fix(svm): no transfer on self-relay

programs/svm-spoke/src/instructions/fill.rs

@@ -124,24 +124,25 @@ pub fn fill_v3_relay(
         _ => FillType::FastFill,
     };
 
-    // TODO: EVM SpokePool skips the transfer if relayer and receiver are the same, should we do the same here?
-    // Invoke the transfer_checked instruction on the token program
-    let transfer_accounts = TransferChecked {
-        // TODO: check what happens if the relayer and recipient are the same
-        from: ctx.accounts.relayer_token_account.to_account_info(),
-        mint: ctx.accounts.mint_account.to_account_info(),
-        to: ctx.accounts.recipient_token_account.to_account_info(),
-        authority: ctx.accounts.signer.to_account_info(),
-    };
-    let cpi_context = CpiContext::new(
-        ctx.accounts.token_program.to_account_info(),
-        transfer_accounts,
-    );
-    transfer_checked(
-        cpi_context,
-        relay_data.output_amount,
-        ctx.accounts.mint_account.decimals,
-    )?;
+    // If relayer and receiver are the same, there is no need to do the transfer. This might be a case when relayers
+    // intentionally self-relay in a capital efficient way (no need to have funds on the destination).
+    if ctx.accounts.relayer_token_account.key() != ctx.accounts.recipient_token_account.key() {
+        let transfer_accounts = TransferChecked {
+            from: ctx.accounts.relayer_token_account.to_account_info(),
+            mint: ctx.accounts.mint_account.to_account_info(),
+            to: ctx.accounts.recipient_token_account.to_account_info(),
+            authority: ctx.accounts.signer.to_account_info(),
+        };
+        let cpi_context = CpiContext::new(
+            ctx.accounts.token_program.to_account_info(),
+            transfer_accounts,
+        );
+        transfer_checked(
+            cpi_context,
+            relay_data.output_amount,
+            ctx.accounts.mint_account.decimals,
+        )?;
+    }
 
     // Update the fill status to Filled and set the relayer
     fill_status_account.status = FillStatus::Filled;

test/svm/SvmSpoke.Fill.ts

@@ -327,4 +327,38 @@ describe("svm_spoke.fill", () => {
       assert.strictEqual(err.error.errorCode.code, "InvalidMint", "Expected error code InvalidMint");
     }
   });
+
+  it("Self-relay does not invoke token transfer", async () => {
+    // Set recipient to be the same as relayer.
+    updateRelayData({ ...relayData, depositor: relayer.publicKey, recipient: relayer.publicKey });
+    accounts.recipient = relayer.publicKey;
+    accounts.recipientTA = relayerTA;
+
+    // Store relayer's balance before the fill
+    const iRelayerBalance = (await getAccount(connection, relayerTA)).amount;
+
+    const relayHash = Array.from(calculateRelayHashUint8Array(relayData, chainId));
+    const txSignature = await program.methods
+      .fillV3Relay(relayHash, relayData, new BN(1))
+      .accounts(accounts)
+      .signers([relayer])
+      .rpc();
+
+    // Verify relayer's balance after the fill is unchanged
+    const fRelayerBalance = (await getAccount(connection, relayerTA)).amount;
+    assertSE(fRelayerBalance, iRelayerBalance, "Relayer's balance should not have changed");
+
+    await new Promise((resolve) => setTimeout(resolve, 1000)); // Wait for tx processing
+    const txResult = await connection.getTransaction(txSignature, {
+      commitment: "confirmed",
+      maxSupportedTransactionVersion: 0,
+    });
+    if (txResult === null || txResult.meta === null) throw new Error("Transaction meta not confirmed");
+    if (txResult.meta.logMessages === null || txResult.meta.logMessages === undefined)
+      throw new Error("Transaction logs not found");
+    assert.isTrue(
+      txResult.meta.logMessages.every((log) => !log.includes(`Program ${TOKEN_PROGRAM_ID} invoke`)),
+      "Token Program should not be invoked"
+    );
+  });
 });