Fix memory leaks in vipsGetPoint and vipsImageGetAsString

vips/image_test.go

@@ -1474,6 +1474,53 @@ func TestNewImageFromGoImage(t *testing.T) {
 	assert.Equal(t, []float64{255, 0, 0, 255}, pixel)
 }
 
+// TestGetPoint_RepeatedCalls verifies that GetPoint returns a Go-owned slice
+// whose data remains valid across multiple calls. Previously, vipsGetPoint
+// returned a slice backed by C memory and deferred a g_free on a nil pointer
+// (captured before the C call), leaking the allocation.
+func TestGetPoint_RepeatedCalls(t *testing.T) {
+	require.NoError(t, Startup(nil))
+
+	img, err := NewImageFromFile(resources + "png-24bit.png")
+	require.NoError(t, err)
+	defer img.Close()
+
+	// Call GetPoint multiple times and retain results.
+	// If the returned slice were backed by C memory, earlier results could
+	// be corrupted by later calls.
+	var results [][]float64
+	for i := 0; i < 10; i++ {
+		p, err := img.GetPoint(10, 10)
+		require.NoError(t, err)
+		results = append(results, p)
+	}
+
+	// All results should be identical and independently owned.
+	for i, p := range results {
+		assert.Equal(t, 3, len(p), "iteration %d", i)
+		assert.Equal(t, 255.0, p[0], "iteration %d", i)
+		assert.Equal(t, 255.0, p[1], "iteration %d", i)
+		assert.Equal(t, 255.0, p[2], "iteration %d", i)
+	}
+}
+
+// TestGetAsString_RoundTrip verifies that GetAsString correctly returns
+// string metadata. Previously, vipsImageGetAsString deferred freeCString
+// on a nil pointer (captured before the C call), leaking the allocated string.
+func TestGetAsString_RoundTrip(t *testing.T) {
+	require.NoError(t, Startup(nil))
+
+	img, err := NewImageFromFile(resources + "jpg-24bit.jpg")
+	require.NoError(t, err)
+	defer img.Close()
+
+	img.SetString("test-field", "hello-world")
+
+	// GetAsString returns a formatted version of the field value.
+	result := img.GetAsString("test-field")
+	assert.Contains(t, result, "hello-world")
+}
+
 func TestNewImageFromGoImage_RoundTrip(t *testing.T) {
 	require.NoError(t, Startup(nil))
 

vips/operations.go

@@ -30,14 +30,16 @@ func vipsFindTrim(in *C.VipsImage, threshold float64, backgroundColor *Color) (i
 func vipsGetPoint(in *C.VipsImage, n int, x int, y int) ([]float64, error) {
 	incOpCounter("getpoint")
 	var out *C.double
-	defer gFreePointer(unsafe.Pointer(out))
 
 	if err := C.getpoint(in, &out, C.int(n), C.int(x), C.int(y)); err != 0 {
 		return nil, handleVipsError()
 	}
 
-	// maximum n is 4
-	return (*[4]float64)(unsafe.Pointer(out))[:n:n], nil
+	// Copy from C memory into a Go slice, then free the C allocation.
+	result := make([]float64, n)
+	copy(result, (*[4]float64)(unsafe.Pointer(out))[:n:n])
+	gFreePointer(unsafe.Pointer(out))
+	return result, nil
 }
 
 // https://www.libvips.org/API/current/libvips-arithmetic.html#vips-min
@@ -866,7 +868,7 @@ func vipsImageGetAsString(in *C.VipsImage, name string) string {
 	cField := C.CString(name)
 	defer freeCString(cField)
 	var cFieldValue *C.char
-	defer freeCString(cFieldValue)
+	defer func() { freeCString(cFieldValue) }()
 	if int(C.image_get_as_string(in, cField, &cFieldValue)) == 0 {
 		return C.GoString(cFieldValue)
 	}