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NFT Storefront Smart Contract

Primer​

The NFTStorefrontV2 contract lets you create a non-custodial Resource (NFT) marketplace on the FLOW blockchain.

NFTStorefrontV2 makes it simple for Sellers to list NFTs in dApp specific marketplaces. DApp developers leverage the APIs provided by the contract to manage listings being offered for sale and to transact NFT trades.

dapps_1

Developers should use the NFTStorefrontV2 to create their marketplace and to enable p2p purchases. The diagram below shows how dApps can facilitate the creation of NFT listings for different marketplaces and how marketplaces can filter their listings.

Listings made through a specific dApp storefront can be simultaneously listed on 3rd party marketplaces beyond that dApp. Well known 3rd party marketplaces listen for compatible NFT listing events enabling the automation of listings into their marketplace dashboards.

dapps_2

Using the NFTStorefrontV2, marketplaces can instantly and easily tap into the vibrant FLOW NFT ecosystem and allow NFT holders to list their NFTs and enables creator royalties.

Marketplaces then process an NFT trade by interacting directly with seller storefronts. Flow's account based model ensures that NFTs listed for sale always reside in the Seller account until traded, regardless of how many listings are posted across any number of marketplaces, for the same NFT.

marketplace_1

Functional Overview​

A general purpose sale support contract for NFTs implementing the Flow NonFungibleToken standard. Each account that wants to list NFTs for sale creates a Storefront resource to store in their account and lists individual sales within that Storefront as Listings. There is usually one Storefront per account held at the /storage/NFTStorefrontV2.

Each listing can define one or more sale cuts taken out of the sale price to go to one or more addresses. Listing fees, royalties, or other considerations can be paid using sale cuts. Also, the listing can include a commission as one of these sale cuts is paid to whoever facilitates the purchase.

Listings can have an optional list of marketplace receiver capabilities used to receive the commission for fulfilling the listing. An NFT may be listed in one or more Listings, and the validity of each listing can easily be checked.

Interested parties can globally track Listing events on-chain and filter by NFT types, IDs and other characteristics to determine which to make available for purchase within their own marketplace UIs."

Selling NFTs​

NFTStorefrontV2 offers a generic process for creating the listing for an NFT. It provides all the essential APIs to manage those listings independently.

Many marketplaces create a single storefront resource to manage different individual listings. We recommend creating the listing under the user-owned storefront resource to make it trustless and platform-independent. Users should possess the Storefront resource under their account to create the listing using the storefront contract.

Creating a successful listing using the NFTStorefrontV2 contract.​

As recommended above, the first step is to create and store the Storefront resource in the user account using the setup_account transaction.

The next step is to create a listing under the newly created storefront resource. If the user (repetitive) already holds the storefront resource, then use the existing resource. The seller can come with multiple requirements for listing their NFTs, and We try our best to cover most of them below.

Scenario 1: Selling NFTs corresponds to more than one cryptocurrency, i.e. FLOW, FUSD etc.​

The NFTStorefrontV2 contract doesn’t support selling an NFT for multiple different currencies with a single listing. However, this can be achieved by creating multiple listings for the same NFT for each different currency.

Example - Alice wants to sell a kitty and is open to receiving FLOW and FUSD

scenario_1

Putting an NFT on sell called listing, seller can create a listing using sell_item transaction by providing some required details to list an NFT, i.e. Receiving currency type, Capability from where NFT will be deducted etc. If interested look here for more details.

To receive a different currency seller has to provide a different Receiver currency type , i.e. salePaymentVaultType As depicted in the above diagram, There are two listing formations with almost the same inputs. The only differentiator is the salePaymentVaultType parameter that needs to be different when creating duplicate NFT listings with different sale currency types.

Scenario 2: Peer-to-Peer (p2p) listing of NFT: A listing anyone can fulfil.​

Dapps can leverage the NFTStorefrontV2 to facilitate the creation of a listing for the seller independent of any marketplace. Dapps or marketplaces can list those listings on their platforms, or seller can settle it p2p.

The seller can use sell_item transaction to create a p2p listing, providing the marketplacesAddress with an empty array. The seller has a choice of providing commission to the facilitator of sale, which can also act as a discount if the facilitator and the purchaser are the same.

Scenario 3: The seller wants to list its NFT in different marketplaces.​

NFTStorefrontV2 offers two different ways of doing it.

  • The seller can create a listing and provide the marketplacesAddress that it wants to have a listing on using sell_item transaction.

    Marketplaces can listen to ListingAvailable events and check whether their address is included in the commissionReceivers list; If yes, the marketplace would be rewarded during the successful fulfilment of the listing.

    Example - Bob wants to list on marketplace 0xA, 0xB & 0xC and is willing to offer 10% commission on the sale price of the listing to the marketplaces.

    scenario_3

  • Another way to accomplish this is to create separate listings for each marketplace on which a user wants their listing using sell_item_with_marketplace_cut transaction. In this case, the marketplace would be incentivized by earning one of the parts of the saleCut by appending marketplace saleCut in saleCuts array during the creation of the listing.

Considerations​

  1. Ghost listings - Ghost listings are listings which don’t have an underlying NFT in the seller’s account. However, the listing is still available for buyers to attempt to purchase. StorefrontV2 is not immune to ghost listings. Usually, ghost listings will cause a purchaser’s transaction to fail, which is annoying but isn’t a significant problem. Ghost listings become a problem for the seller when the listed NFT comes back to the seller’s account after its original sale. The ghost listing will no longer be invalid when it comes back, and anyone can purchase it even if the seller doesn’t want to sell it at that price anymore.

    Note - We recommend that marketplaces and p2p dApps create an off-chain notification service that tells their users (i.e., sellers) to remove the listings if they don’t hold the NFT anymore in the same account.

  2. Expired listings - NFTStorefrontV2 introduces a safety measure to specify that a listing will expire after a certain period that can be set during the creation so no one can purchase the listing anymore. It is not a fool-proof safety measure, but it does give some safe ground to the sellers for the ghost listings & stale listings.

    Note - We recommended for marketplaces and p2p dApps not to show the expired listings on their dashboards.

Purchasing NFTs​

Purchasing NFTs through the NFTStorefrontV2 is simple. The buyer has to provide the payment vault and the commissionRecipient , if applicable, during the purchase. p2p dApps don’t need any intermediaries to facilitate the purchase of listings. purchase API offered by the Listing resource gets used to facilitate the purchase of NFT.

During the listing purchase all saleCuts are paid automatically. This also includes distributing royalties for that NFT, if applicable. If the vault provided by the buyer lacks sufficient funds then the transaction will fail.

Considerations​

  1. Auto cleanup - NFTStorefrontV2 offers a unique ability to do auto cleanup of duplicate listings during a purchase. It comes with a drawback if one NFT has thousands of duplicate listings. It will become the bottleneck during purchasing one of the listings as it will likely trigger an out-of-gas error.

    Note - We recommended NOT to have more than 50 (TBD) duplicate listings of any given NFT.

  2. Unsupported receiver capability - A common pitfall during the purchase of an NFT that some saleCut receivers don’t have a supported receiver capability because that entitled sale cut would transfer to first valid sale cut receiver. However, it can be partially solved by providing the generic receiver using the FungibleTokenSwitchboard contract and adding all the currency capabilities the beneficiary wants to receive. More on the FungibleTokenSwitchboard can be read here

Enabling creator royalties for NFTs​

The NFTStorefrontV2 contract optionally supports paying royalties to the minter account for secondary resales of that NFT after the original sale. Marketplaces decide for themselves whether to support creator royalties when validating listings for sale eligibility. We encourage all marketplaces to support creator royalties and support community creators in the FLOW ecosystem.

Providing that a seller's NFT supports the Royalty Metadata View standard, then marketplaces can honor royalties payments at time of purchase. NFTStorefrontV2 dynamically calculates the royalties owed at the time of listing creation and applies it as a saleCut of the listing at the time of purchase.


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// Check whether the NFT implements the MetadataResolver or not.
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if nft.getViews().contains(Type<MetadataViews.Royalties>()) {
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// Resolve the royalty view
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let royaltiesRef = nft.resolveView(Type<MetadataViews.Royalties>())?? panic("Unable to retrieve the royalties")
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// Fetch the royalties.
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let royalties = (royaltiesRef as! MetadataViews.Royalties).getRoyalties()
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// Append the royalties as the salecut
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for royalty in royalties {
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self.saleCuts.append(NFTStorefrontV2.SaleCut(receiver: royalty.receiver, amount: royalty.cut * effectiveSaleItemPrice))
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totalRoyaltyCut = totalRoyaltyCut + royalty.cut * effectiveSaleItemPrice
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}
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}

Complete transaction can be viewed here.

saleCut only supports a single token receiver type and therefore beneficiaries of a saleCut can also only receive the token type used for the purchase. To support different token types for saleCuts we recommend using the FungibleTokenSwitchboard contract. The contract defines a generic receiver for fungible tokens which itself handles routing of tokens to the respective vault for that token type. Learn more about this here.

Enabling marketplace commissions for NFT sales​

NFTStorefrontV2 enables optional commissions on trades for marketplaces which require it as a condition to list a NFT for sale. Commission & commission receivers are set by the seller during initial listing creation. At time of purchase the commission amount is paid once only to the commission receiver matching the marketplace receiver address which facilitated the sale.

For NFT listings in marketplaces which don't require commission, commission receivers can be set as nil. Setting the buyer of the NFT and commissionRecipient to the same has the effect of applying a discount for the buyer.

scenario_2.

APIs & Events offered by NFTStorefrontV2​

Resource Interface ListingPublic​


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resource interface ListingPublic {
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pub fun borrowNFT(): &NonFungibleToken.NFT?
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pub fun purchase(
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payment: @FungibleToken.Vault,
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commissionRecipient: Capability<&{FungibleToken.Receiver}>?,
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): @NonFungibleToken.NFT
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pub fun getDetails(): ListingDetail
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pub fun getAllowedCommissionReceivers(): [Capability<&{FungibleToken.Receiver}>]?
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}

An interface providing a useful public interface to a Listing.

Functions​

fun borrowNFT()


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fun borrowNFT(): &NonFungibleToken.NFT?

This will assert in the same way as the NFT standard borrowNFT() if the NFT is absent, for example if it has been sold via another listing.

fun purchase()


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fun purchase(payment FungibleToken.Vault, commissionRecipient Capability<&{FungibleToken.Receiver}>?): NonFungibleToken.NFT

Facilitates the purchase of the listing by providing the payment vault and the commission recipient capability if there is a non-zero commission for the given listing. Respective saleCuts are transferred to beneficiaries and funtion return underlying or listed NFT.

fun getDetails()


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fun getDetails(): ListingDetails

Fetches the details of the listings

fun getAllowedCommissionReceivers()


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fun getAllowedCommissionReceivers(): [Capability<&{FungibleToken.Receiver}>]?

Fetches the allowed marketplaces capabilities or commission receivers for the underlying listing. If it returns nil then commission is up to grab by anyone.

Resource Storefront​


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resource Storefront {
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pub fun createListing(
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nftProviderCapability: Capability<&{NonFungibleToken.Provider, NonFungibleToken.CollectionPublic}>,
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nftType: Type,
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nftID: UInt64,
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salePaymentVaultType: Type,
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saleCuts: [SaleCut],
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marketplacesCapability: [Capability<&{FungibleToken.Receiver}>]?,
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customID: String?,
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commissionAmount: UFix64,
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expiry: UInt64
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): UInt64
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pub fun removeListing(listingResourceID: UInt64)
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pub fun getListingIDs(): [UInt64]
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pub fun getDuplicateListingIDs(nftType: Type, nftID: UInt64, listingID: UInt64): [UInt64]
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pub fun cleanupExpiredListings(fromIndex: UInt64, toIndex: UInt64)
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pub fun borrowListing(listingResourceID: UInt64): &Listing{ListingPublic}?
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}

A resource that allows its owner to manage a list of Listings, and anyone to interact with them in order to query their details and purchase the NFTs that they represent.

Implemented Interfaces:

  • StorefrontManager
  • StorefrontPublic

Initializer​


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fun init()

Functions​

fun createListing()


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fun createListing(nftProviderCapability Capability<&{NonFungibleToken.Provider, NonFungibleToken.CollectionPublic}>, nftType Type, nftID UInt64, salePaymentVaultType Type, saleCuts [SaleCut], marketplacesCapability [Capability<&{FungibleToken.Receiver}>]?, customID String?, commissionAmount UFix64, expiry UInt64): UInt64

insert Create and publish a Listing for an NFT.

fun removeListing()


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fun removeListing(listingResourceID UInt64)

removeListing Remove a Listing that has not yet been purchased from the collection and destroy it.

fun getListingIDs()


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fun getListingIDs(): [UInt64]

getListingIDs Returns an array of the Listing resource IDs that are in the collection

fun getDuplicateListingIDs()


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fun getDuplicateListingIDs(nftType Type, nftID UInt64, listingID UInt64): [UInt64]

getDuplicateListingIDs Returns an array of listing IDs that are duplicates of the given nftType and nftID.

fun cleanupExpiredListings()


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fun cleanupExpiredListings(fromIndex UInt64, toIndex UInt64)

cleanupExpiredListings Cleanup the expired listing by iterating over the provided range of indexes.

fun borrowListing()


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fun borrowListing(listingResourceID UInt64): &Listing{ListingPublic}?

borrowListing Returns a read-only view of the listing for the given listingID if it is contained by this collection.

Resource Interface StorefrontPublic​


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resource interface StorefrontPublic {
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pub fun getListingIDs(): [UInt64]
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pub fun getDuplicateListingIDs(nftType: Type, nftID: UInt64, listingID: UInt64): [UInt64]
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pub fun cleanupExpiredListings(fromIndex: UInt64, toIndex: UInt64)
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pub fun borrowListing(listingResourceID: UInt64): &Listing{ListingPublic}?
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pub fun cleanupPurchasedListings(listingResourceID: UInt64)
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pub fun getExistingListingIDs(nftType: Type, nftID: UInt64): [UInt64]
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}

StorefrontPublic An interface to allow listing and borrowing Listings, and purchasing items via Listings in a Storefront.

Functions​

fun getListingIDs()


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fun getListingIDs(): [UInt64]

getListingIDs Returns an array of the Listing resource IDs that are in the collection

fun getDuplicateListingIDs()


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fun getDuplicateListingIDs(nftType Type, nftID UInt64, listingID UInt64): [UInt64]

getDuplicateListingIDs Returns an array of listing IDs that are duplicates of the given nftType and nftID.

fun borrowListing()


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fun borrowListing(listingResourceID UInt64): &Listing{ListingPublic}?

borrowListing Returns a read-only view of the listing for the given listingID if it is contained by this collection.

fun cleanupExpiredListings()


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fun cleanupExpiredListings(fromIndex UInt64, toIndex UInt64)

cleanupExpiredListings Cleanup the expired listing by iterating over the provided range of indexes.

fun cleanupPurchasedListings()


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fun cleanupPurchasedListings(listingResourceID: UInt64)

cleanupPurchasedListings Allows anyone to remove already purchased listings.

fun getExistingListingIDs()


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fun getExistingListingIDs(nftType Type, nftID UInt64): [UInt64]

getExistingListingIDs Returns an array of listing IDs of the given nftType and nftID.

Events​

event StorefrontInitialized


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event StorefrontInitialized(storefrontResourceID: UInt64)

A Storefront resource has been created. Consumers can now expect events from this Storefront. Note that we do not specify an address: we cannot and should not. Created resources do not have an owner address, and may be moved after creation in ways we cannot check. ListingAvailable events can be used to determine the address of the owner of the Storefront at the time of the listing but only at that precise moment in that precise transaction. If the seller moves the Storefront while the listing is valid, that is on them.

event StorefrontDestroyed


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event StorefrontDestroyed(storefrontResourceID: UInt64)

A Storefront has been destroyed. Event consumers can now stop processing events from this Storefront. Note - we do not specify an address.

event ListingAvailable


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event ListingAvailable(storefrontAddress: Address, listingResourceID: UInt64, nftType: Type, nftUUID: UInt64, nftID: UInt64, salePaymentVaultType: Type, salePrice: UFix64, customID: String?, commissionAmount: UFix64, commissionReceivers: [Address]?, expiry: UInt64)

Above event gets emitted when a listing has been created and added to a Storefront resource. The Address values here are valid when the event is emitted, but the state of the accounts they refer to may change outside of the NFTStorefrontV2 workflow, so be careful to check when using them.

event ListingCompleted


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event ListingCompleted(listingResourceID: UInt64, storefrontResourceID: UInt64, purchased: Bool, nftType: Type, nftUUID: UInt64, nftID: UInt64, salePaymentVaultType: Type, salePrice: UFix64, customID: String?, commissionAmount: UFix64, commissionReceiver: Address?, expiry: UInt64)

The listing has been resolved. It has either been purchased, removed or destroyed.

event UnpaidReceiver


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event UnpaidReceiver(receiver: Address, entitledSaleCut: UFix64)

A entitled receiver has not been paid during the sale of the NFT.

Holistic process flow diagram of NFTStorefrontV2 -

NFT Storefront Process flow

Glossary​

SaleCut - A struct consists a recipient and amount of token ,i.e. cut that must be sent to recipient when a NFT get sold.