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SRML Executive Documentation #2144

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Apr 12, 2019
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SRML Executive Documentation #2144

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executive docs first draft
joepetrowski Mar 28, 2019
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72 changes: 55 additions & 17 deletions srml/executive/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,45 @@
// You should have received a copy of the GNU General Public License
// along with Substrate. If not, see <http://www.gnu.org/licenses/>.

//! Executive: Handles all of the top-level stuff; essentially just executing blocks/extrinsics.
//! # Executive Module
//!
//! The Executive module acts as the orchestration layer for the runtime. It dispatches incoming
//! extrinsic calls to the respective modules in the runtime.
//!
//! ## Overview
//!
//! The executive module is not a typical SRML module providing functionality around a specific feature.
//! It is a cross-cutting framework component for the SRML. It works in conjunction with the
//! [SRML System module](../srml_system/index.html) to perform these cross-cutting functions.
//!
//! The Executive module provides functions to:
//!
//! - Check transaction validity.
//! - Initialize a block.
//! - Apply extrinsics.
//! - Execute a block.
//! - Finalize a block.
//! - Start an off-chain worker.
//!
//! ### Implementations
//!
//! The Executive module provides the following implementations:
//!
//! - `ExecuteBlock`: Trait that can be used to execute a block.
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@gautamdhameja gautamdhameja Mar 29, 2019

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Do we need this section? I think we decided not to mention implementation details in this section of the docs.

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@joepetrowski joepetrowski Mar 29, 2019

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It's not really describing the logic. I see it as, "avoid coupling with this module if these traits have what you need." Since executive in particular doesn't have a decl_module! or impl Module, then maybe it's not necessary at all.

//! - `Executive`: Type that can be used to make the SRML available from the runtime.
//!
//! ## Usage
//!
//! The default Substrate node template declares the [`Executive`](./struct.Executive.html) type in its library.
//!
//! ### Example
//!
//! `Executive` type declaration from the node template.
//!
//! ```ignore
//! /// Executive: handles dispatch to the various modules.
//! pub type Executive = executive::Executive<Runtime, Block, Context, Balances, AllModules>;
//! ```

#![cfg_attr(not(feature = "std"), no_std)]

Expand Down Expand Up @@ -48,9 +86,9 @@ mod internal {
}
}

/// Something that can be used to execute a block.
/// Trait that can be used to execute a block.
pub trait ExecuteBlock<Block: BlockT> {
/// Actually execute all transitioning for `block`.
/// Actually execute all transitions for `block`.
fn execute_block(block: Block);
}

Expand Down Expand Up @@ -100,20 +138,20 @@ impl<
fn initial_checks(block: &Block) {
let header = block.header();

// check parent_hash is correct.
// Check that `parent_hash` is correct.
let n = header.number().clone();
assert!(
n > System::BlockNumber::zero() && <system::Module<System>>::block_hash(n - System::BlockNumber::one()) == *header.parent_hash(),
"Parent hash should be valid."
);

// check transaction trie root represents the transactions.
// Check that transaction trie root represents the transactions.
let xts_root = extrinsics_root::<System::Hashing, _>(&block.extrinsics());
header.extrinsics_root().check_equal(&xts_root);
assert!(header.extrinsics_root() == &xts_root, "Transaction trie root must be valid.");
}

/// Actually execute all transitioning for `block`.
/// Actually execute all transitions for `block`.
pub fn execute_block(block: Block) {
Self::initialize_block(block.header());

Expand All @@ -128,11 +166,11 @@ impl<
Self::final_checks(&header);
}

/// Execute given extrinsics and take care of post-extrinsics book-keeping
/// Execute given extrinsics and take care of post-extrinsics book-keeping.
fn execute_extrinsics_with_book_keeping(extrinsics: Vec<Block::Extrinsic>, block_number: NumberFor<Block>) {
extrinsics.into_iter().for_each(Self::apply_extrinsic_no_note);

// post-extrinsics book-keeping.
// post-extrinsics book-keeping
<system::Module<System>>::note_finished_extrinsics();
<AllModules as OnFinalize<System::BlockNumber>>::on_finalize(block_number);
}
Expand All @@ -143,7 +181,7 @@ impl<
<system::Module<System>>::note_finished_extrinsics();
<AllModules as OnFinalize<System::BlockNumber>>::on_finalize(<system::Module<System>>::block_number());

// setup extrinsics
// set up extrinsics
<system::Module<System>>::derive_extrinsics();
<system::Module<System>>::finalize()
}
Expand Down Expand Up @@ -180,7 +218,7 @@ impl<

/// Actually apply an extrinsic given its `encoded_len`; this doesn't note its hash.
fn apply_extrinsic_with_len(uxt: Block::Extrinsic, encoded_len: usize, to_note: Option<Vec<u8>>) -> result::Result<internal::ApplyOutcome, internal::ApplyError> {
// Verify the signature is good.
// Verify that the signature is good.
let xt = uxt.check(&Default::default()).map_err(internal::ApplyError::BadSignature)?;

// Check the size of the block if that extrinsic is applied.
Expand All @@ -195,7 +233,7 @@ impl<
if index < &expected_index { internal::ApplyError::Stale } else { internal::ApplyError::Future }
) }

// pay any fees.
// pay any fees
Payment::make_payment(sender, encoded_len).map_err(|_| internal::ApplyError::CantPay)?;

// AUDIT: Under no circumstances may this function panic from here onwards.
Expand All @@ -204,13 +242,13 @@ impl<
<system::Module<System>>::inc_account_nonce(sender);
}

// make sure to `note_extrinsic` only after we know it's going to be executed
// Make sure to `note_extrinsic` only after we know it's going to be executed
// to prevent it from leaking in storage.
if let Some(encoded) = to_note {
<system::Module<System>>::note_extrinsic(encoded);
}

// decode parameters and dispatch
// Decode parameters and dispatch
let (f, s) = xt.deconstruct();
let r = f.dispatch(s.into());
<system::Module<System>>::note_applied_extrinsic(&r, encoded_len as u32);
Expand All @@ -222,10 +260,10 @@ impl<
}

fn final_checks(header: &System::Header) {
// remove temporaries.
// remove temporaries
let new_header = <system::Module<System>>::finalize();

// check digest.
// check digest
assert_eq!(
header.digest().logs().len(),
new_header.digest().logs().len(),
Expand All @@ -246,7 +284,7 @@ impl<
/// Check a given transaction for validity. This doesn't execute any
/// side-effects; it merely checks whether the transaction would panic if it were included or not.
///
/// Changes made to the storage should be discarded.
/// Changes made to storage should be discarded.
pub fn validate_transaction(uxt: Block::Extrinsic) -> TransactionValidity {
// Note errors > 0 are from ApplyError
const UNKNOWN_ERROR: i8 = -127;
Expand All @@ -267,7 +305,7 @@ impl<
};

if let (Some(sender), Some(index)) = (xt.sender(), xt.index()) {
// pay any fees.
// pay any fees
if Payment::make_payment(sender, encoded_len).is_err() {
return TransactionValidity::Invalid(ApplyError::CantPay as i8)
}
Expand Down