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1 | =head1 NAME |
2 | |
3 | perliol - C API for Perl's implementation of IO in Layers. |
4 | |
5 | =head1 SYNOPSIS |
6 | |
7 | /* Defining a layer ... */ |
8 | #include <perliol.h> |
9 | |
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10 | =head1 DESCRIPTION |
11 | |
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12 | This document describes the behavior and implementation of the PerlIO |
13 | abstraction described in L<perlapio> when C<USE_PERLIO> is defined (and |
14 | C<USE_SFIO> is not). |
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15 | |
16 | =head2 History and Background |
17 | |
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18 | The PerlIO abstraction was introduced in perl5.003_02 but languished as |
19 | just an abstraction until perl5.7.0. However during that time a number |
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20 | of perl extensions switched to using it, so the API is mostly fixed to |
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21 | maintain (source) compatibility. |
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22 | |
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23 | The aim of the implementation is to provide the PerlIO API in a flexible |
24 | and platform neutral manner. It is also a trial of an "Object Oriented |
25 | C, with vtables" approach which may be applied to perl6. |
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26 | |
27 | =head2 Layers vs Disciplines |
28 | |
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29 | Initial discussion of the ability to modify IO streams behaviour used |
30 | the term "discipline" for the entities which were added. This came (I |
31 | believe) from the use of the term in "sfio", which in turn borrowed it |
32 | from "line disciplines" on Unix terminals. However, this document (and |
33 | the C code) uses the term "layer". |
34 | |
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35 | This is, I hope, a natural term given the implementation, and should |
36 | avoid connotations that are inherent in earlier uses of "discipline" |
37 | for things which are rather different. |
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38 | |
39 | =head2 Data Structures |
40 | |
41 | The basic data structure is a PerlIOl: |
42 | |
43 | typedef struct _PerlIO PerlIOl; |
44 | typedef struct _PerlIO_funcs PerlIO_funcs; |
45 | typedef PerlIOl *PerlIO; |
46 | |
47 | struct _PerlIO |
48 | { |
49 | PerlIOl * next; /* Lower layer */ |
50 | PerlIO_funcs * tab; /* Functions for this layer */ |
51 | IV flags; /* Various flags for state */ |
52 | }; |
53 | |
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54 | A C<PerlIOl *> is a pointer to the struct, and the I<application> |
55 | level C<PerlIO *> is a pointer to a C<PerlIOl *> - i.e. a pointer |
56 | to a pointer to the struct. This allows the application level C<PerlIO *> |
57 | to remain constant while the actual C<PerlIOl *> underneath |
58 | changes. (Compare perl's C<SV *> which remains constant while its |
59 | C<sv_any> field changes as the scalar's type changes.) An IO stream is |
60 | then in general represented as a pointer to this linked-list of |
61 | "layers". |
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62 | |
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63 | It should be noted that because of the double indirection in a C<PerlIO *>, |
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64 | a C<< &(perlio->next) >> "is" a C<PerlIO *>, and so to some degree |
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65 | at least one layer can use the "standard" API on the next layer down. |
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66 | |
67 | A "layer" is composed of two parts: |
68 | |
69 | =over 4 |
70 | |
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71 | =item 1. |
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72 | |
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73 | The functions and attributes of the "layer class". |
74 | |
75 | =item 2. |
76 | |
77 | The per-instance data for a particular handle. |
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78 | |
79 | =back |
80 | |
81 | =head2 Functions and Attributes |
82 | |
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83 | The functions and attributes are accessed via the "tab" (for table) |
84 | member of C<PerlIOl>. The functions (methods of the layer "class") are |
85 | fixed, and are defined by the C<PerlIO_funcs> type. They are broadly the |
86 | same as the public C<PerlIO_xxxxx> functions: |
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87 | |
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88 | struct _PerlIO_funcs |
89 | { |
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90 | Size_t fsize; |
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91 | char * name; |
92 | Size_t size; |
93 | IV kind; |
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94 | IV (*Pushed)(pTHX_ PerlIO *f,const char *mode,SV *arg, PerlIO_funcs *tab); |
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95 | IV (*Popped)(pTHX_ PerlIO *f); |
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96 | PerlIO * (*Open)(pTHX_ PerlIO_funcs *tab, |
97 | AV *layers, IV n, |
98 | const char *mode, |
99 | int fd, int imode, int perm, |
100 | PerlIO *old, |
101 | int narg, SV **args); |
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102 | IV (*Binmode)(pTHX_ PerlIO *f); |
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103 | SV * (*Getarg)(pTHX_ PerlIO *f, CLONE_PARAMS *param, int flags) |
104 | IV (*Fileno)(pTHX_ PerlIO *f); |
105 | PerlIO * (*Dup)(pTHX_ PerlIO *f, PerlIO *o, CLONE_PARAMS *param, int flags) |
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106 | /* Unix-like functions - cf sfio line disciplines */ |
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107 | SSize_t (*Read)(pTHX_ PerlIO *f, void *vbuf, Size_t count); |
108 | SSize_t (*Unread)(pTHX_ PerlIO *f, const void *vbuf, Size_t count); |
109 | SSize_t (*Write)(pTHX_ PerlIO *f, const void *vbuf, Size_t count); |
110 | IV (*Seek)(pTHX_ PerlIO *f, Off_t offset, int whence); |
111 | Off_t (*Tell)(pTHX_ PerlIO *f); |
112 | IV (*Close)(pTHX_ PerlIO *f); |
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113 | /* Stdio-like buffered IO functions */ |
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114 | IV (*Flush)(pTHX_ PerlIO *f); |
115 | IV (*Fill)(pTHX_ PerlIO *f); |
116 | IV (*Eof)(pTHX_ PerlIO *f); |
117 | IV (*Error)(pTHX_ PerlIO *f); |
118 | void (*Clearerr)(pTHX_ PerlIO *f); |
119 | void (*Setlinebuf)(pTHX_ PerlIO *f); |
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120 | /* Perl's snooping functions */ |
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121 | STDCHAR * (*Get_base)(pTHX_ PerlIO *f); |
122 | Size_t (*Get_bufsiz)(pTHX_ PerlIO *f); |
123 | STDCHAR * (*Get_ptr)(pTHX_ PerlIO *f); |
124 | SSize_t (*Get_cnt)(pTHX_ PerlIO *f); |
125 | void (*Set_ptrcnt)(pTHX_ PerlIO *f,STDCHAR *ptr,SSize_t cnt); |
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126 | }; |
127 | |
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128 | The first few members of the struct give a function table size for |
129 | compatibility check "name" for the layer, the size to C<malloc> for the per-instance data, |
130 | and some flags which are attributes of the class as whole (such as whether it is a buffering |
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131 | layer), then follow the functions which fall into four basic groups: |
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132 | |
133 | =over 4 |
134 | |
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135 | =item 1. |
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136 | |
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137 | Opening and setup functions |
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138 | |
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139 | =item 2. |
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140 | |
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141 | Basic IO operations |
142 | |
143 | =item 3. |
144 | |
145 | Stdio class buffering options. |
146 | |
147 | =item 4. |
148 | |
149 | Functions to support Perl's traditional "fast" access to the buffer. |
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150 | |
151 | =back |
152 | |
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153 | A layer does not have to implement all the functions, but the whole |
154 | table has to be present. Unimplemented slots can be NULL (which will |
155 | result in an error when called) or can be filled in with stubs to |
156 | "inherit" behaviour from a "base class". This "inheritance" is fixed |
157 | for all instances of the layer, but as the layer chooses which stubs |
158 | to populate the table, limited "multiple inheritance" is possible. |
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159 | |
160 | =head2 Per-instance Data |
161 | |
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162 | The per-instance data are held in memory beyond the basic PerlIOl |
163 | struct, by making a PerlIOl the first member of the layer's struct |
164 | thus: |
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165 | |
166 | typedef struct |
167 | { |
168 | struct _PerlIO base; /* Base "class" info */ |
169 | STDCHAR * buf; /* Start of buffer */ |
170 | STDCHAR * end; /* End of valid part of buffer */ |
171 | STDCHAR * ptr; /* Current position in buffer */ |
172 | Off_t posn; /* Offset of buf into the file */ |
173 | Size_t bufsiz; /* Real size of buffer */ |
174 | IV oneword; /* Emergency buffer */ |
175 | } PerlIOBuf; |
176 | |
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177 | In this way (as for perl's scalars) a pointer to a PerlIOBuf can be |
178 | treated as a pointer to a PerlIOl. |
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179 | |
180 | =head2 Layers in action. |
181 | |
182 | table perlio unix |
183 | | | |
184 | +-----------+ +----------+ +--------+ |
185 | PerlIO ->| |--->| next |--->| NULL | |
186 | +-----------+ +----------+ +--------+ |
187 | | | | buffer | | fd | |
188 | +-----------+ | | +--------+ |
189 | | | +----------+ |
190 | |
191 | |
192 | The above attempts to show how the layer scheme works in a simple case. |
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193 | The application's C<PerlIO *> points to an entry in the table(s) |
194 | representing open (allocated) handles. For example the first three slots |
195 | in the table correspond to C<stdin>,C<stdout> and C<stderr>. The table |
196 | in turn points to the current "top" layer for the handle - in this case |
197 | an instance of the generic buffering layer "perlio". That layer in turn |
198 | points to the next layer down - in this case the lowlevel "unix" layer. |
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199 | |
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200 | The above is roughly equivalent to a "stdio" buffered stream, but with |
201 | much more flexibility: |
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202 | |
203 | =over 4 |
204 | |
205 | =item * |
206 | |
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207 | If Unix level C<read>/C<write>/C<lseek> is not appropriate for (say) |
208 | sockets then the "unix" layer can be replaced (at open time or even |
209 | dynamically) with a "socket" layer. |
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210 | |
211 | =item * |
212 | |
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213 | Different handles can have different buffering schemes. The "top" |
214 | layer could be the "mmap" layer if reading disk files was quicker |
215 | using C<mmap> than C<read>. An "unbuffered" stream can be implemented |
216 | simply by not having a buffer layer. |
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217 | |
218 | =item * |
219 | |
220 | Extra layers can be inserted to process the data as it flows through. |
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221 | This was the driving need for including the scheme in perl 5.7.0+ - we |
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222 | needed a mechanism to allow data to be translated between perl's |
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223 | internal encoding (conceptually at least Unicode as UTF-8), and the |
224 | "native" format used by the system. This is provided by the |
225 | ":encoding(xxxx)" layer which typically sits above the buffering layer. |
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226 | |
227 | =item * |
228 | |
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229 | A layer can be added that does "\n" to CRLF translation. This layer |
230 | can be used on any platform, not just those that normally do such |
231 | things. |
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232 | |
233 | =back |
234 | |
235 | =head2 Per-instance flag bits |
236 | |
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237 | The generic flag bits are a hybrid of C<O_XXXXX> style flags deduced |
238 | from the mode string passed to C<PerlIO_open()>, and state bits for |
239 | typical buffer layers. |
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240 | |
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241 | =over 4 |
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242 | |
243 | =item PERLIO_F_EOF |
244 | |
245 | End of file. |
246 | |
247 | =item PERLIO_F_CANWRITE |
248 | |
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249 | Writes are permitted, i.e. opened as "w" or "r+" or "a", etc. |
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250 | |
251 | =item PERLIO_F_CANREAD |
252 | |
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253 | Reads are permitted i.e. opened "r" or "w+" (or even "a+" - ick). |
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254 | |
255 | =item PERLIO_F_ERROR |
256 | |
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257 | An error has occurred (for C<PerlIO_error()>). |
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258 | |
259 | =item PERLIO_F_TRUNCATE |
260 | |
261 | Truncate file suggested by open mode. |
262 | |
263 | =item PERLIO_F_APPEND |
264 | |
265 | All writes should be appends. |
266 | |
267 | =item PERLIO_F_CRLF |
268 | |
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269 | Layer is performing Win32-like "\n" mapped to CR,LF for output and CR,LF |
270 | mapped to "\n" for input. Normally the provided "crlf" layer is the only |
271 | layer that need bother about this. C<PerlIO_binmode()> will mess with this |
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272 | flag rather than add/remove layers if the C<PERLIO_K_CANCRLF> bit is set |
273 | for the layers class. |
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274 | |
275 | =item PERLIO_F_UTF8 |
276 | |
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277 | Data written to this layer should be UTF-8 encoded; data provided |
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278 | by this layer should be considered UTF-8 encoded. Can be set on any layer |
279 | by ":utf8" dummy layer. Also set on ":encoding" layer. |
280 | |
281 | =item PERLIO_F_UNBUF |
282 | |
283 | Layer is unbuffered - i.e. write to next layer down should occur for |
284 | each write to this layer. |
285 | |
286 | =item PERLIO_F_WRBUF |
287 | |
288 | The buffer for this layer currently holds data written to it but not sent |
289 | to next layer. |
290 | |
291 | =item PERLIO_F_RDBUF |
292 | |
293 | The buffer for this layer currently holds unconsumed data read from |
294 | layer below. |
295 | |
296 | =item PERLIO_F_LINEBUF |
297 | |
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298 | Layer is line buffered. Write data should be passed to next layer down |
299 | whenever a "\n" is seen. Any data beyond the "\n" should then be |
300 | processed. |
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301 | |
302 | =item PERLIO_F_TEMP |
303 | |
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304 | File has been C<unlink()>ed, or should be deleted on C<close()>. |
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305 | |
306 | =item PERLIO_F_OPEN |
307 | |
308 | Handle is open. |
309 | |
310 | =item PERLIO_F_FASTGETS |
311 | |
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312 | This instance of this layer supports the "fast C<gets>" interface. |
313 | Normally set based on C<PERLIO_K_FASTGETS> for the class and by the |
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314 | existence of the function(s) in the table. However a class that |
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315 | normally provides that interface may need to avoid it on a |
316 | particular instance. The "pending" layer needs to do this when |
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317 | it is pushed above a layer which does not support the interface. |
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318 | (Perl's C<sv_gets()> does not expect the streams fast C<gets> behaviour |
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319 | to change during one "get".) |
320 | |
321 | =back |
322 | |
323 | =head2 Methods in Detail |
324 | |
325 | =over 4 |
326 | |
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327 | =item fsize |
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328 | |
329 | Size_t fsize; |
330 | |
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331 | Size of the function table. This is compared against the value PerlIO |
332 | code "knows" as a compatibility check. Future versions I<may> be able |
333 | to tolerate layers compiled against an old version of the headers. |
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334 | |
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335 | =item name |
336 | |
337 | char * name; |
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338 | |
339 | The name of the layer whose open() method Perl should invoke on |
340 | open(). For example if the layer is called APR, you will call: |
341 | |
342 | open $fh, ">:APR", ... |
343 | |
344 | and Perl knows that it has to invoke the PerlIOAPR_open() method |
345 | implemented by the APR layer. |
346 | |
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347 | =item size |
348 | |
349 | Size_t size; |
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350 | |
351 | The size of the per-instance data structure, e.g.: |
352 | |
353 | sizeof(PerlIOAPR) |
354 | |
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355 | If this field is zero then C<PerlIO_pushed> does not malloc anything |
356 | and assumes layer's Pushed function will do any required layer stack |
357 | manipulation - used to avoid malloc/free overhead for dummy layers. |
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358 | If the field is non-zero it must be at least the size of C<PerlIOl>, |
359 | C<PerlIO_pushed> will allocate memory for the layer's data structures |
360 | and link new layer onto the stream's stack. (If the layer's Pushed |
361 | method returns an error indication the layer is popped again.) |
362 | |
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363 | =item kind |
364 | |
365 | IV kind; |
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366 | |
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367 | =over 4 |
368 | |
369 | =item * PERLIO_K_BUFFERED |
370 | |
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371 | The layer is buffered. |
372 | |
373 | =item * PERLIO_K_RAW |
374 | |
375 | The layer is acceptable to have in a binmode(FH) stack - i.e. it does not |
376 | (or will configure itself not to) transform bytes passing through it. |
377 | |
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378 | =item * PERLIO_K_CANCRLF |
379 | |
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380 | Layer can translate between "\n" and CRLF line ends. |
381 | |
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382 | =item * PERLIO_K_FASTGETS |
383 | |
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384 | Layer allows buffer snooping. |
385 | |
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386 | =item * PERLIO_K_MULTIARG |
387 | |
388 | Used when the layer's open() accepts more arguments than usual. The |
389 | extra arguments should come not before the C<MODE> argument. When this |
390 | flag is used it's up to the layer to validate the args. |
391 | |
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392 | =back |
393 | |
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394 | =item Pushed |
395 | |
396 | IV (*Pushed)(pTHX_ PerlIO *f,const char *mode, SV *arg); |
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397 | |
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398 | The only absolutely mandatory method. Called when the layer is pushed |
399 | onto the stack. The C<mode> argument may be NULL if this occurs |
400 | post-open. The C<arg> will be non-C<NULL> if an argument string was |
401 | passed. In most cases this should call C<PerlIOBase_pushed()> to |
402 | convert C<mode> into the appropriate C<PERLIO_F_XXXXX> flags in |
403 | addition to any actions the layer itself takes. If a layer is not |
404 | expecting an argument it need neither save the one passed to it, nor |
405 | provide C<Getarg()> (it could perhaps C<Perl_warn> that the argument |
406 | was un-expected). |
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407 | |
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408 | Returns 0 on success. On failure returns -1 and should set errno. |
409 | |
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410 | =item Popped |
411 | |
412 | IV (*Popped)(pTHX_ PerlIO *f); |
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413 | |
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414 | Called when the layer is popped from the stack. A layer will normally |
415 | be popped after C<Close()> is called. But a layer can be popped |
416 | without being closed if the program is dynamically managing layers on |
417 | the stream. In such cases C<Popped()> should free any resources |
418 | (buffers, translation tables, ...) not held directly in the layer's |
419 | struct. It should also C<Unread()> any unconsumed data that has been |
420 | read and buffered from the layer below back to that layer, so that it |
421 | can be re-provided to what ever is now above. |
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422 | |
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423 | Returns 0 on success and failure. |
424 | |
5cb3728c |
425 | =item Open |
426 | |
427 | PerlIO * (*Open)(...); |
b76cc8ba |
428 | |
1d11c889 |
429 | The C<Open()> method has lots of arguments because it combines the |
430 | functions of perl's C<open>, C<PerlIO_open>, perl's C<sysopen>, |
431 | C<PerlIO_fdopen> and C<PerlIO_reopen>. The full prototype is as |
432 | follows: |
b76cc8ba |
433 | |
434 | PerlIO * (*Open)(pTHX_ PerlIO_funcs *tab, |
435 | AV *layers, IV n, |
436 | const char *mode, |
437 | int fd, int imode, int perm, |
438 | PerlIO *old, |
439 | int narg, SV **args); |
440 | |
1d11c889 |
441 | Open should (perhaps indirectly) call C<PerlIO_allocate()> to allocate |
442 | a slot in the table and associate it with the layers information for |
443 | the opened file, by calling C<PerlIO_push>. The I<layers> AV is an |
444 | array of all the layers destined for the C<PerlIO *>, and any |
445 | arguments passed to them, I<n> is the index into that array of the |
446 | layer being called. The macro C<PerlIOArg> will return a (possibly |
447 | C<NULL>) SV * for the argument passed to the layer. |
448 | |
449 | The I<mode> string is an "C<fopen()>-like" string which would match |
450 | the regular expression C</^[I#]?[rwa]\+?[bt]?$/>. |
451 | |
452 | The C<'I'> prefix is used during creation of C<stdin>..C<stderr> via |
453 | special C<PerlIO_fdopen> calls; the C<'#'> prefix means that this is |
454 | C<sysopen> and that I<imode> and I<perm> should be passed to |
455 | C<PerlLIO_open3>; C<'r'> means B<r>ead, C<'w'> means B<w>rite and |
456 | C<'a'> means B<a>ppend. The C<'+'> suffix means that both reading and |
a489db4d |
457 | writing/appending are permitted. The C<'b'> suffix means file should |
458 | be binary, and C<'t'> means it is text. (Almost all layers should do |
459 | the IO in binary mode, and ignore the b/t bits. The C<:crlf> layer |
460 | should be pushed to handle the distinction.) |
1d11c889 |
461 | |
462 | If I<old> is not C<NULL> then this is a C<PerlIO_reopen>. Perl itself |
463 | does not use this (yet?) and semantics are a little vague. |
464 | |
465 | If I<fd> not negative then it is the numeric file descriptor I<fd>, |
466 | which will be open in a manner compatible with the supplied mode |
467 | string, the call is thus equivalent to C<PerlIO_fdopen>. In this case |
468 | I<nargs> will be zero. |
469 | |
470 | If I<nargs> is greater than zero then it gives the number of arguments |
471 | passed to C<open>, otherwise it will be 1 if for example |
472 | C<PerlIO_open> was called. In simple cases SvPV_nolen(*args) is the |
473 | pathname to open. |
474 | |
475 | Having said all that translation-only layers do not need to provide |
476 | C<Open()> at all, but rather leave the opening to a lower level layer |
477 | and wait to be "pushed". If a layer does provide C<Open()> it should |
478 | normally call the C<Open()> method of next layer down (if any) and |
479 | then push itself on top if that succeeds. |
b76cc8ba |
480 | |
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481 | Returns C<NULL> on failure. |
482 | |
86e05cf2 |
483 | =item Binmode |
484 | |
485 | IV (*Binmode)(pTHX_ PerlIO *f); |
486 | |
487 | Optional. Used when C<:raw> layer is pushed (explicitly or as a result |
488 | of binmode(FH)). If not present layer will be popped. If present |
489 | should configure layer as binary (or pop itself) and return 0. |
490 | If it returns -1 for error C<binmode> will fail with layer |
491 | still on the stack. |
492 | |
5cb3728c |
493 | =item Getarg |
494 | |
495 | SV * (*Getarg)(pTHX_ PerlIO *f, |
496 | CLONE_PARAMS *param, int flags); |
b76cc8ba |
497 | |
d4165bde |
498 | Optional. If present should return an SV * representing the string |
499 | argument passed to the layer when it was |
500 | pushed. e.g. ":encoding(ascii)" would return an SvPV with value |
501 | "ascii". (I<param> and I<flags> arguments can be ignored in most |
502 | cases) |
b76cc8ba |
503 | |
5cb3728c |
504 | =item Fileno |
505 | |
506 | IV (*Fileno)(pTHX_ PerlIO *f); |
b76cc8ba |
507 | |
d1be9408 |
508 | Returns the Unix/Posix numeric file descriptor for the handle. Normally |
b76cc8ba |
509 | C<PerlIOBase_fileno()> (which just asks next layer down) will suffice |
510 | for this. |
50b80e25 |
511 | |
a489db4d |
512 | Returns -1 on error, which is considered to include the case where the |
513 | layer cannot provide such a file descriptor. |
d4165bde |
514 | |
5cb3728c |
515 | =item Dup |
516 | |
517 | PerlIO * (*Dup)(pTHX_ PerlIO *f, PerlIO *o, |
518 | CLONE_PARAMS *param, int flags); |
d4165bde |
519 | |
2dc2558e |
520 | XXX: Needs more docs. |
521 | |
a489db4d |
522 | Used as part of the "clone" process when a thread is spawned (in which |
523 | case param will be non-NULL) and when a stream is being duplicated via |
524 | '&' in the C<open>. |
d4165bde |
525 | |
526 | Similar to C<Open>, returns PerlIO* on success, C<NULL> on failure. |
527 | |
5cb3728c |
528 | =item Read |
529 | |
530 | SSize_t (*Read)(pTHX_ PerlIO *f, void *vbuf, Size_t count); |
d4165bde |
531 | |
532 | Basic read operation. |
50b80e25 |
533 | |
d4165bde |
534 | Typically will call C<Fill> and manipulate pointers (possibly via the |
535 | API). C<PerlIOBuf_read()> may be suitable for derived classes which |
536 | provide "fast gets" methods. |
50b80e25 |
537 | |
d4165bde |
538 | Returns actual bytes read, or -1 on an error. |
539 | |
5cb3728c |
540 | =item Unread |
541 | |
542 | SSize_t (*Unread)(pTHX_ PerlIO *f, |
543 | const void *vbuf, Size_t count); |
50b80e25 |
544 | |
9d799145 |
545 | A superset of stdio's C<ungetc()>. Should arrange for future reads to |
546 | see the bytes in C<vbuf>. If there is no obviously better implementation |
547 | then C<PerlIOBase_unread()> provides the function by pushing a "fake" |
548 | "pending" layer above the calling layer. |
50b80e25 |
549 | |
d4165bde |
550 | Returns the number of unread chars. |
551 | |
5cb3728c |
552 | =item Write |
553 | |
554 | SSize_t (*Write)(PerlIO *f, const void *vbuf, Size_t count); |
50b80e25 |
555 | |
d4165bde |
556 | Basic write operation. |
50b80e25 |
557 | |
d4165bde |
558 | Returns bytes written or -1 on an error. |
559 | |
5cb3728c |
560 | =item Seek |
561 | |
562 | IV (*Seek)(pTHX_ PerlIO *f, Off_t offset, int whence); |
50b80e25 |
563 | |
1d11c889 |
564 | Position the file pointer. Should normally call its own C<Flush> |
565 | method and then the C<Seek> method of next layer down. |
50b80e25 |
566 | |
d4165bde |
567 | Returns 0 on success, -1 on failure. |
568 | |
5cb3728c |
569 | =item Tell |
570 | |
571 | Off_t (*Tell)(pTHX_ PerlIO *f); |
50b80e25 |
572 | |
9d799145 |
573 | Return the file pointer. May be based on layers cached concept of |
574 | position to avoid overhead. |
50b80e25 |
575 | |
d4165bde |
576 | Returns -1 on failure to get the file pointer. |
577 | |
5cb3728c |
578 | =item Close |
579 | |
580 | IV (*Close)(pTHX_ PerlIO *f); |
50b80e25 |
581 | |
9d799145 |
582 | Close the stream. Should normally call C<PerlIOBase_close()> to flush |
583 | itself and close layers below, and then deallocate any data structures |
584 | (buffers, translation tables, ...) not held directly in the data |
585 | structure. |
50b80e25 |
586 | |
d4165bde |
587 | Returns 0 on success, -1 on failure. |
588 | |
5cb3728c |
589 | =item Flush |
590 | |
591 | IV (*Flush)(pTHX_ PerlIO *f); |
50b80e25 |
592 | |
9d799145 |
593 | Should make stream's state consistent with layers below. That is, any |
594 | buffered write data should be written, and file position of lower layers |
d1be9408 |
595 | adjusted for data read from below but not actually consumed. |
b76cc8ba |
596 | (Should perhaps C<Unread()> such data to the lower layer.) |
50b80e25 |
597 | |
d4165bde |
598 | Returns 0 on success, -1 on failure. |
599 | |
5cb3728c |
600 | =item Fill |
601 | |
602 | IV (*Fill)(pTHX_ PerlIO *f); |
d4165bde |
603 | |
604 | The buffer for this layer should be filled (for read) from layer |
605 | below. When you "subclass" PerlIOBuf layer, you want to use its |
606 | I<_read> method and to supply your own fill method, which fills the |
607 | PerlIOBuf's buffer. |
50b80e25 |
608 | |
d4165bde |
609 | Returns 0 on success, -1 on failure. |
50b80e25 |
610 | |
5cb3728c |
611 | =item Eof |
612 | |
613 | IV (*Eof)(pTHX_ PerlIO *f); |
50b80e25 |
614 | |
9d799145 |
615 | Return end-of-file indicator. C<PerlIOBase_eof()> is normally sufficient. |
50b80e25 |
616 | |
d4165bde |
617 | Returns 0 on end-of-file, 1 if not end-of-file, -1 on error. |
618 | |
5cb3728c |
619 | =item Error |
620 | |
621 | IV (*Error)(pTHX_ PerlIO *f); |
50b80e25 |
622 | |
9d799145 |
623 | Return error indicator. C<PerlIOBase_error()> is normally sufficient. |
50b80e25 |
624 | |
d4165bde |
625 | Returns 1 if there is an error (usually when C<PERLIO_F_ERROR> is set, |
626 | 0 otherwise. |
627 | |
5cb3728c |
628 | =item Clearerr |
629 | |
630 | void (*Clearerr)(pTHX_ PerlIO *f); |
50b80e25 |
631 | |
9d799145 |
632 | Clear end-of-file and error indicators. Should call C<PerlIOBase_clearerr()> |
633 | to set the C<PERLIO_F_XXXXX> flags, which may suffice. |
50b80e25 |
634 | |
5cb3728c |
635 | =item Setlinebuf |
636 | |
637 | void (*Setlinebuf)(pTHX_ PerlIO *f); |
50b80e25 |
638 | |
b76cc8ba |
639 | Mark the stream as line buffered. C<PerlIOBase_setlinebuf()> sets the |
640 | PERLIO_F_LINEBUF flag and is normally sufficient. |
50b80e25 |
641 | |
5cb3728c |
642 | =item Get_base |
643 | |
644 | STDCHAR * (*Get_base)(pTHX_ PerlIO *f); |
50b80e25 |
645 | |
646 | Allocate (if not already done so) the read buffer for this layer and |
d4165bde |
647 | return pointer to it. Return NULL on failure. |
50b80e25 |
648 | |
5cb3728c |
649 | =item Get_bufsiz |
650 | |
651 | Size_t (*Get_bufsiz)(pTHX_ PerlIO *f); |
50b80e25 |
652 | |
9d799145 |
653 | Return the number of bytes that last C<Fill()> put in the buffer. |
50b80e25 |
654 | |
5cb3728c |
655 | =item Get_ptr |
656 | |
657 | STDCHAR * (*Get_ptr)(pTHX_ PerlIO *f); |
50b80e25 |
658 | |
3039a93d |
659 | Return the current read pointer relative to this layer's buffer. |
50b80e25 |
660 | |
5cb3728c |
661 | =item Get_cnt |
662 | |
663 | SSize_t (*Get_cnt)(pTHX_ PerlIO *f); |
50b80e25 |
664 | |
665 | Return the number of bytes left to be read in the current buffer. |
666 | |
5cb3728c |
667 | =item Set_ptrcnt |
668 | |
669 | void (*Set_ptrcnt)(pTHX_ PerlIO *f, |
670 | STDCHAR *ptr, SSize_t cnt); |
50b80e25 |
671 | |
672 | Adjust the read pointer and count of bytes to match C<ptr> and/or C<cnt>. |
673 | The application (or layer above) must ensure they are consistent. |
674 | (Checking is allowed by the paranoid.) |
675 | |
676 | =back |
677 | |
678 | |
679 | =head2 Core Layers |
680 | |
681 | The file C<perlio.c> provides the following layers: |
682 | |
683 | =over 4 |
684 | |
685 | =item "unix" |
686 | |
9d799145 |
687 | A basic non-buffered layer which calls Unix/POSIX C<read()>, C<write()>, |
688 | C<lseek()>, C<close()>. No buffering. Even on platforms that distinguish |
689 | between O_TEXT and O_BINARY this layer is always O_BINARY. |
50b80e25 |
690 | |
691 | =item "perlio" |
692 | |
9d799145 |
693 | A very complete generic buffering layer which provides the whole of |
694 | PerlIO API. It is also intended to be used as a "base class" for other |
1d11c889 |
695 | layers. (For example its C<Read()> method is implemented in terms of |
696 | the C<Get_cnt()>/C<Get_ptr()>/C<Set_ptrcnt()> methods). |
50b80e25 |
697 | |
9d799145 |
698 | "perlio" over "unix" provides a complete replacement for stdio as seen |
699 | via PerlIO API. This is the default for USE_PERLIO when system's stdio |
1d11c889 |
700 | does not permit perl's "fast gets" access, and which do not |
701 | distinguish between C<O_TEXT> and C<O_BINARY>. |
50b80e25 |
702 | |
703 | =item "stdio" |
704 | |
9d799145 |
705 | A layer which provides the PerlIO API via the layer scheme, but |
706 | implements it by calling system's stdio. This is (currently) the default |
707 | if system's stdio provides sufficient access to allow perl's "fast gets" |
708 | access and which do not distinguish between C<O_TEXT> and C<O_BINARY>. |
50b80e25 |
709 | |
710 | =item "crlf" |
711 | |
9d799145 |
712 | A layer derived using "perlio" as a base class. It provides Win32-like |
713 | "\n" to CR,LF translation. Can either be applied above "perlio" or serve |
714 | as the buffer layer itself. "crlf" over "unix" is the default if system |
715 | distinguishes between C<O_TEXT> and C<O_BINARY> opens. (At some point |
716 | "unix" will be replaced by a "native" Win32 IO layer on that platform, |
717 | as Win32's read/write layer has various drawbacks.) The "crlf" layer is |
718 | a reasonable model for a layer which transforms data in some way. |
50b80e25 |
719 | |
720 | =item "mmap" |
721 | |
9d799145 |
722 | If Configure detects C<mmap()> functions this layer is provided (with |
723 | "perlio" as a "base") which does "read" operations by mmap()ing the |
724 | file. Performance improvement is marginal on modern systems, so it is |
725 | mainly there as a proof of concept. It is likely to be unbundled from |
726 | the core at some point. The "mmap" layer is a reasonable model for a |
727 | minimalist "derived" layer. |
50b80e25 |
728 | |
729 | =item "pending" |
730 | |
9d799145 |
731 | An "internal" derivative of "perlio" which can be used to provide |
1d11c889 |
732 | Unread() function for layers which have no buffer or cannot be |
733 | bothered. (Basically this layer's C<Fill()> pops itself off the stack |
734 | and so resumes reading from layer below.) |
50b80e25 |
735 | |
736 | =item "raw" |
737 | |
9d799145 |
738 | A dummy layer which never exists on the layer stack. Instead when |
86e05cf2 |
739 | "pushed" it actually pops the stack removing itself, it then calls |
740 | Binmode function table entry on all the layers in the stack - normally |
741 | this (via PerlIOBase_binmode) removes any layers which do not have |
742 | C<PERLIO_K_RAW> bit set. Layers can modify that behaviour by defining |
743 | their own Binmode entry. |
50b80e25 |
744 | |
745 | =item "utf8" |
746 | |
9d799145 |
747 | Another dummy layer. When pushed it pops itself and sets the |
1d11c889 |
748 | C<PERLIO_F_UTF8> flag on the layer which was (and now is once more) |
749 | the top of the stack. |
50b80e25 |
750 | |
751 | =back |
752 | |
9d799145 |
753 | In addition F<perlio.c> also provides a number of C<PerlIOBase_xxxx()> |
754 | functions which are intended to be used in the table slots of classes |
755 | which do not need to do anything special for a particular method. |
50b80e25 |
756 | |
757 | =head2 Extension Layers |
758 | |
1d11c889 |
759 | Layers can made available by extension modules. When an unknown layer |
760 | is encountered the PerlIO code will perform the equivalent of : |
b76cc8ba |
761 | |
762 | use PerlIO 'layer'; |
763 | |
1d11c889 |
764 | Where I<layer> is the unknown layer. F<PerlIO.pm> will then attempt to: |
b76cc8ba |
765 | |
766 | require PerlIO::layer; |
767 | |
1d11c889 |
768 | If after that process the layer is still not defined then the C<open> |
769 | will fail. |
b76cc8ba |
770 | |
771 | The following extension layers are bundled with perl: |
50b80e25 |
772 | |
773 | =over 4 |
774 | |
b76cc8ba |
775 | =item ":encoding" |
50b80e25 |
776 | |
777 | use Encoding; |
778 | |
1d11c889 |
779 | makes this layer available, although F<PerlIO.pm> "knows" where to |
780 | find it. It is an example of a layer which takes an argument as it is |
781 | called thus: |
50b80e25 |
782 | |
b31b80f9 |
783 | open( $fh, "<:encoding(iso-8859-7)", $pathname ); |
50b80e25 |
784 | |
385e1f9f |
785 | =item ":scalar" |
b76cc8ba |
786 | |
b31b80f9 |
787 | Provides support for reading data from and writing data to a scalar. |
b76cc8ba |
788 | |
385e1f9f |
789 | open( $fh, "+<:scalar", \$scalar ); |
50b80e25 |
790 | |
1d11c889 |
791 | When a handle is so opened, then reads get bytes from the string value |
792 | of I<$scalar>, and writes change the value. In both cases the position |
793 | in I<$scalar> starts as zero but can be altered via C<seek>, and |
794 | determined via C<tell>. |
b76cc8ba |
795 | |
385e1f9f |
796 | Please note that this layer is implied when calling open() thus: |
797 | |
798 | open( $fh, "+<", \$scalar ); |
799 | |
800 | =item ":via" |
b76cc8ba |
801 | |
4f7853f4 |
802 | Provided to allow layers to be implemented as Perl code. For instance: |
803 | |
e934609f |
804 | use PerlIO::via::StripHTML; |
385e1f9f |
805 | open( my $fh, "<:via(StripHTML)", "index.html" ); |
4f7853f4 |
806 | |
e934609f |
807 | See L<PerlIO::via> for details. |
b76cc8ba |
808 | |
809 | =back |
50b80e25 |
810 | |
d4165bde |
811 | =head1 TODO |
812 | |
813 | Things that need to be done to improve this document. |
814 | |
815 | =over |
816 | |
817 | =item * |
818 | |
819 | Explain how to make a valid fh without going through open()(i.e. apply |
820 | a layer). For example if the file is not opened through perl, but we |
821 | want to get back a fh, like it was opened by Perl. |
822 | |
823 | How PerlIO_apply_layera fits in, where its docs, was it made public? |
824 | |
825 | Currently the example could be something like this: |
826 | |
827 | PerlIO *foo_to_PerlIO(pTHX_ char *mode, ...) |
828 | { |
829 | char *mode; /* "w", "r", etc */ |
830 | const char *layers = ":APR"; /* the layer name */ |
831 | PerlIO *f = PerlIO_allocate(aTHX); |
832 | if (!f) { |
833 | return NULL; |
834 | } |
835 | |
836 | PerlIO_apply_layers(aTHX_ f, mode, layers); |
837 | |
838 | if (f) { |
839 | PerlIOAPR *st = PerlIOSelf(f, PerlIOAPR); |
840 | /* fill in the st struct, as in _open() */ |
841 | st->file = file; |
842 | PerlIOBase(f)->flags |= PERLIO_F_OPEN; |
843 | |
844 | return f; |
845 | } |
846 | return NULL; |
847 | } |
848 | |
849 | =item * |
850 | |
851 | fix/add the documentation in places marked as XXX. |
852 | |
853 | =item * |
854 | |
855 | The handling of errors by the layer is not specified. e.g. when $! |
856 | should be set explicitly, when the error handling should be just |
857 | delegated to the top layer. |
858 | |
859 | Probably give some hints on using SETERRNO() or pointers to where they |
860 | can be found. |
861 | |
862 | =item * |
863 | |
864 | I think it would help to give some concrete examples to make it easier |
865 | to understand the API. Of course I agree that the API has to be |
866 | concise, but since there is no second document that is more of a |
867 | guide, I think that it'd make it easier to start with the doc which is |
868 | an API, but has examples in it in places where things are unclear, to |
869 | a person who is not a PerlIO guru (yet). |
870 | |
871 | =back |
872 | |
50b80e25 |
873 | =cut |