Message Dispatch

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In src/cmd/main.cpp, we assign Zilliqa::Dispatch as the dispatcher inside P2PComm::StartMessagePump. Every message that is read from a socket by P2PComm then gets sent to Zilliqa::Dispatch.

When Zilliqa starts to process a message, it will call Zilliqa::ProcessMessage. The first byte of any message defines the message type.

Note

The “first byte” here refers to the payload part of a socket message. At the P2PComm level, each socket message consists of a predefined header plus the payload.

Depending on the type, Zilliqa::ProcessMessage will forward the message to the appropriate handler for it. The list of message types can be found in enum MessageType inside src/common/Messages.h.

Any class that inherits from Executable will be a message handler. For example, type 0x01 means DIRECTORY, and this message will be handled by libDirectoryService. If you go into libDirectoryService, you will find a function DirectoryService::Execute.

All classes that inherit from Executable will first check the second byte in the message, which defines the instruction type. The list of instruction types can be found in src/common/Messages.h.

From there, Execute() will further forward the message to a private function inside the class, and these functions are all named ProcessXXX.