From 72f11997d496e283a8d924607559ea251deede96 Mon Sep 17 00:00:00 2001
From: Felix Fontein <felix@fontein.de>
Date: Thu, 28 Sep 2023 22:15:30 +0200
Subject: [PATCH] Handle return values of dec.Token() to improve error
 messages.

Signed-off-by: Felix Fontein <felix@fontein.de>
---
 stores/json/store.go      | 12 +++++++++++-
 stores/json/store_test.go | 15 +++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/stores/json/store.go b/stores/json/store.go
index 81b8bfead..16a4b5d05 100644
--- a/stores/json/store.go
+++ b/stores/json/store.go
@@ -221,7 +221,17 @@ func (store Store) jsonFromTreeBranch(branch sops.TreeBranch) ([]byte, error) {
 
 func (store Store) treeBranchFromJSON(in []byte) (sops.TreeBranch, error) {
 	dec := json.NewDecoder(bytes.NewReader(in))
-	dec.Token()
+	value, err := dec.Token()
+	if err != nil {
+		return nil, err
+	}
+	if delim, ok := value.(json.Delim); ok {
+		if delim.String() != "{" {
+			return nil, fmt.Errorf("Expected JSON object start, got delimiter %s instead", value)
+		}
+	} else {
+		return nil, fmt.Errorf("Expected JSON object start, got %#v of type %T instead", value, value)
+	}
 	return store.treeBranchFromJSONDecoder(dec)
 }
 
diff --git a/stores/json/store_test.go b/stores/json/store_test.go
index be5e30be3..311276d0d 100644
--- a/stores/json/store_test.go
+++ b/stores/json/store_test.go
@@ -130,6 +130,21 @@ func TestDecodeNumber(t *testing.T) {
 	in := `42`
 	_, err := Store{}.treeBranchFromJSON([]byte(in))
 	assert.NotNil(t, err)
+	assert.Equal(t, "Expected JSON object start, got 42 of type float64 instead", err.Error())
+}
+
+func TestDecodeArray(t *testing.T) {
+	in := ` [42] `
+	_, err := Store{}.treeBranchFromJSON([]byte(in))
+	assert.NotNil(t, err)
+	assert.Equal(t, "Expected JSON object start, got delimiter [ instead", err.Error())
+}
+
+func TestDecodeEmpty(t *testing.T) {
+	in := ``
+	_, err := Store{}.treeBranchFromJSON([]byte(in))
+	assert.NotNil(t, err)
+	assert.Equal(t, "EOF", err.Error())
 }
 
 func TestDecodeNestedJSONObject(t *testing.T) {