From ee4ecc02ae2573ab644c61683f96a27949a52194 Mon Sep 17 00:00:00 2001
From: Vitali Lovich <vlovich@gmail.com>
Date: Sat, 31 Dec 2011 02:47:35 +0800
Subject: [PATCH] Fix output report length bug

On Windows, data shorter than the output report length must be padded.
This is because in the case of multiple reports, Windows expects the number
of bytes which are in the _longest_ report to be given to WriteFile() even
if the user is sending a report which has fewer bytes.

This allocates a temporary buffer in the case that the user passes in too
few bytes.

From: Vitali Lovich <vlovich@gmail.com>
Modified-by: Alan Ott <alan@signal11.us>
---
 windows/hid.c | 34 +++++++++++++++++++++++++++++++---
 1 file changed, 31 insertions(+), 3 deletions(-)

diff --git a/windows/hid.c b/windows/hid.c
index 26d870f..7fbeaee 100644
--- a/windows/hid.c
+++ b/windows/hid.c
@@ -125,6 +125,7 @@ extern "C" {
 struct hid_device_ {
 		HANDLE device_handle;
 		BOOL blocking;
+		USHORT output_report_length;
 		size_t input_report_length;
 		void *last_error_str;
 		DWORD last_error_num;
@@ -138,6 +139,7 @@ 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->output_report_length = 0;
 	dev->input_report_length = 0;
 	dev->last_error_str = NULL;
 	dev->last_error_num = 0;
@@ -553,6 +555,7 @@ HID_API_EXPORT hid_device * HID_API_CALL hid_open_path(const char *path)
 		register_error(dev, "HidP_GetCaps");	
 		goto err_pp_data;
 	}
+	dev->output_report_length = caps.OutputReportByteLength;
 	dev->input_report_length = caps.InputReportByteLength;
 	HidD_FreePreparsedData(pp_data);
 
@@ -574,15 +577,35 @@ int HID_API_EXPORT HID_API_CALL hid_write(hid_device *dev, const unsigned char *
 	BOOL res;
 
 	OVERLAPPED ol;
+	unsigned char *buf;
 	memset(&ol, 0, sizeof(ol));
 
-	res = WriteFile(dev->device_handle, data, length, NULL, &ol);
+	/* Make sure the right number of bytes are passed to WriteFile. Windows
+	   expects the number of bytes which are in the _longest_ report (plus
+	   one for the report number) bytes even if the data is a report
+	   which is shorter than that. Windows gives us this value in
+	   caps.OutputReportByteLength. If a user passes in fewer bytes than this,
+	   create a temporary buffer which is the proper size. */
+	if (length >= dev->output_report_length) {
+		/* The user passed the right number of bytes. Use the buffer as-is. */
+		buf = (unsigned char *) data;
+	} else {
+		/* Create a temporary buffer and copy the user's data
+		   into it, padding the rest with zeros. */
+		buf = (unsigned char *) malloc(dev->output_report_length);
+		memcpy(buf, data, length);
+		memset(buf + length, 0, dev->output_report_length - length);
+		length = dev->output_report_length;
+	}
+
+	res = WriteFile(dev->device_handle, buf, length, NULL, &ol);
 	
 	if (!res) {
 		if (GetLastError() != ERROR_IO_PENDING) {
 			// WriteFile() failed. Return error.
 			register_error(dev, "WriteFile");
-			return -1;
+			bytes_written = -1;
+			goto end_of_function;
 		}
 	}
 
@@ -592,9 +615,14 @@ int HID_API_EXPORT HID_API_CALL hid_write(hid_device *dev, const unsigned char *
 	if (!res) {
 		// The Write operation failed.
 		register_error(dev, "WriteFile");
-		return -1;
+		bytes_written = -1;
+		goto end_of_function;
 	}
 
+end_of_function:
+	if (buf != data)
+		free(buf);
+
 	return bytes_written;
 }