php如何使用JSON-RPC查找以太坊中的最新块哈希hash值？

{"jsonrpc":"2.0","id":1,"result":{"difficulty":"0x31962a3fc82b",
 "extraData":"0x4477617266506f6f6c",
 "gasLimit":"0x47c3d8",
 "gasUsed":"0x0",
 "hash":"0x78bfef68fccd4507f9f4804ba5c65eb2f928ea45b3383ade88aaa720f1209cba",
 "logsBloom":"0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
 "miner":"0x2a65aca4d5fc5b5c859090a6c34d164135398226",
 "nonce":"0xa5e8fb780cc2cd5e",
 "number":"0x1e655a",
 "parentHash":"0x8b535592eb3192017a527bbf8e3596da86b3abea51d6257898b2ced9d3a83826",
 "receiptRoot":"0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
 "sha3Uncles":"0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347",
 "size":"0x20e",
 "stateRoot":"0xdc6ed0a382e50edfedb6bd296892690eb97eb3fc88fd55088d5ea753c48253dc",
 "timestamp":"0x579f4981",
 "totalDifficulty":"0x25cff06a0d96f4bee",
 "transactions":[],
 "transactionsRoot":"0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
 "uncles":[]}}

用latest也可以用eth_blockNumber，来得到最新块。