test(HTTP): add case-insensitive header matching tests

Add comprehensive tests for RFC 7230 compliance (header field names
are case-insensitive):

- HTTPReq: GetHeader, GetNumHeaders, UpdateHeader, RemoveHeader
- HTTPRes: content_length(), is_chunked(), is_gzipped(), add_header,
  del_header, to_string() duplicate prevention

These tests currently fail and document the expected behavior.

tests/test-http-req.cpp

@@ -83,6 +83,59 @@ int main() {
   assert(req->GetHeader("Accept-Encoding") == "");
   delete req;
 
+  /* test: case-insensitive header matching (RFC 7230) */
+  buf =
+    "GET / HTTP/1.1\r\n"
+    "HOST: example.i2p\r\n"
+    "content-type: text/html\r\n"
+    "Content-Length: 100\r\n"
+    "X-Custom-Header: value\r\n"
+    "\r\n";
+  len = strlen(buf);
+  req = new HTTPReq;
+  assert((ret = req->parse(buf, len)) == len);
+  /* GetHeader should be case-insensitive */
+  assert(req->GetHeader("Host") == "example.i2p");
+  assert(req->GetHeader("host") == "example.i2p");
+  assert(req->GetHeader("HOST") == "example.i2p");
+  assert(req->GetHeader("Content-Type") == "text/html");
+  assert(req->GetHeader("content-type") == "text/html");
+  assert(req->GetHeader("CONTENT-TYPE") == "text/html");
+  assert(req->GetHeader("Content-Length") == "100");
+  assert(req->GetHeader("content-length") == "100");
+  assert(req->GetHeader("x-custom-header") == "value");
+  assert(req->GetHeader("X-CUSTOM-HEADER") == "value");
+  /* GetNumHeaders should be case-insensitive */
+  assert(req->GetNumHeaders("Host") == 1);
+  assert(req->GetNumHeaders("host") == 1);
+  assert(req->GetNumHeaders("HOST") == 1);
+  assert(req->GetNumHeaders("content-type") == 1);
+  delete req;
+
+  /* test: UpdateHeader case-insensitivity */
+  req = new HTTPReq;
+  req->AddHeader("Content-Type", "text/plain");
+  assert(req->GetHeader("Content-Type") == "text/plain");
+  req->UpdateHeader("content-type", "application/json");
+  assert(req->GetHeader("Content-Type") == "application/json");
+  assert(req->GetHeader("CONTENT-TYPE") == "application/json");
+  req->UpdateHeader("CONTENT-TYPE", "text/html");
+  assert(req->GetHeader("content-type") == "text/html");
+  delete req;
+
+  /* test: RemoveHeader case-insensitivity */
+  req = new HTTPReq;
+  req->AddHeader("X-Forwarded-For", "1.2.3.4");
+  req->AddHeader("X-Forwarded-Host", "proxy.i2p");
+  req->AddHeader("Accept", "*/*");
+  assert(req->GetNumHeaders() == 3);
+  /* remove headers starting with "x-forwarded" (case-insensitive), exempt "X-Forwarded-Host" */
+  req->RemoveHeader("X-Forwarded", "x-forwarded-host");
+  assert(req->GetNumHeaders() == 2);
+  assert(req->GetHeader("X-Forwarded-Host") == "proxy.i2p");
+  assert(req->GetHeader("X-Forwarded-For") == "");
+  delete req;
+
   return 0;
 }