Re: [PATCH] transport-helper.c: don't leak fdopen'd stream buffers

[Jim Meyering <jim@meyering.net>]

Junio C Hamano wrote:
> Jim Meyering <jim@meyering.net> writes:
>
>> diff --git a/transport-helper.c b/transport-helper.c
>> index f57e84c..0bbd014 100644
>> --- a/transport-helper.c
>> +++ b/transport-helper.c
>> @@ -49,6 +49,7 @@ static struct child_process *get_helper(struct transport *transport)
>>  		if (!strcmp(buf.buf, "fetch"))
>>  			data->fetch = 1;
>>  	}
>> +	fclose (file);
>>  	return data->helper;
>>  }
>>
>> @@ -88,6 +89,7 @@ static int fetch_with_fetch(struct transport *transport,
>>  		if (strbuf_getline(&buf, file, '\n') == EOF)
>>  			exit(128); /* child died, message supplied already */
>>  	}
>> +	fclose (file);
>>  	return 0;
>>  }
>
> The callchain of fetch_with_fetch() looks like:
>
>     fetch_with_fetch()
>         helper = get_helper();
>         --> get_helper()
>             - start helper with start_command();
>             - read from helper->out until it sees an empty line;
>             - break out of the loop;
>         <-- return helper
>         - file = xfdopen(helper->out) to get another FILE on the fd
>         - read the rest of the output from helper->out via file
>
> It seems to me that the fclose() in get_helper() will close the underlying
> fd and would break the caller, no?

I confess that my sole test was to run "make test", which passed.
If the fd must live on, a slightly less invasive change would be to
xdup each descriptor just before each of the three xfdopen calls, e.g.,

-       file = xfdopen(helper->out, "r");
+       file = xfdopen(xdup(helper->out), "r");

> I think "struct helper_data" should get a new FILE* field and once
> somebody creates a FILE* out of its helper->out, that FILE* can be passed
> around without a new xfdopen().
>
> Or something like that.

That's probably best.

> Who is responsible for closing the underlying helper->out fd in the
> start_command() API, by the way?