FIDL internal library zx

The fidlc compiler automatically generates library zx (internally) into //zircon/tools/fidl/lib/

You will find content similar to the following:

library zx;
using status = int32;
using time = int64;
using duration = int64;
using koid = uint64;
using vaddr = uint64;
using paddr = uint64;
using paddr32 = uint32;
using gpaddr = uint64;
using off = uint64;
using procarg = uint32;
const uint64 CHANNEL_MAX_MSG_BYTES = 65536;
const uint64 CHANNEL_MAX_MSG_HANDLES = 64;
const uint64 MAX_NAME_LEN = 32;
const uint64 MAX_CPUS = 512;

You can reference this library with the using statement:

using zx;

The types generally correspond to Zircon System Types. For example, zx.duration corresponds to zx_duration_t.

The CHANNEL_MAX_MSG_BYTES and CHANNEL_MAX_MSG_HANDLES are bound at fidlc compile time (that is, when the compiler is compiled) and reflect the constants present at that time.