Determine CMS/PKCS7 type

[Phillip Hellewell]

I'm in the process of refactoring my code to use the new CMS API instead of
PKCS7.

In my code before I was able to determine the type of pkcs7, and even
distinguish between a signed data (.p7m), signature (.p7s) and cert chain
(.p7b), using this function:

    PKCS7Type determine_pkcs7_type(PKCS7* p7)
    {
        int nid = OBJ_obj2nid(p7->type);
        switch( nid ) {
            case NID_pkcs7_data:
                return PKCS7Type_Data;
            case NID_pkcs7_enveloped:
            case NID_pkcs7_encrypted:
                return PKCS7Type_EncData;
            case NID_pkcs7_digest:
                return PKCS7Type_Digest;
            case NID_pkcs7_signed:
                if( p7->d.sign->contents &&
OBJ_obj2nid(p7->d.sign->contents->type) == NID_pkcs7_data &&
p7->d.sign->contents->d.data != NULL )
                    return PKCS7Type_SignedData;
                if( sk_PKCS7_SIGNER_INFO_num(p7->d.sign->signer_info) > 0 )
                    return PKCS7Type_Signature;
                if( sk_X509_num(p7->d.sign->cert) > 0 ||
sk_X509_CRL_num(p7->d.sign->crl) > 0 )
                    return PKCS7Type_Certs;
                return PKCS7Type_UNKNOWN;
        }
        return PKCS7Type_UNKNOWN;
    }

Now I am trying to do the same thing with CMS, but the struct contents are
encapsulated from me (yes yes, that is good I know), so I'm currently at a
loss as to how to differentiate the types, see below:

    PKCS7Type determine_pkcs7_type(CMS_ContentInfo* cms)
    {
        int nid = OBJ_obj2nid(CMS_get0_type(cms));
        switch( nid ) {
            case NID_pkcs7_data:
                return PKCS7Type_Data;
            case NID_id_smime_ct_compressedData:
                return PKCS7Type_CompData;
            case NID_pkcs7_enveloped:
            case NID_pkcs7_encrypted:
                return PKCS7Type_EncData;
            case NID_pkcs7_digest:
                return PKCS7Type_Digest;
            case NID_pkcs7_signed:
            {
                // HELP!!  How can I tell if this is a signed data, or just
a signature (i.e., a .p7s with no data), or it is a cert chain (i.e., a
.p7b with just certs)
            }
        }
        return PKCS7Type_UNKNOWN;
    }

Thanks,
Phillip