LayerZero V2 IOTA L1 Protocol Implementation

This page provides a deep technical dive into the LayerZero V2 protocol implementation on IOTA, documenting the complete message lifecycle with actual contract code, function signatures, and transaction analysis. What you’ll find:

Complete send workflow (7 steps from OApp to MessagingReceipt)
DVN verification and commit process with storage management
Executor delivery and OApp receive handling
Real transaction analysis from mainnet
Event emissions and monitoring
Recovery operations (skip, clear, nilify, burn)

Target audience: Developers who understand IOTA basics and want to deeply understand the protocol implementation.

Prerequisites

Before reading this page, familiarize yourself with IOTA fundamentals in Technical Overview. For SDK usage and practical implementation, see OFT SDK or implementation guides for OApp and OFT.

This page documents the complete message lifecycle with contract-level implementation details:

Send Workflow: Message initiation, fee calculation, nonce management, and packet dispatch
Verification Workflow: DVN submission, threshold checking, and verification commitment
Receive Workflow: Executor delivery, payload clearing, and OApp processing

Send Overview

When a user sends a crosschain message, the following high-level steps occur within a single Programmable Transaction Block (PTB):

OApp Initiates Send: User calls the OApp module’s send() function, which creates a Call<SendParam, MessagingReceipt> object
Endpoint Processes: The Endpoint increments the outbound nonce, constructs a packet with GUID, and routes to the send library
ULN302 Assigns Jobs: The message library creates child Call objects for the executor and each DVN
Workers Calculate Fees: Executor and DVNs estimate their fees and return FeeRecipient results
Confirmation Chain: Results flow back through confirm functions, aggregating fees and emitting events
OApp Finalizes: The OApp confirms the send call to extract the MessagingReceipt

Endpoint Send

The EndpointV2 module orchestrates message sending through its shared object.

EndpointV2 Shared Object

/// The main endpoint object that coordinates all crosschain messaging operations
public struct EndpointV2 has key {
    id: UID,
    eid: u32,                               // This chain's LayerZero endpoint ID
    call_cap: CallCap,                      // Capability for creating calls
    oapp_registry: OAppRegistry,            // Registry of all registered OApps
    composer_registry: ComposerRegistry,    // Registry for compose handlers
    message_lib_manager: MessageLibManager, // Manages send/receive libraries
}

MessagingChannel per OApp

Each OApp gets a dedicated MessagingChannel shared object for parallel execution:

/// Shared object managing message channels for a specific OApp
public struct MessagingChannel has key {
    id: UID,
    oapp: address,                        // OApp owner of this channel
    channels: Table<ChannelKey, Channel>, // Maps (eid, remote_oapp) → channel state
    is_sending: bool,                     // Prevents reentrancy
}

/// Composite key identifying a specific channel path
public struct ChannelKey has copy, drop, store {
    remote_eid: u32,      // Destination endpoint ID
    remote_oapp: Bytes32, // Remote OApp address (32 bytes)
}

/// State for a specific channel path
public struct Channel has store {
    outbound_nonce: u64,                          // Next nonce for sends
    lazy_inbound_nonce: u64,                      // Last cleared (executed) nonce
    inbound_payload_hashes: Table<u64, Bytes32>, // Verified messages awaiting execution
}

Step 1: OApp Creates Send Call

The OApp module creates a Call object targeting the Endpoint:

/// From oapp::send()
public fun send(
    self: &mut OApp,
    oapp_cap: &CallCap,         // Proves OApp ownership
    dst_eid: u32,                // Destination endpoint ID
    message: vector<u8>,         // Message payload
    options: vector<u8>,         // Execution options
    native_fee: Coin<IOTA>,      // Fee payment in IOTA
    lz_token_fee: Option<Coin<ZRO>>, // Optional ZRO payment
    refund_address: address,     // Address for refunds
    ctx: &mut TxContext,
): Call<SendParam, MessagingReceipt> {
    self.assert_oapp_cap(oapp_cap);

    // Lookup peer address for destination
    let receiver = self.peer.get_peer(dst_eid);

    // Combine enforced options with provided options
    let final_options = self.enforced_options.combine_options(dst_eid, SEND_MSG_TYPE, options);

    // Create send parameters
    let send_param = endpoint_send::create_param(
        dst_eid,
        receiver,
        message,
        final_options,
        native_fee,
        lz_token_fee,
        refund_address,
    );

    // Create Call object targeting the Endpoint
    call::create(oapp_cap, endpoint!(), false, send_param, ctx)
}

Key Points:

Returns a Call object (hot potato—must be consumed)
The Call has no drop or store abilities
PTB must route this Call to the Endpoint module
oapp_cap validates ownership via ID comparison

Step 2: Endpoint Processes Send

The Endpoint receives the Call, manages state, and delegates to the send library:

/// From endpoint_v2::send()
public fun send(
    self: &EndpointV2,
    messaging_channel: &mut MessagingChannel,
    call: &mut Call<EndpointSendParam, MessagingReceipt>,
    ctx: &mut TxContext,
): Call<MessageLibSendParam, MessageLibSendResult> {
    // Validate Call came from the OApp that owns this channel
    call.assert_caller(messaging_channel.oapp());

    // Get the configured send library for this destination
    let (send_lib, _) = self.message_lib_manager.get_send_library(
        call.caller(),
        call.param().dst_eid()
    );

    // Create outbound packet with incremented nonce
    // This is where the nonce++ happens:
    let send_param = messaging_channel.send(self.eid(), call.param());

    // Create child Call targeting the send library
    call.create_single_child(&self.call_cap, send_lib, send_param, ctx)
}

Inside messaging_channel.send():

/// From messaging_channel::send()
public(package) fun send(
    self: &mut MessagingChannel,
    src_eid: u32,
    param: &EndpointSendParam,
): MessageLibSendParam {
    assert!(!self.is_sending, ESendReentrancy);
    self.is_sending = true;

    // Get or create the channel for this destination
    let channel_key = ChannelKey {
        remote_eid: param.dst_eid(),
        remote_oapp: param.receiver()
    };

    if (!self.channels.contains(channel_key)) {
        // Initialize channel if first send
        let channel = Channel {
            outbound_nonce: 0,
            lazy_inbound_nonce: 0,
            inbound_payload_hashes: table::new(ctx),
        };
        self.channels.add(channel_key, channel);
    };

    // Increment nonce
    let channel = &mut self.channels[channel_key];
    channel.outbound_nonce = channel.outbound_nonce + 1;

    // Build packet with GUID
    let packet = outbound_packet::create(
        channel.outbound_nonce,
        src_eid,
        self.oapp,              // Sender address
        param.dst_eid(),
        param.receiver(),
        param.message(),
    );

    // Create send parameters for message library
    message_lib_send::create_param(
        packet,
        param.options(),
        param.pay_in_zro(),
        param.native_fee_ref(),
        param.lz_token_fee_ref(),
    )
}

GUID Generation: Uses keccak256 hashing with BCS-encoded parameters:

/// From outbound_packet module
public fun create(...): OutboundPacket {
    let guid = hash::keccak256!(
        &vector[
            nonce.to_be_bytes(),      // Convert to bytes (big-endian)
            src_eid.to_be_bytes(),
            sender.to_bytes(),
            dst_eid.to_be_bytes(),
            receiver.data(),
            message,
        ]
    );

    OutboundPacket { nonce, src_eid, sender, dst_eid, receiver, guid, message }
}

Step 3: ULN302 Assigns Jobs to Workers

The ULN302 message library creates child Call objects for the executor and DVNs:

/// From uln_302::send()
public fun send(
    self: &Uln302,
    call: &mut Call<MessageLibSendParam, MessageLibSendResult>,
    ctx: &mut TxContext,
): (Call<ExecutorAssignJobParam, FeeRecipient>, MultiCall<DvnAssignJobParam, FeeRecipient>) {
    call.assert_caller(endpoint!());
    assert!(self.is_supported_eid(call.param().base().packet().dst_eid()), EUnsupportedEid);

    // Get executor and DVN parameters from SendUln
    let (executor, executor_param, dvns, dvn_params) = self.send_uln.send(call.param());

    // Create a new child batch (capacity: 1 executor + N DVNs)
    call.new_child_batch(&self.call_cap, 1);

    // Create child Call for each DVN
    let dvn_calls = dvns.zip_map!(dvn_params, |dvn, param|
        call.create_child(&self.call_cap, dvn, param, false, ctx)
    );

    // Create child Call for executor (marked as last child)
    let executor_call = call.create_child(&self.call_cap, executor, executor_param, true, ctx);

    // Return executor call and MultiCall wrapper for DVN calls
    (executor_call, multi_call::create(&self.call_cap, dvn_calls))
}

Inside send_uln::send():

/// From send_uln::send() - prepares worker parameters
public(package) fun send(
    self: &SendUln,
    param: &MessageLibSendParam,
): (address, ExecutorAssignJobParam, vector<address>, vector<DvnAssignJobParam>) {
    let packet = param.base().packet();
    let sender = packet.sender();
    let dst_eid = packet.dst_eid();

    // Get effective executor configuration (OApp-specific or default)
    let executor_config = self.get_executor_config(sender, dst_eid);

    // Validate message size
    assert!(packet.message().length() <= executor_config.max_message_size(), EInvalidMessageSize);

    // Split options into executor and DVN options
    let (executor_options, dvn_options) = worker_options::split_worker_options(param.base().options());

    // Create executor job parameters
    let executor_param = executor_assign_job::create_param(
        packet.guid(),
        packet.dst_eid(),
        sender,
        packet.message().length(),
        executor_options,
    );

    // Get effective ULN configuration (OApp-specific or default)
    let uln_config = self.get_uln_config(sender, dst_eid);

    // Encode packet header for DVN verification
    let packet_header = packet_v1_codec::encode_packet_header(packet);
    let payload_hash = packet_v1_codec::payload_hash(packet);

    // Create DVN job parameters for each configured DVN
    let (dvns, dvn_params) = self.create_dvn_params(
        packet.guid(),
        packet.dst_eid(),
        sender,
        packet_header,
        payload_hash,
        uln_config,
        dvn_options,
    );

    (executor_config.executor(), executor_param, dvns, dvn_params)
}

Step 4: Workers Process Job Assignments

Executor Assignment:

/// From executor::assign_job()
public fun assign_job(
    self: &Executor,
    call: &mut Call<AssignJobParam, FeeRecipient>,
    ctx: &mut TxContext,
): Call<FeelibGetFeeParam, u64> {
    // Extract parameters
    let param = *call.param().base();

    // Create child call to fee library for fee calculation
    self.create_feelib_get_fee_call(call, param, ctx)
}

/// Executor confirms fee calculation
public fun confirm_assign_job(
    self: &Executor,
    executor_call: &mut Call<AssignJobParam, FeeRecipient>,
    feelib_call: Call<FeelibGetFeeParam, u64>,
) {
    // Destroy fee library call and extract fee
    let (_, _, fee) = executor_call.destroy_child(self.worker.worker_cap(), feelib_call);

    // Complete executor call with FeeRecipient
    executor_call.complete(
        self.worker.worker_cap(),
        fee_recipient::create(fee, self.worker.deposit_address())
    );
}

DVN Assignment (similar pattern):

/// From dvn::assign_job()
public fun assign_job(
    self: &DVN,
    call: &mut Call<DvnAssignJobParam, FeeRecipient>,
    ctx: &mut TxContext,
): Call<FeelibGetFeeParam, u64> {
    let param = *call.param().base();
    self.create_feelib_get_fee_call(call, param, ctx)
}

Step 5: ULN302 Confirms Send

The ULN302 destroys worker Call objects and aggregates fees:

/// From uln_302::confirm_send()
public fun confirm_send(
    self: &Uln302,
    endpoint: &EndpointV2,
    treasury: &Treasury,
    messaging_channel: &mut MessagingChannel,
    endpoint_call: &mut Call<EndpointSendParam, MessagingReceipt>,
    mut send_library_call: Call<MessageLibSendParam, MessageLibSendResult>,
    executor_call: Call<ExecutorAssignJobParam, FeeRecipient>,
    dvn_multi_call: MultiCall<DvnAssignJobParam, FeeRecipient>,
    ctx: &mut TxContext,
) {
    send_library_call.assert_caller(endpoint!());

    // Destroy DVN calls and collect fee recipients
    let (mut dvns, mut dvn_recipients) = (vector[], vector[]);
    dvn_multi_call.destroy(&self.call_cap).do!(|dvn_call| {
        let (dvn, _, dvn_recipient) = send_library_call.destroy_child(&self.call_cap, dvn_call);
        dvns.push_back(dvn);
        dvn_recipients.push_back(dvn_recipient);
    });

    // Destroy executor call and collect fee recipient
    let (executor, _, executor_recipient) = send_library_call.destroy_child(&self.call_cap, executor_call);

    // Calculate total fees and encoded packet
    let send_result = send_uln::confirm_send(
        send_library_call.param(),
        executor,
        executor_recipient,
        dvns,
        dvn_recipients,
        treasury,
    );
    send_library_call.complete(&self.call_cap, send_result);

    // Call endpoint for final confirmation
    let (native_token, zro_token) = endpoint.confirm_send(
        &self.call_cap,
        messaging_channel,
        endpoint_call,
        send_library_call,
        ctx,
    );

    // Distribute fees to workers
    send_uln::handle_fees(treasury, executor_recipient, dvn_recipients, native_token, zro_token, ctx);
}

Inside send_uln::confirm_send():

public(package) fun confirm_send(
    param: &MessageLibSendParam,
    executor: address,
    executor_recipient: FeeRecipient,
    dvns: vector<address>,
    dvn_recipients: vector<FeeRecipient>,
    treasury: &Treasury,
): MessageLibSendResult {
    let packet = param.base().packet();

    // Aggregate worker fees
    let mut native_recipients = vector[executor_recipient];
    native_recipients.append(dvn_recipients);

    let total_native_fee = native_recipients.fold!(0, |acc, r| acc + r.fee());

    // Calculate treasury fee
    let (treasury_recipient, zro_recipient) = treasury.quote_treasury_fee(
        packet.sender(),
        packet.dst_eid(),
        total_native_fee,
        param.base().pay_in_zro()
    );

    if (treasury_recipient.fee() > 0) {
        native_recipients.push_back(treasury_recipient);
    };

    let zro_recipients = if (zro_recipient.fee() > 0) {
        vector[zro_recipient]
    } else {
        vector[]
    };

    // Encode packet for event emission
    let encoded_packet = packet_v1_codec::encode_packet(packet);

    // Emit events
    event::emit(ExecutorFeePaidEvent { guid: packet.guid(), executor, fee: executor_recipient });
    event::emit(DVNFeePaidEvent { guid: packet.guid(), dvns, fees: dvn_recipients });

    // Return result with fee recipients
    message_lib_send::create_result(encoded_packet, native_recipients, zro_recipients)
}

Step 6: Endpoint Finalizes Send

/// From endpoint_v2::confirm_send()
public fun confirm_send(
    self: &EndpointV2,
    send_library: &CallCap,              // Library's capability (static call)
    messaging_channel: &mut MessagingChannel,
    endpoint_call: &mut Call<EndpointSendParam, MessagingReceipt>,
    send_library_call: Call<MessageLibSendParam, MessageLibSendResult>,
    ctx: &mut TxContext,
): (Coin<IOTA>, Coin<ZRO>) {
    messaging_channel.assert_ownership(endpoint_call.caller());

    // Destroy library call and extract results
    let (send_lib, param, result) = endpoint_call.destroy_child(&self.call_cap, send_library_call);
    assert!(send_lib == send_library.id(), EUnauthorizedSendLibrary);

    // Process fee payment and emit events
    let (receipt, paid_native_token, paid_zro_token) = messaging_channel.confirm_send(
        send_lib,
        endpoint_call.param_mut(&self.call_cap),
        param,
        result,
        ctx,
    );

    // Complete the Call with MessagingReceipt
    endpoint_call.complete(&self.call_cap, receipt);

    // Return collected fees for distribution
    (paid_native_token, paid_zro_token)
}

Inside messaging_channel.confirm_send():

public(package) fun confirm_send(
    self: &mut MessagingChannel,
    send_library: address,
    endpoint_param: &mut EndpointSendParam,
    message_lib_param: MessageLibSendParam,
    result: MessageLibSendResult,
    ctx: &mut TxContext,
): (MessagingReceipt, Coin<IOTA>, Coin<ZRO>) {
    // Extract fee recipients
    let (encoded_packet, native_recipients, zro_recipients) = result.destroy();

    // Calculate total fees required
    let total_native_fee = native_recipients.fold!(0, |acc, r| acc + r.fee());
    let total_zro_fee = zro_recipients.fold!(0, |acc, r| acc + r.fee());

    // Split coins from endpoint_param
    let paid_native = coin::split(endpoint_param.native_fee_mut(), total_native_fee, ctx);
    let paid_zro = if (total_zro_fee > 0) {
        coin::split(endpoint_param.lz_token_fee_mut().borrow_mut(), total_zro_fee, ctx)
    } else {
        coin::zero(ctx)
    };

    // Emit PacketSentEvent
    event::emit(PacketSentEvent {
        encoded_packet,
        options: *message_lib_param.base().options(),
        send_library,
    });

    // Create receipt
    let packet = message_lib_param.base().packet();
    let receipt = messaging_receipt::create(packet.guid(), packet.nonce(), total_native_fee, total_zro_fee);

    // Reset sending flag
    self.is_sending = false;

    (receipt, paid_native, paid_zro)
}

Step 7: OApp Extracts Receipt

The OApp confirms the send call to extract the receipt:

/// From oapp::confirm_lz_send()
public fun confirm_lz_send(
    self: &OApp,
    oapp_cap: &CallCap,
    call: Call<SendParam, MessagingReceipt>,
): (SendParam, MessagingReceipt) {
    self.assert_oapp_cap(oapp_cap);

    // Destroy the Call and extract results
    let (endpoint, param, receipt) = call.destroy(oapp_cap);
    assert!(endpoint == endpoint!(), EOnlyEndpoint);

    (param, receipt)
}

Example PTB for Send (from actual transaction)

Based on transaction HXZqH1RdANEkstz3MTFGMuLQ74CfgAkwQCq1YW8TMHHH:

// PTB commands in order:
SplitCoins - Split fee from sender's IOTA
MoveCall - bytes32::from_bytes (convert recipient to Bytes32)
MoveCall - send_param::create (create SendParam struct)
MoveCall - oft_sender::tx_sender (create OFTSender context)
SplitCoins - Split token amount from sender's coin
MoveCall - oft::send (initiate OFT send, returns Call)
MoveCall - endpoint::send (route Call to endpoint)
MoveCall - uln_302::send (create worker calls)
MoveCall - executor::assign_job (executor processes)
MoveCall - dvn::assign_job (each DVN processes)
MoveCall - executor::confirm_assign_job
MoveCall - dvn::confirm_assign_job (for each DVN)
MoveCall - uln_302::confirm_send
MoveCall - oft::confirm_send (extract receipt)

// Events emitted:
- ExecutorFeePaidEvent
- DVNFeePaidEvent
- PacketSentEvent
- OFTSentEvent

Send Limitations

Max Message Size

The maxMessageSize is configured per executor and OApp:

/// From ExecutorConfig struct
public struct ExecutorConfig has copy, drop, store {
    executor: address,        // Executor address
    max_message_size: u64,   // Maximum message bytes (default varies by network)
}

Default is typically 10,000 bytes, but OApps can configure custom limits.

Fee Payment Model

Unlike EVM’s direct fee transfer, IOTA uses Coin object splitting:

// Split exact fee amount from provided coins
let paid_native = coin::split(native_fee_coin, required_fee, ctx);

// Transfer to fee recipient
transfer::public_transfer(paid_native, recipient_address);

// Refund excess
transfer::public_transfer(remaining_coin, refund_address);

Verification Workflow

After the PacketSentEvent is emitted on the source chain, DVNs independently verify the message on the destination chain.

DVN Verification Process

Step 1: DVN Monitors Source Chain

DVNs watch for PacketSentEvent and wait for the configured number of block confirmations (finality).

Step 2: DVN Submits Verification

Each DVN calls the verify() function on the ULN302:

/// From uln_302::verify()
public fun verify(
    self: &Uln302,
    verification: &mut Verification,  // Shared verification object
    call: Call<DvnVerifyParam, Void>,
) {
    let dvn = call.caller();  // DVN's CallCap proves identity
    let param = call.complete_and_destroy(&self.call_cap);

    // Store verification in the Verification shared object
    receive_uln::verify(
        verification,
        dvn,
        *param.packet_header(),
        param.payload_hash(),
        param.confirmations()
    )
}

Inside receive_uln::verify():

/// From receive_uln::verify()
public(package) fun verify(
    self: &mut Verification,
    dvn: address,
    packet_header: vector<u8>,
    payload_hash: Bytes32,
    confirmations: u64,
) {
    // Create confirmation key
    let key = ConfirmationKey {
        header_hash: hash::keccak256!(&packet_header),
        payload_hash,
        dvn,
    };

    // Store confirmations in Table
    table_ext::upsert!(&mut self.confirmations, key, confirmations);

    // Emit event for monitoring
    event::emit(PayloadVerifiedEvent {
        dvn,
        header: packet_header,
        confirmations,
        proof_hash: payload_hash,
    });
}

Verification Storage:

/// Shared object storing all DVN confirmations
public struct Verification has key {
    id: UID,
    // Maps (header_hash, payload_hash, dvn) → confirmation_count
    confirmations: Table<ConfirmationKey, u64>,
}

Commit Verification

After sufficient DVNs have verified (meeting the X of Y of N threshold), anyone can call commit_verification():

/// From uln_302::commit_verification()
public fun commit_verification(
    self: &Uln302,
    endpoint: &EndpointV2,
    verification: &mut Verification,
    messaging_channel: &mut MessagingChannel,
    packet_header: vector<u8>,
    payload_hash: Bytes32,
    clock: &Clock,
) {
    // Verify and reclaim storage from Verification object
    let header = self.receive_uln.verify_and_reclaim_storage(
        verification,
        endpoint.eid(),
        packet_header,
        payload_hash,
    );

    // Call endpoint to insert verified payload hash
    endpoint.verify(
        &self.call_cap,              // Library capability
        messaging_channel,            // Destination OApp's channel
        header.src_eid(),             // Source endpoint ID
        header.sender(),              // Source OApp address
        header.nonce(),               // Message nonce
        payload_hash,                 // Payload hash
        clock,                        // For timeout validation
    );
}

Inside receive_uln::verify_and_reclaim_storage():

public(package) fun verify_and_reclaim_storage(
    self: &ReceiveUln,
    verification: &mut Verification,
    local_eid: u32,
    encoded_packet_header: vector<u8>,
    payload_hash: Bytes32,
): PacketHeader {
    // Decode and validate packet header
    let header = packet_v1_codec::decode_header(encoded_packet_header);
    assert!(header.dst_eid() == local_eid, EInvalidEid);

    let header_hash = hash::keccak256!(&encoded_packet_header);
    let receiver = header.receiver();
    let src_eid = header.src_eid();

    // Get effective ULN configuration
    let uln_config = self.get_uln_config(receiver, src_eid);

    // Check all required DVNs have verified
    let mut verified_count = 0;
    uln_config.required_dvns().do!(|dvn| {
        let key = ConfirmationKey { header_hash, payload_hash, dvn: *dvn };
        assert!(verification.confirmations.contains(key), EVerifying);

        // Remove confirmation (reclaim storage)
        verification.confirmations.remove(key);
        verified_count = verified_count + 1;
    });

    // Check optional DVN threshold is met
    if (uln_config.optional_dvn_count() > 0) {
        let mut optional_verified = 0;
        uln_config.optional_dvns().do!(|dvn| {
            let key = ConfirmationKey { header_hash, payload_hash, dvn: *dvn };
            if (verification.confirmations.contains(key)) {
                verification.confirmations.remove(key);
                optional_verified = optional_verified + 1;
            };
        });
        assert!(optional_verified >= uln_config.optional_dvn_threshold(), EVerifying);
    };

    header
}

Endpoint Verify

The Endpoint inserts the verified payload hash into the messaging channel:

/// From endpoint_v2::verify()
public fun verify(
    self: &EndpointV2,
    receive_library: &CallCap,          // Library's capability
    messaging_channel: &mut MessagingChannel,
    src_eid: u32,
    sender: Bytes32,
    nonce: u64,
    payload_hash: Bytes32,
    clock: &Clock,
) {
    // Validate receive library is authorized
    self.message_lib_manager.assert_receive_library(
        messaging_channel.oapp(),
        src_eid,
        receive_library.id(),
        clock
    );

    // Insert payload hash into messaging channel
    messaging_channel.verify(src_eid, sender, nonce, payload_hash);
}

Inside messaging_channel::verify():

public(package) fun verify(
    self: &mut MessagingChannel,
    src_eid: u32,
    sender: Bytes32,
    nonce: u64,
    payload_hash: Bytes32,
) {
    assert!(payload_hash != EMPTY_PAYLOAD_HASH, EInvalidPayloadHash);

    // Get or create channel for this pathway
    let channel_key = ChannelKey { remote_eid: src_eid, remote_oapp: sender };
    if (!self.channels.contains(channel_key)) {
        self.init_channel(src_eid, sender);
    };

    // Insert payload hash into the channel
    let channel = &mut self.channels[channel_key];
    channel.inbound_payload_hashes.add(nonce, payload_hash);

    // Emit verification event
    event::emit(PacketVerifiedEvent {
        src_eid,
        sender,
        nonce,
        receiver: self.oapp,
        payload_hash,
    });
}

Message State Transition:

Send → PacketSentEvent emitted on source chain
    ↓
DVNs monitor and verify (off-chain)
    ↓
DVNs call verify() (onchain submission)
    ↓
Verification confirmations stored in Verification object
    ↓
commit_verification() checks threshold
    ↓
Payload hash inserted into MessagingChannel
    ↓
Message ready for execution

Receive Workflow

After verification is committed, the Executor can deliver the message to the destination OApp.

Executor Delivery

The Executor initiates message delivery by constructing a PTB with all required objects.

Step 1: Executor Queries OApp Metadata

The Executor queries the OApp’s execution metadata to determine which objects are needed:

// OApp implements this to provide execution metadata
public fun get_oapp_info(oapp: &OApp): vector<u8> {
    // Returns encoded OAppInfoV1 containing required Move calls
}

Step 2: Executor Creates PTB

Based on the transaction 9fqmkJYFQyQs6u1vVmMSuqhZyobpSW7P4i7MaNVzbSFg, the PTB contains:

1. MoveCall - bytes32::from_bytes (decode sender)
2. MoveCall - bytes32::from_bytes (decode receiver)
3. MoveCall - option::none<Coin<IOTA>> (no value transfer)
4. MoveCall - executor_worker::execute_lz_receive (entry point)
5. MoveCall - counter::lz_receive (OApp business logic)

Objects passed:
- Executor shared object (immutable reference)
- Executor capability (owned object)
- EndpointV2 shared object (immutable reference)
- MessagingChannel shared object (mutable reference)
- Clock object (for validation)
- Counter OApp shared object (mutable reference)
- Counter Peer object (immutable reference)

Step 3: Executor Calls execute_lz_receive

/// From executor::execute_lz_receive()
public fun execute_lz_receive(
    self: &Executor,
    endpoint: &EndpointV2,
    messaging_channel: &mut MessagingChannel,
    src_eid: u32,
    sender: Bytes32,
    nonce: u64,
    guid: Bytes32,
    message: vector<u8>,
    extra_data: vector<u8>,
    value: Option<Coin<IOTA>>,
    ctx: &mut TxContext,
): Call<LzReceiveParam, Void> {
    // Create lz_receive call via endpoint
    endpoint.lz_receive(
        &self.worker.worker_cap(),  // Executor's capability
        messaging_channel,
        src_eid,
        sender,
        nonce,
        guid,
        message,
        extra_data,
        value,
        ctx,
    )
}

Step 4: Endpoint Creates lz_receive Call

/// From endpoint_v2::lz_receive()
public fun lz_receive(
    self: &EndpointV2,
    executor: &CallCap,              // Executor's capability
    messaging_channel: &mut MessagingChannel,
    src_eid: u32,
    sender: Bytes32,
    nonce: u64,
    guid: Bytes32,
    message: vector<u8>,
    extra_data: vector<u8>,
    value: Option<Coin<IOTA>>,
    ctx: &mut TxContext,
): Call<LzReceiveParam, Void> {
    // Clear the payload first (prevents reentrancy)
    messaging_channel.clear(src_eid, sender, nonce, guid, &message);

    // Create lz_receive parameters
    let lz_receive_param = lz_receive::create_param(
        src_eid,
        sender,
        nonce,
        guid,
        message,
        extra_data,
        value,
    );

    // Create Call object targeting the OApp
    call::create(
        executor,                      // Executor creates the Call
        messaging_channel.oapp(),      // Target: OApp address
        true,                          // One-way call (no result expected)
        lz_receive_param,
        ctx,
    )
}

Inside messaging_channel::clear():

public(package) fun clear(
    self: &mut MessagingChannel,
    src_eid: u32,
    sender: Bytes32,
    nonce: u64,
    guid: Bytes32,
    message: &vector<u8>,
) {
    let channel_key = ChannelKey { remote_eid: src_eid, remote_oapp: sender };
    let channel = &mut self.channels[channel_key];

    // Lazy nonce update: clear all messages up to this nonce
    if (nonce > channel.lazy_inbound_nonce) {
        let mut i = channel.lazy_inbound_nonce + 1;
        while (i <= nonce) {
            assert!(channel.inbound_payload_hashes.contains(i), EInvalidNonce);
            i = i + 1;
        };
        channel.lazy_inbound_nonce = nonce;
    };

    // Verify payload hash matches verified hash
    let expected_hash = channel.inbound_payload_hashes[nonce];
    let actual_hash = hash::keccak256!(&vector[guid.data(), *message]);
    assert!(expected_hash == actual_hash, EPayloadHashNotFound);

    // Remove from storage (prevents double execution)
    channel.inbound_payload_hashes.remove(nonce);

    // Emit delivery event
    event::emit(PacketDeliveredEvent {
        src_eid,
        sender,
        receiver: self.oapp,
        nonce,
    });
}

Key Security Features:

Lazy nonce validation: Ensures all prior messages have been verified
Payload hash verification: Confirms executor provided the correct message
Storage cleanup: Removes hash to prevent double execution
Event emission: Signals successful delivery

Step 5: OApp Processes Message

The OApp’s lz_receive() function is invoked via the Call object:

/// Example from counter OApp
public fun lz_receive(
    self: &mut Counter,
    peer: &Peer,
    call: Call<LzReceiveParam, Void>,
) {
    // Validate Call came from Endpoint
    let (callee, param, _) = call.complete_and_destroy(&self.call_cap);
    assert!(callee == endpoint_address(), EOnlyEndpoint);

    // Validate sender is configured peer
    assert!(param.sender() == peer.address, EOnlyPeer);

    // Process message (application-specific logic)
    self.count = self.count + 1;

    // Note: No need to manually call clear() - already done by Endpoint
}

OApp Responsibilities:

- Validate Call came from authorized Endpoint
- Validate sender matches configured peer
- Process message and update state
- No need to call clear() (done by Endpoint before Call creation)

Example PTB for Receive (from actual transaction)

Based on transaction 9fqmkJYFQyQs6u1vVmMSuqhZyobpSW7P4i7MaNVzbSFg:

// PTB commands in order:
1. MoveCall - bytes32::from_bytes (decode sender parameter)
2. MoveCall - bytes32::from_bytes (decode guid parameter)
3. MoveCall - option::none<Coin<IOTA>> (no native token transfer)
4. MoveCall - executor_worker::execute_lz_receive
   - Passes: Executor, Endpoint, MessagingChannel, src_eid, sender, nonce, guid, message
   - Returns: Call<LzReceiveParam, Void>
5. MoveCall - counter::lz_receive
   - Receives the Call object
   - Validates and processes
   - Destroys the Call

Objects used:
- 0x5f24...0c8e: Executor shared object (immutable)
- 0x00a7...9fc2: Executor CallCap (owned)
- 0xd45b...bf91: EndpointV2 shared object (immutable)
- 0x9b01...1843: MessagingChannel shared object (mutable)
- 0x6903...8c4d: Counter OApp shared object (mutable)
- 0x224b...fbb3: Counter Peer shared object (immutable)
- 0x608a...6f27: Counter's internal state (mutable)

// Events emitted:
- PacketDeliveredEvent

Key IOTA-Specific Patterns

Object Ownership in Message Flow

Object Type	Ownership	Access Pattern	Example
`EndpointV2`	Shared	Anyone reads, admin writes	`&EndpointV2` or `&mut EndpointV2`
`MessagingChannel`	Shared	Anyone reads, owner writes	`&mut MessagingChannel`
`OApp`	Shared	Anyone reads, admin writes	`&mut OApp`
`CallCap`	Owned	Must own to use	Owned by OApp module or user
`AdminCap`	Owned	Must own to use	Owned by admin address
`Call<P, R>`	Neither	Must be consumed in PTB	Created and destroyed in same TX

Call Pattern vs EVM/Solana

Aspect	EVM	Solana	IOTA
Cross-Contract Calls	`delegatecall`	CPI (Cross-Program Invocation)	`Call<Param, Result>` objects
Authorization	`msg.sender`	Signer checks + PDAs	`CallCap` validation
Return Values	Function returns	CPI returns	`Call.complete()` sets result
Call Hierarchy	Call stack (implicit)	CPI depth limit (4)	`Call` parent/child relationships
Atomicity	Transaction revert	Transaction revert	PTB revert

Nonce Management

EVM:

// Mapping-based nonce storage
mapping(address => mapping(uint32 => mapping(bytes32 => uint64))) outboundNonce;

Solana:

// PDA account per pathway
#[account(seeds = [NONCE_SEED, sender, dst_eid, receiver], bump)]
pub nonce: Account<'info, Nonce>,

IOTA:

// Table within MessagingChannel, nested in Channel struct
public struct MessagingChannel has key {
    channels: Table<ChannelKey, Channel>,  // Maps (eid, remote_oapp) → Channel
}

public struct Channel has store {
    outbound_nonce: u64,           // Incremented on each send
    lazy_inbound_nonce: u64,       // Last executed inbound nonce
    inbound_payload_hashes: Table<u64, Bytes32>,  // Maps nonce → hash
}

Fee Payment Model

EVM:

// Direct transfer in msg.value
Transfer.native(executor, executorFee);

Solana:

// Token account transfer
transfer(from_account, to_account, amount);

IOTA:

// Coin object splitting and transfer
let fee_coin = coin::split(&mut provided_coin, fee_amount, ctx);
transfer::public_transfer(fee_coin, recipient_address);

Configuration Management

Send Library Configuration

OApps can set custom send libraries per destination:

/// From endpoint_v2 (called by OApp with AdminCap)
public fun set_send_library(
    self: &mut EndpointV2,
    caller: &CallCap,
    oapp: address,
    dst_eid: u32,
    new_lib: address,
) {
    self.assert_authorized(caller.id(), oapp);
    self.message_lib_manager.set_send_library(oapp, dst_eid, new_lib);
}

Default Fallback:

/// From message_lib_manager
public(package) fun get_send_library(
    self: &MessageLibManager,
    sender: address,
    dst_eid: u32,
): (address, bool) {
    // Try OApp-specific config first
    let key = SendLibraryKey { sender, dst_eid };
    if (self.send_libraries.contains(key)) {
        return (self.send_libraries[key], false)  // Custom library
    };

    // Fall back to default
    let default_lib = self.default_send_libraries[dst_eid];
    (default_lib, true)  // Default library
}

DVN Configuration

OApps configure DVN sets through the ULN:

/// ULN configuration structure
public struct UlnConfig has copy, drop, store {
    confirmations: u64,                 // Block confirmations required
    required_dvn_count: u8,             // Number of required DVNs
    optional_dvn_count: u8,             // Number of optional DVNs
    optional_dvn_threshold: u8,         // How many optional DVNs must verify
    required_dvns: vector<address>,     // Required DVN addresses
    optional_dvns: vector<address>,     // Optional DVN addresses
}

Setting Configuration (via Endpoint):

/// From endpoint_v2::set_config()
public fun set_config(
    self: &mut EndpointV2,
    caller: &CallCap,                  // OApp or delegate
    oapp: address,
    config_type: u32,
    eid: u32,
    config: vector<u8>,
    ctx: &mut TxContext,
) {
    self.assert_authorized(caller.id(), oapp);

    // Get message library
    let (lib, _) = if (is_send_config(config_type)) {
        self.message_lib_manager.get_send_library(oapp, eid)
    } else {
        self.message_lib_manager.get_receive_library(oapp, eid, clock)
    };

    // Create Call to library's set_config
    let set_config_param = message_lib_set_config::create_param(oapp, config_type, eid, config);
    let call = call::create(caller, lib, true, set_config_param, ctx);

    // Library processes configuration immediately (one-way call)
    // No confirmation needed
}

Recovery Operations

The Endpoint provides several recovery mechanisms for stuck or problematic messages.

Skip

Increments the lazy nonce without executing the message:

/// From endpoint_v2::skip()
public fun skip(
    self: &EndpointV2,
    caller: &CallCap,
    messaging_channel: &mut MessagingChannel,
    src_eid: u32,
    sender: Bytes32,
    nonce: u64,
) {
    self.assert_authorized(caller.id(), messaging_channel.oapp());
    messaging_channel.skip(src_eid, sender, nonce);
}

Inside messaging_channel::skip():

public(package) fun skip(
    self: &mut MessagingChannel,
    src_eid: u32,
    sender: Bytes32,
    nonce: u64,
) {
    let channel_key = ChannelKey { remote_eid: src_eid, remote_oapp: sender };
    let channel = &mut self.channels[channel_key];

    // Validate nonce is next expected
    assert!(nonce == channel.lazy_inbound_nonce + 1, EInvalidNonce);

    // Increment lazy nonce (skipping this message)
    channel.lazy_inbound_nonce = nonce;

    event::emit(InboundNonceSkippedEvent {
        src_eid,
        sender,
        receiver: self.oapp,
        nonce,
    });
}

Nilify

Removes verification but keeps nonce ordering:

public fun nilify(
    self: &EndpointV2,
    caller: &CallCap,
    messaging_channel: &mut MessagingChannel,
    src_eid: u32,
    sender: Bytes32,
    nonce: u64,
    payload_hash: Bytes32,
) {
    self.assert_authorized(caller.id(), messaging_channel.oapp());
    messaging_channel.nilify(src_eid, sender, nonce, payload_hash);
}

Burn

Permanently blocks a nonce (irreversible):

public fun burn(
    self: &EndpointV2,
    caller: &CallCap,
    messaging_channel: &mut MessagingChannel,
    src_eid: u32,
    sender: Bytes32,
    nonce: u64,
    payload_hash: Bytes32,
) {
    self.assert_authorized(caller.id(), messaging_channel.oapp());
    messaging_channel.burn(src_eid, sender, nonce, payload_hash);
}

Comparison with EVM and Solana

Architecture Comparison

Component	EVM	Solana	IOTA
Code Organization	Solidity contracts	Rust programs	Move packages/modules
State Storage	Contract storage slots	PDA accounts	Shared/owned objects
Nonce Management	Nested mappings	PDA per pathway	Table in MessagingChannel
Message Channel	Contract storage	PDA accounts	MessagingChannel shared object
Call Pattern	delegatecall	CPI	`Call<Param, Result>` objects
Authorization	msg.sender	Signers + PDA derivation	CallCap validation
Fee Payment	msg.value transfer	Token account ops	Coin object splitting
Atomicity	Transaction revert	Transaction revert	PTB revert

Send Flow Comparison

Step	EVM	Solana	IOTA
Initiate	OApp.send() internal	OApp CPI to Endpoint	OApp creates Call object
Nonce	Mapping increment	PDA account write	Table field increment
Library Call	Direct function call	CPI to SendUln302	Child Call creation
Worker Calls	Direct function calls	CPI to each worker	Child Call per worker
Fee Collection	Transfer to library	Record in library	Coin splitting
Event	`emit PacketSent`	`emit_cpi!(PacketSent)`	`event::emit(PacketSent)`

Receive Flow Comparison

Step	EVM	Solana	IOTA
Entry Point	Executor calls Endpoint.lzReceive	Executor invokes with all accounts	Executor calls execute_lz_receive
Clear Payload	Endpoint clears before calling OApp	OApp CPIs back to Endpoint.clear	Endpoint clears before creating Call
OApp Invocation	delegatecall to OApp.lzReceive	Instruction with account list	Call object to OApp module
Validation	Modifier checks	Account constraints + CPI auth	Call validation + peer check
Processing	Override _lzReceive	Implement lz_receive instruction	Implement lz_receive function

Event Monitoring

Events Emitted During Send

ExecutorFeePaidEvent (from ULN):

public struct ExecutorFeePaidEvent has copy, drop {
    guid: Bytes32,
    executor: address,
    fee: FeeRecipient,
}

DVNFeePaidEvent (from ULN):

public struct DVNFeePaidEvent has copy, drop {
    guid: Bytes32,
    dvns: vector<address>,
    fees: vector<FeeRecipient>,
}

PacketSentEvent (from MessagingChannel):

public struct PacketSentEvent has copy, drop {
    encoded_packet: vector<u8>,  // Full packet with header + payload
    options: vector<u8>,          // Execution options
    send_library: address,        // Library that processed send
}

OFTSentEvent (from OFT, if applicable):

public struct OFTSentEvent has copy, drop {
    guid: Bytes32,
    dst_eid: u32,
    from_address: address,
    amount_sent_ld: u64,        // Amount in local decimals
    amount_received_ld: u64,    // Amount after dust removal
}

Events Emitted During Verification

PayloadVerifiedEvent (per DVN):

public struct PayloadVerifiedEvent has copy, drop {
    dvn: address,
    header: vector<u8>,
    confirmations: u64,
    proof_hash: Bytes32,
}

PacketVerifiedEvent (after commit):

public struct PacketVerifiedEvent has copy, drop {
    src_eid: u32,
    sender: Bytes32,
    nonce: u64,
    receiver: address,
    payload_hash: Bytes32,
}

Events Emitted During Receive

PacketDeliveredEvent:

public struct PacketDeliveredEvent has copy, drop {
    src_eid: u32,
    sender: Bytes32,
    receiver: address,
    nonce: u64,
}

OFTReceivedEvent (from OFT, if applicable):

public struct OFTReceivedEvent has copy, drop {
    guid: Bytes32,
    src_eid: u32,
    to_address: address,
    amount_received_ld: u64,
}

Capabilities and Authorization

CallCap Pattern

CallCap is IOTA’s capability-based authorization for creating Call objects:

/// From call_cap module
public struct CallCap has key, store {
    id: UID,
    package_id: address,  // Package that owns this capability
}

/// Create a package-level CallCap using one-time witness
public fun new_package_cap<T: drop>(otw: &T, ctx: &mut TxContext): CallCap {
    CallCap {
        id: object::new(ctx),
        package_id: package::from_witness(otw),
    }
}

Usage in Validation:

/// OApp validates its CallCap
fun assert_oapp_cap(self: &OApp, cap: &CallCap) {
    assert!(self.oapp_cap.id() == cap.id(), EInvalidOAppCap);
}

/// Endpoint validates library CallCap
fun assert_send_library(lib_cap: &CallCap, expected_lib: address) {
    assert!(lib_cap.id() == expected_lib, EUnauthorizedSendLibrary);
}

AdminCap Pattern

AdminCap authorizes administrative operations:

public struct AdminCap has key, store {
    id: UID,
}

/// Setting a peer requires AdminCap
public fun set_peer(
    self: &mut OApp,
    admin_cap: &AdminCap,  // Must own this object
    eid: u32,
    peer: Bytes32,
) {
    // AdminCap ownership proves authorization
    self.peer.set_peer(self.oapp_object_address(), eid, peer);
}

Ownership Transfer:

// Transfer AdminCap to new admin
transfer::public_transfer(admin_cap, new_admin_address);

PTB Construction Patterns

Simple Send PTB

const tx = new Transaction();

// 1. Split fee from gas coin
const [feeCoin] = tx.splitCoins(tx.gas, [tx.pure.u64(feeAmount)]);

// 2. Create send parameters
const sendParam = tx.moveCall({
  target: `${oappPackage}::oapp::create_send_param`,
  arguments: [
    tx.pure.u32(dstEid),
    tx.pure.vector('u8', receiverBytes),
    tx.pure.vector('u8', messageBytes),
    tx.pure.vector('u8', optionsBytes),
    feeCoin,
    tx.pure.option('object', null), // No ZRO payment
    tx.pure.address(refundAddress),
  ],
});

// 3. Call OApp send (returns Call object)
const sendCall = tx.moveCall({
  target: `${oappPackage}::oapp::send`,
  arguments: [tx.object(oappObjectId), tx.object(callCapObjectId), sendParam],
});

// 4. Route through Endpoint (processes Call)
const libCall = tx.moveCall({
  target: `${endpointPackage}::endpoint_v2::send`,
  arguments: [tx.object(endpointObjectId), tx.object(messagingChannelId), sendCall],
});

// 5-N. Worker assignments (handled by PTB builder)

// N+1. Confirm send (destroys Call, extracts receipt)
tx.moveCall({
  target: `${oappPackage}::oapp::confirm_lz_send`,
  arguments: [
    tx.object(oappObjectId),
    tx.object(callCapObjectId),
    sendCall, // Original Call object (now completed)
  ],
});

await client.signAndExecuteTransaction({transaction: tx});

Receive PTB

const tx = new Transaction();

// 1. Decode parameters
const senderBytes32 = tx.moveCall({
  target: `${utilsPackage}::bytes32::from_bytes`,
  arguments: [tx.pure.vector('u8', senderBytes)],
});

const guidBytes32 = tx.moveCall({
  target: `${utilsPackage}::bytes32::from_bytes`,
  arguments: [tx.pure.vector('u8', guidBytes)],
});

// 2. Create empty value option (no native transfer)
const noValue = tx.moveCall({
  target: '0x1::option::none',
  typeArguments: ['0x2::coin::Coin<0x2::iota::SUI>'],
  arguments: [],
});

// 3. Execute lz_receive via Executor
const lzReceiveCall = tx.moveCall({
  target: `${executorPackage}::executor_worker::execute_lz_receive`,
  arguments: [
    tx.object(executorObjectId), // Executor shared object
    tx.object(executorCapId), // Executor CallCap
    tx.object(endpointObjectId), // Endpoint shared object
    tx.object(messagingChannelId), // Messaging channel
    tx.pure.u32(srcEid),
    senderBytes32,
    tx.pure.u64(nonce),
    guidBytes32,
    tx.pure.vector('u8', messageBytes),
    tx.pure.vector('u8', extraDataBytes),
    noValue,
  ],
});

// 4. OApp processes (receives Call object from step 3)
tx.moveCall({
  target: `${oappPackage}::counter::lz_receive`,
  arguments: [
    tx.object(counterObjectId), // OApp shared object
    tx.object(peerObjectId), // Peer validation
    lzReceiveCall, // Call from executor
  ],
});

await client.signAndExecuteTransaction({transaction: tx});

IOTA-Specific Considerations

Object Abilities

IOTA’s ability system controls what can be done with types:

Ability	Meaning	LayerZero Usage
`key`	Can be stored at top-level	`OApp`, `EndpointV2`, `AdminCap`
`store`	Can be stored in other structs	`Peer`, `Channel`, `UlnConfig`
`copy`	Can be copied	`ChannelKey`, `MessagingFee`
`drop`	Can be ignored/discarded	One-time witnesses, config structs

Call Object Abilities:

public struct Call<Param, Result> {
    // Has NO abilities - cannot be dropped or stored
    // Must be explicitly destroyed via destroy() or complete_and_destroy()
}

This enforces the hot potato pattern—Call objects must be handled.

Phantom Type Parameters

IOTA uses phantom type parameters for type safety without storage:

/// OFT uses phantom T for the coin type
public struct OFT<phantom T> has key {
    id: UID,
    treasury: OFTTreasury<T>,  // T only appears in nested types
    // ...
}

/// TreasuryCap also uses phantom T
public struct TreasuryCap<phantom T> has key, store {
    id: UID,
    total_supply: Supply<T>,
}

The phantom keyword means T is for type safety only—not stored directly.

Table vs Vector

IOTA uses Table<K, V> for dynamic key-value storage:

/// Peer mappings by EID
public struct Peer has store {
    peers: Table<u32, Bytes32>,  // EID → peer address
}

/// vs fixed-size vector
required_dvns: vector<address>,  // Known size, stored directly

Trade-offs:

Table: Dynamic size, gas per access, better for sparse data
vector: Fixed size, cheaper access, better for dense data

Summary

LayerZero on IOTA achieves crosschain messaging through:

Object-Based State: Shared objects (EndpointV2, MessagingChannel, OApp) enable parallel execution
Capability Authorization: CallCap and AdminCap replace msg.sender checks
Call Pattern: Call<Param, Result> objects enable dynamic routing without delegatecall
PTB Composition: Atomic multi-step workflows ensure message integrity
Type Safety: Move’s ability system and phantom types provide compile-time guarantees

Key Differences from Other VMs:

No inheritance (explicit capability validation)
No dynamic dispatch (Call pattern workaround)
Object ownership model (shared vs owned vs immutable)
Coin object model (split/merge instead of balance transfer)
Table-based storage (not mappings or PDAs)

For implementation guides and code examples, see:

OApp Implementation - Build custom crosschain applications
OFT Implementation - Deploy crosschain tokens
OFT SDK - Complete SDK methods and patterns
Configuration Guide - DVN, executor, and gas configuration
Technical Overview - IOTA fundamentals and architecture

​Prerequisites

​Send Overview

​Endpoint Send

​EndpointV2 Shared Object

​MessagingChannel per OApp

​Step 1: OApp Creates Send Call

​Step 2: Endpoint Processes Send

​Step 3: ULN302 Assigns Jobs to Workers

​Step 4: Workers Process Job Assignments

​Step 5: ULN302 Confirms Send

​Step 6: Endpoint Finalizes Send

​Step 7: OApp Extracts Receipt

​Example PTB for Send (from actual transaction)

​Send Limitations

​Max Message Size

​Fee Payment Model

​Verification Workflow

​DVN Verification Process

​Step 1: DVN Monitors Source Chain

​Step 2: DVN Submits Verification

​Commit Verification

​Endpoint Verify

​Receive Workflow

​Executor Delivery

​Step 1: Executor Queries OApp Metadata

​Step 2: Executor Creates PTB

​Step 3: Executor Calls execute_lz_receive

​Step 4: Endpoint Creates lz_receive Call

​Step 5: OApp Processes Message

​Example PTB for Receive (from actual transaction)

​Key IOTA-Specific Patterns

​Object Ownership in Message Flow

​Call Pattern vs EVM/Solana

​Nonce Management

​Fee Payment Model

​Configuration Management

​Send Library Configuration

​DVN Configuration

​Recovery Operations

​Skip

​Nilify

​Burn

​Comparison with EVM and Solana

​Architecture Comparison

​Send Flow Comparison

​Receive Flow Comparison

​Event Monitoring

​Events Emitted During Send

​Events Emitted During Verification

​Events Emitted During Receive

​Capabilities and Authorization

​CallCap Pattern

​AdminCap Pattern

​PTB Construction Patterns

​Simple Send PTB

​Receive PTB

​IOTA-Specific Considerations

​Object Abilities

​Phantom Type Parameters

​Table vs Vector

​Summary

Prerequisites

Send Overview

Endpoint Send

EndpointV2 Shared Object

MessagingChannel per OApp

Step 1: OApp Creates Send Call

Step 2: Endpoint Processes Send

Step 3: ULN302 Assigns Jobs to Workers

Step 4: Workers Process Job Assignments

Step 5: ULN302 Confirms Send

Step 6: Endpoint Finalizes Send

Step 7: OApp Extracts Receipt

Example PTB for Send (from actual transaction)

Send Limitations

Max Message Size

Fee Payment Model

Verification Workflow

DVN Verification Process

Step 1: DVN Monitors Source Chain

Step 2: DVN Submits Verification

Commit Verification

Endpoint Verify

Receive Workflow

Executor Delivery

Step 1: Executor Queries OApp Metadata

Step 2: Executor Creates PTB

Step 3: Executor Calls execute_lz_receive

Step 4: Endpoint Creates lz_receive Call

Step 5: OApp Processes Message

Example PTB for Receive (from actual transaction)

Key IOTA-Specific Patterns

Object Ownership in Message Flow

Call Pattern vs EVM/Solana

Nonce Management

Fee Payment Model

Configuration Management

Send Library Configuration

DVN Configuration

Recovery Operations

Skip

Nilify

Burn

Comparison with EVM and Solana

Architecture Comparison

Send Flow Comparison

Receive Flow Comparison

Event Monitoring

Events Emitted During Send

Events Emitted During Verification

Events Emitted During Receive

Capabilities and Authorization

CallCap Pattern

AdminCap Pattern

PTB Construction Patterns

Simple Send PTB

Receive PTB

IOTA-Specific Considerations

Object Abilities

Phantom Type Parameters

Table vs Vector

Summary