go-libwebp

commit 5b89d308e57cde1ac64afa7cb259ec89c9013e96
parent 6e91d0e9e45341b48781fb3ff4cccecee6770af0
Author: Jack Mordaunt <jackmordaunt.dev@gmail.com>
Date:   Thu, 19 Oct 2023 16:08:19 +0800

webp/encode: fix use of out pointer

First, we must use a uintptr so we don't truncate the memory address.
Second, we must declare the uintptr in a place the runtime will not
optimize away.

Signed-off-by: Jack Mordaunt <jackmordaunt.dev@gmail.com>

Diffstat:
M
webp/encode.go
 | 
29
+++++++++++++++++++++--------

1 file changed, 21 insertions(+), 8 deletions(-)
diff --git a/webp/encode.go b/webp/encode.go
@@ -45,9 +45,15 @@ type Encoder struct {
 	// Lossless indicates whether to use the lossless compression
 	// strategy. If true, the Quality field is ignored.
 	Lossless bool
+
+	// out pointer contains the output memory address from webp.
+	// Must be a field because stack variables are optimized out
+	// by the runtime.
+	out uintptr
 }
 
 // Encode specified image as webp to w.
+// Not threadsafe.
 func (enc *Encoder) Encode(w io.Writer, m image.Image) error {
 	if enc.Quality <= 0.0 || enc.Quality > 1 {
 		enc.Quality = 1.0
@@ -63,14 +69,16 @@ func (enc *Encoder) Encode(w io.Writer, m image.Image) error {
 }
 
 func (enc *Encoder) encode(w io.Writer, m *image.RGBA) error {
-	var (
-		// out buffer to contain webp data.
-		out *byte = nil
-	)
+	return encode(enc, w, m)
+}
+
+func encode(enc *Encoder, w io.Writer, m *image.RGBA) error {
 	tls := libc.NewTLS()
 	defer tls.Close()
+
 	buf, free := unmanage(tls, m.Pix)
 	defer free()
+
 	size := lib.Encode(
 		tls,
 		buf,
@@ -89,18 +97,23 @@ func (enc *Encoder) encode(w io.Writer, m *image.RGBA) error {
 		// quality for libwebp is [0,100].
 		float32(enc.Quality*100),
 		libc.Bool32(enc.Lossless),
-		uintptr(unsafe.Pointer(&out)),
+		uintptr(unsafe.Pointer(&enc.out)),
 	)
-	defer lib.WebPFree(tls, uintptr(unsafe.Pointer(out)))
+
+	defer lib.WebPFree(tls, enc.out)
 	if size == 0 {
 		return fmt.Errorf("encoding webp image: size %d", size)
 	}
-	if out == nil {
+
+	if enc.out == 0 {
 		return fmt.Errorf("failed to allocate memory; probably errored")
 	}
-	if _, err := w.Write(libc.GoBytes(uintptr(unsafe.Pointer(out)), int(size))); err != nil {
+
+	data := libc.GoBytes(enc.out, int(size))
+	if _, err := w.Write(data); err != nil {
 		return fmt.Errorf("writing webp data: %w", err)
 	}
+
 	return nil
 }