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Version: Endpoint V2 Docs

Message Send Library

The Message Send Library is a core component of the LayerZero protocol that manages the internal mechanics of sending messages between blockchain networks. It functions as a dedicated message handler and routing contract that connects high-level application logic with the low-level workers responsible for cross-chain communication.

What Is a Message Send Library?​

The Message Send Library is responsible for several key tasks that enable reliable message delivery:

  • Encoding Packets: It packages outgoing message packets from the LayerZero Endpoint by encoding the unique identifiers, nonces (which help maintain the correct order), and other metadata. This process ensures that each message is uniquely identifiable and traceable across networks.

  • Calculating Fees: While processing a packet, the library computes and returns fee details back to the endpoint based on the worker settings defined by the application. This ensures that all cost-related aspects of message delivery are handled accurately.

  • Managing Configuration: Applications set configuration parameters via the LayerZero Endpoint, which are then applied to the library’s internal worker logic. This means that the library processes messages based on custom application settings for routing and fee management.

The Message Send Library acts as a specialized routing contract to direct how packets are encoded, how fees are computed, and how configurations shape the overall message delivery process.

How It Fits Into the Protocol​

LayerZero’s design splits the cross-chain messaging process into clear, sequential steps:

Send Model Flow:
Application → Endpoint → Message Send Library → Workers

  1. Application: The sender smart contract initiates a message for a fee.

  2. Endpoint: Acting as the entrypoint, the endpoint moves the message inside a packet, and leverages the application’s settings to determine which Message Send Library to invoke.

  3. Message Send Library: The library processes the packet by encoding it, calculating fees for the given configuration settings, and routing the encodedPacket to the appropriate workers.

  4. Workers: These service providers handle the actual transmission and execution of the encodedPacket, ensuring it reaches its intended destination.

Send Ultra Light Node (ULN)​

A specialized version of the Message Library is the Ultra Light Node (ULN). A ULN focuses on efficiently streaming and encoding only the critical packet headers along with the application's message. In other words, while every Message Library can define its own outbound message encoding, the ULN variant is tailored for push-based messaging to a destination chain.

The ULN concept borrows from the idea of a Light Node in blockchain systems, which processes only block headers rather than entire blocks. Similarly, the ULN transmits a specific, optimized encoded format called the encodedPacket. This format is constructed in two key steps:

Message Encoding with ULN​

  1. Packet Header Encoding:
    The ULN first creates a concise header containing vital routing and identification information. This includes:

    • Version Information: To ensure consistent interpretation of the packet.

    • Nonce: To maintain the correct order of messages.

    • Source and Destination Information: Such as endpoint identifiers and sender/receiver contract addresses.

    This header functions as a roadmap for subsequent processing by workers.

  2. Payload Encoding:
    Next, the ULN encodes the remaining contents of the protocol packet. In this context:

    • The Application's Message: Represents the actual content sent by the application.

    • GUID: A global unique identifier that ties the message to its metadata.

    The ULN combines these two components (packetHeader and payload) to create the final encodedPacket. This composite packet includes both the serialized header (providing essential metadata) and the payload (containing the GUID and the actual message), enabling downstream workers to efficiently process and verify the message.

You can see how these data structures differ under Message, Packet, and Payload.

Key Takeaways​

  • Adaptability: The overall encoding process is flexible. Different Message Libraries can adopt their own strategies based on performance or security considerations. The ULN is just one example that emphasizes efficiency by transmitting minimal yet critical data.

  • Future-Proofing: This modular approach to encoding allows for technological advancements to be integrated into the protocol without disrupting existing application logic.

In Summary​

  • Purpose: The Message Send Library manages the processes of encoding, configuring, and fee-calculating messages within the LayerZero protocol.

  • Function: Acting as a dedicated handler and routing contract, it bridges the gap between applications and the underlying message workers, ensuring proper packaging and delivery.

  • Design: By clearly separating responsibilities, the protocol remains modular and adaptable. The ULN exemplifies how a specialized Message Library can optimize for specific functions, such as ultra-lightweight packet header transmission.

  • User Benefit: For developers and end-users, this robust, configurable routing mechanism simplifies cross-chain communication while ensuring high efficiency and security.