NeoFS N3 oracle example

oracle.go

package oracleexample

import (
	"github.com/nspcc-dev/neo-go/pkg/interop/native/oracle"
	"github.com/nspcc-dev/neo-go/pkg/interop/native/std"
	"github.com/nspcc-dev/neo-go/pkg/interop/runtime"
	"github.com/nspcc-dev/neo-go/pkg/interop/storage"
)

// NeoFS URI of object with JSON encoded database of items.
const database = "neofs:6pJtLUnGqDxE2EitZYLsDzsfTDVegD6BrRUn8QAFZWyt/5pHkykmTC6vBpx19y5r26YUBqrEx8J5wVAntCU42bFYQ"

type CallbackDetails struct {
	id int
	username string
}

func _deploy(_ interface{}, isUpdate bool) {
	ctx := storage.GetContext()
	storage.Put(ctx, "Marie", 4000) // 4000 coins for Marie
}

func Balance(username string) int {
	ctx := storage.GetReadOnlyContext()
	return storage.Get(ctx, username).(int)
}

func Purchase(id int, user string) {
	url := database
	idString := std.Itoa(id, 10)

	// JSONPath filter to find price value in item with specified ID, e.g.:
	// $..item[?(@.id==1)].price
	filter := []byte("$..item[?(@.id==" + idString + ")].price")

	details := CallbackDetails{
		id:       id,
		username: user,
	}

	// Make oracle request. Add extra GAS to process deserialization and storage
	// update in callback.
	oracle.Request(url, filter, "oracleCallback", std.Serialize(details), oracle.MinimumResponseGas*2)
}

func OracleCallback(url string, data interface{}, code int, res []byte) {
	if string(runtime.GetCallingScriptHash()) != oracle.Hash {
		panic("not called from oracle contract")
	}

	if code != oracle.Success {
		panic("request failed for " + url + " with code " + std.Itoa(code, 10))
	}

	// Decode invocation details to get username and current balance.
	details := std.Deserialize(data.([]byte)).(CallbackDetails)
	currentBalance := Balance(details.username)

	// Convert oracle response `[N]` to `N`.
	stringPrice := string(res[1:len(res)-1])
	price := std.Atoi(stringPrice, 10)

	// Check if there are enough assets to make "purchase".
	if currentBalance < price {
		panic("not enough assets")
	}

	// Make purchase by updating user's balance.
	ctx := storage.GetContext()
	storage.Put(ctx, details.username, currentBalance-price)
}