The sample contract serves as a demonstration of general QVM logic.
It is capable of:
registering users into the database
storing the last registered user's name in the database
echoing the previous user's name to STDOUT
incrementing the total registered user count
storing above counter in the database
Sample smart contract code
use std::env;
fn get_env(key: String, default: String) -> String {
env::var(key).unwrap_or(default)
}
fn atoi(val: String) -> i32 {
val.parse().unwrap_or(0)
}
fn main() {
let args: Vec<String> = env::args().collect();
// THIS SAMPLE ONLY SUPPORTS THE "register" FUNCTION
if args.len() == 3 && args[1] == "register" {
// GET THE CURRENT USER'S NAME OR DEFAULT TO "unknown" IF THIS IS THE FIRST CALL
let previous_name = get_env("DB_USER_CURRENT".to_string(),"unknown".to_string());
// GET THE TOTAL USER COUNT
let total_user_count= atoi(get_env("DB_TOTALUSERS".to_string(),"0".to_string()));
// WRITE PREVIOUS USER NAME TO STDOUT
println!("OUT=prevname: {}", previous_name);
// UPDATE CURRENT USER NAME BY WRITING IT TO DB
println!("DBW=USER_CURRENT={}", args[2]);
// STORE USER NAME UNDER A STORAGE SLOT FOR PERSISTENCE (CURRENT GETS OVERWRITTEN ON EACH CALL)
println!("DBW=USER_{}={}", total_user_count, args[2]);
// INCREMENT THE TOTAL USER COUNT
println!("DBW=TOTALUSERS={}", total_user_count+1);
std::process::exit(0);
}
if args.len() >= 2 {
eprintln!("Wrong CMD: {}", args[1]);
std::process::exit(1);
}
eprintln!("Wrong args!");
std::process::exit(1);
}
Save the smart contract
Open a text editor and save above sample contract as main.rs file.
