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1 | package PerlIO::via; |
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2 | our $VERSION = '0.02'; |
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3 | use XSLoader (); |
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4 | XSLoader::load 'PerlIO::via'; |
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5 | 1; |
6 | __END__ |
7 | |
8 | =head1 NAME |
9 | |
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10 | PerlIO::via - Helper class for PerlIO layers implemented in perl |
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11 | |
12 | =head1 SYNOPSIS |
13 | |
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14 | use PerlIO::via::Layer; |
15 | open($fh,"<:via(Layer)",...); |
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16 | |
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17 | use Some::Other::Package; |
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18 | open($fh,">:via(Some::Other::Package)",...); |
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19 | |
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20 | =head1 DESCRIPTION |
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21 | |
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22 | The PerlIO::via module allows you to develop PerlIO layers in Perl, without |
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23 | having to go into the nitty gritty of programming C with XS as the interface |
24 | to Perl. |
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25 | |
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26 | One example module, L<PerlIO::via::QuotedPrint>, is included with Perl |
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27 | 5.8.0, and more example modules are available from CPAN, such as |
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28 | L<PerlIO::via::StripHTML> and L<PerlIO::via::Base64>. The |
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29 | PerlIO::via::StripHTML module for instance, allows you to say: |
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30 | |
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31 | use PerlIO::via::StripHTML; |
32 | open( my $fh, "<:via(StripHTML)", "index.html" ); |
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33 | my @line = <$fh>; |
34 | |
35 | to obtain the text of an HTML-file in an array with all the HTML-tags |
36 | automagically removed. |
37 | |
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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 |
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41 | fully qualified module name. |
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42 | |
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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 |
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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. |
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50 | |
51 | Please note that this is an area of recent development in Perl and that the |
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52 | interface described here is therefore still subject to change (and hopefully |
53 | will have better documentation and more examples). |
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54 | |
55 | In the method descriptions below I<$fh> will be |
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56 | a reference to a glob which can be treated as a perl file handle. |
57 | It refers to the layer below. I<$fh> is not passed if the layer |
58 | is at the bottom of the stack, for this reason and to maintain |
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59 | some level of "compatibility" with TIEHANDLE classes it is passed last. |
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60 | |
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61 | =over 4 |
62 | |
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63 | =item $class->PUSHED([$mode[,$fh]]) |
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64 | |
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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. |
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68 | |
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69 | When layer is pushed as part of an C<open> call, C<PUSHED> will be called |
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70 | I<before> the actual open occurs whether than be via C<OPEN>, C<SYSOPEN>, |
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71 | C<FDOPEN> or by letting lower layer do the open. |
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72 | |
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73 | =item $obj->POPPED([$fh]) |
74 | |
75 | Optional - layer is about to be removed. |
76 | |
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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 | |
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91 | =item $obj->OPEN($path,$mode[,$fh]) |
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92 | |
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93 | Optional - if not present lower layer does open. |
94 | If present called for normal opens after layer is pushed. |
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95 | This function is subject to change as there is no easy way |
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96 | to get lower layer to do open and then regain control. |
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97 | |
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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 | |
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104 | =item $obj->FDOPEN($fd[,$fh]) |
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105 | |
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106 | Optional - if not present lower layer does open. |
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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 |
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110 | to get lower layer to do open and then regain control. |
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111 | |
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112 | =item $obj->SYSOPEN($path,$imode,$perm,[,$fh]) |
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113 | |
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114 | Optional - if not present lower layer does open. |
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115 | If present called for sysopen style opens which pass a numeric mode |
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116 | and permissions after layer is pushed. |
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117 | This function is subject to change as there is no easy way |
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118 | to get lower layer to do open and then regain control. |
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119 | |
120 | =item $obj->FILENO($fh) |
121 | |
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122 | Returns a numeric value for Unix-like file descriptor. Return -1 if |
123 | there isn't one. Optional. Default is fileno($fh). |
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124 | |
125 | =item $obj->READ($buffer,$len,$fh) |
126 | |
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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. |
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129 | |
130 | =item $obj->WRITE($buffer,$fh) |
131 | |
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132 | Returns the number of octets from buffer that have been successfully written. |
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133 | |
134 | =item $obj->FILL($fh) |
135 | |
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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. |
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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. |
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148 | Optional. Default is to fail, but that is likely to be changed |
149 | in future. |
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150 | |
151 | =item $obj->TELL($fh) |
152 | |
153 | Returns file postion. |
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154 | Optional. Default to be determined. |
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155 | |
156 | =item $obj->UNREAD($buffer,$fh) |
157 | |
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158 | Returns the number of octets from buffer that have been successfully |
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159 | saved to be returned on future FILL/READ calls. Optional. Default is |
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160 | to push data into a temporary layer above this one. |
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161 | |
162 | =item $obj->FLUSH($fh) |
163 | |
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164 | Flush any buffered write data. May possibly be called on readable |
165 | handles too. Should return 0 on success, -1 on error. |
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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 | |
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182 | Optional. Returns end-of-file state. Default is function of return |
183 | value of FILL or READ. |
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184 | |
185 | =back |
186 | |
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187 | =head1 EXAMPLES |
188 | |
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189 | Check the PerlIO::via:: namespace on CPAN for examples of PerlIO layers |
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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 | |
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193 | =head2 Example - a Hexadecimal Handle |
194 | |
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195 | Given the following module, PerlIO::via::Hex : |
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196 | |
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197 | package PerlIO::via::Hex; |
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198 | |
199 | sub PUSHED |
200 | { |
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201 | my ($class,$mode,$fh) = @_; |
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202 | # When writing we buffer the data |
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203 | my $buf = ''; |
204 | return bless \$buf,$class; |
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205 | } |
206 | |
207 | sub FILL |
208 | { |
209 | my ($obj,$fh) = @_; |
210 | my $line = <$fh>; |
211 | return (defined $line) ? pack("H*", $line) : undef; |
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212 | } |
213 | |
214 | sub WRITE |
215 | { |
216 | my ($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 | |
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236 | use PerlIO::via::Hex; |
237 | open(my $fh, ">:via(Hex)", "foo.hex"); |
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238 | |
239 | and the following code will read the hexdump in and convert it |
240 | on the fly back into bytes: |
241 | |
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242 | open(my $fh, "<:via(Hex)", "foo.hex"); |
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243 | |
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244 | =cut |