# transaction_extensions.rs - source
Source of the Rust file `docs/sdk/src/reference_docs/transaction_extensions.rs`.

#
pezkuwi_sdk_docs/reference_docs/
transaction_extensions.rs

    1//! Transaction extensions are, briefly, a means for different chains to extend the "basic"
    2//! extrinsic format with custom data that can be checked by the runtime.
    3//!
    4//! # FRAME provided transaction extensions
    5//!
    6//! FRAME by default already provides the following transaction extensions:
    7//!
    8//! - [`CheckGenesis`](pezframe_system::CheckGenesis): Ensures that a transaction was sent for the
    9//!   same network. Determined based on genesis.
    10//!
    11//! - [`CheckMortality`](pezframe_system::CheckMortality): Extends a transaction with a configurable
    12//!   mortality.
    13//!
    14//! - [`CheckNonZeroSender`](pezframe_system::CheckNonZeroSender): Ensures that the sender of a
    15//!   transaction is not the *all zero account* (all bytes of the accountid are zero).
    16//!
    17//! - [`CheckNonce`](pezframe_system::CheckNonce): Extends a transaction with a nonce to prevent
    18//!   replay of transactions and to provide ordering of transactions.
    19//!
    20//! - [`CheckSpecVersion`](pezframe_system::CheckSpecVersion): Ensures that a transaction was built
    21//!   for the currently active runtime.
    22//!
    23//! - [`CheckTxVersion`](pezframe_system::CheckTxVersion): Ensures that the transaction signer used
    24//!   the correct encoding of the call.
    25//!
    26//! - [`CheckWeight`](pezframe_system::CheckWeight): Ensures that the transaction fits into the
    27//!   block before dispatching it.
    28//!
    29//! - [`ChargeTransactionPayment`](pezpallet_transaction_payment::ChargeTransactionPayment): Charges
    30//!   transaction fees from the signer based on the weight of the call using the native token.
    31//!
    32//! - [`ChargeAssetTxPayment`](pezpallet_asset_tx_payment::ChargeAssetTxPayment): Charges
    33//!   transaction fees from the signer based on the weight of the call using any supported asset
    34//!   (including the native token).
    35//!
    36//! - [`ChargeAssetTxPayment`(using
    37//!   conversion)](pezpallet_asset_conversion_tx_payment::ChargeAssetTxPayment): Charges transaction
    38//!   fees from the signer based on the weight of the call using any supported asset (including the
    39//!   native token). The asset is converted to the native token using a pool.
    40//!
    41//! - [`SkipCheckIfFeeless`](pezpallet_skip_feeless_payment::SkipCheckIfFeeless): Allows
    42//!   transactions to be processed without paying any fee. This requires that the `call` that should
    43//!   be dispatched is augmented with the
    44//!   [`feeless_if`](pezframe_support::pezpallet_macros::feeless_if) attribute.
    45//!
    46//! - [`CheckMetadataHash`](pezframe_metadata_hash_extension::CheckMetadataHash): Extends
    47//!   transactions to include the so-called metadata hash. This is required by chains to support the
    48//!   generic Ledger application and other similar offline wallets.
    49//!
    50//! - [`WeightReclaim`](pezframe_system::WeightReclaim): A transaction extension for the relay chain
    51//!   that reclaims unused weight after executing a transaction.
    52//!
    53//! - [`StorageWeightReclaim`](pezcumulus_pezpallet_weight_reclaim::StorageWeightReclaim): A
    54//!   transaction extension for teyrchains that reclaims unused storage weight after executing a
    55//!   transaction.
    56//!
    57//! For more information about these extensions, follow the link to the type documentation.
    58//!
    59//! # Building a custom transaction extension
    60//!
    61//! Defining a couple of very simple transaction extensions looks like the following:
    62#![doc = docify::embed!("./src/reference_docs/transaction_extensions.rs", transaction_extensions_example)]
    63
    64#[docify::export]
    65pub mod transaction_extensions_example {
    66	use codec::{Decode, DecodeWithMemTracking, Encode};
    67	use pezsp_runtime::{
    68		impl_tx_ext_default,
    69		traits::{Dispatchable, TransactionExtension},
    70		transaction_validity::TransactionValidityError,
    71	};
    72	use scale_info::TypeInfo;
    73
    74	// This doesn't actually check anything, but simply allows
    75	// some arbitrary `u32` to be added to the extrinsic payload
    76	#[derive(Debug, Encode, Decode, DecodeWithMemTracking, Clone, Eq, PartialEq, TypeInfo)]
    77	pub struct AddToPayload(pub u32);
    78
    79	impl<Call: Dispatchable> TransactionExtension<Call> for AddToPayload {
    80		const IDENTIFIER: &'static str = "AddToPayload";
    81		type Implicit = ();
    82		type Pre = ();
    83		type Val = ();
    84
    85		impl_tx_ext_default!(Call; weight validate prepare);
    86	}
    87
    88	// This is the opposite; nothing will be added to the extrinsic payload,
    89	// but the Implicit type (`1234u32`) will be added to the
    90	// payload to be signed.
    91	#[derive(Debug, Encode, Decode, DecodeWithMemTracking, Clone, Eq, PartialEq, TypeInfo)]
    92	pub struct AddToSignaturePayload;
    93
    94	impl<Call: Dispatchable> TransactionExtension<Call> for AddToSignaturePayload {
    95		const IDENTIFIER: &'static str = "AddToSignaturePayload";
    96		type Implicit = u32;
    97
    98		fn implicit(&self) -> Result<Self::Implicit, TransactionValidityError> {
    99			Ok(1234)
    100		}
    101		type Pre = ();
    102		type Val = ();
    103
    104		impl_tx_ext_default!(Call; weight validate prepare);
    105	}
    106}