Use gather send [10657]

[MiguelCompany]

This PR extends the transport interface to avoid copying user data when encapsulating the serialized payload into the RTPS datagram.

[EduPonz]

@richiprosima please test discovery-server

[JLBuenoLopez]

There are some tests that are failing consistently with this PR and not in master (running --repeat-until-fail 100 in master succeeds):

• 242: BlackboxTests_FastRTPS.PubSubFragments.AsyncPubSubAsNonReliableVolatileData300kb.Transport
• 897: BlackboxTests_DDS_PIM.PubSubFragments.AsyncPubSubAsNonReliableVolatileData300kb.Transport (this one has failed in the Linux CI)
• 555: BlackboxTests_FastRTPS.BlackBox.TCP_TLS: the following error message appears:

[RTCP_MSG_IN Error] Bad RTCP header identifier, closing connection. -> Function Receive

• 1353: BlackboxTests_DDS_PIM.BlackBox.TCP_TLS: master sometimes blocks and timeouts (rarely). This also happens with this PR (frequently) but the following message is printed that in master does not appear:

[RTCP_MSG_IN Error] Bad RTCP header identifier, closing connection. -> Function Receive

• 1831: SHMTransportTests.buffer_recover: in master sometimes happens but locally in my machine is failing consistently with this PR:

1845: terminate called without an active exception
    Test #1845: SHMTransportTests.buffer_recover ...Child aborted***Exception:  12.57 sec

[MiguelCompany]

@JLBuenoLopez-eProsima Doxygen changes are still pending, but the rest can be reviewed

[MiguelCompany]

• 242: BlackboxTests_FastRTPS.PubSubFragments.AsyncPubSubAsNonReliableVolatileData300kb.Transport
• 897: BlackboxTests_DDS_PIM.PubSubFragments.AsyncPubSubAsNonReliableVolatileData300kb.Transport (this one has failed in the Linux CI)

I think these have been solved by 7c930df4d59cbfced843475b216a930cc777b417

• 555: BlackboxTests_FastRTPS.BlackBox.TCP_TLS: the following error message appears:
• 1353: BlackboxTests_DDS_PIM.BlackBox.TCP_TLS: master sometimes blocks and timeouts (rarely). This also happens with this PR (frequently) but the following message is printed that in master does not appear:

I think these have been solved by 4fc658f34714513879d91a688ef15761c67ea39c

• 1831: SHMTransportTests.buffer_recover: in master sometimes happens but locally in my machine is failing consistently with this PR:

All the code used by that test has not been modified by this PR...

[MiguelCompany]

@JLBuenoLopez-eProsima I think this is finished! 🤞

[JLBuenoLopez]

The following tests are failing:

• 908: BlackboxTests_DDS_PIM.PubSubFragments.AsyncPubSubAsNonReliableVolatileData300kb.Transport: running this test in master 100 times passes successfully, but with these changes the test fails frequently.
• 1812: TCPv4Tests.send_and_receive_between_both_secure_ports: running this test in master prints the following warning and passes successfully:

[DEBUG Warning] Error reading TCP header: Operation aborted. -> Function Receive

whereas running this PR prints:

[DEBUG Warning] Failed to send RTCP message (14 of 19 b): Success -> Function send
[RTCP_MSG_IN Warning] Bad TCP header CRC -> Function Receive
[RTCP_MSG_IN Error] Bad RTCP header identifier, closing connection. -> Function Receive

and the test timeouts.

• 1814: TCPv4Tests.send_and_receive_between_secure_clients_1: the error is probably the same as the previous test because the outputs are similar.
• TCP_TLS tests (556 FastRTPS & 1364 DDS PIM) are also finishing with a timeout after printing:

[RTCP_MSG_IN Error] Bad RTCP header identifier, closing connection. -> Function Receive

It seems the issue could be the same as the previous tests. This does not happen in master.

[JLBuenoLopez]

Closing this PR. If in the future this feature is revisited, it would probably be easier to start again due to changes in the transport layer.