Add SIP-010 print detection post-execution to the example folder

example/contracts/rendezvous-token.clar

@@ -2,6 +2,10 @@
 
 (define-fungible-token rendezvous)
 
+(define-constant deployer tx-sender)
+
+(define-constant ERR_UNAUTHORIZED (err u400))
+
 ;; SIP-010 methods.
 
 (define-read-only (get-total-supply)
@@ -34,8 +38,22 @@
     (recipient principal)
     (memo (optional (buff 34)))
   )
-  (match (ft-transfer? rendezvous amount sender recipient)
-    response (ok response)
-    error (err error)
+  (begin
+    ;; This print event is required for rendezvous to be a SIP-010 compliant
+    ;; fungible token. Comment out this line and run the following command to
+    ;; see the `dialers` in action:
+    ;; ```rv example rendezvous-token invariant --dial=example/sip010.js```
+    ;; (match memo to-print (print to-print) 0x)
+    (match (ft-transfer? rendezvous amount sender recipient)
+      response (ok response)
+      error (err error)
+    )
+  )
+)
+
+(define-public (mint (recipient principal) (amount uint))
+  (begin
+    (asserts! (is-eq contract-caller deployer) ERR_UNAUTHORIZED)
+    (ft-mint? rendezvous amount recipient)
   )
 )

example/contracts/rendezvous-token.tests.clar

@@ -0,0 +1,7 @@
+;; Invariants
+
+;; This invariant returns true regardless of the state of the contract. Its
+;; purpose is to allow the demonstration of the `dialers` feature.
+(define-read-only (invariant-always-true)
+  true
+)

example/sip010.js

@@ -0,0 +1,63 @@
+const { cvToHex } = require("@stacks/transactions");
+
+async function postTransferSip010PrintEvent(context) {
+  const selectedFunction = context.selectedFunction;
+  // A fungible token complies with the SIP-010 standard if the transfer event
+  // always emits the print event with the `memo` content.
+  if (selectedFunction.name !== "transfer") {
+    return;
+  }
+
+  const functionCall = context.functionCall;
+  const functionCallEvents = functionCall.events;
+
+  if (functionCallEvents.length === 0) {
+    throw new Error(
+      "No transfer events. The transfer function must emit the SIP-010 print event!"
+    );
+  }
+
+  // The `memo` parameter is the fourth parameter of the `transfer` function.
+  const memoParameterIndex = 3;
+
+  const memoArg = context.clarityValueArguments[memoParameterIndex];
+
+  // The `memo` argument is optional. If `none`, nothing has to be printed.
+  if (memoArg.type === 9) {
+    return;
+  }
+
+  // The `memo` argument must be `some`. Otherwise, the generated clarity
+  // argument is invalid.
+  if (memoArg.type !== 10) {
+    return;
+  }
+
+  // Turn the inner value of the `some` type into a hex to compare it with the
+  // print event data.
+  const hexMemoArgValue = cvToHex(memoArg.value);
+
+  const sip010PrintEvent = functionCallEvents.find(
+    (ev) => ev.event === "print_event"
+  );
+
+  if (!sip010PrintEvent) {
+    throw new Error(
+      "No print event found. The transfer function must emit the SIP-010 print event!"
+    );
+  }
+
+  const sip010PrintEventValue = sip010PrintEvent.data.raw_value;
+
+  if (sip010PrintEventValue !== hexMemoArgValue) {
+    throw new Error(
+      `The print event memo value is not equal to the memo parameter value: ${hexMemoArgValue} !== ${sip010PrintEventValue}`
+    );
+  }
+
+  return;
+}
+
+module.exports = {
+  postTransferSip010PrintEvent,
+};