fix: ensure we associate correct memory for the user_metadata attached to a cache item (#734)

Author: JakeChampion

runtime/js-compute-runtime/builtins/cache-core.cpp

@@ -263,8 +263,7 @@ JS::Result<host_api::CacheWriteOptions> parseTransactionUpdateOptions(JSContext
     size_t length;
     JS::UniqueChars data;
     std::tie(data, length) = result.unwrap();
-    host_api::HostBytes metadata(std::move(data), length);
-    options.metadata = std::move(metadata);
+    options.metadata = host_api::HostBytes(std::move(data), length);
   }
 
   return options;

runtime/js-compute-runtime/host_interface/host_api.cpp

@@ -1370,7 +1370,7 @@ void init_write_options(fastly_compute_at_edge_cache_write_options_t &options,
 
   options.length = opts.length;
 
-  if (opts.metadata.empty()) {
+  if (!opts.metadata.len || !opts.metadata.ptr) {
     options.user_metadata.ptr = 0;
     options.user_metadata.len = 0;
   } else {

runtime/js-compute-runtime/host_interface/host_api.h

@@ -679,7 +679,7 @@ struct CacheWriteOptions final {
 
   uint64_t length = 0;
 
-  std::span<uint8_t> metadata;
+  HostBytes metadata;
 
   bool sensitive = false;
 };