I'd be interested to know the risks involved.

The most obvious risk involved is that your program can halt if you have malformed internal data. The error "Malformed UTF-8 character" is fatal. Less obvious risks include security bugs because things may be interpreted differently at different levels: something may pass an untainting regex, but still be unsafe in a library call. This is because there is no single standard way of dealing with malformed byte sequences. With naive (yet common) C code it can even lead to data corruption.

The following change is in current blead: 

--- perl-current/pod/perldiag.pod       2007-01-02 19:17:01.000000000 
++0100
+++ mijn/pod/perldiag.pod       2007-03-03 18:12:23.000000000 +0100
@@ -2263,12 +2263,19 @@

 =item Malformed UTF-8 character (%s)

-(S utf8) (F) Perl detected something that didn't comply with UTF-8
-encoding rules.
+(S utf8) (F) Perl detected a string that didn't comply with UTF-8
+encoding rules, even though it had the UTF8 flag on.

-One possible cause is that you read in data that you thought to be in
-UTF-8 but it wasn't (it was for example legacy 8-bit data).  Another
-possibility is careless use of utf8::upgrade().
+One possible cause is that you set the UTF8 flag yourself for data th
+at
+you thought to be in UTF-8 but it wasn't (it was for example legacy
+8-bit data). To guard against this, you can use Encode::decode_utf8.
+
+If you use the C<:encoding(UTF-8)> PerlIO layer for input, invalid by
+te
+sequences are handled gracefully, but if you use C<:utf8>, the flag i
+s
+set without validating the data, possibly resulting in this error
+message.
+
+See also L<Encode/"Handling Malformed Data">.

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Juerd # { site => 'juerd.nl', do_not_use => 'spamtrap', perl6_server => 'feather' }

In reply to Re^4: A UTF8 round trip with MySQL by Juerd
in thread A UTF8 round trip with MySQL by clinton

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