From 8c19b8f2a19e3e7005347c3c51642663274e7744 Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Mon, 18 May 2020 19:04:20 +0300
Subject: [PATCH] compiler/interop: add support for working with witnesses

---
 pkg/compiler/syscall.go                |  4 ++++
 pkg/interop/transaction/transaction.go |  8 ++++++++
 pkg/interop/witness/witness.go         | 14 ++++++++++++++
 3 files changed, 26 insertions(+)
 create mode 100644 pkg/interop/witness/witness.go

diff --git a/pkg/compiler/syscall.go b/pkg/compiler/syscall.go
index bb6429f10..26307270d 100644
--- a/pkg/compiler/syscall.go
+++ b/pkg/compiler/syscall.go
@@ -69,6 +69,7 @@ var syscalls = map[string]map[string]string{
 		"GetReferences": "Neo.Transaction.GetReferences",
 		"GetScript":     "Neo.InvocationTransaction.GetScript",
 		"GetType":       "Neo.Transaction.GetType",
+		"GetWitnesses":  "Neo.Transaction.GetWitnesses",
 	},
 	"asset": {
 		"Create":       "Neo.Asset.Create",
@@ -114,4 +115,7 @@ var syscalls = map[string]map[string]string{
 		"Value":  "Neo.Iterator.Value",
 		"Values": "Neo.Iterator.Values",
 	},
+	"witness": {
+		"GetVerificationScript": "Neo.Witness.GetVerificationScript",
+	},
 }
diff --git a/pkg/interop/transaction/transaction.go b/pkg/interop/transaction/transaction.go
index 0969da5b7..00d06c25e 100644
--- a/pkg/interop/transaction/transaction.go
+++ b/pkg/interop/transaction/transaction.go
@@ -7,6 +7,7 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/interop/attribute"
 	"github.com/nspcc-dev/neo-go/pkg/interop/input"
 	"github.com/nspcc-dev/neo-go/pkg/interop/output"
+	"github.com/nspcc-dev/neo-go/pkg/interop/witness"
 )
 
 // Transaction represents a NEO transaction, it's an opaque data structure
@@ -72,3 +73,10 @@ func GetOutputs(t Transaction) []output.Output {
 func GetScript(t Transaction) []byte {
 	return nil
 }
+
+// GetWitnesses returns a slice of witnesses of a given Transaction. Refer to
+// witness package on how to use them. This function uses
+// `Neo.Transaction.GetWitnesses` syscall.
+func GetWitnesses(t Transaction) []witness.Witness {
+	return []witness.Witness{}
+}
diff --git a/pkg/interop/witness/witness.go b/pkg/interop/witness/witness.go
new file mode 100644
index 000000000..5bf742f83
--- /dev/null
+++ b/pkg/interop/witness/witness.go
@@ -0,0 +1,14 @@
+/*
+Package witness provides functions dealing with transaction's witnesses.
+*/
+package witness
+
+// Witness is an opaque data structure that can only be created by
+// transaction.GetWitnesses and representing transaction's witness.
+type Witness struct{}
+
+// GetVerificationScript returns verification script stored in the given
+// witness. It uses `Neo.Witness.GetVerificationScript` syscall.
+func GetVerificationScript(w Witness) []byte {
+	return nil
+}