Expose function to find a USB device

The device was automatically found by sc_usb_connect(). Instead, expose
a function to find a device from a serial, and let the caller connect to
the device found (if any).

This will allow to list all devices first, then select one device to
connect to.

PR #2974 <https://github.com/Genymobile/scrcpy/pull/2974>

app/src/scrcpy.c

@@ -431,7 +431,17 @@ scrcpy(struct scrcpy_options *options) {
                 goto aoa_hid_end;
             }
 
-            ok = sc_usb_connect(&s->usb, serial);
+            assert(serial);
+            libusb_device *device = sc_usb_find_device(&s->usb, serial);
+            if (!device) {
+                LOGE("Could not find USB device %s", serial);
+                sc_usb_destroy(&s->usb);
+                sc_acksync_destroy(&s->acksync);
+                goto aoa_hid_end;
+            }
+
+            ok = sc_usb_connect(&s->usb, device);
+            libusb_unref_device(device);
             if (!ok) {
                 LOGE("Failed to connect to USB device %s", serial);
                 sc_usb_destroy(&s->usb);

app/src/usb/usb.c

@@ -57,8 +57,10 @@ accept_device(libusb_device *device, const char *serial) {
     return matches;
 }
 
-static libusb_device *
+libusb_device *
 sc_usb_find_device(struct sc_usb *usb, const char *serial) {
+    assert(serial);
+
     libusb_device **list;
     libusb_device *result = NULL;
     ssize_t count = libusb_get_device_list(usb->context, &list);
@@ -103,19 +105,9 @@ sc_usb_destroy(struct sc_usb *usb) {
 }
 
 bool
-sc_usb_connect(struct sc_usb *usb, const char *serial) {
+sc_usb_connect(struct sc_usb *usb, libusb_device *device) {
-    assert(serial);
-
-    libusb_device *device = sc_usb_find_device(usb, serial);
-    if (!device) {
-        LOGW("USB device %s not found", serial);
-        return false;
-    }
-
     usb->handle = sc_usb_open_handle(device);
-    libusb_unref_device(device);
     if (!usb->handle) {
-        LOGW("Could not open USB device %s", serial);
         return false;
     }
 

app/src/usb/usb.h

@@ -17,8 +17,11 @@ sc_usb_init(struct sc_usb *usb);
 void
 sc_usb_destroy(struct sc_usb *usb);
 
+libusb_device *
+sc_usb_find_device(struct sc_usb *usb, const char *serial);
+
 bool
-sc_usb_connect(struct sc_usb *usb, const char *serial);
+sc_usb_connect(struct sc_usb *usb, libusb_device *device);
 
 void
 sc_usb_disconnect(struct sc_usb *usb);