Commented by: @pavel-zotov

Consider following script:

set list on;
set count on;
set term ^;
execute block as
begin
rdb$set_context('USER_SESSION', '12345678901234567890123456789012345678901234567890123456789012345678901234567890abcdefghij', '1');
rdb$set_context('USER_SESSION', 'ASDFGHJKLP€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€€', '1');
end
^
set term ;^

select
c.mon$variable_name as mon_context_name
,octet_length(c.mon$variable_name) mon_context_length
from mon$context_variables c
where mon$variable_name starting with '1234567890'
;

select
c.mon$variable_name as mon_context_name
,octet_length(c.mon$variable_name) mon_context_length
from mon$context_variables c
where mon$variable_name starting with 'ASDFGHJKLP€€€'
;

Being tested on 4.0.0.2228, it issues:

1) expected result for context variable = '1234567890...' ,i.e. it truncates it to 80 octets:

MON_CONTEXT_NAME 12345678901234567890123456789012345678901234567890123456789012345678901234567890
MON_CONTEXT_LENGTH 80

2) string which is cuted on some position where 'euro' character must be:

MON_CONTEXT_NAME ASDFGHJKLP€€€€€€€€€€€€€€€€€€€€€€€�
MON_CONTEXT_LENGTH 80

Is it OK ?

Commented by: @pavel-zotov

PS.

On 4.0.0.2225 second query ( "... where mon$variable_name starting with 'ASDFGHJKLP€€€' ) issues expected result:

Statement failed, SQLSTATE = 22001
arithmetic exception, numeric overflow, or string truncation
-string right truncation
-expected length 80, actual 90

Commented by: @asfernandes

> 2) string which is cuted on some position where 'euro' character must be:
>
> MON_CONTEXT_NAME ASDFGHJKLP€€€€€€€€€€€€€€€€€€€€€€€�
> MON_CONTEXT_LENGTH 80
>
> Is it OK ?

Yes, considering that mon$variable_name uses charset NONE.

Commented by: @asfernandes

> On 4.0.0.2225 second query ( "... where mon$variable_name starting with 'ASDFGHJKLP€€€' ) issues expected result:
>
> Statement failed, SQLSTATE = 22001
> arithmetic exception, numeric overflow, or string truncation
> -string right truncation
> -expected length 80, actual 90

So it was a bug.