handle when hcl parser panics

Apparently `\` followed by a digit number can cause hcl parser to panic!
Will fix in hcl library, but using a hammer to squash any similar issue
here.

acl/policy.go

@@ -238,7 +238,7 @@ func Parse(rules string) (*Policy, error) {
 	}
 
 	// Attempt to parse
-	if err := hcl.Decode(p, rules); err != nil {
+	if err := hclDecode(p, rules); err != nil {
 		return nil, fmt.Errorf("Failed to parse ACL Policy: %v", err)
 	}
 
@@ -312,3 +312,15 @@ func Parse(rules string) (*Policy, error) {
 	}
 	return p, nil
 }
+
+// hclDecode wraps hcl.Decode function but handles any unexpected panics
+func hclDecode(p *Policy, rules string) (err error) {
+	defer func() {
+		if rerr := recover(); rerr != nil {
+			err = fmt.Errorf("invalid acl policy: %v", rerr)
+		}
+	}()
+
+	err = hcl.Decode(p, rules)
+	return err
+}

acl/policy_test.go

@@ -327,3 +327,16 @@ func TestParse(t *testing.T) {
 		})
 	}
 }
+
+func TestParse_BadInput(t *testing.T) {
+	inputs := []string{
+		`namespace "\500" {}`,
+	}
+
+	for i, c := range inputs {
+		t.Run(fmt.Sprintf("%d: %v", i, c), func(t *testing.T) {
+			_, err := Parse(c)
+			assert.Error(t, err)
+		})
+	}
+}