Expose simple API to select a single USB device

The caller just wants a single device. Handle all cases and error
messages internally.

PR #3005 <https://github.com/Genymobile/scrcpy/pull/3005>

app/src/scrcpy.c

@@ -430,32 +430,19 @@ scrcpy(struct scrcpy_options *options) {
             }
 
             assert(serial);
-            struct sc_usb_device usb_devices[16];
+            struct sc_usb_device usb_device;
-            ssize_t count = sc_usb_find_devices(&s->usb, serial, usb_devices,
+            ok = sc_usb_select_device(&s->usb, serial, &usb_device);
-                                                ARRAY_LEN(usb_devices));
+            if (!ok) {
-            if (count <= 0) {
-                LOGE("Could not find USB device %s", serial);
                 sc_usb_destroy(&s->usb);
-                sc_acksync_destroy(&s->acksync);
                 goto aoa_hid_end;
             }
 
-            if (count > 1) {
-                LOGE("Multiple (%d) devices with serial %s", (int) count, serial);
-                sc_usb_devices_destroy_all(usb_devices, count);
-                sc_usb_destroy(&s->usb);
-                sc_acksync_destroy(&s->acksync);
-                goto aoa_hid_end;
-            }
-
-            struct sc_usb_device *usb_device = &usb_devices[0];
-
             LOGI("USB device: %s (%04" PRIx16 ":%04" PRIx16 ") %s %s",
-                 usb_device->serial, usb_device->vid, usb_device->pid,
+                 usb_device.serial, usb_device.vid, usb_device.pid,
-                 usb_device->manufacturer, usb_device->product);
+                 usb_device.manufacturer, usb_device.product);
 
-            ok = sc_usb_connect(&s->usb, usb_device->device, NULL, NULL);
+            ok = sc_usb_connect(&s->usb, usb_device.device, NULL, NULL);
-            sc_usb_device_destroy(usb_device);
+            sc_usb_device_destroy(&usb_device);
             if (!ok) {
                 LOGE("Failed to connect to USB device %s", serial);
                 sc_usb_destroy(&s->usb);

app/src/usb/scrcpy_otg.c

@@ -83,50 +83,17 @@ scrcpy_otg(struct scrcpy_options *options) {
         return false;
     }
 
-    struct sc_usb_device usb_devices[16];
+    struct sc_usb_device usb_device;
-    ssize_t count = sc_usb_find_devices(&s->usb, serial, usb_devices,
+    ok = sc_usb_select_device(&s->usb, serial, &usb_device);
-                                        ARRAY_LEN(usb_devices));
+    if (!ok) {
-    if (count < 0) {
-        LOGE("Could not list USB devices");
         goto end;
     }
 
-    if (count == 0) {
-        if (serial) {
-            LOGE("Could not find USB device %s", serial);
-        } else {
-            LOGE("Could not find any USB device");
-        }
-        goto end;
-    }
-
-    if (count > 1) {
-        if (serial) {
-            LOGE("Multiple (%d) USB devices with serial %s:", (int) count,
-                 serial);
-        } else {
-            LOGE("Multiple (%d) USB devices:", (int) count);
-        }
-        for (size_t i = 0; i < (size_t) count; ++i) {
-            struct sc_usb_device *d = &usb_devices[i];
-            LOGE("    %-18s (%04" PRIx16 ":%04" PRIx16 ")  %s %s",
-                 d->serial, d->vid, d->pid, d->manufacturer, d->product);
-        }
-        if (!serial) {
-            LOGE("Specify the device via -s or --serial");
-        }
-        sc_usb_devices_destroy_all(usb_devices, count);
-        goto end;
-    }
-    usb_device_initialized = true;
-
-    struct sc_usb_device *usb_device = &usb_devices[0];
-
     LOGI("USB device: %s (%04" PRIx16 ":%04" PRIx16 ") %s %s",
-         usb_device->serial, usb_device->vid, usb_device->pid,
+         usb_device.serial, usb_device.vid, usb_device.pid,
-         usb_device->manufacturer, usb_device->product);
+         usb_device.manufacturer, usb_device.product);
 
-    ok = sc_usb_connect(&s->usb, usb_device->device, &cbs, NULL);
+    ok = sc_usb_connect(&s->usb, usb_device.device, &cbs, NULL);
     if (!ok) {
         goto end;
     }
@@ -173,7 +140,7 @@ scrcpy_otg(struct scrcpy_options *options) {
 
     const char *window_title = options->window_title;
     if (!window_title) {
-        window_title = usb_device->product ? usb_device->product : "scrcpy";
+        window_title = usb_device.product ? usb_device.product : "scrcpy";
     }
 
     struct sc_screen_otg_params params = {
@@ -192,7 +159,7 @@ scrcpy_otg(struct scrcpy_options *options) {
     }
 
     // usb_device not needed anymore
-    sc_usb_device_destroy(usb_device);
+    sc_usb_device_destroy(&usb_device);
     usb_device_initialized = false;
 
     ret = event_loop(s);
@@ -223,7 +190,7 @@ end:
     }
 
     if (usb_device_initialized) {
-        sc_usb_device_destroy(usb_device);
+        sc_usb_device_destroy(&usb_device);
     }
 
     sc_usb_destroy(&s->usb);

app/src/usb/usb.c

@@ -96,7 +96,7 @@ sc_usb_devices_destroy_all(struct sc_usb_device *usb_devices, size_t count) {
     }
 }
 
-ssize_t
+static ssize_t
 sc_usb_find_devices(struct sc_usb *usb, const char *serial,
                     struct sc_usb_device *devices, size_t len) {
     libusb_device **list;
@@ -119,6 +119,49 @@ sc_usb_find_devices(struct sc_usb *usb, const char *serial,
     return idx;
 }
 
+bool
+sc_usb_select_device(struct sc_usb *usb, const char *serial,
+                     struct sc_usb_device *out_device) {
+    struct sc_usb_device usb_devices[16];
+    ssize_t count = sc_usb_find_devices(usb, serial, usb_devices,
+                                        ARRAY_LEN(usb_devices));
+    if (count == -1) {
+        LOGE("Could not list USB devices");
+        return false;
+    }
+
+    if (count == 0) {
+        if (serial) {
+            LOGE("Could not find USB device %s", serial);
+        } else {
+            LOGE("Could not find any USB device");
+        }
+        return false;
+    }
+
+    if (count > 1) {
+        if (serial) {
+            LOGE("Multiple (%" SC_PRIsizet ") USB devices with serial %s:",
+                 count, serial);
+        } else {
+            LOGE("Multiple (%" SC_PRIsizet ") USB devices:", count);
+        }
+        for (size_t i = 0; i < (size_t) count; ++i) {
+            struct sc_usb_device *d = &usb_devices[i];
+            LOGE("    %-18s (%04" PRIx16 ":%04" PRIx16 ")  %s %s",
+                 d->serial, d->vid, d->pid, d->manufacturer, d->product);
+        }
+        LOGE("Select a device via -s (--serial)");
+        sc_usb_devices_destroy_all(usb_devices, count);
+        return false;
+    }
+
+    assert(count == 1);
+    // Move usb_devices[0] into out_device (do not destroy usb_devices[0])
+    *out_device = usb_devices[0];
+    return true;
+}
+
 bool
 sc_usb_init(struct sc_usb *usb) {
     usb->handle = NULL;

app/src/usb/usb.h

@@ -61,9 +61,9 @@ sc_usb_init(struct sc_usb *usb);
 void
 sc_usb_destroy(struct sc_usb *usb);
 
-ssize_t
+bool
-sc_usb_find_devices(struct sc_usb *usb, const char *serial,
+sc_usb_select_device(struct sc_usb *usb, const char *serial,
-                    struct sc_usb_device *devices, size_t len);
+                     struct sc_usb_device *out_device);
 
 bool
 sc_usb_connect(struct sc_usb *usb, libusb_device *device,