Crate ic_logging 

Bounded caller-owned logs with explicit time, retention and scan limits.

The heap engine owns no global recorder, endpoint, clock, timer or lifecycle. See the package guide for paging and retention semantics.

ic-logging

Requires Rust 1.99.1 on native and Wasm, matching the workspace compiler policy.

Bounded, caller-owned heap logs without a framework or IC runtime dependency. The library is no_std with alloc; it has no dependency on Metrics or any other crate.

[dependencies]
ic-logging = "0.23"

Logging has its own version and changelog. Maintainers select RELEASE_GROUP=logging for release and publication; see independent releases.

use ic_logging::{EntryInput, Filter, Level, Limits, Log, PageRequest};
use std::num::NonZeroUsize;

let mut log = Log::new(Limits {
    max_entries: NonZeroUsize::new(100).unwrap(),
    max_message_bytes: 1_024,
    max_label_bytes: 64,
    max_text_bytes: 64 * 1024,
});
let receipt = log.append(EntryInput {
    created_at_secs: 10,
    level: Level::Info,
    source: "worker",
    topic: Some("delivery"),
    message: "delivery accepted",
}).unwrap();
assert_eq!(receipt.sequence, 0);
assert!(!receipt.truncated);
assert_eq!(receipt.evicted, 0);

let page = log.page(Filter::default(), PageRequest {
    before: None,
    max_results: NonZeroUsize::new(10).unwrap(),
    max_scanned: NonZeroUsize::new(100).unwrap(),
});
assert_eq!(page.entries[0].message, "delivery accepted");
assert_eq!(log.next_expiry_secs(5), Some(16));
assert_eq!(log.prune_expired(16, 5, 20).removed, 1);

Limits are fixed for the lifetime of a log. Source and topic limits apply individually; oversized labels refuse before mutation. Message limits apply to retained UTF-8 bytes, including any truncation suffix. A zero message limit keeps metadata and an empty message. The count is always positive; a caller disables logging by not appending or not constructing a log. max_text_bytes caps the sum of retained source, topic and message lengths. It excludes row metadata, spare capacity, allocator overhead, transient append buffers and checkpoint copies. An individually oversized row returns TextBudgetExceeded before mutation. An admitted row evicts oldest rows until both count and byte ceilings fit; append work can therefore visit up to the configured retained row count. Its AppendReceipt reports the issued sequence, message truncation and number of evicted rows. retained_text_bytes() reports current payload use. Zero total text bytes still permits empty text and metadata. Append refusals implement core::error::Error and preserve typed label/size/time context for callers using ? or their own error wrappers.

Sequence IDs start at zero and never repeat within one log, even after all rows expire. Timestamps cannot move backwards after retention. Sequence exhaustion returns a typed error before eviction. This is an in-memory generation only: creating another log starts a new sequence namespace.

An entry remains retained through created_at_secs + max_age_secs; it becomes due in the next second. Overflowing deadlines return None and are never scheduled early. Pruning removes at most the caller’s batch limit. Appending does not prune by age automatically; callers invoke retention and schedule their own work using the reported deadline.

Pages scan from newest to oldest, after an optional exclusive sequence cursor. Positioning uses a binary search; filtering examines at most max_scanned rows and returns at most max_results borrowed entries. Follow next_before even when a page contains no matches. Filters should stay the same across pages. Retention may remove rows between calls; paging is not a frozen snapshot and scanned is not a total matching count. Borrowed rows cannot mutate the log. Topic selection is explicit: TopicMatch::Any, TopicMatch::Absent and TopicMatch::Exact(label). An absent topic differs from a present empty label. visit_page runs the same scan without allocating a result collection. Its callback returns ControlFlow::Continue(()) or stops with Break(()); the stopping row counts as delivered and the returned PageScan resumes before it. The callback owns any allocation or encoding work it performs.

For a response byte ceiling, see the compiled byte-budgeted export example. It bounds the returned UTF-8 body and keeps the next un-emitted row available when a candidate does not fit. The callback’s Break consumes that candidate in the engine, so this recipe resumes from the last emitted sequence instead of blindly using PageScan::next_before. A first matching row larger than the entire body budget returns a typed EntryTooLarge error; callers can enlarge the budget or apply an explicit policy. Empty filtered scans still follow the engine cursor. The scan count includes an examined row that was not emitted. Temporary encoding allocations and any transport envelope need their own host-selected limits.

Log::checkpoint() borrows the complete oldest-first entry iterator and both watermarks without allocation, copying text or consuming the log. Its immutable borrow keeps them fixed during encoding. The host still chooses codec limits, allocation policy and write cadence. This view is not a serialized format.

Log::into_snapshot() consumes a log and moves its retained entries into a checkpoint without cloning their owned text. Use Log::snapshot() to keep the original log available: it explicitly copies a complete checkpoint, including limits, oldest-first entries and sequence/time watermarks. Log::restore() admits that checkpoint without replaying entries. It rejects invalid bounds, noncontiguous identities, regressed timestamps, contradictory watermarks and inconsistent truncation state, including a combined text-budget violation. Fully pruned and sequence-exhausted checkpoints retain their append restrictions. Restoration proves internal consistency, not authenticity, instance identity or continuity with another checkpoint. Byte decoders must bound allocation before constructing it; LogSnapshot is not a serialized format. An empty checkpoint cannot retain u64::MAX as its last timestamp: a row at that timestamp can never expire. Nonempty checkpoints at that timestamp remain valid.

let checkpoint = log.snapshot();
let restored = Log::restore(checkpoint.clone()).unwrap();
assert_eq!(restored.into_snapshot(), checkpoint);

The library performs no authorization, timer registration, IC calls, serialization or stable writes. IC Persistence owns the separately selected ic-logging-stable adapter, its durable format and governed Memory/Storage integration. Hosts own checkpoint cadence, lifecycle, retention scheduling and stable identity; linking the heap crate selects no persistence. Diagnostic logs must not be treated as evidence that a paid effect completed.

Applications may count Logging receipts and refusals with Metrics while keeping the libraries and their reset lifetimes independent. The host owns those counters and any report DTOs; linking Logging adds no Metrics or schema dependency.

Structs

AppendReceipt

Receipt for one admitted append; eviction is oldest-first across both ceilings.

Entry

Immutable retained row; sequence identities belong to one log instance.

EntryInput

Borrowed append input; bounded retained strings are copied only after admission.

Filter

Optional exact label filters and a minimum severity; all supplied filters apply.

Limits

Fixed limits chosen by the host before constructing a log.

Log

Caller-owned heap history with fixed limits and monotonic append watermarks.

LogCheckpoint

Borrowed complete checkpoint view; obtaining/iterating it allocates nothing. Hosts own encoding budgets. The immutable borrow keeps rows and watermarks fixed.

LogSnapshot

Complete passive checkpoint, with rows ordered oldest first.

Page

Borrowed page; a continuation can be present even when no row matched.

PageRequest

One newest-first scan using an exclusive sequence cursor.

PageScan

Progress of one bounded visitor scan, including a caller-requested early stop.

RetentionBatch

Result of a bounded age-retention call.

Enums

AppendError

Append refusal; every variant leaves entries and watermarks unchanged.

Label

Label rejected by append admission.

Level

Severity ordering used by minimum-level filters.

RestoreError

Refusal of a checkpoint that the maintained engine cannot produce.

TopicMatch

Match any topic, no topic, or one exact topic (including an empty label).