Windows: ensure buffer passed to HidD_SetFeature is large enough (#224)

windows/hid.c

@@ -145,6 +145,8 @@ struct hid_device_ {
 		BOOL blocking;
 		USHORT output_report_length;
 		size_t input_report_length;
+		USHORT feature_report_length;
+		unsigned char *feature_buf;
 		void *last_error_str;
 		DWORD last_error_num;
 		BOOL read_pending;
@@ -160,6 +162,8 @@ static hid_device *new_hid_device()
 	dev->blocking = TRUE;
 	dev->output_report_length = 0;
 	dev->input_report_length = 0;
+	dev->feature_report_length = 0;
+	dev->feature_buf = NULL;
 	dev->last_error_str = NULL;
 	dev->last_error_num = 0;
 	dev->read_pending = FALSE;
@@ -178,6 +182,7 @@ static void free_hid_device(hid_device *dev)
 	CloseHandle(dev->write_ol.hEvent);							   
 	CloseHandle(dev->device_handle);
 	LocalFree(dev->last_error_str);
+	free(dev->feature_buf);
 	free(dev->read_buf);
 	free(dev);
 }
@@ -640,6 +645,7 @@ HID_API_EXPORT hid_device * HID_API_CALL hid_open_path(const char *path)
 	}
 	dev->output_report_length = caps.OutputReportByteLength;
 	dev->input_report_length = caps.InputReportByteLength;
+	dev->feature_report_length = caps.FeatureReportByteLength;
 	HidD_FreePreparsedData(pp_data);
 
 	dev->read_buf = (char*) malloc(dev->input_report_length);
@@ -811,7 +817,29 @@ int HID_API_EXPORT HID_API_CALL hid_set_nonblocking(hid_device *dev, int nonbloc
 
 int HID_API_EXPORT HID_API_CALL hid_send_feature_report(hid_device *dev, const unsigned char *data, size_t length)
 {
-	BOOL res = HidD_SetFeature(dev->device_handle, (PVOID)data, (DWORD) length);
+	BOOL res = FALSE;
+	unsigned char *buf;
+	size_t length_to_send;
+
+	/* Windows expects at least caps.FeatureReportByteLength bytes passed
+	   to HidD_SetFeature(), even if the report is shorter. Any less sent and
+	   the function fails with error ERROR_INVALID_PARAMETER set. Any more
+	   and HidD_SetFeature() silently truncates the data sent in the report
+	   to caps.FeatureReportByteLength. */
+	if (length >= dev->feature_report_length) {
+		buf = (unsigned char *) data;
+		length_to_send = length;
+	} else {
+		if (dev->feature_buf == NULL)
+			dev->feature_buf = (unsigned char *) malloc(dev->feature_report_length);
+		buf = dev->feature_buf;
+		memcpy(buf, data, length);
+		memset(buf + length, 0, dev->feature_report_length - length);
+		length_to_send = dev->feature_report_length;
+	}
+
+	res = HidD_SetFeature(dev->device_handle, (PVOID)buf, (DWORD) length_to_send);
+
 	if (!res) {
 		register_error(dev, "HidD_SetFeature");
 		return -1;