feat(entropy-v2): request with callback (#1342)

* request with callback

* address comments

* pre-commit

* compilation successful

* pre-commit

* add tests

* generate-abis

* pre-commit

* correct version

* address comments

* pre-commit

* remove unused

* add comments

* pre-commit

* gen abi

* naming consistency

* remove gas limit comment

* requestWithCallback comment

* remove unnecessary asserts

* pre commit

* update request with callback coment

* abis regen

* refactor as per feedback

* abi gen

* rename

* implement ientropyconsumer

* gen abi

* comment entropy consumer

* test fix

* add comment

* reintroduce blockhash

* add error for invalid reveal call

* use getEntropy in entropy consumer

* add test for requestAndRevealWithCallback

* pass through for entropy consumer

* pre commit fix

* abi gen

* address comments

* address feedback

* gen abis

* pre commit run

Author: Dev Kalra

target_chains/ethereum/contracts/contracts/entropy/Entropy.sol

@@ -6,6 +6,7 @@ import "@pythnetwork/entropy-sdk-solidity/EntropyStructs.sol";
 import "@pythnetwork/entropy-sdk-solidity/EntropyErrors.sol";
 import "@pythnetwork/entropy-sdk-solidity/EntropyEvents.sol";
 import "@pythnetwork/entropy-sdk-solidity/IEntropy.sol";
+import "@pythnetwork/entropy-sdk-solidity/IEntropyConsumer.sol";
 import "@openzeppelin/contracts/utils/math/SafeCast.sol";
 import "./EntropyState.sol";
 
@@ -163,29 +164,23 @@ abstract contract Entropy is IEntropy, EntropyState {
         require(sent, "withdrawal to msg.sender failed");
     }
 
-    // As a user, request a random number from `provider`. Prior to calling this method, the user should
-    // generate a random number x and keep it secret. The user should then compute hash(x) and pass that
-    // as the userCommitment argument. (You may call the constructUserCommitment method to compute the hash.)
-    //
-    // This method returns a sequence number. The user should pass this sequence number to
-    // their chosen provider (the exact method for doing so will depend on the provider) to retrieve the provider's
-    // number. The user should then call fulfillRequest to construct the final random number.
-    //
-    // This method will revert unless the caller provides a sufficient fee (at least getFee(provider)) as msg.value.
-    // Note that excess value is *not* refunded to the caller.
-    function request(
+    // requestHelper allocates and returns a new request for the given provider.
+    // Note: This method will revert unless the caller provides a sufficient fee
+    // (at least getFee(provider)) as msg.value.
+    function requestHelper(
         address provider,
         bytes32 userCommitment,
-        bool useBlockHash
-    ) public payable override returns (uint64 assignedSequenceNumber) {
+        bool useBlockhash,
+        bool isRequestWithCallback
+    ) internal returns (EntropyStructs.Request storage req) {
         EntropyStructs.ProviderInfo storage providerInfo = _state.providers[
             provider
         ];
         if (_state.providers[provider].sequenceNumber == 0)
             revert EntropyErrors.NoSuchProvider();
 
         // Assign a sequence number to the request
-        assignedSequenceNumber = providerInfo.sequenceNumber;
+        uint64 assignedSequenceNumber = providerInfo.sequenceNumber;
         if (assignedSequenceNumber >= providerInfo.endSequenceNumber)
             revert EntropyErrors.OutOfRandomness();
         providerInfo.sequenceNumber += 1;
@@ -200,10 +195,7 @@ abstract contract Entropy is IEntropy, EntropyState {
         // Store the user's commitment so that we can fulfill the request later.
         // Warning: this code needs to overwrite *every* field in the request, because the returned request can be
         // filled with arbitrary data.
-        EntropyStructs.Request storage req = allocRequest(
-            provider,
-            assignedSequenceNumber
-        );
+        req = allocRequest(provider, assignedSequenceNumber);
         req.provider = provider;
         req.sequenceNumber = assignedSequenceNumber;
         req.numHashes = SafeCast.toUint32(
@@ -216,51 +208,87 @@ abstract contract Entropy is IEntropy, EntropyState {
         req.requester = msg.sender;
 
         req.blockNumber = SafeCast.toUint64(block.number);
-        req.useBlockhash = useBlockHash;
+        req.useBlockhash = useBlockhash;
+        req.isRequestWithCallback = isRequestWithCallback;
+    }
 
+    // As a user, request a random number from `provider`. Prior to calling this method, the user should
+    // generate a random number x and keep it secret. The user should then compute hash(x) and pass that
+    // as the userCommitment argument. (You may call the constructUserCommitment method to compute the hash.)
+    //
+    // This method returns a sequence number. The user should pass this sequence number to
+    // their chosen provider (the exact method for doing so will depend on the provider) to retrieve the provider's
+    // number. The user should then call fulfillRequest to construct the final random number.
+    //
+    // This method will revert unless the caller provides a sufficient fee (at least getFee(provider)) as msg.value.
+    // Note that excess value is *not* refunded to the caller.
+    function request(
+        address provider,
+        bytes32 userCommitment,
+        bool useBlockHash
+    ) public payable override returns (uint64 assignedSequenceNumber) {
+        EntropyStructs.Request storage req = requestHelper(
+            provider,
+            userCommitment,
+            useBlockHash,
+            false
+        );
+        assignedSequenceNumber = req.sequenceNumber;
         emit Requested(req);
     }
 
-    // Fulfill a request for a random number. This method validates the provided userRandomness and provider's proof
-    // against the corresponding commitments in the in-flight request. If both values are validated, this function returns
-    // the corresponding random number.
+    // Request a random number. The method expects the provider address and a secret random number
+    // in the arguments. It returns a sequence number.
     //
-    // Note that this function can only be called once per in-flight request. Calling this function deletes the stored
-    // request information (so that the contract doesn't use a linear amount of storage in the number of requests).
-    // If you need to use the returned random number more than once, you are responsible for storing it.
+    // The address calling this function should be a contract that inherits from the IEntropyConsumer interface.
+    // The `entropyCallback` method on that interface will receive a callback with the generated random number.
     //
-    // This function must be called by the same `msg.sender` that originally requested the random number. This check
-    // prevents denial-of-service attacks where another actor front-runs the requester's reveal transaction.
-    function reveal(
+    // This method will revert unless the caller provides a sufficient fee (at least getFee(provider)) as msg.value.
+    // Note that excess value is *not* refunded to the caller.
+    function requestWithCallback(
         address provider,
-        uint64 sequenceNumber,
-        bytes32 userRandomness,
-        bytes32 providerRevelation
-    ) public override returns (bytes32 randomNumber) {
-        EntropyStructs.Request storage req = findRequest(
+        bytes32 userRandomNumber
+    ) public payable override returns (uint64) {
+        EntropyStructs.Request storage req = requestHelper(
             provider,
-            sequenceNumber
+            constructUserCommitment(userRandomNumber),
+            // If useBlockHash is set to true, it allows a scenario in which the provider and miner can collude.
+            // If we remove the blockHash from this, the provider would have no choice but to provide its committed
+            // random number. Hence, useBlockHash is set to false.
+            false,
+            true
+        );
+
+        emit RequestedWithCallback(
+            provider,
+            req.requester,
+            req.sequenceNumber,
+            userRandomNumber,
+            req
         );
-        // Check that there is an active request for the given provider / sequence number.
-        if (
-            req.sequenceNumber == 0 ||
-            req.provider != provider ||
-            req.sequenceNumber != sequenceNumber
-        ) revert EntropyErrors.NoSuchRequest();
 
-        if (req.requester != msg.sender) revert EntropyErrors.Unauthorized();
+        return req.sequenceNumber;
+    }
 
+    // This method validates the provided user's revelation and provider's revelation against the corresponding
+    // commitment in the in-flight request. If both values are validated, this method will update the provider
+    // current commitment and returns the generated random number.
+    function revealHelper(
+        EntropyStructs.Request storage req,
+        bytes32 userRevelation,
+        bytes32 providerRevelation
+    ) internal returns (bytes32 randomNumber, bytes32 blockHash) {
         bytes32 providerCommitment = constructProviderCommitment(
             req.numHashes,
             providerRevelation
         );
-        bytes32 userCommitment = constructUserCommitment(userRandomness);
+        bytes32 userCommitment = constructUserCommitment(userRevelation);
         if (
             keccak256(bytes.concat(userCommitment, providerCommitment)) !=
             req.commitment
         ) revert EntropyErrors.IncorrectRevelation();
 
-        bytes32 blockHash = bytes32(uint256(0));
+        blockHash = bytes32(uint256(0));
         if (req.useBlockhash) {
             bytes32 _blockHash = blockhash(req.blockNumber);
 
@@ -277,28 +305,110 @@ abstract contract Entropy is IEntropy, EntropyState {
         }
 
         randomNumber = combineRandomValues(
-            userRandomness,
+            userRevelation,
             providerRevelation,
             blockHash
         );
 
+        EntropyStructs.ProviderInfo storage providerInfo = _state.providers[
+            req.provider
+        ];
+        if (providerInfo.currentCommitmentSequenceNumber < req.sequenceNumber) {
+            providerInfo.currentCommitmentSequenceNumber = req.sequenceNumber;
+            providerInfo.currentCommitment = providerRevelation;
+        }
+    }
+
+    // Fulfill a request for a random number. This method validates the provided userRandomness and provider's proof
+    // against the corresponding commitments in the in-flight request. If both values are validated, this function returns
+    // the corresponding random number.
+    //
+    // Note that this function can only be called once per in-flight request. Calling this function deletes the stored
+    // request information (so that the contract doesn't use a linear amount of storage in the number of requests).
+    // If you need to use the returned random number more than once, you are responsible for storing it.
+    //
+    // This function must be called by the same `msg.sender` that originally requested the random number. This check
+    // prevents denial-of-service attacks where another actor front-runs the requester's reveal transaction.
+    function reveal(
+        address provider,
+        uint64 sequenceNumber,
+        bytes32 userRevelation,
+        bytes32 providerRevelation
+    ) public override returns (bytes32 randomNumber) {
+        EntropyStructs.Request storage req = findActiveRequest(
+            provider,
+            sequenceNumber
+        );
+
+        if (req.isRequestWithCallback) {
+            revert EntropyErrors.InvalidRevealCall();
+        }
+
+        if (req.requester != msg.sender) {
+            revert EntropyErrors.Unauthorized();
+        }
+        bytes32 blockHash;
+        (randomNumber, blockHash) = revealHelper(
+            req,
+            userRevelation,
+            providerRevelation
+        );
         emit Revealed(
             req,
-            userRandomness,
+            userRevelation,
             providerRevelation,
             blockHash,
             randomNumber
         );
-
         clearRequest(provider, sequenceNumber);
+    }
 
-        EntropyStructs.ProviderInfo storage providerInfo = _state.providers[
-            provider
-        ];
-        if (providerInfo.currentCommitmentSequenceNumber < sequenceNumber) {
-            providerInfo.currentCommitmentSequenceNumber = sequenceNumber;
-            providerInfo.currentCommitment = providerRevelation;
+    // Fulfill a request for a random number and call back the requester. This method validates the provided userRandomness
+    // and provider's revelation against the corresponding commitment in the in-flight request. If both values are validated,
+    // this function calls the requester's entropyCallback method with the sequence number and the random number as arguments.
+    //
+    // Note that this function can only be called once per in-flight request. Calling this function deletes the stored
+    // request information (so that the contract doesn't use a linear amount of storage in the number of requests).
+    // If you need to use the returned random number more than once, you are responsible for storing it.
+    //
+    // Anyone can call this method to fulfill a request, but the callback will only be made to the original requester.
+    function revealWithCallback(
+        address provider,
+        uint64 sequenceNumber,
+        bytes32 userRandomNumber,
+        bytes32 providerRevelation
+    ) public override {
+        EntropyStructs.Request storage req = findActiveRequest(
+            provider,
+            sequenceNumber
+        );
+
+        if (!req.isRequestWithCallback) {
+            revert EntropyErrors.InvalidRevealCall();
         }
+        bytes32 blockHash;
+        bytes32 randomNumber;
+        (randomNumber, blockHash) = revealHelper(
+            req,
+            userRandomNumber,
+            providerRevelation
+        );
+
+        address callAddress = req.requester;
+
+        emit RevealedWithCallback(
+            req,
+            userRandomNumber,
+            providerRevelation,
+            randomNumber
+        );
+
+        clearRequest(provider, sequenceNumber);
+
+        IEntropyConsumer(callAddress)._entropyCallback(
+            sequenceNumber,
+            randomNumber
+        );
     }
 
     function getProviderInfo(
@@ -408,6 +518,23 @@ abstract contract Entropy is IEntropy, EntropyState {
         }
     }
 
+    // Find an in-flight active request for given the provider and the sequence number.
+    // This method returns a reference to the request, and will revert if the request is
+    // not active.
+    function findActiveRequest(
+        address provider,
+        uint64 sequenceNumber
+    ) internal view returns (EntropyStructs.Request storage req) {
+        req = findRequest(provider, sequenceNumber);
+
+        // Check there is an active request for the given provider and sequence number.
+        if (
+            !isActive(req) ||
+            req.provider != provider ||
+            req.sequenceNumber != sequenceNumber
+        ) revert EntropyErrors.NoSuchRequest();
+    }
+
     // Find an in-flight request.
     // Note that this method can return requests that are not currently active. The caller is responsible for checking
     // that the returned request is active (if they care).

target_chains/ethereum/contracts/contracts/entropy/EntropyUpgradable.sol

@@ -105,6 +105,6 @@ contract EntropyUpgradable is
     }
 
     function version() public pure returns (string memory) {
-        return "0.1.0";
+        return "0.2.0";
     }
 }