TypeError: cannot use a bytes pattern on a string-like object

[sbmthakur]

The following snippet crashes with the above error when it comes across a system call that passes the filter.

import traceback
import ptracer
import re
import os

def callback(syscall):
    print(syscall.name, syscall.result.raw_value)

flt = [
    ptracer.SysCallPattern(
        name='openat',
        args=[
            re.compile(b'/tmp/.*'),
            lambda arg: arg.value & os.O_WRONLY
        ],
        result=lambda res: res.value > 0
    )
]

with ptracer.context(callback, filter=flt):
    open('/tmp/domf', mode='w')

Here's the error stack.

$ py a.py 
Traceback (most recent call last):
  File "/home/shubham/workspace/tracer/a.py", line 21, in <module>
    open('/tmp/domf', mode='w')
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/__init__.py", line 106, in __exit__
    _context.disable()
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/__init__.py", line 92, in disable
    raise error
ptracer._ptracer.PtracerError: Unhandled exception in ptrace process
Traceback (most recent call last):
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/_ptracer.py", line 276, in _debugger_thread
    _debugger_thread_inner(main_pid, dbgproc_started, dbgthread_stop,
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/_ptracer.py", line 405, in _debugger_thread_inner
    elif filter_ is None or filter_(syscall):
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/_ptracer.py", line 294, in <lambda>
    filter_ = lambda sc: any(m.match(sc) for m in syscall_filter)
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/_ptracer.py", line 294, in <genexpr>
    filter_ = lambda sc: any(m.match(sc) for m in syscall_filter)
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/_syscall.py", line 52, in match
    return all(m[1](m[0](syscall)) for m in self.matcher)
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/_syscall.py", line 52, in <genexpr>
    return all(m[1](m[0](syscall)) for m in self.matcher)
TypeError: cannot use a bytes pattern on a string-like object

[jparise]

Have you tried using a string (not bytes) pattern? re.compile('/tmp/.*')

[sbmthakur]

No system calls are captured if I do that. Also, my co-worker just informed me that the filter works as expected if we remove the args argument from it.

[jparise]

@sbmthakur #9 should fix the root issue.

Also note that openat takes a file descriptor as its first argument (unlike open), so you'll need to add a placeholder for that argument position to your pattern:

    ptracer.SysCallPattern(
        name='openat',
        args=[
            None,  # fd argument
            re.compile(b'/tmp/.*'),
            lambda arg: arg.value & os.O_WRONLY
        ],
        result=lambda res: res.value > 0
    )

Please let me know if this solves your problem.

[sbmthakur]

The snippet is working as expected. Thanks for the fix.

[jparise]

Great! I just published version 0.6.1 with this fix.