Re: [Boost-users] Enhancing the boost::asio::connect() socket interface

Subject: Re: [Boost-users] Enhancing the boost::asio::connect() socket interface
From: Richard Hodges (hodges.r_at_[hidden])
Date: 2017-09-27 06:03:34

> As boost::asio::connect() closes an open socket passed to it before
making the remote connection, it's not possible to pass connect() a
prebaked socket.

I think the class template you're looking for is basic_raw_socket<>.

http://www.boost.org/doc/libs/1_64_0/doc/html/boost_asio/reference/basic_raw_socket.html

On 24 September 2017 at 21:02, Maarten de Vries via Boost-users <
boost-users_at_[hidden]> wrote:

>
>
> On 24 September 2017 at 19:37, Vinnie Falco via Boost-users <
> boost-users_at_[hidden]> wrote:
>
>> >On Sun, Sep 24, 2017 at 1:15 AM, martin doc via Boost-users <
>> boost-users_at_[hidden]> wrote:
>> > As boost::asio::connect() closes an open socket passed to it before
>> making
>> > the remote connection, it's not possible to pass connect() a prebaked
>> > socket.
>>
>> What makes you think that? My reading of the implementation is that
>> the socket is only closed when:
>>
>> 1. The range of addresses passed to connect() has more than one element,
>> and
>> 2. The connection attempt for the first address fails.
>>
>> See:
>>
>> <https://github.com/boostorg/asio/blob/b002097359f246b7b1478
>> 775251dfb153ab3ff4b/include/boost/asio/impl/connect.hpp#L108
>>
>> You can avoid the socket closure by only attempting to connect to one
>> address.
>>
>
> ​Judging from that code, the socket is always closed before attempting a
> connect. The `s.close()`​ is right above the `s.connect()`.
>
> My guess is this is because the iterated endpoints may be using different
> protocols (TCP/IPv4 or TCP/IPv6 for example). Things become a bit hairy
> when you take that into account. You can't use a local TCP/IPv4 endpoint
> and connect to a TCP/IPv6 peer. What should `asio::connect` do in that
> case? Ignore the IPv6 endpoint? Or just not bind to a specific local
> endpoint? Or should you give it an iterator with at least one local
> endpoint per protocol in the iterated remote endpoints? And in that case,
> what should `asio::connect` do if there isn't a matching local endpoint?
> Return an error? Or not bind to a local endpoint? Personally I'm not sure
> which behaviour makes the most sense here. It seems like ASIO decided to
> sidestep the whole issue.
>
> You can still use `socket.connect()` directly with a single endpoint.
> Alternatively, you can wrap an already connected socket by passing the file
> descriptor to asio:
>
> http://www.boost.org/doc/libs/1_65_1/doc/html/boost_asio/
> reference/basic_stream_socket/basic_stream_socket/overload4.html
> http://www.boost.org/doc/libs/1_65_1/doc/html/boost_asio/
> reference/basic_stream_socket/assign.html
> ​
> Another option is to write your own `connect` function that does support
> binding to a local endpoint. If you have a nice way of dealing with
> different protocols in the iterated remote endpoints, you could even
> suggest your function for inclusion in ASIO.
>
> --
> ​ Maarten​
>
>
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