# Advanced ic-memory
This document covers the lower-level pieces behind the macro runtime. Most
applications should start with the README.
## How It Fits
`ic-stable-structures` stores the data.
`ic-memory` checks that each logical store is still opening the same physical
slot it owned before.
The native IC ledger anchor is:
```text
MemoryManager ID 0
-> ic-stable-structures::Cell<StableCellLedgerRecord, _>
-> LedgerCommitStore
-> dual protected committed AllocationLedger payloads
```
`CborLedgerCodec` is the built-in codec for those committed ledger payloads.
A typical framework flow is:
1. Recover the saved allocation ledger.
2. Declare the stores this binary expects.
3. Validate those declarations against history and policy.
4. Commit the new generation.
5. Open stable-memory handles only after validation passes.
The important rule: validate layout before touching stable data.
The default runtime also preflights the ledger stable-cell before opening it
through `ic-stable-structures::Cell`. Corrupt cell envelopes or ledger-record
bytes are reported as bootstrap errors instead of relying on panic behavior
inside `Cell::init`.
## Runtime Ownership
Exactly one owner should bootstrap the default `ic-memory` runtime in a
canister. Canic can be that owner, IcyDB can be that owner, or the application
can be that owner.
All crates using the default runtime compose into one bootstrap authority.
If multiple layers need separate allocation domains, they should use distinct
ledger stores and custom integration code.
## Policy Authority
There is one authority order in the default runtime:
1. `ic-memory` always owns its governance range.
2. Registered `ic_memory_range!` claims are authoritative generic range policy.
3. The caller-supplied `AllocationPolicy` is applied after generic range checks.
That means a framework adapter must choose deliberately which layer owns range
decisions.
If a package registers a user range, `ic-memory` enforces that the package's
declarations stay inside that range. If any user range is registered, all user
`MemoryManager` declarations are checked against registered range ownership.
This is the standalone multi-crate composition mode.
If a framework such as Canic wants its own policy to decide application space,
it should not register `ic_memory_range!` claims for that application space.
It can still use `bootstrap_default_memory_manager_with_policy(...)` and reject
keys or slots in its `AllocationPolicy`.
Canic-specific namespace and framework range rules are Canic policy. They are
not hard-coded `ic-memory` rules. Canic should adapt to `ic-memory` by either:
- registering the framework and package ranges it wants `ic-memory` to enforce;
- or leaving application ranges unclaimed and enforcing those rules in Canic's
policy adapter.
## Declaration-Only Hooks
Use `eager_init!` when a crate needs to register declarations before bootstrap
without opening a TLS stable structure:
```rust,ignore
ic_memory::eager_init!({
ic_memory::register_static_memory_manager_declaration(
121,
env!("CARGO_PKG_NAME"),
"OrdersDataStore",
"icydb.test_db.orders.data.v1",
)
.expect("valid ic-memory declaration");
});
```
Hooks registered with `eager_init!` run before the declaration snapshot is
sealed. Stable structures opened with `ic_memory_key!` require validated
allocations to be published first.
Frameworks or libraries that need custom policy metadata can inspect
`static_memory_declarations()` and `static_memory_range_declarations()`, then
bootstrap with `runtime::bootstrap_default_memory_manager_with_policy(...)`.
## Manual Bootstrap
The macro runtime is built on the lower-level ledger API. Frameworks that need
to own a custom ledger substrate can still drive that API directly.
The safe order is fixed:
```text
recover persisted allocation ledger
declare this binary's expected stable stores
validate declarations against ledger/history/policy
commit the new generation
only then open stable-memory handles
```
Decoded ledger and declaration DTOs are not trusted just because serde accepted
them. The validation boundary rechecks ledger compatibility, committed-ledger
integrity, stable-key grammar, slot descriptor shape, schema metadata,
duplicate claims, policy, and historical ownership before a
`ValidatedAllocations` capability is produced.
Manual sketch:
```rust,ignore
let declarations = DeclarationCollector::new()
.with_memory_manager("app.orders.v1", 100, "orders")?
.seal()?;
let commit = AllocationBootstrap::new(record.store_mut()).initialize_validate_and_commit(
&CborLedgerCodec,
&genesis_ledger,
declarations,
&policy,
runtime_fingerprint,
)?;
let orders =
AllocationSession::new(storage, commit.validated).open(&StableKey::parse("app.orders.v1")?)?;
```
The helper names for `record`, `genesis_ledger`, `policy`,
`runtime_fingerprint`, and `storage` are placeholders. Frameworks and libraries
wire those to their own stable-memory persistence and collection construction.
The ordering is the contract.
`AllocationLedger::new(...)` builds a structurally valid ledger DTO. Use
`AllocationLedger::new_committed(...)` only when you are manually constructing
committed ledger state and want the stricter committed-generation checks.
Normal integrations should usually recover through the commit/recovery flow
instead of hand-assembling committed state.
`ValidatedAllocations` is intentionally opaque and non-serializable. It is a
runtime capability produced by validation/bootstrap, not a durable record or a
diagnostic export format.
## Stable Key Rules
Stable keys are permanent logical store names. They should describe ownership
and purpose, not the current memory ID.
Format:
```text
namespace.component.store_or_role.vN
```
Rules:
- ASCII only.
- Lowercase only.
- Dot-separated segments.
- Each segment starts with a lowercase letter.
- Segments may contain lowercase letters, digits, and underscores.
- No whitespace, slashes, or hyphens.
- Must end with a nonzero version suffix such as `.v1` or `.v12`.
- Maximum length is 128 bytes.
Suggested namespace conventions:
- `ic_memory.*` is reserved for `ic-memory` governance records.
- Application-owned stores can use an application namespace, such as
`app.orders.v1` or `myapp.audit_log.v1`.
- Frameworks and generated stores should use namespaces they own, such as
`framework.cache.index.v1` or `database.users.data.v1`.
Canic and IcyDB examples:
- `canic.core.*` is appropriate for Canic framework-owned stores.
- `icydb.<memory_namespace>.<store_name>.<role>.vN` works for generated IcyDB
stores, such as `icydb.test_db.users.data.v1`.
Changing a key creates a new logical allocation identity. If the durable store
is the same, keep the stable key and update schema metadata instead.
## Range Authority
Range authority is policy metadata. It does not allocate stable-memory IDs and
does not write to the allocation ledger. In the default runtime, however,
registered range authority is enforced before the caller-supplied policy, as
described in [Policy Authority](#policy-authority).
Packages should publish only the ranges they own:
```rust
use ic_memory::{
IC_MEMORY_AUTHORITY_OWNER, MemoryManagerRangeAuthority, MemoryManagerRangeMode,
memory_manager_governance_range,
};
let authority = MemoryManagerRangeAuthority::new()
.reserve(memory_manager_governance_range(), IC_MEMORY_AUTHORITY_OWNER)
.expect("ic-memory governance range")
.reserve_ids(10, 99, "framework.example")
.expect("framework range");
authority
.validate_id_authority_mode(42, "framework.example", MemoryManagerRangeMode::Reserved)
.expect("framework-owned ID");
```
An open stack composes records from multiple packages and rejects overlaps:
```rust
use ic_memory::MemoryManagerRangeAuthority;
let framework_records = MemoryManagerRangeAuthority::new()
.reserve_ids(10, 99, "framework.example")
.expect("framework range")
.authorities()
.to_vec();
let database_records = MemoryManagerRangeAuthority::new()
.reserve_ids(120, 149, "database.framework")
.expect("database range")
.authorities()
.to_vec();
let authority = MemoryManagerRangeAuthority::from_records(
framework_records
.into_iter()
.chain(database_records)
.collect(),
)
.expect("non-overlapping package ranges");
assert_eq!(authority.authorities().len(), 2);
```
A final closed policy may claim the remaining application space and require full
coverage:
```rust
use ic_memory::{
IC_MEMORY_AUTHORITY_OWNER, MEMORY_MANAGER_MAX_ID, MemoryManagerIdRange,
MemoryManagerRangeAuthority, memory_manager_governance_range,
};
let authority = MemoryManagerRangeAuthority::new()
.reserve(memory_manager_governance_range(), IC_MEMORY_AUTHORITY_OWNER)
.expect("ic-memory governance range")
.reserve_ids(10, 99, "framework.example")
.expect("framework range")
.allow_ids(100, MEMORY_MANAGER_MAX_ID, "applications")
.expect("application range");
authority
.validate_complete_coverage(MemoryManagerIdRange::all_usable())
.expect("closed policy covers every usable ID");
```
## Current MemoryManager Rules
For the built-in `ic-stable-structures::MemoryManager` slot descriptor:
- IDs `0..=254` are usable stable-memory slots.
- ID `255` is rejected because it is the unallocated sentinel.
- IDs `0..=9` are reserved for `ic-memory` governance.
- ID `0` is assigned to the allocation ledger.
The crate also exposes range-authority helpers for frameworks that want to split
ID ranges between infrastructure and application stores.
Canic can reserve framework ranges such as `10..=99` through its adapter. That
kind of range is Canic policy, not an `ic-memory` rule.
## What It Does Not Do
`ic-memory` does not replace `ic-stable-structures`.
It owns allocation governance. It re-exports the `ic-stable-structures`
namespace for convenience, but it does not wrap collection types such as
`StableBTreeMap` as `ic-memory` APIs.
It also does not handle:
- schema migrations
- schema compatibility or data semantics
- controller authorization
- application data validation
- endpoint routing
- IC management-canister calls
- malicious-controller protection
- disaster recovery
It only protects stable-memory allocation ownership.
## Status
`ic-memory` is early infrastructure extracted from Canic. The public API is
intended to stabilize around persistent allocation ownership, but framework
authors should still treat this line as young infrastructure while the
standalone boundary settles.
Earlier drafts exposed some durable DTO fields directly. Current versions use
checked constructors and accessors so invalid allocation state is harder to
construct accidentally.
The protected physical checksum detects torn writes and accidental corruption.
It is not a cryptographic integrity mechanism and must not be treated as
adversarial tamper resistance.