use nostr-zapper crate to implement sell::verify_zap

[plebhash]

the mine JSON-RPC method allows a buyer to submit:

• an event to be mined
• the desired PoW difficulty
• the zap paying for the PoW

$ curl -s -X POST \
     -H "Content-Type: application/json" \
     -d '{
           "jsonrpc": "2.0",
           "method": "mine",
           "params": {
             "event": {
               "pubkey": "98590c0f4959a49f3524b7c009c190798935eeaa50b1232ba74195b419eaa2f2",
               "created_at": 1668680774,
               "kind": 1,
               "tags": [],
               "content": "hello world"
             },
             "difficulty": 15,
             "zap": "f481897ee877321783bb76133622b3cc344d691bb79cd6be88f44e819c3b2306"
           },
           "id": 1
         }' \
     http://localhost:1337

it is assumed that the buyer has previously called the quote JSON-RPC method, so they know how many sats they should send in the zap.

but maybe they send an invalid zap, or the zap does not have enough sats.

so the JSON-RPC handler needs to validate the zap before it starts mining:

notemine_hw/src/lib/service.rs

Lines 101 to 111 in ade25cb

	io.add_method("mine", move |params: Params| async move {
	let parsed: Result<MineRpc, _> = serde_json::from_value(params.parse()?)
	.map_err(|_| Error::invalid_params("Invalid params"));
	match parsed {
	Ok(MineRpc {
	event,
	difficulty,
	zap,
	}) => {
	if verify_zap(zap, args.pow_price_factor, difficulty).await {
	// mine

currently, verify_zap has a dummy placeholder implementation:

notemine_hw/src/lib/sell.rs

Lines 7 to 25 in 7591774

	pub async fn verify_zap(
	_zap: String,
	pow_price_factor: f64,
	difficulty: u32,
	) -> Result<(), ZapError> {
	let _pow_price = pow_price(pow_price_factor, difficulty);
	// todo: check zap is valid
	// if !valid_zap {
	// return Err(ZapError::InvalidZap);
	// }
	// todo: read zap value
	// if (zap_value as f64) < pow_price {
	// return Err(ZapError::InsufficientZap);
	// }
	Ok(())
	}

this implementation should leverage nostr-zapper crate to actually verify if:

• zap is valid
• zap contains more sats than pow_price

only if those two verifications are succesful, should we start mining

[plebhash]

https://nostr.how/en/zaps