Message Handling

The Vara network allows users and programs to interact with other users and programs via messages. Messages can contain a payload that will be able to be processed during message execution. Interaction with messages is possible thanks to the module gstd::msg:

use gstd::msg;

Message processing is possible only inside the defined functions init(), handle(), hadle_reply(), and state() (more details about the state() function will be later). They also define the context for processing such messages.

The common way to get input data is to use the msg::load_bytes / msg::load functions. The first function loads the payload of the message as a byte vector. The second function loads the payload of the message as a structure that derives the Decode trait. Actually, the second function is a wrapper around the first one that decodes the byte vector into the structure.

Example of getting a payload of the message currently being processed and decode it:

#![no_std]
use gstd::{msg, prelude::*};

#[no_mangle]
extern "C" fn handle() {
    let payload_string: String = msg::load().expect("Unable to decode `String`");
}

Replying to the incoming message is possible by using the msg::reply_bytes / msg::reply functions. The first function sends a byte sequence as a reply to the message that was received by the program. The second function sends a structure that derives the Encode trait. Actually, the second function is a wrapper around the first one that encodes the structure into the byte vector.

Example of replying to the message currently being processed:

#![no_std]
use gstd::msg;

#[no_mangle]
extern "C" fn handle() {
    msg::reply("PONG", 0).expect("Unable to reply");
}

Sending messages to other programs or users is possible by using the msg::send_bytes / msg::send functions. The first function sends a byte sequence to a program or user. The second function sends a structure that derives the Encode trait.

Example of sending a message to a program or user:

#![no_std]
use gstd::{msg, prelude::*};

#[no_mangle]
extern "C" fn handle() {
    // ...
    let id = msg::source();
    let message_string = "Hello there".to_string();
    msg::send(id, message_string, 0).expect("Unable to send message");
}