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view ch03.roff @ 96:12348d620245
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| author | markus schnalke <meillo@marmaro.de> |
|---|---|
| date | Sat, 16 Jun 2012 13:31:25 +0200 |
| parents | edac7e46a9f2 |
| children | 29a7454fcded |
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1 .H0 "Discussion
2 .P
3 This main chapter discusses the practical work done in the mmh project.
4 It is structured along the goals to achieve. The concrete work done
5 is described in the examples of how the general goals were achieved.
6 The discussion compares the current version of mmh with the state of
7 nmh just before the mmh project started, i.e. Fall 2011.
8 Current changes of nmh will be mentioned only as side notes.
9 .\" XXX where do I discuss the parallel development of nmh?
13 .H1 "Stream-lining
15 .P
16 MH had been considered an all-in-one system for mail handling.
17 The community around nmh has a similar understanding.
18 In fundamental difference, mmh shall be a MUA only.
19 I believe that the development of all-in-one mail systems is obsolete.
20 Today, email is too complex to be fully covered by single projects.
21 Such a project won't be able to excel in all aspects.
22 Instead, the aspects of email should be covered my multiple projects,
23 which then can be combined to form a complete system.
24 Excellent implementations for the various aspects of email exist already.
25 Just to name three examples: Postfix is a specialized MTA,
26 Procmail is a specialized MDA, and Fetchmail is a specialized MRA.
27 I believe that it is best to use such specialized tools instead of
28 providing the same function again as a side-component in the project.
29 .P
30 Doing something well, requires to focus on a small set of specific aspects.
31 Under the assumption that focused development produces better results
32 in the particular area, specialized projects will likely be superior
33 in their field of focus.
34 Hence, all-in-one mail system projects \(en no matter if monolithic
35 or modular \(en will never be the best choice in any of the fields.
36 Even in providing the best consistent all-in-one system they are likely
37 to be beaten by projects that focus only on integrating existing mail
38 components to a homogeneous system.
39 .P
40 The limiting resource in Free Software community development
41 is usually man power.
42 If the development power is spread over a large development area,
43 it becomes even more difficult to compete with the specialists in the
44 various fields.
45 The concrete situation for MH-based mail systems is even tougher,
46 given the small and aged community, including both developers and users,
47 it has.
48 .P
49 In consequence, I believe that the available development resources
50 should be focused on the point where MH is most unique.
51 This is clearly the user interface \(en the MUA.
52 Peripheral parts should be removed to stream-line mmh for the MUA task.
55 .H2 "Removal of the Mail Transfer Facilities
56 .P
57 In contrast to nmh, which also provides mail submission and mail retrieval
58 agents, mmh is a MUA only.
59 This general difference in the view on the character of nmh
60 initiated the development of mmh.
61 Removing the mail transfer facilities had been the first work task
62 in the mmh project.
63 .P
64 The MSA is called \fIMessage Transfer Service\fP (MTS) in nmh.
65 The facility established network connections and spoke SMTP to submit
66 messages for relay to the outside world.
67 This part was implemented by the
68 .Pn post
69 command.
70 The changes in email in the last years
71 demanded changes in this part of nmh too.
72 Encryption and authentication for network connections
73 needed to be supported, hence TLS and SASL were introduced into nmh.
74 This added complexity to nmh without improving it in its core functions.
75 Also, keeping up with recent developments in the field of
76 mail transfer requires development power and specialists.
77 In mmh this whole facility was simply cut off.
78 .Ci f6aa95b724fd8c791164abe7ee5468bf5c34f226
79 .Ci fecd5d34f65597a4dfa16aeabea7d74b191532c3
80 .Ci 156d35f6425bea4c1ed3c4c79783dc613379c65b
81 Instead, mmh depends on an external MSA.
82 The only outgoing interface available to mmh is the
83 .Pn sendmail
84 command, which almost any MSA provides.
85 If not, a wrapper program can be written.
86 It must read the message from the standard input, extract the
87 recipient addresses from the message header, and hand the message
88 over to the MSA.
89 For example, a wrapper script for qmail would be:
90 .VS
91 #!/bin/sh
92 # ignore command line arguments
93 exec qmail-inject
94 VE
95 The requirement to parse the recipient addresses out of the message header
96 is likely to be removed in the future.
97 Then mmh would give the recipient addresses as command line arguments.
98 This is clearly the better interface, but mmh does not provide it yet.
99 .\" XXX implement it
100 .P
101 To retrieve mail, the
102 .Pn inc
103 command established network connections
104 and spoke POP3 to retrieve mail from remote servers.
105 As with mail submission, the network connections required encryption and
106 authentication, thus TLS and SASL were added.
107 Support for message retrieval through IMAP will become necessary
108 to be added soon, too, and so on for any changes in mail transfer.
109 Mmh has dropped the support for retrieving mail from remote locations.
110 .Ci ab7b48411962d26439f92f35ed084d3d6275459c
111 Instead, it depends on an external tool to cover this task.
112 In mmh there exist two paths for messages to enter mmh's mail storage:
113 (1) Mail can be incorporate with
114 .Pn inc
115 from the system maildrop, or (2) with
116 .Pn rcvstore
117 by reading them, one at a time, from the standard input.
118 .P
119 With the removal of the MSA and MRA, mmh converted from an all-in-one
120 mail system to being a MUA only.
121 Following the Unix philosophy, it now focuses on one job and
122 tries to do that one well.
123 Not only the programs follow that tenet but also the project itself does so.
124 Now, of course, mmh depends on third-party software.
125 An external MSA is required to transfer mail to the outside world;
126 an external MRA is required to retrieve mail from remote machines.
127 There exist excellent implementations of such software,
128 which do this specific task likely better than the internal
129 versions had done it.
130 Also, the best suiting programs can be freely chosen.
131 .P
132 As it had already been possible to use an external MSA or MRA,
133 why not keep the internal version for convenience?
134 The question whether there is sense in having a fall-back pager in all
135 the command line tools, for the cases when
136 .Pn more
137 or
138 .Pn less
139 aren't available, appears to be ridiculous.
140 Now, an MSA or MRA is more complex than a text pager
141 and not necessarily available but still the concept of orthogonal
142 design holds: ``Write programs that do one thing and do it well.''
143 .[
144 mcilroy unix phil
145 p. 53
146 .]
147 .[
148 mcilroy bstj foreword
149 .]
150 Here, this part of the Unix philosophy was applied not only
151 to the programs but to the project itself.
152 In other words:
153 ``Develop projects that focus on one thing and do it well.''
154 Projects grown complex should be split for the same reasons programs grown
155 complex should be split.
156 If it is conceptionally more elegant to have the MSA and MRA
157 separate projects then they should be separated.
158 This is the case here, in my opinion.
159 The RFCs propose this separation by clearly distinguishing the different
160 mail handling tasks.
161 .[
162 rfc 821
163 .]
164 The small interfaces between the mail agents support the separation.
165 .P
166 In the beginning, email had been small and simple.
167 (\c
168 .Pn /bin/mail
169 had once covered anything there was to email and still had been small
170 and simple.)
171 Then the essential complexity of email increased.
172 (Essential complexity is the complexity defined by the problem itself.\0
173 .[[
174 brooks no silver bullet
175 .]])
176 Email systems reacted to this change: They grew.
177 RFCs started to introduce mail agents and separated the various tasks
178 because the existing tasks became more extensive and new tasks appeared.
179 Again, email systems grew, or they split parts off.
180 In nmh, for instance, the POP server, which the original MH had included,
181 was removed.
182 Now is the time to go one step further and remove the MSA and MRA, too.
183 Not only does this decrease the code size of the project,
184 but, more important, it unburdens mmh of the whole field of
185 message transfer with all its implications for the project.
186 There's no more need to concern with changes in network transfer.
187 This independence is received by depending on an external program
188 that covers the field.
189 Today, this is a reasonable exchange.
190 .P
191 Function can be added in three different ways:
192 .BU
193 Implementing the function originally in the project.
194 .BU
195 Depending on a library that provides the function.
196 .BU
197 Depending on a program that provides the function.
198 .P
199 Whereas adding the function originally to the project increases the
200 code size most and requires most maintenance and development work,
201 it makes the project most independent of other software.
202 Using libraries or external programs require less maintenance work
203 but introduces dependencies on external software.
204 Programs have the smallest interfaces and provide the best separation
205 but possibly limit the information exchange.
206 External libraries are stronger connected than external programs,
207 thus information can be exchanged more flexible.
208 Adding code to a project increases maintenance work.
209 .\" XXX ref
210 Implementing complex functions originally in the project will add
211 a lot of code.
212 This should be avoided if possible.
213 Hence, the dependencies only change in kind, not in their existence.
214 In mmh, library dependencies on
215 .Pn libsasl2
216 and
217 .Pn libcrypto /\c
218 .Pn libssl
219 were treated against program dependencies on an MSA and an MRA.
220 This also meant treating build-time dependencies against run-time
221 dependencies.
222 Besides program dependencies providing the stronger separation
223 and being more flexible, they also allowed
224 over 6\|000 lines of code to be removed from mmh.
225 This made mmh's code base about 12\|% smaller.
226 Reducing the project's code size by such an amount without actually
227 losing functionality is a convincing argument.
228 Actually, as external MSAs and MRAs are likely superior to the
229 project's internal versions, the common user even gains functionality.
230 .P
231 Users of MH should not have problems to set up an external MSA and MRA.
232 Also, the popular MSAs and MRAs have large communities and a lot
233 of documentation available.
234 Choices for MSAs range from full-featured MTAs like
235 .I Postfix
236 over mid-size MTAs like
237 .I masqmail
238 and
239 .I dma
240 to small forwarders like
241 .I ssmtp
242 and
243 .I nullmailer .
244 Choices for MRAs include
245 .I fetchmail ,
246 .I getmail ,
247 .I mpop
248 and
249 .I fdm .
252 .H2 "Removal of non-MUA Tools
253 .P
254 One goal of mmh is to remove the tools that are not part of the MUA's task.
255 Further more, any tools that don't improve the MUA's job significantly
256 should be removed.
257 Loosely related and rarely used tools distract from the lean appearance.
258 They require maintenance work without adding much to the core task.
259 On removing these tools, the project shall become more stream-lined
260 and focused.
261 In mmh the following tools are not available anymore:
262 .BU
263 .Pn conflict
264 was removed
265 .Ci 8b235097cbd11d728c07b966cf131aa7133ce5a9
266 because it is a mail system maintenance tool that is not MUA-related.
267 It even checked
268 .Fn /etc/passwd
269 and
270 .Fn /etc/group
271 for consistency, which is completely unrelated to email.
272 A tool like
273 .Pn conflict
274 is surely useful, but it should not be shipped with mmh.
275 .\" XXX historic reasons?
276 .BU
277 .Pn rcvtty
278 was removed
279 .Ci 14767c94b3827be7c867196467ed7aea5f6f49b0
280 because its use case of writing to the user's terminal
281 on receiving of mail is obsolete.
282 If users like to be informed of new mail, the shell's
283 .Ev MAILPATH
284 variable or graphical notifications are technically more appealing.
285 Writing directly to a terminals is hardly ever wanted today.
286 If though one wants to have it this way, the standard tool
287 .Pn write
288 can be used in a way similar to:
289 .VS
290 scan -file - | write `id -un`
291 VE
292 .BU
293 .Pn viamail
294 was removed
295 .Ci eda72d6a7a7c20ff123043fb7f19c509ea01f932
296 when the new attachment system was activated, because
297 .Pn forw
298 could then cover the task itself.
299 The program
300 .Pn sendfiles
301 was rewritten as a shell script wrapper around
302 .Pn forw .
303 .Ci 0e82199cf3c991a173e0ac8aa776efdb3ded61e6
304 .BU
305 .Pn msgchk
306 was removed
307 .Ci bb9360ead7eb7a3fedcce2eeedfc660014e41dbe ,
308 because it lost its use case when POP support was removed.
309 A call to
310 .Pn msgchk
311 provided hardly more information than:
312 .VS
313 ls -l /var/mail/meillo
314 VE
315 It did distinguished between old and new mail, but
316 this detail information and can be retrieved with
317 .Pn stat (1),
318 too.
319 A very small shell script could be written to output the information
320 in a similar way, if truly necessary.
321 As mmh's
322 .Pn inc
323 only incorporates mail from the user's local maildrop,
324 and thus no data transfers over slow networks are involved,
325 there's hardly any need to check for new mail before incorporating it.
326 .BU
327 .Pn msh
328 was removed
329 .Ci 916690191222433a6923a4be54b0d8f6ac01bd02
330 because the tool was in conflict with the philosophy of MH.
331 It provided an interactive shell to access the features of MH,
332 but it wasn't just a shell, tailored to the needs of mail handling.
333 Instead it was one large program that had several MH tools built in.
334 This conflicts with the major feature of MH of being a tool chest.
335 .Pn msh 's
336 main use case had been accessing Bulletin Boards, which have seized to
337 be popular.
338 .P
339 Removing
340 .Pn msh ,
341 together with the truly archaic code relicts
342 .Pn vmh
343 and
344 .Pn wmh ,
345 saved more than 7\|000 lines of C code \(en
346 about 15\|% of the project's original source code amount.
347 .P
348 Having less code (with equal readability, of course)
349 for the same functionality is an advantage.
350 Less code means less bugs and less maintenance work.
351 As
352 .Pn rcvtty
353 and
354 .Pn msgchk
355 are assumed to be rarely used and can be implemented in different ways,
356 why should one keep them?
357 Removing them stream-lines mmh.
358 .Pn viamail 's
359 use case is now partly obsolete and partly covered by
360 .Pn forw ,
361 hence there's no reason to still maintain it.
362 .Pn conflict
363 is not related to the mail client, and
364 .Pn msh
365 conflicts with the basic concept of MH.
366 Theses two tools might still be useful, but they should not be part of mmh.
367 .P
368 Finally, there's
369 .Pn slocal .
370 .Pn slocal
371 is an MDA and thus not directly MUA-related.
372 It should be removed, because including it is a violation
373 of the idea that mmh is a MUA only.
374 It should become a separate project.
375 However,
376 .Pn slocal
377 provides rule-based processing of messages, like filing them into
378 different folders, which is otherwise not available in mmh.
379 Although
380 .Pn slocal
381 does neither pull in dependencies nor does it include a separate
382 technical area (cf. Sec. XXX),
383 still it accounts for about 1\|000 lines of code that need to be maintained.
384 As
385 .Pn slocal
386 is almost self-standing, it should be split off into a separate project.
387 This would cut the strong connection between the MUA mmh and the MDA
388 .Pn slocal .
389 For anyone not using MH,
390 .Pn slocal
391 would become yet another independent MDA, like
392 .I procmail .
393 The need to install a complete MH system to have
394 .Pn slocal
395 would be gone.
396 Likewise, mmh users could decide to use
397 .I procmail
398 without having a second, unused MDA,
399 .Pn slocal ,
400 installed.
401 That's conceptionally the best solution.
402 Yet,
403 .Pn slocal
404 is not split off.
405 I feel unsure with removing it from mmh.
406 Hence, I defer the decision over
407 .Pn slocal .
408 In the meanwhile
409 .Pn slocal
410 does not hurt because it is unrelated to the rest of mmh.
413 .H2 "\fLshow\fP and \fPmhshow\fP
414 .P
415 Since the very beginning \(en already in the first concept paper \(en
416 .Pn show
417 had been MH's message display program.
418 .Pn show
419 mapped message numbers and sequences to files and invoked
420 .Pn mhl
421 to have the files formatted.
422 With MIME, this approach wasn't sufficient anymore.
423 MIME messages can consist of multiple parts, some of which aren't
424 directly displayable, further more text content might be encoded in
425 foreign charsets.
426 .Pn show 's
427 understanding of messages and
428 .Pn mhl 's
429 display capabilities couldn't cope with the task any longer.
430 .P
431 Instead of extending these tools, additional tools were written from
432 scratch and added to the MH tool chest.
433 Doing so is encouraged by the tool chest approach.
434 Modular design is a great advantage for extending a system,
435 as new tools can be added without interfering with existing ones.
436 First, the new MIME features were added in form of the single program
437 .Pn mhn .
438 The command
439 .Cl "mhn -show 42
440 would show the MIME message numbered 42.
441 With the 1.0 release of nmh in February 1999, Richard Coleman finished
442 the split of
443 .Pn mhn
444 into a set of specialized tools, which together covered the
445 multiple aspects of MIME.
446 One of them was
447 .Pn mhshow ,
448 which replaced
449 .Cl "mhn -show" .
450 It was capable of displaying MIME messages appropriately.
451 .P
452 From then on, two message display tools were part of nmh,
453 .Pn show
454 and
455 .Pn mhshow .
456 To ease the life of users,
457 .Pn show
458 was extended to automatically hand the job over to
459 .Pn mhshow
460 if displaying the message would be beyond
461 .Pn show 's
462 abilities.
463 In consequence, the user would simply invoke
464 .Pn show
465 (possibly through
466 .Pn next
467 or
468 .Pn prev )
469 and get the message printed with either
470 .Pn show
471 or
472 .Pn mhshow ,
473 whatever was more appropriate.
474 .P
475 Having two similar tools for essentially the same task is redundant.
476 Usually,
477 users wouldn't distinguish between
478 .Pn show
479 and
480 .Pn mhshow
481 in their daily mail reading.
482 Having two separate display programs was therefore mainly unnecessary
483 from a user's point of view.
484 Besides, the development of both programs needed to be in sync,
485 to ensure that the programs behaved in a similar way,
486 because they were used like a single tool.
487 Different behavior would have surprised the user.
488 .P
489 Today, non-MIME messages are rather seen to be a special case of
490 MIME messages, although it's the other way round.
491 As
492 .Pn mhshow
493 had already be able to display non-MIME messages, it appeared natural
494 to drop
495 .Pn show
496 in favor of using
497 .Pn mhshow
498 exclusively.
499 .Ci 4c1efddfd499300c7e74263e57d8aa137e84c853
500 Removing
501 .Pn show
502 is no loss in function, because functionally
503 .Pn mhshow
504 covers it completely.
505 The old behavior of
506 .Pn show
507 can still be emulated with the simple command line:
508 .VS
509 mhl `mhpath c`
510 VE
511 .P
512 For convenience,
513 .Pn mhshow
514 was renamed to
515 .Pn show
516 after
517 .Pn show
518 was gone.
519 It is clear that such a rename may confuse future developers when
520 trying to understand the history.
521 Nevertheless, I consider the convenience on the user's side,
522 to call
523 .Pn show
524 when they want a message to be displayed, to outweigh the inconvenience
525 on the developer's side when understanding the project history.
526 .P
527 To prepare for the transition,
528 .Pn mhshow
529 was reworked to behave more like
530 .Pn show
531 first.
532 (cf. Sec. XXX)
533 Once the tools behaved more alike, the replacing appeared to be
534 even more natural.
535 Today, mmh's new
536 .Pn show
537 became the one single message display program again, with the difference
538 that today it handles MIME messages as well as non-MIME messages.
539 The outcome of the transition is one program less to maintain,
540 no second display program for users to deal with,
541 and less system complexity.
542 .P
543 Still, removing the old
544 .Pn show
545 hurts in one regard: It had been such a simple program.
546 Its lean elegance is missing to the new
547 .Pn show .
548 But there is no chance;
549 supporting MIME demands for higher essential complexity.
552 .H2 "Removal of Configure Options
553 .P
554 Customization is a double-edged sword.
555 It allows better suiting setups, but not for free.
556 There is the cost of code complexity to be able to customize.
557 There is the cost of less tested setups, because there are
558 more possible setups and especially corner-cases.
559 And, there is the cost of choice itself.
560 The code complexity directly affects the developers.
561 Less tested code affects both, users and developers.
562 The problem of choice affects the users, for once by having to
563 choose, but also by complexer interfaces that require more documentation.
564 Whenever options add little advantages, they should be considered for
565 removal.
566 I have reduced the number of project-specific configure options from
567 fifteen to three.
569 .U3 "Mail Transfer Facilities
570 .P
571 With the removal of the mail transfer facilities five configure
572 options vanished:
573 .P
574 The switches
575 .Sw --with-tls
576 and
577 .Sw --with-cyrus-sasl
578 had activated the support for transfer encryption and authentication.
579 This is not needed anymore.
580 .Ci fecd5d34f65597a4dfa16aeabea7d74b191532c3
581 .Ci 156d35f6425bea4c1ed3c4c79783dc613379c65b
582 .P
583 The configure switch
584 .Sw --enable-pop
585 activated the message retrieval facility.
586 The code area that would be conditionally compiled in for TLS and SASL
587 support had been small.
588 The conditionally compiled code area for POP support had been much larger.
589 Whereas the code base changes would only slightly change on toggling
590 TLS or SASL support, it changed much on toggling POP support.
591 The changes in the code base could hardly be overviewed.
592 By having POP support togglable a second code base had been created,
593 one that needed to be tested.
594 This situation is basically similar for the conditional TLS and SASL
595 code, but there the changes are minor and can yet be overviewed.
596 Still, conditional compilation of a code base creates variations
597 of the original program.
598 More variations require more testing and maintenance work.
599 .P
600 Two other options only specified default configuration values:
601 .Sw --with-mts=[smtp|sendmail]
602 defined the default transport service.
603 In mmh this fixed to
604 .Ar sendmail .
605 .Ci f6aa95b724fd8c791164abe7ee5468bf5c34f226
606 With
607 .Sw --with-smtpservers=[server1...]
608 default SMTP servers for the
609 .Ar smtp
610 transport service could be specified.
611 .Ci 128545e06224233b7e91fc4c83f8830252fe16c9
612 Both of them became irrelevant.
614 .U3 "Backup Prefix
615 .P
616 The backup prefix is the string that was prepended to message
617 filenames to tag them as deleted.
618 By default it had been the comma character `\f(CW,\fP'.
619 In July 2000, Kimmo Suominen introduced
620 the configure option
621 .Sw --with-hash-backup
622 to change the default to the hash symbol `\f(CW#\fP'.
623 The choice was probably personal preference, because first, the
624 option was named
625 .Sw --with-backup-prefix.
626 and had the prefix symbol as argument.
627 Because giving the hash symbol as argument caused to many problems
628 for configure,
629 the option was limited to use the hash symbol as the default prefix.
630 This makes me believe, that the choice for the hash was personal preference.
631 Being it related or not, words that start with the hash symbol
632 introduce a comment in the Unix shell.
633 Thus, the command line
634 .Cl "rm #13 #15
635 calls
636 .Pn rm
637 without arguments because the first hash symbol starts the comment
638 that reaches until the end of the line.
639 To delete the backup files,
640 .Cl "rm ./#13 ./#15"
641 needs to be used.
642 Using the hash as backup prefix can be seen as a precaution agains
643 data loss.
644 .P
645 I removed the configure option but added the profile entry
646 .Pe backup-prefix ,
647 which allows to specify an arbitrary string as backup prefix.
648 .Ci 6c40d481d661d532dd527eaf34cebb6d3f8ed086
649 Profile entries are the common method to change mmh's behavior.
650 This change did not remove the choice but moved it to a location where
651 it suited better.
652 .P
653 Eventually, however, the new trash folder concept
654 .Cf "Sec. XXX
655 obsoleted the concept of the backup prefix completely.
656 .Ci 8edc5aaf86f9f77124664f6801bc6c6cdf258173
657 (Well, there still are corner-cases to remove until the backup
658 prefix can be laid to rest, eventually.)
659 .\" FIXME: Do this work in the code!
661 .U3 "Editor and Pager
662 .P
663 The two configure options
664 .CW --with-editor=EDITOR
665 .CW --with-pager=PAGER
666 were used to specify the default editor and pager at configure time.
667 Doing so at configure time made sense in the Eighties,
668 when the set of available editors and pagers varied much across
669 different systems.
670 Today, the situation is more homogeneous.
671 The programs
672 .Pn vi
673 and
674 .Pn more
675 can be expected to be available on every Unix system,
676 as they are specified by POSIX since two decades.
677 (The specifications for
678 .Pn vi
679 and
680 .Pn more
681 appeared in
682 .[
683 posix 1987
684 .]
685 and,
686 .[
687 posix 1992
688 .]
689 respectively.)
690 As a first step, these two tools were hard-coded as defaults.
691 .Ci 5d43a99db70c12a673028c7758c20cbe3e13ef5f
692 Not changed were the
693 .Pe editor
694 and
695 .Pe moreproc
696 profile entries, which allowed the user to override the system defaults.
697 Later, the concept was reworked to respect the standard environment
698 variables
699 .Ev VISUAL
700 and
701 .Ev PAGER
702 if they are set.
703 Today, mmh determines the editor to use in the following order,
704 taking the first available and non-empty item:
705 .IP (1)
706 Environment variable
707 .Ev MMHEDITOR
708 .IP (2)
709 Profile entry
710 .Pe Editor
711 .IP (3)
712 Environment variable
713 .Ev VISUAL
714 .IP (4)
715 Environment variable
716 .Ev EDITOR
717 .IP (5)
718 Command
719 .Pn vi .
720 .P
721 .Ci f85f4b7ae62e3d05a945dcd46ead51f0a2a89a9b
722 .P
723 The pager to use is determined in a similar order,
724 also taking the first available and non-empty item:
725 .IP (1)
726 Environment variable
727 .Ev MMHPAGER
728 .IP (2)
729 Profile entry
730 .Pe Pager
731 (replaces
732 .Pe moreproc )
733 .IP (3)
734 Environment variable
735 .Ev PAGER
736 .IP (4)
737 Command
738 .Pn more .
739 .P
740 .Ci 0c4214ea2aec6497d0d67b436bbee9bc1d225f1e
741 .P
742 By respecting the
743 .Ev VISUAL /\c
744 .Ev EDITOR
745 and
746 .Ev PAGER
747 environment variables,
748 the new behavior confirms better to the common style on Unix systems.
749 Additionally, the new approach is more uniform and clearer to users.
751 .U3 "Locale
752 .P
753 The configure option
754 .Sw --disable-locale
755 was removed because POSIX provides locale support and there's
756 hardly any need to disable locale support.
757 .Ci ccf4f175ef4c4e7522f9510a4a1149c15d810dd9
759 .U3 "ndbm
760 .P
761 .Pn slocal
762 used to depend on
763 .I ndbm ,
764 a database library.
765 The database is used to store the `\fLMessage-ID\fP's of all
766 messages delivered.
767 This enables
768 .Pn slocal
769 to suppress delivering the same message to the same user twice.
770 (This features was enabled by the
771 .Sw -suppressdup
772 switch.)
773 .P
774 A variety of version of the database library exist.
775 .[
776 wolter unix incompat notes dbm
777 .]
778 Complicated autoconf code was needed to detect them correctly.
779 Further more, the configure switches
780 .Sw --with-ndbm=ARG
781 and
782 .Sw --with-ndbmheader=ARG
783 were added to help with difficult setups that would
784 not be detected automatically or correctly.
785 .P
786 By removing the suppress duplicates feature of
787 .Pn slocal ,
788 the dependency on
789 .I ndbm
790 vanished and 120 lines of complex autoconf code could be saved.
791 .Ci ecd6d6a20cb7a1507e3a20d6c4cb3a1cf14c6bbf
792 The change removed functionality too, but that is minor to the
793 improvement by dropping the dependency and the complex autoconf code.
795 .U3 "mh-e Support
796 .P
797 The configure option
798 .Sw --disable-mhe
799 was removed when the mh-e support was reworked.
800 Mh-e is the Emacs front-end to MH.
801 It requires MH to provide minor additional functions.
802 The
803 .Sw --disable-mhe
804 configure option could switch these extensions off.
805 After removing the support for old versions of mh-e,
806 only the
807 .Sw -build
808 switches of
809 .Pn forw
810 and
811 .Pn repl
812 are left to be mh-e extensions.
813 They are now always built in because they add little code and complexity.
814 In consequence, the
815 .Sw --disable-mhe
816 configure option was removed
817 .Ci a7ce7b4a580d77b6c2c4d980812beb589aa4c643
818 Removing the option removed a second code setup that would have
819 needed to be tested.
820 This change was first done in nmh and thereafter merged into mmh.
821 .P
822 The interface changes in mmh require mh-e to be adjusted in order
823 to be able to use mmh as back-end.
824 This will require minor changes to mh-e, but removing the
825 .Sw -build
826 switches would require more rework.
828 .U3 "Masquerading
829 .P
830 The configure option
831 .Sw --enable-masquerade
832 could take up to three arguments:
833 `draft_from', `mmailid', and `username_extension'.
834 They activated different types of address masquerading.
835 All of them were implemented in the SMTP-speaking
836 .Pn post
837 command, which provided an MSA.
838 Address masquerading is an MTA's task and mmh does not cover
839 this field anymore.
840 Hence, true masquerading needs to be implemented in the external MTA.
841 .P
842 The
843 .I mmailid
844 masquerading type is the oldest one of the three and the only one
845 available in the original MH.
846 It provided a
847 .I username
848 to
849 .I fakeusername
850 mapping, based on the password file's GECOS field.
851 The man page
852 .Mp mh-tailor(5)
853 described the use case as being the following:
854 .QP
855 This is useful if you want the messages you send to always
856 appear to come from the name of an MTA alias rather than your
857 actual account name. For instance, many organizations set up
858 `First.Last' sendmail aliases for all users. If this is
859 the case, the GECOS field for each user should look like:
860 ``First [Middle] Last <First.Last>''
861 .P
862 As mmh sends outgoing mail via the local MTA only,
863 the best location to do such global rewrites is there.
864 Besides, the MTA is conceptionally the right location because it
865 does the reverse mapping for incoming mail (aliasing), too.
866 Further more, masquerading set up there is readily available for all
867 mail software on the system.
868 Hence, mmailid masquerading was removed.
869 .Ci 0836c8000ccb34b59410ef1c15b1b7feac70ce5f
870 .P
871 The
872 .I username_extension
873 masquerading type did not replace the username but would append a suffix,
874 specified by the
875 .Ev USERNAME_EXTENSION
876 environment variable, to it.
877 This provided support for the
878 .I user-extension
879 feature of qmail and the similar
880 .I "plussed user
881 processing of sendmail.
882 The decision to remove this username_extension masquerading was
883 motivated by the fact that
884 .Pn spost
885 hadn't supported it already.
886 .Ci 2abae0bfd0ad5bf898461e50aa4b466d641f23d9
887 Username extensions are possible in mmh, but less convenient to use.
888 .\" XXX format file %(getenv USERNAME_EXTENSION)
889 .P
890 The
891 .I draft_from
892 masquerading type instructed
893 .Pn post
894 to use the value of the
895 .Hd From
896 header field as SMTP envelope sender.
897 Sender addresses could be replaced completely.
898 .Ci b14ea6073f77b4359aaf3fddd0e105989db9
899 Mmh offers a kind of masquerading similar in effect, but
900 with technical differences.
901 As mmh does not transfer messages itself, the local MTA has final control
902 over the sender's address. Any masquerading mmh introduces may be reverted
903 by the MTA.
904 In times of pedantic spam checking, an MTA will take care to use
905 sensible envelope sender addresses to keep its own reputation up.
906 Nonetheless, the MUA can set the
907 .Hd From
908 header field and thereby propose
909 a sender address to the MTA.
910 The MTA may then decide to take that one or generate the canonical sender
911 address for use as envelope sender address.
912 .P
913 In mmh, the MTA will always extract the recipient and sender from the
914 message header (\c
915 .Pn sendmail 's
916 .Sw -t
917 switch).
918 The
919 .Hd From
920 header field of the draft may be set arbitrary by the user.
921 If it is missing, the canonical sender address will be generated by the MTA.
923 .U3 "Remaining Options
924 .P
925 Two configure options remain in mmh.
926 One is the locking method to use:
927 .Sw --with-locking=[dot|fcntl|flock|lockf] .
928 The idea of removing all methods except the portable dot locking
929 and having that one as the default is appealing, but this change
930 requires deeper technical investigation into the topic.
931 The other option,
932 .Sw --enable-debug ,
933 compiles the programs with debugging symbols and does not strip them.
934 This option is likely to stay.
939 .H2 "Removal of Switches
940 .P
941 The command line switches of MH tools follow the X Window style.
942 They are words, introduced by a single dash.
943 For example:
944 .Cl "-truncate" .
945 Every program in mmh has two generic switches:
946 .Sw -help ,
947 to print a short message on how to use the program, and
948 .Sw -Version ,
949 to tell what version of mmh the program belongs to.
950 .P
951 Switches change the behavior of programs.
952 Programs that do one thing in one way require no switches.
953 In most cases, doing something in exactly one way is too limiting.
954 If it is basically the same task to accomplish, but it should be done
955 in various ways, switches are a good approach to alter the behavior
956 of a program.
957 Changing the behavior of programs provides flexibility and customization
958 to users, but in the same way it complicates the code, documentation and
959 usage of the program.
960 Therefore, the number of switches should be kept small.
961 A small set of well-chosen switches does no harm.
962 But usually, the number of switches increases over time.
963 Already in 1985, Rose and Romine have identified this as a major
964 problem of MH:
965 .[ [
966 rose romine real work
967 .], p. 12]
968 .sp
969 .QP
970 A complaint often heard about systems which undergo substantial development
971 by many people over a number of years, is that more and more options are
972 introduced which add little to the functionality but greatly increase the
973 amount of information a user needs to know in order to get useful work done.
974 This is usually referred to as creeping featurism.
975 .QP
976 Unfortunately MH, having undergone six years of off-and-on development by
977 ten or so well-meaning programmers (the present authors included),
978 suffers mightily from this.
979 .sp
980 .P
981 Adding new switches only reluctantly is one part of the counter-action,
982 the other is removing hardly used switches.
983 Now that there are lots of switches already implemented,
984 removing some of them is more important.
985 Removing existing functionality is always difficult because it
986 breaks programs that use these functions.
987 Also, for every obsolete feature, there'll always be someone who still
988 uses it and thus opposes its removal.
989 This puts the developer into the position,
990 where sensible improvements to style are regarded as destructive acts.
991 Yet, living with the featurism is far worse, in my eyes.
992 Future needs will demand adding new features,
993 worsening the situation more and more.
994 Rose and Romine added in a footnote,
995 ``[...]
996 .Pn send
997 will no doubt acquire an endless number of switches in the years to come.''
998 Although clearly humorous, the comment displays the nature of
999 the problem.
1000 Though refusing to add any new switches would encounter the problem
1001 at its root, it is not practical.
1002 But removing obsolete switches is an effective approach to deal with the
1003 problem.
1004 Working on an experimental branch,
1005 eased this work because I had not to offend users.
1006 .P
1007 Rose and Romine counted 24 visible and 9 more hidden switches for
1008 .Pn send .
1009 At the beginning of mmh, it were 32 visible and 12 hidden ones.
1010 At the time of writing, mmh's
1011 .Pn send
1012 has 7 visible switches and 1 hidden switch.
1013 (In each of the examples, the two generic help and version switches
1014 are included.)
1015 .P
1016 Figure XXX
1017 .\" XXX Ref
1018 displays the number of switches for each of the tools that was not
1019 removed from or newly added to mmh.
1020 Both, visible and hidden switches, were counted, but
1021 not the generic help and version switches.
1022 Whereas in the beginning of the project, the average tool had 11 switches,
1023 now it has no more than 5 \(en only half as many.
1024 If the `no' switches and similar inverse variant are folded onto
1025 their counter-parts, the numbers are 8 in pre-mmh to 4 now.
1026 The total number of functional switches in mmh dropped from 465
1027 to 234.
1029 .KS
1030 .in 1c
1031 .so input/switches.grap
1032 .KE
1034 .P
1035 A part of the switches vanished after functions were removed.
1036 This was the case for network mail transfer, for instance.
1037 Sometimes the work flow was the other way:
1038 The trying to reduce the number of switches suggested the removal of
1039 functions.
1041 .U3 "Draft Folder Facility
1042 .P
1043 A change early in the project was the completely transition from
1044 the single draft message to the draft folder facility.
1045 The draft folder facility was introduced in the mid-Eighties.
1046 (Rose and Romine called it a ``relatively new feature''
1047 .[
1048 rose romine real work
1049 .]
1050 in 1985.)
1051 Since then, the facility had existed but had remained deactivated
1052 by default.
1053 The default activation and the related rework of the tools made it
1054 possible to remove the
1055 .Sw -[no]draftfolder ,
1056 and
1057 .Sw -draftmessage
1058 switches from
1059 .Pn comp ,
1060 .Pn repl ,
1061 .Pn forw ,
1062 .Pn dist ,
1063 .Pn whatnow ,
1064 and
1065 .Pn send .
1066 The only flexibility removed is having multiple draft folders
1067 within one profile.
1068 I consider this only a theoretical setup.
1069 In the same go, the
1070 .Sw -draft
1071 switch of
1072 .Pn anno ,
1073 .Pn refile ,
1074 and
1075 .Pn send
1076 was removed.
1077 The special-casing of `the' draft message became irrelevant after
1078 the rework of the draft system.
1079 (See Sec. XXX.)
1080 Equally,
1081 .Pn comp
1082 lost its
1083 .Sw -file
1084 switch.
1085 The draft folder facility, together with the
1086 .Sw -form
1087 switch, are sufficient.
1090 .U3 "Inplace Editing
1091 .P
1092 .Pn anno
1093 had the switches
1094 .Sw -[no]inplace
1095 to either annotate the message inplace and thus preserve hard links,
1096 or annotate a copy to replace the original message, breaking hard links.
1097 Following the assumption that linked messages are the same message,
1098 and annotating it should not break the link, the
1099 .Sw -[no]inplace
1100 switches were removed and the previous default
1101 .Sw -inplace
1102 was made the only behavior.
1103 The
1104 .Sw -[no]inplace
1105 switches of
1106 .Pn repl ,
1107 .Pn forw ,
1108 and
1109 .Pn dist
1110 could be removed, too, as they were simply passed through to
1111 .Pn anno .
1112 .P
1113 .Pn burst
1114 also had
1115 .Sw -[no]inplace
1116 switches, but with different meaning.
1117 With
1118 .Sw -inplace ,
1119 the digest had been replaced by the table of contents (i.e. the
1120 introduction text) and the bursted messages were placed right
1121 after this message, renumbering all following messages.
1122 Also, any trailing text of the digest was lost, though,
1123 in practice, it usually consists of an end-of-digest marker only.
1124 Nontheless, this behavior appeared less elegant than the
1125 .Sw -noinplace
1126 behavior, which already had been the default.
1127 Nmh's
1128 .Mp burst (1)
1129 man page reads:
1130 .sp \n(PDu
1131 .QP
1132 If -noinplace is given, each digest is preserved, no table
1133 of contents is produced, and the messages contained within
1134 the digest are placed at the end of the folder. Other messages
1135 are not tampered with in any way.
1136 .sp \n(PDu
1137 .LP
1138 The decision to drop the
1139 .Sw -inplace
1140 behavior was supported by the code complexity and the possible data loss
1141 it caused.
1142 .Sw -noinplace
1143 was chosen to be the definitive behavior.
1146 .U3 "Forms and Format Strings
1147 .P
1148 Historically, the tools that had
1149 .Sw -form
1150 switches to supply a form file had
1151 .Sw -format
1152 switches as well to supply the contents of a form file as a string
1153 on the command line directly.
1154 In consequence, the following two lines equaled:
1155 .VS
1156 scan -form scan.mailx
1157 scan -format "`cat .../scan.mailx`"
1158 VE
1159 The
1160 .Sw -format
1161 switches were dropped in favor for extending the
1162 .Sw -form
1163 switches.
1164 If their argument starts with an equal sign (`='),
1165 then the rest of the argument is taken as a format string,
1166 otherwise the arguments is treated as the name of a format file.
1167 Thus, now the following two lines equal:
1168 .VS
1169 scan -form scan.mailx
1170 scan -form "=`cat .../scan.mailx`"
1171 VE
1172 This rework removed the prefix collision between
1173 .Sw -form
1174 and
1175 .Sw -format .
1176 Now, typing
1177 .Sw -fo
1178 suffices to specify form or format string.
1179 .P
1180 The different meaning of
1181 .Sw -format
1182 for
1183 .Pn repl
1184 and
1185 .Pn forw
1186 was removed in mmh.
1187 .Pn forw
1188 was completely switched to MIME-type forwarding, thus removing the
1189 .Sw -[no]format .
1190 For
1191 .Pn repl ,
1192 the
1193 .Sw -[no]format
1194 switches were reworked to
1195 .Sw -[no]filter
1196 switches.
1197 The
1198 .Sw -format
1199 switches of
1200 .Pn send
1201 and
1202 .Pn post ,
1203 which had a third meaning,
1204 were removed likewise.
1205 Eventually, the ambiguity of the
1206 .Sw -format
1207 switches was resolved by not anymore having any such switch in mmh.
1210 .U3 "MIME Tools
1211 .P
1212 The MIME tools, which were once part of
1213 .Pn mhn ,
1214 had several switches that added little practical value to the programs.
1215 The
1216 .Sw -[no]realsize
1217 switches of
1218 .Pn mhbuild
1219 and
1220 .Pn mhlist
1221 were removed, doing real size calculations always now, as
1222 ``This provides an accurate count at the expense of a small delay.''
1223 This small delay is not noticable on modern systems.
1224 .P
1225 The
1226 .Sw -[no]check
1227 switches were removed together with the support for
1228 .Hd Content-MD5
1229 header fields.
1230 .[
1231 rfc 1864
1232 .]
1233 (See Sec. XXX)
1234 .P
1235 The
1236 .Sw -[no]ebcdicsafe
1237 and
1238 .Sw -[no]rfc934mode
1239 switches of
1240 .Pn mhbuild
1241 were removed because they are considered obsolete.
1242 .P
1243 Content caching of external MIME parts, activated with the
1244 .Sw -rcache
1245 and
1246 .Sw -wcache
1247 switches was completely removed.
1248 External MIME parts are truly rare today, having a caching facility
1249 for them is appears to be unnecessary.
1250 .P
1251 In pre-MIME times,
1252 .Pn mhl
1253 had covered many tasks that are part of MIME handling today.
1254 Therefore,
1255 .Pn mhl
1256 could be simplified to a large extend, reducing the number of its
1257 switches from 21 to 6.
1260 .U3 "Mail Transfer Switches
1261 .P
1262 With the removal of the mail transfer facilities, a lot of switches
1263 vanished automatically.
1264 .Pn inc
1265 lost 9 switches, namely
1266 .Sw -host ,
1267 .Sw -port ,
1268 .Sw -user ,
1269 .Sw -proxy ,
1270 .Sw -snoop ,
1271 .Sw -[no]pack ,
1272 as well as
1273 .Sw -sasl
1274 and
1275 .Sw -saslmech .
1276 .Pn send
1277 and
1278 .Pn post
1279 lost 11 switches each, namely
1280 .Sw -server ,
1281 .Sw -port ,
1282 .Sw -client ,
1283 .Sw -user ,
1284 .Sw -mail ,
1285 .Sw -saml ,
1286 .Sw -send ,
1287 .Sw -soml ,
1288 .Sw -snoop ,
1289 as well as
1290 .Sw -sasl ,
1291 .Sw -saslmech ,
1292 and
1293 .Sw -tls .
1294 .Pn send
1295 had the switches only to pass them further to
1296 .Pn post ,
1297 because the user would invoke
1298 .Pn post
1299 not directly, but through
1300 .Pn send .
1301 All these switches, except
1302 .Sw -snoop
1303 were usually defined as default switches in the user's profile,
1304 but hardly given in interactive usage.
1305 .P
1306 Of course, those switches did not really ``vanish'', but the configuration
1307 they did was handed over to external MSAs and MRAs.
1308 Instead of setting up the mail transfer in mmh, it is set up in
1309 external tools.
1310 Yet, this simplifies mmh.
1311 Specialized external tools will likely have simple configuration files.
1312 Hence, instead of having one complicated central configuration file,
1313 the configuration of each domain is separate.
1314 Although the user needs to learn to configure each of the tools,
1315 each configuration is likely much simpler.
1318 .U3 "Maildrop Formats
1319 .P
1320 With the removal of MMDF maildrop format support,
1321 .Pn packf
1322 and
1323 .Pn rcvpack
1324 no longer needed their
1325 .Sw -mbox
1326 and
1327 .Sw -mmdf
1328 switches.
1329 .Sw -mbox
1330 is the sole behavior now.
1331 In the same go,
1332 .Pn packf
1333 was reworked (see Sec. XXX) and its
1334 .Sw -file
1335 switch became unnecessary.
1338 .U3 "Terminal Magic
1339 .P
1340 Mmh's tools will no longer clear the screen (\c
1341 .Pn scan 's
1342 and
1343 .Pn mhl 's
1344 .Sw -[no]clear
1345 switches).
1346 Neither will
1347 .Pn mhl
1348 ring the bell (\c
1349 .Sw -[no]bell )
1350 nor page the output itself (\c
1351 .Sw -length ).
1352 .P
1353 Generally, the pager to use is no longer specified with the
1354 .Sw -[no]moreproc
1355 command line switches for
1356 .Pn mhl
1357 and
1358 .Pn show /\c
1359 .Pn mhshow .
1360 .P
1361 .Pn prompter
1362 lost its
1363 .Sw -erase
1364 and
1365 .Sw -kill
1366 switches because today the terminal cares for the line editing keys.
1369 .U3 "Header Printing
1370 .P
1371 .Pn folder 's
1372 data output is self-explaining enough that
1373 displaying the header line makes few sense.
1374 Hence, the
1375 .Sw -[no]header
1376 switch was removed and headers are never printed.
1377 .P
1378 In
1379 .Pn mhlist ,
1380 the
1381 .Sw -[no]header
1382 switches were removed, too.
1383 But in this case headers are always printed,
1384 because the output is not self-explaining.
1385 .P
1386 .Pn scan
1387 also had
1388 .Sw -[no]header
1389 switches.
1390 Printing the header had been sensible until the introduction of
1391 format strings made it impossible to display the column headings.
1392 Only the folder name and the current date remained to be printed.
1393 As this information can be perfectly retrieved by
1394 .Pn folder
1395 and
1396 .Pn date ,
1397 consequently, the switches were removed.
1398 .P
1399 By removing all
1400 .Sw -header
1401 switches, the collision with
1402 .Sw -help
1403 on the first two letters was resolved.
1404 Currently,
1405 .Sw -h
1406 evaluates to
1407 .Sw -help
1408 for all tools of mmh.
1411 .U3 "Suppressing Edits or the WhatNow Shell
1412 .P
1413 The
1414 .Sw -noedit
1415 switches of
1416 .Pn comp ,
1417 .Pn repl ,
1418 .Pn forw ,
1419 .Pn dist ,
1420 and
1421 .Pn whatnow
1422 was removed, but it can now be replaced by specifying
1423 .Sw -editor
1424 with an empty argument.
1425 (Specifying
1426 .Cl "-editor true
1427 is nearly the same, only differing by the previous editor being set.)
1428 .P
1429 The more important change is the removal of the
1430 .Sw -nowhatnowproc
1431 switch.
1432 This switch had introduced an awkward behavior, as explained in nmh's
1433 man page for
1434 .Mp comp (1):
1435 .QP
1436 The \-editor editor switch indicates the editor to use for
1437 the initial edit. Upon exiting from the editor, comp will
1438 invoke the whatnow program. See whatnow(1) for a discussion
1439 of available options. The invocation of this program can be
1440 inhibited by using the \-nowhatnowproc switch. (In truth of
1441 fact, it is the whatnow program which starts the initial
1442 edit. Hence, \-nowhatnowproc will prevent any edit from
1443 occurring.)
1444 .P
1445 Effectively, the
1446 .Sw -nowhatnowproc
1447 switch stored a copy of the form file into the draft folder.
1448 As
1449 .Cl "-whatnowproc true
1450 causes the same behavior, the
1451 .Sw -nowhatnowproc
1452 switch was removed for being redundant.
1453 Likely, however, the intention for specifying
1454 .Sw -nowhatnowproc
1455 is sending a fully prepared form file at once.
1456 This can be done with
1457 .Cl "-whatnowproc send" .
1460 .U3 "Compatibility Switches
1461 .BU
1462 The hidden
1463 .Sw -[no]total
1464 switches of
1465 .Pn flist .
1466 They were simply the inverse of the visible
1467 .Sw -[no]fast
1468 switches:
1469 .Sw -total
1470 was
1471 .Sw -nofast
1472 and
1473 .Sw -nototal
1474 was
1475 .Sw -fast .
1476 I removed the
1477 .Sw -[no]total
1478 legacy.
1479 .BU
1480 The
1481 .Sw -subject
1482 switch of
1483 .Pn sortm
1484 existed for compatibility only.
1485 It can be fully replaced by
1486 .Cl "-textfield subject
1487 thus it was removed.
1490 .U3 "Various
1491 .BU
1492 In order to avoid prefix collisions among switch names, the
1493 .Sw -version
1494 switch was renamed to
1495 .Sw -Version
1496 (with capital `V').
1497 Every program has the
1498 .Sw -version
1499 switch but its first three letters collided with the
1500 .Sw -verbose
1501 switch, present in many programs.
1502 The rename solved this problem once for all.
1503 Although this rename breaks a basic interface, having the
1504 .Sw -V
1505 abbreviation to display the version information, isn't all too bad.
1506 .BU
1507 .Sw -[no]preserve
1508 of
1509 .Pn refile
1510 was removed because what use was it anyway?
1511 .QP
1512 Normally when a message is refiled, for each destination
1513 folder it is assigned the number which is one above the current
1514 highest message number in that folder. Use of the
1515 \-preserv [sic!] switch will override this message renaming, and try
1516 to preserve the number of the message. If a conflict for a
1517 particular folder occurs when using the \-preserve switch,
1518 then refile will use the next available message number which
1519 is above the message number you wish to preserve.
1520 .BU
1521 The removal of the
1522 .Sw -[no]reverse
1523 switches of
1524 .Pn scan
1525 is a bug fix, supported by the comments
1526 ``\-[no]reverse under #ifdef BERK (I really HATE this)''
1527 by Rose and
1528 ``Lists messages in reverse order with the `\-reverse' switch.
1529 This should be considered a bug.'' by Romine in the documentation.
1530 The question remaining is why neither Rose and Romine had fixed this
1531 bug in the Eighties when they wrote these comments nor has anyone
1532 thereafter.
1535 .ig
1537 forw: [no]dashstuffing(mhl)
1539 mhshow: [no]pause [no]serialonly
1541 mhmail: resent queued
1542 inc: snoop, (pop)
1544 mhl: [no]faceproc folder sleep
1545 [no]dashstuffing(forw) digest list volume number issue number
1547 prompter: [no]doteof
1549 refile: [no]preserve [no]unlink [no]rmmproc
1551 send: [no]forward [no]mime [no]msgid
1552 [no]push split [no]unique (sasl) width snoop [no]dashstuffing
1553 attach attachformat
1554 whatnow: (noedit) attach
1556 slocal: [no]suppressdups
1558 spost: [no]filter [no]backup width [no]push idanno
1559 [no]check(whom) whom(whom)
1561 whom: ???
1563 ..
1566 .ig
1568 .P
1569 To ease typing, the switches can be abbreviated as much as the remaining
1570 prefix remains unambiguous.
1571 If in our example no other switch would start with the letter `t', then
1572 .Cl "-truncate" ,
1573 .Cl "-trunc" ,
1574 .Cl "-tr" ,
1575 and
1576 .Cl "-t
1577 would all be the same.
1578 As a result, switches can neither be grouped (as in
1579 .Cl "ls -ltr" )
1580 nor can switch arguments be appended directly to the switch (as in
1581 .Cl "sendmail -q30m" ).
1582 .P
1583 Many switches have negating counter-parts, which start with `no'.
1584 For example
1585 .Cl "-notruncate
1586 inverts the
1587 .Cl "-truncate
1588 switch.
1589 They exist to undo the effect of default switches in the profile.
1590 If the user has chosen to change the default behavior of some tool
1591 by adding a default switch to the profile,
1592 he can still undo this change in behavior by specifying the inverse
1593 switch on the command line.
1594 .P
1595 In the best case, all switches are unambiguous on the first character,
1596 or on the three-letter prefix for the `no' variants.
1597 Reducing switch prefix collisions, shortens the necessary prefix length
1598 the user must type.
1599 Having less switches helps best.
1601 ..
1606 .H1 "Modernizing
1609 .H2 "Removal of Code Relicts
1610 .P
1611 The code base of mmh originates from the late Seventies,
1612 had been extensively
1613 worked on in the mid Eighties, and had been partly reorganized and extended
1614 in the Nineties. Relicts of all those times had gathered in the code base.
1615 My goal was to remove any ancient code parts. One part of the task was
1616 converting obsolete code constructs to standard constructs, the other part
1617 was dropping obsolete functions.
1618 .P
1619 As I'm not even thirty years old and have no more than seven years of
1620 Unix experience, I needed to learn about the history in retrospective.
1621 Older people likely have used those ancient constructs themselves
1622 and have suffered from their incompatibilities and have longed for
1623 standardization. Unfortunately, I have only read that others had done so.
1624 This put me in a much more difficult positions when working on the old
1625 code. I needed to recherche what other would have known by heart from
1626 experience. All my programming experience comes from a time past ANSI C
1627 and past POSIX. Although I knew about the times before, I took the
1628 current state implicitly for granted most of the time.
1629 .P
1630 Being aware of
1631 these facts, I rather let people with more historic experience solve the
1632 task of converting the ancient code constructs to standardized ones.
1633 Luckily, Lyndon Nerenberg focused on this task at the nmh project.
1634 He converted large parts of the code to POSIX constructs, removing
1635 the conditionals compilation for now standardized features.
1636 I'm thankful for this task being solved. I only pulled the changes into
1637 mmh.
1638 .P
1639 The other task \(en dropping ancient functionality to remove old code \(en
1640 I did myself, though. My position to strip mmh to the bare minimum of
1641 frequently used features is much more revolutional than the nmh community
1642 likes it. Without the need to justify my decisions, I was able to quickly
1643 remove functionality I considered ancient.
1644 The need to discuss my decisions with
1645 peers likely would have slowed this process down. Of course, I researched
1646 if a particular feature really should be dropped. Having not had any
1647 contact to this feature within my computer life was a first indicator to
1648 drop it, but I also asked others and searched the literature for modern
1649 usage of the feature. If it appeared to be truly ancient, I dropped it.
1650 The reason for dropping is always part of the commit message in the
1651 version control system. Thus, it is easy for others to check their
1652 view on the topic with mine and possibly to argue for reinclusion.
1654 .U2 "MMDF maildrop support
1655 .P
1656 I did drop any support for the MMDF maildrop format. This type of format
1657 is conceptionally similar to the mbox format, but uses four bytes with
1658 value 1 (\fL^A^A^A^A\fP) as message delimiter,
1659 instead of the string ``\fLFrom\ \fP''.
1660 Due to the similarity and mbox being the de-facto standard maildrop
1661 format on Unix, but also due to the larger influence of Sendmail than MMDF,
1662 the MMDF maildrop format had vanished.
1663 .P
1664 The simplifications within the code were only moderate. Switches could
1665 be removed from tools like
1666 .L packf ,
1667 which generate packed mailboxes. Only one packed mailbox format remained:
1668 mbox.
1669 The most important changes affect the equally named mail parsing routine in
1670 .L sbr/m_getfld.c .
1671 The direct MMDF code had been removed, but as now only one packed mailbox
1672 format is left, code structure simplifications are likely possible.
1673 The reason why they are still outstanding is the heavily optimized code
1674 of
1675 .Fu m_getfld() .
1676 Changes beyond a small local scope \(en
1677 which restructuring in its core is \(en cause a high risk of damaging
1678 the intricate workings of the optimized code. This problem is know
1679 to the developers of nmh, too. They also avoid touching this minefield
1680 if possible.
1682 .U2 "UUCP Bang Paths
1683 .P
1684 More questionably than the former topic is the removal of support for the
1685 UUCP bang path address style. However, the user may translate the bang
1686 paths on retrieval to Internet addresses and the other way on posting
1687 messages. The former can be done my an MDA like procmail; the latter
1688 by a sendmail wrapper. This would ensure that any address handling would
1689 work as expected. However, it might just work well without any
1690 such modifications, as mmh does not touch addresses much, in general.
1691 But I can't ensure as I have never used an environment with bang paths.
1692 Also, the behavior might break at any point in further development.
1694 .U2 "Hardcopy terminal support
1695 .P
1696 More of a funny anecdote is the remaining of a check for printing to a
1697 hardcopy terminal until Spring 2012, when I finally removed it.
1698 I surely would be very happy to see such a terminal in action, maybe
1699 actually being able to work on it, but I fear my chances are null.
1700 .P
1701 The check only prevented a pager to be placed between the outputting
1702 program (\c
1703 .Pn mhl )
1704 and the terminal. This could have been ensured with
1705 the
1706 .Sw -nomoreproc
1707 at the command line statically, too.
1709 .U2 "Removed support for header fields
1710 .P
1711 The
1712 .Hd Encrypted
1713 header field had been introduced by RFC\^822, but already
1714 marked legacy in RFC 2822. It was superseded by FIXME.
1715 Mmh does no more support this header field.
1716 .P
1717 Native support for
1718 .Hd Face
1719 header fields had been removed, as well.
1720 The feature is similar to the
1721 .Hd X-Face
1722 header field in its intent,
1723 but takes a different approach to store the image.
1724 Instead of encoding the image data directly into the header field,
1725 the it contains the hostname and UDP port where the image
1726 date could be retrieved.
1727 Neither
1728 .Hd X-Face
1729 nor the here described
1730 .Hd Face
1731 system
1732 \**
1733 .FS
1734 There is also a newer but different system, invented 2005,
1735 using
1736 .Hd Face
1737 headers.
1738 It is the successor of
1739 .Hd X-Face
1740 providing colored PNG images.
1741 .FE
1742 became well used in the large scale.
1743 It's still possible to use a Face systems,
1744 although mmh does not provide support for any of the different systems
1745 anymore. It's fairly easy to write a small shell script to
1746 extract the embedded or fetch the external Face data and display the image.
1747 Own
1748 .Hd Face
1749 header field can be added into the draft template files.
1750 .P
1751 .Hd Content-MD5
1752 header fields were introduced by RFC\^1864. They provide only
1753 a verification of data corruption during the transfer. By no means can
1754 they ensure verbatim end-to-end delivery of the contents. This is clearly
1755 stated in the RFC. The proper approach to provide verificationability
1756 of content in an end-to-end relationship is the use of digital cryptography
1757 (RFCs FIXME). On the other hand, transfer protocols should ensure the
1758 integrity of the transmission. In combinations these two approaches
1759 make the
1760 .Hd Content-MD5
1761 header field useless. In consequence, I removed
1762 the support for it. By this removal, MD5 computation is not needed
1763 anywhere in mmh. Hence, over 500 lines of code were removed by this one
1764 change. Even if the
1765 .Hd Content-MD5
1766 header field is useful sometimes,
1767 I value its usefulness less than the improvement in maintainability, caused
1768 by the removal.
1770 .U2 "Prompter's Control Keys
1771 .P
1772 The program
1773 .Pn prompter
1774 queries the user to fill in a message form. When used by
1775 .Pn comp
1776 as:
1777 .VS
1778 comp -editor prompter
1779 VE
1780 the resulting behavior is similar to
1781 .Pn mailx .
1782 Apparently,
1783 .Pn prompter
1784 hadn't been touched lately. Otherwise it's hardly explainable why it
1785 still offered the switches
1786 .Sw -erase
1787 .Ar chr
1788 and
1789 .Sw -kill
1790 .Ar chr
1791 to name the characters for command line editing.
1792 The times when this had been necessary are long time gone.
1793 Today these things work out-of-the-box, and if not, are configured
1794 with the standard tool
1795 .Pn stty .
1797 .U2 "Vfork and Retry Loops
1798 .P
1799 MH creates many processes, which is a consequence of the tool chest approach.
1800 In earlier times
1801 .Fu fork()
1802 had been an expensive system call, as the process's whole image needed
1803 to be duplicated. One common case is replacing the image with
1804 .Fu exec()
1805 right after having forked the child process.
1806 To speed up this case, the
1807 .Fu vfork()
1808 system call was invented at Berkeley. It completely omits copying the
1809 image. If the image gets replaced right afterwards then unnecessary
1810 work is omited. On old systems this results in large speed ups.
1811 MH uses
1812 .Fu vfork()
1813 whenever possible.
1814 .P
1815 Memory management units that support copy-on-write semantics make
1816 .Fu fork()
1817 almost as fast as
1818 .Fu vfork()
1819 in the cases when they can be exchanged.
1820 With
1821 .Fu vfork()
1822 being more error-prone and hardly faster, it's preferable to simply
1823 use
1824 .Fu fork()
1825 instead.
1826 .P
1827 Related to the costs of
1828 .Fu fork()
1829 is the probability of its success.
1830 Today on modern systems, the system call will succeed almost always.
1831 In the Eighties on heavy loaded systems, as they were common at
1832 universities, this had been different. Thus, many of the
1833 .Fu fork()
1834 calls were wrapped into loops to retry to fork several times in
1835 short intervals, in case of previous failure.
1836 In mmh, the program aborts at once if the fork failed.
1837 The user can reexecute the command then. This is expected to be a
1838 very rare case on modern systems, especially personal ones, which are
1839 common today.
1842 .H2 "Attachments
1843 .P
1844 MIME
1847 .H2 "Digital Cryptography
1848 .P
1849 Signing and encryption.
1852 .H2 "Good Defaults
1853 .P
1854 foo
1859 .H1 "Code style
1860 .P
1861 foo
1864 .H2 "Standard Code
1865 .P
1866 POSIX
1869 .H2 "Separation
1871 .U2 "MH Directory Split
1872 .P
1873 In MH and nmh, a personal setup had consisted of two parts:
1874 The MH profile, named
1875 .Fn \&.mh_profile
1876 and being located directly in the user's home directory.
1877 And the MH directory, where all his mail messages and also his personal
1878 forms, scan formats, other configuration files are stored. The location
1879 of this directory could be user-chosen. The default was to name it
1880 .Fn Mail
1881 and have it directly in the home directory.
1882 .P
1883 I've never liked the data storage and the configuration to be intermixed.
1884 They are different kinds of data. One part, are the messages,
1885 which are the data to operate on. The other part, are the personal
1886 configuration files, which are able to change the behavior of the operations.
1887 The actual operations are defined in the profile, however.
1888 .P
1889 When storing data, one should try to group data by its type.
1890 There's sense in the Unix file system hierarchy, where configuration
1891 file are stored separate (\c
1892 .Fn /etc )
1893 to the programs (\c
1894 .Fn /bin
1895 and
1896 .Fn /usr/bin )
1897 to their sources (\c
1898 .Fn /usr/src ).
1899 Such separation eases the backup management, for instance.
1900 .P
1901 In mmh, I've reorganized the file locations.
1902 Still there are two places:
1903 There's the mail storage directory, which, like in MH, contains all the
1904 messages, but, unlike in MH, nothing else.
1905 Its location still is user-chosen, with the default name
1906 .Fn Mail ,
1907 in the user's home directory. This is much similar to the case in nmh.
1908 The configuration files, however, are grouped together in the new directory
1909 .Fn \&.mmh
1910 in the user's home directory.
1911 The user's profile now is a file, named
1912 .Fn profile ,
1913 in this mmh directory.
1914 Consistently, the context file and all the personal forms, scan formats,
1915 and the like, are also there.
1916 .P
1917 The naming changed with the relocation.
1918 The directory where everything, except the profile, had been stored (\c
1919 .Fn $HOME/Mail ),
1920 used to be called \fIMH directory\fP. Now, this directory is called the
1921 user's \fImail storage\fP. The name \fImmh directory\fP is now given to
1922 the new directory
1923 (\c
1924 .Fn $HOME/.mmh ),
1925 containing all the personal configuration files.
1926 .P
1927 The separation of the files by type of content is logical and convenient.
1928 There are no functional differences as any possible setup known to me
1929 can be implemented with both approaches, although likely a bit easier
1930 with the new approach. The main goal of the change had been to provide
1931 sensible storage locations for any type of personal mmh file.
1932 .P
1933 In order for one user to have multiple MH setups, he can use the
1934 environment variable
1935 .Ev MH
1936 the point to a different profile file.
1937 The MH directory (mail storage plus personal configuration files) is
1938 defined by the
1939 .Pe Path
1940 profile entry.
1941 The context file could be defined by the
1942 .Pe context
1943 profile entry or by the
1944 .Ev MHCONTEXT
1945 environment variable.
1946 The latter is useful to have a distinct context (e.g. current folders)
1947 in each terminal window, for instance.
1948 In mmh, there are three environment variables now.
1949 .Ev MMH
1950 may be used to change the location of the mmh directory.
1951 .Ev MMHP
1952 and
1953 .Ev MMHC
1954 change the profile and context files, respectively.
1955 Besides providing a more consistent feel (which simply is the result
1956 of being designed anew), the set of personal configuration files can
1957 be chosen independently from the profile (including mail storage location)
1958 and context, now. Being it relevant for practical use or not, it
1959 de-facto is an improvement. However, the main achievement is the
1960 split between mail storage and personal configuration files.
1963 .H2 "Modularization
1964 .P
1965 whatnowproc
1966 .P
1967 The \fIMH library\fP
1968 .Fn libmh.a
1969 collects a bunch of standard functions that many of the MH tools need,
1970 like reading the profile or context files.
1971 This doesn't hurt the separation.
1974 .H2 "Style
1975 .P
1976 Code layout, goto, ...
1981 .H1 "Concept Exploitation/Homogeneity
1984 .H2 "Draft Folder
1985 .P
1986 Historically, MH provided exactly one draft message, named
1987 .Fn draft
1988 and
1989 being located in the MH directory. When starting to compose another message
1990 before the former one was sent, the user had been questioned whether to use,
1991 refile or replace the old draft. Working on multiple drafts at the same time
1992 was impossible. One could only work on them in alteration by refiling the
1993 previous one to some directory and fetching some other one for reediting.
1994 This manual draft management needed to be done each time the user wanted
1995 to switch between editing one draft to editing another.
1996 .P
1997 To allow true parallel editing of drafts, in a straight forward way, the
1998 draft folder facility exists. It had been introduced already in July 1984
1999 by Marshall T. Rose. The facility was deactivated by default.
2000 Even in nmh, the draft folder facility remained deactivated by default.
2001 At least, Richard Coleman added the man page
2002 .Mp mh-draft(5)
2003 to document
2004 the feature well.
2005 .P
2006 The only advantage of not using the draft folder facility is the static
2007 name of the draft file. This could be an issue for MH front-ends like mh-e.
2008 But as they likely want to provide working on multiple drafts in parallel,
2009 the issue is only concerning compatibility. The aim of nmh to stay compatible
2010 prevented the default activation of the draft folder facility.
2011 .P
2012 On the other hand, a draft folder is the much more natural concept than
2013 a draft message. MH's mail storage consists of folders and messages,
2014 the messages named with ascending numbers. A draft message breaks with this
2015 concept by introducing a message in a file named
2016 .Fn draft .
2017 This draft
2018 message is special. It can not be simply listed with the available tools,
2019 but instead requires special switches. I.e. corner-cases were
2020 introduced. A draft folder, in contrast, does not introduce such
2021 corner-cases. The available tools can operate on the messages within that
2022 folder like on any messages within any mail folders. The only difference
2023 is the fact that the default folder for
2024 .Pn send
2025 is the draft folder,
2026 instead of the current folder, like for all other tools.
2027 .P
2028 The trivial part of the change was activating the draft folder facility
2029 by default and setting a default name for this folder. Obviously, I chose
2030 the name
2031 .Fn +drafts .
2032 This made the
2033 .Sw -draftfolder
2034 and
2035 .Sw -draftmessage
2036 switches useless, and I could remove them.
2037 The more difficult but also the part that showed the real improvement,
2038 was updating the tools to the new concept.
2039 .Sw -draft
2040 switches could
2041 be dropped, as operating on a draft message became indistinguishable to
2042 operating on any other message for the tools.
2043 .Pn comp
2044 still has its
2045 .Sw -use
2046 switch for switching between its two modes: (1) Compose a new
2047 draft, possibly by taking some existing message as a form. (2) Modify
2048 an existing draft. In either case, the behavior of
2049 .Pn comp is
2050 deterministic. There is no more need to query the user. I consider this
2051 a major improvement. By making
2052 .Pn send
2053 simply operate on the current
2054 message in the draft folder by default, with message and folder both
2055 overridable by specifying them on the command line, it is now possible
2056 to send a draft anywhere within the storage by simply specifying its folder
2057 and name.
2058 .P
2059 All theses changes converted special cases to regular cases, thus
2060 simplifying the tools and increasing the flexibility.
2063 .H2 "Trash Folder
2064 .P
2065 Similar to the situation for drafts is the situation for removed messages.
2066 Historically, a message was deleted by renaming. A specific
2067 \fIbackup prefix\fP, often comma (\c
2068 .Fn , )
2069 or hash (\c
2070 .Fn # ),
2071 being prepended to the file name. Thus, MH wouldn't recognize the file
2072 as a message anymore, as only files whose name consists of digits only
2073 are treated as messages. The removed messages remained as files in the
2074 same directory and needed some maintenance job to truly delete them after
2075 some grace time. Usually, by running a command similar to
2076 .VS
2077 find /home/user/Mail -ctime +7 -name ',*' | xargs rm
2078 VE
2079 in a cron job. Within the grace time interval
2080 the original message could be restored by stripping the
2081 the backup prefix from the file name. If however, the last message of
2082 a folder is been removed \(en say message
2083 .Fn 6
2084 becomes file
2085 .Fn ,6
2086 \(en and a new message enters the same folder, thus the same
2087 numbered being given again \(en in our case
2088 .Fn 6
2089 \(en, if that one
2090 is removed too, then the backup of the former message gets overwritten.
2091 Thus, the ability to restore removed messages does not only depend on
2092 the ``sweeping cron job'' but also on the removing of further messages.
2093 This is undesirable, because the real mechanism is hidden from the user
2094 and the consequences of further removals are not always obvious.
2095 Further more, the backup files are scattered within the whole mail
2096 storage, instead of being collected at one place.
2097 .P
2098 To improve the situation, the profile entry
2099 .Pe rmmproc
2100 (previously named
2101 .Pe Delete-Prog )
2102 was introduced, very early.
2103 It could be set to any command, which would care for the mail removal
2104 instead of taking the default action, described above.
2105 Refiling the to-be-removed files to some garbage folder was a common
2106 example. Nmh's man page
2107 .Mp rmm(1)
2108 proposes
2109 .Cl "refile +d
2110 to move messages to the garbage folder and
2111 .Cl "rm `mhpath +d all`
2112 the empty the garbage folder.
2113 Managing the message removal this way is a sane approach. It keeps
2114 the removed messages in one place, makes it easy to remove the backup
2115 files, and, most important, enables the user to use the tools of MH
2116 itself to operate on the removed messages. One can
2117 .Pn scan
2118 them,
2119 .Pn show
2120 them, and restore them with
2121 .Pn refile .
2122 There's no more
2123 need to use
2124 .Pn mhpath
2125 to switch over from MH tools to Unix tools \(en MH can do it all itself.
2126 .P
2127 This approach matches perfect with the concepts of MH, thus making
2128 it powerful. Hence, I made it the default. And even more, I also
2129 removed the old backup prefix approach, as it is clearly less powerful.
2130 Keeping unused alternative in the code is a bad choice as they likely
2131 gather bugs, by not being constantly tested. Also, the increased code
2132 size and more conditions crease the maintenance costs. By strictly
2133 converting to the trash folder approach, I simplified the code base.
2134 .Pn rmm
2135 calls
2136 .Pn refile
2137 internally to move the to-be-removed
2138 message to the trash folder (\c
2139 .Fn +trash
2140 by default). Messages
2141 there can be operated on like on any other message in the storage.
2142 The sweep clean, one can use
2143 .Cl "rmm -unlink +trash a" ,
2144 where the
2145 .Sw -unlink
2146 switch causes the files to be truly unliked instead
2147 of moved to the trash folder.
2150 .H2 "Path Notations
2151 .P
2152 foo
2155 .H2 "MIME Integration
2156 .P
2157 user-visible access to whole messages and MIME parts are inherently
2158 different
2161 .H2 "Of One Cast
2162 .P