before trigger doesn't, on insert of too long data

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POSTGRESQL BUG REPORT TEMPLATE
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Your name : Thomas Erskine
Your email address : thomaserskine(at)yahoo(dot)com

System Configuration
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Architecture (example: Intel Pentium) :Intel Pentium III

Operating System (example: Linux 2.0.26 ELF) :Linux 2.4.20 ELF

PostgreSQL version (example: PostgreSQL-7.2.3):PostgreSQL-7.3.4-1PGDG

Compiler used (example: gcc 2.95.2) : the RPM did it :-)

Please enter a FULL description of your problem:
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A before trigger doesn't always fire. If a column being inserted into is
too small for the incoming data, psql complains:
ERROR: value too long for type ...
without giving the trigger procedure a chance to deal with it.

Please describe a way to repeat the problem. Please try to provide a
concise reproducible example, if at all possible:
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------ cut here ------
CREATE TABLE test(
id INTEGER,
code CHARACTER(4)
);

CREATE FUNCTION test_func()
RETURNS TRIGGER
AS 'BEGIN
IF LENGTH(new.code) > 4
THEN new.code = ''xxxx'';
END IF;
new.code = upper(new.code);
RETURN new;
END;'
LANGUAGE 'plpgsql';

CREATE TRIGGER test_trig
BEFORE INSERT
ON test
FOR EACH ROW
EXECUTE PROCEDURE test_func();

INSERT INTO test VALUES( 1, 'aaaa');

INSERT INTO test VALUES( 2, 'bbbbb');
------ cut here ------
The first INSERT works fine and the function is triggered. The second
INSERT never triggers the function; it just complains.

If you know how this problem might be fixed, list the solution below:
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Thomas Erskine <thomas(dot)erskine(at)sympatico(dot)ca> +1.613.591.8490