Function snapshot_chunk_admission 

pub fn snapshot_chunk_admission(
    identity_matches: bool,
    fixed_size: Option<i64>,
    received: i64,
    declared_size: i64,
    position: i64,
    chunk_len: i64,
    max_size: i64,
) -> SnapshotChunkDecision

Admit exactly the next bounded chunk for one fixed snapshot identity and size.