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IWMDMStorage::GetRights

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The GetRights method retrieves rights information for a licensed storage.

Syntax

HRESULT GetRights(PWMDMRIGHTS*ppRights,UINT*pnRightsCount,BYTE[WMDM_MAC_LENGTH]abMac);

Parameters

ppRights

[out]  Pointer to an array of WMDMRIGHTS structures that contain the storage rights. This parameter is included in the message authentication code. Windows Media Device Manager allocates this memory, and the application must release it with CoTaskMemFree.

pnRightsCount

[out]  Pointer to the number of WMDMRIGHTS structures in the ppRights array. This parameter is included in the message authentication code.

abMac

[in, out]  Array of bytes containing the message authentication code (MAC) for the parameter data of this method.

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.
S_FALSE The file has no associated rights, or is not licensed.
E_INVALIDARG The ppRights or pnRightsCount parameter is an invalid or NULL pointer.
WMDM_E_NOTSUPPORTED Rights are not supported for this object.
E_FAIL An unspecified error occurred.
WMDM_E_NOTCERTIFIED The caller has not been certified using the secure authenticated channel client class, or object is not licensed.
WMDM_E_MAC_CHECK_FAILED The message authentication check failed.

Remarks

Object rights describe the usage permissions for digital media content. For example, the WMDMRIGHTS structure can contain information concerning how many times a file can be played and who can play it. This method will fail if this is not a licensed file.

The ppRights array is allocated by this method, and must be freed by the application using CoTaskMemFree, a standard Win32 function.

To receive progress events for this call, use IWMDMStorage4::GetRightsWithProgress.

After calling this method, an application can calculate the message authentication code (MAC) values of parameters and compare them with output MAC values to ensure that the parameters have not been tampered with. The following example code shows one way to do this.

Example Code

CSecureChannelClient  *pSCClient;
IWMDMStorage  *pStorgae;

HMAC  hMAC;
BYTE  abMAC[WMDM_MAC_LENGTH];
BYTE  abMACVerify[WMDM_MAC_LENGTH];

hr = pStorage->GetRights(&pRights, &nRightsCount, abMAC);
if (SUCCEEDED(hr))
{
    //
    // First verify the integrity of the retrieved rights.
    //
    pSCClient->MACInit(&hMAC);
    pSCClient->MACUpdate(hMAC, (BYTE*)(pRights), 
                    sizeof(WMDMRIGHTS) * nRightsCount);
    pSCClient->MACUpdate(hMAC, (BYTE*)(&nRightsCount), 
                                 sizeof(nRightsCount));
    pSCClient->MACFinal(hMAC, (BYTE*)abMACVerify);
    if (memcmp(abMACVerify, abMAC, sizeof(abMAC)) != 0)
    {
        hr = WMDM_E_MAC_CHECK_FAILED;
    }
}

Requirements

Header: Defined in mswmdm.h.

Library: mssachlp.lib

See Also