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code/trunk/maintain/README revision 111 by ph10, Thu Mar 8 16:53:09 2007 UTC code/trunk/maint/README revision 454 by ph10, Tue Sep 22 09:42:11 2009 UTC
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1  The files in the "maintain" directory of the PCRE source contain data, scripts,  MAINTENANCE README FOR PCRE
2  and programs that are used for the maintenance of PCRE, but do not form part of  ---------------------------
3  the PCRE distribution tarballs.  
4    The files in the "maint" directory of the PCRE source contain data, scripts,
5  Builducptable   A Perl script that creates the contents of the ucptable.h file  and programs that are used for the maintenance of PCRE, but which do not form
6                  from two Unicode data files, which themselves are downloaded  part of the PCRE distribution tarballs. This document describes these files and
7                  from the Unicode web site. Run this script in the "maintain"  also contains some notes for maintainers. Its contents are:
8                  directory.  
9      Files in the maint directory
10  Tech.Notes      Some notes about the internals of the PCRE code.    Updating to a new Unicode release
11      Preparing for a PCRE release
12  Unicode.tables  The files in this directory, Scripts.txt and UnicodeData.txt,    Making a PCRE release
13                  were downloaded from the Unicode web site. They contain    Long-term ideas (wish list)
14                  information about Unicode characters and scripts.  
15    
16  ucptest.c       A short C program for testing the Unicode property functions in  Files in the maint directory
17                  pcre_ucp_searchfuncs.c, mainly useful after rebuilding the  ----------------------------
18                  Unicode property table. Compile and run this in the "maintain"  
19                  directory.  ----------------- This file is now OBSOLETE and no longer used ----------------
20    Builducptable    A Perl script that creates the contents of the ucptable.h file
21  ucptestdata     A directory containing two files, testinput1 and testoutput1,                   from two Unicode data files, which themselves are downloaded
22                  to use in conjunction with the ucptest program.                   from the Unicode web site. Run this script in the "maint"
23                     directory.
24  utf8.c          A short, freestanding C program for converting a Unicode code  ----------------- This file is now OBSOLETE and no longer used ----------------
25                  point into a sequence of bytes in the UTF-8 encoding, and vice  
26                  versa. If its argument is a hex number such as 0x1234, it  GenerateUtt.py   A Python script to generate part of the pcre_tables.c file
27                  outputs a list of the equivalent UTF-8 bytes. If its argument                   that contains Unicode script names in a long string with
28                  is sequence of concatenated UTF-8 bytes (e.g. e188b4) it treats                   offsets, which is tedious to maintain by hand.
29                  them as a UTF-8 character and outputs the equivalent code point  
30                  in hex.  ManyConfigTests  A shell script that runs "configure, make, test" a number of
31                     times with different configuration settings.
32  When there is a new release of Unicode, the files in Unicode.tables must be  
33  refreshed from the web site, and the Buildupctable script can then be run to  MultiStage2.py   A Python script that generates the file pcre_ucd.c from three
34  generate a new version of ucptable.h. The ucptest program can be used to check                   Unicode data tables, which are themselves downloaded from the
35  that the resulting table works properly, using the data files in ucptestdata to                   Unicode web site. Run this script in the "maint" directory.
36  check a number of test characters.                   The generated file contains the tables for a 2-stage lookup
37                     of Unicode properties.
38  ****  
39    README           This file.
40    
41    Unicode.tables   The files in this directory, DerivedGeneralCategory.txt,
42                     Scripts.txt and UnicodeData.txt, were downloaded from the
43                     Unicode web site. They contain information about Unicode
44                     characters and scripts.
45    
46    ucptest.c        A short C program for testing the Unicode property macros
47                     that do lookups in the pcre_ucd.c data, mainly useful after
48                     rebuilding the Unicode property table. Compile and run this in
49                     the "maint" directory (see comments at its head).
50    
51    ucptestdata      A directory containing two files, testinput1 and testoutput1,
52                     to use in conjunction with the ucptest program.
53    
54    utf8.c           A short, freestanding C program for converting a Unicode code
55                     point into a sequence of bytes in the UTF-8 encoding, and vice
56                     versa. If its argument is a hex number such as 0x1234, it
57                     outputs a list of the equivalent UTF-8 bytes. If its argument
58                     is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
59                     treats them as a UTF-8 character and outputs the equivalent
60                     code point in hex.
61    
62    
63    Updating to a new Unicode release
64    ---------------------------------
65    
66    When there is a new release of Unicode, the files in Unicode.tables must be
67    refreshed from the web site. If the new version of Unicode adds new character
68    scripts, the source file ucp.h and both the MultiStage2.py and the
69    GenerateUtt.py scripts must be edited to add the new names. Then MultiStage2.py
70    can be run to generate a new version of pcre_ucd.c, and GenerateUtt.py can be
71    run to generate the tricky tables for inclusion in pcre_tables.c.
72    
73    The ucptest program can be compiled and used to check that the new tables in
74    pcre_ucd.c work properly, using the data files in ucptestdata to check a number
75    of test characters.
76    
77    
78    Preparing for a PCRE release
79    ----------------------------
80    
81    This section contains a checklist of things that I consult before building a
82    distribution for a new release.
83    
84    . Ensure that the version number and version date are correct in configure.ac.
85    
86    . If new build options have been added, ensure that they are added to the CMake
87      files as well as to the autoconf files.
88    
89    . Run ./autogen.sh to ensure everything is up-to-date.
90    
91    . Compile and test with many different config options, and combinations of
92      options. The maint/ManyConfigTests script now encapsulates this testing.
93    
94    . Run perltest.pl on the test data for tests 1, 4, 6, and 11. The first two can
95      be run with Perl 5.8 or 5.10; the last two require Perl 5.10. The output
96      should match the PCRE test output, apart from the version identification at
97      the start of each test. The other tests are not Perl-compatible (they use
98      various PCRE-specific features or options).
99    
100    . Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
101      valgrind", though that takes quite a long time.
102    
103    . It may also useful to test with Electric Fence, though the fact that it
104      grumbles for missing free() calls can be a nuisance. (A missing free() in
105      pcretest is hardly a big problem.) To build with EF, use:
106    
107        LIBS='/usr/lib/libefence.a -lpthread' with ./configure.
108    
109      Then all normal runs use it to check for buffer overflow. Also run everything
110      with:
111    
112        EF_PROTECT_BELOW=1 <whatever>
113    
114      because there have been problems with lookbehinds that looked too far.
115    
116    . Test with the emulated memmove() function by undefining HAVE_MEMMOVE and
117      HAVE_BCOPY in config.h. You may see a number of "pcre_memmove defined but not
118      used" warnings for the modules in which there is no call to memmove(). These
119      can be ignored.
120    
121    . Documentation: check AUTHORS, COPYING, ChangeLog (check version and date),
122      INSTALL, LICENCE, NEWS (check version and date), NON-UNIX-USE, and README.
123      Many of these won't need changing, but over the long term things do change.
124    
125    . Man pages: Check all man pages for \ not followed by e or f or " because
126      that indicates a markup error.
127    
128    . When the release is built, test it on a number of different operating
129      systems if possible, and using different compilers as well. For example,
130      on Solaris it is helpful to test using Sun's cc compiler as a change from
131      gcc. Adding -xarch=v9 to the cc options does a 64-bit test, but it also
132      needs -S 64 for pcretest to increase the stack size for test 2.
133    
134    
135    Making a PCRE release
136    ---------------------
137    
138    Run PrepareRelease and commit the files that it changes (by removing trailing
139    spaces). Then run "make distcheck" to create the tarballs and the zipball.
140    Double-check with "svn status", then create an SVN tagged copy:
141    
142      svn copy svn://vcs.exim.org/pcre/code/trunk \
143               svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
144    
145    Don't forget to update Freshmeat when the new release is out, and to tell
146    webmaster@pcre.org and the mailing list.
147    
148    
149    Future ideas (wish list)
150    ------------------------
151    
152    This section records a list of ideas so that they do not get forgotten. They
153    vary enormously in their usefulness and potential for implementation. Some are
154    very sensible; some are rather wacky. Some have been on this list for years;
155    others are relatively new.
156    
157    . Optimization
158    
159      There are always ideas for new optimizations so as to speed up pattern
160      matching. Most of them try to save work by recognizing a non-match without
161      having to scan all the possibilities. These are some that I've recorded:
162    
163      * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
164        slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
165        OTOH, this is pathological - the user could easily fix it.
166    
167      * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
168        to have little effect, and maybe makes things worse.
169    
170      * "Ends with literal string" - note that a single character doesn't gain much
171        over the existing "required byte" (reqbyte) feature that just remembers one
172        byte.
173    
174      * These probably need to go in study():
175    
176        o Remember an initial string rather than just 1 char?
177    
178        o A required byte from alternatives - not just the last char, but an
179          earlier one if common to all alternatives.
180    
181        o Minimum length of subject needed (see also next . bullet).
182    
183        o Friedl contains other ideas.
184    
185    . There was a request for a way of finding the minimum subject length that can
186      match a given pattern. (If this were available, it could be usefully added
187      to study() - see above.) This is easy for simple cases, but I haven't figured
188      out how to handle recursion.
189    
190    . If Perl gets to a consistent state over the settings of capturing sub-
191      patterns inside repeats, see if we can match it. One example of the
192      difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
193      leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
194      because I think it needs much more state to be remembered.
195    
196    . Perl 6 will be a revolution. Is it a revolution too far for PCRE?
197    
198    . Unicode
199    
200      * Note that in Perl, \s matches \pZ and similarly for \d, \w and the POSIX
201        character classes. For the moment, I've chosen not to support this for
202        backward compatibility, for speed, and because it would be messy to
203        implement.
204    
205      * A different approach to Unicode might be to use a typedef to do everything
206        in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
207        new typedef to distinguish data from bits of compiled pattern that are in
208        bytes, I think. There would need to be conversion functions in and out. I
209        don't think this is particularly trivial - and anyway, Unicode now has
210        characters that need more than 16 bits, so is this at all sensible?
211    
212      * There has been a request for direct support of 16-bit characters and
213        UTF-16. However, since Unicode is moving beyond purely 16-bit characters,
214        is this worth it at all? One possible way of handling 16-bit characters
215        would be to "load" them in the same way that UTF-8 characters are loaded.
216    
217    . Allow errorptr and erroroffset to be NULL. I don't like this idea.
218    
219    . Line endings:
220    
221      * Option to use NUL as a line terminator in subject strings. This could now
222        be done relatively easily since the extension to support LF, CR, and CRLF.
223        If it is done, a suitable option for pcregrep is also required.
224    
225    . Option to provide the pattern with a length instead of with a NUL terminator.
226      This affects quite a few places in the code and is not trivial.
227    
228    . Catch SIGSEGV for stack overflows?
229    
230    . A feature to suspend a match via a callout was once requested.
231    
232    . Option to convert results into character offsets and character lengths.
233    
234    . Option for pcregrep to scan only the start of a file. I am not keen - this is
235      the job of "head".
236    
237    . A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
238      preceded by a blank line, instead of adding it to every matched line, and (b)
239      support --outputfile=name.
240    
241    . Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
242    
243    . Add a user pointer to pcre_malloc/free functions -- some option would be
244      needed to retain backward compatibility.
245    
246    . Define a union for the results from pcre_fullinfo().
247    
248    . Provide a "random access to the subject" facility so that the way in which it
249      is stored is independent of PCRE. For efficiency, it probably isn't possible
250      to switch this dynamically. It would have to be specified when PCRE was
251      compiled. PCRE would then call a function every time it wanted a character.
252    
253    . Wild thought: the ability to compile from PCRE's internal byte code to a real
254      FSM and a very fast (third) matcher to process the result. There would be
255      even more restrictions than for pcre_dfa_exec(), however. This is not easy.
256    
257    . Should pcretest have some private locale data, to avoid relying on the
258      available locales for the test data, since different OS have different ideas?
259      This won't be as thorough a test, but perhaps that doesn't really matter.
260    
261    . pcregrep: add -rs for a sorted recurse? Having to store file names and sort
262      them will of course slow it down.
263    
264    . Someone suggested --disable-callout to save code space when callouts are
265      never wanted. This seems rather marginal.
266    
267    . Check names that consist entirely of digits: PCRE allows, but do Perl and
268      Python, etc?
269    
270    . A user suggested a parameter to limit the length of string matched, for
271      example if the parameter is N, the current match should fail if the matched
272      substring exceeds N. This could apply to both match functions. The value
273      could be a new field in the extra block.
274    
275    . Callouts with arguments: (?Cn:ARG) for instance.
276    
277    . A user is going to supply a patch to generalize the API for user-specific
278      memory allocation so that it is more flexible in threaded environments. Thiw
279      was promised a long time ago, and never appeared...
280    
281    . Write a function that generates random matching strings for a compiled regex.
282    
283    . Write a wrapper to maintain a structure with specified runtime parameters,
284      such as recurse limit, and pass these to PCRE each time it is called. Also
285      maybe malloc and free. A user sent a prototype.
286    
287    . Pcregrep: an option to specify the output line separator, either as a string
288      or select from a fixed list. This is not dead easy, because at the moment it
289      outputs whatever is in the input file.
290    
291    . Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
292      non-thread-safe patch showed that this can help performance for patterns
293      where there are many alternatives. However, a simple thread-safe
294      implementation that I tried made things worse in many simple cases, so this
295      is not an obviously good thing.
296    
297    . Make the longest lookbehind available via pcre_fullinfo(). This is not
298      straightforward because lookbehinds can be nested inside lookbehinds. This
299      case will have to be identified, and the amounts added. This should then give
300      the maximum possible lookbehind length. The reason for wanting this is to
301      help when implementing multi-segment matching using pcre_exec() with partial
302      matching and overlapping segments.
303    
304    . PCRE cannot at present distinguish between subpatterns with different names,
305      but the same number (created by the use of ?|). In order to do so, a way of
306      remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
307    
308    Philip Hazel
309    Email local part: ph10
310    Email domain: cam.ac.uk
311    Last updated: 20 September 2009

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