Re: Boost SSL handshake(http_server_sync_ssl) : still reachable memory keeps increasing

From: Richard Hodges (hodges.r_at_[hidden])
Date: 2022-03-04 13:44:21

On Fri, 4 Mar 2022 at 12:14, Sandeep Bhardwaj via Boost-users <
boost-users_at_[hidden]> wrote:

> Need to check that. Just to be a little more clear, my requirements for
> the http server are pretty basic and if it can serve just one request at a
> time, it would serve my requirement. With this requirement, if io_context
> object can be stopped and post that if we clear the ssl related stuff and
> then start io_context again to serve the next request, would it help in
> clearing the memory being held? Any thoughts?
>

The io_context is a separate, orthogonal concern to the ssl::context.

The io_context represents your program's io loop. Normally there would be
only one per program.

The ssl::context represents a common set of parameters for negotiating SSL
sessions and acts as a container for those sessions. Note that these SSL
sessions are not necessarily associated with any particular TCP connection
- they merely represent the state of an encrypted tunnel over some
transport. You would normally have one ssl::context per domain in your
program. For example, a server that accepted inbound connections from the
internet but then made outbound connections to a specific set of servers
guarded by private keys, might use two ssl::context objects - one for all
inbound connections and one for all outbound.

Destroying the ssl::context and recreating is possible but I don't think it
gains you anything. It might be that the context simply keeps hold of
allocated memory in anticipation of re-using it. In this case, allowing it
to cache memory is harmless. If the memory use grows during the lifetime of
the program, then this might be more serious. But I have never experienced
this.

Destroying and recreating the io_context serves no purpose whatsoever. It
simply means that cached services will be destroyed and re-created each
time you service a request.

>
> On Fri, 4 Mar 2022 at 13:29, Richard Hodges via Boost-users <
> boost-users_at_[hidden]> wrote:
>
>> Yes this is too early. I would expect these functions ti be called in the
>> destructor of your ssl stream object
>> Can you confirm that this is actually destroyed?
>> Maybe put a breakpoint in the destructor of asio::ssl::stream ?
>>
>> On Fri, 4 Mar 2022 at 08:34, Sandeep Bhardwaj via Boost-users <
>> boost-users_at_[hidden]> wrote:
>>
>>> My bad. I probably spoke too soon. It is resulting in invalid write.
>>>
>>>
>>>
>>> On Fri, 4 Mar 2022 at 11:21, Sandeep Bhardwaj <sandybharblore_at_[hidden]>
>>> wrote:
>>>
>>>> I have added some code in on_shutdown to get the session object and
>>>> free it explicitly. The same stack is not observed in the valgrind report
>>>> anymore.
>>>> Is this fine? any comments?
>>>>
>>>>     void
>>>>     on_shutdown(beast::error_code ec)
>>>>     {
>>>>         if(ec)
>>>>             return fail(ec, "shutdown");
>>>>
>>>>
>>>>
>>>>
>>>> *        std::cout<<"Shutting down"<<std::endl;        SSL *ssl =
>>>> stream_.native_handle();        SSL_SESSION *session_object =
>>>> SSL_get_session(ssl);        SSL_SESSION_free(session_object);*
>>>>         // At this point the connection is closed gracefully
>>>>     }
>>>>
>>>> On Fri, 4 Mar 2022 at 01:53, Richard Hodges via Boost-users <
>>>> boost-users_at_[hidden]> wrote:
>>>>
>>>>>
>>>>>
>>>>> On Thu, 3 Mar 2022 at 18:25, Sandeep Bhardwaj via Boost-users <
>>>>> boost-users_at_[hidden]> wrote:
>>>>>
>>>>>> Hi,
>>>>>>
>>>>>>   I tried the async program as suggested and I still see one of the
>>>>>> stacks where the "still reachable" memory keeps increasing with duration. I
>>>>>> have attached the relevant stack and the program. Sorry I had to resend
>>>>>> this email multiple times due to size limitations. Hopefully this will go
>>>>>> through.
>>>>>>
>>>>>
>>>>> It's entirely possible that OpenSSL caches memory, which would be
>>>>> beyond the responsibility of Beast or Asio.
>>>>>
>>>>> I don't see anything controversial in your program.
>>>>>
>>>>> I see this on stack overflow, but no answers:
>>>>>
>>>>> https://stackoverflow.com/questions/56355690/valgrind-reports-memory-leak-related-with-crypto-zalloc-in-a-c-app-but-no-addi
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Fri, 4 Feb 2022 at 12:28, Sandeep Bhardwaj <
>>>>>> sandybharblore_at_[hidden]> wrote:
>>>>>>
>>>>>>> Thanks a lot. I will give it a try.
>>>>>>>
>>>>>>> On Thu, 3 Feb 2022 at 23:15, Vinnie Falco <vinnie.falco_at_[hidden]>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> On Thu, Feb 3, 2022 at 9:41 AM Sandeep Bhardwaj via Boost-users
>>>>>>>> <boost-users_at_[hidden]> wrote:
>>>>>>>> > http_server_sync_ssl.cpp
>>>>>>>>
>>>>>>>> Oh, right. Synchronous APIs have no way to time out. So if the
>>>>>>>> remote
>>>>>>>> host does not close gracefully (i.e. just slams the connection shut)
>>>>>>>> then you will be left with a connection object which either has no
>>>>>>>> way
>>>>>>>> to be destroyed, or has to wait what could be a very long time (up
>>>>>>>> to
>>>>>>>> 2 hours) for the operating system to time out the synchronous read.
>>>>>>>>
>>>>>>>> Please try the asynchronous example, http_server_async_ssl.cpp and
>>>>>>>> determine if the problem persists.
>>>>>>>>
>>>>>>>> Thanks
>>>>>>>>
>>>>>>> _______________________________________________
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>>>>>>
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>> --
>> Richard Hodges
>> hodges.r_at_[hidden]
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