SeismicGasFiller

Gas estimation filler with deferred support for seismic transactions

SeismicGasFiller handles gas estimation for both Seismic and standard transactions. For Seismic transactions, it defers gas estimation to the fill phase so that estimation happens on the encrypted calldata rather than the plaintext.

Overview

Gas estimation for shielded transactions presents a unique challenge: the node needs to estimate gas on the encrypted calldata (because that is what will actually be executed), but the calldata is not encrypted until SeismicElementsFiller runs. SeismicGasFiller solves this by:

1. For Seismic transactions -- Deferring gas estimation to the fill() phase, which runs after SeismicElementsFiller has encrypted the calldata

2. For standard transactions -- Delegating to Alloy's built-in GasFiller, which estimates gas in the normal prepare phase

Additionally, SeismicGasFiller validates that Seismic transactions are not contract creation (CREATE) transactions, which are not supported for the Seismic transaction type.

Definition

pub struct SeismicGasFiller {
    inner: GasFiller,
    rpc_url: Option<reqwest::Url>,
}

Field	Type	Description
inner	GasFiller	Standard Alloy gas filler for non-seismic transactions
rpc_url	Option<reqwest::Url>	RPC URL used for deferred gas estimation on seismic transactions

Constructor

with_url

Create a SeismicGasFiller with an RPC URL for deferred gas estimation.

pub fn with_url(rpc_url: reqwest::Url) -> Self

Parameter	Type	Required	Description
rpc_url	reqwest::Url	Yes	RPC endpoint for gas estimation calls

Returns: A new SeismicGasFiller configured for deferred estimation.

The RPC URL is needed because deferred gas estimation happens during the fill() phase, which makes a separate RPC call to eth_estimateGas with the encrypted calldata. This is typically the same URL used by the provider.

Two-Phase Design

Like all Alloy fillers, SeismicGasFiller implements TxFiller<N> with prepare and fill phases.

Prepare Phase

• For Seismic transactions: Returns immediately without estimating gas (deferred to fill phase)

• For standard transactions: Delegates to the inner GasFiller, which calls eth_estimateGas as normal

Fill Phase

• For Seismic transactions: Now that the calldata is encrypted (by SeismicElementsFiller), makes an eth_estimateGas call using rpc_url and fills in the gas limit

• For standard transactions: Delegates to the inner GasFiller to apply the prepared gas estimate

Validation

SeismicGasFiller enforces that Seismic transactions cannot be CREATE transactions (i.e., transactions without a to address that deploy new contracts). If a Seismic transaction request has no to field, the filler returns an error.

This restriction exists because the Seismic transaction type (0x4A) is designed for calling existing contracts with encrypted calldata, not for deploying new contracts.

Usage

Default (Automatic)

In most cases, SeismicGasFiller is configured automatically by the provider:

use seismic_prelude::foundry::*;
use alloy_signer_local::PrivateKeySigner;

let signer: PrivateKeySigner = "0xYOUR_PRIVATE_KEY".parse()?;
let wallet = SeismicWallet::from(signer);
let url = "https://gcp-1.seismictest.net/rpc".parse()?;

// SeismicGasFiller is set up automatically with the same URL
let provider = sreth_signed_provider(wallet, url).await?;

Manual Construction

If building a custom provider stack:

use seismic_prelude::foundry::*;

let rpc_url: reqwest::Url = "https://gcp-1.seismictest.net/rpc".parse()?;
let gas_filler = SeismicGasFiller::with_url(rpc_url);

Pipeline Position

SeismicGasFiller must come after SeismicElementsFiller in the filler chain:

NonceFiller + ChainIdFiller
  -> SeismicElementsFiller  (encrypts calldata)
  -> SeismicGasFiller       (estimates gas on encrypted calldata)
  -> WalletFiller            (signs the transaction)

If SeismicGasFiller ran before SeismicElementsFiller, it would estimate gas on the plaintext calldata, which would produce an incorrect gas estimate.

Notes

• For Seismic transactions, gas estimation happens on the encrypted calldata, which may differ slightly from the plaintext gas cost

• The GasFiller inner field handles all non-Seismic gas estimation logic

• Seismic CREATE transactions are explicitly rejected with an error

• The rpc_url field is Option to support cases where deferred estimation is not needed (e.g., when gas is pre-specified)

See Also

• Fillers Overview - How fillers compose in the pipeline

• SeismicElementsFiller - Encryption filler (runs before this one)

• SeismicSignedProvider - Provider that uses this filler

• SeismicNetwork Trait - Network trait methods used for type checking