The Replica returned an error: code 5, message: "Canister trapped explicitly: RTS error: blob_of_principal: principal too short"

Developers Language Support
1

Hello!

I got an error when I redeployed after editing the backend canister.
I have tried to search for the reason for the error, but I am not sure why.
The Replica returned an error: code 5, message: "Canister trapped explicitly: RTS error: blob_of_principal: principal too short"

Under what circumstances would such an error appear?
Also, what should I check?

[ Error ]

$ dfx deploy app_backend

Deploying: app_backend
All canisters have already been created.
Building canisters...
Installing canisters...
Upgrading code for canister app_backend, with canister ID rno2w-sqaaa-aaaaa-aaacq-cai
Error: Failed while trying to deploy canisters.
Caused by: Failed while trying to deploy canisters.
  Failed while trying to install all canisters.
    Failed to install wasm module to canister 'app_backend'.
      Failed to install wasm in canister 'rno2w-sqaaa-aaaaa-aaacq-cai'.
        Failed to install wasm.
          The Replica returned an error: code 5, message: "Canister rno2w-sqaaa-aaaaa-aaacq-cai trapped explicitly: RTS error: blob_of_principal: principal too short"

[ What I did when I redeployed ]
I wanted to check the functionality of the stable variable and preupgrade / postupgrade methods, so I defined a dummy variable and tried to redeploy.

Thank you in advance for your answer.

2

Can you show the code you use for preupgrade and postupgrade? Otherwise this will be very hard to debug.

3

Our apologies.

Here is the actual method (preupgrade / postupgrade).

I had tried to create a simpler DEX myself, using Definity/example/motoko/defi as a reference.

actor class SimpleDex() = this {
  stable var orders_stable : [T.Order] = [];
  private stable var book_stable : [var (Principal, [(T.Token, Nat)])] = [var];

  // ===== UPGRADE METHODS =====

  system func preupgrade() {
    book_stable := Array.init(book.size(), (Principal.fromText(""), []));
    var i = 0;
    for ((x, y) in book.entries()) {
      book_stable[i] := (x, Iter.toArray(y.entries()));
      i += 1;
    };

    // Save order
    orders_stable := exchange.getOrders();
  };

  system func postupgrade() {
    // Reload book.
    for ((key : Principal, value : [(T.Token, Nat)]) in book_stable.vals()) {
      let tmp : HashMap.HashMap<T.Token, Nat>
        = HashMap.fromIter<T.Token, Nat>(
            Iter.fromArray<(T.Token, Nat)>(value), 
            10, 
            Principal.equal, 
            Principal.hash);
      book.put(key, tmp);
    };

    // Reload order
    for (order in orders_stable.vals()) {
      exchange.addOrder(order);
    };

    // Clean stable memory.
    book_stable := [var];
    orders_stable := [];
  };
};
4

Empty String is not a valid principal and this will panic, as you observed in the error message. Please use a valid one instead. The two most common ones are the management canister’s Principal "aaaaa-aa" and the anonymous Principal "2vxsx-fae", but you can use any valid principal you like.

1 Like
5

Thank you very much.
I set the initial values as follows, and the redeployment worked fine, and I even checked stable!

system func preupgrade() {
    book_stable := Array.init(book.size(), (Principal.fromText("aaaaa-aa"), []));

I was thinking something was failing in the loop, but the initial value was the error…
Thanks again!