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Re: Output character encoding

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  • Arnon Weinberg
    ... Er, not sure how I can be more specific - the test cases are provided in my initial post (http://www.mail-archive.com/asp%40perl.apache.org/msg02662.html),
    Message 1 of 9 , Jun 5, 2012
      On 2012-06-05 14:13, Thanos Chatziathanassiou wrote:
      >> With my test cases (provided) I have carefully narrowed down the
      >> inconsistency to Apache::ASP, since everything else is either not
      >> applicable or the same.
      >>
      > Could you be a bit more specific on this ?
      >

      Er, not sure how I can be more specific - the test cases are provided in
      my initial post
      (http://www.mail-archive.com/asp%40perl.apache.org/msg02662.html), they
      don't use a database, web server, or browser, so those can easily be
      eliminated as possible culprits. Ideally, the test cases should speak
      for themselves.

      > How does file handling come into play here ? Not that it's relevant but
      > it works quite the same way as outside of Apache::ASP.
      >

      I'm afraid it doesn't, as the test cases clearly demonstrate. Note:
      It's not "file handling", it's PerlIO, which refers to all I/O,
      including STDOUT.

      > Have a look at Text::Iconv, iconv(1), iconv(3) and friends. Also, Encode.

      iconv converts text files, not Perl code - that still requires wetware
      as far as I know. Encode is being used in the test cases, and clearly
      messes things up in Apache::ASP.


      --

      -------------------------------------------------------------------------------
      Arnon Weinberg
      www.back2front.ca



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    • Josh Chamas
      ... Hi Arnon, All, I have gone over the thread and been stumped on this for a while. Bottom line it looks like Apache::ASP does not play well with Encode, and
      Message 2 of 9 , Jun 5, 2012
        On 6/5/12 2:02 AM, Arnon Weinberg wrote:
        >
        > How can I set the output character encoding of Apache::ASP output?
        > ...

        Hi Arnon, All,

        I have gone over the thread and been stumped on this for a while. Bottom line
        it looks like Apache::ASP does not play well with Encode, and this seems to me
        to be around the PerlIO interactions and something not quite connecting right on
        a tied file handle. But I do know know the answer to solve this. :(

        To explain where there is some magic at play:

        Apache::ASP::Response does a "use bytes" which is to deal with the output stream
        correctly I believe this is around content length calculations. I think this is
        fine here, and turning this off makes things worse for these examples.

        Apache::ASP::Response is more importantly tied as a file handle when this code
        is run:

        tie *RESPONSE, 'Apache::ASP::Response', $self->{Response};
        select(RESPONSE);

        This is to allow for print to go to $Response->PRINT which aliases to
        $Response->Write. Fundamentally all output is going through $Response->Write at
        the end of the day including the script static content itself.

        What I have found is that this will output the correct bytes in this Apache::ASP
        script:

        <% print STDOUT Encode::decode('ISO-8859-1',"\xE2"); %>

        as it bypasses the tied file handle layer to $Response, so we know perl is
        working at this point!

        but doing this is where we have a problem:

        <% print Encode::decode('ISO-8859-1',"\xE2"); %>

        and immediately in the Apache::ASP::Response::Write() method the data has
        already been converted incorrectly without any processing occurring. Its as if
        by merely going through the tied interface that data goes through some
        conversion process. I have played with various IO settings as in "open ..." and
        various "use" pragmas to no avail but really shooting blind here on what could
        not be working.

        So the way I see it..

        Encoding Magic
        File handle tie Magic <--- data conversion
        Data to $Response->Write

        Encode and perltie seem to have some conflicting bits here.

        If there were some workaround here I would be glad to hear it but I seem to have
        exhausted my ability to troubleshoot this.

        Regards,

        Josh



        > # Latin-1.rasp: #############
        >
        > <%
        > #use open ( ":utf8", ":std" );
        > #binmode ( STDOUT, ":encoding(ISO-8859-1)" );
        >
        > $::Response->{Charset} = "ISO-8859-1";
        >
        > use Encode;
        >
        > print Encode::decode('ISO-8859-1',"\xE2"),
        > Encode::decode('UTF-8',Encode::encode('UTF-8',"\xE2")),
        > "\x{00E2}",
        > chr(0x00E2);
        > %>
        >
        > #############################
        >
        >>asp-perl Latin-1.rasp
        > Content-Type: text/html; charset=ISO-8859-1
        > Content-Length: 6
        > Cache-Control: private
        >
        > ââââ
        >>asp-perl Latin-1.rasp | tail -1 | hexdump
        > 0000000 a2c3 a2c3 e2e2
        > 0000006
        >
        > For some reason, the first 2 test characters are UTF-8 encoded, and the last 2
        > are ISO-8859-1 encoded.
        > How can I get the same results as the CGI script above?
        >
        >

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      • Thanos Chatziathanassiou
        Apologies Arnon, I got your original message with the problem description after I had sent mine... ... That rang a bell for me: Read the section ``The UTF8
        Message 3 of 9 , Jun 6, 2012
          Apologies Arnon, I got your original message with the problem
          description after I had sent mine...

          >
          > To explain where there is some magic at play:
          >
          > Apache::ASP::Response does a "use bytes" which is to deal with the
          > output stream correctly I believe this is around content length
          > calculations. I think this is fine here, and turning this off makes
          > things worse for these examples.
          >
          > Apache::ASP::Response is more importantly tied as a file handle when
          > this code is run:
          >
          > tie *RESPONSE, 'Apache::ASP::Response', $self->{Response};
          > select(RESPONSE);
          >
          > This is to allow for print to go to $Response->PRINT which aliases to
          > $Response->Write. Fundamentally all output is going through
          > $Response->Write at the end of the day including the script static
          > content itself.
          >
          > What I have found is that this will output the correct bytes in this
          > Apache::ASP script:
          >
          > <% print STDOUT Encode::decode('ISO-8859-1',"\xE2"); %>
          >
          > as it bypasses the tied file handle layer to $Response, so we know perl
          > is working at this point!
          >
          > but doing this is where we have a problem:
          >
          > <% print Encode::decode('ISO-8859-1',"\xE2"); %>
          >
          > and immediately in the Apache::ASP::Response::Write() method the data
          > has already been converted incorrectly without any processing
          > occurring. Its as if by merely going through the tied interface that
          > data goes through some conversion process. I have played with various
          > IO settings as in "open ..." and various "use" pragmas to no avail but
          > really shooting blind here on what could not be working.
          >
          > So the way I see it..
          >

          That rang a bell for me:
          Read the section ``The UTF8 flag'' in Encode to see the problem.
          ${$Response->{out}} contains a copy of the stuff you're sending to
          $Response->Write(), AKA $Response->WriteRef() but without copying the
          utf-8 flag.
          You can make the example work by simply turning the utf8 flag
          unconditionally on via ``Encode::_utf8_on(${$Response->{out}});''
          after the print statements in Latin-1.rasp.
          Of course, your data should either ALL have the utf8 flag on (eg via
          Encode::decode) or ALL have it off, because ${$Response->{out}} can
          either have it on or off but obviously not both.

          > Encode and perltie seem to have some conflicting bits here.
          >
          > If there were some workaround here I would be glad to hear it but I seem
          > to have exhausted my ability to troubleshoot this.

          I'm not sure there is a generic solution, except perhaps mess around
          with ``is_utf8($$dataref)'' before appending it to $Response->{out} and
          make sure that the same kind of data is appended (either ON or OFF) to
          $Response->{out}.
          See below for why this is a problem

          >
          >> # Latin-1.rasp: #############
          >>
          >> <%
          >> #use open ( ":utf8", ":std" );
          >> #binmode ( STDOUT, ":encoding(ISO-8859-1)" );
          >>
          >> $::Response->{Charset} = "ISO-8859-1";
          >>
          >> use Encode;
          >>
          >> print Encode::decode('ISO-8859-1',"\xE2"),
          >> Encode::decode('UTF-8',Encode::encode('UTF-8',"\xE2")),

          #these will now work if
          #Encode::_utf8_on(${$Response->{out}});
          #is set because they have the flag themselves

          >> "\x{00E2}",
          >> chr(0x00E2);

          #these, on the other hand will not
          #
          #the opposite holds true for
          #Encode::_utf8_off(${$Response->{out}});
          #of course

          >> %>

          I'm sure we can design a ``proper'' solution but not without some
          user-configurable settings and a bit of ugly code.

          Best Regards,
          Thanos Chatziathanassiou



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        • Arnon Weinberg
          Thanks very much Josh for investigating this - it saved me some time narrowing down the issue. Even still, I did spend quite a lot of time working out a
          Message 4 of 9 , Jun 14, 2012
            Thanks very much Josh for investigating this - it saved me some time
            narrowing down the issue. Even still, I did spend quite a lot of time
            working out a solution for my needs, and still I don't think it is
            generalizable as-is. However, in case someone else wants to give it a
            crack, I provide details below.

            On 2012-06-05 19:30, Josh Chamas wrote:
            > doing this is where we have a problem:
            >
            > <% print Encode::decode('ISO-8859-1',"\xE2"); %>
            >
            > and immediately in the Apache::ASP::Response::Write() method the data
            > has already been converted incorrectly

            The fact that such a simple use of Encode causes an issue is a little
            surprising. Surely others are using Apache::ASP in multi-language
            environments - is no one using Encode this way? How are others coping
            with this limitation right now?

            > Its as if by merely going through the tied interface that data goes
            > through some conversion process.

            Not quite, as the same results happen without a tie'd interface. The
            "use bytes" pragma is what causes the conversion (see test script below).

            > Apache::ASP::Response does a "use bytes" which is to deal with the
            > output stream correctly I believe this is around content length
            > calculations.
            > I think this is fine here, and turning this off makes things worse for
            > these examples.

            It looks like "use bytes" is now deprecated and should indeed be
            removed. The documentation doesn't mention any trivial substitute.
            However, this pragma mostly just overrides some built-in functions with
            byte-oriented versions. So I made the following changes to Response.pm:
            - changed use bytes => no bytes (just import the namespace)
            - changed all occurrences of length() => bytes::length()
            This resolved the mixed-encoding issue originally posted, but introduced
            a new (more manageable) issue.

            For debugging purposes, I peeked at the "UTF-8 flag" (Perl's internal
            flag that indicates that a string has a known decoding). This flag
            should be transparent in principle, but it helped make sense of the
            behaviour of Apache::ASP.
            Results of testing are summarized as follows:

            1. Testing Perl/CGI, asp-perl, and Apache::ASP, all 3 give the same
            results with the "use bytes" pragma turned on:
            - For any string with the UTF-8 flag off, output is correctly encoded.
            - Any string with the flag on is (double-)encoded as UTF-8, regardless
            of the actual output encoding.
            2. Testing Perl/CGI and asp-perl with "no bytes" produces correct results:
            - The UTF-8 flag does not affect output - it is correctly encoded in
            every case.
            - However, an interesting test case is that of the double-encoding
            problem (see http://ahinea.com/en/tech/perl-unicode-struggle.html). This
            case is indicative of bad code, so is not a concern here, but it
            illustrates how a tie'd filehandle differs from plain STDOUT. In this
            case, a single "wide character" double-encodes the entire output (with
            buffering on, this can be the entire page), instead of just the string.
            - These test cases are demonstrated by the script below.
            3. Testing Apache::ASP with "no bytes" produces different results from
            the command-line (asp-perl) version, as well as different results from
            Perl/CGI running on Apache. This suggests an interaction effect between
            Apache and Apache::ASP (both are required to produce these results).
            - With the UTF-8 flag off, output is correctly encoded as before.
            - However, with "no bytes", Apache::ASP, and the UTF-8 flag on, the
            entire output is double-encoded. This result is similar to the
            double-encoding problem in the previous test case, except that it
            doesn't require a "wide character" - any string with the UTF-8 flag on
            will do.

            This test script demonstrates all but the last test case:

            #!/usr/bin/perl

            use Encode;

            foreach ( "STDOUT", "tie_use_bytes", "tie_no_bytes" )
            {
            print "$_: ";
            tie *FH, $_ if ! /^S/;
            my $STDOUT = select ( FH ) if ! /^S/;
            print "\x{263a}",
            Encode::decode('ISO-8859-1',"\xE2"),
            "\xE2";
            print "\n";
            close ( FH ) if ! /^S/;
            select ( $STDOUT ) if ! /^S/;
            }

            use strict;

            package tie_use_bytes;
            use bytes;

            sub TIEHANDLE { bless {}, shift; }
            sub PRINT { shift()->{out} .= join ( $,, @_ ); }
            sub CLOSE { print STDOUT delete ( shift()->{out} ); }

            package tie_no_bytes;
            no bytes;

            sub TIEHANDLE { bless {}, shift; }
            sub PRINT { shift()->{out} .= join ( $,, @_ ); }
            sub CLOSE { print STDOUT delete ( shift()->{out} ); }

            # Output: ##################

            Wide character in print at ...
            STDOUT: ☺ââ # STDOUT output is correct in all cases
            tie_use_bytes: ☺ââ # with "use bytes", the UTF-8-flagged 2nd character
            is double-encoded
            Wide character in print at ...
            tie_no_bytes: ☺ââ # with "no bytes", the output is correct, but a
            "wide character" double-encodes the entire string because of the way the
            tie'd file handle is implemented

            #########################

            By the way, if it's getting difficult to wrap your head around this,
            you're not alone.

            At this point, I peeked at the $Response->{out} data buffer, and could
            see that it was encoded correctly. However, the output from Apache (when
            the UTF-8 flag is on) was not correct, suggesting that Apache is doing
            something to encode the string in this case.
            I decided therefore to address the problem by turning off the UTF-8
            flag. The most fault-tolerant method I managed to come up with to do
            this was the following:

            ${$Response->{BinaryRef}}
            = Encode::encode ( 'ISO-8859-1', ${$Response->{BinaryRef}},
            sub{ Encode::encode ( 'UTF-8', chr ( shift() ) ) } )
            if ! grep ( /^utf8$/, PerlIO::get_layers ( STDOUT ) );

            which can go at the top of the $Response->Flush() method, or in
            global.asa/Script_OnFlush().

            With this solution I can now modify Apache::ASP's output encoding (eg,
            using binmode ( STDOUT );), as originally desired, and the output
            appears correct in all my test cases.


            --
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            Arnon Weinberg
            www.back2front.ca


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          • Warren Young
            ... This answer by Tom Christiansen (yes, the guy who wrote that one book) may shed some light: http://goo.gl/miOFU Here I thought all the Unicode tweaks after
            Message 5 of 9 , Jul 2, 2012
              On 6/5/2012 5:30 PM, Josh Chamas wrote:
              > On 6/5/12 2:02 AM, Arnon Weinberg wrote:
              >>
              >> How can I set the output character encoding of Apache::ASP output?
              >
              > I have gone over the thread and been stumped on this for a while.

              This answer by Tom Christiansen (yes, the guy who wrote that one book)
              may shed some light: http://goo.gl/miOFU

              Here I thought all the Unicode tweaks after 5.8 were minor things, that
              it was all but finished a decade ago.

              Then later, reading chromatic's Modern Perl, he only grudgingly allows
              that 5.12 might be tolerable for some of his Unicode example code, and
              recommends 5.14 instead.

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