Rewriting HTTP::host

At the risk of looking like a newbie, is this supposed to work?:

 

 

when HTTP_REQUEST {

 

HTTP::host "foo.bar.com"

 

HTTP::uri "/some_uri"

 

}

 

 

Darned if I can get it to work, at least on v9.3.1:

 

 

BIGpipe: rule modification error:

 

01070151:3: Rule [my_rewrite] error:

 

line 2: [wrong args] [HTTP::host "foo.bar.com"]

 

 

I see lots of examples of rewriting HTTP::uri, or redirecting via a 302, but don't see any mechanism to directly rewrite the destination host.domain.

 

 

What am I missing? Thx.