From a968f040503e86274f7ac9c522110ce66e99b110 Mon Sep 17 00:00:00 2001
From: Philip Stanislaus <6912756+philipstanislaus@users.noreply.github.com>
Date: Thu, 28 May 2020 12:25:53 +0200
Subject: [PATCH] Change error handling to not panic when querying block info
 from runtime

---
 runtime/interface.go    |  4 ++--
 runtime/runtime.go      | 23 +++++++++++++++++------
 runtime/runtime_test.go |  7 ++++---
 3 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/runtime/interface.go b/runtime/interface.go
index 1e39f558f1..dc1304afe9 100644
--- a/runtime/interface.go
+++ b/runtime/interface.go
@@ -65,7 +65,7 @@ type Interface interface {
 	// GetCurrentBlockHeight returns the current block height.
 	GetCurrentBlockHeight() uint64
 	// GetBlockAtHeight returns the block at the given height.
-	GetBlockAtHeight(height uint64) (hash BlockHash, timestamp int64, exists bool)
+	GetBlockAtHeight(height uint64) (hash BlockHash, timestamp int64, exists bool, err error)
 }
 
 type Metrics interface {
@@ -142,6 +142,6 @@ func (i *EmptyRuntimeInterface) GetCurrentBlockHeight() uint64 {
 	return 0
 }
 
-func (i *EmptyRuntimeInterface) GetBlockAtHeight(_ uint64) (hash BlockHash, timestamp int64, exists bool) {
+func (i *EmptyRuntimeInterface) GetBlockAtHeight(_ uint64) (hash BlockHash, timestamp int64, exists bool, err error) {
 	return
 }
diff --git a/runtime/runtime.go b/runtime/runtime.go
index b599acbab1..dd1981ce6e 100644
--- a/runtime/runtime.go
+++ b/runtime/runtime.go
@@ -1206,28 +1206,36 @@ func (r *interpreterRuntime) getCurrentBlockHeight(runtimeInterface Interface) (
 	return
 }
 
-func (r *interpreterRuntime) getBlockAtHeight(height uint64, runtimeInterface Interface) *BlockValue {
+func (r *interpreterRuntime) getBlockAtHeight(height uint64, runtimeInterface Interface) (*BlockValue, error) {
 
 	var hash BlockHash
 	var timestamp int64
 	var exists bool
+	var err error
 
 	wrapPanic(func() {
-		hash, timestamp, exists = runtimeInterface.GetBlockAtHeight(height)
+		hash, timestamp, exists, err = runtimeInterface.GetBlockAtHeight(height)
 	})
 
+	if err != nil {
+		return nil, err
+	}
+
 	if !exists {
-		return nil
+		return nil, nil
 	}
 
 	block := NewBlockValue(height, hash, time.Unix(0, timestamp))
-	return &block
+	return &block, nil
 }
 
 func (r *interpreterRuntime) newGetCurrentBlockFunction(runtimeInterface Interface) interpreter.HostFunction {
 	return func(invocation interpreter.Invocation) trampoline.Trampoline {
 		height := r.getCurrentBlockHeight(runtimeInterface)
-		block := r.getBlockAtHeight(height, runtimeInterface)
+		block, err := r.getBlockAtHeight(height, runtimeInterface)
+		if err != nil {
+			panic(err)
+		}
 		return trampoline.Done{Result: *block}
 	}
 }
@@ -1235,7 +1243,10 @@ func (r *interpreterRuntime) newGetCurrentBlockFunction(runtimeInterface Interfa
 func (r *interpreterRuntime) newGetBlockFunction(runtimeInterface Interface) interpreter.HostFunction {
 	return func(invocation interpreter.Invocation) trampoline.Trampoline {
 		height := uint64(invocation.Arguments[0].(interpreter.UInt64Value))
-		block := r.getBlockAtHeight(height, runtimeInterface)
+		block, err := r.getBlockAtHeight(height, runtimeInterface)
+		if err != nil {
+			panic(err)
+		}
 		var result interpreter.Value
 		if block == nil {
 			result = interpreter.NilValue{}
diff --git a/runtime/runtime_test.go b/runtime/runtime_test.go
index bf49ce2c12..29727111fd 100644
--- a/runtime/runtime_test.go
+++ b/runtime/runtime_test.go
@@ -222,9 +222,10 @@ func (i *testRuntimeInterface) GetCurrentBlockHeight() uint64 {
 	return 1
 }
 
-func (i *testRuntimeInterface) GetBlockAtHeight(height uint64) (hash BlockHash, timestamp int64, exists bool) {
+func (i *testRuntimeInterface) GetBlockAtHeight(height uint64) (hash BlockHash, timestamp int64, exists bool,
+	err error) {
 	buf := new(bytes.Buffer)
-	err := binary.Write(buf, binary.BigEndian, height)
+	err = binary.Write(buf, binary.BigEndian, height)
 	if err != nil {
 		panic(err)
 	}
@@ -232,7 +233,7 @@ func (i *testRuntimeInterface) GetBlockAtHeight(height uint64) (hash BlockHash,
 	encoded := buf.Bytes()
 	copy(hash[stdlib.BlockIDSize-len(encoded):], encoded)
 
-	return hash, time.Unix(int64(height), 0).UnixNano(), true
+	return hash, time.Unix(int64(height), 0).UnixNano(), true, nil
 }
 
 func TestRuntimeImport(t *testing.T) {