fix(crypto): encrypted_notes example: use persistent actor (#235)

Adapts the encrypted_notes_dapp example so that it works again with ICP
Ninja, which recently upgraded to DFX 0.29.1, which ships with a new
motoko compiler (0.16.1). The necessary changes for this were

* Declaring the actor as `persistent`
* Marking all transient variables explicitly as transient, and removing
the redundant stable keywords.

Note that the example still uses the old way to persist data across
updates, which is serialize/deserialize data in the preupgrade and
postupgrade methods.

The Github workflow sets the `DFX_VERSION` environment variable, so that
only this example uses the new DFX version 0.29.1. This also required to
change the bind host from `localhost` to `127.0.0.1` as otherwise this
new DFX version hits the following error:
```
Error: The replica returned an HTTP Error: Http Error: status 400 Bad Request, content type "text/plain; charset=utf-8", content: error: no_authority
details:
The request is missing the required authority information (e.g. 'Host' header).
```

The changes were tested in ICP Ninja with the following link:


[![](https://icp.ninja/assets/open.svg)](http://icp.ninja/editor?g=https://github.com/dfinity/vetkeys/tree/franzstefan/CRP-2924-enc-notes/examples/encrypted_notes_dapp_vetkd/motoko)

Author: fspreiss

.github/workflows/examples-encrypted-notes-dapp.yml

@@ -12,6 +12,8 @@ on:
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
+env:
+  DFX_VERSION: 0.29.1
 jobs:
   examples-encrypted-notes-dapp-rust-darwin:
     runs-on: macos-15

examples/encrypted_notes_dapp_vetkd/motoko/backend/main.mo

@@ -16,7 +16,7 @@ import Hex "./utils/Hex";
 
 // Declare a shared actor class
 // Bind the caller and the initializer
-shared ({ caller = initializer }) actor class (keyName: Text) {
+shared ({ caller = initializer }) persistent actor class (keyName: Text) {
 
     // Currently, a single canister smart contract is limited to 4 GB of heap size.
     // For the current limits see https://internetcomputer.org/docs/current/developer-docs/production/resource-limits.
@@ -27,10 +27,10 @@ shared ({ caller = initializer }) actor class (keyName: Text) {
     // memory usage must be calculated or monitored and the various restrictions adapted accordingly.
 
     // Define dapp limits - important for security assurance
-    private let MAX_USERS = 500;
-    private let MAX_NOTES_PER_USER = 200;
-    private let MAX_NOTE_CHARS = 1000;
-    private let MAX_SHARES_PER_NOTE = 50;
+    private transient let MAX_USERS = 500;
+    private transient let MAX_NOTES_PER_USER = 200;
+    private transient let MAX_NOTE_CHARS = 1000;
+    private transient let MAX_SHARES_PER_NOTE = 50;
 
     private type PrincipalName = Text;
     private type NoteId = Nat;
@@ -58,23 +58,23 @@ shared ({ caller = initializer }) actor class (keyName: Text) {
     // The keyword `stable` makes this (scalar) variable keep its value across canister upgrades.
     //
     // See https://internetcomputer.org/docs/current/developer-docs/setup/manage-canisters#upgrade-a-canister
-    private stable var nextNoteId : Nat = 1;
+    private var nextNoteId : Nat = 1;
 
     // Store notes by their ID, so that note-specific encryption keys can be derived.
-    private var notesById = Map.HashMap<NoteId, EncryptedNote>(0, Nat.equal, Hash.hash);
+    private transient var notesById = Map.HashMap<NoteId, EncryptedNote>(0, Nat.equal, Hash.hash);
     // Store which note IDs are owned by a particular principal
-    private var noteIdsByOwner = Map.HashMap<PrincipalName, List.List<NoteId>>(0, Text.equal, Text.hash);
+    private transient var noteIdsByOwner = Map.HashMap<PrincipalName, List.List<NoteId>>(0, Text.equal, Text.hash);
     // Store which notes are shared with a particular principal. Does not include the owner, as this is tracked by `noteIdsByOwner`.
-    private var noteIdsByUser = Map.HashMap<PrincipalName, List.List<NoteId>>(0, Text.equal, Text.hash);
+    private transient var noteIdsByUser = Map.HashMap<PrincipalName, List.List<NoteId>>(0, Text.equal, Text.hash);
 
     // While accessing _heap_ data is more efficient, we use the following _stable memory_
     // as a buffer to preserve data across canister upgrades.
     // Stable memory is currently 96GB. For the current limits see
     // https://internetcomputer.org/docs/current/developer-docs/production/resource-limits.
     // See also: [preupgrade], [postupgrade]
-    private stable var stable_notesById : [(NoteId, EncryptedNote)] = [];
-    private stable var stable_noteIdsByOwner : [(PrincipalName, List.List<NoteId>)] = [];
-    private stable var stable_noteIdsByUser : [(PrincipalName, List.List<NoteId>)] = [];
+    private var stable_notesById : [(NoteId, EncryptedNote)] = [];
+    private var stable_noteIdsByOwner : [(PrincipalName, List.List<NoteId>)] = [];
+    private var stable_noteIdsByUser : [(PrincipalName, List.List<NoteId>)] = [];
 
     // Utility function that helps writing assertion-driven code more concisely.
     private func expect<T>(opt : ?T, violation_msg : Text) : T {
@@ -322,7 +322,7 @@ shared ({ caller = initializer }) actor class (keyName: Text) {
         }) -> async ({ encrypted_key : Blob });
     };
 
-    let management_canister : VETKD_API = actor ("aaaaa-aa");
+    transient let management_canister : VETKD_API = actor ("aaaaa-aa");
 
     public shared func symmetric_key_verification_key_for_note() : async Text {
         let { public_key } = await management_canister.vetkd_public_key({

examples/encrypted_notes_dapp_vetkd/motoko/dfx.json

@@ -32,7 +32,7 @@
     },
     "networks": {
       "local": {
-        "bind": "localhost:8000",
+        "bind": "127.0.0.1:8000",
         "type": "ephemeral"
       }
     }

examples/encrypted_notes_dapp_vetkd/rust/dfx.json

@@ -32,7 +32,7 @@
   },
   "networks": {
     "local": {
-      "bind": "localhost:8000",
+      "bind": "127.0.0.1:8000",
       "type": "ephemeral"
     }
   }