WIP more robust: curl could leave partial file

examples/apt-archive/proxy.ss

@@ -108,13 +108,19 @@
       [status
        (match scheme
          ["https"
-          (let-values ([(to-stdin from-stdout from-stderr os-pid)
-                        (spawn-os-process "curl"
-                          `("-s" "-o" ,(make-directory-path target-file) ,(format "https://~a~a" host path))
-                          self)])
+          (define tmp-file (path-combine archive (uuid->string (osi_make_uuid))))
+          (define-values (to-stdin from-stdout from-stderr os-pid)
+            (spawn-os-process "curl"
+              `("-s" "-o" ,tmp-file ,(format "https://~a~a" host path))
+              self))
+          (on-exit (delete-file tmp-file)
             (receive
              [#(process-terminated ,@os-pid ,exit-status ,term-signal)
-              (and (= exit-status 0) (file-exists? target-file))]))]
+              (and (= exit-status 0)
+                   (file-exists? tmp-file)
+                   (begin
+                     (rename-path tmp-file (make-directory-path target-file))
+                     #t))]))]
          ["http"
           (let-values ([(ip op) (connect-tcp host port)])
             (on-exit (begin (close-port ip) (close-port op))