solana/sdk/program/src/message/mod.rs

//! A library for generating a message from a sequence of instructions

mod legacy;
mod v0;
mod versions;

pub use legacy::Message;
pub use versions::MESSAGE_VERSION_PREFIX;

pub const MESSAGE_HEADER_LENGTH: usize = 3;

#[derive(Serialize, Deserialize, Default, Debug, PartialEq, Eq, Clone, AbiExample)]
#[serde(rename_all = "camelCase")]
pub struct MessageHeader {
    /// The number of signatures required for this message to be considered valid. The
    /// signatures must match the first `num_required_signatures` of `account_keys`.
    /// NOTE: Serialization-related changes must be paired with the direct read at sigverify.
    pub num_required_signatures: u8,

    /// The last num_readonly_signed_accounts of the signed keys are read-only accounts. Programs
    /// may process multiple transactions that load read-only accounts within a single PoH entry,
    /// but are not permitted to credit or debit lamports or modify account data. Transactions
    /// targeting the same read-write account are evaluated sequentially.
    pub num_readonly_signed_accounts: u8,

    /// The last num_readonly_unsigned_accounts of the unsigned keys are read-only accounts.
    pub num_readonly_unsigned_accounts: u8,
}