[openssl-users] how to implement functions for STACK OF custom type?

[Dr. Stephen Henson]

On Tue, Mar 21, 2017, lists wrote:

> Sorry, I first posted this on the -dev list, likely inappropriate... now with an update:
> 
> I am exploring my options with OpenSSL and specifically I am trying to manage the stacks for some custom objects.
> Currently, I have this code (sort of) in the headers:
> 
> typedef struct myThingA_st
> {
>      ASN1_OBJECT aID;
>      ASN1_OCTET_STRING aOCST;
> }
>      myThingA;
> 
> DECLARE_ASN1_ITEM(myThingA)
> DECLARE_ASN1_FUNCTIONS(myThingA)
> DECLARE_STACK_OF(myThingA)
> // the next one seems to be ininfluent for my purpose, is it?
> DECLARE_ASN1_SET_OF(myThingA)
> 
> typedef struct myThingB_st
> {
>      // SEQUENCE OF { ... }
>      STACK_OF(myThingA) myThingA_sk;
> }
>      myThingB;
> 
> // DECLARE_ASN1_ITEM(myThingB)
> DECLARE_STACK_OF(myThingB)
> // DECLARE_ASN1_FUNCTIONS(myThingB)
> // the next one seems to be ininfluent for my purpose, is it?
> DECLARE_ASN1_SET_OF(myThingB)
> 
> Then, in the .c file...
> 
> IMPLEMENT_STACK_OF(myThingA)
> IMPLEMENT_STACK_OF(myThingB)
> 
> I thought that the basic functions for the stacks to be available (such as sk_myThingA_new, sk_myThingA_push...), yet by compiling a main, for 
> the first one that I try to use I get:
> 
>        undefined reference to `sk_myThingA_value'
> 
> What am I doing wrong here?

If you're using OpenSSL 1.1.0 you need to include:

DEFINE_STACK_OF(FOO)

in a header file and that should be it. That implements a set of inline
functions that do the right thing.

For OpenSSL versions before 1.1.0 it's a bit messier. The type specific
STACK_OF functions are actually macros which are generated by the mkstack.pl
script and appear in the safestack.h header file. If you want to create your
own one way is to extract a type specific section from safestack.h, copy it
to your own header file and do a search/replace for the new type.

So for example extract the sk_OPENSSL_BLOCK macros and replace OPENSSL_BLOCK
with FOO.

Steve.
--
Dr Stephen N. Henson. OpenSSL project core developer.
Commercial tech support now available see: http://www.openssl.org