How get module hash in motoko?

Developers
1

I’d like to know how we get module hash in motoko. I tried to get module hash using management canister “aaaaa-aa”, but it always returned null.
This is my code.

import Principal "mo:base/Principal";
import Canister "./Canister";
import Cycles "mo:base/ExperimentalCycles";


actor class ModuleHash() = this {
    let IC0 = actor("aaaaa-aa") : 
      actor {
        canister_status : shared { canister_id : Principal } -> 
          async {
            module_hash : ?[Nat];
            status : { #stopped; #stopping; #running };
            cycles : Nat;
          };
      };
    stable var principal : Principal = Principal.fromText("aaaaa-aa");
    
    public func init() : async Principal {
      Cycles.add(200_000_000_000);
      let canister = await Canister.Canister();
      let amountAccepted = await canister.wallet_receive();
      principal := Principal.fromActor(canister);
      principal;
    };
    
    public func get(principal : Principal) : async (?[Nat], Nat, Principal) {
      let r = await IC0.canister_status({canister_id = principal});
      (r.module_hash,r.cycles, principal);
    };

    public func peek() : async Principal {
      principal;
    };
};

import Cycles "mo:base/ExperimentalCycles";
import Nat64 "mo:base/Nat64";

actor class Canister() = this {
  stable var capacity = 1000000000000000000;
  stable var balance = Cycles.balance();


  // Returns the cycles received up to the capacity allowed
  public func wallet_receive() : async { accepted: Nat64 } {
      let amount = Cycles.available();
      let limit : Nat = capacity - balance;
      let accepted = 
          if (amount <= limit) amount
          else limit;
      let deposit = Cycles.accept(accepted);
      assert (deposit == accepted);
      balance += accepted;
      { accepted = Nat64.fromNat(accepted) };
  };   
}
2

The caller has to be one of the controllers of the target canister in order to call canister_status. For simplicity, you can always add blackhole canster to the controller list of your target canister, and then call blackhole’s canister_status method instead.

Introduce the black hole to help with canister status lookup + make them immutable

4 Likes
3

yes, so the main canister create child canister and call it as controller.
The other fields return correctly(cycles, status…), but only the module hash is null.

4

You should have module_hash: ?[Nat8] instead of Nat.

2 Likes
5

Thank you!
It’s solved!

1 Like