Make sure when the backend cannot be downloaded or the site resolved that we're forgiving until we try to use the provided FFI functions.

example1/example.rkt

@@ -10,7 +10,9 @@
 
 (provide
  (all-from-out racket/gui)
+ (all-from-out "../main.rkt")
  example-1-window%
+ run-example
  )
 
 (define ww-debug displayln)

info.rkt

@@ -1,7 +1,7 @@
 #lang info
 
 (define pkg-authors '(hnmdijkema))
-(define version "0.1.1")
+(define version "0.1.2")
 (define license 'MIT)   
 (define collection "racket-webview")
 (define pkg-desc "racket-webview - A Web Based GUI library, based on a Qt WebEngine backend")

main.rkt

@@ -1,5 +1,6 @@
 #lang racket/base
 
+(require "private/racket-webview-downloader.rkt")
 (require "private/racket-webview.rkt")
 (require "private/wv-context.rkt")
 (require "private/wv-window.rkt")
@@ -18,6 +19,7 @@
                        "private/rgba.rkt"
                        "private/mimetypes.rkt"
                        "private/menu.rkt"
+                       "private/racket-webview-downloader.rkt"
                        )
          webview-set-loglevel
          webview-version

private/racket-webview-downloader.rkt

@@ -4,6 +4,7 @@
          net/sendurl
          net/url
          net/url-connect
+         net/dns
          racket/file
          racket/system
          racket/string
@@ -15,6 +16,7 @@
          racket-webview-qt-directory
          racket-webview-qt-is-available?
          racket-webview-qt-is-downloadable?
+         racket-webview-qt-resolves?
          )
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
@@ -101,20 +103,30 @@
 
 (define (racket-webview-qt-directory)
   (if (racket-webview-qt-is-available?)
-      (build-path (format "~a/~a-~a" install-path rkt-qt-os rkt-qt-arch))
+      (build-path install-path (format "~a-~a" rkt-qt-os rkt-qt-arch))
       #f))
 
+(define (racket-webview-qt-resolves?)
+  (if (eq? (dns-find-nameserver) #f)
+    #f
+    (with-handlers ([exn:fail? (λ (e) #f)])
+      (dns-get-address (dns-find-nameserver) rkt-qt-download-site)
+      #t)
+    )
+  )
+
 (define (racket-webview-qt-version)
   (if (racket-webview-qt-is-available?)
       (file->value version-file)
       #f))
 
 (define (racket-webview-qt-is-downloadable?)
-  (let ((in (download-port rkt-download-url)))
+  (with-handlers ([exn:fail? (λ (e) #f)])
-    (let ((d (input-port? in)))
+    (let ((in (download-port rkt-download-url)))
-      (when d
+      (let ((d (input-port? in)))
-        (close-input-port in))
+        (when d
-      d)))
+          (close-input-port in))
+        d))))
 
 (define (download-racket-webview-qt)
   (let ((in (download-port rkt-download-url)))

private/racket-webview-qt.rkt

@@ -14,6 +14,7 @@
          racket/path
          "utils.rkt"
          "racket-webview-downloader.rkt"
+         openssl/libssl
          )
 
 (provide rkt-wv
@@ -55,12 +56,44 @@
 
 (define lib-type 'release)
 
+;; Check if racket-webview-qt backend is available or downloadable
+
+(define do-ffi #t)
+(define reason "")
+
 (unless (racket-webview-qt-is-available?)
-  (unless (racket-webview-qt-is-downloadable?)
+  (if (racket-webview-qt-resolves?)
-    (error (format "There is no version of the racket-webview Qt backend available for OS '~a', Architectur '~a'"
+      (if (racket-webview-qt-is-downloadable?)
-                   (system-type 'os*)
+          (begin
-                   (system-type 'arch))))
+            (set! do-ffi (download-racket-webview-qt))
-  (download-racket-webview-qt))
+            (when (eq? do-ffi #f)
+              (set! reason "Racket Webview Qt backend could not be downloaded"))
+            )
+          (begin
+            (displayln "There is no version of the racket-webview Qt backend available\n")
+            (displayln
+             (format "for OS '~a', Architecture '~a'"
+                     (system-type 'os*)
+                     (system-type 'arch)))
+            (set! do-ffi #f)
+            (set! reason (format
+                          "There is no version of Racket Webview Qt for os '~a', architecture '~a' available"
+                          (system-type 'os*)
+                          (system-type 'arch)
+                          )
+                  )
+            )
+          )
+      (begin
+        (displayln "Warning: Cannot resolve racket webview download site.")
+        (displayln "Cannot download backend libraries and programs.")
+        (set! do-ffi #f)
+        (set! reason "Racket Webview Qt backend download site could not be resolved")
+        )
+      )
+  )
+
+;; Make sure we can load the FFI library, if at all possible (i.e. do-ffi equals #t)
 
 (define os (system-type 'os*))
 
@@ -71,11 +104,11 @@
    )
   )
 
-(define os-lib-dir (racket-webview-qt-directory))
+(define os-lib-dir
-
+  (let ((dir (racket-webview-qt-directory)))
-(let ((files (directory-list os-lib-dir)))
+    (if (eq? dir #f)
-  (displayln (format "os-lib-dir: ~a" os-lib-dir))
+        (build-path ".")
-  (displayln (format "os-lib-dir-contents: ~a" files)))
+        dir)))
 
 (define (libname lib-symbol)
   (build-path os-lib-dir (symbol->string lib-symbol)))
@@ -94,41 +127,75 @@
 
 (define webview-lib-file (libname ffi-library))
 (define webview-lib
-  (with-handlers ([exn:fail?
+  (if (eq? do-ffi #f)
-                   (λ (exp)
+      libssl
-                     (cond
+      (with-handlers ([exn:fail?
-                       ([eq? os 'linux]
+                       (λ (exp)
-                        (error (format
+                         (cond
-                                (string-append "Cannot load ~a.\n"
+                           ([eq? os 'linux]
-                                               "Make sure you installed Qt6 on your system\n"
+                            (error (format
-                                               "NB. the minimum Qt version that is supported is Qt 6.10.\n"
+                                    (string-append "Cannot load ~a.\n"
-                                               "This probably means you will need to install it separately from\n"
+                                                   "Make sure you installed Qt6 on your system\n"
-                                               "the standard distro packages (e.g. libqt6webenginewidgets6 on\n"
+                                                   "NB. the minimum Qt version that is supported is Qt 6.10.\n"
-                                               "debian based systems).\n"
+                                                   "This probably means you will need to install it separately from\n"
-                                               "\n"
+                                                   "the standard distro packages (e.g. libqt6webenginewidgets6 on\n"
-                                               "Exception:\n\n~a")
+                                                   "debian based systems).\n"
-                                ffi-library exp)))
+                                                   "\n"
-                       (else (error
+                                                   "Exception:\n\n~a")
-                              (format "Cannot load ~a for os ~a\n\nException:\n\n~a"
+                                    ffi-library exp)))
-                                      ffi-library os exp))))
+                           (else (error
-                     )
+                                  (format "Cannot load ~a for os ~a\n\nException:\n\n~a"
-                   ])
+                                          ffi-library os exp))))
-    (ffi-lib webview-lib-file '("6" #f)
+                         )
-             #:get-lib-dirs (list os-lib-dir)
+                       ])
-             ;#:custodian (current-custodian)
+        (ffi-lib webview-lib-file '("6" #f)
-             )
+                 #:get-lib-dirs (list os-lib-dir)
-    )
+                 ;#:custodian (current-custodian)
+                 )
+        )
+      )
   )
 
-(define-ffi-definer define-rktwebview webview-lib)
+;; Make sure we are forgiving with the function loading. 
+;; forgiving with the function loading.
 
+(define (make-ffi-repl id err . ret)
+  (let ((warned #f)
+        (msg (if (eq? do-ffi #t)
+                 (string-append
+                  "'~a' could not be loaded from "
+                  (format "~a" webview-lib-file))
+                 (string-append
+                  "'~a' could not be loaded.\n"
+                  reason)))
+        )
+    (λ () (λ args
+            (if err
+                (error (format msg id))
+                (begin
+                  (unless warned
+                    (displayln (format msg id))
+                    (set! warned #t))
+                  (car ret)))))))
 
-
+(define-ffi-definer define-rktwebview
-;;; Callbacks from the OS library
+                    webview-lib
-
+                    #:default-make-fail (λ (id)
-;(define callback-box (box '()))
+                                          (if (eq? do-ffi #f)
-;(define (applier thunk)
+                                              (cond
-;  (thunk))
+                                                ((eq? id 'rkt_webview_env)
+                                                 (make-ffi-repl id #f #t))
+                                                ((eq? id 'rkt_webview_events_waiting)
+                                                 (make-ffi-repl id #f 0))
+                                                ((eq? id 'rkt_webview_init)
+                                                 (make-ffi-repl id #f #t))
+                                                ((eq? id 'rkt_webview_cleanup)
+                                                 (make-ffi-repl id #f #t))
+                                                (else
+                                                 (make-ffi-repl id #t))
+                                                )
+                                              (make-ffi-repl id #t)))
+  )
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Types / Functions