add test, use margin

e2e/bash/send.bash

@@ -0,0 +1,43 @@
+#!/usr/bin/env bats
+
+# shellcheck source=/dev/null
+source "$BATS_SUPPORT/load.bash"
+
+load util/assertions
+
+setup() {
+    # We want to work from a temporary directory, different for every test.
+    x=$(mktemp -d -t dfx-usage-env-home-XXXXXXXX)
+    cd "$x" || exit
+    export DFX_CONFIG_ROOT=$x
+
+    dfx new --no-frontend e2e_project
+    cd e2e_project || exit 1
+    dfx start --background --clean
+}
+
+teardown() {
+    dfx stop
+    rm -rf "$DFX_CONFIG_ROOT"
+}
+
+@test "wallet_call_with_max_cycles" {
+    dfx identity new alice --storage-mode plaintext
+    dfx identity new bob --storage-mode plaintext
+    WALLET_ALICE=$(dfx --identity alice identity get-wallet)
+    WALLET_BOB=$(dfx --identity bob identity get-wallet)
+
+    ALICE_CYCLES_BEFORE_SEND=$(dfx --identity alice wallet balance --precise | sed 's/[^0-9]//g')
+    if (( ${ALICE_CYCLES_BEFORE_SEND} < 2000000000000 )); then 
+        echo "alice has unexpectedly few cycles before sending: ${ALICE_CYCLES_BEFORE_SEND}"
+        exit 1
+    fi
+    dfx --identity alice canister call "${WALLET_ALICE}" wallet_call_with_max_cycles "(record { canister = principal \"${WALLET_BOB}\"; method_name = \"wallet_receive\"; args = blob \"\44\49\44\4c\00\00\"; })"
+
+    # has less than 0.2T cycles afterwards
+    ALICE_CYCLES_AFTER_SEND=$(dfx --identity alice wallet balance --precise | sed 's/[^0-9]//g')
+    if (( ${ALICE_CYCLES_AFTER_SEND} > 200000000000 )); then 
+        echo "expected alice to have <1TC after wallet_call_with_max_cycles, actually has ${ALICE_CYCLES_AFTER_SEND}, before was ${ALICE_CYCLES_BEFORE_SEND}"
+        exit 1
+    fi
+}

wallet/src/lib.rs

@@ -949,11 +949,15 @@ mod wallet {
     )]
     async fn call_with_max_cycles(args: CallWithMaxCyclesArgs) -> Result<CallResult, String> {
         let available_cycles = ic_cdk::api::canister_balance128();
+        // If no margin is used then the call either fails locally with `Couldn't send message` or processing the response traps with `Canister out of cycles`.
+        // On the local network the margin needs to be ~1.7B cycles. (Experimentally determined in August 2024)
+        // Extrapolating, a margin of 100B should work up to a subnet of ~60 nodes.
+        const MARGIN: u128 = 100_000_000_000;
         call128(CallCanisterArgs {
             canister: args.canister,
             method_name: args.method_name,
             args: args.args,
-            cycles: available_cycles,
+            cycles: available_cycles.saturating_sub(MARGIN),
         })
         .await
     }