nghttpx: Ignore Content-Length and Transfer-Encoding in 1xx or 200 to CONNECT

A well known server sends content-length: 0 in 101 response.  RFC 7230
says Content-Length or Transfer-Encoding in 200 response to CONNECT
request: https://tools.ietf.org/html/rfc7230#section-3.3.3

src/shrpx_downstream.cc

@@ -573,6 +573,18 @@ void FieldStore::append_last_trailer_value(const char *data, size_t len) {
                                   trailers_, data, len);
 }
 
+void FieldStore::erase_content_length_and_transfer_encoding() {
+  for (auto &kv : headers_) {
+    switch (kv.token) {
+    case http2::HD_CONTENT_LENGTH:
+    case http2::HD_TRANSFER_ENCODING:
+      kv.name = StringRef{};
+      kv.token = -1;
+      break;
+    }
+  }
+}
+
 void Downstream::set_request_start_time(
     std::chrono::high_resolution_clock::time_point time) {
   request_start_time_ = std::move(time);

src/shrpx_downstream.h

@@ -119,6 +119,10 @@ public:
 
   bool trailer_key_prev() const { return trailer_key_prev_; }
 
+  // erase_content_length_and_transfer_encoding erases content-length
+  // and transfer-encoding header fields.
+  void erase_content_length_and_transfer_encoding();
+
   // content-length, -1 if it is unknown.
   int64_t content_length;
 

src/shrpx_http_downstream_connection.cc

@@ -935,18 +935,15 @@ int htp_hdrs_completecb(llhttp_t *htp) {
       return -1;
     }
     if (resp.fs.content_length == 0) {
-      auto cl = resp.fs.header(http2::HD_CONTENT_LENGTH);
-      assert(cl);
-      http2::erase_header(cl);
+      resp.fs.erase_content_length_and_transfer_encoding();
     } else if (resp.fs.content_length != -1) {
       return -1;
     }
   } else if (resp.http_status / 100 == 1 ||
              (resp.http_status / 100 == 2 && req.method == HTTP_CONNECT)) {
-    if (resp.fs.header(http2::HD_CONTENT_LENGTH) ||
-        resp.fs.header(http2::HD_TRANSFER_ENCODING)) {
-      return -1;
-    }
+    // Server MUST NOT send Content-Length and Transfer-Encoding in
+    // these responses.
+    resp.fs.erase_content_length_and_transfer_encoding();
   } else if (resp.fs.parse_content_length() != 0) {
     downstream->set_response_state(DownstreamState::MSG_BAD_HEADER);
     return -1;