest.cpp

@@ -0,0 +1,39 @@
+/*
+ * Copyright (C) 2004-2026 ZNC, see the NOTICE file for details.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <gtest/gtest.h>
+#include <znc/HTTPSock.h>
+
+// Validation contract used by AddHeader to keep CR/LF (and therefore
+// response-splitting bytes) out of the response stream (#2010).
+TEST(HTTPSockTest, IsValidHeaderField) {
+    // Plain field names and values are accepted.
+    EXPECT_TRUE(CHTTPSock::IsValidHeaderField(""));
+    EXPECT_TRUE(CHTTPSock::IsValidHeaderField("X-Custom"));
+    EXPECT_TRUE(CHTTPSock::IsValidHeaderField("text/html; charset=utf-8"));
+    EXPECT_TRUE(CHTTPSock::IsValidHeaderField("a value with spaces and tabs\t"));
+
+    // CR or LF anywhere is rejected; both halves of a CRLF pair are
+    // rejected even individually.
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("\r"));
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("\n"));
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("\r\n"));
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("X\rFoo"));
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("X\nFoo"));
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("safe\r\nInjected: yes"));
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("trailing\n"));
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("\rleading"));
+}