X402.Scheme.ExactEVM (X402 v0.9.0)

Built-in X402.Scheme for exact payments on EVM (eip155:*) networks.

The exact-EVM scheme specification defines several asset transfer methods, selected by the requirements' extra.assetTransferMethod:

`extra.assetTransferMethod`	Transfer method	Scheme payload
absent or `"eip3009"`	EIP-3009	`%{"signature", "authorization"}`
`"permit2"`	Permit2	`%{"signature", "permit2Authorization"}`

Any other value is unsupported (transfer_method/1). Both methods are implemented for both roles:

Client — sign/3 signs an EIP-3009 TransferWithAuthorization through X402.EIP3009 for the default method, or a Permit2 PermitWitnessTransferFrom through X402.Permit2.sign_exact/2 when the requirements select "permit2" (spender: the x402ExactPermit2Proxy, witness: payTo, permitted amount: the exact amount). An entry is signable when the selected method's EIP-712 domain can be derived from the requirements — extra.name / extra.version for EIP-3009, an eip155:* network for Permit2.
Server — precheck/3 runs the local pre-checks before the facilitator round-trip on whichever authorization object the payload carries: for EIP-3009, to must equal payTo, value must equal the advertised amount, and the validAfter/validBefore window must cover now plus a settlement buffer (X402.Scheme.EVM.authorization_precheck/3); for Permit2, witness.to must equal payTo, permitted.amount must equal amount, permitted.token must equal asset, spender must be the x402ExactPermit2Proxy, and the witness.validAfter/deadline window must cover now plus the buffer (X402.Scheme.EVM.permit2_precheck/3). Payloads carrying neither map are skipped.

Envelope validation of the PAYMENT-SIGNATURE payload is handled by X402.PaymentSignature; this scheme adds no extra structural checks (X402.Scheme.validate_payload/3 returns :ok).

Summary

Types

transfer_method()

An asset transfer method of the exact-EVM scheme.

Functions

networks()

Returns ["eip155:*"] — every EVM network.

precheck(payload, requirements, opts)

Runs the local pre-checks with exact-amount equality enforced.

scheme()

Returns "exact".

sign(requirements, signer, opts)

Signs the scheme payload for the selected transfer method.

signable?(requirements)

Whether the selected transfer method's EIP-712 domain can be derived from the requirements.

transfer_method(requirements)

Resolves the asset transfer method selected by the requirements.

validate_payload(payload, requirements, opts)

Always :ok — envelope validation covers the exact payload shape.

Types

transfer_method()

@type transfer_method() :: :eip3009 | :permit2

An asset transfer method of the exact-EVM scheme.

Functions

networks()

(since 0.6.0)

@spec networks() :: [String.t()]

Returns ["eip155:*"] — every EVM network.

Examples

iex> X402.Scheme.ExactEVM.networks()
["eip155:*"]

precheck(payload, requirements, opts)

(since 0.6.0)

@spec precheck(map(), map(), keyword()) ::
  :ok | {:error, {:precheck_failed, X402.Scheme.EVM.precheck_failure()}}

Runs the local pre-checks with exact-amount equality enforced.

Dispatches on the payload shape: payload.authorization runs X402.Scheme.EVM.authorization_precheck/3, payload.permit2Authorization runs X402.Scheme.EVM.permit2_precheck/3 against the x402ExactPermit2Proxy spender. Both run when both maps are present; neither present passes.

scheme()

(since 0.6.0)

@spec scheme() :: String.t()

Returns "exact".

Examples

iex> X402.Scheme.ExactEVM.scheme()
"exact"

sign(requirements, signer, opts)

(since 0.6.0)

@spec sign(map(), X402.Signer.t(), keyword()) :: {:ok, map()} | {:error, term()}

Signs the scheme payload for the selected transfer method.

EIP-3009 requirements sign via X402.EIP3009.sign/3, honoring the client's :valid_after_buffer option; Permit2 requirements sign via X402.Permit2.sign_exact/2 (valid immediately, expiring after maxTimeoutSeconds). Other options are ignored.

signable?(requirements)

(since 0.6.0)

@spec signable?(map()) :: boolean()

Whether the selected transfer method's EIP-712 domain can be derived from the requirements.

Examples

iex> X402.Scheme.ExactEVM.signable?(%{
...>   "network" => "eip155:84532",
...>   "asset" => "0x036CbD53842c5426634e7929541eC2318f3dCF7e",
...>   "extra" => %{"name" => "USDC", "version" => "2"}
...> })
true

iex> X402.Scheme.ExactEVM.signable?(%{
...>   "network" => "eip155:84532",
...>   "asset" => "0x036CbD53842c5426634e7929541eC2318f3dCF7e",
...>   "extra" => %{"assetTransferMethod" => "permit2"}
...> })
true

iex> X402.Scheme.ExactEVM.signable?(%{"extra" => %{}})
false

iex> X402.Scheme.ExactEVM.signable?(%{
...>   "network" => "eip155:84532",
...>   "extra" => %{"assetTransferMethod" => "erc7710"}
...> })
false

transfer_method(requirements)

(since 0.9.0)

@spec transfer_method(map()) ::
  {:ok, transfer_method()} | {:error, {:unsupported_transfer_method, term()}}

Resolves the asset transfer method selected by the requirements.

Reads extra.assetTransferMethod: absent or "eip3009" selects :eip3009, "permit2" selects :permit2, anything else is {:error, {:unsupported_transfer_method, value}}.

Examples

iex> X402.Scheme.ExactEVM.transfer_method(%{"extra" => %{"name" => "USDC"}})
{:ok, :eip3009}

iex> X402.Scheme.ExactEVM.transfer_method(%{"extra" => %{"assetTransferMethod" => "permit2"}})
{:ok, :permit2}

iex> X402.Scheme.ExactEVM.transfer_method(%{"extra" => %{"assetTransferMethod" => "erc7710"}})
{:error, {:unsupported_transfer_method, "erc7710"}}

iex> X402.Scheme.ExactEVM.transfer_method(%{})
{:ok, :eip3009}

validate_payload(payload, requirements, opts)

(since 0.6.0)

@spec validate_payload(map(), map(), keyword()) :: :ok

Always :ok — envelope validation covers the exact payload shape.

Examples

iex> X402.Scheme.ExactEVM.validate_payload(%{}, %{}, [])
:ok