fix decoding empty dynamic array

Author: Alex Vlasov

web3swift/ABIv2/Classes/ABIv2Decoding.swift

@@ -110,7 +110,7 @@ extension ABIv2Decoder {
                     var dataSlice = elementItself[0 ..< 32]
                     let length = UInt64(BigUInt(dataSlice))
                     guard elementItself.count >= 32 + subType.memoryUsage*length else {break}
-                    dataSlice = elementItself[32 ..< subType.memoryUsage*length]
+                    dataSlice = elementItself[32 ..< 32 + subType.memoryUsage*length]
                     var subpointer: UInt64 = 32;
                     var toReturn = [AnyObject]()
                     for _ in 0 ..< length {

web3swift/Contract/Classes/ContractProtocol.swift

@@ -67,6 +67,10 @@ public struct EventFilter {
         }
     }
 
+    public init() {
+        
+    }
+    
     public init(fromBlock: Block?, toBlock: Block?,
                 addresses: [EthereumAddress]? = nil,
                 parameterFilters: [[EventFilterable]?]? = nil) {

web3swiftTests/web3swiftTests.swift

@@ -1830,7 +1830,7 @@ class web3swiftTests: XCTestCase {
 
     func testAdvancedABIv2staticArrayOfStrings() {
         let abiString = "[{\"constant\":true,\"inputs\":[],\"name\":\"testDynOfDyn\",\"outputs\":[{\"name\":\"ts\",\"type\":\"string[]\"}],\"payable\":false,\"stateMutability\":\"pure\",\"type\":\"function\"},{\"constant\":true,\"inputs\":[],\"name\":\"testStOfDyn\",\"outputs\":[{\"name\":\"ts\",\"type\":\"string[2]\"}],\"payable\":false,\"stateMutability\":\"pure\",\"type\":\"function\"},{\"constant\":true,\"inputs\":[],\"name\":\"testDynArray\",\"outputs\":[{\"components\":[{\"name\":\"number\",\"type\":\"uint256\"},{\"name\":\"someText\",\"type\":\"string\"},{\"name\":\"staticArray\",\"type\":\"uint256[2]\"},{\"name\":\"dynamicArray\",\"type\":\"uint256[]\"},{\"name\":\"anotherDynamicArray\",\"type\":\"string[2]\"}],\"name\":\"ts\",\"type\":\"tuple[]\"}],\"payable\":false,\"stateMutability\":\"pure\",\"type\":\"function\"},{\"constant\":true,\"inputs\":[],\"name\":\"testStaticArray\",\"outputs\":[{\"components\":[{\"name\":\"number\",\"type\":\"uint256\"},{\"name\":\"someText\",\"type\":\"string\"},{\"name\":\"staticArray\",\"type\":\"uint256[2]\"},{\"name\":\"dynamicArray\",\"type\":\"uint256[]\"},{\"name\":\"anotherDynamicArray\",\"type\":\"string[2]\"}],\"name\":\"ts\",\"type\":\"tuple[2]\"}],\"payable\":false,\"stateMutability\":\"pure\",\"type\":\"function\"},{\"constant\":true,\"inputs\":[],\"name\":\"testSingle\",\"outputs\":[{\"components\":[{\"name\":\"number\",\"type\":\"uint256\"},{\"name\":\"someText\",\"type\":\"string\"},{\"name\":\"staticArray\",\"type\":\"uint256[2]\"},{\"name\":\"dynamicArray\",\"type\":\"uint256[]\"},{\"name\":\"anotherDynamicArray\",\"type\":\"string[2]\"}],\"name\":\"t\",\"type\":\"tuple\"}],\"payable\":false,\"stateMutability\":\"pure\",\"type\":\"function\"},{\"inputs\":[],\"payable\":false,\"stateMutability\":\"nonpayable\",\"type\":\"constructor\"}]"
-        let contractAddress = EthereumAddress("0xd14630167f878e92a40a1c12db4532f29cb3065e")
+        let contractAddress = EthereumAddress("0xd14630167f878e92a40a1c12db4532f29cb3065e")!
         let web3 = Web3.InfuraRinkebyWeb3()
         let contract = web3.contract(abiString, at: contractAddress, abiVersion: 2)
         var options = Web3Options.defaultOptions()
@@ -1851,6 +1851,29 @@ class web3swiftTests: XCTestCase {
         }
     }
 
+    func testEmptyArrayDecoding() {
+        let abiString = "[{\"inputs\":[],\"payable\":false,\"stateMutability\":\"nonpayable\",\"type\":\"constructor\"},{\"constant\":true,\"inputs\":[],\"name\":\"empty\",\"outputs\":[{\"name\":\"\",\"type\":\"uint256[]\"}],\"payable\":false,\"stateMutability\":\"view\",\"type\":\"function\"}]"
+        let contractAddress = EthereumAddress("0x200eb5ccda1c35b0f5bf82552fdd65a8aee98e79")!
+        let web3 = Web3.InfuraRinkebyWeb3()
+        let contract = web3.contract(abiString, at: contractAddress, abiVersion: 2)
+        var options = Web3Options.defaultOptions()
+        options.from = contractAddress
+        XCTAssert(contract != nil)
+        print(contract?.contract.allMethods)
+        let rawContract = contract?.contract as! ContractV2
+        print(rawContract)
+        let intermediate = contract?.method("empty", options: options)
+        XCTAssertNotNil(intermediate)
+        let result = intermediate!.call(options: nil)
+        switch result {
+        case .success(let payload):
+            print(payload)
+        case .failure(let error):
+            print(error)
+            XCTFail()
+        }
+    }
+    
     func testUserCase() {
         let abiString =  "[{\"constant\":true,\"inputs\":[],\"name\":\"getFlagData\",\"outputs\":[{\"name\":\"data\",\"type\":\"string\"}],\"payable\":false,\"stateMutability\":\"view\",\"type\":\"function\"},{\"constant\":false,\"inputs\":[{\"name\":\"data\",\"type\":\"string\"}],\"name\":\"setFlagData\",\"outputs\":[],\"payable\":false,\"stateMutability\":\"nonpayable\",\"type\":\"function\"}]"
         let contractAddress = EthereumAddress("0x811411e3cdfd4750cdd3552feb3b89a46ddb612e")