rpdb

Wrapper around pdb allowing remote debugging via netcat or telnet. This is especially useful in a Tomcat/Jython environment where little debugging tools are available.

tamentis
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Python

rpdb - remote debugger based on pdb

rpdb is a wrapper around pdb that re-routes stdin and stdout to a socket
handler. By default it opens the debugger on port 4444:

import rpdb; rpdb.set_trace()

But you can change that by simply instantiating Rpdb manually:

import rpdb
debugger = rpdb.Rpdb(port=12345)
debugger.set_trace()

It is known to work on Jython 2.5 to 2.7, Python 2.5 to 3.1. It was written
originally for Jython since this is pretty much the only way to debug it when
running it on Tomcat.

Upon reaching set_trace(), your script will “hang” and the only way to get it
to continue is to access rpdb using telnet, netcat, etc…:

nc 127.0.0.1 4444

Or, even better, you can use socat to enable some additional readline-related features (tab completion still doesn’t work, though):

socat TCP:0.0.0.0:444 READLINE

Use Cases

  • breakpoints in a fastapi development server. Stdin gets corrupted because of the subprocess setup such that interactive debuggers don’t work.
  • systems which consume stdin (such as Estuary connector which consumes jsonlines over stdin)

Installation in CPython (standard Python)

pip install rpdb

For a quick, ad hoc alternative, you can copy the entire rpdb subdirectory
(the directory directly containing the init.py file) to somewhere on your
$PYTHONPATH.

Installation in a Tomcat webapp

Just copy the rpdb directory (the one with the init.py file) in your
WEB-INF/lib/Lib folder along with the standard Jython library (required).

Trigger rpdb with signal

set_trace() can be triggered at any time by using the TRAP signal handler.
This allows you to debug a running process independently of a specific failure
or breakpoint:

import rpdb
rpdb.handle_trap()

# As with set_trace, you can optionally specify addr and port
rpdb.handle_trap("0.0.0.0", 54321)

Calling handle_trap will overwrite the existing handler for SIGTRAP if one has
already been defined in your application.

Known bugs

  • The socket is not always closed properly so you will need to ^C in netcat
    and Esc+q in telnet to exit after a continue or quit.
  • There is a bug in Jython 2.5/pdb that causes rpdb to stop on ghost
    breakpoints after you continue (‘c’), this is fixed in 2.7b1.

Author(s)

Bertrand Janin [email protected] - http://tamentis.com/

With contributions from (chronological, latest first):

This is inspired by: