Policy — Weave Docs

StrandPolicy exposes only can_append(writer_public_key, data). It is not a read or replication policy. Enable the crate’s policy-hooks feature for the append call site to consult the optional global hook. set_strand_policy is one-time initialization backed by OnceCell; installing a policy without that feature does not enforce it. The hook receives a raw writer key, not a resolved DID.

This example is checked against source signatures; it was not compiled or run during this documentation pass.

use strand::{set_strand_policy, StrandPolicy};

/// Reject blocks larger than 4 KiB. Policies are evaluated before append commits.
struct MaxSizePolicy {
    max_bytes: usize,
}

impl StrandPolicy for MaxSizePolicy {
    fn can_append(&self, _writer_public_key: &[u8; 32], data: &[u8]) -> bool {
        data.len() <= self.max_bytes
    }
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Install a process-global policy. The backing OnceCell guarantees the policy
    // is observed by every Strand instance for the rest of the process; setting
    // it twice returns Err with the rejected policy box.
    let policy: Box<dyn StrandPolicy> = Box::new(MaxSizePolicy { max_bytes: 4 * 1024 });
    set_strand_policy(policy).map_err(|_| "policy already set")?;

    println!("strand policy installed: MaxSizePolicy(max_bytes=4096)");
    Ok(())
}

Source declarations