Add hid_set_input_report_buffer_size() API

hidapi/hidapi.h

@@ -423,6 +423,44 @@ extern "C" {
 		*/
 		int  HID_API_EXPORT HID_API_CALL hid_set_nonblocking(hid_device *dev, int nonblock);
 
+		/** @brief Upper bound for hid_set_input_report_buffer_size().
+
+		    Values passed above this limit are rejected by
+		    hid_set_input_report_buffer_size(). Guards against
+		    memory-exhaustion via unbounded input report queue growth.
+		*/
+		#define HID_API_MAX_INPUT_REPORT_BUFFER_SIZE 1024
+
+		/** @brief Set the size of the input report buffer/queue.
+
+		    Some HID devices emit input reports in bursts at rates
+		    that exceed the default internal queue capacity, causing
+		    silent report drops on macOS and the libusb Linux backend.
+		    This function allows callers to resize the per-device
+		    input report buffer.
+
+		    Defaults per backend:
+		    - macOS:        30 reports
+		    - Linux libusb: 30 reports
+		    - Windows:      64 reports (via HidD_SetNumInputBuffers)
+		    - Linux hidraw: kernel-managed, no userspace queue
+		    - NetBSD:       kernel-managed, no userspace queue
+
+		    Call after hid_open() and before the first hid_read()
+		    to avoid losing reports buffered at open time.
+
+		    @ingroup API
+		    @param dev A device handle returned from hid_open().
+		    @param buffer_size The desired buffer size in reports.
+		        Must be in range [1, HID_API_MAX_INPUT_REPORT_BUFFER_SIZE].
+
+		    @returns
+		        0 on success, -1 on failure (invalid parameters or
+		        backend-specific error). Call hid_error(dev) for
+		        details where supported.
+		*/
+		int HID_API_EXPORT HID_API_CALL hid_set_input_report_buffer_size(hid_device *dev, int buffer_size);
+
 		/** @brief Send a Feature report to the device.
 
 			Feature reports are sent over the Control endpoint as a

libusb/hid.c

@@ -110,6 +110,9 @@ struct hid_device_ {
 	/* Whether blocking reads are used */
 	int blocking; /* boolean */
 
+	/* Maximum number of input reports to queue before dropping oldest. */
+	int input_report_buffer_size;
+
 	/* Read thread objects */
 	hidapi_thread_state thread_state;
 	int shutdown_thread;
@@ -143,6 +146,7 @@ static hid_device *new_hid_device(void)
 		return NULL;
 
 	dev->blocking = 1;
+	dev->input_report_buffer_size = 30;
 
 	hidapi_thread_state_init(&dev->thread_state);
 
@@ -985,7 +989,7 @@ static void LIBUSB_CALL read_callback(struct libusb_transfer *transfer)
 			/* Pop one off if we've reached 30 in the queue. This
 			   way we don't grow forever if the user never reads
 			   anything from the device. */
-			if (num_queued > 30) {
+			if (num_queued > dev->input_report_buffer_size) {
 				return_data(dev, NULL, 0);
 			}
 		}
@@ -1574,6 +1578,21 @@ HID_API_EXPORT const wchar_t * HID_API_CALL hid_read_error(hid_device *dev)
 }
 
 
+
+int HID_API_EXPORT hid_set_input_report_buffer_size(hid_device *dev, int buffer_size)
+{
+	/* Note: libusb backend currently has no error reporting infrastructure
+	   (hid_error returns a fixed string). This function returns -1 on
+	   invalid arguments but cannot provide a descriptive error message
+	   until the backend gains error registration. */
+	if (buffer_size <= 0 || buffer_size > HID_API_MAX_INPUT_REPORT_BUFFER_SIZE)
+		return -1;
+	hidapi_thread_mutex_lock(&dev->thread_state);
+	dev->input_report_buffer_size = buffer_size;
+	hidapi_thread_mutex_unlock(&dev->thread_state);
+	return 0;
+}
+
 int HID_API_EXPORT hid_set_nonblocking(hid_device *dev, int nonblock)
 {
 	dev->blocking = !nonblock;

linux/hid.c

@@ -1199,6 +1199,21 @@ HID_API_EXPORT const wchar_t * HID_API_CALL  hid_read_error(hid_device *dev)
 	return dev->last_read_error_str;
 }
 
+
+int HID_API_EXPORT hid_set_input_report_buffer_size(hid_device *dev, int buffer_size)
+{
+	if (buffer_size <= 0 || buffer_size > HID_API_MAX_INPUT_REPORT_BUFFER_SIZE) {
+		register_error_str(&dev->last_error_str, "buffer_size out of range");
+		return -1;
+	}
+	/* No-op on Linux hidraw and BSD backends: the kernel manages input
+	   report buffering and there is no userspace queue to resize. The
+	   call is accepted (returns 0) to preserve a consistent cross-platform
+	   API so callers do not need per-backend conditional code. */
+	(void)buffer_size;
+	return 0;
+}
+
 int HID_API_EXPORT hid_set_nonblocking(hid_device *dev, int nonblock)
 {
 	/* Do all non-blocking in userspace using poll(), since it looks

mac/hid.c

@@ -127,6 +127,7 @@ struct hid_device_ {
 	IOOptionBits open_options;
 	int blocking;
 	int disconnected;
+	int input_report_buffer_size;
 	CFStringRef run_loop_mode;
 	CFRunLoopRef run_loop;
 	CFRunLoopSourceRef source;
@@ -156,6 +157,7 @@ static hid_device *new_hid_device(void)
 	dev->open_options = device_open_options;
 	dev->blocking = 1;
 	dev->disconnected = 0;
+	dev->input_report_buffer_size = 30;
 	dev->run_loop_mode = NULL;
 	dev->run_loop = NULL;
 	dev->source = NULL;
@@ -908,7 +910,7 @@ static void hid_report_callback(void *context, IOReturn result, void *sender,
 		/* Pop one off if we've reached 30 in the queue. This
 		   way we don't grow forever if the user never reads
 		   anything from the device. */
-		if (num_queued > 30) {
+		if (num_queued > dev->input_report_buffer_size) {
 			return_data(dev, NULL, 0);
 		}
 	}
@@ -1347,6 +1349,19 @@ HID_API_EXPORT const wchar_t * HID_API_CALL hid_read_error(hid_device *dev)
 	return dev->last_read_error_str;
 }
 
+
+int HID_API_EXPORT hid_set_input_report_buffer_size(hid_device *dev, int buffer_size)
+{
+	if (buffer_size <= 0 || buffer_size > HID_API_MAX_INPUT_REPORT_BUFFER_SIZE) {
+		register_error_str(&dev->last_error_str, "buffer_size out of range");
+		return -1;
+	}
+	pthread_mutex_lock(&dev->mutex);
+	dev->input_report_buffer_size = buffer_size;
+	pthread_mutex_unlock(&dev->mutex);
+	return 0;
+}
+
 int HID_API_EXPORT hid_set_nonblocking(hid_device *dev, int nonblock)
 {
 	/* All Nonblocking operation is handled by the library. */

netbsd/hid.c

@@ -955,6 +955,21 @@ HID_API_EXPORT const wchar_t* HID_API_CALL hid_read_error(hid_device *dev)
 	return dev->last_read_error_str;
 }
 
+
+int HID_API_EXPORT HID_API_CALL hid_set_input_report_buffer_size(hid_device *dev, int buffer_size)
+{
+	if (buffer_size <= 0 || buffer_size > HID_API_MAX_INPUT_REPORT_BUFFER_SIZE) {
+		register_error_str(&dev->last_error_str, "buffer_size out of range");
+		return -1;
+	}
+	/* No-op on Linux hidraw and BSD backends: the kernel manages input
+	   report buffering and there is no userspace queue to resize. The
+	   call is accepted (returns 0) to preserve a consistent cross-platform
+	   API so callers do not need per-backend conditional code. */
+	(void)buffer_size;
+	return 0;
+}
+
 int HID_API_EXPORT HID_API_CALL hid_set_nonblocking(hid_device *dev, int nonblock)
 {
 	dev->blocking = !nonblock;

windows/hid.c

@@ -1257,6 +1257,20 @@ HID_API_EXPORT const wchar_t * HID_API_CALL hid_read_error(hid_device *dev)
 	return dev->last_read_error_str;
 }
 
+
+int HID_API_EXPORT HID_API_CALL hid_set_input_report_buffer_size(hid_device *dev, int buffer_size)
+{
+	if (buffer_size <= 0 || buffer_size > HID_API_MAX_INPUT_REPORT_BUFFER_SIZE) {
+		register_string_error(dev, L"buffer_size out of range");
+		return -1;
+	}
+	if (!HidD_SetNumInputBuffers(dev->device_handle, (ULONG)buffer_size)) {
+		register_winapi_error(dev, L"HidD_SetNumInputBuffers");
+		return -1;
+	}
+	return 0;
+}
+
 int HID_API_EXPORT HID_API_CALL hid_set_nonblocking(hid_device *dev, int nonblock)
 {
 	dev->blocking = !nonblock;