> ## Documentation Index
> Fetch the complete documentation index at: https://whatsapp-rust.jlucaso.com/llms.txt
> Use this file to discover all available pages before exploring further.

# September 13, 2026 — History sync admission policy

> New opt-in HistorySyncAdmission trait lets you reject inbound history-sync chunks before they enter the major-sync queue. Zero cost when unset. Preserves skip_history_sync precedence and require_full_sync behavior.

## Features

**Generic history-sync admission policy ([#1501](https://github.com/oxidezap/whatsapp-rust/pull/1501))**

A new `HistorySyncAdmission` trait, re-exported from the crate root, gates inbound history-sync notifications before the client starts any history-sync activity. The policy receives a small `HistorySyncMetadata` view — sync type, chunk order, progress, sender-declared file length, inline payload length, and any peer-data-request session id — and returns `Accept` or `RejectAndAcknowledge`. A rejected notification sends a `hist_sync` receipt and is never enqueued.

Register on either builder:

```rust theme={null}
use whatsapp_rust::{HistorySyncAdmission, HistorySyncDecision, HistorySyncMetadata};

struct RejectPeerDataResponses;

impl HistorySyncAdmission for RejectPeerDataResponses {
    fn decide(&self, metadata: &HistorySyncMetadata<'_>) -> HistorySyncDecision {
        if metadata.peer_data_request_session_id.is_some() {
            HistorySyncDecision::RejectAndAcknowledge
        } else {
            HistorySyncDecision::Accept
        }
    }
}

Bot::builder()
    .with_history_sync_admission(RejectPeerDataResponses)
    // ...
```

Leaving the policy unset keeps the default behavior at zero cost — the receive path only checks that the optional policy is `None`. The `skip_history_sync` toggle still takes precedence: when it is on, the client sends the receipt and never consults the policy. Device registration and `require_full_sync` are unchanged.

See [History Sync Admission Hook](/advanced/history-sync-admission) for the full contract, the metadata field reference, and worked examples.