fedimint_ln_client/

incoming.rs

//! # Incoming State Machine
//!
//! This shared state machine is used by clients
//! that want to pay other clients within the federation
//!
//! It's applied in two places:
//!   - `fedimint-ln-client` for internal payments without involving the gateway
//!   - `gateway` for receiving payments into the federation

use core::fmt;
use std::time::Duration;

use assert_matches::assert_matches;
use bitcoin::hashes::sha256;
use fedimint_client_module::DynGlobalClientContext;
use fedimint_client_module::sm::{ClientSMDatabaseTransaction, State, StateTransition};
use fedimint_client_module::transaction::{ClientInput, ClientInputBundle};
use fedimint_core::core::OperationId;
use fedimint_core::encoding::{Decodable, Encodable};
use fedimint_core::module::Amounts;
use fedimint_core::runtime::sleep;
use fedimint_core::{Amount, OutPoint, TransactionId};
use fedimint_ln_common::LightningInput;
use fedimint_ln_common::contracts::incoming::IncomingContractAccount;
use fedimint_ln_common::contracts::{ContractId, Preimage};
use lightning_invoice::Bolt11Invoice;
use serde::{Deserialize, Serialize};
use thiserror::Error;
use tracing::{debug, info, warn};

use crate::api::LnFederationApi;
use crate::{LightningClientContext, PayType, set_payment_result};

/// State machine that executes a transaction between two users
/// within a federation. This creates and funds an incoming contract
/// based on an existing offer within the federation.
///
/// ```mermaid
/// graph LR
/// classDef virtual fill:#fff,stroke-dasharray: 5 5
///
///    FundingOffer -- funded incoming contract --> DecryptingPreimage
///    FundingOffer -- funding incoming contract failed --> FundingFailed
///    DecryptingPreimage -- successfully decrypted preimage --> Preimage
///    DecryptingPreimage -- invalid preimage --> RefundSubmitted
///    DecryptingPreimage -- error decrypting preimage --> Failure
/// ```
#[derive(Debug, Clone, Eq, PartialEq, Hash, Decodable, Encodable)]
pub enum IncomingSmStates {
    FundingOffer(FundingOfferState),
    DecryptingPreimage(DecryptingPreimageState),
    Preimage(Preimage),
    RefundSubmitted {
        out_points: Vec<OutPoint>,
        error: IncomingSmError,
    },
    FundingFailed {
        error: IncomingSmError,
    },
    Failure(String),
}

impl fmt::Display for IncomingSmStates {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            IncomingSmStates::FundingOffer(_) => write!(f, "FundingOffer"),
            IncomingSmStates::DecryptingPreimage(_) => write!(f, "DecryptingPreimage"),
            IncomingSmStates::Preimage(_) => write!(f, "Preimage"),
            IncomingSmStates::RefundSubmitted { .. } => write!(f, "RefundSubmitted"),
            IncomingSmStates::FundingFailed { .. } => write!(f, "FundingFailed"),
            IncomingSmStates::Failure(_) => write!(f, "Failure"),
        }
    }
}

#[derive(Debug, Clone, Eq, PartialEq, Hash, Decodable, Encodable)]
pub struct IncomingSmCommon {
    pub operation_id: OperationId,
    pub contract_id: ContractId,
    pub payment_hash: sha256::Hash,
}

#[derive(Debug, Clone, Eq, PartialEq, Hash, Decodable, Encodable)]
pub struct IncomingStateMachine {
    pub common: IncomingSmCommon,
    pub state: IncomingSmStates,
}

impl fmt::Display for IncomingStateMachine {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(
            f,
            "Incoming State Machine Operation ID: {:?} State: {}",
            self.common.operation_id, self.state
        )
    }
}

impl State for IncomingStateMachine {
    type ModuleContext = LightningClientContext;

    fn transitions(
        &self,
        context: &Self::ModuleContext,
        global_context: &DynGlobalClientContext,
    ) -> Vec<fedimint_client_module::sm::StateTransition<Self>> {
        match &self.state {
            IncomingSmStates::FundingOffer(state) => state.transitions(global_context),
            IncomingSmStates::DecryptingPreimage(_state) => {
                DecryptingPreimageState::transitions(&self.common, global_context, context)
            }
            _ => {
                vec![]
            }
        }
    }

    fn operation_id(&self) -> fedimint_core::core::OperationId {
        self.common.operation_id
    }
}

#[derive(
    Error, Debug, Serialize, Deserialize, Encodable, Decodable, Hash, Clone, Eq, PartialEq,
)]
#[serde(rename_all = "snake_case")]
pub enum IncomingSmError {
    #[error("Violated fee policy. Offer amount {offer_amount} Payment amount: {payment_amount}")]
    ViolatedFeePolicy {
        offer_amount: Amount,
        payment_amount: Amount,
    },
    #[error("Invalid offer. Offer hash: {offer_hash} Payment hash: {payment_hash}")]
    InvalidOffer {
        offer_hash: sha256::Hash,
        payment_hash: sha256::Hash,
    },
    #[error("Timed out fetching the offer")]
    TimeoutFetchingOffer { payment_hash: sha256::Hash },
    #[error("Error fetching the contract {payment_hash}. Error: {error_message}")]
    FetchContractError {
        payment_hash: sha256::Hash,
        error_message: String,
    },
    #[error("Invalid preimage. Contract: {contract:?}")]
    InvalidPreimage {
        contract: Box<IncomingContractAccount>,
    },
    #[error("There was a failure when funding the contract: {error_message}")]
    FailedToFundContract { error_message: String },
    #[error("Failed to parse the amount from the invoice: {invoice}")]
    AmountError { invoice: Bolt11Invoice },
    // New variants have to be appended: the `Encodable` derive assigns indices by
    // declaration order and this type is persisted inside `RefundSubmitted` and
    // `FundingFailed` states, so inserting one mid-enum makes existing client
    // databases fail to decode.
    #[error(
        "A contract already exists for payment hash {payment_hash}, funding it again would credit the existing account"
    )]
    ContractAlreadyExists { payment_hash: sha256::Hash },
}

#[derive(Debug, Clone, Eq, PartialEq, Hash, Decodable, Encodable)]
pub struct FundingOfferState {
    pub txid: TransactionId,
}

impl FundingOfferState {
    fn transitions(
        &self,
        global_context: &DynGlobalClientContext,
    ) -> Vec<StateTransition<IncomingStateMachine>> {
        let txid = self.txid;
        vec![StateTransition::new(
            Self::await_funding_success(global_context.clone(), txid),
            |_dbtx, result, old_state| {
                Box::pin(async { Self::transition_funding_success(result, old_state) })
            },
        )]
    }

    async fn await_funding_success(
        global_context: DynGlobalClientContext,
        txid: TransactionId,
    ) -> Result<(), IncomingSmError> {
        global_context
            .await_tx_accepted(txid)
            .await
            .map_err(|error_message| IncomingSmError::FailedToFundContract { error_message })
    }

    fn transition_funding_success(
        result: Result<(), IncomingSmError>,
        old_state: IncomingStateMachine,
    ) -> IncomingStateMachine {
        let txid = match old_state.state {
            IncomingSmStates::FundingOffer(refund) => refund.txid,
            _ => panic!("Invalid state transition"),
        };

        match result {
            Ok(()) => IncomingStateMachine {
                common: old_state.common,
                state: IncomingSmStates::DecryptingPreimage(DecryptingPreimageState { txid }),
            },
            Err(error) => IncomingStateMachine {
                common: old_state.common,
                state: IncomingSmStates::FundingFailed { error },
            },
        }
    }
}

#[derive(Debug, Clone, Eq, PartialEq, Hash, Decodable, Encodable)]
pub struct DecryptingPreimageState {
    txid: TransactionId,
}

impl DecryptingPreimageState {
    fn transitions(
        common: &IncomingSmCommon,
        global_context: &DynGlobalClientContext,
        context: &LightningClientContext,
    ) -> Vec<StateTransition<IncomingStateMachine>> {
        let success_context = global_context.clone();
        let gateway_context = context.clone();

        vec![StateTransition::new(
            Self::await_preimage_decryption(success_context.clone(), common.contract_id),
            move |dbtx, result, old_state| {
                let gateway_context = gateway_context.clone();
                let success_context = success_context.clone();
                Box::pin(Self::transition_incoming_contract_funded(
                    result,
                    old_state,
                    dbtx,
                    success_context,
                    gateway_context,
                ))
            },
        )]
    }

    async fn await_preimage_decryption(
        global_context: DynGlobalClientContext,
        contract_id: ContractId,
    ) -> Result<Preimage, IncomingSmError> {
        loop {
            debug!("Awaiting preimage decryption for contract {contract_id:?}");
            match global_context
                .module_api()
                .wait_preimage_decrypted(contract_id)
                .await
            {
                Ok((incoming_contract_account, preimage)) => {
                    if let Some(preimage) = preimage {
                        debug!("Preimage decrypted for contract {contract_id:?}");
                        return Ok(preimage);
                    }

                    info!("Invalid preimage for contract {contract_id:?}");
                    return Err(IncomingSmError::InvalidPreimage {
                        contract: Box::new(incoming_contract_account),
                    });
                }
                Err(error) => {
                    warn!(
                        "Incoming contract {contract_id:?} error waiting for preimage decryption: {error:?}, will keep retrying..."
                    );
                }
            }

            sleep(Duration::from_secs(1)).await;
        }
    }

    async fn transition_incoming_contract_funded(
        result: Result<Preimage, IncomingSmError>,
        old_state: IncomingStateMachine,
        dbtx: &mut ClientSMDatabaseTransaction<'_, '_>,
        global_context: DynGlobalClientContext,
        context: LightningClientContext,
    ) -> IncomingStateMachine {
        assert_matches!(old_state.state, IncomingSmStates::DecryptingPreimage(_));

        match result {
            Ok(preimage) => {
                let contract_id = old_state.common.contract_id;
                let payment_hash = old_state.common.payment_hash;
                set_payment_result(
                    &mut dbtx.module_tx(),
                    payment_hash,
                    PayType::Internal(old_state.common.operation_id),
                    contract_id,
                    Amount::from_msats(0),
                )
                .await;

                // client_ctx is None for the gateway since it does not emit the client events
                if let Some(ref client_ctx) = context.client_ctx {
                    client_ctx
                        .log_event(
                            &mut dbtx.module_tx(),
                            crate::events::SendPaymentUpdateEvent {
                                operation_id: old_state.common.operation_id,
                                status: crate::events::SendPaymentStatus::Success(preimage.0),
                            },
                        )
                        .await;
                }

                IncomingStateMachine {
                    common: old_state.common,
                    state: IncomingSmStates::Preimage(preimage),
                }
            }
            Err(IncomingSmError::InvalidPreimage { contract }) => {
                Self::refund_incoming_contract(dbtx, global_context, context, old_state, contract)
                    .await
            }
            Err(e) => IncomingStateMachine {
                common: old_state.common,
                state: IncomingSmStates::Failure(format!(
                    "Unexpected internal error occurred while decrypting the preimage: {e:?}"
                )),
            },
        }
    }

    async fn refund_incoming_contract(
        dbtx: &mut ClientSMDatabaseTransaction<'_, '_>,
        global_context: DynGlobalClientContext,
        context: LightningClientContext,
        old_state: IncomingStateMachine,
        contract: Box<IncomingContractAccount>,
    ) -> IncomingStateMachine {
        debug!("Refunding incoming contract {contract:?}");
        let claim_input = contract.claim();
        let client_input = ClientInput::<LightningInput> {
            input: claim_input,
            amounts: Amounts::new_bitcoin(contract.amount),
            keys: vec![context.redeem_key],
        };

        let change_range = global_context
            .claim_inputs(dbtx, ClientInputBundle::new_no_sm(vec![client_input]))
            .await
            .expect("Cannot claim input, additional funding needed");
        debug!("Refunded incoming contract {contract:?} with {change_range:?}");

        // client_ctx is None for the gateway since it does not emit the client events
        if let Some(ref client_ctx) = context.client_ctx {
            client_ctx
                .log_event(
                    &mut dbtx.module_tx(),
                    crate::events::SendPaymentUpdateEvent {
                        operation_id: old_state.common.operation_id,
                        status: crate::events::SendPaymentStatus::Refunded,
                    },
                )
                .await;
        }

        IncomingStateMachine {
            common: old_state.common,
            state: IncomingSmStates::RefundSubmitted {
                out_points: change_range.into_iter().collect(),
                error: IncomingSmError::InvalidPreimage { contract },
            },
        }
    }
}

#[derive(Debug, Clone, Eq, PartialEq, Decodable, Encodable)]
pub struct AwaitingPreimageDecryption {
    txid: TransactionId,
}

#[derive(Debug, Clone, Eq, PartialEq, Decodable, Encodable)]
pub struct PreimageState {
    preimage: Preimage,
}

#[derive(Debug, Clone, Eq, PartialEq, Decodable, Encodable)]
pub struct RefundSuccessState {
    refund_txid: TransactionId,
}