canic-memory

Shared stable-memory helpers you can drop into any IC canister, even if you are not using the rest of Canic. It keeps you honest about which IDs you use and makes TLS-backed stable structures initialize in a predictable order.

What you get:

Reserve and validate a per-crate stable-memory ID range.
One place to register stable structures (ic_memory! + registry).
Eager TLS init so thread-locals that allocate memory are ready before entrypoints.
Zero dependency on the canic crate (only canic-utils and canic-cdk).

Sample boot logs when everything is wired correctly:

17:27:24.796 [...] [Init] 🔧 --------------------- 'canic v0.6.x -----------------------
17:27:24.796 [...] [Init] 🏁 init: root (Prime)
17:27:24.796 [...] [Memory] 💾 memory.range: canic-core [5-30] (15/26 slots used)
17:27:24.796 [...] [Wasm] 📄 registry.insert: app (1013.10 KB)
...
17:27:26.879 [...] [CanisterLifecycle] ⚡ create_canister: nssc3-p7777-77777-aaawa-cai (5.000 TC)
17:27:27.549 [...] [Init] 🏁 init: app
17:27:27.549 [...] [Memory] 💾 memory.range: canic-core [5-30] (15/26 slots used)

Modules

manager — thread-local MemoryManager<DefaultMemoryImpl> used by all helpers.
registry — range reservation + ID registry with pending queues for macro-driven registration.
ops — helper to flush pending reservations/registrations into the registry during startup.
runtime — eager TLS initialization helper.
macros — ic_memory!, ic_memory_range!, eager_static!, eager_init!.

Quick start

Add the crate to your Cargo.toml:

canic-memory = { workspace = true }

Reserve a range and declare a memory slot

// Reserve IDs 10–19 for this crate (usually in a module's init or ctor).
canic_memory::ic_memory_range!(10, 19);

// Declare a stable-memory slot at ID 10 and wrap it in a stable BTreeMap.
use canic_memory::ic_memory;
use canic_memory::cdk::structures::{BTreeMap, DefaultMemoryImpl, memory::VirtualMemory};
use std::cell::RefCell;

thread_local! {
    static USERS: RefCell<BTreeMap<u64, u64, VirtualMemory<DefaultMemoryImpl>>> =
        RefCell::new(BTreeMap::init(ic_memory!(Users, 10)));
}

Flush pending registrations during startup

Call the ops helper once during init/post-upgrade to validate ranges and apply any pending registrations queued by macros. Repeated calls are allowed when the initial range is identical; conflicts return a MemoryRegistryError.

use canic_memory::ops::MemoryRegistryOps;

fn init_memory() {
    // Optionally reserve an initial range for this crate before flushing queues.
    // Pass `None` if you reserve exclusively via `ic_memory_range!` calls.
    MemoryRegistryOps::init_memory(Some((env!("CARGO_PKG_NAME"), 10, 19))).unwrap();
}

init_memory will:

reserve the optional initial range,
apply all pending range reservations,
apply all pending ID registrations (sorted),
return a summary of ranges/entries for logging or inspection.

Eagerly initialize thread-locals that allocate memory

Why bother? thread_local! values are lazy. If a stable BTreeMap (or similar) spins up the first time an endpoint is called, you get:

unpredictable init order (especially across upgrades),
memory allocations happening under a user call instead of during init,
possible panics if the registry/ranges were not flushed yet.

eager_static! and eager_init! make TLS setup a deliberate part of your init flow: run init_eager_tls() → run eager_init! blocks → flush the registry. After that, every endpoint starts with the same, prebuilt memory layout.

use canic_memory::{eager_init, eager_static, runtime::init_eager_tls};
use std::cell::RefCell;

eager_static! {
    static CACHE: RefCell<u32> = const { RefCell::new(0) };
}

eager_init!({
    // any one-time setup before entrypoints (optional)
});

fn init() {
    // force eager TLS initialization first
    init_eager_tls();
    // then flush memory registrations
    canic_memory::ops::MemoryRegistryOps::init_memory(None).unwrap();
}

Error handling

The registry surfaces MemoryRegistryError for:

duplicate ranges, overlapping ranges, invalid range (start > end)
crate keys or labels longer than 256 bytes
registration outside the crate's reserved ranges
conflicting registrations on an ID with a different label
missing range for the crate

Handle these at init time so your canister fails fast on invalid memory layout.

Testing helpers

registry::reset_for_tests() clears the registry and pending queues to keep unit tests isolated. Example:

#[test]
fn reserves_and_registers() {
    canic_memory::registry::reset_for_tests();
    canic_memory::ops::MemoryRegistryOps::init_memory(Some(("my_crate", 1, 2))).unwrap();
    canic_memory::registry::MemoryRegistry::register(1, "my_crate", "Slot").unwrap();
}

Notes

The macros automatically namespace memory IDs by crate (CARGO_PKG_NAME) when validating ranges.
If you don't want an initial range, omit it and rely solely on ic_memory_range! calls before init_memory.
Consumers outside Canic can import only canic-memory plus canic-utils and canic-cdk; the rest of the stack is optional.

canic-memory 0.6.19