[wasm-api] Respect existing blob allocation in face_copy_blob

src/hb-wasm-api-face.hh

@@ -44,10 +44,25 @@ HB_WASM_API (bool_t, face_copy_table) (HB_WASM_EXEC_ENV
   hb_blob_t *hb_blob = hb_face_reference_table (face, table_tag);
 
   unsigned length;
-  const char *data = hb_blob_get_data (hb_blob, &length);
+  const char *hb_data = hb_blob_get_data (hb_blob, &length);
+
+  if (length <= blob->length)
+  {
+    char *data = (char *) (validate_app_addr (blob->data, blob->length) ? addr_app_to_native (blob->data) : nullptr);
+
+    if (unlikely (!data))
+    {
+      blob->length = 0;
+      return false;
+    }
+
+    memcpy (data, hb_data, length);
+
+    return true;
+  }
 
   blob->length = length;
-  blob->data = wasm_runtime_module_dup_data (module_inst, data, length);
+  blob->data = wasm_runtime_module_dup_data (module_inst, hb_data, length);
 
   hb_blob_destroy (hb_blob);
 

src/hb-wasm-api.h

@@ -108,6 +108,7 @@ typedef struct
   uint32_t length;
   ptr_t(char) data;
 } blob_t;
+#define BLOB_INIT {0, 0}
 
 HB_WASM_API (void, blob_free) (HB_WASM_EXEC_ENV
 			       ptr_d(blob_t, blob));

src/wasm/graphite/shape.cc

@@ -21,7 +21,7 @@ uint32_t heap_size = 2 * 1024 * 1024;
 static const void *copy_table (const void *data, unsigned int tag, size_t *len)
 {
   face_t *face = (face_t *) data;
-  blob_t blob;
+  blob_t blob = BLOB_INIT;
   if (!face_copy_table (face, tag, &blob))
     abort ();
 

src/wasm/sample/c/shape-fallback.cc

@@ -18,7 +18,7 @@ shape (void *shape_plan,
 {
   face_t *face = font_get_face (font);
 
-  blob_t blob;
+  blob_t blob = BLOB_INIT;
   if (!face_copy_table (face, TAG ('c','m','a','p'), &blob))
     abort ();