IWMDMStorage::SendOpaqueCommand
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The SendOpaqueCommand method sends a command to the storage through Windows Media Device Manager, without processing it.
Syntax
HRESULT SendOpaqueCommand(OPAQUECOMMAND*pCommand);
Parameters
pCommand
[in, out] Pointer to an OPAQUECOMMAND structure containing the command to execute. Data can be passed two ways—from the application to the device, and from the device back to the application when the call finishes.
Return Values
The method returns an HRESULT. All the interface methods in Windows Media Device Manager can return any of the following classes of error codes:
- Standard COM error codes
- Windows error codes converted to HRESULT values
- Windows Media Device Manager error codes
For an extenstive list of possible error codes, see Error Codes.
Possible values include, but are not limited to, those in the following table.
| Return code | Description |
| S_OK | The method succeeded. |
| E_INVALIDARG | A parameter is invalid or a NULL pointer. |
| E_FAIL | An unspecified error occurred. |
| WMDM_E_NOTCERTIFIED | The caller is not certified. |
| WMDM_E_MAC_CHECK_FAILED | The message authentication check failed. |
Remarks
This method is intended for storage media commands that do not affect the operation of Windows Media Device Manager and should be passed through unchanged.
Example Code
The following C++ code calls SendOpaqueCommand to perform a simple custom authentication step with a device. The caller sends its certificate and MAC to the device, which sends back its own certificate and MAC. The application compares the retrieved certificate with the one it has stored, and if they match (and the MAC is correct), it sets bExtraCertified to TRUE.
// Call SendOpaqueCommand to exchange extended authentication information.
{
HMAC hMAC;
OPAQUECOMMAND Command;
CERTINFOEX *pCertInfoEx;
DWORD cbData_App = sizeof(bCertInfoEx_App)/sizeof(bCertInfoEx_App[0]);
DWORD cbData_SP = sizeof(bCertInfoEx_SP)/sizeof(bCertInfoEx_SP[0]);
DWORD cbData_Send = sizeof(CERTINFOEX) + cbData_App;
// Fill opaque command structure with the application's certificate.
memcpy(&(Command.guidCommand), &guidCertInfoEx, sizeof(GUID));
Command.pData = (BYTE *)CoTaskMemAlloc(cbData_Send);
if (!Command.pData)
{
ExitOnFail(hr = E_OUTOFMEMORY);
}
Command.dwDataLen = cbData_Send;
// Map the data in the opaque command to a CERTINFOEX structure, and
// fill in the cert info to send.
pCertInfoEx = (CERTINFOEX *)Command.pData;
pCertInfoEx->hr = S_OK;
pCertInfoEx->cbCert = cbData_App;
memcpy(pCertInfoEx->pbCert, bCertInfoEx_App, cbData_App);
// Compute MAC on the data, and add to the OPAQUECOMMAND struct.
g_cWmdm.m_pSAC->MACInit(&hMAC);
g_cWmdm.m_pSAC->MACUpdate(hMAC, (BYTE*)(&(Command.guidCommand)), sizeof(GUID));
g_cWmdm.m_pSAC->MACUpdate(hMAC, (BYTE*)(&(Command.dwDataLen)), sizeof(Command.dwDataLen));
if (Command.pData)
{
g_cWmdm.m_pSAC->MACUpdate(hMAC, Command.pData, Command.dwDataLen);
}
g_cWmdm.m_pSAC->MACFinal(hMAC, Command.abMAC);
// Send the opaque command.
hr = pDevice->SendOpaqueCommand(&Command);
if (SUCCEEDED(hr))
{
// Now verify the retrieved MAC.
BYTE abMACVerify2[ WMDM_MAC_LENGTH ];
g_cWmdm.m_pSAC->MACInit(&hMAC);
g_cWmdm.m_pSAC->MACUpdate(hMAC, (BYTE*)(&(Command.guidCommand)), sizeof(GUID));
g_cWmdm.m_pSAC->MACUpdate(hMAC, (BYTE*)(&(Command.dwDataLen)), sizeof(Command.dwDataLen));
if (Command.pData)
{
g_cWmdm.m_pSAC->MACUpdate(hMAC, Command.pData, Command.dwDataLen);
}
g_cWmdm.m_pSAC->MACFinal(hMAC, abMACVerify2);
// Verify MAC matches.
if (memcmp(abMACVerify2, Command.abMAC, WMDM_MAC_LENGTH) == 0)
{
// They match; verify the retrieved certificate.
// Map the data in the opaque command to a CERTINFOEX structure
//
pCertInfoEx = (CERTINFOEX *)Command.pData;
// In this simple extended authentication scheme, the callee must
// provide the exact certificate information.
//
if ((pCertInfoEx->cbCert != cbData_SP) &&
(memcmp(pCertInfoEx->pbCert, bCertInfoEx_SP, cbData_SP) == 0))
{
bExtraCertified = TRUE;
}
}
}
if (Command.pData)
{
CoTaskMemFree(Command.pData);
}
}
Requirements
Header: Defined in mswmdm.h.
Library: mssachlp.lib
See Also