Pumpkin-MC/Pumpkin · error · VineError

Missing expected challenge from pending connection

Error message

Missing expected challenge from pending connection

What it means

VineError::MissingChallenge is returned at the start of receive_vine_plugin_response when expected_challenge is None (vine.rs:150) — i.e. no challenge nonce was recorded on the pending connection — yet a Vine plugin response arrived. The server cannot validate replay protection without the stored nonce, so it rejects the packet. This indicates an internal state inconsistency rather than a bad packet.

Solutions

1. Ensure vine_login is always invoked before any plugin response can arrive for that connection
2. Reject/drop unsolicited login plugin responses from clients early
3. Check connection state management so vine_challenge is not cleared before the response is handled
4. Verify each PendingConnection handles exactly one Vine exchange per login

// gate the response handler: only process if a Vine exchange was initiated
if pending.vine_challenge.is_none() {
    drop(pending); // unsolicited response — ignore instead of panicking on state
    return;
}

fn expecting_vine_response(conn: &PendingConnection) -> bool {
    conn.vine_challenge.is_some()
}

match receive_vine_plugin_response(port, &config, response, pending.vine_challenge) {
    Err(VineError::MissingChallenge) => {
        tracing::debug!("Got Vine response without a stored challenge; ignoring unsolicited packet");
        disconnect(DisconnectReason::InvalidLoginState);
    }
    result => result?,
}

When it happens

Trigger: A SLoginPluginResponse on the vine:player_info channel is processed for a PendingConnection whose vine_challenge field is None: vine_login was never invoked for this connection, the state was cleared/consumed already, or the response was dispatched to the wrong connection object.

Common situations: A client sends an unsolicited login plugin response without a prior request; the server processed two responses for one login and the stored challenge was already consumed; a code path reset or skipped vine_login (e.g. forwarding config changed mid-flight).

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

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AI-assisted analysis of Pumpkin-MC/Pumpkin@8d4639e25a (2026-09-09). Data as JSON: /api/errors/cd1c0c91beb1b941. Report an issue: GitHub.

Appendix: source

Thrown at crates/pumpkin/src/net/proxy/vine.rs:44

    #[error("No response data received")]
    NoData,
    #[error("Vine response data too short (minimum 89 bytes)")]
    DataTooShort,
    #[error("No public key or secret configured for Vine proxy")]
    MissingKeyConfig,
    #[error("Invalid Ed25519 public key")]
    InvalidPublicKey,
    #[error("Failed to verify Ed25519 signature")]
    InvalidSignature,
    #[error("Failed to read forward version")]
    FailedReadForwardVersion,
    #[error("Unsupported forwarding version {0}. Expected {1}")]
    UnsupportedForwardVersion(i32, i32),
    #[error("Vine timestamp expired or desynchronized: skew of {0}s exceeds limit of {1}s")]
    TimestampExpired(i64, i64),
    #[error("Vine challenge nonce mismatch")]
    ChallengeMismatch,
    #[error("Missing expected challenge from pending connection")]
    MissingChallenge,
    #[error("Failed to read address")]
    FailedReadAddress,
    #[error("Failed to parse address")]
    FailedParseAddress,
    #[error("Failed to read game profile name")]
    FailedReadProfileName,
    #[error("Failed to read game profile UUID")]
    FailedReadProfileUUID,
    #[error("Failed to read game profile properties")]
    FailedReadProfileProperties,
}

/// Initiates Vine modern forwarding handshake by sending a `CLoginPluginRequest`
/// with a unique 16-byte challenge nonce to protect against replay attacks.
pub async fn vine_login(connection: &mut PendingConnection) {
    let message_id: i32 = rand::random();
    let challenge: [u8; 16] = rand::random();

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