Improve const correctness for P11KitUri

[npmccallum]

This does not improve const for the getters. The reason for this is that
they are usually passed into the PKCS#11 APIs directly and these APIs
are not const correct. Trying to force const correctnesss here would
result in pain for library consumers.

This is an API and ABI compatible change.

[ueno]

Thank you. But actually, adding const to the public interface seems to affect the ABI:

$ abidiff /usr/lib64/libp11-kit.so .libs/libp11-kit.so
Functions changes summary: 0 Removed, 5 Changed (1 filtered out), 0 Added functions
Variables changes summary: 0 Removed, 0 Changed, 0 Added variable

5 functions with some indirect sub-type change:

  [C]'function const char* p11_kit_uri_get_pin_source(P11KitUri*)' at uri.c:690:1 has some indirect sub-type changes:
    parameter 1 of type 'P11KitUri*' changed:
      in pointed to type 'typedef P11KitUri':
        entity changed from 'typedef P11KitUri' to 'const P11KitUri'
        type size hasn't changed
...

I suppose these are harmless, but I am not completely sure. @nmav do you happen to have an experience of applying such changes?

[npmccallum]

I believe this is a false positive. See here: https://stackoverflow.com/questions/5083765/does-changing-fmystruct-a-to-fconst-mystruct-a-breaks-api-abi-in-c

[nmav]

I also think that const-addition changes don't affect ABI. abi-compliance-checker may be more explicit about it.

[ueno]

Should we add const to other const char * getters, such as p11_kit_uri_get_module_name() and p11_kit_uri_get_module_path()?

[npmccallum]

@ueno I have added const to the following functions:

• p11_kit_uri_get_pinfile()
• p11_kit_uri_get_module_name()
• p11_kit_uri_get_module_path()
• p11_kit_uri_get_vendor_query()

I believe this now covers all of the low hanging fruit.

[ueno]

Thank you!

[asavah]

This breaks building gnutls 3.6.2 with p11-kit

In file included from ./../pkcs11_int.h:34:0,
                 from x509.c:37:
/home/asavah/kross/build/rpi3/rootfs/usr/include/p11-kit-1/p11-kit/uri.h:99:68: error: unknown type name 'CK_INFO'
                                                              const CK_INFO *info);
                                                                    ^~~~~~~
/home/asavah/kross/build/rpi3/rootfs/usr/include/p11-kit-1/p11-kit/uri.h:104:68: error: unknown type name 'CK_SLOT_INFO'
                                                              const CK_SLOT_INFO *slot_info);
                                                                    ^~~~~~~~~~~~
/home/asavah/kross/build/rpi3/rootfs/usr/include/p11-kit-1/p11-kit/uri.h:113:68: error: unknown type name 'CK_TOKEN_INFO'
                                                              const CK_TOKEN_INFO *token_info);
                                                                    ^~~~~~~~~~~~~
/home/asavah/kross/build/rpi3/rootfs/usr/include/p11-kit-1/p11-kit/uri.h:134:68: error: unknown type name 'CK_ATTRIBUTE'
                                                              const CK_ATTRIBUTE *attrs,
                                                                    ^~~~~~~~~~~~
Makefile:1512: recipe for target 'x509.lo' failed

[nmav]

Ouch, indeed this patch also changes the types while adding the const. It seems that the block inside #ifdef CRYPTOKI_GNU has to be updated as well for the new types used. It seems that the testsuite doesn't compile any program with this definition on. Changing test-uri.c to define that, catches the issue.