Catch tcp failures in the http verification.

collects/meta/web/download/mirror-link.rkt

@@ -127,12 +127,10 @@ Polling a URL can result in one of four options:
 ;; need to mimic HEAD requests too.
 
 (define (verify-http url)
-  (call/input-url (string->url url) head-impure-port
-    (lambda (inp)
+  (define (check-contents inp)
     (define status (read-line inp))
     (define status* (regexp-match #rx"^HTTP/[0-9.]+ ([0-9]+)" status))
-      (cond
-        [(not status*)
+    (cond [(not status*)
            (eprintf "WARNING: bad status line for ~a:\n  ~s\n" url status)
            #f]
           [(not (regexp-match #rx"^2..$" (cadr status*)))
@@ -145,7 +143,14 @@ Polling a URL can result in one of four options:
                         => (compose string->number cadr)]
                        [else #f]))
                (begin (eprintf "WARNING: no `content-length' for ~a" url)
-                    #t))]))))
+                      #t))]))
+  (define r
+    (with-handlers ([exn:fail? exn-message])
+      (call/input-url (string->url url) head-impure-port check-contents)))
+  (if (boolean? r)
+    r
+    (begin (eprintf "WARNING: failure getting http info for ~a (~a)\n" url r)
+           #f)))
 
 (define (verify-ftp url)
   (define-values [host port? path]