Make sure only one report is returned per call to hid_read().

windows/hid.cpp

@@ -52,28 +52,49 @@ extern "C" {
 		USHORT ProductID;
 		USHORT VersionNumber;
 	} HIDD_ATTRIBUTES, *PHIDD_ATTRIBUTES;
+
+	typedef USHORT USAGE;
+	typedef struct _HIDP_CAPS {
+		USAGE Usage;
+		USAGE UsagePage;
+		USHORT InputReportByteLength;
+		USHORT OutputReportByteLength;
+		USHORT FeatureReportByteLength;
+		USHORT Reserved[17];
+		USHORT fields_not_used_by_hidapi[10];
+	} HIDP_CAPS, *PHIDP_CAPS;
+	typedef char* HIDP_PREPARSED_DATA;
+	#define HIDP_STATUS_SUCCESS 0x0
+
 	typedef BOOLEAN (__stdcall *HidD_GetAttributes_)(HANDLE device, PHIDD_ATTRIBUTES attrib);
 	typedef BOOLEAN (__stdcall *HidD_GetSerialNumberString_)(HANDLE device, PVOID buffer, ULONG buffer_len);
 	typedef BOOLEAN (__stdcall *HidD_GetManufacturerString_)(HANDLE handle, PVOID buffer, ULONG buffer_len);
 	typedef BOOLEAN (__stdcall *HidD_GetProductString_)(HANDLE handle, PVOID buffer, ULONG buffer_len);
 	typedef BOOLEAN (__stdcall *HidD_SetFeature_)(HANDLE handle, PVOID data, ULONG length);
 	typedef BOOLEAN (__stdcall *HidD_GetFeature_)(HANDLE handle, PVOID data, ULONG length);
 	typedef BOOLEAN (__stdcall *HidD_GetIndexedString_)(HANDLE handle, ULONG string_index, PVOID buffer, ULONG buffer_len);
-
+	typedef BOOLEAN (__stdcall *HidD_GetPreparsedData_)(HANDLE handle, HIDP_PREPARSED_DATA **preparsed_data);
+	typedef BOOLEAN (__stdcall *HidD_FreePreparsedData_)(HIDP_PREPARSED_DATA *preparsed_data);
+	typedef BOOLEAN (__stdcall *HidP_GetCaps_)(HIDP_PREPARSED_DATA *preparsed_data, HIDP_CAPS *caps);
+
 	static HidD_GetAttributes_ HidD_GetAttributes;
 	static HidD_GetSerialNumberString_ HidD_GetSerialNumberString;
 	static HidD_GetManufacturerString_ HidD_GetManufacturerString;
 	static HidD_GetProductString_ HidD_GetProductString;
 	static HidD_SetFeature_ HidD_SetFeature;
 	static HidD_GetFeature_ HidD_GetFeature;
 	static HidD_GetIndexedString_ HidD_GetIndexedString;
+	static HidD_GetPreparsedData_ HidD_GetPreparsedData;
+	static HidD_FreePreparsedData_ HidD_FreePreparsedData;
+	static HidP_GetCaps_ HidP_GetCaps;
 
 	static BOOLEAN initialized = FALSE;
 #endif // HIDAPI_USE_DDK
 
 struct hid_device_ {
 		HANDLE device_handle;
 		BOOL blocking;
+		int input_report_length;
 		void *last_error_str;
 		DWORD last_error_num;
 };
@@ -83,6 +104,7 @@ static hid_device *new_hid_device()
 	hid_device *dev = (hid_device*) calloc(1, sizeof(hid_device));
 	dev->device_handle = INVALID_HANDLE_VALUE;
 	dev->blocking = true;
+	dev->input_report_length = -1;
 	dev->last_error_str = NULL;
 	dev->last_error_num = 0;
 
@@ -133,6 +155,9 @@ static void lookup_functions()
 		RESOLVE(HidD_SetFeature);
 		RESOLVE(HidD_GetFeature);
 		RESOLVE(HidD_GetIndexedString);
+		RESOLVE(HidD_GetPreparsedData);
+		RESOLVE(HidD_FreePreparsedData);
+		RESOLVE(HidP_GetCaps);
 		//FreeLibrary(lib);
 #undef RESOLVE
 	}
@@ -368,6 +393,10 @@ HID_API_EXPORT hid_device * HID_API_CALL hid_open(unsigned short vendor_id, unsi
 HID_API_EXPORT hid_device * HID_API_CALL hid_open_path(const char *path)
 {
 	hid_device *dev;
+	HIDP_CAPS caps;
+	HIDP_PREPARSED_DATA *pp_data = NULL;
+	BOOLEAN res;
+	NTSTATUS nt_res;
 
 #ifndef HIDAPI_USE_DDK
 	if (!initialized)
@@ -389,12 +418,31 @@ HID_API_EXPORT hid_device * HID_API_CALL hid_open_path(const char *path)
 	if (dev->device_handle == INVALID_HANDLE_VALUE) {
 		// Unable to open the device.
 		register_error(dev, "CreateFile");
-		CloseHandle(dev->device_handle);
-		free(dev);
-		return NULL;
+		goto err;
+	}
+
+	// Get the Input Report length for the device.
+	res = HidD_GetPreparsedData(dev->device_handle, &pp_data);
+	if (!res) {
+		register_error(dev, "HidD_GetPreparsedData");
+		goto err;
 	}
+	nt_res = HidP_GetCaps(pp_data, &caps);
+	if (nt_res != HIDP_STATUS_SUCCESS) {
+		register_error(dev, "HidP_GetCaps");	
+		goto err_pp_data;
+	}
+	dev->input_report_length = caps.InputReportByteLength;
+	HidD_FreePreparsedData(pp_data);
 
 	return dev;
+
+err_pp_data:
+		HidD_FreePreparsedData(pp_data);
+err:	
+		CloseHandle(dev->device_handle);
+		free(dev);
+		return NULL;
 }
 
 int HID_API_EXPORT HID_API_CALL hid_write(hid_device *dev, const unsigned char *data, size_t length)
@@ -447,6 +495,10 @@ int HID_API_EXPORT HID_API_CALL hid_read(hid_device *dev, unsigned char *data, s
 	ol.Pointer = 0x0;
 	ol.hEvent = ev;
 
+	// Limit the data to be returned. This ensures we get
+	// only one report returned per call to hid_read().
+	length = (length < dev->input_report_length)? length: dev->input_report_length;
+
 	res = ReadFile(dev->device_handle, data, length, &bytes_read, &ol);