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Re: [PATCH] Allow "cease invocation" return from Python callback for repos.svn_repos_history2()

From: Роман Донченко <DXDragon_at_yandex.ru>
Date: Fri, 19 Mar 2010 01:50:35 +0300

Alexey Neyman <stilor_at_att.net> писал в своём письме Thu, 18 Mar 2010
21:51:53 +0300:

> On Wednesday 17 March 2010 04:59:34 pm Роман Донченко wrote:
>> Alexey Neyman <stilor_at_att.net> писал в своём письме Wed, 17 Mar 2010
>>
>> 00:05:01 +0300:
>> > Hi all,
>> >
>> > The svn_repos_history2() function allows the history_func() to return
>> > a special error, SVN_ERR_CEASE_INVOCATION, to stop the search. This
>> > is not supported in Python bindings, though: attempt to return
>> > core.SVN_ERR_CEASE_INVOCATION from the history receiver results in an
>> > exception:
>> >
>> > def history_lookup(path, rev, pool):
>> > return core.SVN_ERR_CEASE_INVOCATION
>> >
>> > repos.svn_repos_history2(..., history_lookup, ...)
>> >
>> > svn.core.SubversionException: ('Python callback returned an invalid
>> > object', 20014)
>> >
>> > Indeed, svn_swig_py_repos_history_func() only expects a return of
>> > None. This patch allows the callback to return
>> > core.SVN_ERR_CEASE_INVOCATION. Currently, this is only used in
>> > svn_repos_history2() - apparently, it's the only function that
>> > supports SVN_ERR_CEASE_INVOCATION. However, there is a FIXME at least
>> > in copyfrom_info_receiver() in libsvn_client/log.c, stating that
>> > other callbacks may eventually be able to return
>> > SVN_ERR_CEASE_INVOCATION as well.
>>
>> Good idea, but I think that the callback should signal an error the
>> same way the Subversion functions do it - namely, by throwing
>> core.SubversionException. The wrapper would then translate the
>> exception's fields into an svn_error_t. It looks like tweaking
>> callback_exception_error is the most obvious way to do that. You don't
>> even have to special-case SVN_ERR_CEASE_INVOCATION, just copy whatever
>> code the exception had into the error.
>
> I think that may be beyond my current knowledge of Python's C API... I
> tried that:
>
> /* Return a Subversion error about a failed callback. */
> static svn_error_t *callback_exception_error(void)
> {
> PyObject *err = PyErr_Occurred();
> PyObject *svn_module, *exc_class;
> PyObject *message, *apr_err;
>
> if ((svn_module = PyImport_ImportModule((char *)"svn.core")) == NULL)
> goto finished;
> if ((exc_class = PyObject_GetAttrString(svn_module,
> (char *)"SubversionException")) == NULL)
> goto finished;
> if (PyErr_GivenExceptionMatches(exc_class, err))
> {
> message = PyObject_GetAttrString(err, (char *)"message");
> apr_err = PyObject_GetAttrString(err, (char *)"apr_err");
> if (message && apr_err && PyString_Check(message)
> && PyInt_Check(apr_err))
> {
> return svn_error_create(PyInt_AsLong(apr_err), NULL,
> PyString_AsString(message));
> }
> }
>
> finished:
> return svn_error_create(SVN_ERR_SWIG_PY_EXCEPTION_SET, NULL,
> "Python callback raised an exception");
> }
>
> First, it cannot find "apr_err" in the instance of
> core.Subversion_Exception; PyObject_GetAttrString(err, (char *)"apr_err")
> returns NULL.
>
> And, it produces the following error:
>
> SystemError: NULL result without error in PyObject_Call
>
> Can you help? What's wrong with that code?

Hmm. How are you testing this? I'd write a test script, but I'm short on
time, and you probably already have one. 8=]

>> It would also be great if you added a relevant test to the testsuite.
>
> I thought about it, that would be the next step once the API is settled
> and implemented.

Okay.

>
> Regards,
> Alexey.

Ditto,
Roman.
Received on 2010-03-18 23:51:09 CET

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