Prior to this patch, the size of the buffer given to pack_into() was checked
for being too small by using the count of the arguments, not their actual
size. For example, a format spec of '4I' would only check that there was 4
bytes available, not 16; and 'I' would check for 1 byte, not 4.
The pack() function is ok because its buffer is created to be exactly the
correct size.
The fix in this patch calculates the total size of the format spec at the
start of pack_into() and verifies that the buffer is large enough. This
adds some computational overhead, to iterate through the whole format spec.
The alternative is to check during the packing, but that requires extra
code to handle alignment, and the check is anyway not needed for pack().
So to maintain minimal code size the check is done using struct_calcsize.
Prior to this patch, the size of the buffer given to unpack/unpack_from was
checked for being too small by using the count of the arguments, not their
actual size. For example, a format spec of '4I' would only check that
there was 4 bytes available, not 16; and 'I' would check for 1 byte, not 4.
This bug is fixed in this patch by calculating the total size of the format
spec at the start of the unpacking function. This function anyway needs to
calculate the number of items at the start, so calculating the total size
can be done at the same time.
This patch makes a repeat counter behave the same as repeating the
typecode, when there are not enough args. For example:
struct.pack('2I', 1) now behave the same as struct.pack('II', 1).
NotImplemented means "try other fallbacks (like calling __rop__
instead of __op__) and if nothing works, raise TypeError". As
MicroPython doesn't implement any fallbacks, signal to raise
TypeError right away.
The unary-op/binary-op enums are already defined, and there are no
arithmetic tricks used with these types, so it makes sense to use the
correct enum type for arguments that take these values. It also reduces
code size quite a bit for nan-boxing builds.
Otherwise, it will silently get incorrect result on other values types,
including CPython tuple form like "foo.png".endswith(("png", "jpg"))
(which MicroPython doesn't support for unbloatedness).
For SEEK_SET, offset should be treated as unsigned, to allow full-width
stream sizes (e.g. 32-bit instead of 31-bit). This is now fully documented
in stream.h. Also, seek symbolic constants are added.
Too big positive, or too big negative offset values could lead to overflow
and address space wraparound and thus access to unrelated areas of memory
(a security issue).
The value of 0 can't be used because otherwise mp_binary_get_size will let
a null byte through as the type code (intepreted as byterray). This can
lead to invalid type-specifier strings being let through without an error
in the struct module, and even buffer overruns.
Damien George
Paul Sokolovsky
Tom Collins
Stefan Naumann