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Merge pull request #871 from maksymar/maksym/ic-272-logs
add `canister_logs` examples for rust and motoko
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‎motoko/canister_logs/README.md

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---
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keywords: [beginner, motoko, canister logs, logging]
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---
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# Canister logs
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[View this sample's code on GitHub](https://github.com/dfinity/examples/tree/master/motoko/canister_logs)
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## Prerequisites
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This example requires an installation of:
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- [x] Install the [IC SDK](https://internetcomputer.org/docs/current/developer-docs/setup/install/).
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- [x] Download the following project files from GitHub: `git clone https://github.com/dfinity/examples/`
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You will need to have 3 terminal windows:
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- Terminal A: Running a DFX instance and separating its output from anything else
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- Terminal B: Deploying a canister and seeing its output
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- Terminal C: Reading logs interactively
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### Step 1: Navigate into the folder containing the project's files and start a local instance of the replica with the command:
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```shell
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# Terminal A -- for running DFX and separating its output from anything else.
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$ cd examples/motoko/canister_logs
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$ dfx start --clean
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# Terminal B -- for deploying the canister and calling its methods.
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$ cd examples/motoko/canister_logs
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# Terminal C -- for polling logs.
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$ cd examples/motoko/canister_logs
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```
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### Step 2: Deploy the canister:
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```shell
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# Terminal B
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$ dfx deploy
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```
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### Step 3: Check canister logs:
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Expect to see logs from timer traps.
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```shell
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# Terminal B
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$ dfx canister logs CanisterLogs
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[0. 2024-05-23T08:32:26.203980235Z]: right before timer trap
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[1. 2024-05-23T08:32:26.203980235Z]: [TRAP]: timer trap
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[2. 2024-05-23T08:32:31.836721763Z]: right before timer trap
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[3. 2024-05-23T08:32:31.836721763Z]: [TRAP]: timer trap
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```
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### Step 4: Call `print` method and check the logs:
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```shell
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# Terminal B
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$ dfx canister call CanisterLogs print hi
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()
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# Expect to see new log entry.
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$ dfx canister logs CanisterLogs
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...
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[8. 2024-05-23T08:32:46.598972616Z]: right before timer trap
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[9. 2024-05-23T08:32:46.598972616Z]: [TRAP]: timer trap
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[10. 2024-05-23T08:32:48.713755238Z]: hi
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[11. 2024-05-23T08:32:51.623988313Z]: right before timer trap
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[12. 2024-05-23T08:32:51.623988313Z]: [TRAP]: timer trap
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...
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```
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### Step 5: Start constantly polling logs:
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In order not to call `dfx canister logs CanisterLogs` after every canister call in a separate terminal window/pane C start a script that will constantly poll logs:
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```shell
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# Terminal C
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$ ./poll_logs.sh
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...
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[8. 2024-05-23T08:32:46.598972616Z]: right before timer trap
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[9. 2024-05-23T08:32:46.598972616Z]: [TRAP]: timer trap
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[10. 2024-05-23T08:32:48.713755238Z]: hi
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[11. 2024-05-23T08:32:51.623988313Z]: right before timer trap
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[12. 2024-05-23T08:32:51.623988313Z]: [TRAP]: timer trap
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...
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```
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### Step 6: Call `print`, `trap` and other canister methods:
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```shell
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# Terminal B
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$ dfx canister call CanisterLogs print hi!
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()
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$ dfx canister call CanisterLogs print hello!
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()
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$ dfx canister call CanisterLogs print yey!
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()
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$ dfx canister call CanisterLogs trap oops!
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Error: Failed update call.
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Caused by: Failed update call.
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The replica returned a rejection error: reject code CanisterError, reject message Canister bkyz2-fmaaa-aaaaa-qaaaq-cai trapped explicitly: oops!, error code None
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$ dfx canister call CanisterLogs memory_oob
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Error: Failed update call.
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Caused by: Failed update call.
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The replica returned a rejection error: reject code CanisterError, reject message Canister bkyz2-fmaaa-aaaaa-qaaaq-cai trapped explicitly: StableMemory range out of bounds, error code None
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```
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Observe recorded logs that might look similar to this:
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```shell
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# Terminal C
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...
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[19. 2024-05-23T08:33:11.319493785Z]: right before timer trap
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[20. 2024-05-23T08:33:11.319493785Z]: [TRAP]: timer trap
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[21. 2024-05-23T08:33:14.229855179Z]: hi!
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[22. 2024-05-23T08:33:16.413512126Z]: right before timer trap
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[23. 2024-05-23T08:33:16.413512126Z]: [TRAP]: timer trap
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[24. 2024-05-23T08:33:18.622686552Z]: hello!
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[25. 2024-05-23T08:33:21.519088681Z]: right before timer trap
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[26. 2024-05-23T08:33:21.519088681Z]: [TRAP]: timer trap
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[27. 2024-05-23T08:33:22.96101893Z]: yey!
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[28. 2024-05-23T08:33:26.601860526Z]: right before timer trap
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[29. 2024-05-23T08:33:26.601860526Z]: [TRAP]: timer trap
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[30. 2024-05-23T08:33:28.039227914Z]: right before trap
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[31. 2024-05-23T08:33:28.039227914Z]: [TRAP]: oops!
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[32. 2024-05-23T08:33:31.634215234Z]: right before timer trap
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[33. 2024-05-23T08:33:31.634215234Z]: [TRAP]: timer trap
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[34. 2024-05-23T08:33:35.96761902Z]: right before memory out of bounds
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[35. 2024-05-23T08:33:35.96761902Z]: [TRAP]: StableMemory range out of bounds
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[36. 2024-05-23T08:33:36.712223153Z]: right before timer trap
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[37. 2024-05-23T08:33:36.712223153Z]: [TRAP]: timer trap
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...
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```

‎motoko/canister_logs/dfx.json

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{
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"version": 1,
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"canisters": {
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"CanisterLogs": {
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"type": "motoko",
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"main": "src/Main.mo"
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}
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},
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"defaults": {
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"build": {
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"packtool": ""
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}
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}
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}

‎motoko/canister_logs/poll_logs.sh

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#!/bin/bash
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# Function to fetch logs and filter out new lines
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fetch_and_filter_logs() {
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# Fetch logs
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new_logs=$(dfx canister logs CanisterLogs)
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# Compare with previous logs to find new ones
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while IFS= read -r line; do
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if [[ ! "${previous_logs[*]}" =~ "$line" ]]; then
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echo "$line"
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fi
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done <<< "$new_logs"
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# Update previous logs
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previous_logs=("$new_logs")
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}
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# Initial fetch and filter
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fetch_and_filter_logs
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# Infinite loop to continuously fetch and filter logs
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while true; do
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fetch_and_filter_logs
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sleep 1
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done

‎motoko/canister_logs/src/Main.mo

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import Debug "mo:base/Debug";
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import { abs } = "mo:base/Int";
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import { now } = "mo:base/Time";
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import { setTimer; recurringTimer } = "mo:base/Timer";
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import StableMemory "mo:base/ExperimentalStableMemory";
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actor CanisterLogs {
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let timerDelaySeconds = 5;
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let second = 1_000_000_000;
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private func execute_timer() : async () {
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Debug.print("right before timer trap");
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Debug.trap("timer trap");
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};
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ignore setTimer<system>(#seconds (timerDelaySeconds - abs(now() / second) % timerDelaySeconds),
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func () : async () {
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ignore recurringTimer<system>(#seconds timerDelaySeconds, execute_timer);
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await execute_timer();
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});
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public func print(text : Text) : async () {
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Debug.print(text);
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};
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public func trap(text : Text) : async () {
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Debug.print("right before trap");
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Debug.trap(text);
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};
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public func memory_oob() : async () {
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Debug.print("right before memory out of bounds");
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let offset : Nat64 = 10;
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let value : Nat = 20;
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let _blob = StableMemory.loadBlob(offset, value); // Expect reading outside of memory bounds to trap.
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};
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};

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