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1 | package PerlIO::via; |
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2 | our $VERSION = '0.09'; |
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3 | use XSLoader (); |
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4 | XSLoader::load 'PerlIO::via'; |
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5 | 1; |
6 | __END__ |
7 | |
8 | =head1 NAME |
9 | |
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10 | PerlIO::via - Helper class for PerlIO layers implemented in perl |
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11 | |
12 | =head1 SYNOPSIS |
13 | |
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14 | use PerlIO::via::Layer; |
15 | open($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 the layer is pushed as part of an C<open> call, C<PUSHED> will be called |
70 | I<before> the actual open occurs, whether that be via C<OPEN>, C<SYSOPEN>, |
71 | C<FDOPEN> or by letting a lower layer do the open. |
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72 | |
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73 | =item $obj->POPPED([$fh]) |
74 | |
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75 | Optional - called when the layer is about to be removed. |
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76 | |
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77 | =item $obj->UTF8($bellowFlag,[$fh]) |
78 | |
79 | Optional - if present it will be called immediately after PUSHED has |
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80 | returned. It should return a true value if the layer expects data to be |
81 | UTF-8 encoded. If it returns true, the result is as if the caller had done |
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82 | |
83 | ":via(YourClass):utf8" |
84 | |
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85 | If not present or if it returns false, then the stream is left with |
86 | the UTF-8 flag clear. |
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87 | The I<$bellowFlag> argument will be true if there is a layer below |
88 | and that layer was expecting UTF-8. |
89 | |
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90 | =item $obj->OPEN($path,$mode,[$fh]) |
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91 | |
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92 | Optional - if not present a lower layer does the open. |
93 | If present, called for normal opens after the layer is pushed. |
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94 | This function is subject to change as there is no easy way |
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95 | to get a lower layer to do the open and then regain control. |
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96 | |
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97 | =item $obj->BINMODE([$fh]) |
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98 | |
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99 | Optional - if not present the layer is popped on binmode($fh) or when C<:raw> |
100 | is pushed. If present it should return 0 on success, -1 on error, or undef |
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101 | to pop the layer. |
102 | |
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103 | =item $obj->FDOPEN($fd,[$fh]) |
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104 | |
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105 | Optional - if not present a lower layer does the open. |
106 | If present, called after the layer is pushed for opens which pass |
107 | a numeric file descriptor. |
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108 | This function is subject to change as there is no easy way |
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109 | to get a lower layer to do the open and then regain control. |
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110 | |
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111 | =item $obj->SYSOPEN($path,$imode,$perm,[$fh]) |
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112 | |
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113 | Optional - if not present a lower layer does the open. |
114 | If present, called after the layer is pushed for sysopen style opens |
115 | which pass a numeric mode and permissions. |
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116 | This function is subject to change as there is no easy way |
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117 | to get a lower layer to do the open and then regain control. |
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118 | |
119 | =item $obj->FILENO($fh) |
120 | |
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121 | Returns a numeric value for a Unix-like file descriptor. Returns -1 if |
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122 | there isn't one. Optional. Default is fileno($fh). |
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123 | |
124 | =item $obj->READ($buffer,$len,$fh) |
125 | |
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126 | Returns the number of octets placed in $buffer (must be less than or |
127 | equal to $len). Optional. Default is to use FILL instead. |
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128 | |
129 | =item $obj->WRITE($buffer,$fh) |
130 | |
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131 | Returns the number of octets from $buffer that have been successfully written. |
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132 | |
133 | =item $obj->FILL($fh) |
134 | |
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135 | Should return a string to be placed in the buffer. Optional. If not |
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136 | provided, must provide READ or reject handles open for reading in |
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137 | PUSHED. |
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138 | |
139 | =item $obj->CLOSE($fh) |
140 | |
141 | Should return 0 on success, -1 on error. |
142 | Optional. |
143 | |
144 | =item $obj->SEEK($posn,$whence,$fh) |
145 | |
146 | Should return 0 on success, -1 on error. |
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147 | Optional. Default is to fail, but that is likely to be changed |
148 | in future. |
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149 | |
150 | =item $obj->TELL($fh) |
151 | |
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152 | Returns file position. |
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153 | Optional. Default to be determined. |
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154 | |
155 | =item $obj->UNREAD($buffer,$fh) |
156 | |
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157 | Returns the number of octets from $buffer that have been successfully |
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158 | saved to be returned on future FILL/READ calls. Optional. Default is |
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159 | to push data into a temporary layer above this one. |
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160 | |
161 | =item $obj->FLUSH($fh) |
162 | |
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163 | Flush any buffered write data. May possibly be called on readable |
164 | handles too. Should return 0 on success, -1 on error. |
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165 | |
166 | =item $obj->SETLINEBUF($fh) |
167 | |
168 | Optional. No return. |
169 | |
170 | =item $obj->CLEARERR($fh) |
171 | |
172 | Optional. No return. |
173 | |
174 | =item $obj->ERROR($fh) |
175 | |
176 | Optional. Returns error state. Default is no error until a mechanism |
177 | to signal error (die?) is worked out. |
178 | |
179 | =item $obj->EOF($fh) |
180 | |
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181 | Optional. Returns end-of-file state. Default is a function of the return |
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182 | value of FILL or READ. |
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183 | |
184 | =back |
185 | |
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186 | =head1 EXAMPLES |
187 | |
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188 | Check the PerlIO::via:: namespace on CPAN for examples of PerlIO layers |
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189 | implemented in Perl. To give you an idea how simple the implementation of |
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190 | a PerlIO layer can look, a simple example is included here. |
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191 | |
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192 | =head2 Example - a Hexadecimal Handle |
193 | |
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194 | Given the following module, PerlIO::via::Hex : |
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195 | |
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196 | package PerlIO::via::Hex; |
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197 | |
198 | sub PUSHED |
199 | { |
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200 | my ($class,$mode,$fh) = @_; |
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201 | # When writing we buffer the data |
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202 | my $buf = ''; |
203 | return bless \$buf,$class; |
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204 | } |
205 | |
206 | sub FILL |
207 | { |
208 | my ($obj,$fh) = @_; |
209 | my $line = <$fh>; |
210 | return (defined $line) ? pack("H*", $line) : undef; |
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211 | } |
212 | |
213 | sub WRITE |
214 | { |
215 | my ($obj,$buf,$fh) = @_; |
216 | $$obj .= unpack("H*", $buf); |
217 | return length($buf); |
218 | } |
219 | |
220 | sub FLUSH |
221 | { |
222 | my ($obj,$fh) = @_; |
223 | print $fh $$obj or return -1; |
224 | $$obj = ''; |
225 | return 0; |
226 | } |
227 | |
228 | 1; |
229 | |
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230 | The following code opens up an output handle that will convert any |
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231 | output to a hexadecimal dump of the output bytes: for example "A" will |
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232 | be converted to "41" (on ASCII-based machines, on EBCDIC platforms |
233 | the "A" will become "c1") |
234 | |
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235 | use PerlIO::via::Hex; |
236 | open(my $fh, ">:via(Hex)", "foo.hex"); |
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237 | |
238 | and the following code will read the hexdump in and convert it |
239 | on the fly back into bytes: |
240 | |
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241 | open(my $fh, "<:via(Hex)", "foo.hex"); |
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242 | |
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243 | =cut |