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CustomHeaders

property CustomHeaders: TStrings read write;

Example​

procedure ScriptEvent(var Value: variant);
begin
  if Response <> nil then
  begin
    Response.SetCustomHeader('X-Request-Reference', 'example-123');
    Value := Response.CustomHeaders.Values['X-Request-Reference'];
  end;
end;

Usage​

CustomHeaders exposes the live persistent WebBroker response-field list that replaces Velox's custom fields immediately before sending.

Additional Technical Info​

CustomHeaders returns WebBroker's actual host-owned TStringList. Each normal entry uses Name=Value because the list's name/value separator is =. Mutating the returned object immediately changes shared pre-send response state; do not free, retain or replace the object reference.

Writing another TStrings value calls Assign: it copies the source list's contents and relevant settings into the existing host list rather than transferring ownership of the source object. This includes NameValueSeparator/options; a TStringList source also copies case-sensitivity, sorting and duplicate policy. A non-default separator can stop Name=Value entries being parsed as intended, case-sensitive lookup can create differently cased duplicates, and sorting/duplicate rules can alter order or reject data. Prefer SetCustomHeader over assigning a configured list. A nil/incompatible source can raise. The response still owns its original list.

This is the authoritative persistent additional-field store for the current bridge. Immediately before automatic send, the bridge:

  1. clears Indy's existing custom-header list;
  2. iterates every WebBroker CustomHeaders entry; and
  3. adds each entry whose parsed name and value are both nonempty to Indy.

That replacement explains why direct Allow, DerivedFrom and Title property assignments can disappear. Use SetCustomHeader or CustomHeaders.Values[Name] when such a field must survive.

SetCustomHeader provides single-name replacement/removal semantics and should be preferred for ordinary fields. Direct Add('Name=Value') can retain duplicate names/order in the WebBroker list, and the bridge can transfer those as repeated fields. Only use repetition when the specific HTTP field permits it; generic comma-combination rules do not apply safely to every field.

The list validates neither HTTP token syntax nor field semantics. Reject CR, LF and other control characters; do not add secrets, Content-Length, Transfer-Encoding, Connection, Host or ad-hoc Set-Cookie fields. Use the response's content/cookie interfaces and let Indy create framing. Empty values are dropped during transfer rather than emitted as empty fields.

List iteration/mutation can raise and is not thread-safe. Automatic sending uses its state only after the action completes. Test Response for nil.

External references

Created 2026-07-15