9316d96240 test: sock: Enable socket pair tests on Windows (David Gumberg)
Pull request description:
Some `class Sock` tests were previously disabled because Windows lacks [`socketpair(2)`](https://man7.org/linux/man-pages/man2/socketpair.2.html) which is used as a helper function in the socket tests, but is not strictly necessary or related to the `Socket` class under testing. This PR adds a `CreateSocketPair()` helper which creates a sender socket and receiver socket with a TCP connection, enabling these test cases for Windows. This also enables future tests that require more granular control over sockets than what `socketpair()` allows for, like using `setsockopt()` before connecting a socket.
This change is generally an improvement, but is also broken out of a [branch](github.com/davidgumberg/bitcoin/tree/2025-09-02-0xB10C-prefill-rebase) that does compact block prefilling up to the available bytes in the connection's current TCP window (see [delving post](https://delvingbitcoin.org/t/stats-on-compact-block-reconstructions/1052/34)). Creating connected socket pairs is useful for added tests in that branch that validate querying the current TCP window state, and without this change those tests don't run on Windows.
ACKs for top commit:
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sedited:
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w0xlt:
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Tree-SHA512: 23ad7070555bb934b0eb18d114e918bd2d50657d20d2221d8c98cd0e558e27e32e5ef89e8074c108a90d7309e539318d23cea43d2ad8eb10e635b114f5f1a87d
Adds a helper struct `socket_pair` for constructing and connecting TCP
sockets, this replaces socketpair() which is not available on Windows.
Making the socket pair TCP sockets instead of Unix sockets, and
separating socket creation from socket connection also enables more
detailed tests to be added in the future.
Avoid providing the entire unit test framework dependency to tests that only
require access to the HasReason utility class.
E.g. reverselock_tests.cpp, sync_tests.cpp, util_check_tests.cpp, util_string_tests.cpp,
and script_parse_tests.cpp only require access to HasReason and nothing else.
These methods in the Sock class wrap corresponding syscalls,
accepting void* arguments and casting to char* internally, which is
needed for Windows support and ignored on other platforms because
the syscall itself accepts void*:
Send()
Recv()
GetSockOpt()
SetSockOpt()
`Sock::Get()` was used only in `sock.{cpp,h}`. Remove it and access
`Sock::m_socket` directly.
Unit tests that used `Get()` to test for equality still verify that the
behavior is correct by using the added `operator==()`.
Since the kernel library no longer depends on the system file, move it
to the common library instead in accordance to the diagram in
doc/design/libraries.md.
Outside of `Sock`, `Sock::Reset()` was used in just one place (in
`i2p.cpp`) which can use the assignment operator instead.
This simplifies the public `Sock` API by having one method less.
This fixes:
```bash
In file included from test/sock_tests.cpp:10:
In file included from /usr/local/include/boost/test/unit_test.hpp:18:
In file included from /usr/local/include/boost/test/test_tools.hpp:46:
/usr/local/include/boost/test/tools/old/impl.hpp:107:17: warning: comparison of integers of different signs: 'const long' and 'const unsigned long' [-Wsign-compare]
return left == right;
~~~~ ^ ~~~~~
```
which was introduced in #20788.
