`The resurgence of CERT_FindUserCertByUsage function in JavaScript`

Question

`The resurgence of CERT_FindUserCertByUsage function in JavaScript`

I am currently grappling with unraveling the connection between C++ dlls and JavaScript. There is a snippet of js code that reads:

cert = CERT_FindUserCertByUsage(certDB, certName.nickname,certUsageEmailSigner, true, null);

where the variable cert is initialized as

let cert = null;

However, in the realm of C++, cert represents a structured data type known as CERTCertificateStr:

CERTCertificateStr {
    char *subjectName;
    char *issuerName;
    SECItem derCert;            /* original DER for the cert */
    .... }

My quest now is to access the subject name in Javascript, so I proceeded with the line:

let a = cert.contents.subjectName;

Unfortunately, this results in an error stating "cannot get content of undefined size."

Is there anything crucial that I might be overlooking in translating from C++ to Javascript? And how can I successfully retrieve and display the subjectName in my Javascript code?

javascript c++firefox-addon jsctypes nss

Answer 1

Answer №1

It seems like you are diving into jsctypes and making good progress. In order to extract a JavaScript string, you need to cast it to an array of a specific length and then use the readString() method. Don't worry about exceeding the actual length because readString() will only read up to the first null character (\x00). However, if you know the exact length beforehand, that's preferable as it saves memory by avoiding unnecessary buffer allocation.

Here's a suggested approach:

let a = ctypes.cast(cert.contents.subjectName, ctypes.char.array(100).ptr).contents.readString();
console.log('a:', a);

The error message "

cannot get contents of undefined size

" typically occurs in scenarios like this:

var a = ctypes.voidptr_t(ctypes.char.array()('rawr'))
console.log('a:', a.contents);

To resolve this issue, you can do the following:

var b = ctypes.cast(a, ctypes.char.array(5).ptr)
console.log('b:', b.contents);

This will successfully access the contents. You can also omit specifying the length for efficiency purposes as shown with the example using 'rawr'.

Once you have accessed the contents, you can convert them to a JavaScript string like so:

console.log('b:', b.contents.readString());

Moreover, considering the function returns a struct, ensure whether it returns a pointer or the actual struct itself. If it returns a pointer, you can handle it like this:

let certPtr = CERT_FindUserCertByUsage(certDB, certName.nickname,certUsageEmailSigner, true, null);

let certStruct = ctypes.StructType('CERTCertificateStr', [
   {'subjectName': ctypes.char.ptr},
   {issuerName: ctypes.char.ptr},
   {derCert: ctypes.voidptr_t}
]);

let cert = ctypes.cast(certPtr, certStruct.ptr).contents;
let a = cert.contents.subjectName.readString();

Answer 2

It seems like you are diving into jsctypes and making good progress. In order to extract a JavaScript string, you need to cast it to an array of a specific length and then use the readString() method. Don't worry about exceeding the actual length because readString() will only read up to the first null character (\x00). However, if you know the exact length beforehand, that's preferable as it saves memory by avoiding unnecessary buffer allocation.

Here's a suggested approach:

let a = ctypes.cast(cert.contents.subjectName, ctypes.char.array(100).ptr).contents.readString();
console.log('a:', a);

The error message "

cannot get contents of undefined size

" typically occurs in scenarios like this:

var a = ctypes.voidptr_t(ctypes.char.array()('rawr'))
console.log('a:', a.contents);

To resolve this issue, you can do the following:

var b = ctypes.cast(a, ctypes.char.array(5).ptr)
console.log('b:', b.contents);

This will successfully access the contents. You can also omit specifying the length for efficiency purposes as shown with the example using 'rawr'.

Once you have accessed the contents, you can convert them to a JavaScript string like so:

console.log('b:', b.contents.readString());

Moreover, considering the function returns a struct, ensure whether it returns a pointer or the actual struct itself. If it returns a pointer, you can handle it like this:

let certPtr = CERT_FindUserCertByUsage(certDB, certName.nickname,certUsageEmailSigner, true, null);

let certStruct = ctypes.StructType('CERTCertificateStr', [
   {'subjectName': ctypes.char.ptr},
   {issuerName: ctypes.char.ptr},
   {derCert: ctypes.voidptr_t}
]);

let cert = ctypes.cast(certPtr, certStruct.ptr).contents;
let a = cert.contents.subjectName.readString();

`The resurgence of CERT_FindUserCertByUsage function in JavaScript`

Answer №1

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