Fetching DF segfaults when outputtypehandler is present

[mauropagano]

1. What versions are you using?
   3.1.0, repro in python 3.9 and 3.12, issue is on client side I think, DB version is irrelevant

2. Is it an error or a hang or a crash?
   Hard crash, segfault

3. What error(s) or behavior you are seeing?
   Segmentation fault

4. Does your application call init_oracle_client()?
   Reproduces both in thin and thick mode

5. Include a runnable Python script that shows the problem.

import oracledb

# this is copy&paste from doc                                                                                                                                                                                                                                                                                                                                                                
def output_type_handler(cursor, metadata):
    def out_converter(d):
        if isinstance(d, str):
            return f"{d} was a string"
        else:
            return f"{d} was not a string"

    if metadata.type_code is oracledb.DB_TYPE_NUMBER:
        return cursor.var(
            oracledb.DB_TYPE_VARCHAR,
            arraysize=cursor.arraysize,
            outconverter=out_converter,
        )


conn = oracledb.connect("...")
# comment out the line below and the issue goes away
conn.outputtypehandler = output_type_handler
sql = "select 1 n from dual"
t = conn.fetch_df_all(sql)
print(t)

[cjbj]

Thanks for the report. We can replicate it.

One item on our task list is to look at type handling etc. Were you wanting something similar, or does your code base have the handler/converter in place for non-dataframe queries?

[mauropagano]

I do have already a handler in place for non-df, I hit this when porting existing code to df fetching.

(I like that issue you linked! 😉 )

[anthony-tuininga]

This patch can be used to avoid the segfault. More effort is needed to get to the true source of the issue, but this is will "work" for you. The other workaround is to simply not specify an output type handler -- since it won't do you any good anyway!

diff --git a/src/oracledb/impl/base/cursor.pyx b/src/oracledb/impl/base/cursor.pyx
index 3a78fa40..0815be2b 100644
--- a/src/oracledb/impl/base/cursor.pyx
+++ b/src/oracledb/impl/base/cursor.pyx
@@ -306,6 +306,8 @@ cdef class BaseCursorImpl:
         cdef:
             BaseConnImpl conn_impl
             object type_handler
+        if self.fetching_arrow:
+            return None
         if self.outputtypehandler is not None:
             type_handler = self.outputtypehandler
         else: