http_stream:cgi_property/2

Inquire the status of the CGI stream. Defined properties are:

request(-Term): The original request
header(-Term): Term is the header term as registered using cgi_set/2
client(-Stream): Stream is the original output stream used to create this stream.
thread(-ThreadID): ThreadID is the identifier of the `owning thread'
transfer_encoding(-Tranfer): One of chunked or none.
connection(-Connection): One of Keep-Alive or close
content_length(-ContentLength): Total byte-size of the content. Available in the close handler if the transfer_encoding is none.
header_codes(-Codes): Codes represents the header collected. Available in the header handler.
state(-State): One of header, data or discarded
id(-ID): Request sequence number. This number is guaranteed to be unique.