[racket] port open or closed?

May be I am myopic, but I have not found any tools in the docs to check
whether a port is open or closed. After a port is closed, it may survive. It
would be handy to have:
 
1: a procedure that tells whether or not a port is open.
2: a procedure that given a closed port, reopens it or returns its path (or
other info about the port, for example, it may be an output-string or a
console)
 
This can be useful for procedures that accept port arguments and want to
check first. Using some tricks I can make these procedures myself in a
rather stupid way that I rather would like to avoid (writing the port to an
output-string and inspect the output and displaying an empty string while
catching a port is closed exception)
 
Best wishes, Jos
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