decdn-node 0.1.0

//! Client-side `cdn/dht/v1` request primitives.
//!
//! The handler in [`crate::handlers::dht`] is the server half — it
//! receives `FindNode` / `FindValue` / `Store` / `BatchStore` requests
//! and writes responses. This module is the *client* half: outbound
//! requests issued by the bootstrap path (initial
//! `FindNode(self.node_id)`), the republish scheduler (a per-hash
//! `Store` on eager publish and one `BatchStore` per receiver on the
//! periodic drain), and the iterative requester-side `FindValue` lookup
//! in [`crate::dht::lookup`].
//!
//! Each call:
//! 1. Connects to the peer's [`EndpointAddr`] with ALPN `cdn/dht/v1`.
//! 2. Opens a bi stream.
//! 3. Writes one framed [`wire::DhtMessage`] request.
//! 4. Reads one framed response, decodes, and returns it.
//! 5. Closes the connection with `0u32` (no app error).
//!
//! The signatures mirror the server-side message types: callers
//! provide the request fields, get back the response struct. Error
//! handling surfaces via `anyhow::Result`; a peer that closes the
//! stream with an ADR 013 application error code (rate-limited,
//! malformed) surfaces as an `anyhow` error the caller logs and retries
//! on its next cycle.

use std::time::Duration;

use anyhow::Context;
use decdn_protocol::{
    ALPN_DHT, ContentHash, Coverage, NodeId, decode_message, dht as wire, encode_message,
    encode_store_request, read_frame, write_frame,
};
use iroh::endpoint::{ConnectOptions, Connection};
use iroh::{Endpoint, EndpointAddr};

/// Per-request hard timeout for outbound DHT exchanges. Shorter than
/// the sum of the server-side accept-bi timeout (5s) and read
/// timeout (5s) in [`crate::handlers::dht`] so a hung peer doesn't
/// wedge a republish sweep.
pub const DHT_CLIENT_TIMEOUT: Duration = Duration::from_secs(8);

/// Send a single `FindNode` request to `target` and return the response.
///
/// Used by the bootstrap path (`FindNode(self.node_id)` to seed the
/// routing table) and by the bucket-refresh task
/// (`FindNode(random_id_in_bucket)`).
pub async fn find_node(
    endpoint: &Endpoint,
    target: EndpointAddr,
    target_id: NodeId,
    requester: NodeId,
) -> anyhow::Result<wire::FindNodeResponse> {
    let request = wire::DhtMessage::FindNode(wire::FindNodeRequest {
        target: target_id,
        requester,
    });
    let response = exchange(endpoint, target, &request).await?;
    match response {
        wire::DhtMessage::FindNodeResponse(r) => Ok(r),
        other => anyhow::bail!(
            "dht client: expected FindNodeResponse, got {} variant",
            variant_name(&other)
        ),
    }
}

/// Send a single `Store` request to `target` and return the ack.
///
/// Used by the republish scheduler's eager publish of a newly advertisable
/// hash — one call per K+3 closest peer, per ADR 022 §STORE Flow steps 1-2.
pub async fn store(
    endpoint: &Endpoint,
    target: EndpointAddr,
    hash: ContentHash,
    holder: NodeId,
    coverage: Coverage,
) -> anyhow::Result<wire::StoreAck> {
    let request = wire::StoreRequest {
        hash,
        holder,
        coverage,
    };
    // Encode through the typed two-phase helper (ADR 013 §Tier 1) so the
    // client half mirrors the server's `parse_store_request_ext` seam: the
    // `StoreRequestExt` is appended here (empty today) and the payload is
    // sent as pre-encoded bytes via `exchange_payload`.
    let payload =
        encode_store_request(&request, None).context("dht client: encode store request")?;
    let response = exchange_payload(endpoint, target, &payload).await?;
    match response {
        wire::DhtMessage::StoreAck(a) => Ok(a),
        other => anyhow::bail!(
            "dht client: expected StoreAck, got {} variant",
            variant_name(&other)
        ),
    }
}

/// Send a single `BatchStore` request to `target` and return the ack
/// (ADR 022 §STORE Flow Batched STORE). One `bool` per request hash comes
/// back in request order. Used by the re-publish scheduler, which groups
/// a drain cycle's hashes by receiver and sends each receiver its set via
/// this. Every
/// DHT node implements `BatchStore`, so there is no per-hash fallback.
///
/// `entries` MUST be ≤ [`decdn_protocol::dht::MAX_BATCH_STORE_HASHES`];
/// an oversize batch is rejected by the receiver at wire decode with
/// `MALFORMED_MESSAGE` and surfaces here as an error (the caller must
/// split the set, not retry).
pub async fn batch_store(
    endpoint: &Endpoint,
    target: EndpointAddr,
    entries: Vec<(ContentHash, Coverage)>,
    holder: NodeId,
) -> anyhow::Result<wire::BatchStoreAck> {
    let n = entries.len();
    let request = wire::DhtMessage::BatchStore(wire::BatchStoreRequest { entries, holder });
    let response = exchange(endpoint, target, &request).await?;
    match response {
        // A conformant receiver returns exactly one `bool` per request hash
        // (`results[i]` ↔ `hashes[i]`); the wire type only caps the max
        // length. Reject a mis-sized ack as an error rather than hand back a
        // result vector that silently mis-maps onto the request hashes.
        wire::DhtMessage::BatchStoreAck(a) if a.results.len() == n => Ok(a),
        wire::DhtMessage::BatchStoreAck(a) => anyhow::bail!(
            "dht client: BatchStoreAck has {} results for a {n}-hash request",
            a.results.len(),
        ),
        other => anyhow::bail!(
            "dht client: expected BatchStoreAck, got {} variant",
            variant_name(&other)
        ),
    }
}

/// Send a single `FindValue` request to `target` and return the response.
///
/// Used by the requester-side iterative lookup ([`crate::dht::lookup`]).
/// Exposed here so the same connect/encode/decode plumbing isn't
/// duplicated across the bootstrap / republish / lookup call sites.
pub async fn find_value(
    endpoint: &Endpoint,
    target: EndpointAddr,
    hash: ContentHash,
    requester: NodeId,
) -> anyhow::Result<wire::FindValueResponse> {
    let request = wire::DhtMessage::FindValue(wire::FindValueRequest { hash, requester });
    let response = exchange(endpoint, target, &request).await?;
    match response {
        wire::DhtMessage::FindValueResponse(r) => Ok(r),
        other => anyhow::bail!(
            "dht client: expected FindValueResponse, got {} variant",
            variant_name(&other)
        ),
    }
}

/// Inner: connect, `open_bi`, write request frame, read response
/// frame, decode. Wraps the whole sequence in a single
/// [`DHT_CLIENT_TIMEOUT`] so a hung peer can't block the caller's
/// scheduler indefinitely.
async fn exchange(
    endpoint: &Endpoint,
    target: EndpointAddr,
    request: &wire::DhtMessage,
) -> anyhow::Result<wire::DhtMessage> {
    let payload = encode_message(request).context("dht client: encode request")?;
    exchange_payload(endpoint, target, &payload).await
}

/// Inner: connect, `open_bi`, write a pre-encoded request frame, read
/// response frame, decode. The payload is already encoded so a caller
/// that needs a typed two-phase encode (e.g. `store` via
/// [`encode_store_request`]) can hand over its bytes directly, keeping
/// the connect/exchange plumbing in one place.
async fn exchange_payload(
    endpoint: &Endpoint,
    target: EndpointAddr,
    payload: &[u8],
) -> anyhow::Result<wire::DhtMessage> {
    let response = tokio::time::timeout(DHT_CLIENT_TIMEOUT, async {
        let connecting = endpoint
            .connect_with_opts(target, ALPN_DHT, ConnectOptions::new())
            .await
            .context("dht client: connect failed")?;
        let conn = connecting.await.context("dht client: handshake failed")?;
        let resp = exchange_on(&conn, payload).await?;
        // `0u32` = "no app error"; matches the server's normal-close
        // code so the peer's `conn.closed()` arm reads the same way
        // it does for a probe.
        conn.close(0u32.into(), b"dht-done");
        Ok::<_, anyhow::Error>(resp)
    })
    .await
    .map_err(|_| {
        anyhow::anyhow!(
            "dht client: request timed out after {} ms",
            DHT_CLIENT_TIMEOUT.as_millis()
        )
    })??;
    Ok(response)
}

/// Inner-inner: do the bi-stream exchange on an already-connected
/// [`Connection`]. A separate function so a caller that wants to bundle
/// multiple DHT requests on one connection (e.g. a republish sweep to
/// the same target peer) can re-use the connection.
async fn exchange_on(conn: &Connection, payload: &[u8]) -> anyhow::Result<wire::DhtMessage> {
    let (mut send, mut recv) = conn
        .open_bi()
        .await
        .map_err(|e| anyhow::anyhow!("dht client: open_bi failed: {e}"))?;
    write_frame(&mut send, payload)
        .await
        .map_err(|e| anyhow::anyhow!("dht client: write request: {e}"))?;
    send.finish()
        .map_err(|e| anyhow::anyhow!("dht client: finish send: {e}"))?;
    let frame = read_frame(&mut recv)
        .await
        .map_err(|e| anyhow::Error::new(e).context("dht client: read response"))?;
    let (msg, _tail) = decode_message::<wire::DhtMessage>(&frame)
        .map_err(|e| anyhow::anyhow!("dht client: decode response: {e}"))?;
    Ok(msg)
}

const fn variant_name(msg: &wire::DhtMessage) -> &'static str {
    match msg {
        wire::DhtMessage::FindValue(_) => "FindValue",
        wire::DhtMessage::FindValueResponse(_) => "FindValueResponse",
        wire::DhtMessage::Store(_) => "Store",
        wire::DhtMessage::StoreAck(_) => "StoreAck",
        wire::DhtMessage::BatchStore(_) => "BatchStore",
        wire::DhtMessage::BatchStoreAck(_) => "BatchStoreAck",
        wire::DhtMessage::FindNode(_) => "FindNode",
        wire::DhtMessage::FindNodeResponse(_) => "FindNodeResponse",
    }
}