Crate ic_memory

Expand description

§ic-memory

Animated warning banner

EARLY INFRASTRUCTURE: validate before opening stable memory.

ic-memory helps Internet Computer canisters avoid opening the wrong stable memory after an upgrade.

It remembers this mapping forever:

logical store -> physical stable-memory slot

If a future version tries to move that store to a different slot, or reuse that slot for a different store, ic-memory rejects the layout before stable-memory handles are opened.

§Why Use It?

Use ic-memory when a canister has more than one stable store and the layout can change over time.

It is most useful for frameworks, generated canisters, multi-store apps, plugin systems, and canister families that evolve across releases.

You probably do not need it for a tiny canister with one hand-written stable structure and a fixed layout.

Meme showing ic-memory keeping ic-stable-structures stable memory allocations from drifting

§The Bug

Version 1 ships with:

app.users.v1  -> MemoryManager ID 100
app.orders.v1 -> MemoryManager ID 101

A later upgrade accidentally ships with:

app.users.v1  -> MemoryManager ID 101
app.orders.v1 -> MemoryManager ID 100

That can still compile. It can even install.

But now the canister may open orders data as users data, and users data as orders data. ic-memory catches that mismatch first.

§Quick Start

Declare both direct dependencies:

[dependencies]
ic-memory = "0.12.3"
ic-stable-structures = "0.7.2"

Declare the MemoryManager IDs your crate owns. A shared compile-time constant keeps the explicit authority identical across the range and each key:

const MEMORY_AUTHORITY: &str = "icydb.test_db";

ic_memory::ic_memory_range!(authority = MEMORY_AUTHORITY, start = 120, end = 129);

The authority string is explicit stable policy metadata. It is not persisted allocation identity; the stable key and memory ID fill that role. Use the same authority value for the package’s range and key declarations, and do not derive it from a Cargo package name or module path.

Open stable structures through ic_memory_key!:

use std::cell::RefCell;

thread_local! {
    pub static USERS: RefCell<UsersStore> = RefCell::new(UsersStore::init(
        ic_memory::ic_memory_key!(
            authority = MEMORY_AUTHORITY,
            key = "icydb.test_db.users.data.v1",
            ty = UsersStore,
            id = 120,
        )
        .expect("committed users memory")
    ));
}

Bootstrap once per concrete memory runtime before touching stable data:

#[ic_cdk::init]
fn init() {
    ic_memory::bootstrap_default_memory_manager().expect("valid stable-memory layout");
}

#[ic_cdk::post_upgrade]
fn post_upgrade() {
    ic_memory::bootstrap_default_memory_manager().expect("valid stable-memory layout");
}

That is the normal path.

The default runtime API is exported from the crate root. It is one thread-local MemoryRuntime<DefaultMemoryImpl>, so every native thread owns an independent backing memory, lifecycle, committed capability, and diagnostic view. On IC Wasm, execution is single-threaded and the same TLS object naturally has canister-instance lifetime.

Use helpers such as ic_memory::bootstrap_default_memory_manager(), ic_memory::bootstrap_default_memory_manager_with_policy(...), ic_memory::committed_allocations(), ic_memory::open_default_memory_manager_memory(...), and the macros shown above; implementation modules are private.

The no-argument bootstrap helper uses ic-memory’s built-in versioned PolicyIdentity. A custom policy implements both AllocationPolicy and RuntimeBootstrapPolicy. Its bounded identity contains a policy-family name, a nonzero semantic version, and an optional caller-computed 32-byte configuration digest. Change the version when policy semantics change and use the digest when effective runtime configuration changes.

§Multi-Crate Composition

Every crate registers into the same linked declaration registry. Crates do not need to import or name each other:

mod package_a {
    ic_memory::ic_memory_range!(authority = "package_a", start = 100, end = 109);

    thread_local! {
        pub static USERS: RefCell<UsersStore> = RefCell::new(UsersStore::init(
            ic_memory::ic_memory_key!(
                authority = "package_a",
                key = "package_a.users.v1",
                ty = UsersStore,
                id = 100,
            )
            .expect("committed users memory")
        ));
    }
}

mod package_b {
    ic_memory::ic_memory_range!(authority = "package_b", start = 110, end = 119);

    thread_local! {
        pub static ORDERS: RefCell<OrdersStore> = RefCell::new(OrdersStore::init(
            ic_memory::ic_memory_key!(
                authority = "package_b",
                key = "package_b.orders.v1",
                ty = OrdersStore,
                id = 110,
            )
            .expect("committed orders memory")
        ));
    }
}

The linked program seals one immutable, canonical declaration snapshot. Bootstrap supplies that snapshot to the calling thread’s default runtime, recovers and commits that runtime’s allocation ledger, and publishes committed allocations into that runtime only. TLS-backed stores open when your code first touches the thread_local!.

Duplicate stable keys, duplicate MemoryManager IDs, overlapping ranges, and out-of-range declarations fail before stable structures open.

ic-memory follows the ic-stable-structures::MemoryManager ID domain exactly: IDs 0..=254 are usable, and ID 255 is always the unallocated sentinel. It is not an application slot and cannot be declared or reserved.

The default runtime reserves MemoryManager IDs 0..=9 and stable keys under ic_memory.* for allocation-governance records. The ledger itself lives at ID 0; it remains in the durable ledger for recovery, but public runtime helpers do not publish or open that internal allocation as application memory.

Range claims are authoritative in the default runtime. If a crate registers ic_memory_range!, its declared memories must stay inside that range. Framework adapters that want their own range policy, such as Canic, should register only the ranges they want ic-memory to enforce and put the rest in their policy adapter.

The committed allocation state is an in-memory capability published into one runtime only after that runtime’s stable-cell persistence succeeds. It is not a serde payload and should not be treated as configuration.

§Explicit Runtimes

Frameworks and tests that own backing memory directly should use MemoryRuntime<M> as the canonical API:

use ic_memory::{MemoryRuntime, sealed_declaration_snapshot};

let declarations = sealed_declaration_snapshot()?;
let mut runtime = MemoryRuntime::new(backing_memory)?;
runtime.bootstrap(&declarations, &policy)?;

let rows = runtime.open_memory("app.rows.v1", 120)?;
let diagnostics = runtime.diagnostic_export()?;

Construction is fallible. Empty backing memory is initialized as an ic-stable-structures MemoryManager; nonempty backing memory must already contain the current MGR header and layout version. Foreign or unsupported memory is rejected before MemoryManager::init() can overwrite its header. A pre-grown blank memory is nonempty and is rejected rather than assumed disposable.

Each runtime owns all facts derived from backing_memory: recovery, ledger cell, lifecycle, committed allocations, opens, diagnostics, and live sizes. Multiple runtimes share only the immutable linked declaration snapshot. A failed bootstrap publishes no capability, and repeated bootstrap on the same runtime object is idempotent only when the snapshot and RuntimeBootstrapPolicy::runtime_bootstrap_identity() match the successful bootstrap. A changed snapshot or policy identity returns a typed error without touching the ledger. Policy implementations should change their identity whenever policy configuration or semantics change. This binding is intentionally in-memory lifecycle and diagnostic state; it is not upgrade audit history and is not persisted in the allocation ledger.

There is intentionally no public reset API. Native tests should construct a new explicit runtime or use the naturally independent default TLS runtime; changing global flags cannot reset a concrete stable-memory instance safely.

§Diagnostics

Use default_memory_manager_doctor_report() for operator-facing preflight and runtime diagnostics. It returns a typed error if the default TLS runtime is re-entered. Otherwise it can be called before or after bootstrap and reports the stable-cell status, protected commit recovery state, recovered ledger export, registered declarations, range authority, validation preflight, and live MemoryManager slot sizes when they can be recovered. This no-argument entry point evaluates the built-in policy. Integrations that bootstrap with a custom policy should call default_memory_manager_doctor_report_with_policy(&policy), or call runtime.doctor_report(&declarations, &policy) on an explicit runtime.

Doctor output includes the tested policy identity and sealed-declaration fingerprint, the binding established by successful bootstrap, and a typed binding comparison. Live size measurement is also per allocation: one invalid slot is reported as a DiagnosticMemorySizeOutcome::Failed value without discarding successful measurements for other slots. Diagnostic failures carry stable DiagnosticCode values alongside their human-readable messages for operator automation.

Use default_memory_manager_commit_recovery_diagnostic() when you only need commit-slot presence and validity, the selected authoritative generation, and any corruption or ambiguity error.

§Stable Keys

Stable keys are permanent logical store names. They should describe ownership and purpose, not the current memory ID.

namespace.component.store_or_role.vN

Examples:

use ic_memory::StableKey;

StableKey::parse("app.orders.v1").expect("app key");
StableKey::parse("myapp.audit_log.v1").expect("app key");
StableKey::parse("icydb.test_db.users.data.v1").expect("database key");

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.

Schema metadata is optional diagnostic metadata for the in-place store schema. Construct it with SchemaMetadata::new(Some(version)); version 0 is reserved for absence and is rejected.

§More Detail

The short version:

declare ranges
register stable stores
seal linked declarations
bootstrap once per memory runtime
only then open stable memory

Framework authors and policy adapters should read ADVANCED.md. The non-negotiable invariants are recorded in SAFETY.md. The protocol whitepaper lives in whitepaper/src/SUMMARY.md and builds as an mdBook with make maintainer-build.

ic-memory is early infrastructure extracted from Canic. It owns allocation governance, not schema migration, endpoint routing, authorization, or data semantics. Stable-memory allocation-governance primitives for Internet Computer canister upgrades.

ic-memory prevents stable-memory slot drift.

Once a stable key is committed to a physical allocation slot, future binaries must either reopen that same stable key on that same slot or declare a new stable key.

The crate records and validates durable ownership in both directions: an active stable key cannot move to a different physical slot, and an active physical slot cannot be reused by a different stable key.

The intended integration flow is:

Recover the persisted allocation ledger.
Declare the stable stores expected by the current binary.
Validate those declarations against ledger history and any framework policy.
Commit the next generation.
Only then open stable-memory handles through committed allocation authority.

This crate owns allocation invariants, not framework policy. Namespace rules, controller authorization, endpoint lifecycle, schema migrations, and application validation belong to the framework or application.

For the default MemoryManager runtime, registered ic-memory range claims are generic allocation policy and are enforced before caller-supplied policy. A framework such as Canic that wants higher-level range semantics should adapt to this contract deliberately: either register the ranges it wants ic-memory to enforce, or omit user ranges and enforce application space through its own AllocationPolicy.

Use these primitives before opening stable-memory handles. Integrations should recover the historical ledger, declare the stores expected by the current binary, validate declarations against history and policy, commit a new generation, and only then publish committed allocation authority before opening slots through the storage owner.

MemoryRuntime is the canonical owner for one backing memory instance. It contains that memory’s manager, ledger cell, bootstrap lifecycle, committed capability, opens, and diagnostics. Linked code contributes declarations to one immutable SealedDeclarationSnapshot, which is supplied to each runtime independently.

AllocationBootstrap is the golden path for whichever layer owns a given ledger store. Canic may own bootstrap for a framework canister and compose IcyDB/application declarations through its registry; IcyDB may own bootstrap directly for generated database stores; or a standalone application canister may own bootstrap itself. Exactly one owner should bootstrap one ledger store. Multiple layers in the same canister must either compose declarations into that owner or use distinct ledger stores and allocation domains.

ic-stable-structures MemoryManager IDs are the first-class supported physical slot substrate. That ID domain is u8: IDs 0..=254 are usable, and ID 255 is always the ic-stable-structures unallocated sentinel. The crate still keeps narrow internal abstractions for storage adapters and diagnostics, but the native IC path is MemoryManager ID 0 -> ic-stable-structures::Cell<StableCellLedgerRecord, _> -> LedgerCommitStore -> CommittedGenerationBytes -> LedgerPayloadEnvelope -> RecoveredLedger -> ValidatedAllocations -> CommittedAllocations.

ic-memory is not a replacement for ic-stable-structures collections and does not wrap typed stores such as StableBTreeMap.

Macros§

eager_init: Register one pre-bootstrap hook.
ic_memory_declaration: Register a MemoryManager allocation declaration during static initialization.
ic_memory_key: Declare and open a committed MemoryManager slot by stable key.
ic_memory_range: Declare a MemoryManager allocation range during static initialization.

Structs§

AllocationBootstrap: AllocationBootstrap
AllocationDeclaration: AllocationDeclaration
AllocationHistory: AllocationHistory
AllocationLedger: AllocationLedger
AllocationRecord: AllocationRecord
AllocationRetirement: AllocationRetirement
AllocationSlotDescriptor: AllocationSlotDescriptor
CommitStoreDiagnostic: CommitStoreDiagnostic
CommittedAllocations: CommittedAllocations
CommittedGenerationBytes: CommittedGenerationBytes
DeclarationCollector: DeclarationCollector
DeclarationSnapshot: DeclarationSnapshot
DiagnosticDeclaration: DiagnosticDeclaration
DiagnosticExport: DiagnosticExport
DiagnosticFailure: DiagnosticFailure
DiagnosticGeneration: DiagnosticGeneration
DiagnosticMemorySize: DiagnosticMemorySize
DiagnosticRangeAuthority: DiagnosticRangeAuthority
DiagnosticRecord: DiagnosticRecord
DiagnosticRuntimeBinding: DiagnosticRuntimeBinding
DiagnosticStableCell: DiagnosticStableCell
DualCommitStore: DualCommitStore
GenerationRecord: GenerationRecord
LedgerCommitStore: LedgerCommitStore
LedgerPayloadEnvelope: LedgerPayloadEnvelope
MemoryManagerAuthorityRecord: MemoryManagerAuthorityRecord
MemoryManagerIdRange: MemoryManagerIdRange
MemoryManagerRangeAuthority: MemoryManagerRangeAuthority
MemoryRuntime: MemoryRuntime
MemoryRuntimeDoctorReport: MemoryRuntimeDoctorReport
PendingBootstrapCommit: PendingBootstrapCommit
PolicyIdentity: PolicyIdentity
RecoveredLedger: RecoveredLedger
SchemaMetadata: SchemaMetadata
SchemaMetadataRecord: SchemaMetadataRecord
SealedDeclarationFingerprint: SealedDeclarationFingerprint
SealedDeclarationSnapshot: SealedDeclarationSnapshot
StableCellLedgerRecord: StableCellLedgerRecord
StableKey: StableKey
StableKeyError: StableKeyError
StaticMemoryDeclaration: StaticMemoryDeclaration
StaticMemoryRangeDeclaration: StaticMemoryRangeDeclaration
ValidatedAllocations: ValidatedAllocations

Enums§

AllocationReservationError: AllocationReservationError
AllocationRetirementError: AllocationRetirementError
AllocationSlot: AllocationSlot
AllocationStageError: AllocationStageError
AllocationState: AllocationState
AllocationValidationError: AllocationValidationError
BootstrapError: BootstrapError
BootstrapReservationError: BootstrapReservationError
BootstrapRetirementError: BootstrapRetirementError
CommitRecoveryError: CommitRecoveryError
CommitSlotDiagnostic: CommitSlotDiagnostic
DeclarationSnapshotError: DeclarationSnapshotError
DiagnosticCheck: DiagnosticCheck
DiagnosticCode: DiagnosticCode
DiagnosticMemorySizeOutcome: DiagnosticMemorySizeOutcome
DiagnosticStableCellStatus: DiagnosticStableCellStatus
LedgerCommitError: LedgerCommitError
LedgerIntegrityError: LedgerIntegrityError
LedgerPayloadEnvelopeError: LedgerPayloadEnvelopeError
MemoryManagerRangeAuthorityError: MemoryManagerRangeAuthorityError
MemoryManagerRangeError: MemoryManagerRangeError
MemoryManagerRangeMode: MemoryManagerRangeMode
MemoryManagerSlotError: MemoryManagerSlotError
PolicyIdentityError: PolicyIdentityError
RuntimeBootstrapError: RuntimeBootstrapError
RuntimeConstructionError: RuntimeConstructionError
RuntimeDiagnosticError: RuntimeDiagnosticError
RuntimeOpenError: RuntimeOpenError
RuntimePolicyError: RuntimePolicyError
RuntimeStateError: RuntimeStateError
SchemaMetadataError: SchemaMetadataError
StableCellLedgerError: StableCellLedgerError
StableCellPayloadError: StableCellPayloadError
StaticMemoryDeclarationError: StaticMemoryDeclarationError

Constants§

IC_MEMORY_AUTHORITY_OWNER: Diagnostic owner label for ic-memory allocation-governance infrastructure.
IC_MEMORY_AUTHORITY_PURPOSE: Diagnostic purpose for the ic-memory allocation-governance authority range.
IC_MEMORY_LEDGER_LABEL: Diagnostic label of the allocation ledger when backed by the current MemoryManager substrate.
IC_MEMORY_LEDGER_STABLE_KEY: Stable key of the allocation ledger when backed by the current MemoryManager substrate.
IC_MEMORY_STABLE_KEY_PREFIX: Stable-key namespace prefix reserved for ic-memory allocation-governance infrastructure.
LEDGER_PAYLOAD_FORMAT_VERSION: Current durable ledger payload format version.
MEMORY_MANAGER_GOVERNANCE_MAX_ID: Last MemoryManager ID reserved for ic-memory governance in the current substrate.
MEMORY_MANAGER_INVALID_ID: MemoryManager unallocated-bucket sentinel. This is not a usable slot.
MEMORY_MANAGER_LEDGER_ID: MemoryManager ID used by the allocation ledger in the current MemoryManager substrate.
MEMORY_MANAGER_MAX_ID: Last usable MemoryManager virtual memory ID.
MEMORY_MANAGER_MIN_ID: First usable MemoryManager virtual memory ID.
STABLE_CELL_HEADER_SIZE: Stable-cell header byte length.
STABLE_CELL_LAYOUT_VERSION: Stable-cell layout version supported by this adapter.
STABLE_CELL_MAGIC: Stable-cell magic prefix written by ic-stable-structures::Cell.
STABLE_CELL_VALUE_OFFSET: Byte offset where the stable-cell value payload starts.
WASM_PAGE_SIZE_BYTES: WebAssembly page size used by ic-stable-structures memory implementations.

Traits§

AllocationPolicy: AllocationPolicy
RuntimeBootstrapPolicy: RuntimeBootstrapPolicy
Validate: Validate

Functions§

bootstrap_default_memory_manager: Bootstrap this thread’s default runtime using generic range policy.
bootstrap_default_memory_manager_with_policy: Bootstrap this thread’s default runtime with caller-supplied policy.
committed_allocations: Return this thread’s default runtime committed allocation capability.
decode_stable_cell_ledger_record: Decode a StableCellLedgerRecord from stable-cell value bytes.
decode_stable_cell_payload: Decode the raw value payload from an ic-stable-structures::Cell memory.
default_memory_manager_commit_recovery_diagnostic: Diagnose protected commit recovery for this thread’s default runtime.
default_memory_manager_diagnostic_export: Export this thread’s default runtime ledger and live memory sizes.
default_memory_manager_doctor_report: Build preflight and lifecycle diagnostics for this thread’s default runtime.
default_memory_manager_doctor_report_with_policy: Build diagnostics for this thread’s default runtime under one explicit policy.
is_default_memory_manager_bootstrapped: Return whether this thread’s default runtime has completed bootstrap.
is_ic_memory_stable_key: Return true when stable_key belongs to the ic-memory namespace.
memory_manager_governance_range: MemoryManager range reserved for ic-memory governance in the current substrate.
open_default_memory_manager_memory: Open a committed memory from this thread’s default runtime.
register_static_memory_declaration: Register one allocation declaration before bootstrap seals the snapshot.
register_static_memory_manager_declaration: Register one MemoryManager declaration before bootstrap seals the snapshot.
register_static_memory_manager_declaration_with_schema: Register one MemoryManager declaration with schema metadata.
register_static_memory_manager_range: Register one MemoryManager authority range before bootstrap seals the snapshot.
register_static_memory_range_declaration: Register one authority range declaration before bootstrap seals the snapshot.
sealed_declaration_snapshot: Seal and return the canonical linked-program declaration snapshot.
validate_allocations: Validate a committed ledger and current declarations before opening.
validate_memory_manager_id: Validate that a MemoryManager ID is usable as an allocation slot.
validate_stable_cell_ledger_memory: Validate an existing stable-cell ledger record before opening it with ic-stable-structures::Cell.

Crate ic_memory

Crate ic_memory Copy item path

§ic-memory

§Why Use It?

§The Bug

§Quick Start

§Multi-Crate Composition

§Explicit Runtimes

§Diagnostics

§Stable Keys

§More Detail

Macros§

Structs§

Enums§

Constants§

Traits§

Functions§

Crate ic_memory