Reads the FDv1 fallback directive from an FDv2 goodbye event's data.
SDKs that cannot read streaming response headers (e.g. browsers using the
native EventSource API) receive the fallback directive in-band via the
goodbye message's protocolFallbackTTL field.
Presence of a finite numeric protocolFallbackTTL signals FDv1 fallback;
the value carries the same semantics as the x-ld-fd-fallback-ttl header
(0 indicates indefinite fallback). A missing, non-numeric, or non-finite
value is not a fallback signal and yields { fdv1Fallback: false }.
Parameters
data: unknown
The raw, parsed goodbye event data (typed unknown because the
caller has not narrowed it).
Reads the FDv1 fallback directive from an FDv2
goodbyeevent's data.SDKs that cannot read streaming response headers (e.g. browsers using the native
EventSourceAPI) receive the fallback directive in-band via the goodbye message'sprotocolFallbackTTLfield. Presence of a finite numericprotocolFallbackTTLsignals FDv1 fallback; the value carries the same semantics as thex-ld-fd-fallback-ttlheader (0indicates indefinite fallback). A missing, non-numeric, or non-finite value is not a fallback signal and yields{ fdv1Fallback: false }.