net/url: fix problems with new implementation on net/http-client

Various `net/url` operations need to request a close of the
connection after the operation completes, and `het/http-client`
needs to actually close the input-port half of a connection.

Also, add `http-conn-abandon!`.

Also also, add limits on internal pipes, so that data doesn't pile
up in a connection-processing thread, and fix POST/PUT by adding
a needed CRLF after posted data.

original commit: 0dcaa5e19f

pkgs/racket-pkgs/racket-doc/net/scribblings/http-client.scrbl

@@ -61,6 +61,13 @@ Closes @racket[hc] if it is live.
 
 }
 
+@defproc[(http-conn-abandon! [hc http-conn?])
+         void?]{
+
+Closes the output side of @racket[hc], if it is live.
+
+}
+
 @defproc[(http-conn-send! [hc http-conn-live?] [uri (or/c bytes? string?)]
                           [#:version version (or/c bytes? string?) #"1.1"]
                           [#:method method (or/c bytes? string? symbol?) #"GET"]

pkgs/racket-pkgs/racket-test/tests/net/url-port.rkt

@@ -151,12 +151,14 @@
 (module+ main (tests))
 (define (tests)
   (test
-   (run-tests "http" values #f)
+   (for ([i 100]) ; repeat to catch port leaks
+     (run-tests "http" values #f))
+   (for ([i 100])
      (run-tests "https" (let ([ctx (ssl-make-server-context)])
                           (ssl-load-certificate-chain! ctx (collection-file-path "test.pem" "openssl"))
                           (ssl-load-private-key! ctx (collection-file-path "test.pem" "openssl"))
                           (lambda (in out)
                             (ports->ssl-ports in out #:mode 'accept #:context ctx)))
-              #t)))
+                #t))))
 
 (module+ test (require (submod ".." main))) ; for raco test & drdr