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Module 0x2::transfer_policy

Defines the TransferPolicy type and the logic to approve TransferRequests.

use 0x1::option;
use 0x1::type_name;
use 0x2::balance;
use 0x2::coin;
use 0x2::dynamic_field;
use 0x2::event;
use 0x2::object;
use 0x2::package;
use 0x2::sui;
use 0x2::transfer;
use 0x2::tx_context;
use 0x2::vec_set;

Struct TransferRequest

A "Hot Potato" forcing the buyer to get a transfer permission from the item type (T) owner on purchase attempt.

struct TransferRequest<T>
item: object::ID
The ID of the transferred item. Although the T has no constraints, the main use case for this module is to work with Objects.
paid: u64
Amount of SUI paid for the item. Can be used to calculate the fee / transfer policy enforcement.
from: object::ID
The ID of the Kiosk / Safe the object is being sold from. Can be used by the TransferPolicy implementors.
receipts: vec_set::VecSet<type_name::TypeName>
Collected Receipts. Used to verify that all of the rules were followed and TransferRequest can be confirmed.

Resource TransferPolicy

A unique capability that allows the owner of the T to authorize transfers. Can only be created with the Publisher object. Although there's no limitation to how many policies can be created, for most of the cases there's no need to create more than one since any of the policies can be used to confirm the TransferRequest.

struct TransferPolicy<T> has store, key
id: object::UID
balance: balance::Balance<sui::SUI>
The Balance of the TransferPolicy which collects SUI. By default, transfer policy does not collect anything , and it's a matter of an implementation of a specific rule - whether to add to balance and how much.
rules: vec_set::VecSet<type_name::TypeName>
Set of types of attached rules - used to verify receipts when a TransferRequest is received in confirm_request function.

Additionally provides a way to look up currently attached Rules.

Resource TransferPolicyCap

A Capability granting the owner permission to add/remove rules as well as to withdraw and destroy_and_withdraw the TransferPolicy.

struct TransferPolicyCap<T> has store, key
id: object::UID
policy_id: object::ID

Struct TransferPolicyCreated

Event that is emitted when a publisher creates a new TransferPolicyCap making the discoverability and tracking the supported types easier.

struct TransferPolicyCreated<T> has copy, drop

Struct TransferPolicyDestroyed

Event that is emitted when a publisher destroys a TransferPolicyCap. Allows for tracking supported policies.

struct TransferPolicyDestroyed<T> has copy, drop

Struct RuleKey

Key to store "Rule" configuration for a specific TransferPolicy.

struct RuleKey<T: drop> has copy, drop, store
dummy_field: bool


Trying to withdraw more than there is.

const ENotEnough: u64 = 5;

Trying to withdraw or close_and_withdraw with a wrong Cap.

const ENotOwner: u64 = 4;

A completed rule is not set in the TransferPolicy.

const EIllegalRule: u64 = 1;

The number of receipts does not match the TransferPolicy requirement.

const EPolicyNotSatisfied: u64 = 0;

Attempting to create a Rule that is already set.

const ERuleAlreadySet: u64 = 3;

A Rule is not set.

const EUnknownRequrement: u64 = 2;

Function new_request

Construct a new TransferRequest hot potato which requires an approving action from the creator to be destroyed / resolved. Once created, it must be confirmed in the confirm_request call otherwise the transaction will fail.

public fun new_request<T>(item: object::ID, paid: u64, from: object::ID): transfer_policy::TransferRequest<T>
public fun new_request<T>(
    item: ID, paid: u64, from: ID
): TransferRequest<T> {
    TransferRequest { item, paid, from, receipts: vec_set::empty() }

Function new

Register a type in the Kiosk system and receive a TransferPolicy and a TransferPolicyCap for the type. The TransferPolicy is required to confirm kiosk deals for the T. If there's no TransferPolicy available for use, the type can not be traded in kiosks.

public fun new<T>(pub: &package::Publisher, ctx: &mut tx_context::TxContext): (transfer_policy::TransferPolicy<T>, transfer_policy::TransferPolicyCap<T>)
public fun new<T>(
    pub: &Publisher, ctx: &mut TxContext
): (TransferPolicy<T>, TransferPolicyCap<T>) {
    assert!(package::from_package<T>(pub), 0);
    let id = object::new(ctx);
    let policy_id = id.to_inner();

    event::emit(TransferPolicyCreated<T> { id: policy_id });

        TransferPolicy { id, rules: vec_set::empty(), balance: balance::zero() },
        TransferPolicyCap { id: object::new(ctx), policy_id }

Function default

Initialize the Tranfer Policy in the default scenario: Create and share the TransferPolicy, transfer TransferPolicyCap to the transaction sender.

entry fun default<T>(pub: &package::Publisher, ctx: &mut tx_context::TxContext)
entry fun default<T>(pub: &Publisher, ctx: &mut TxContext) {
    let (policy, cap) = new<T>(pub, ctx);
    sui::transfer::transfer(cap, ctx.sender());

Function withdraw

Withdraw some amount of profits from the TransferPolicy. If amount is not specified, all profits are withdrawn.

public fun withdraw<T>(self: &mut transfer_policy::TransferPolicy<T>, cap: &transfer_policy::TransferPolicyCap<T>, amount: option::Option<u64>, ctx: &mut tx_context::TxContext): coin::Coin<sui::SUI>
public fun withdraw<T>(
    self: &mut TransferPolicy<T>,
    cap: &TransferPolicyCap<T>,
    amount: Option<u64>,
    ctx: &mut TxContext
): Coin<SUI> {
    assert!(object::id(self) == cap.policy_id, ENotOwner);

    let amount = if (amount.is_some()) {
        let amt = amount.destroy_some();
        assert!(amt <= self.balance.value(), ENotEnough);
    } else {

    coin::take(&mut self.balance, amount, ctx)

Function destroy_and_withdraw

Destroy a TransferPolicyCap. Can be performed by any party as long as they own it.

public fun destroy_and_withdraw<T>(self: transfer_policy::TransferPolicy<T>, cap: transfer_policy::TransferPolicyCap<T>, ctx: &mut tx_context::TxContext): coin::Coin<sui::SUI>
public fun destroy_and_withdraw<T>(
    self: TransferPolicy<T>, cap: TransferPolicyCap<T>, ctx: &mut TxContext
): Coin<SUI> {
    assert!(object::id(&self) == cap.policy_id, ENotOwner);

    let TransferPolicyCap { id: cap_id, policy_id } = cap;
    let TransferPolicy { id, rules: _, balance } = self;

    event::emit(TransferPolicyDestroyed<T> { id: policy_id });

Function confirm_request

Allow a TransferRequest for the type T. The call is protected by the type constraint, as only the publisher of the T can get TransferPolicy<T>.

Note: unless there's a policy for T to allow transfers, Kiosk trades will not be possible.

public fun confirm_request<T>(self: &transfer_policy::TransferPolicy<T>, request: transfer_policy::TransferRequest<T>): (object::ID, u64, object::ID)
public fun confirm_request<T>(
    self: &TransferPolicy<T>, request: TransferRequest<T>
): (ID, u64, ID) {
    let TransferRequest { item, paid, from, receipts } = request;
    let mut completed = receipts.into_keys();
    let mut total = completed.length();

    assert!(total == self.rules.size(), EPolicyNotSatisfied);

    while (total > 0) {
        let rule_type = completed.pop_back();
        assert!(self.rules.contains(&rule_type), EIllegalRule);
        total = total - 1;

    (item, paid, from)

Function add_rule

Add a custom Rule to the TransferPolicy. Once set, TransferRequest must receive a confirmation of the rule executed so the hot potato can be unpacked.

  • T: the type to which TransferPolicy is applied.
  • Rule: the witness type for the Custom rule
  • Config: a custom configuration for the rule

Config requires drop to allow creators to remove any policy at any moment, even if graceful unpacking has not been implemented in a "rule module".

public fun add_rule<T, Rule: drop, Config: drop, store>(_: Rule, policy: &mut transfer_policy::TransferPolicy<T>, cap: &transfer_policy::TransferPolicyCap<T>, cfg: Config)
public fun add_rule<T, Rule: drop, Config: store + drop>(
    _: Rule, policy: &mut TransferPolicy<T>, cap: &TransferPolicyCap<T>, cfg: Config
) {
    assert!(object::id(policy) == cap.policy_id, ENotOwner);
    assert!(!has_rule<T, Rule>(policy), ERuleAlreadySet);
    df::add(&mut, RuleKey<Rule> {}, cfg);

Function get_rule

Get the custom Config for the Rule (can be only one per "Rule" type).

public fun get_rule<T, Rule: drop, Config: drop, store>(_: Rule, policy: &transfer_policy::TransferPolicy<T>): &Config
public fun get_rule<T, Rule: drop, Config: store + drop>(
    _: Rule, policy: &TransferPolicy<T>)
: &Config {
    df::borrow(&, RuleKey<Rule> {})

Function add_to_balance

Add some SUI to the balance of a TransferPolicy.

public fun add_to_balance<T, Rule: drop>(_: Rule, policy: &mut transfer_policy::TransferPolicy<T>, coin: coin::Coin<sui::SUI>)
public fun add_to_balance<T, Rule: drop>(
    _: Rule, policy: &mut TransferPolicy<T>, coin: Coin<SUI>
) {
    assert!(has_rule<T, Rule>(policy), EUnknownRequrement);
    coin::put(&mut policy.balance, coin)

Function add_receipt

Adds a Receipt to the TransferRequest, unblocking the request and confirming that the policy requirements are satisfied.

public fun add_receipt<T, Rule: drop>(_: Rule, request: &mut transfer_policy::TransferRequest<T>)
public fun add_receipt<T, Rule: drop>(
    _: Rule, request: &mut TransferRequest<T>
) {

Function has_rule

Check whether a custom rule has been added to the TransferPolicy.

public fun has_rule<T, Rule: drop>(policy: &transfer_policy::TransferPolicy<T>): bool
public fun has_rule<T, Rule: drop>(policy: &TransferPolicy<T>): bool {
    df::exists_(&, RuleKey<Rule> {})

Function remove_rule

Remove the Rule from the TransferPolicy.

public fun remove_rule<T, Rule: drop, Config: drop, store>(policy: &mut transfer_policy::TransferPolicy<T>, cap: &transfer_policy::TransferPolicyCap<T>)
public fun remove_rule<T, Rule: drop, Config: store + drop>(
    policy: &mut TransferPolicy<T>, cap: &TransferPolicyCap<T>
) {
    assert!(object::id(policy) == cap.policy_id, ENotOwner);
    let _: Config = df::remove(&mut, RuleKey<Rule> {});

Function uid

Allows reading custom attachments to the TransferPolicy if there are any.

public fun uid<T>(self: &transfer_policy::TransferPolicy<T>): &object::UID
public fun uid<T>(self: &TransferPolicy<T>): &UID { & }

Function uid_mut_as_owner

Get a mutable reference to the to enable custom attachments to the TransferPolicy.

public fun uid_mut_as_owner<T>(self: &mut transfer_policy::TransferPolicy<T>, cap: &transfer_policy::TransferPolicyCap<T>): &mut object::UID
public fun uid_mut_as_owner<T>(
    self: &mut TransferPolicy<T>, cap: &TransferPolicyCap<T>,
): &mut UID {
    assert!(object::id(self) == cap.policy_id, ENotOwner);

Function rules

Read the rules field from the TransferPolicy.

public fun rules<T>(self: &transfer_policy::TransferPolicy<T>): &vec_set::VecSet<type_name::TypeName>
public fun rules<T>(self: &TransferPolicy<T>): &VecSet<TypeName> {

Function item

Get the item field of the TransferRequest.

public fun item<T>(self: &transfer_policy::TransferRequest<T>): object::ID
public fun item<T>(self: &TransferRequest<T>): ID { self.item }

Function paid

Get the paid field of the TransferRequest.

public fun paid<T>(self: &transfer_policy::TransferRequest<T>): u64
public fun paid<T>(self: &TransferRequest<T>): u64 { self.paid }

Function from

Get the from field of the TransferRequest.

public fun from<T>(self: &transfer_policy::TransferRequest<T>): object::ID
public fun from<T>(self: &TransferRequest<T>): ID { self.from }