[BUG] Cython 1D byte arrays incompatible with `io.BufferedWriter.write(ar)`

[johnboy2]

Describe the bug
ValueError raised when passing a Cython 1D byte array to io.BufferedWriter.write(ar)

To Reproduce

"test_module.pyx":

# cython: language_level=3

from libc.string cimport strlen


cdef const char* data = b'simulates something from a C-based source'

def get_data_array():
    cdef size_t data_len = strlen(data)

    result = <const char[:data_len]> data
    return result

"tester.py":

#!/usr/bin/env python3
import sys
import test_module
ar = test_module.get_data_array()
sys.stdout.buffer.write(ar)
sys.stdout.buffer.write(b'\n')

Expected behavior
Prints the following to the console: simulates something from a C-based source\n

Actual behavior

Traceback (most recent call last):
  File "./test_it.py", line 5, in <module>
    sys.stdout.buffer.write(ar)
  File "stringsource", line 185, in View.MemoryView.array.__getbuffer__
ValueError: Can only create a buffer that is contiguous in memory.

Environment (please complete the following information):

• OS: Linux (Debian)
• Version 3.0a6

Additional context

• Works okay if the output IO object is an io.BytesIO.
• As a workaround, you can wrap the Cython array in a memoryview before sending to the write() method; e.g. sys.stdout.buffer.write(memoryview(ar)). This does add a small cost (temporary object), but is otherwise about as cheap as it gets.

[johnboy2]

So this really comes down to the type of buffer requested by the applicable write() method.

With io.BufferedWriter.write(), it ends up parsing the exporter argument (i.e. the Cython array object) as a y* argument code in the same sense as PyArg_ParseTuple() -- which causes the flags sent into __getbuffer__() to be PyBUF_SIMPLE.

In contrast, an io.BytesIO.write() ends up asking for a PyBUF_CONTIG_RO (which works fine), while memoryview ends up asking for a PyBUF_FULL_RO (which also works, as previously mentioned).

This all seems to be because the array's __getbuffer__() method is essentially enforcing an unnecessary constraint on the requester (i.e. the write() method).

[scoder]

Thanks for the report and the analysis. I can confirm this. Will push a fix soon.