From 8f94997472d04843b6fd1aec9602d6d29b469612 Mon Sep 17 00:00:00 2001
From: Ethan Buchman <ethan@coinculture.info>
Date: Fri, 26 Jun 2015 01:50:31 +0000
Subject: [PATCH] label/remove panics in vm

---
 vm/native.go | 2 ++
 vm/stack.go  | 1 +
 vm/vm.go     | 3 ++-
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/vm/native.go b/vm/native.go
index 8aff146d9..fef0a7718 100644
--- a/vm/native.go
+++ b/vm/native.go
@@ -52,6 +52,7 @@ func sha256Func(input []byte, gas *uint64) (output []byte, err error) {
 	}
 	// Hash
 	hasher := sha256.New()
+	// CONTRACT: this does not err
 	_, err = hasher.Write(input)
 	if err != nil {
 		panic(err)
@@ -69,6 +70,7 @@ func ripemd160Func(input []byte, gas *uint64) (output []byte, err error) {
 	}
 	// Hash
 	hasher := ripemd160.New()
+	// CONTRACT: this does not err
 	_, err = hasher.Write(input)
 	if err != nil {
 		panic(err)
diff --git a/vm/stack.go b/vm/stack.go
index 500ff4d15..f0d88d2a1 100644
--- a/vm/stack.go
+++ b/vm/stack.go
@@ -47,6 +47,7 @@ func (st *Stack) Push(d Word256) {
 	st.ptr++
 }
 
+// currently only called after Sha3
 func (st *Stack) PushBytes(bz []byte) {
 	if len(bz) != 32 {
 		panic("Invalid bytes size: expected 32")
diff --git a/vm/vm.go b/vm/vm.go
index 6a814655b..caffed1ef 100644
--- a/vm/vm.go
+++ b/vm/vm.go
@@ -100,6 +100,7 @@ func (vm *VM) Call(caller, callee *Account, code, input []byte, value uint64, ga
 			*exception = err.Error()
 			err := transfer(callee, caller, value)
 			if err != nil {
+				// data has been corrupted in ram
 				panic("Could not return value to caller")
 			}
 		}
@@ -784,7 +785,7 @@ func (vm *VM) call(caller, callee *Account, code, input []byte, value uint64, ga
 
 		default:
 			dbg.Printf("(pc) %-3v Invalid opcode %X\n", pc, op)
-			panic(fmt.Errorf("Invalid opcode %X", op))
+			return nil, fmt.Errorf("Invalid opcode %X", op)
 		}
 
 		pc++