Re: BUG #17450: SUBSTRING function extracting lesser characters than specified

On Mon, 28 Mar 2022 at 20:35, Pavel Borisov <pashkin.elfe@gmail.com> wrote:
> пн, 28 мар. 2022 г. в 15:01, hubert depesz lubaczewski <depesz@depesz.com>:
>
>> On Mon, Mar 28, 2022 at 10:30:07AM +0000, PG Bug reporting form wrote:
>> > The following bug has been logged on the website:
>> >
>> > Bug reference:      17450
>> > Logged by:          Suman Ganguly
>> > Email address:      ganguly.04@gmail.com
>> > PostgreSQL version: 10.17
>> > Operating system:   x86_64-pc-linux-gnu
>> > Description:
>> >
>> > select substring('123456', 0 , 5)
>> > On running this, Postgres returns '1234'
>> > Expecting '12345' to be returned as per the documentation
>>
>> Well, the problem is that you're trying to provide character number 0,
>> which is leading to bad results.
>>
>> substring works on base-1 numbering.
>>
> Yes, the behavior expected in a report seems to be right. I've attached a
> very small fix for that issue. Probably it should be backpatched into all
> versions having 4bd3fad80e5c i.e. since v11.

It seems bytea_substring also has the problem.

diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index 22ab5a4329..a48f2fa2a7 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -3335,7 +3335,7 @@ bytea_substring(Datum str,
                  errmsg("negative substring length not allowed")));
         L1 = -1;                /* silence stupider compilers */
     }
-    else if (pg_add_s32_overflow(S, L, &E))
+    else if (pg_add_s32_overflow(S1, L, &E))
     {
         /*
          * L could be large enough for S + L to overflow, in which case the


--
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.