Function encode

nodedb-codec/src/crdt_compress.rs:40–92

Compressed CRDT operation batch. Wire format: ```text [4 bytes] op count (LE u32) [2 bytes] actor dictionary size (LE u16) [actor_count × 8 bytes] actor IDs (LE u64) [N bytes] Delta-encoded Lamport timestamps (nodedb-codec delta format) [4 bytes] actor_index block size (LE u32) [M bytes] actor indices (u8 if ≤256 actors, u16 otherwise) [4 bytes] content block size (LE u32) [K bytes] FSST-compress

(ops: &[CrdtOp])

/// [K bytes] FSST-compressed content (newline-delimited)
/// ```
pub fn encode(ops: &[CrdtOp]) -> Result<Vec<u8>, CodecError> {
    if ops.is_empty() {
        return Ok(0u32.to_le_bytes().to_vec());
    }

    let count = ops.len() as u32;

    // Build actor dictionary.
    let mut actor_dict: Vec<u64> = Vec::new();
    let mut actor_map = std::collections::HashMap::new();
    for op in ops {
        actor_map.entry(op.actor_id).or_insert_with(|| {
            let idx = actor_dict.len() as u16;
            actor_dict.push(op.actor_id);
            idx
        });
    }

    // Delta-encode Lamport timestamps.
    let lamports: Vec<i64> = ops.iter().map(|op| op.lamport as i64).collect();
    let lamport_block = crate::delta::encode(&lamports);

    // Actor indices.
    let use_u8 = actor_dict.len() <= 256;
    let actor_indices: Vec<u8> = if use_u8 {
        ops.iter().map(|op| actor_map[&op.actor_id] as u8).collect()
    } else {
        ops.iter()
            .flat_map(|op| actor_map[&op.actor_id].to_le_bytes())
            .collect()
    };

    // FSST-compress content (treat each op's content as a separate string).
    let content_refs: Vec<&[u8]> = ops.iter().map(|op| op.content.as_slice()).collect();
    let content_block = crate::fsst::encode(&content_refs);

    // Build output.
    let mut out = Vec::new();
    out.extend_from_slice(&count.to_le_bytes());
    out.extend_from_slice(&(actor_dict.len() as u16).to_le_bytes());
    for &actor in &actor_dict {
        out.extend_from_slice(&actor.to_le_bytes());
    }
    out.extend_from_slice(&(lamport_block.len() as u32).to_le_bytes());
    out.extend_from_slice(&lamport_block);
    out.push(if use_u8 { 1 } else { 2 }); // index width marker
    out.extend_from_slice(&(actor_indices.len() as u32).to_le_bytes());
    out.extend_from_slice(&actor_indices);
    out.extend_from_slice(&(content_block.len() as u32).to_le_bytes());
    out.extend_from_slice(&content_block);

    Ok(out)
}

/// Decode compressed CRDT operations.
pub fn decode(data: &[u8]) -> Result<Vec<CrdtOp>, CodecError> {