dynomite-engine 0.0.2

//! Memcached response coalescing helpers.
//!
//! When a `get` / `gets` request fans out across shards, the
//! per-shard responses need to be stitched back into a single
//! reply. The reference engine implements this with two helpers:
//! `memcache_pre_coalesce` adjusts each shard response in place to
//! drop the `END` marker, and `memcache_post_coalesce` concatenates
//! the per-shard payloads and appends a single trailing
//! `END\r\n`.
//!
//! This stage builds the data-shape side of those helpers; the
//! mbuf-level wiring that the reactor needs lives next to the
//! Stage 9 connection FSM.

use crate::msg::{Msg, MsgType};

/// Adjust `rsp` in place ahead of post-coalesce.
///
/// For `VALUE` and `END` shard responses, the helper records that
/// the trailing `END` marker should be dropped during merge. For
/// any other response on a fragmented request the helper flags the
/// parent request as errored.
///
/// # Examples
///
/// ```
/// use dynomite::msg::{Msg, MsgType};
/// use dynomite::proto::memcache::memcache_pre_coalesce;
///
/// let mut rsp = Msg::new(0, MsgType::RspMcEnd, false);
/// rsp.set_frag_id(1);
/// memcache_pre_coalesce(&mut rsp);
/// // No mbuf side-effects in the data-shape path; the function
/// // returns without panicking.
/// ```
pub fn memcache_pre_coalesce(rsp: &mut Msg) {
    if rsp.is_request() {
        return;
    }
    if rsp.frag_id() == 0 {
        return;
    }
    match rsp.ty() {
        MsgType::RspMcValue | MsgType::RspMcEnd => {
            // Real engine drops the trailing END marker from the
            // response chain. The Stage 9 conn FSM owns the mbuf
            // chain mutation; the data-shape side just records the
            // intent via the existing `end_marker` field.
            // No-op here: the parser already populated `end_marker`.
        }
        _ => {
            rsp.set_is_error(true);
            rsp.set_dyn_error_code(crate::msg::DynErrorCode::BadFormat);
        }
    }
}

/// Post-coalesce hook for the parent request once every shard
/// response has arrived.
///
/// In the reference engine this concatenates each shard's value
/// payload onto the parent response and writes a single trailing
/// `END\r\n`. The data-shape side is to flag the parent request
/// as fully done; the mbuf-level concatenation lives in Stage 9.
///
/// # Examples
///
/// ```
/// use dynomite::msg::{Msg, MsgType};
/// use dynomite::proto::memcache::memcache_post_coalesce;
///
/// let mut req = Msg::new(0, MsgType::ReqMcGet, true);
/// memcache_post_coalesce(&mut req);
/// // The data-shape path is a no-op when there are no fragments
/// // attached.
/// ```
pub fn memcache_post_coalesce(request: &mut Msg) {
    if !request.is_request() {
        return;
    }
    if request.flags().is_error || request.flags().is_ferror {
        // Reference engine marks the owner connection as errored;
        // the conn-coupled path lands in Stage 9.
        return;
    }
    request.set_done(true);
}