Re: Make printTableAddCell/printTableAddHeader string argument const

On 05.08.26 05:36, Chao Li wrote:
>
>
>> On Aug 4, 2026, at 17:36, Peter Eisentraut <peter(at)eisentraut(dot)org> wrote:
>>
>> These functions are used in psql to assemble tables to print.
>>
>> They would sometimes overwrite the string argument they are passed, namely via mbvalidate(), which removes invalid UTF-8 characters (or potentially analogously in other encodings, but that is not implemented). However, many callers are not expecting that. In many callers, the input value comes directly from libpq structures, such as from PQgetvalue() or PQsslAttribute(). The latter actually has a const char * return type, and that was cast away. But even the former is not expecting its return value to be modified.
>>
>> Fix that by making these arguments const. Internally, we add a separate function that does only the checking part of mbvalidate(). Only if the validation returns a negative result, we make a copy and run mbvalidate() on the copy. printTableAddCell() already had internal infrastructure for keeping track of what values needed to be freed. We add the same for printTableAddHeader().
>>
>> In passing, also simplify the code a bit. There were essentially duplicate mechanisms for keeping track of the most recently added
>> cell (fields .cell and .cellsadded). Make that consistent by using an integer counter for everything. That makes the code arguably easier to read than with the "current pointer" approaches.
>>
>> The first three patches are preparation patches to further clean up the nearby code a bit.
>> <0001-Remove-useless-confusing-const-qualifiers.patch><0002-Remove-useless-ENABLE_NLS-conditionals.patch><0003-Use-frontend-logging-API-in-fe_utils-print.c.patch><0004-Make-printTableAddCell-printTableAddHeader-string-ar.patch>
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> 0001, 0002 and 0003 look good to me.
>
> For 0001 and 0003, I searched over the source tree, and found a few more occurrences, see the attached diff files.

Ok, I added these. (I added your 0001 to my 0001 and added your 0003 as
a separate patch.)

Note that your 0001 was incomplete: It did not update the "const bool
newline" in the add_tablespace_footer() definition.

Also, in your 0003, the messages still contained newlines, but the
logging API adds its own newlines and in fact rejects strings that end
with newlines, so that patch wouldn't have worked. I have fixed that.

> For 0004, it seems to introduce a memory leak in printTableAddCell():

Thanks, I have fixed that in the attached patch.