Support for flexible array members

[yallop]

A common pattern in C libraries is to make the final member of a struct an array whose length is determined at runtime, like this example from the sanlock library:

struct sanlk_resource {
    char lockspace_name[SANLK_NAME_LEN]; /* terminating \0 not required */
    char name[SANLK_NAME_LEN]; /* terminating \0 not required */

       /* ... */

    uint32_t num_disks;
    /* followed by num_disks sanlk_disk structs */
    struct sanlk_disk disks[0];
};

Ctypes doesn't currently offer much/any support for this pattern, but it's sufficiently common that we ought to support it.

[yallop]

/cc @simonjbeaumont

[simonjbeaumont]

@yallop thanks for confirming the workaround too :)

[simonjbeaumont]

I took the time to blog about the current workaround when these are required. http://simonjbeaumont.com/posts/ocaml-ctypes-flexible-array-member/

[yallop]

Thanks! These blog posts are extremely useful.