Subject Re: [ib-support] Firbird 1 Release Version
Author Raf Schandevyl
Any idea how i can concatinate some strings to a Blob ?

The reason why i need to concatinate such large varchars is to create a
blob wich contains a HTML description for my objects.

I have written a function to convert a string to a blob, but I do not
succeed to create a function to concatinate 2 blob, or to add a string
to a blob.

Is there any library that does this ? (On linux and windows if possible).

Raf

Claudio Valderrama C. wrote:

>"Raf Schandevyl" <Raf.Schandevyl@...> wrote in message
>news:3C91F521.8030409@......
>
>>Now I found it has nothing to do with the blob I was returning but with=20
>>concatination off 2 varchars.
>>
>>Try creating this procedure. You'll get the error.
>>
>>CREATE PROCEDURE TEST$VARCHAR
>>AS
>> DECLARE VARIABLE varTest1 VARCHAR(20000);
>> DECLARE VARIABLE varTest2 VARCHAR(32000);
>>BEGIN
>> /* Procedure body */
>> varTest2 =3D 'Test';
>> varTest1 =3D 'Concatinated';
>> varTest2 =3D varTest2 || varTest1;
>> SUSPEND;
>>END
>>
>
>Hi, Raf.
>There's a valid reason why concatenation was tightened. In your example
>above, with RC2 and earlier, you could concatenate other varchar more with
>length near 30K if you like. But this is way beyond the maximum defined that
>64K-1. Since there was no check, you would get bizarre behavior.
>
>Now, why the limit was set at only 32K: if you try to create the longest
>field from DSQL, you can't get past 32K. Now, with this artifact, you are
>surpassing that limit, not only inside a procedure, but in a direct SELECT
>statement. This means you're able to use "||" to create a field that by
>other means it's illegal.
>
>I've bumped the limit to 64K-1 to see what happens. This is the largest
>concatenation you can produce:
>select cast(1 as varchar(32752))||cast(0 as varchar(32765)) from
>rdb$database;
>
>Now, there's a problem: some places might treat lengths as signed short
>integers. Don't ask me what would happen with values between 32768 and
>65535, because anyone that has doing a bit of programming knows.
>Furthermore, even if you can concatenate such long fields, you can't use
>a computed field with the same expression. Since DSQL restricts fields to
>32K-1, one would expect it to catch the problem, but it doesn't and the core
>engine doesn't too. Therefore, we create an invalid table that will be
>rejected at run-time:
>
>SQL> create table talud(a varchar(23000), b varchar(32000), d computed by
>(a||b||a));
>SQL> select * from talud;
>Statement failed, SQLCODE = -104
>invalid request BLR at offset 38
>-Implementation limit exceeded
>-block size exceeds implementation restriction
>
>SQL> select d from talud;
>Statement failed, SQLCODE = -104
>invalid request BLR at offset 38
>-Implementation limit exceeded
>-block size exceeds implementation restriction
>
>This backdoor definitely stinks. The stored length in rdb$fields is 12464
>for the computed fields. Obviously, a wrapping by numeric overflow. Now if
>you want to smile, older versions simply will crash while trying to execute
>it.
>
>System tables use signed integers to contain field lengths. Hence, in
>practical terms, this computed field cannot be expressed in system tables,
>unless you force the result to be interpreted as unsigned. This is one of
>the nasty effects of setting again the limit for concatenation at 64K-1. You
>create invalid tables.
>
>SQL> create view valud(a,b,c) as select a,b,d from talud;
>=> It succeeds. Again, we have an invalid view.
>
>SQL> select * from valud;
>Statement failed, SQLCODE = -104
>invalid request BLR at offset 38
>-Implementation limit exceeded
>-block size exceeds implementation restriction
>
>SQL> create view valud2(a,z) as select a, a||b||a from talud;
>SQL> select * from valud2;
>Statement failed, SQLCODE = -904
>Implementation limit exceeded
>-block size exceeds implementation restriction
>
>Therefore, anything in the range 32K..64K-1 is at your own risk. I will
>extend the range to 64K-1, but if you got sometimes strange results, you
>will get them again. 64K and above is illegal if you read Borland's
>specifications: maximum row size can't reach this value. This is because
>lengths are kept in unsigned short ints, but there may be places where
>signed variables are used.
>
>It seems that the last resort is to be boring, repetitive & pedant but try
>to educate users on how not to stuff themselves. However, hackers by default
>act as uneducated and find those gaps for possible vulnerabilities. Hence,
>the engine should protect itself.
>
>C.
>--
>Claudio Valderrama C. - http://www.cvalde.com - http://www.firebirdSql.org
>Independent developer
>Owner of the Interbase´┐Ż WebRing
>
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