eth_getFilterChanges on Block Filter returns previous block on first poll

[dylanjw]

Before filing a new issue, please provide the following information.

I'm running:

• Which Parity version?: Parity/v1.8.7-stable-e322fd8-20180124/x86_64-linux-gnu/rustc1.23.0
• Which operating system?: Linux
• How installed?: binaries
• Are you fully synchronized?: no
• Which network are you connected to?: ropsten
• Did you try to restart the node?: yes

_Your issue description goes here below. Try to include actual vs. expected behavior and steps to reproduce the issue.

The first poll of a newly created block filter returns the last block. The expected behavior on first poll is to return only changes since the creation of the blockFilter.

The following example is with an unsynced parity node using the ropstein chain. The last block is the genesis block.

Checking the latest block:

curl --data '{"method":"eth_getBlockByNumber","params":["latest", false], "id":0,"jsonrpc":"2.0"}' -H "Content-Type: application/json" -X POST localhost:8545
{
  "jsonrpc": "2.0",
  "result": {
    "author": "0x0000000000000000000000000000000000000000",
    "difficulty": "0x100000",
    "extraData": "0x3535353535353535353535353535353535353535353535353535353535353535",
    "gasLimit": "0x1000000",
    "gasUsed": "0x0",
    "hash": "0x41941023680923e0fe4d74a34bdac8141f2540e3ae90623718e47d66d1ca4a2d",
    "logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
    "miner": "0x0000000000000000000000000000000000000000",
    "mixHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "nonce": "0x0000000000000042",
    "number": "0x0",
    "parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "receiptsRoot": "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
    "sealFields": [
      "0xa00000000000000000000000000000000000000000000000000000000000000000",
      "0x880000000000000042"
    ],
    "sha3Uncles": "0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347",
    "size": "0x21c",
    "stateRoot": "0x217b0bbcfb72e2d57e28f33cb361b9983513177755dc3f33ce3e7022ed62b77b",
    "timestamp": "0x0",
    "totalDifficulty": "0x100000",
    "transactions": [],
    "transactionsRoot": "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
    "uncles": []
  },
  "id": 0
}

Creation of the block filter:

curl --data '{"method":"eth_newBlockFilter","id":1,"jsonrpc":"2.0"}' -H "Content-Type: application/json" -X POST localhost:8545                 
{"jsonrpc":"2.0","result":"0x0","id":1}

First poll with expected empty result. Instead it returns the hash of the genesis block present before filter creation.

curl --data '{"method":"eth_getFilterChanges","params":["0x0"], "id":2,"jsonrpc":"2.0"}' -H "Content-Type: application/json" -X POST localhost:8545
{"jsonrpc":"2.0","result":["0x41941023680923e0fe4d74a34bdac8141f2540e3ae90623718e47d66d1ca4a2d"],"id":2}

Subsequent polls are empty as expected:

 curl --data '{"method":"eth_getFilterChanges","params":["0x0"], "id":3,"jsonrpc":"2.0"}' -H "Content-Type: application/json" -X POST localhost:8545
{"jsonrpc":"2.0","result":[],"id":3}

This has been tested on a synced client as well, with similar results.