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1 | package PerlIO::Via; |
2 | our $VERSION = '0.01'; |
3 | use XSLoader (); |
4 | XSLoader::load 'PerlIO::Via'; |
5 | 1; |
6 | __END__ |
7 | |
8 | =head1 NAME |
9 | |
10 | PerlIO::Via - Helper class for PerlIO layers implemented in perl |
11 | |
12 | =head1 SYNOPSIS |
13 | |
14 | use Some::Package; |
15 | |
16 | open($fh,"<:Via(Some::Package)",...); |
17 | |
18 | =head1 DESCRIPTION |
19 | |
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 |
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25 | some level of "compatibility" with TIEHANDLE classes it is passed last. |
26 | |
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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 |
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29 | |
30 | use MIME::QuotedPrint; |
31 | open(my $fh, ">Via(MIME::QuotedPrint)", "qp"); |
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32 | |
33 | =over 4 |
34 | |
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35 | =item $class->PUSHED([$mode[,$fh]]) |
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36 | |
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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. |
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40 | |
41 | =item $obj->POPPED([$fh]) |
42 | |
43 | Optional - layer is about to be removed. |
44 | |
45 | =item $class->OPEN($path,$mode[,$fh]) |
46 | |
47 | Not yet in use. |
48 | |
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49 | =item $obj->BINMODE([,$fh]) |
50 | |
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 |
53 | to pop the layer. |
54 | |
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55 | =item $class->FDOPEN($fd) |
56 | |
57 | Not yet in use. |
58 | |
59 | =item $class->SYSOPEN($path,$imode,$perm,$fh) |
60 | |
61 | Not yet in use. |
62 | |
63 | =item $obj->FILENO($fh) |
64 | |
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65 | Returns a numeric value for Unix-like file descriptor. Return -1 if |
66 | there isn't one. Optional. Default is fileno($fh). |
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67 | |
68 | =item $obj->READ($buffer,$len,$fh) |
69 | |
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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. |
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72 | |
73 | =item $obj->WRITE($buffer,$fh) |
74 | |
75 | Returns the number of octets from buffer that have been sucessfully written. |
76 | |
77 | =item $obj->FILL($fh) |
78 | |
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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 |
81 | PUSHED. |
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82 | |
83 | =item $obj->CLOSE($fh) |
84 | |
85 | Should return 0 on success, -1 on error. |
86 | Optional. |
87 | |
88 | =item $obj->SEEK($posn,$whence,$fh) |
89 | |
90 | Should return 0 on success, -1 on error. |
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91 | Optional. Default is to fail, but that is likely to be changed |
92 | in future. |
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93 | |
94 | =item $obj->TELL($fh) |
95 | |
96 | Returns file postion. |
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97 | Optional. Default to be determined. |
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98 | |
99 | =item $obj->UNREAD($buffer,$fh) |
100 | |
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101 | Returns the number of octets from buffer that have been sucessfully |
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102 | saved to be returned on future FILL/READ calls. Optional. Default is |
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103 | to push data into a temporary layer above this one. |
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104 | |
105 | =item $obj->FLUSH($fh) |
106 | |
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107 | Flush any buffered write data. May possibly be called on readable |
108 | handles too. Should return 0 on success, -1 on error. |
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109 | |
110 | =item $obj->SETLINEBUF($fh) |
111 | |
112 | Optional. No return. |
113 | |
114 | =item $obj->CLEARERR($fh) |
115 | |
116 | Optional. No return. |
117 | |
118 | =item $obj->ERROR($fh) |
119 | |
120 | Optional. Returns error state. Default is no error until a mechanism |
121 | to signal error (die?) is worked out. |
122 | |
123 | =item $obj->EOF($fh) |
124 | |
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125 | Optional. Returns end-of-file state. Default is function of return |
126 | value of FILL or READ. |
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127 | |
128 | =back |
129 | |
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130 | =head2 Example - a Hexadecimal Handle |
131 | |
132 | Given the following module, Hex.pm: |
133 | |
134 | package Hex; |
135 | |
136 | sub PUSHED |
137 | { |
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138 | my ($class,$mode,$fh) = @_; |
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139 | # When writing we buffer the data |
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140 | my $buf = ''; |
141 | return bless \$buf,$class; |
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142 | } |
143 | |
144 | sub FILL |
145 | { |
146 | my ($obj,$fh) = @_; |
147 | my $line = <$fh>; |
148 | return (defined $line) ? pack("H*", $line) : undef; |
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149 | } |
150 | |
151 | sub WRITE |
152 | { |
153 | my ($obj,$buf,$fh) = @_; |
154 | $$obj .= unpack("H*", $buf); |
155 | return length($buf); |
156 | } |
157 | |
158 | sub FLUSH |
159 | { |
160 | my ($obj,$fh) = @_; |
161 | print $fh $$obj or return -1; |
162 | $$obj = ''; |
163 | return 0; |
164 | } |
165 | |
166 | 1; |
167 | |
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") |
172 | |
173 | use Hex; |
174 | open(my $fh, ">:Via(Hex)", "foo.hex"); |
175 | |
176 | and the following code will read the hexdump in and convert it |
177 | on the fly back into bytes: |
178 | |
179 | open(my $fh, "<:Via(Hex)", "foo.hex"); |
180 | |
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181 | =cut |
182 | |
183 | |