fileReadStreamingLimit

fn fileReadStreamingLimit(
    handle: File.Handle,
    data: []const []u8,
    limit: Io.Limit,
) File.ReadStreamingError!usize {
    var iovecs: [max_iovecs_len]iovec = undefined;
    var iovlen: iovlen_t = 0;
    // .nothing can mean that the write side has been closed,
    // in which case the buffer still needs to be drained
    var remaining = if (limit == .nothing) .unlimited else limit;
    for (data) |buf| addBuf(false, &iovecs, &iovlen, &remaining, buf);
    if (iovlen == 0) return 0;
    while (true) {
        const rc = c.readv(handle, &iovecs, iovlen);
        switch (c.errno(rc)) {
            .SUCCESS => return if (rc == 0) error.EndOfStream else @intCast(rc),
            .INTR => continue,
            .INVAL => |err| return errnoBug(err),
            .FAULT => |err| return errnoBug(err),
            .AGAIN => return error.WouldBlock,
            .BADF => |err| return errnoBug(err), // File descriptor used after closed
            .IO => return error.InputOutput,
            .ISDIR => return error.IsDir,
            .NOBUFS => return error.SystemResources,
            .NOMEM => return error.SystemResources,
            .NOTCONN => return error.SocketUnconnected,
            .CONNRESET => return error.ConnectionResetByPeer,
            else => |err| return unexpectedErrno(err),
        }
    }
}