ffi array bounds checking 2

bounds

ffi = require "ffi"

local VHOST_VRING_SIZE = 32*1024

ffi.cdef [[
enum { VHOST_VRING_SIZE = 32*1024 };

struct vring_avail {
  uint16_t flags;
  uint16_t idx;
  uint16_t ring[VHOST_VRING_SIZE];
};
]]

vring_avail = ffi.metatype("struct vring_avail",
  {__index = function(v, i)
               if i < 0 or i > VHOST_VRING_SIZE then error "out of bounds" end
               return v.ring[i]
             end,
  __newindex = function(v, i, k)
               if i < 0 or i > VHOST_VRING_SIZE then error "out of bounds" end
               v.ring[i] = k
             end,
})

v = vring_avail()

v[2] = 4
assert(v[2] == 4)

x = v[65000]