examples: add a perfect oracle example

examples/oracle/oracle.go

@@ -0,0 +1,36 @@
+package oraclecontract
+
+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"
+)
+
+// Request does an oracle request for the URL specified. It adds minimum
+// response fee which should suffice for small requests. The data from this
+// URL is subsequently processed by OracleCallback function. This request
+// has no JSONPath filters or user data.
+func Request(url string) {
+	oracle.Request(url, nil, "oracleCallback", nil, oracle.MinimumResponseGas)
+}
+
+// FilteredRequest is similar to Request but allows you to specify JSONPath filter
+// to run against data got from the url specified.
+func FilteredRequest(url string, filter []byte) {
+	oracle.Request(url, filter, "oracleCallback", nil, oracle.MinimumResponseGas)
+}
+
+// OracleCallback is called by Oracle native contract when request is finished.
+// It either throws an error (if the result is not successful) or logs the data
+// got as a result.
+func OracleCallback(url string, data interface{}, code int, res []byte) {
+	// This function shouldn't be called directly, we only expect oracle native
+	// contract to be calling it.
+	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))
+	}
+	runtime.Log("result for " + url + ": " + string(res))
+}