Merge pull request #22 from ethstorage/get_ret

memory bug when return from precompile

contracts/DecentralizedKV.sol

@@ -106,19 +106,20 @@ contract DecentralizedKV {
     }
 
     // Return the keyed data given off and len.  This function can be only called in JSON-RPC context of ES L2 node.
-    function get(bytes32 key, uint256 off, uint256 len) public view virtual returns (bytes memory result) {
+    function get(bytes32 key, uint256 off, uint256 len) public view virtual returns (bytes memory) {
         require(len > 0, "data len should be non zero");
 
         bytes32 skey = keccak256(abi.encode(msg.sender, key));
         PhyAddr memory paddr = kvMap[skey];
         require(paddr.hash != 0, "data not exist");
         require(paddr.kvSize >= off + len, "beyond the range of kvSize");
         bytes memory input = abi.encode(paddr.kvIdx, off, len, paddr.hash);
+        bytes memory output = new bytes(len);
 
         uint256 retSize = 0;
 
         assembly {
-            if iszero(staticcall(not(0), 0x33301, add(input, 0x20), 0x80, 0x0, len)) {
+            if iszero(staticcall(not(0), 0x33301, add(input, 0x20), 0x80, add(output, 0x20), len)) {
                 revert(0, 0)
             }
             retSize := returndatasize()
@@ -128,17 +129,7 @@ contract DecentralizedKV {
         // and it will simply return immediately instead of revert
         require(retSize > 0, "get() must be called on ES node");
 
-        assembly {
-            // Allocate memory for the result
-            result := mload(0x40)
-            mstore(result, returndatasize())
-
-            // Update free memory pointer
-            mstore(0x40, add(result, add(returndatasize(), 0x20)))
-
-            // Copy the result to the allocated memory
-            returndatacopy(add(result, 0x20), 0, returndatasize())
-        }
+        return output;
     }
 
     // Remove an existing KV pair to a recipient.  Refund the cost accordingly.

scripts/deploy.js

@@ -17,7 +17,8 @@ async function main() {
     0, // dcfFactor
     1048576, // nonceLimit
     "0x0000000000000000000000000000000000000000", // treasury
-    0 // prepaidAmount
+    0, // prepaidAmount
+    { gasPrice: 30000000000 }
   );
   await storageContract.deployed();
   console.log("storage contract address is ", storageContract.address);