Otherwise they may be called on a socket that no longer exists.
For example, if the GC calls the finaliser on the socket and then reuses
its heap memory, the "callback" entry of the old socket may contain invalid
data. If lwIP then calls the TCP callback the code may try to call the
user callback object which is now invalid. The lwIP callbacks must be
deregistered during the closing of the socket, before all the pcb pointers
are set to NULL.
This matches CPython behaviour on Linux: a socket that is new and not
listening or connected is considered "hung up".
Thanks to @rkojedzinszky for the initial patch, PR #3457.
This patch moves the implementation of stream closure from a dedicated
method to the ioctl of the stream protocol, for each type that implements
closing. The benefits of this are:
1. Rounds out the stream ioctl function, which already includes flush,
seek and poll (among other things).
2. Makes calling mp_stream_close() on an object slightly more efficient
because it now no longer needs to lookup the close method and call it,
rather it just delegates straight to the ioctl function (if it exists).
3. Reduces code size and allows future types that implement the stream
protocol to be smaller because they don't need a dedicated close method.
Code size reduction is around 200 bytes smaller for x86 archs and around
30 bytes smaller for the bare-metal archs.
Dramatically improves TCP sending throughput because without an explicit
call to tcp_output() the data is only sent to the lower layers via the
lwIP slow timer which (by default) ticks every 500ms.
Header files that are considered internal to the py core and should not
normally be included directly are:
py/nlr.h - internal nlr configuration and declarations
py/bc0.h - contains bytecode macro definitions
py/runtime0.h - contains basic runtime enums
Instead, the top-level header files to include are one of:
py/obj.h - includes runtime0.h and defines everything to use the
mp_obj_t type
py/runtime.h - includes mpstate.h and hence nlr.h, obj.h, runtime0.h,
and defines everything to use the general runtime support functions
Additional, specific headers (eg py/objlist.h) can be included if needed.
- Changed: ValueError, TypeError, NotImplementedError
- OSError invocations unchanged, because the corresponding utility
function takes ints, not strings like the long form invocation.
- OverflowError, IndexError and RuntimeError etc. not changed for now
until we decide whether to add new utility functions.
Peer-closed socket is both readable and writable: read will return EOF,
write - error. Without this poll will hang on such socket.
Note that we don't return POLLHUP, based on argumentation in
http://www.greenend.org.uk/rjk/tech/poll.html that it should apply to
deeper disconnects, for example for networking, that would be link layer
disconnect (e.g. WiFi went down).
This follows the pattern of how all other headers are now included, and
makes it explicit where the header file comes from. This patch also
removes -I options from Makefile's that specify the mp-readline/timeutils/
netutils directories, which are no longer needed.
Storing a chain of pbuf was an original design of @pfalcon's lwIP socket
module. The problem with storing just one, like modlwip does is that
"peer closed connection" notification is completely asynchronous and out of
band. So, there may be following sequence of actions:
1. pbuf #1 arrives, and stored in a socket.
2. pbuf #2 arrives, and rejected, which causes lwIP to put it into a
queue to re-deliver later.
3. "Peer closed connection" is signaled, and socket is set at such status.
4. pbuf #1 is processed.
5. There's no stored pbufs in teh socket, and socket status is "peer closed
connection", so EOF is returned to a client.
6. pbuf #2 gets redelivered.
Apparently, there's no easy workaround for this, except to queue all
incoming pbufs in a socket. This may lead to increased memory pressure,
as number of pending packets would be regulated only by TCP/IP flow
control, whereas with previous setup lwIP had a global overlook of number
packets waiting for redelivery and could regulate them centrally.
Calling it from lwIP accept callback will lead incorrect functioning
and/or packet leaks if Python callback has any networking calls, due
to lwIP non-reentrancy. So, instead schedule "poll" callback to do
that, which will be called by lwIP when it does not perform networking
activities. "Poll" callback is called infrequently though (docs say
every 0.5s by default), so for better performance, lwIP needs to be
patched to call poll callback soon after accept callback, but when
current packet is already processed.
To use: .setsockopt(SOL_SOCKET, 20, lambda sock: print(sock)). There's a
single underlying callback slot. For normal sockets, it serves as data
received callback, for listening sockets - connection arrived callback.
When lwIP creates a incoming connection socket of a listen socket, it
sets its recv callback to one which discards incoming data. We set
proper callback only in accept() call, when we allocate Python-level
socket where we can queue incoming data. So, in lwIP accept callback
be sure to set recv callback to one which tells lwIP to not discard
incoming data.
Per POSIX http://pubs.opengroup.org/onlinepubs/9699919799/functions/send.html :
"If space is not available at the sending socket to hold the message to be
transmitted, and the socket file descriptor does not have O_NONBLOCK set,
send() shall block until space is available. If space is not available at the
sending socket to hold the message to be transmitted, and the socket file
descriptor does have O_NONBLOCK set, send() shall fail [with EAGAIN]."
