Microshine Microshine - 2 months ago 25
Javascript Question

NodeJS: node-ffi, ref-struct, ref-array

I'm writing PKCS11 cryptoki wrapper using nodejs plugins

ffi
,
ref
,
ref-struct
and
ref-array
. I have this code.

var hSession = this.session.handle;
var hObject = this.handle;
var $label = new (arrayType(cki.CK_UTF8CHAR))(80);

var template = new (arrayType(cki.CK_ATTRIBUTE))(1);
template[0] = new cki.CK_ATTRIBUTE({
type:cki.CKA_LABEL,
pValue: $label.ref(),
ulValueLen: 80})
var res = this.cki.C_GetAttributeValue(hSession, hObject, template.ref(), 1);
if (res == cki.CKR_OK) {
console.log("Ok");
}
else{
console.log("Wrong "+res);
}


When I call this function I have wrong results (CKR_ARGUMENTS_BAD, CKR_ATTRIBUTE_TYPE_INVALID).
Please, help me to find error.

FFI function

"C_GetAttributeValue":[t.CK_RV, [t.CK_SESSION_HANDLE, t.CK_OBJECT_HANDLE, t.CK_ATTRIBUTE_PTR, t.CK_ULONG]],


Types



/* CK_ATTRIBUTE is a structure that includes the type, length
* and value of an attribute */
t.CK_ATTRIBUTE = struct({
type: t.CK_ATTRIBUTE_TYPE,
pValue: t.CK_VOID_PTR,

/* ulValueLen went from CK_USHORT to CK_ULONG for v2.0 */
ulValueLen: t.CK_ULONG /* in bytes */
});




vlp vlp
Answer

(Transcript of discussion in comments)

Use pure Buffer to provide the buffer to store the attribute value:

var $label = new Buffer(80);

Pass it in the structure as follows:

template[0] = new cki.CK_ATTRIBUTE({
    type:cki.CKA_LABEL, 
    pValue: $label, 
    ulValueLen: $label.length}) 

Then use $label.toString('utf8',0,<ulValueLen>) to get the actual string.

Note: I am not proficient with Node FFI, but this approach just seem to work.