FileStream should flush on network operation complete #58
Description
In gist I have code like this..
std::string filePath = "some/local/path";
std::shared_ptr<Aws::Http::HttpRequest> request;
request->SetResponseStreamFactory(
[&filePath, &offset]() -> Aws::IOStream* {
constexpr auto OpenFlag = std::ios_base::out
| std::ios_base::binary;
Aws::IOStream* ofs =
Aws::New<Aws::FStream>(ALLOCATION_TAG, filePath, OpenFlag);
CHECK(ofs->good());
CHECK(ofs->seekp(offset, ofs->beg));
return ofs;
});
std::shared_ptr<Aws::Http::HttpResponse> response(std::move(m_client->MakeRequest(*request)));
std::ifstream ifs(filePath); // ! DATA NOT YET FLUSHED TO FILE HERE
However if I artificially scope everything as follows...
std::string filePath = "some/local/path";
{ // BEGIN BOGUS SCOPE
std::shared_ptr<Aws::Http::HttpRequest> request;
request->SetResponseStreamFactory(
[&filePath, &offset]() -> Aws::IOStream* {
constexpr auto OpenFlag = std::ios_base::out
| std::ios_base::binary;
Aws::IOStream* ofs =
Aws::New<Aws::FStream>(ALLOCATION_TAG, filePath, OpenFlag);
CHECK(ofs->good());
CHECK(ofs->seekp(offset, ofs->beg));
return ofs;
});
std::shared_ptr<Aws::Http::HttpResponse> response(std::move(m_client->MakeRequest(*request)));
} // END BOGUS SCOPE
std::ifstream ifs(filePath); // DATA IS NOW FLUSHED
This indicates to me a few things:
- You're not flushing the file stream.
- You're lazily deleting the Aws::IOstream object
This behavior is surprising and cost me ~45 minute of debug time.
This may /seem obvious/ in this contrived example. But the entire AWS SDK is designed using shared pointers practically everywhere, and as such... it can be come less clear in complicated code what the precise lifetime of objects will be.