libusb example

examples/README.md

@@ -52,3 +52,6 @@ The guide in [doc/guide.md](../doc/guide.md) explains the API these use.
   SDL3 package of your distribution). On macOS the JVM run needs
   `-XstartOnFirstThread` as well, because SDL uses thread 0 for the Cocoa
   event loop.
+- `libusb.cljc` lists the USB devices with their IDs and names, like
+  `lsusb` (`brew install libusb`, or the libusb package of your
+  distribution).

examples/libusb.cljc

@@ -0,0 +1,81 @@
+(ns libusb)
+
+(require '[babashka.ffi :as ffi :refer [defcfn]])
+
+(ffi/load-library {:mac ["libusb-1.0.dylib" "libusb-1.0.0.dylib"]
+                   :linux ["libusb-1.0.so.0" "libusb-1.0.so"]
+                   :windows "libusb-1.0.dll"})
+
+(defcfn libusb-init "libusb_init" [:pointer] :int)
+(defcfn libusb-exit "libusb_exit" [:pointer] :void)
+(defcfn libusb-get-device-list "libusb_get_device_list" [:pointer :pointer] :ssize_t)
+(defcfn libusb-free-device-list "libusb_free_device_list" [:pointer :int] :void)
+(defcfn libusb-get-device-descriptor "libusb_get_device_descriptor" [:pointer :pointer] :int)
+(defcfn libusb-get-bus-number "libusb_get_bus_number" [:pointer] :uint8)
+(defcfn libusb-get-device-address "libusb_get_device_address" [:pointer] :uint8)
+(defcfn libusb-open "libusb_open" [:pointer :pointer] :int)
+(defcfn libusb-close "libusb_close" [:pointer] :void)
+(defcfn libusb-get-string-descriptor-ascii
+  "libusb_get_string_descriptor_ascii" [:pointer :uint8 :pointer :int] :int)
+(defcfn libusb-error-name "libusb_error_name" [:int] :string)
+
+(def device-descriptor
+  [:struct [[:bLength :uint8]
+            [:bDescriptorType :uint8]
+            [:bcdUSB :uint16]
+            [:bDeviceClass :uint8]
+            [:bDeviceSubClass :uint8]
+            [:bDeviceProtocol :uint8]
+            [:bMaxPacketSize0 :uint8]
+            [:idVendor :uint16]
+            [:idProduct :uint16]
+            [:bcdDevice :uint16]
+            [:iManufacturer :uint8]
+            [:iProduct :uint8]
+            [:iSerialNumber :uint8]
+            [:bNumConfigurations :uint8]]])
+
+(defn check [rc]
+  (when (neg? rc)
+    (throw (ex-info (libusb-error-name rc) {:rc rc})))
+  rc)
+
+(defn pad [s width]
+  (let [s (str s)]
+    (str (apply str (repeat (- width (count s)) "0")) s)))
+
+(defn hex4 [n]
+  (pad #?(:clj (Long/toHexString n) :cljs (.toString n 16)) 4))
+
+(defn string-descriptor [arena dev idx]
+  (when (pos? idx)
+    (let [ph (ffi/alloc arena :pointer)]
+      (when (zero? (libusb-open dev ph))
+        (let [handle (ffi/read ph :pointer)
+              buf (ffi/alloc arena 256)
+              n (libusb-get-string-descriptor-ascii handle idx buf 256)]
+          (libusb-close handle)
+          (when (pos? n)
+            (ffi/ptr->string buf)))))))
+
+(#?(:clj with-open :cljs ffi/with-open) [arena (ffi/confined-arena)]
+  (let [pctx (ffi/alloc arena :pointer)
+        _ (check (libusb-init pctx))
+        ctx (ffi/read pctx :pointer)
+        plist (ffi/alloc arena :pointer)
+        n (check (libusb-get-device-list ctx plist))
+        list (ffi/reinterpret (ffi/read plist :pointer) (* n (ffi/sizeof :pointer)))]
+    (try
+      (doseq [i (range n)]
+        (let [dev (ffi/read list :pointer (* i (ffi/sizeof :pointer)))
+              pdesc (ffi/alloc arena device-descriptor)
+              _ (check (libusb-get-device-descriptor dev pdesc))
+              desc (ffi/read pdesc device-descriptor)]
+          (println (str "Bus " (pad (libusb-get-bus-number dev) 3)
+                        " Device " (pad (libusb-get-device-address dev) 3)
+                        ": ID " (hex4 (:idVendor desc)) ":" (hex4 (:idProduct desc))
+                        " " (or (string-descriptor arena dev (:iManufacturer desc)) "")
+                        " " (or (string-descriptor arena dev (:iProduct desc)) "")))))
+      (finally
+        (libusb-free-device-list (ffi/read plist :pointer) 1)
+        (libusb-exit ctx)))))