From 8297382580f0acca4dcb64b63bce989c4902c655 Mon Sep 17 00:00:00 2001
From: folbrich <frank.olbricht@gmail.com>
Date: Tue, 4 Aug 2026 09:20:32 +0200
Subject: [PATCH] Add tests locking down ChunkID hex formatting

ChunkID.String() and MarshalJSON() were briefly moved to pointer
receivers in #273, which meant a ChunkID value was rendered by fmt's
byte-array fallback and marshalled as an array of numbers. #379 moved
them back to value receivers but added no test, so the same regression
could slip in again unnoticed.

Cover both the formatting and the JSON encoding of a ChunkID value,
including the non-addressable map-value case that skips a
pointer-receiver MarshalJSON, plus compile-time assertions that the
value type implements fmt.Stringer and json.Marshaler.
---
 types_test.go | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 types_test.go

diff --git a/types_test.go b/types_test.go
new file mode 100644
index 0000000..b7cbea7
--- /dev/null
+++ b/types_test.go
@@ -0,0 +1,56 @@
+package desync
+
+import (
+	"encoding/json"
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// String() and MarshalJSON() must stay on value receivers. With pointer
+// receivers, a ChunkID value doesn't implement these interfaces and gets
+// formatted or marshalled as a raw byte array instead of hex.
+var (
+	_ fmt.Stringer   = ChunkID{}
+	_ json.Marshaler = ChunkID{}
+)
+
+const testChunkIDHex = "dda036cc9be7d1b1c3f6f4d3d1e2ed0f9e1f74e8b0d1a2b3c4d5e6f708192a3b"
+
+func TestChunkIDFormatting(t *testing.T) {
+	id, err := ChunkIDFromString(testChunkIDHex)
+	require.NoError(t, err)
+
+	// A value, not just a pointer, needs to render as hex
+	require.Equal(t, testChunkIDHex, fmt.Sprintf("%s", id))
+	require.Equal(t, testChunkIDHex, fmt.Sprintf("%v", id))
+	require.Equal(t, `"`+testChunkIDHex+`"`, fmt.Sprintf("%q", id))
+	require.Equal(t, testChunkIDHex, fmt.Sprintf("%s", &id))
+
+	// Same for values carried in errors, which are printed by value
+	require.Equal(t,
+		fmt.Sprintf("chunk %s missing from store", testChunkIDHex),
+		ChunkMissing{ID: id}.Error(),
+	)
+}
+
+func TestChunkIDMarshalJSON(t *testing.T) {
+	id, err := ChunkIDFromString(testChunkIDHex)
+	require.NoError(t, err)
+
+	// Map values aren't addressable, so a pointer-receiver MarshalJSON would
+	// be skipped here and the ID emitted as an array of numbers
+	b, err := json.Marshal(map[string]ChunkID{"id": id})
+	require.NoError(t, err)
+	require.JSONEq(t, `{"id":"`+testChunkIDHex+`"}`, string(b))
+
+	// Round-trip through a struct, as done by inspect-chunks
+	b, err = json.Marshal([]ChunkAdditionalInfo{{ID: id, UncompressedSize: 1024}})
+	require.NoError(t, err)
+	require.JSONEq(t, `[{"id":"`+testChunkIDHex+`","uncompressed_size":1024}]`, string(b))
+
+	var got []ChunkAdditionalInfo
+	require.NoError(t, json.Unmarshal(b, &got))
+	require.Equal(t, id, got[0].ID)
+}