Method copy_header_fields

src/proxy/http/HttpTransactHeaders.cc:214–272

/////////////////////////////////////////////////////////////////// Copy all non hop-by-hop header fields from src_hdr to new_hdr. If header Date: is not present or invalid in src_hdr, then the given date will be used.

// If header Date: is not present or invalid in src_hdr,
// then the given date will be used.
void
HttpTransactHeaders::copy_header_fields(HTTPHdr *src_hdr, HTTPHdr *new_hdr, bool retain_proxy_auth_hdrs, ink_time_t date)
{
  ink_assert(src_hdr->valid());
  ink_assert(!new_hdr->valid());

  bool date_hdr = false;

  // Start with an exact duplicate
  new_hdr->copy(src_hdr);

  // Nuke hop-by-hop headers
  //
  //    The hop-by-hop header fields are laid out by the spec
  //    with two adjustments
  //      1) we treat TE as hop-by-hop because spec implies
  //         that it is by declaring anyone who sends a TE must
  //         include TE in the connection header.  This in
  //         my opinion error prone and if the client doesn't follow the spec
  //         we'll have problems with the TE being forwarded to the server
  //         and us caching the transfer encoded documents and then
  //         serving it to a client that can not handle it. The exception
  //         to this is that we will allow "TE: trailers" to be forwarded
  //         because that is required for gRPC traffic.
  //      2) Transfer encoding is copied.  If the transfer encoding
  //         is changed for example by dechunking, the transfer encoding
  //         should be modified when the decision is made to dechunk it

  for (auto &field : *new_hdr) {
    if (field.m_wks_idx == -1) {
      continue;
    }

    int field_flags = hdrtoken_index_to_flags(field.m_wks_idx);

    if (field_flags & HTIF_HOPBYHOP) {
      std::string_view name(field.name_get());
      std::string_view value(field.value_get());
      bool const       is_te_trailers = name == MIME_FIELD_TE && value == "trailers";
      if (is_te_trailers) {
        // te: trailers is used by gRPC, do not delete it.
        continue;
      }

      // Delete header if not in special proxy_auth retention mode
      if (retain_proxy_auth_hdrs && (field_flags & HTIF_PROXYAUTH)) {
        continue;
      }
      new_hdr->field_delete(&field);
    } else if (field.m_wks_idx == MIME_WKSIDX_DATE) {
      date_hdr = true;
    }
  }

  // Set date hdr if not already set and valid value passed in
  if ((date_hdr == false) && (date > 0)) {
    new_hdr->set_date(date);
  }