4 XSLoader::load 'PerlIO::Via';
10 PerlIO::Via - Helper class for PerlIO layers implemented in perl
16 open($fh,"<:Via(Some::Package)",...);
20 The package to be used as a layer should implement at least some of the
21 following methods. In the method descriptions below I<$fh> will be
22 a reference to a glob which can be treated as a perl file handle.
23 It refers to the layer below. I<$fh> is not passed if the layer
24 is at the bottom of the stack, for this reason and to maintain
25 some level of "compatibility" with TIEHANDLE classes it is passed last.
27 As an example, in Perl release 5.8.0 the included MIME::QuotedPrint
28 module defines the required TIEHANDLE methods so that you can say
30 use MIME::QuotedPrint;
31 open(my $fh, ">Via(MIME::QuotedPrint)", "qp");
35 =item $class->PUSHED([$mode[,$fh]])
37 Should return an object or the class, or -1 on failure. (Compare
38 TIEHANDLE.) The arguments are an optional mode string ("r", "w",
39 "w+", ...) and a filehandle for the PerlIO layer below. Mandatory.
41 =item $obj->POPPED([$fh])
43 Optional - layer is about to be removed.
45 =item $class->OPEN($path,$mode[,$fh])
49 =item $obj->BINMODE([,$fh])
51 Optional - if not available layer is popped on binmode($fh) or when C<:raw>
52 is pushed. If present it should return 0 on success -1 on error and undef
55 =item $class->FDOPEN($fd)
59 =item $class->SYSOPEN($path,$imode,$perm,$fh)
63 =item $obj->FILENO($fh)
65 Returns a numeric value for Unix-like file descriptor. Return -1 if
66 there isn't one. Optional. Default is fileno($fh).
68 =item $obj->READ($buffer,$len,$fh)
70 Returns the number of octets placed in $buffer (must be less than or
71 equal to $len). Optional. Default is to use FILL instead.
73 =item $obj->WRITE($buffer,$fh)
75 Returns the number of octets from buffer that have been sucessfully written.
79 Should return a string to be placed in the buffer. Optional. If not
80 provided must provide READ or reject handles open for reading in
83 =item $obj->CLOSE($fh)
85 Should return 0 on success, -1 on error.
88 =item $obj->SEEK($posn,$whence,$fh)
90 Should return 0 on success, -1 on error.
91 Optional. Default is to fail, but that is likely to be changed
97 Optional. Default to be determined.
99 =item $obj->UNREAD($buffer,$fh)
101 Returns the number of octets from buffer that have been sucessfully
102 saved to be returned on future FILL/READ calls. Optional. Default is
103 to push data into a temporary layer above this one.
105 =item $obj->FLUSH($fh)
107 Flush any buffered write data. May possibly be called on readable
108 handles too. Should return 0 on success, -1 on error.
110 =item $obj->SETLINEBUF($fh)
114 =item $obj->CLEARERR($fh)
118 =item $obj->ERROR($fh)
120 Optional. Returns error state. Default is no error until a mechanism
121 to signal error (die?) is worked out.
125 Optional. Returns end-of-file state. Default is function of return
126 value of FILL or READ.
130 =head2 Example - a Hexadecimal Handle
132 Given the following module, Hex.pm:
138 my ($class,$mode,$fh) = @_;
139 # When writing we buffer the data
141 return bless \$buf,$class;
148 return (defined $line) ? pack("H*", $line) : undef;
153 my ($obj,$buf,$fh) = @_;
154 $$obj .= unpack("H*", $buf);
161 print $fh $$obj or return -1;
168 the following code opens up an output handle that will convert any
169 output to hexadecimal dump of the output bytes: for example "A" will
170 be converted to "41" (on ASCII-based machines, on EBCDIC platforms
171 the "A" will become "c1")
174 open(my $fh, ">:Via(Hex)", "foo.hex");
176 and the following code will read the hexdump in and convert it
177 on the fly back into bytes:
179 open(my $fh, "<:Via(Hex)", "foo.hex");