compat/json: Valid: Check for EOF

3 files changed, 46 insertions, 2 deletions

diff --git a/ReleaseNotes.md b/ReleaseNotes.md
index 623d5da..613ea0c 100644
--- a/ReleaseNotes.md
+++ b/ReleaseNotes.md
@@ -9,6 +9,11 @@
       + Encoder, ReEncoder: Now correctly trims unnecessary the
         trailing '0's from the fraction-part when compacting numbers.
 
+   - Compatibility bugfixes:
+
+      + compat/json.Valid: No longer considers truncated JSON
+        documents to be valid.
+
 # v0.3.6 (2023-02-16)
 
   Theme: Architectural improvements
diff --git a/compat/json/compat.go b/compat/json/compat.go
index c96470d..300ab2f 100644
--- a/compat/json/compat.go
+++ b/compat/json/compat.go
@@ -175,8 +175,13 @@ func Valid(data []byte) bool {
 	formatter := lowmemjson.NewReEncoder(io.Discard, lowmemjson.ReEncoderConfig{
 		Compact: true,
 	})
-	_, err := formatter.Write(data)
-	return err == nil
+	if _, err := formatter.Write(data); err != nil {
+		return false
+	}
+	if err := formatter.Close(); err != nil {
+		return false
+	}
+	return true
 }
 
 // Decode wrappers ///////////////////////////////////////////////////
diff --git a/compat/json/compat_test.go b/compat/json/compat_test.go
new file mode 100644
index 0000000..5c8f3ee
--- /dev/null
+++ b/compat/json/compat_test.go
@@ -0,0 +1,34 @@
+// Copyright (C) 2023  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package json
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCompatValid(t *testing.T) {
+	t.Parallel()
+	type testcase struct {
+		In  string
+		Exp bool
+	}
+	testcases := map[string]testcase{
+		"empty":  {In: ``, Exp: false},
+		"num":    {In: `1`, Exp: true},
+		"trunc":  {In: `{`, Exp: false},
+		"object": {In: `{}`, Exp: true},
+	}
+	for tcName, tc := range testcases {
+		tc := tc
+		t.Run(tcName, func(t *testing.T) {
+			t.Parallel()
+			t.Logf("in=%q", tc.In)
+			act := Valid([]byte(tc.In))
+			assert.Equal(t, tc.Exp, act)
+		})
+	}
+}