glibcVerFromRPath

fn glibcVerFromRPath(io: Io, rpath: []const u8) !std.SemanticVersion {
    const cwd: Io.Dir = .cwd();

    var dir = cwd.openDir(io, rpath, .{}) catch |err| switch (err) {
        error.NameTooLong => return error.Unexpected,
        error.BadPathName => return error.Unexpected,
        error.NetworkNotFound => return error.Unexpected, // Windows-only

        error.FileNotFound => return error.GLibCNotFound,
        error.NotDir => return error.GLibCNotFound,
        error.AccessDenied => return error.GLibCNotFound,
        error.PermissionDenied => return error.GLibCNotFound,
        error.NoDevice => return error.GLibCNotFound,

        error.ProcessFdQuotaExceeded => |e| return e,
        error.SystemFdQuotaExceeded => |e| return e,
        error.SystemResources => |e| return e,
        error.SymLinkLoop => |e| return e,
        error.Unexpected => |e| return e,
        error.Canceled => |e| return e,
    };
    defer dir.close(io);

    // Now we have a candidate for the path to libc shared object. In
    // the past, we used readlink() here because the link name would
    // reveal the glibc version. However, in more recent GNU/Linux
    // installations, there is no symlink. Thus we instead use a more
    // robust check of opening the libc shared object and looking at the
    // .dynstr section, and finding the max version number of symbols
    // that start with "GLIBC_2.".
    const glibc_so_basename = "libc.so.6";
    var file = dir.openFile(io, glibc_so_basename, .{}) catch |err| switch (err) {
        error.NameTooLong => return error.Unexpected,
        error.BadPathName => return error.Unexpected,
        error.PipeBusy => return error.Unexpected, // Windows-only
        error.NetworkNotFound => return error.Unexpected, // Windows-only
        error.AntivirusInterference => return error.Unexpected, // Windows-only
        error.FileLocksUnsupported => return error.Unexpected, // No lock requested.
        error.NoSpaceLeft => return error.Unexpected, // read-only
        error.PathAlreadyExists => return error.Unexpected, // read-only
        error.DeviceBusy => return error.Unexpected, // read-only
        error.FileBusy => return error.Unexpected, // read-only
        error.ReadOnlyFileSystem => return error.Unexpected, // read-only
        error.NoDevice => return error.Unexpected, // not asking for a special device
        error.FileTooBig => return error.Unexpected,
        error.WouldBlock => return error.Unexpected, // not opened in non-blocking

        error.AccessDenied => return error.GLibCNotFound,
        error.PermissionDenied => return error.GLibCNotFound,
        error.FileNotFound => return error.GLibCNotFound,
        error.NotDir => return error.GLibCNotFound,
        error.IsDir => return error.GLibCNotFound,

        error.ProcessFdQuotaExceeded => |e| return e,
        error.SystemFdQuotaExceeded => |e| return e,
        error.SystemResources => |e| return e,
        error.SymLinkLoop => |e| return e,
        error.Unexpected => |e| return e,
        error.Canceled => |e| return e,
    };
    defer file.close(io);

    // Empirically, glibc 2.34 libc.so .dynstr section is 32441 bytes on my system.
    var buffer: [8000]u8 = undefined;
    var file_reader: Io.File.Reader = .init(file, io, &buffer);

    return glibcVerFromSoFile(&file_reader) catch |err| switch (err) {
        error.InvalidElfMagic,
        error.InvalidElfEndian,
        error.InvalidElfClass,
        error.InvalidElfVersion,
        error.InvalidGnuLibCVersion,
        error.EndOfStream,
        => return error.GLibCNotFound,

        error.ReadFailed => return file_reader.err.?,
        else => |e| return e,
    };
}