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 undef on failure.
38 (Compare TIEHANDLE.) Mandatory.
40 =item $obj->POPPED([$fh])
42 Optional - layer is about to be removed.
44 =item $class->OPEN($path,$mode[,$fh])
48 =item $class->FDOPEN($fd)
52 =item $class->SYSOPEN($path,$imode,$perm,$fh)
56 =item $obj->FILENO($fh)
58 Returns a numeric value for Unix-like file descriptor. Return -1 if
59 there isn't one. Optional. Default is fileno($fh).
61 =item $obj->READ($buffer,$len,$fh)
63 Returns the number of octets placed in $buffer (must be less than or
64 equal to $len). Optional. Default is to use FILL instead.
66 =item $obj->WRITE($buffer,$fh)
68 Returns the number of octets from buffer that have been sucessfully written.
72 Should return a string to be placed in the buffer. Optional. If not
73 provided must provide READ or reject handles open for reading in
76 =item $obj->CLOSE($fh)
78 Should return 0 on success, -1 on error.
81 =item $obj->SEEK($posn,$whence,$fh)
83 Should return 0 on success, -1 on error.
84 Optional. Default is to fail, but that is likely to be changed
90 Optional. Default to be determined.
92 =item $obj->UNREAD($buffer,$fh)
94 Returns the number of octets from buffer that have been sucessfully
95 saved to be returned on future FILL/READ calls. Optional. Default is
96 to push data into a temporary layer above this one.
98 =item $obj->FLUSH($fh)
100 Flush any buffered write data. May possibly be called on readable
101 handles too. Should return 0 on success, -1 on error.
103 =item $obj->SETLINEBUF($fh)
107 =item $obj->CLEARERR($fh)
111 =item $obj->ERROR($fh)
113 Optional. Returns error state. Default is no error until a mechanism
114 to signal error (die?) is worked out.
118 Optional. Returns end-of-file state. Default is function of return
119 value of FILL or READ.
123 =head2 Example - a Hexadecimal Handle
125 Given the following module, Hex.pm:
131 my ($class,$mode,$fh) = @_;
132 # When writing we buffer the data
134 return bless \$buf,$class;
141 return (defined $line) ? pack("H*", $line) : undef;
146 my ($obj,$buf,$fh) = @_;
147 $$obj .= unpack("H*", $buf);
154 print $fh $$obj or return -1;
161 the following code opens up an output handle that will convert any
162 output to hexadecimal dump of the output bytes: for example "A" will
163 be converted to "41" (on ASCII-based machines, on EBCDIC platforms
164 the "A" will become "c1")
167 open(my $fh, ">:Via(Hex)", "foo.hex");
169 and the following code will read the hexdump in and convert it
170 on the fly back into bytes:
172 open(my $fh, "<:Via(Hex)", "foo.hex");