C++ REST SDK http_client doesn't fully support HTTP/1.0 with ASIO-based implementation

[garethsb]

This only affects nmos-cpp Nodes which are built against cpprestsdk configured (at CMake time) with CPPREST_HTTP_CLIENT_IMPL=asio, which is the default on Linux but not Windows.

It only affects such Nodes when communicating with a Registry which only supports HTTP/1.0.
And it only causes any trouble when that Registry does not respond with a Connection: Keep-Alive header, but closes the connection after each response.

In this case, cpprestsdk still attempts to reuse the connection, and so the next request always fails.
This connection failure causes nmos-cpp Nodes to try the next available Registry.

This can be resolved by microsoft/cpprestsdk#1032, but this is not yet merged to cpprestsdk master.

[garethsb]

I have identified that this issue could cause the NMOS Test Suite test_05 to fail with "Heartbeats are too frequent". See AMWA-TV/nmos-testing#120.

I have confirmed the cpprestsdk PR mentioned solves this problem.

[garethsb]

Merged to cpprestsdk master at microsoft/cpprestsdk@f940d55.

Will close this when we can update the docs to point at a cpprestsdk version.

[garethsb]

C++ REST SDK v2.10.11 includes the fixes for this (microsoft/cpprestsdk#1032), and also the two PRs related to security (microsoft/cpprestsdk#1049, microsoft/cpprestsdk#1051).