How to identify the buyer (trans. sender) of node event res (Received confirmed transaction)

Technical Discussion
#1

nem.com.websockets.subscribe.account.transactions.confirmed > func(res)

"data":[
		{
			"meta":
				{
					"innerHash":{},
					"id":131757,
					"hash":
						{
							"data":"some_data"},
							"height":1106515
						},
					"transaction":
						{
							"timeStamp":77097839,
							"amount":140441504,
							"signature":"some_sig",
							"fee":2000000,
							"recipient":"some_recipient",
							"type":257,
							"deadline":77141039,
							"message":
								{
									"payload":"6631",
									"type":1
								},
							"version":-1744830463,
							"signer":"some_signer"
						}
				}
			]
		}

How to identify the buyer? addr or other unique id
for online store

#2

signer is the account that innitiated the tx. So if the buyer send the tx that is who the buyer is.

#3

how convert “signer” to addr
"signer" string 0000000000843f391e6485c5172b0e1332bf0032b04c4abe23822754214caec3

addr (in wallet) string TDEK3D-OKN54X-WEVUNX-JOLWDJ-MYEF2G-7HPK2L-RU5W

#4

Hey!
Did you get the solution to this question?
Of course you can use this API request /account/get/from-public-key?publicKey=0000000000843f391e6485c5172b0e1332bf0032b04c4abe23822754214caec3

but it’s overhead (you have to make extra API call). How can I calculate it by some function?