dbms_lob.append bug in function or am I doing it wrong

Question

I created following function

function lob_replace( p_lob in out clob,p_what in varchar2,p_with in clob ) return clob
  as
      l_temp_number   number;
      l_temp_number_1 number;
      l_temp_clob clob;
      l_return_clob clob;
      l_temp1_clob clob;
      l_temp2_clob clob;
  begin
                l_temp_number:=dbms_lob.instr(p_lob, p_what);
                --Create a lob locator
                 DBMS_LOB.createtemporary(l_temp_clob,true);
                 DBMS_LOB.createtemporary(l_temp1_clob,true);
                 DBMS_LOB.createtemporary(l_temp2_clob,true);

                ---substract and build the LOBs
                l_temp_number_1:=length(p_lob);
                l_temp_clob:=dbms_lob.substr(p_lob,l_temp_number-1,1);
                l_temp1_clob:=dbms_lob.substr(p_lob,l_temp_number_1-l_temp_number+1 ,l_temp_number +length(p_what) );

                --append three diff lob to one
                dbms_lob.append(l_temp2_clob,l_temp_clob);
                dbms_lob.append(l_temp2_clob,p_with);
                dbms_lob.append(l_temp2_clob,l_temp1_clob);

                l_return_clob :=l_temp2_clob;

                --remove the tmp lob
                DBMS_LOB.freetemporary(l_temp_clob);
                DBMS_LOB.freetemporary(l_temp1_clob);
                DBMS_LOB.freetemporary(l_temp2_clob);

                return l_return_clob;
  end;

this will throw error if I call this function as below

declare
   temp clob;
begin
  temp:='replace this #a#';
  temp:=lob_replace(temp,'#a#','with this');
end;

it will throw below error

 ORA-06502: PL/SQL: numeric or value error: invalid LOB locator specified: ORA-22275
    ORA-06512: at "SYS.DBMS_LOB", line 639
    ORA-06512: at "LOB_REPLACE", line 24
    ORA-06512: at line 5

but this will not throw error

declare
   temp clob;
begin
  temp:='replace this #a# ';
  temp:=lob_replace(temp,'#a#','with this');
end;

please note the extra space at the end on temp:='replace this #a# ';

does any one knows the reason for this?

Answer 1

When you are constructing l_temp1_clob, you can only add the rest of the lob, if there is anything to add. Change you code:

l_temp1_clob:=dbms_lob.substr(p_lob,l_temp_number_1-l_temp_number+1 ,l_temp_number +length(p_what) );

To this:

if l_temp_number +length(p_what) < l_temp_number_1
then
   l_temp1_clob := dbms_lob.substr(p_lob, l_temp_number_1 - l_temp_number - 1 , l_temp_number +length(p_what) );
end if;

The logic is: if the start of the lob substr is before the end of the lob.

Also, the dd variable is not declared in your test call:

declare
   temp clob;
begin
  temp:='replace this #a#';
  temp:=lob_replace(dd,'#a#','with this');
end;