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Add Burner contract to allow resource callbacks before destruction #407
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,79 @@ | ||
| // Burner is a contract that can facilitate the destruction of any resource on flow. | ||
| // | ||
| // Contributors | ||
| // - Austin Kline - https://twitter.com/austin_flowty | ||
| // - Deniz Edincik - https://twitter.com/bluesign | ||
| // - Bastian Müller - https://twitter.com/turbolent | ||
| pub contract Burner { | ||
| // When Crescendo (Cadence 1.0) is released, custom destructors will be removed from cadece. | ||
| // Burnable is an interface meant to replace this lost feature, allowing anyone to add a callback | ||
| // method to ensure they do not destroy something which is not meant to be, or to add logic based on destruction | ||
| // such as tracking the supply of an NFT Collection | ||
| // | ||
| // NOTE: The only way to see benefit from this interface is to call the burnCallback method yourself, | ||
| // or to always use the burn method in this contract. Anyone who owns a resource can always elect **not** | ||
| // to destroy a resource this way | ||
| pub resource interface Burnable { | ||
| pub fun burnCallback() | ||
| } | ||
|
|
||
| // burn is a global method which will destroy any resource it is given. | ||
| // If the provided resource implements the Burnable interface, it will call the burnCallback | ||
| // method and then destroy afterwards. | ||
| pub fun burn(_ r: @AnyResource) { | ||
| if let s <- r as? @{Burnable} { | ||
| s.burnCallback() | ||
| destroy s | ||
| } else if let arr <- r as? @[AnyResource] { | ||
| while arr.length > 0 { | ||
| let item <- arr.removeFirst() | ||
| self.burn(<-item) | ||
| } | ||
| destroy arr | ||
| } else if let stringDict <- r as? @{String: AnyResource} { | ||
| let keys = stringDict.keys | ||
| while keys.length > 0 { | ||
| let item <- stringDict.remove(key: keys.removeFirst())! | ||
| self.burn(<-item) | ||
| } | ||
| destroy stringDict | ||
| } else if let numDict <- r as? @{Number: AnyResource} { | ||
| let keys = numDict.keys | ||
| while keys.length > 0 { | ||
| let item <- numDict.remove(key: keys.removeFirst())! | ||
| self.burn(<-item) | ||
| } | ||
| destroy numDict | ||
| } else if let typeDict <- r as? @{Type: AnyResource} { | ||
| let keys = typeDict.keys | ||
| while keys.length > 0 { | ||
| let item <- typeDict.remove(key: keys.removeFirst())! | ||
| self.burn(<-item) | ||
| } | ||
| destroy typeDict | ||
| } else if let addressDict <- r as? @{Address: AnyResource} { | ||
| let keys = addressDict.keys | ||
| while keys.length > 0 { | ||
| let item <- addressDict.remove(key: keys.removeFirst())! | ||
| self.burn(<-item) | ||
| } | ||
| destroy addressDict | ||
| } else if let pathDict <- r as? @{Path: AnyResource} { | ||
| let keys = pathDict.keys | ||
| while keys.length > 0 { | ||
| let item <- pathDict.remove(key: keys.removeFirst())! | ||
| self.burn(<-item) | ||
| } | ||
| destroy pathDict | ||
| } else if let charDict <- r as? @{Character: AnyResource} { | ||
| let keys = charDict.keys | ||
| while keys.length > 0 { | ||
| let item <- charDict.remove(key: keys.removeFirst())! | ||
| self.burn(<-item) | ||
| } | ||
| destroy charDict | ||
| } else { | ||
| destroy r | ||
| } | ||
| } | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,32 @@ | ||
| import "Burner" | ||
|
|
||
| pub contract BurnableTest { | ||
| pub var totalBurned: UInt64 | ||
|
|
||
| pub resource WithCallback: Burner.Burnable { | ||
| pub let allowDestroy: Bool | ||
|
|
||
| pub fun burnCallback() { | ||
| assert(self.allowDestroy, message: "allowDestroy must be set to true") | ||
| BurnableTest.totalBurned = BurnableTest.totalBurned + 1 | ||
| } | ||
|
|
||
| init(_ allowDestroy: Bool) { | ||
| self.allowDestroy = allowDestroy | ||
| } | ||
| } | ||
|
|
||
| pub resource WithoutCallback {} | ||
|
|
||
| pub fun createSafe(allowDestroy: Bool): @WithCallback { | ||
| return <- create WithCallback(allowDestroy) | ||
| } | ||
|
|
||
| pub fun createUnsafe(): @WithoutCallback { | ||
| return <- create WithoutCallback() | ||
| } | ||
|
|
||
| init() { | ||
| self.totalBurned = 0 | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,98 @@ | ||
| import Test | ||
| import BlockchainHelpers | ||
|
|
||
| pub fun setup() { | ||
| Test.deployContract(name: "Burner", path: "../contracts/Burner.cdc", arguments: []) | ||
| Test.deployContract(name: "BurnableTest", path: "../contracts/testContracts/BurnableTest.cdc", arguments: []) | ||
| } | ||
|
|
||
| pub fun testWithCallbackDestory_Allowed() { | ||
| let acct = Test.createAccount() | ||
| txExecutor( | ||
| "burner/create_and_destroy_with_callback.cdc", | ||
| [acct], | ||
| [true] | ||
| ) | ||
| } | ||
|
|
||
| pub fun testWithCallback_NotAllowed() { | ||
| let acct = Test.createAccount() | ||
|
|
||
| Test.expectFailure(fun() { | ||
| txExecutor( | ||
| "burner/create_and_destroy_with_callback.cdc", | ||
| [acct], | ||
| [false] | ||
| ) | ||
| }, errorMessageSubstring: "allowDestroy must be set to true") | ||
| } | ||
|
|
||
| pub fun testWithoutCallbackDestroy_Allowed() { | ||
| let acct = Test.createAccount() | ||
| txExecutor( | ||
| "burner/create_and_destroy_without_callback.cdc", | ||
| [acct], | ||
| [] | ||
| ) | ||
| } | ||
|
|
||
| pub fun testDestroy_Dict() { | ||
| let acct = Test.createAccount() | ||
|
|
||
| let types = [Type<Address>(), Type<String>(), Type<CapabilityPath>(), Type<Number>(), Type<Type>(), Type<Character>()] | ||
| for type in types { | ||
| txExecutor( | ||
| "burner/create_and_destroy_dict.cdc", | ||
| [acct], | ||
| [true, type] | ||
| ) | ||
| } | ||
| } | ||
|
|
||
| pub fun testDestroy_Dict_NotAllowed() { | ||
| let acct = Test.createAccount() | ||
|
|
||
| let types = [Type<Address>(), Type<String>(), Type<CapabilityPath>(), Type<Number>(), Type<Type>(), Type<Character>()] | ||
| for type in types { | ||
| Test.expectFailure(fun() { | ||
| txExecutor( | ||
| "burner/create_and_destroy_dict.cdc", | ||
| [acct], | ||
| [false, type] | ||
| ) | ||
| }, errorMessageSubstring: "allowDestroy must be set to true") | ||
| } | ||
| } | ||
|
|
||
| pub fun testDestroy_Array() { | ||
| let acct = Test.createAccount() | ||
| txExecutor( | ||
| "burner/create_and_destroy_array.cdc", | ||
| [acct], | ||
| [true] | ||
| ) | ||
| } | ||
|
|
||
| pub fun loadCode(_ fileName: String, _ baseDirectory: String): String { | ||
| return Test.readFile("./".concat(baseDirectory).concat("/").concat(fileName)) | ||
| } | ||
|
|
||
| pub fun txExecutor(_ txName: String, _ signers: [Test.Account], _ arguments: [AnyStruct]): Test.TransactionResult { | ||
| let txCode = loadCode(txName, "transactions") | ||
|
|
||
| let authorizers: [Address] = [] | ||
| for signer in signers { | ||
| authorizers.append(signer.address) | ||
| } | ||
| let tx = Test.Transaction( | ||
| code: txCode, | ||
| authorizers: authorizers, | ||
| signers: signers, | ||
| arguments: arguments, | ||
| ) | ||
| let txResult = Test.executeTransaction(tx) | ||
| if let err = txResult.error { | ||
| panic(err.message) | ||
| } | ||
| return txResult | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,17 @@ | ||
| import "BurnableTest" | ||
| import "Burner" | ||
|
|
||
| transaction(allowDestroy: Bool) { | ||
| prepare(acct: AuthAccount) { | ||
| let before = BurnableTest.totalBurned | ||
|
|
||
| let r <- BurnableTest.createSafe(allowDestroy: allowDestroy) | ||
| Burner.burn(<- [<- r]) | ||
|
|
||
| if allowDestroy { | ||
| assert(before + 1 == BurnableTest.totalBurned, message: "totalBurned was lower than expected") | ||
| } else { | ||
| assert(before == BurnableTest.totalBurned, message: "totalBurned value changed unexpectedly") | ||
| } | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,35 @@ | ||
| import "BurnableTest" | ||
| import "Burner" | ||
|
|
||
| transaction(allowDestroy: Bool, dictType: Type) { | ||
| prepare(acct: AuthAccount) { | ||
| let before = BurnableTest.totalBurned | ||
|
|
||
| let r <- BurnableTest.createSafe(allowDestroy: allowDestroy) | ||
| if dictType as? Number != nil { | ||
| let d: @{Number: AnyResource} <- {1: <-r} | ||
| Burner.burn(<-d) | ||
| } else if dictType as? String != nil { | ||
| let d: @{String: AnyResource} <- {"a": <-r} | ||
| Burner.burn(<-d) | ||
| } else if dictType as? Path != nil { | ||
| let d: @{Path: AnyResource} <- {/public/foo: <-r} | ||
| Burner.burn(<-d) | ||
| } else if dictType as? Address != nil { | ||
| let d: @{Address: AnyResource} <- {Address(0x1): <-r} | ||
| Burner.burn(<-d) | ||
| } else if dictType as? Character != nil { | ||
| let d: @{Character: AnyResource} <- {"c": <-r} | ||
| Burner.burn(<-d) | ||
| } else { | ||
| let d: @{Type: AnyResource} <- {Type<Burner>(): <-r} | ||
| Burner.burn(<-d) | ||
| } | ||
|
|
||
| if allowDestroy { | ||
| assert(before + 1 == BurnableTest.totalBurned, message: "totalBurned was lower than expected") | ||
| } else { | ||
| assert(before == BurnableTest.totalBurned, message: "totalBurned value changed unexpectedly") | ||
| } | ||
| } | ||
| } |
17 changes: 17 additions & 0 deletions
17
tests/transactions/burner/create_and_destroy_with_callback.cdc
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,17 @@ | ||
| import "BurnableTest" | ||
| import "Burner" | ||
|
|
||
| transaction(allowDestroy: Bool) { | ||
| prepare(acct: AuthAccount) { | ||
| let before = BurnableTest.totalBurned | ||
|
|
||
| let r <- BurnableTest.createSafe(allowDestroy: allowDestroy) | ||
| Burner.burn(<- r) | ||
|
|
||
| if allowDestroy { | ||
| assert(before + 1 == BurnableTest.totalBurned, message: "totalBurned was lower than expected") | ||
| } else { | ||
| assert(before == BurnableTest.totalBurned, message: "totalBurned value changed unexpectedly") | ||
| } | ||
| } | ||
| } |
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If this method is public and we use it to emit the
FungibleToken.Burnedevent, wouldn't that be able to be spoofed or spammed since anyone can call it from their resource? I propose making thisaccess(contract)so that only theburnfunction in this contract can call it.There was a problem hiding this comment.
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wait, is that even possible? If I make an
access(contract)method in an interface, does that mean that only the contract the defines the resource interface implementation can access it, or does it mean theBurnercontract can access it?