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   1  package PerlIO::via;
   2  our $VERSION = '0.04';
   3  use XSLoader ();
   4  XSLoader::load 'PerlIO::via';
   5  1;
   6  __END__
   7  
   8  =head1 NAME
   9  
  10  PerlIO::via - Helper class for PerlIO layers implemented in perl
  11  
  12  =head1 SYNOPSIS
  13  
  14     use PerlIO::via::Layer;
  15     open($fh,"<:via(Layer)",...);
  16  
  17     use Some::Other::Package;
  18     open($fh,">:via(Some::Other::Package)",...);
  19  
  20  =head1 DESCRIPTION
  21  
  22  The PerlIO::via module allows you to develop PerlIO layers in Perl, without
  23  having to go into the nitty gritty of programming C with XS as the interface
  24  to Perl.
  25  
  26  One example module, L<PerlIO::via::QuotedPrint>, is included with Perl
  27  5.8.0, and more example modules are available from CPAN, such as
  28  L<PerlIO::via::StripHTML> and L<PerlIO::via::Base64>.  The
  29  PerlIO::via::StripHTML module for instance, allows you to say:
  30  
  31      use PerlIO::via::StripHTML;
  32      open( my $fh, "<:via(StripHTML)", "index.html" );
  33          my @line = <$fh>;
  34  
  35  to obtain the text of an HTML-file in an array with all the HTML-tags
  36  automagically removed.
  37  
  38  Please note that if the layer is created in the PerlIO::via:: namespace, it
  39  does B<not> have to be fully qualified.  The PerlIO::via module will prefix
  40  the PerlIO::via:: namespace if the specified modulename does not exist as a
  41  fully qualified module name.
  42  
  43  =head1 EXPECTED METHODS
  44  
  45  To create a Perl module that implements a PerlIO layer in Perl (as opposed to
  46  in C using XS as the interface to Perl), you need to supply some of the
  47  following subroutines.  It is recommended to create these Perl modules in the
  48  PerlIO::via:: namespace, so that they can easily be located on CPAN and use
  49  the default namespace feature of the PerlIO::via module itself.
  50  
  51  Please note that this is an area of recent development in Perl and that the
  52  interface described here is therefore still subject to change (and hopefully
  53  will have better documentation and more examples).
  54  
  55  In the method descriptions below I<$fh> will be
  56  a reference to a glob which can be treated as a perl file handle.
  57  It refers to the layer below. I<$fh> is not passed if the layer
  58  is at the bottom of the stack, for this reason and to maintain
  59  some level of "compatibility" with TIEHANDLE classes it is passed last.
  60  
  61  =over 4
  62  
  63  =item $class->PUSHED([$mode[,$fh]])
  64  
  65  Should return an object or the class, or -1 on failure.  (Compare
  66  TIEHANDLE.)  The arguments are an optional mode string ("r", "w",
  67  "w+", ...) and a filehandle for the PerlIO layer below.  Mandatory.
  68  
  69  When layer is pushed as part of an C<open> call, C<PUSHED> will be called
  70  I<before> the actual open occurs whether than be via C<OPEN>, C<SYSOPEN>,
  71  C<FDOPEN> or by letting lower layer do the open.
  72  
  73  =item $obj->POPPED([$fh])
  74  
  75  Optional - layer is about to be removed.
  76  
  77  =item $obj->UTF8($bellowFlag,[$fh])
  78  
  79  Optional - if present it will be called immediately after PUSHED has
  80  returned. It should return true value if the layer expects data to be
  81  UTF-8 encoded. If it returns true result is as if caller had done
  82  
  83     ":via(YourClass):utf8"
  84  
  85  If not present of it it returns false, then stream is left with
  86  flag clear.
  87  The I<$bellowFlag> argument will be true if there is a layer below
  88  and that layer was expecting UTF-8.
  89  
  90  
  91  =item $obj->OPEN($path,$mode[,$fh])
  92  
  93  Optional - if not present lower layer does open.
  94  If present called for normal opens after layer is pushed.
  95  This function is subject to change as there is no easy way
  96  to get lower layer to do open and then regain control.
  97  
  98  =item $obj->BINMODE([,$fh])
  99  
 100  Optional - if not available layer is popped on binmode($fh) or when C<:raw>
 101  is pushed. If present it should return 0 on success -1 on error and undef
 102  to pop the layer.
 103  
 104  =item $obj->FDOPEN($fd[,$fh])
 105  
 106  Optional - if not present lower layer does open.
 107  If present called for opens which pass a numeric file
 108  descriptor after layer is pushed.
 109  This function is subject to change as there is no easy way
 110  to get lower layer to do open and then regain control.
 111  
 112  =item $obj->SYSOPEN($path,$imode,$perm,[,$fh])
 113  
 114  Optional - if not present lower layer does open.
 115  If present called for sysopen style opens which pass a numeric mode
 116  and permissions after layer is pushed.
 117  This function is subject to change as there is no easy way
 118  to get lower layer to do open and then regain control.
 119  
 120  =item $obj->FILENO($fh)
 121  
 122  Returns a numeric value for Unix-like file descriptor. Return -1 if
 123  there isn't one.  Optional.  Default is fileno($fh).
 124  
 125  =item $obj->READ($buffer,$len,$fh)
 126  
 127  Returns the number of octets placed in $buffer (must be less than or
 128  equal to $len).  Optional.  Default is to use FILL instead.
 129  
 130  =item $obj->WRITE($buffer,$fh)
 131  
 132  Returns the number of octets from buffer that have been successfully written.
 133  
 134  =item $obj->FILL($fh)
 135  
 136  Should return a string to be placed in the buffer.  Optional. If not
 137  provided must provide READ or reject handles open for reading in
 138  PUSHED.
 139  
 140  =item $obj->CLOSE($fh)
 141  
 142  Should return 0 on success, -1 on error.
 143  Optional.
 144  
 145  =item $obj->SEEK($posn,$whence,$fh)
 146  
 147  Should return 0 on success, -1 on error.
 148  Optional.  Default is to fail, but that is likely to be changed
 149  in future.
 150  
 151  =item $obj->TELL($fh)
 152  
 153  Returns file postion.
 154  Optional.  Default to be determined.
 155  
 156  =item $obj->UNREAD($buffer,$fh)
 157  
 158  Returns the number of octets from buffer that have been successfully
 159  saved to be returned on future FILL/READ calls.  Optional.  Default is
 160  to push data into a temporary layer above this one.
 161  
 162  =item $obj->FLUSH($fh)
 163  
 164  Flush any buffered write data.  May possibly be called on readable
 165  handles too.  Should return 0 on success, -1 on error.
 166  
 167  =item $obj->SETLINEBUF($fh)
 168  
 169  Optional. No return.
 170  
 171  =item $obj->CLEARERR($fh)
 172  
 173  Optional. No return.
 174  
 175  =item $obj->ERROR($fh)
 176  
 177  Optional. Returns error state. Default is no error until a mechanism
 178  to signal error (die?) is worked out.
 179  
 180  =item $obj->EOF($fh)
 181  
 182  Optional. Returns end-of-file state. Default is function of return
 183  value of FILL or READ.
 184  
 185  =back
 186  
 187  =head1 EXAMPLES
 188  
 189  Check the PerlIO::via:: namespace on CPAN for examples of PerlIO layers
 190  implemented in Perl.  To give you an idea how simple the implementation of
 191  a PerlIO layer can look, as simple example is included here.
 192  
 193  =head2 Example - a Hexadecimal Handle
 194  
 195  Given the following module, PerlIO::via::Hex :
 196  
 197      package PerlIO::via::Hex;
 198  
 199      sub PUSHED
 200      {
 201       my ($class,$mode,$fh) = @_;
 202       # When writing we buffer the data
 203       my $buf = '';
 204       return bless \$buf,$class;
 205      }
 206  
 207      sub FILL
 208      {
 209       my ($obj,$fh) = @_;
 210       my $line = <$fh>;
 211       return (defined $line) ? pack("H*", $line) : undef;
 212      }
 213  
 214      sub WRITE
 215      {
 216       my ($obj,$buf,$fh) = @_;
 217       $$obj .= unpack("H*", $buf);
 218       return length($buf);
 219      }
 220  
 221      sub FLUSH
 222      {
 223       my ($obj,$fh) = @_;
 224       print $fh $$obj or return -1;
 225       $$obj = '';
 226       return 0;
 227      }
 228  
 229      1;
 230  
 231  the following code opens up an output handle that will convert any
 232  output to hexadecimal dump of the output bytes: for example "A" will
 233  be converted to "41" (on ASCII-based machines, on EBCDIC platforms
 234  the "A" will become "c1")
 235  
 236      use PerlIO::via::Hex;
 237      open(my $fh, ">:via(Hex)", "foo.hex");
 238  
 239  and the following code will read the hexdump in and convert it
 240  on the fly back into bytes:
 241  
 242      open(my $fh, "<:via(Hex)", "foo.hex");
 243  
 244  =cut