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| 129 | .\" ======================================================================== |
| 130 | .\" |
| 131 | .IX Title "PerlIO::via 3" |
| 132 | .TH PerlIO::via 3 "2001-09-21" "perl v5.8.8" "Perl Programmers Reference Guide" |
| 133 | .SH "NAME" |
| 134 | PerlIO::via \- Helper class for PerlIO layers implemented in perl |
| 135 | .SH "SYNOPSIS" |
| 136 | .IX Header "SYNOPSIS" |
| 137 | .Vb 2 |
| 138 | \& use PerlIO::via::Layer; |
| 139 | \& open($fh,"<:via(Layer)",...); |
| 140 | .Ve |
| 141 | .PP |
| 142 | .Vb 2 |
| 143 | \& use Some::Other::Package; |
| 144 | \& open($fh,">:via(Some::Other::Package)",...); |
| 145 | .Ve |
| 146 | .SH "DESCRIPTION" |
| 147 | .IX Header "DESCRIPTION" |
| 148 | The PerlIO::via module allows you to develop PerlIO layers in Perl, without |
| 149 | having to go into the nitty gritty of programming C with \s-1XS\s0 as the interface |
| 150 | to Perl. |
| 151 | .PP |
| 152 | One example module, PerlIO::via::QuotedPrint, is included with Perl |
| 153 | 5.8.0, and more example modules are available from \s-1CPAN\s0, such as |
| 154 | PerlIO::via::StripHTML and PerlIO::via::Base64. The |
| 155 | PerlIO::via::StripHTML module for instance, allows you to say: |
| 156 | .PP |
| 157 | .Vb 3 |
| 158 | \& use PerlIO::via::StripHTML; |
| 159 | \& open( my $fh, "<:via(StripHTML)", "index.html" ); |
| 160 | \& my @line = <$fh>; |
| 161 | .Ve |
| 162 | .PP |
| 163 | to obtain the text of an HTML-file in an array with all the HTML-tags |
| 164 | automagically removed. |
| 165 | .PP |
| 166 | Please note that if the layer is created in the PerlIO::via:: namespace, it |
| 167 | does \fBnot\fR have to be fully qualified. The PerlIO::via module will prefix |
| 168 | the PerlIO::via:: namespace if the specified modulename does not exist as a |
| 169 | fully qualified module name. |
| 170 | .SH "EXPECTED METHODS" |
| 171 | .IX Header "EXPECTED METHODS" |
| 172 | To create a Perl module that implements a PerlIO layer in Perl (as opposed to |
| 173 | in C using \s-1XS\s0 as the interface to Perl), you need to supply some of the |
| 174 | following subroutines. It is recommended to create these Perl modules in the |
| 175 | PerlIO::via:: namespace, so that they can easily be located on \s-1CPAN\s0 and use |
| 176 | the default namespace feature of the PerlIO::via module itself. |
| 177 | .PP |
| 178 | Please note that this is an area of recent development in Perl and that the |
| 179 | interface described here is therefore still subject to change (and hopefully |
| 180 | will have better documentation and more examples). |
| 181 | .PP |
| 182 | In the method descriptions below \fI$fh\fR will be |
| 183 | a reference to a glob which can be treated as a perl file handle. |
| 184 | It refers to the layer below. \fI$fh\fR is not passed if the layer |
| 185 | is at the bottom of the stack, for this reason and to maintain |
| 186 | some level of \*(L"compatibility\*(R" with \s-1TIEHANDLE\s0 classes it is passed last. |
| 187 | .IP "$class\->\s-1PUSHED\s0([$mode[,$fh]])" 4 |
| 188 | .IX Item "$class->PUSHED([$mode[,$fh]])" |
| 189 | Should return an object or the class, or \-1 on failure. (Compare |
| 190 | \&\s-1TIEHANDLE\s0.) The arguments are an optional mode string (\*(L"r\*(R", \*(L"w\*(R", |
| 191 | \&\*(L"w+\*(R", ...) and a filehandle for the PerlIO layer below. Mandatory. |
| 192 | .Sp |
| 193 | When layer is pushed as part of an \f(CW\*(C`open\*(C'\fR call, \f(CW\*(C`PUSHED\*(C'\fR will be called |
| 194 | \&\fIbefore\fR the actual open occurs whether than be via \f(CW\*(C`OPEN\*(C'\fR, \f(CW\*(C`SYSOPEN\*(C'\fR, |
| 195 | \&\f(CW\*(C`FDOPEN\*(C'\fR or by letting lower layer do the open. |
| 196 | .IP "$obj\->\s-1POPPED\s0([$fh])" 4 |
| 197 | .IX Item "$obj->POPPED([$fh])" |
| 198 | Optional \- layer is about to be removed. |
| 199 | .IP "$obj\->\s-1UTF8\s0($bellowFlag,[$fh])" 4 |
| 200 | .IX Item "$obj->UTF8($bellowFlag,[$fh])" |
| 201 | Optional \- if present it will be called immediately after \s-1PUSHED\s0 has |
| 202 | returned. It should return true value if the layer expects data to be |
| 203 | \&\s-1UTF\-8\s0 encoded. If it returns true result is as if caller had done |
| 204 | .Sp |
| 205 | .Vb 1 |
| 206 | \& ":via(YourClass):utf8" |
| 207 | .Ve |
| 208 | .Sp |
| 209 | If not present of it it returns false, then stream is left with |
| 210 | flag clear. |
| 211 | The \fI$bellowFlag\fR argument will be true if there is a layer below |
| 212 | and that layer was expecting \s-1UTF\-8\s0. |
| 213 | .IP "$obj\->\s-1OPEN\s0($path,$mode[,$fh])" 4 |
| 214 | .IX Item "$obj->OPEN($path,$mode[,$fh])" |
| 215 | Optional \- if not present lower layer does open. |
| 216 | If present called for normal opens after layer is pushed. |
| 217 | This function is subject to change as there is no easy way |
| 218 | to get lower layer to do open and then regain control. |
| 219 | .IP "$obj\->\s-1BINMODE\s0([,$fh])" 4 |
| 220 | .IX Item "$obj->BINMODE([,$fh])" |
| 221 | Optional \- if not available layer is popped on binmode($fh) or when \f(CW\*(C`:raw\*(C'\fR |
| 222 | is pushed. If present it should return 0 on success \-1 on error and undef |
| 223 | to pop the layer. |
| 224 | .IP "$obj\->\s-1FDOPEN\s0($fd[,$fh])" 4 |
| 225 | .IX Item "$obj->FDOPEN($fd[,$fh])" |
| 226 | Optional \- if not present lower layer does open. |
| 227 | If present called for opens which pass a numeric file |
| 228 | descriptor after layer is pushed. |
| 229 | This function is subject to change as there is no easy way |
| 230 | to get lower layer to do open and then regain control. |
| 231 | .IP "$obj\->\s-1SYSOPEN\s0($path,$imode,$perm,[,$fh])" 4 |
| 232 | .IX Item "$obj->SYSOPEN($path,$imode,$perm,[,$fh])" |
| 233 | Optional \- if not present lower layer does open. |
| 234 | If present called for sysopen style opens which pass a numeric mode |
| 235 | and permissions after layer is pushed. |
| 236 | This function is subject to change as there is no easy way |
| 237 | to get lower layer to do open and then regain control. |
| 238 | .IP "$obj\->\s-1FILENO\s0($fh)" 4 |
| 239 | .IX Item "$obj->FILENO($fh)" |
| 240 | Returns a numeric value for Unix-like file descriptor. Return \-1 if |
| 241 | there isn't one. Optional. Default is fileno($fh). |
| 242 | .IP "$obj\->\s-1READ\s0($buffer,$len,$fh)" 4 |
| 243 | .IX Item "$obj->READ($buffer,$len,$fh)" |
| 244 | Returns the number of octets placed in \f(CW$buffer\fR (must be less than or |
| 245 | equal to \f(CW$len\fR). Optional. Default is to use \s-1FILL\s0 instead. |
| 246 | .IP "$obj\->\s-1WRITE\s0($buffer,$fh)" 4 |
| 247 | .IX Item "$obj->WRITE($buffer,$fh)" |
| 248 | Returns the number of octets from buffer that have been successfully written. |
| 249 | .IP "$obj\->\s-1FILL\s0($fh)" 4 |
| 250 | .IX Item "$obj->FILL($fh)" |
| 251 | Should return a string to be placed in the buffer. Optional. If not |
| 252 | provided must provide \s-1READ\s0 or reject handles open for reading in |
| 253 | \&\s-1PUSHED\s0. |
| 254 | .IP "$obj\->\s-1CLOSE\s0($fh)" 4 |
| 255 | .IX Item "$obj->CLOSE($fh)" |
| 256 | Should return 0 on success, \-1 on error. |
| 257 | Optional. |
| 258 | .IP "$obj\->\s-1SEEK\s0($posn,$whence,$fh)" 4 |
| 259 | .IX Item "$obj->SEEK($posn,$whence,$fh)" |
| 260 | Should return 0 on success, \-1 on error. |
| 261 | Optional. Default is to fail, but that is likely to be changed |
| 262 | in future. |
| 263 | .IP "$obj\->\s-1TELL\s0($fh)" 4 |
| 264 | .IX Item "$obj->TELL($fh)" |
| 265 | Returns file postion. |
| 266 | Optional. Default to be determined. |
| 267 | .IP "$obj\->\s-1UNREAD\s0($buffer,$fh)" 4 |
| 268 | .IX Item "$obj->UNREAD($buffer,$fh)" |
| 269 | Returns the number of octets from buffer that have been successfully |
| 270 | saved to be returned on future \s-1FILL/READ\s0 calls. Optional. Default is |
| 271 | to push data into a temporary layer above this one. |
| 272 | .IP "$obj\->\s-1FLUSH\s0($fh)" 4 |
| 273 | .IX Item "$obj->FLUSH($fh)" |
| 274 | Flush any buffered write data. May possibly be called on readable |
| 275 | handles too. Should return 0 on success, \-1 on error. |
| 276 | .IP "$obj\->\s-1SETLINEBUF\s0($fh)" 4 |
| 277 | .IX Item "$obj->SETLINEBUF($fh)" |
| 278 | Optional. No return. |
| 279 | .IP "$obj\->\s-1CLEARERR\s0($fh)" 4 |
| 280 | .IX Item "$obj->CLEARERR($fh)" |
| 281 | Optional. No return. |
| 282 | .IP "$obj\->\s-1ERROR\s0($fh)" 4 |
| 283 | .IX Item "$obj->ERROR($fh)" |
| 284 | Optional. Returns error state. Default is no error until a mechanism |
| 285 | to signal error (die?) is worked out. |
| 286 | .IP "$obj\->\s-1EOF\s0($fh)" 4 |
| 287 | .IX Item "$obj->EOF($fh)" |
| 288 | Optional. Returns end-of-file state. Default is function of return |
| 289 | value of \s-1FILL\s0 or \s-1READ\s0. |
| 290 | .SH "EXAMPLES" |
| 291 | .IX Header "EXAMPLES" |
| 292 | Check the PerlIO::via:: namespace on \s-1CPAN\s0 for examples of PerlIO layers |
| 293 | implemented in Perl. To give you an idea how simple the implementation of |
| 294 | a PerlIO layer can look, as simple example is included here. |
| 295 | .Sh "Example \- a Hexadecimal Handle" |
| 296 | .IX Subsection "Example - a Hexadecimal Handle" |
| 297 | Given the following module, PerlIO::via::Hex : |
| 298 | .PP |
| 299 | .Vb 1 |
| 300 | \& package PerlIO::via::Hex; |
| 301 | .Ve |
| 302 | .PP |
| 303 | .Vb 7 |
| 304 | \& sub PUSHED |
| 305 | \& { |
| 306 | \& my ($class,$mode,$fh) = @_; |
| 307 | \& # When writing we buffer the data |
| 308 | \& my $buf = ''; |
| 309 | \& return bless \e$buf,$class; |
| 310 | \& } |
| 311 | .Ve |
| 312 | .PP |
| 313 | .Vb 6 |
| 314 | \& sub FILL |
| 315 | \& { |
| 316 | \& my ($obj,$fh) = @_; |
| 317 | \& my $line = <$fh>; |
| 318 | \& return (defined $line) ? pack("H*", $line) : undef; |
| 319 | \& } |
| 320 | .Ve |
| 321 | .PP |
| 322 | .Vb 6 |
| 323 | \& sub WRITE |
| 324 | \& { |
| 325 | \& my ($obj,$buf,$fh) = @_; |
| 326 | \& $$obj .= unpack("H*", $buf); |
| 327 | \& return length($buf); |
| 328 | \& } |
| 329 | .Ve |
| 330 | .PP |
| 331 | .Vb 7 |
| 332 | \& sub FLUSH |
| 333 | \& { |
| 334 | \& my ($obj,$fh) = @_; |
| 335 | \& print $fh $$obj or return -1; |
| 336 | \& $$obj = ''; |
| 337 | \& return 0; |
| 338 | \& } |
| 339 | .Ve |
| 340 | .PP |
| 341 | .Vb 1 |
| 342 | \& 1; |
| 343 | .Ve |
| 344 | .PP |
| 345 | the following code opens up an output handle that will convert any |
| 346 | output to hexadecimal dump of the output bytes: for example \*(L"A\*(R" will |
| 347 | be converted to \*(L"41\*(R" (on ASCII-based machines, on \s-1EBCDIC\s0 platforms |
| 348 | the \*(L"A\*(R" will become \*(L"c1\*(R") |
| 349 | .PP |
| 350 | .Vb 2 |
| 351 | \& use PerlIO::via::Hex; |
| 352 | \& open(my $fh, ">:via(Hex)", "foo.hex"); |
| 353 | .Ve |
| 354 | .PP |
| 355 | and the following code will read the hexdump in and convert it |
| 356 | on the fly back into bytes: |
| 357 | .PP |
| 358 | .Vb 1 |
| 359 | \& open(my $fh, "<:via(Hex)", "foo.hex"); |
| 360 | .Ve |