Find file Copy path
Fetching contributors…
Cannot retrieve contributors at this time
352 lines (313 sloc) 14.2 KB
// Copyright 2017-2018 Parity Technologies (UK) Ltd.
// This file is part of Substrate.
// Substrate is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
// Substrate is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with Substrate. If not, see <>.
//! The Example: A simple example of a runtime module demonstrating
//! concepts, APIs and structures common to most runtime modules.
// Ensure we're `no_std` when compiling for Wasm.
#![cfg_attr(not(feature = "std"), no_std)]
// Assert macros used in tests.
extern crate sr_std;
// Needed for tests (`with_externalities`).
extern crate sr_io;
// Needed for the set of mock primitives used in our tests.
extern crate substrate_primitives;
// Needed for various traits. In our case, `OnFinalise`.
extern crate sr_primitives;
// Needed for deriving `Encode` and `Decode` for `RawEvent`.
extern crate parity_codec_derive;
extern crate parity_codec as codec;
// Needed for type-safe access to storage DB.
extern crate srml_support as support;
// `system` module provides us with all sorts of useful stuff and macros
// depend on it being around.
extern crate srml_system as system;
// `balances` module is needed for our little example. It's not required in
// general (though if you want your module to be able to work with tokens, then you
// might find it useful).
extern crate srml_balances as balances;
use codec::HasCompact;
use support::{StorageValue, dispatch::Result};
use system::ensure_signed;
/// Our module's configuration trait. All our types and consts go in here. If the
/// module is dependent on specific other modules, then their configuration traits
/// should be added to our implied traits list.
/// `system::Trait` should always be included in our implied traits.
pub trait Trait: balances::Trait {
/// The overarching event type.
type Event: From<Event<Self>> + Into<<Self as system::Trait>::Event>;
// The module declaration. This states the entry points that we handle. The
// macro takes care of the marshalling of arguments and dispatch.
// Anyone can have these functions execute by signing and submitting
// an extrinsic. Ensure that calls into each of these execute in a time, memory and
// using storage space proportional to any costs paid for by the caller or otherwise the
// difficulty of forcing the call to happen.
// Generally you'll want to split these into three groups:
// - Public calls that are signed by an external account.
// - Root calls that are allowed to be made only by the governance system.
// - Inherent calls that are allowed to be made only by the block authors and validators.
// Information about where this dispatch initiated from is provided as the first argument
// "origin". As such functions must always look like:
// `fn foo(origin, bar: Bar, baz: Baz) -> Result;`
// The `Result` is required as part of the syntax (and expands to the conventional dispatch
// result of `Result<(), &'static str>`).
// When you come to `impl` them later in the module, you must specify the full type for `origin`:
// `fn foo(origin: T::Origin, bar: Bar, baz: Baz) { ... }`
// There are three entries in the `system::Origin` enum that correspond
// to the above bullets: `::Signed(AccountId)`, `::Root` and `::Inherent`. You should always match
// against them as the first thing you do in your function. There are three convenience calls
// in system that do the matching for you and return a convenient result: `ensure_signed`,
// `ensure_root` and `ensure_inherent`.
decl_module! {
// Simple declaration of the `Module` type. Lets the macro know what its working on.
pub struct Module<T: Trait> for enum Call where origin: T::Origin {
/// Deposit one of this module's events by using the default implementation.
/// It is also possible to provide a custom implementation.
/// For non-generic events, the generic parameter just needs to be dropped, so that it
/// looks like: `fn deposit_event() = default;`.
fn deposit_event<T>() = default;
/// This is your public interface. Be extremely careful.
/// This is just a simple example of how to interact with the module from the external
/// world.
// This just increases the value of `Dummy` by `increase_by`.
// Since this is a dispatched function there are two extremely important things to
// remember:
// - MUST NOT PANIC: Under no circumstances (save, perhaps, storage getting into an
// irreparably damaged state) must this function panic.
// - NO SIDE-EFFECTS ON ERROR: This function must either complete totally (and return
// `Ok(())` or it must have no side-effects on storage and return `Err('Some reason')`.
// The first is relatively easy to audit for - just ensure all panickers are removed from
// logic that executes in production (which you do anyway, right?!). To ensure the second
// is followed, you should do all tests for validity at the top of your function. This
// is stuff like checking the sender (`origin`) or that state is such that the operation
// makes sense.
// Once you've determined that it's all good, then enact the operation and change storage.
// If you can't be certain that the operation will succeed without substantial computation
// then you have a classic blockchain attack scenario. The normal way of managing this is
// to attach a bond to the operation. As the first major alteration of storage, reserve
// some value from the sender's account (`Balances` module has a `reserve` function for
// exactly this scenario). This amount should be enough to cover any costs of the
// substantial execution in case it turns out that you can't proceed with the operation.
// If it eventually transpires that the operation is fine and, therefore, that the
// expense of the checks should be borne by the network, then you can refund the reserved
// deposit. If, however, the operation turns out to be invalid and the computation is
// wasted, then you can burn it or repatriate elsewhere.
// Security bonds ensure that attackers can't game it by ensuring that anyone interacting
// with the system either progresses it or pays for the trouble of faffing around with
// no progress.
// If you don't respect these rules, it is likely that your chain will be attackable.
fn accumulate_dummy(origin, increase_by: T::Balance) -> Result {
// This is a public call, so we ensure that the origin is some signed account.
let _sender = ensure_signed(origin)?;
// Read the value of dummy from storage.
// let dummy = Self::dummy();
// Will also work using the `::get` on the storage item type itself:
// let dummy = <Dummy<T>>::get();
// Calculate the new value.
// let new_dummy = dummy.map_or(increase_by, |dummy| dummy + increase_by);
// Put the new value into storage.
// <Dummy<T>>::put(new_dummy);
// Will also work with a reference:
// <Dummy<T>>::put(&new_dummy);
// Here's the new one of read and then modify the value.
<Dummy<T>>::mutate(|dummy| {
let new_dummy = dummy.map_or(increase_by, |dummy| dummy + increase_by);
*dummy = Some(new_dummy);
// Let's deposit an event to let the outside world know this happened.
// All good.
/// A privileged call; in this case it resets our dummy value to something new.
// Implementation of a privileged call. This doesn't have an `origin` parameter because
// it's not (directly) from an extrinsic, but rather the system as a whole has decided
// to execute it. Different runtimes have different reasons for allow privileged
// calls to be executed - we don't need to care why. Because it's privileged, we can
// assume it's a one-off operation and substantial processing/storage/memory can be used
// without worrying about gameability or attack scenarios.
// If you not specify `Result` explicitly as return value, it will be added automatically
// for you and `Ok(())` will be returned.
fn set_dummy(new_value: <T::Balance as HasCompact>::Type) {
// Put the new value into storage.
// The signature could also look like: `fn on_finalise()`
fn on_finalise(_n: T::BlockNumber) {
// Anything that needs to be done at the end of the block.
// We just kill our dummy storage item.
/// An event in this module. Events are simple means of reporting specific conditions and
/// circumstances that have happened that users, Dapps and/or chain explorers would find
/// interesting and otherwise difficult to detect.
pub enum Event<T> where B = <T as balances::Trait>::Balance {
// Just a normal `enum`, here's a dummy event to ensure it compiles.
/// Dummy event, just here so there's a generic type that's used.
decl_storage! {
// A macro for the Storage trait, and its implementation, for this module.
// This allows for type-safe usage of the Substrate storage database, so you can
// keep things around between blocks.
trait Store for Module<T: Trait> as Example {
// Any storage declarations of the form:
// `pub? Name get(getter_name)? [config()|config(myname)] [build(|_| {...})] : <type> (= <new_default_value>)?;`
// where `<type>` is either:
// - `Type` (a basic value item); or
// - `map KeyType => ValueType` (a map item).
// Note that there are two optional modifiers for the storage type declaration.
// - `Foo: Option<u32>`:
// - `Foo::put(1); Foo::get()` returns `Some(1)`;
// - `Foo::kill(); Foo::get()` returns `None`.
// - `Foo: u32`:
// - `Foo::put(1); Foo::get()` returns `1`;
// - `Foo::kill(); Foo::get()` returns `0` (u32::default()).
// e.g. Foo: u32;
// e.g. pub Bar get(bar): map T::AccountId => Vec<(T::Balance, u64)>;
// For basic value items, you'll get a type which implements
// `support::StorageValue`. For map items, you'll get a type which
// implements `support::StorageMap`.
// If they have a getter (`get(getter_name)`), then your module will come
// equipped with `fn getter_name() -> Type` for basic value items or
// `fn getter_name(key: KeyType) -> ValueType` for map items.
Dummy get(dummy) config(): Option<T::Balance>;
// this one uses the default, we'll demonstrate the usage of 'mutate' API.
Foo get(foo) config(): T::Balance;
// The main implementation block for the module. Functions here fall into three broad
// categories:
// - Public interface. These are functions that are `pub` and generally fall into inspector
// functions that do not write to storage and operation functions that do.
// - Private functions. These are your usual private utilities unavailable to other modules.
impl<T: Trait> Module<T> {
// Add public immutables and private mutables.
fn accumulate_foo(origin: T::Origin, increase_by: T::Balance) -> Result {
let _sender = ensure_signed(origin)?;
let prev = <Foo<T>>::get();
// Because Foo has 'default', the type of 'foo' in closure is the raw type instead of an Option<> type.
let result = <Foo<T>>::mutate(|foo| {
*foo = *foo + increase_by;
assert!(prev + increase_by == result);
mod tests {
use super::*;
use sr_io::with_externalities;
use substrate_primitives::{H256, Blake2Hasher};
// The testing primitives are very useful for avoiding having to work with signatures
// or public keys. `u64` is used as the `AccountId` and no `Signature`s are requried.
use sr_primitives::{
BuildStorage, traits::{BlakeTwo256, OnFinalise, IdentityLookup}, testing::{Digest, DigestItem, Header}
impl_outer_origin! {
pub enum Origin for Test {}
// For testing the module, we construct most of a mock runtime. This means
// first constructing a configuration type (`Test`) which `impl`s each of the
// configuration traits of modules we want to use.
#[derive(Clone, Eq, PartialEq)]
pub struct Test;
impl system::Trait for Test {
type Origin = Origin;
type Index = u64;
type BlockNumber = u64;
type Hash = H256;
type Hashing = BlakeTwo256;
type Digest = Digest;
type AccountId = u64;
type Lookup = IdentityLookup<u64>;
type Header = Header;
type Event = ();
type Log = DigestItem;
impl balances::Trait for Test {
type Balance = u64;
type OnFreeBalanceZero = ();
type OnNewAccount = ();
type EnsureAccountLiquid = ();
type Event = ();
impl Trait for Test {
type Event = ();
type Example = Module<Test>;
// This function basically just builds a genesis storage key/value store according to
// our desired mockup.
fn new_test_ext() -> sr_io::TestExternalities<Blake2Hasher> {
let mut t = system::GenesisConfig::<Test>::default().build_storage().unwrap().0;
// We use default for brevity, but you can configure as desired if needed.
dummy: 42,
foo: 24,
fn it_works_for_optional_value() {
with_externalities(&mut new_test_ext(), || {
// Check that GenesisBuilder works properly.
assert_eq!(Example::dummy(), Some(42));
// Check that accumulate works when we have Some value in Dummy already.
assert_ok!(Example::accumulate_dummy(Origin::signed(1), 27));
assert_eq!(Example::dummy(), Some(69));
// Check that finalising the block removes Dummy from storage.
<Example as OnFinalise<u64>>::on_finalise(1);
assert_eq!(Example::dummy(), None);
// Check that accumulate works when we Dummy has None in it.
assert_ok!(Example::accumulate_dummy(Origin::signed(1), 42));
assert_eq!(Example::dummy(), Some(42));
fn it_works_for_default_value() {
with_externalities(&mut new_test_ext(), || {
assert_eq!(Example::foo(), 24);
assert_ok!(Example::accumulate_foo(Origin::signed(1), 1));
assert_eq!(Example::foo(), 25);