src: fix reading empty string views in Blob[De]serializer

The string writing/reading was intended for debugging info
in snapshot, which had a CHECK_GT(length, 0) check, it then
got repurposed for SEA resource writing/reading and turned
into a helper for string views, but was not updated to handle
empty views, causing occasional crash in the CI when the
read is protected. This patch fixes it.

PR-URL: #52000
Fixes: #50740
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

src/api/environment.cc

@@ -553,7 +553,9 @@ MaybeLocal<Value> LoadEnvironment(Environment* env,
 MaybeLocal<Value> LoadEnvironment(Environment* env,
                                   std::string_view main_script_source_utf8,
                                   EmbedderPreloadCallback preload) {
-  CHECK_NOT_NULL(main_script_source_utf8.data());
+  // It could be empty when it's used by SEA to load an empty script.
+  CHECK_IMPLIES(main_script_source_utf8.size() > 0,
+                main_script_source_utf8.data());
   return LoadEnvironment(
       env,
       [&](const StartExecutionCallbackInfo& info) -> MaybeLocal<Value> {

src/blob_serializer_deserializer-inl.h

@@ -139,6 +139,11 @@ std::string_view BlobDeserializer<Impl>::ReadStringView(StringLogMode mode) {
   size_t length = ReadArithmetic<size_t>();
   Debug("ReadStringView(), length=%zu: ", length);
 
+  if (length == 0) {
+    Debug("ReadStringView() read an empty view\n");
+    return std::string_view();
+  }
+
   std::string_view result(sink.data() + read_total, length);
   Debug("%p, read %zu bytes", result.data(), result.size());
   if (mode == StringLogMode::kAddressAndContent) {
@@ -269,6 +274,10 @@ size_t BlobSerializer<Impl>::WriteStringView(std::string_view data,
   size_t written_total = WriteArithmetic<size_t>(data.size());
 
   size_t length = data.size();
+  if (length == 0) {
+    Debug("WriteStringView() wrote an empty view\n");
+    return written_total;
+  }
   sink.insert(sink.end(), data.data(), data.data() + length);
   written_total += length;