ic-logging

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.

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,
});
log.append(EntryInput {
    created_at_secs: 10,
    level: Level::Info,
    source: "worker",
    topic: Some("delivery"),
    message: "delivery accepted",
}).unwrap();

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.

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.

The library performs no authorization, timer registration, IC calls, serialization or stable writes. Heap history is lost on replacement. Diagnostic logs must not be treated as evidence that a paid effect completed.