net/http-client: avoid race between EOF and collection close

The race condition can result in an "input port is closed"
error when a connection is used again.

racket/collects/net/http-client.rkt

@@ -184,9 +184,7 @@
 
 (define (http-conn-response-port/chunked! hc #:close? [close? #f])
   (define (http-pipe-chunk ip op)
-    (define (done)
-      (flush-output op)
-      (close-output-port op))
+    (define (done) (void))
     (define crlf-bytes (make-bytes 2))
     (let loop ([last-bytes #f])
       (define in-v (read-line ip eol-type))
@@ -248,11 +246,12 @@
     (or (equal? method-bss #"HEAD")
         (equal? method-bss "HEAD")
         (equal? method-bss 'HEAD)))
-  (define raw-response-port
+  (define-values (raw-response-port wait-for-close?)
     (cond
-      [head? (open-input-bytes #"")]
+      [head? (values (open-input-bytes #"") #f)]
       [(regexp-member #rx#"^(?i:Transfer-Encoding: +chunked)$" headers)
-       (http-conn-response-port/chunked! hc #:close? #t)]
+       (values (http-conn-response-port/chunked! hc #:close? #t)
+               #t)]
       [(ormap (λ (h)
                 (match (regexp-match #rx#"^(?i:Content-Length:) +(.+)$" h)
                   [#f #f]
@@ -262,9 +261,10 @@
               headers)
        =>
        (λ (count)
-         (http-conn-response-port/length! hc count #:close? close?))]
+         (values (http-conn-response-port/length! hc count #:close? close?)
+                 close?))]
       [else
-       (http-conn-response-port/rest! hc)]))
+       (values (http-conn-response-port/rest! hc) #t)]))
   (define decoded-response-port
     (cond
       [head? raw-response-port]
@@ -276,9 +276,13 @@
          (thread
           (λ ()
             (gunzip-through-ports raw-response-port out))))
-       (thread 
+       (thread
         (λ ()
           (thread-wait gunzip-t)
+          (when wait-for-close?
+            ;; Wait for an EOF from the raw port before we
+            ;; send an output on the decoding pipe:
+            (copy-port raw-response-port (open-output-nowhere)))
           (close-output-port out)))
        in]
       [else