Re: [PATCH v2 5/6] connect: advertise OS version

>
> Usman Akinyemi <usmanakinyemi202@gmail.com> writes:
>
> > As some issues that can happen with a Git client can be operating system
> > specific, it can be useful for a server to know which OS a client is
> > using. In the same way it can be useful for a client to know which OS
> > a server is using.
>
> Hmph.  The other end may be running different version of Git, and
> the version difference of _our_ software is probably more relevant.
> For that matter, they may even be running something entirely
> different from our software, like Gerrit.  So I am not sure I am
> convinced that os-version thing is a good thing to have with that
> paragraph.

>
> > Let's introduce a new protocol (`os-version`) allowing Git clients and
> > servers to exchange operating system information. The protocol is
> > controlled by the new `transfer.advertiseOSVersion` config option.
>
> The last sentence is redundant and can safely removed.  The next
> paragraph describes it better than "is controlled by".

>
> > Add the `transfer.advertiseOSVersion` config option to address
> > privacy concerns. It defaults to `true` and can be changed to
> > `false`. When enabled, this option makes clients and servers send each
> > other the OS name (e.g., "Linux" or "Windows"). The information is
> > retrieved using the 'sysname' field of the `uname(2)` system call.
>
> Add "or its equivalent" at the end.
>
> macOS may have one, but it probably is not quite correct to say that
> Windows have uname system call (otherwise we wouldn't be emulating
> it on top of GetVersion ourselves).

>
> > However, there are differences between `uname(1)` (command-line utility)
> > and `uname(2)` (system call) outputs on Windows. These discrepancies
> > complicate testing on Windows platforms. For example:
> >   - `uname(1)` output: MINGW64_NT-10.0-20348.3.4.10-87d57229.x86_64\
> >   .2024-02-14.20:17.UTC.x86_64
> >   - `uname(2)` output: Windows.10.0.20348
> >
> > On Windows, uname(2) is not actually system-supplied but is instead
> > already faked up by Git itself. We could have overcome the test issue
> > on Windows by implementing a new `uname` subcommand in `test-tool`
> > using uname(2), but except uname(2), which would be tested against
> > itself, there would be nothing platform specific, so it's just simpler
> > to disable the tests on Windows.
>
> OK.
>
> > +transfer.advertiseOSVersion::
> > +     When `true`, the `os-version` capability is advertised by clients and
> > +     servers. It makes clients and servers send to each other a string
> > +     representing the operating system name, like "Linux" or "Windows".
> > +     This string is retrieved from the `sysname` field of the struct returned
> > +     by the uname(2) system call. Defaults to true.
>
> Presumably, both ends of the connection independently choose whether
> they enable or disable this variable, so we have 2x2=4 combinations
> (here, versions of Git before the os-version capability support is
> introduced behave the same way as an installation with this
> configuration variable set to false).
>
> And among these four combinations, only one of them results in "send
> to each other", but the description above is fuzzy.

>
> > diff --git a/connect.c b/connect.c
> > index 10fad43e98..6d5792b63c 100644
> > --- a/connect.c
> > +++ b/connect.c
> > @@ -492,6 +492,9 @@ static void send_capabilities(int fd_out, struct packet_reader *reader)
> >       if (server_supports_v2("agent"))
> >               packet_write_fmt(fd_out, "agent=%s", git_user_agent_sanitized());
> >
> > +     if (server_supports_v2("os-version") && advertise_os_version(the_repository))
> > +             packet_write_fmt(fd_out, "os-version=%s", os_version_sanitized());
>
> Not a new problem, because the new code is pretty-much a straight
> copy from the existing "agent" code, but do we ever use unsanitized
> versions of git-user-agent and os-version?  If not, I am wondering
> if we should sanitize immediately when we obtain the raw string and
> keep it, get rid of _santized() function from the public API, and
> make anybody calling git_user_agent() and os_version() to get
> sanitized safe-to-use strings.
>
> I see http.c throws git_user_agent() without doing any sanitization
> at the cURL library, but it may be a mistake that we may want to fix
> (outside the scope of this topic).  Since the contrast between the
> os_version() vs the os_version_sanitized() is *new* in this series,
> however, we probably would want to get it right from the beginning.
>
> So the question is again, do we ever need to use os_version() that
> is a raw string that may require sanitizing?  I do not think of any
> offhand.