Protocols are nice, but there is no way for C code to verify whether
a type's "protocol" structure actually implements some particular
protocol. As a result, you can pass an object that implements the
"vfs" protocol to one that expects the "stream" protocol, and the
opposite of awesomeness ensues.
This patch adds an OPTIONAL (but enabled by default) protocol identifier
as the first member of any protocol structure. This identifier is
simply a unique QSTR chosen by the protocol designer and used by each
protocol implementer. When checking for protocol support, instead of
just checking whether the object's type has a non-NULL protocol field,
use `mp_proto_get` which implements the protocol check when possible.
The existing protocols are now named:
protocol_framebuf
protocol_i2c
protocol_pin
protocol_stream
protocol_spi
protocol_vfs
(most of these are unused in CP and are just inherited from MP; vfs and
stream are definitely used though)
I did not find any crashing examples, but here's one to give a flavor of what
is improved, using `micropython_coverage`. Before the change,
the vfs "ioctl" protocol is invoked, and the result is not intelligible
as json (but it could have resulted in a hard fault, potentially):
>>> import uos, ujson
>>> u = uos.VfsPosix('/tmp')
>>> ujson.load(u)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: syntax error in JSON
After the change, the vfs object is correctly detected as not supporting
the stream protocol:
>>> ujson.load(p)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
OSError: stream operation not supported
Whenever there is more than one argument, delegate the operation to
namedtuple_make_new. This allows other circuitpython-compatible
idioms, like with keywords
time.struct_time(tm_year=2000, tm_mon=1, tm_mday=1, tm_hour=0,
tm_min=0, tm_sec=14, tm_wday=5, tm_yday=5, tm_isdst=-1)
with 9 positional arguments, etc.
The only vaguely plausible CPython behavior still not permitted in
CircuitPython that I found is constructing a timetuple from a length-9
list, a la
time.struct_time(list(time.localtime())
Even better, by getting rid of an error message, the build shrinks a
tiny bit.
This doesn't cover ALL the cases that CPython permits for construction
of a struct_time, but it at least makes constructing from any namedtuple
work.
Closes: #2326
(or deinitialized, for those of us on this side of the pond)
Otherwise, a sequence like
```
audio = audiobusio.I2SOut(bit_clock=board.D6, word_select=board.D9, data=board.D10)
sine_wave_sample = audiocore.RawSample(sine_wave)
audio.play(sine_wave_sample, loop=True)
del audio
```
could free the memory associated with audio without stopping the
related background task. Later, when fresh objects are allocated within
a now-freed memory region, they can get overwritten in the background
task, leading to a hard crash.
This presumably can affect multiple I2S implementations, but it was
reported against the nRF one.
