docs/master: ch03.roff annotate

docs/master

annotate ch03.roff @ 89:83bfb4dbf59f

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author	markus schnalke <meillo@marmaro.de>
date	Tue, 12 Jun 2012 21:00:43 +0200
parents	30830e3b9e98
children	093ccf39a45e

rev	line source
meillo@58	1 .H0 "Discussion
meillo@0	2 .P
meillo@58	3 This main chapter discusses the practical work done in the mmh project.
meillo@58	4 It is structured along the goals to achieve. The concrete work done
meillo@58	5 is described in the examples of how the general goals were achieved.
meillo@87	6 The discussion compares the current version of mmh with the state of
meillo@87	7 nmh just before the mmh project started, i.e. Fall 2011.
meillo@87	8 Current changes of nmh will be mentioned only as side notes.
meillo@87	9 .\" XXX where do I discuss the parallel development of nmh?
meillo@58	10
meillo@58	11
meillo@58	12
meillo@58	13 .H1 "Stream-lining
meillo@58	14
meillo@0	15 .P
meillo@58	16 MH had been considered an all-in-one system for mail handling.
meillo@58	17 The community around nmh has a similar understanding.
meillo@87	18 In fundamental difference, mmh shall be a MUA only.
meillo@87	19 I believe that the development of all-in-one mail systems is obsolete.
meillo@87	20 Today, email is too complex to be fully covered by single projects.
meillo@87	21 Such a project won't be able to excel in all aspects.
meillo@87	22 Instead, the aspects of email should be covered my multiple projects,
meillo@87	23 which then can be combined to form a complete system.
meillo@87	24 Excellent implementations for the various aspects of email exist already.
meillo@87	25 Just to name three examples: Postfix is a specialized MTA,
meillo@87	26 Procmail is a specialized MDA, and Fetchmail is a specialized MRA.
meillo@89	27 I believe that it is best to use such specialized tools instead of
meillo@87	28 providing the same function again as a side-component in the project.
meillo@58	29 .P
meillo@87	30 Doing something well, requires to focus on a small set of specific aspects.
meillo@87	31 Under the assumption that focused development produces better results
meillo@87	32 in the particular area, specialized projects will likely be superior
meillo@87	33 in their field of focus.
meillo@87	34 Hence, all-in-one mail system projects \(en no matter if monolithic
meillo@87	35 or modular \(en will never be the best choice in any of the fields.
meillo@87	36 Even in providing the best consistent all-in-one system they are likely
meillo@87	37 to be beaten by projects that focus only on integrating existing mail
meillo@89	38 components to a homogeneous system.
meillo@87	39 .P
meillo@87	40 The limiting resource in Free Software community development
meillo@87	41 is usually man power.
meillo@87	42 If the development power is spread over a large development area,
meillo@87	43 it becomes even more difficult to compete with the specialists in the
meillo@87	44 various fields.
meillo@87	45 The concrete situation for MH-based mail systems is even tougher,
meillo@87	46 given the small and aged community, including both developers and users,
meillo@87	47 it has.
meillo@87	48 .P
meillo@87	49 In consequence, I believe that the available development resources
meillo@87	50 should be focused on the point where MH is most unique.
meillo@87	51 This is clearly the user interface \(en the MUA.
meillo@87	52 Peripheral parts should be removed to stream-line mmh for the MUA task.
meillo@60	53
meillo@60	54
meillo@87	55 .H2 "Removal of the Mail Transfer Facilities
meillo@60	56 .P
meillo@60	57 In contrast to nmh, which also provides mail submission and mail retrieval
meillo@87	58 agents, mmh is a MUA only.
meillo@66	59 This general difference in the view on the character of nmh
meillo@76	60 initiated the development of mmh.
meillo@66	61 Removing the mail transfer facilities had been the first work task
meillo@76	62 in the mmh project.
meillo@60	63 .P
meillo@66	64 The MSA is called \fIMessage Transfer Service\fP (MTS) in nmh.
meillo@76	65 The facility established network connections and spoke SMTP to submit
meillo@60	66 messages for relay to the outside world.
meillo@76	67 This part was implemented by the
meillo@60	68 .Pn post
meillo@60	69 command.
meillo@87	70 The changes in emailing in the last years
meillo@87	71 demanded changes in this part of nmh too.
meillo@89	72 Encryption and authentication for network connections
meillo@87	73 needed to be supported, hence TLS and SASL were introduced into nmh.
meillo@87	74 This added complexity to nmh without improving it in its core functions.
meillo@87	75 Also, keeping up with recent developments in the field of
meillo@87	76 mail transfer requires development power and specialists.
meillo@87	77 In mmh this whole facility was simply cut off.
meillo@76	78 .Ci f6aa95b724fd8c791164abe7ee5468bf5c34f226
meillo@76	79 .Ci fecd5d34f65597a4dfa16aeabea7d74b191532c3
meillo@76	80 .Ci 156d35f6425bea4c1ed3c4c79783dc613379c65b
meillo@87	81 Instead, mmh depends on an external MSA.
meillo@60	82 The only outgoing interface available to mmh is the
meillo@60	83 .Pn sendmail
meillo@87	84 command, which almost any MSA provides.
meillo@87	85 If not, a wrapper program can be written.
meillo@87	86 It must read the message from the standard input, extract the
meillo@87	87 recipient addresses from the message header, and hand the message
meillo@87	88 over to the MSA.
meillo@87	89 For example, a wrapper script for qmail would be:
meillo@87	90 .VS
meillo@87	91 #!/bin/sh
meillo@87	92 # ignore command line arguments
meillo@87	93 exec qmail-inject
meillo@87	94 VE
meillo@87	95 The requirement to parse the recipient addresses out of the message header
meillo@87	96 is likely to be removed in the future.
meillo@87	97 Then mmh would give the recipient addresses as command line arguments.
meillo@87	98 This is clearly the better interface, but mmh does not provide it yet.
meillo@87	99 .\" XXX implement it
meillo@60	100 .P
meillo@60	101 To retrieve mail, the
meillo@60	102 .Pn inc
meillo@76	103 command established network connections
meillo@76	104 and spoke POP3 to retrieve mail from remote servers.
meillo@76	105 As with mail submission, the network connections required encryption and
meillo@87	106 authentication, thus TLS and SASL were added.
meillo@87	107 Support for message retrieval through IMAP will become necessary
meillo@87	108 to be added soon, too, and so on for any changes in mail transfer.
meillo@76	109 Mmh has dropped the support for retrieving mail from remote locations.
meillo@76	110 .Ci ab7b48411962d26439f92f35ed084d3d6275459c
meillo@76	111 Instead, it depends on an external tool to cover this task.
meillo@87	112 In mmh there exist two paths for messages to enter mmh's mail storage:
meillo@87	113 (1) Mail can be incorporate with
meillo@60	114 .Pn inc
meillo@87	115 from the system maildrop, or (2) with
meillo@60	116 .Pn rcvstore
meillo@87	117 by reading them, one at a time, from the standard input.
meillo@60	118 .P
meillo@60	119 With the removal of the MSA and MRA, mmh converted from an all-in-one
meillo@87	120 mail system to being a MUA only.
meillo@87	121 Following the Unix philosophy, it now focuses on one job and
meillo@76	122 tries to do that one well.
meillo@76	123 Not only the programs follow that tenet but also the project itself does so.
meillo@60	124 Now, of course, mmh depends on third-party software.
meillo@87	125 An external MSA is required to transfer mail to the outside world;
meillo@60	126 an external MRA is required to retrieve mail from remote machines.
meillo@60	127 There exist excellent implementations of such software,
meillo@76	128 which do this specific task likely better than the internal
meillo@87	129 versions had done it.
meillo@87	130 Also, the best suiting programs can be freely chosen.
meillo@60	131 .P
meillo@60	132 As it had already been possible to use an external MSA or MRA,
meillo@60	133 why not keep the internal version for convenience?
meillo@76	134 The question whether there is sense in having a fall-back pager in all
meillo@76	135 the command line tools, for the cases when
meillo@60	136 .Pn more
meillo@60	137 or
meillo@60	138 .Pn less
meillo@76	139 aren't available, appears to be ridiculous.
meillo@87	140 Now, an MSA or MRA is more complex than a text pager
meillo@87	141 and not necessarily available but still the concept of orthogonal
meillo@87	142 design holds: ``Write programs that do one thing and do it well.''
meillo@87	143 .[
meillo@87	144 mcilroy unix phil
meillo@87	145 p. 53
meillo@87	146 .]
meillo@87	147 .[
meillo@87	148 mcilroy bstj foreword
meillo@87	149 .]
meillo@87	150 Here, this part of the Unix philosophy was applied not only
meillo@87	151 to the programs but to the project itself.
meillo@87	152 In other words:
meillo@87	153 ``Develop projects that focus on one thing and do it well.''
meillo@87	154 Projects grown complex should be split for the same reasons programs grown
meillo@87	155 complex should be split.
meillo@87	156 If it is conceptionally more elegant to have the MSA and MRA
meillo@87	157 separate projects then they should be separated.
meillo@87	158 This is the case here, in my opinion.
meillo@87	159 The RFCs propose this separation by clearly distinguishing the different
meillo@87	160 mail handling tasks.
meillo@87	161 .[
meillo@87	162 rfc 821
meillo@87	163 .]
meillo@87	164 The small interfaces between the mail agents support the separation.
meillo@76	165 .P
meillo@87	166 In the beginning, email had been small and simple.
meillo@76	167 (\c
meillo@60	168 .Pn /bin/mail
meillo@76	169 had once covered anything there was to email and still had been small
meillo@76	170 and simple.)
meillo@76	171 Then the essential complexity of email increased.
meillo@87	172 (Essential complexity is the complexity defined by the problem itself.\0
meillo@87	173 .[[
meillo@87	174 brooks no silver bullet
meillo@87	175 .]])
meillo@87	176 Email systems reacted to this change: They grew.
meillo@87	177 RFCs started to introduce mail agents and separated the various tasks
meillo@87	178 because the existing tasks became more extensive and new tasks appeared.
meillo@87	179 Again, email systems grew, or they split parts off.
meillo@76	180 In nmh, for instance, the POP server, which the original MH had included,
meillo@76	181 was removed.
meillo@87	182 Now is the time to go one step further and remove the MSA and MRA, too.
meillo@87	183 Not only does this decrease the code size of the project,
meillo@87	184 but, more important, it unburdens mmh of the whole field of
meillo@87	185 message transfer with all its implications for the project.
meillo@87	186 There's no more need to concern with changes in network transfer.
meillo@76	187 This independence is received by depending on an external program
meillo@76	188 that covers the field.
meillo@76	189 Today, this is a reasonable exchange.
meillo@60	190 .P
meillo@87	191 Function can be added in three different ways:
meillo@87	192 .BU
meillo@87	193 Implementing the function originally in the project.
meillo@87	194 .BU
meillo@87	195 Depending on a library that provides the function.
meillo@87	196 .BU
meillo@87	197 Depending on a program that provides the function.
meillo@87	198 .P
meillo@87	199 Whereas adding the function originally to the project increases the
meillo@76	200 code size most and requires most maintenance and development work,
meillo@87	201 it makes the project most independent of other software.
meillo@87	202 Using libraries or external programs require less maintenance work
meillo@87	203 but introduces dependencies on external software.
meillo@87	204 Programs have the smallest interfaces and provide the best separation
meillo@87	205 but possibly limit the information exchange.
meillo@87	206 External libraries are stronger connected than external programs,
meillo@87	207 thus information can be exchanged more flexible.
meillo@87	208 Adding code to a project increases maintenance work.
meillo@87	209 .\" XXX ref
meillo@87	210 Implementing complex functions originally in the project will add
meillo@87	211 a lot of code.
meillo@87	212 This should be avoided if possible.
meillo@66	213 Hence, the dependencies only change in kind, not in their existence.
meillo@66	214 In mmh, library dependencies on
meillo@66	215 .Pn libsasl2
meillo@66	216 and
meillo@66	217 .Pn libcrypto /\c
meillo@66	218 .Pn libssl
meillo@66	219 were treated against program dependencies on an MSA and an MRA.
meillo@87	220 This also meant treating build-time dependencies against run-time
meillo@87	221 dependencies.
meillo@66	222 Besides program dependencies providing the stronger separation
meillo@66	223 and being more flexible, they also allowed
meillo@66	224 over 6\\|000 lines of code to be removed from mmh.
meillo@66	225 This made mmh's code base about 12\\|% smaller.
meillo@87	226 Reducing the project's code size by such an amount without actually
meillo@87	227 losing functionality is a convincing argument.
meillo@87	228 Actually, as external MSAs and MRAs are likely superior to the
meillo@87	229 project's internal versions, the common user even gains functionality.
meillo@66	230 .P
meillo@76	231 Users of MH should not have problems to set up an external MSA and MRA.
meillo@60	232 Also, the popular MSAs and MRAs have large communities and a lot
meillo@60	233 of documentation available.
meillo@87	234 Choices for MSAs range from full-featured MTAs like
meillo@60	235 .I Postfix
meillo@87	236 over mid-size MTAs like
meillo@60	237 .I masqmail
meillo@60	238 and
meillo@60	239 .I dma
meillo@60	240 to small forwarders like
meillo@60	241 .I ssmtp
meillo@60	242 and
meillo@60	243 .I nullmailer .
meillo@60	244 Choices for MRAs include
meillo@60	245 .I fetchmail ,
meillo@60	246 .I getmail ,
meillo@60	247 .I mpop
meillo@60	248 and
meillo@60	249 .I fdm .
meillo@60	250
meillo@60	251
meillo@60	252 .H2 "Removal of non-MUA Tools
meillo@60	253 .P
meillo@87	254 One goal of mmh is to remove the tools that are not part of the MUA's task.
meillo@89	255 Further more, any tools that don't improve the MUA's job significantly
meillo@87	256 should be removed.
meillo@87	257 Loosely related and rarely used tools distract from the lean appearance.
meillo@87	258 They require maintenance work without adding much to the core task.
meillo@87	259 On removing these tools, the project shall become more stream-lined
meillo@87	260 and focused.
meillo@76	261 In mmh the following tools are not available anymore:
meillo@62	262 .BU
meillo@58	263 .Pn conflict
meillo@87	264 was removed
meillo@76	265 .Ci 8b235097cbd11d728c07b966cf131aa7133ce5a9
meillo@87	266 because it is a mail system maintenance tool that is not MUA-related.
meillo@87	267 It even checked
meillo@58	268 .Fn /etc/passwd
meillo@58	269 and
meillo@58	270 .Fn /etc/group
meillo@87	271 for consistency, which is completely unrelated to email.
meillo@87	272 A tool like
meillo@87	273 .Pn conflict
meillo@87	274 is surely useful, but it should not be shipped with mmh.
meillo@76	275 .\" XXX historic reasons?
meillo@62	276 .BU
meillo@58	277 .Pn rcvtty
meillo@87	278 was removed
meillo@87	279 .Ci 14767c94b3827be7c867196467ed7aea5f6f49b0
meillo@89	280 because its use case of writing to the user's terminal
meillo@76	281 on receiving of mail is obsolete.
meillo@87	282 If users like to be informed of new mail, the shell's
meillo@58	283 .Ev MAILPATH
meillo@87	284 variable or graphical notifications are technically more appealing.
meillo@62	285 Writing directly to a terminals is hardly ever wanted today.
meillo@62	286 If though one wants to have it this way, the standard tool
meillo@58	287 .Pn write
meillo@58	288 can be used in a way similar to:
meillo@82	289 .VS
meillo@58	290 scan -file - \| write `id -un`
meillo@82	291 VE
meillo@62	292 .BU
meillo@58	293 .Pn viamail
meillo@87	294 was removed
meillo@87	295 .Ci eda72d6a7a7c20ff123043fb7f19c509ea01f932
meillo@87	296 when the new attachment system was activated, because
meillo@58	297 .Pn forw
meillo@76	298 could then cover the task itself.
meillo@62	299 The program
meillo@58	300 .Pn sendfiles
meillo@62	301 was rewritten as a shell script wrapper around
meillo@58	302 .Pn forw .
meillo@76	303 .Ci 0e82199cf3c991a173e0ac8aa776efdb3ded61e6
meillo@62	304 .BU
meillo@58	305 .Pn msgchk
meillo@87	306 was removed
meillo@87	307 .Ci bb9360ead7eb7a3fedcce2eeedfc660014e41dbe ,
meillo@87	308 because it lost its use case when POP support was removed.
meillo@76	309 A call to
meillo@58	310 .Pn msgchk
meillo@87	311 provided hardly more information than:
meillo@82	312 .VS
meillo@58	313 ls -l /var/mail/meillo
meillo@82	314 VE
meillo@87	315 It did distinguished between old and new mail, but
meillo@87	316 this detail information and can be retrieved with
meillo@76	317 .Pn stat (1),
meillo@62	318 too.
meillo@62	319 A very small shell script could be written to output the information
meillo@76	320 in a similar way, if truly necessary.
meillo@76	321 As mmh's
meillo@76	322 .Pn inc
meillo@87	323 only incorporates mail from the user's local maildrop,
meillo@62	324 and thus no data transfers over slow networks are involved,
meillo@76	325 there's hardly any need to check for new mail before incorporating it.
meillo@62	326 .BU
meillo@58	327 .Pn msh
meillo@87	328 was removed
meillo@76	329 .Ci 916690191222433a6923a4be54b0d8f6ac01bd02
meillo@87	330 because the tool was in conflict with the philosophy of MH.
meillo@76	331 It provided an interactive shell to access the features of MH,
meillo@76	332 but it wasn't just a shell, tailored to the needs of mail handling.
meillo@76	333 Instead it was one large program that had several MH tools built in.
meillo@76	334 This conflicts with the major feature of MH of being a tool chest.
meillo@76	335 .Pn msh 's
meillo@76	336 main use case had been accessing Bulletin Boards, which have seized to
meillo@62	337 be popular.
meillo@62	338 .P
meillo@62	339 Removing
meillo@58	340 .Pn msh ,
meillo@76	341 together with the truly archaic code relicts
meillo@58	342 .Pn vmh
meillo@58	343 and
meillo@58	344 .Pn wmh ,
meillo@62	345 saved more than 7\\|000 lines of C code \(en
meillo@66	346 about 15\\|% of the project's original source code amount.
meillo@76	347 .P
meillo@76	348 Having less code (with equal readability, of course)
meillo@76	349 for the same functionality is an advantage.
meillo@63	350 Less code means less bugs and less maintenance work.
meillo@76	351 As
meillo@63	352 .Pn rcvtty
meillo@63	353 and
meillo@63	354 .Pn msgchk
meillo@87	355 are assumed to be rarely used and can be implemented in different ways,
meillo@87	356 why should one keep them?
meillo@76	357 Removing them stream-lines mmh.
meillo@63	358 .Pn viamail 's
meillo@63	359 use case is now partly obsolete and partly covered by
meillo@63	360 .Pn forw ,
meillo@76	361 hence there's no reason to still maintain it.
meillo@63	362 .Pn conflict
meillo@76	363 is not related to the mail client, and
meillo@63	364 .Pn msh
meillo@63	365 conflicts with the basic concept of MH.
meillo@76	366 Theses two tools might still be useful, but they should not be part of mmh.
meillo@63	367 .P
meillo@76	368 Finally, there's
meillo@76	369 .Pn slocal .
meillo@76	370 .Pn slocal
meillo@76	371 is an MDA and thus not directly MUA-related.
meillo@78	372 It should be removed, because including it is a violation
meillo@78	373 of the idea that mmh is a MUA only.
meillo@78	374 It should become a separate project.
meillo@87	375 However,
meillo@76	376 .Pn slocal
meillo@76	377 provides rule-based processing of messages, like filing them into
meillo@76	378 different folders, which is otherwise not available in mmh.
meillo@87	379 Although
meillo@76	380 .Pn slocal
meillo@87	381 does neither pull in dependencies nor does it include a separate
meillo@87	382 technical area (cf. Sec. XXX),
meillo@87	383 still it accounts for about 1\\|000 lines of code that need to be maintained.
meillo@76	384 As
meillo@76	385 .Pn slocal
meillo@76	386 is almost self-standing, it should be split off into a separate project.
meillo@76	387 This would cut the strong connection between the MUA mmh and the MDA
meillo@76	388 .Pn slocal .
meillo@87	389 For anyone not using MH,
meillo@87	390 .Pn slocal
meillo@87	391 would become yet another independent MDA, like
meillo@87	392 .I procmail .
meillo@87	393 The need to install a complete MH system to have
meillo@87	394 .Pn slocal
meillo@87	395 would be gone.
meillo@76	396 Likewise, mmh users could decide to use
meillo@76	397 .I procmail
meillo@87	398 without having a second, unused MDA,
meillo@87	399 .Pn slocal ,
meillo@76	400 installed.
meillo@76	401 That's conceptionally the best solution.
meillo@76	402 Yet,
meillo@76	403 .Pn slocal
meillo@87	404 is not split off.
meillo@87	405 I feel unsure with removing it from mmh.
meillo@87	406 Hence, I defer the decision over
meillo@87	407 .Pn slocal .
meillo@87	408 In the meanwhile
meillo@78	409 .Pn slocal
meillo@87	410 does not hurt because it is unrelated to the rest of mmh.
meillo@0	411
meillo@58	412
meillo@76	413 .H2 "\fLshow\fP and \fPmhshow\fP
meillo@58	414 .P
meillo@69	415 Since the very beginning \(en already in the first concept paper \(en
meillo@58	416 .Pn show
meillo@62	417 had been MH's message display program.
meillo@58	418 .Pn show
meillo@76	419 mapped message numbers and sequences to files and invoked
meillo@58	420 .Pn mhl
meillo@89	421 to have the files formatted.
meillo@88	422 With MIME, this approach wasn't sufficient anymore.
meillo@58	423 MIME messages can consist of multiple parts, some of which aren't
meillo@88	424 directly displayable, further more text content might be encoded in
meillo@58	425 foreign charsets.
meillo@58	426 .Pn show 's
meillo@76	427 understanding of messages and
meillo@58	428 .Pn mhl 's
meillo@88	429 display capabilities couldn't cope with the task any longer.
meillo@62	430 .P
meillo@88	431 Instead of extending these tools, additional tools were written from
meillo@88	432 scratch and added to the MH tool chest.
meillo@88	433 Doing so is encouraged by the tool chest approach.
meillo@88	434 Modular design is a great advantage for extending a system,
meillo@88	435 as new tools can be added without interfering with existing ones.
meillo@62	436 First, the new MIME features were added in form of the single program
meillo@58	437 .Pn mhn .
meillo@58	438 The command
meillo@82	439 .Cl "mhn -show 42
meillo@58	440 would show the MIME message numbered 42.
meillo@58	441 With the 1.0 release of nmh in February 1999, Richard Coleman finished
meillo@58	442 the split of
meillo@58	443 .Pn mhn
meillo@88	444 into a set of specialized tools, which together covered the
meillo@88	445 multiple aspects of MIME.
meillo@88	446 One of them was
meillo@69	447 .Pn mhshow ,
meillo@88	448 which replaced
meillo@88	449 .Cl "mhn -show" .
meillo@88	450 It was capable of displaying MIME messages appropriately.
meillo@62	451 .P
meillo@88	452 From then on, two message display tools were part of nmh,
meillo@76	453 .Pn show
meillo@76	454 and
meillo@76	455 .Pn mhshow .
meillo@88	456 To ease the life of users,
meillo@69	457 .Pn show
meillo@69	458 was extended to automatically hand the job over to
meillo@69	459 .Pn mhshow
meillo@69	460 if displaying the message would be beyond
meillo@69	461 .Pn show 's
meillo@69	462 abilities.
meillo@88	463 In consequence, the user would simply invoke
meillo@69	464 .Pn show
meillo@69	465 (possibly through
meillo@69	466 .Pn next
meillo@69	467 or
meillo@69	468 .Pn prev )
meillo@69	469 and get the message printed with either
meillo@69	470 .Pn show
meillo@69	471 or
meillo@69	472 .Pn mhshow ,
meillo@69	473 whatever was more appropriate.
meillo@69	474 .P
meillo@69	475 Having two similar tools for essentially the same task is redundant.
meillo@88	476 Usually,
meillo@88	477 users wouldn't distinguish between
meillo@88	478 .Pn show
meillo@88	479 and
meillo@88	480 .Pn mhshow
meillo@88	481 in their daily mail reading.
meillo@88	482 Having two separate display programs was therefore mainly unnecessary
meillo@88	483 from a user's point of view.
meillo@88	484 Besides, the development of both programs needed to be in sync,
meillo@76	485 to ensure that the programs behaved in a similar way,
meillo@76	486 because they were used like a single tool.
meillo@76	487 Different behavior would have surprised the user.
meillo@69	488 .P
meillo@69	489 Today, non-MIME messages are rather seen to be a special case of
meillo@88	490 MIME messages, although it's the other way round.
meillo@69	491 As
meillo@69	492 .Pn mhshow
meillo@88	493 had already be able to display non-MIME messages, it appeared natural
meillo@69	494 to drop
meillo@69	495 .Pn show
meillo@69	496 in favor of using
meillo@69	497 .Pn mhshow
meillo@69	498 exclusively.
meillo@88	499 .Ci 4c1efddfd499300c7e74263e57d8aa137e84c853
meillo@88	500 Removing
meillo@88	501 .Pn show
meillo@88	502 is no loss in function, because functionally
meillo@88	503 .Pn mhshow
meillo@88	504 covers it completely.
meillo@88	505 The old behavior of
meillo@88	506 .Pn show
meillo@88	507 can still be emulated with the simple command line:
meillo@88	508 .VS
meillo@88	509 mhl `mhpath c`
meillo@88	510 VE
meillo@88	511 .P
meillo@76	512 For convenience,
meillo@76	513 .Pn mhshow
meillo@88	514 was renamed to
meillo@88	515 .Pn show
meillo@88	516 after
meillo@88	517 .Pn show
meillo@88	518 was gone.
meillo@88	519 It is clear that such a rename may confuse future developers when
meillo@88	520 trying to understand the history.
meillo@88	521 Nevertheless, I consider the convenience on the user's side,
meillo@88	522 to call
meillo@88	523 .Pn show
meillo@88	524 when they want a message to be displayed, to outweigh the inconvenience
meillo@88	525 on the developer's side when understanding the project history.
meillo@69	526 .P
meillo@88	527 To prepare for the transition,
meillo@69	528 .Pn mhshow
meillo@69	529 was reworked to behave more like
meillo@69	530 .Pn show
meillo@69	531 first.
meillo@88	532 (cf. Sec. XXX)
meillo@88	533 Once the tools behaved more alike, the replacing appeared to be
meillo@88	534 even more natural.
meillo@88	535 Today, mmh's new
meillo@69	536 .Pn show
meillo@88	537 became the one single message display program again, with the difference
meillo@88	538 that today it handles MIME messages as well as non-MIME messages.
meillo@88	539 The outcome of the transition is one program less to maintain,
meillo@88	540 no second display program for users to deal with,
meillo@88	541 and less system complexity.
meillo@69	542 .P
meillo@88	543 Still, removing the old
meillo@69	544 .Pn show
meillo@88	545 hurts in one regard: It had been such a simple program.
meillo@88	546 Its lean elegance is missing to the new
meillo@69	547 .Pn show .
meillo@88	548 But there is no chance;
meillo@88	549 supporting MIME demands for higher essential complexity.
meillo@58	550
meillo@58	551
meillo@58	552 .H2 "Removal of Configure Options
meillo@58	553 .P
meillo@76	554 Customization is a double-edged sword.
meillo@76	555 It allows better suiting setups, but not for free.
meillo@76	556 There is the cost of code complexity to be able to customize.
meillo@76	557 There is the cost of less tested setups, because there are
meillo@72	558 more possible setups and especially corner-cases.
meillo@76	559 And, there is the cost of choice itself.
meillo@76	560 The code complexity directly affects the developers.
meillo@72	561 Less tested code affects both, users and developers.
meillo@76	562 The problem of choice affects the users, for once by having to
meillo@76	563 choose, but also by complexer interfaces that require more documentation.
meillo@72	564 Whenever options add little advantages, they should be considered for
meillo@72	565 removal.
meillo@72	566 I have reduced the number of project-specific configure options from
meillo@72	567 fifteen to three.
meillo@74	568
meillo@76	569 .U3 "Mail Transfer Facilities
meillo@74	570 .P
meillo@85	571 With the removal of the mail transfer facilities five configure
meillo@85	572 options vanished:
meillo@85	573 .P
meillo@85	574 The switches
meillo@85	575 .Sw --with-tls
meillo@85	576 and
meillo@85	577 .Sw --with-cyrus-sasl
meillo@89	578 had activated the support for transfer encryption and authentication.
meillo@85	579 This is not needed anymore.
meillo@85	580 .Ci fecd5d34f65597a4dfa16aeabea7d74b191532c3
meillo@85	581 .Ci 156d35f6425bea4c1ed3c4c79783dc613379c65b
meillo@85	582 .P
meillo@85	583 The configure switch
meillo@85	584 .Sw --enable-pop
meillo@85	585 activated the message retrieval facility.
meillo@85	586 The code area that would be conditionally compiled in for TLS and SASL
meillo@85	587 support had been small.
meillo@85	588 The conditionally compiled code area for POP support had been much larger.
meillo@85	589 Whereas the code base changes would only slightly change on toggling
meillo@85	590 TLS or SASL support, it changed much on toggling POP support.
meillo@85	591 The changes in the code base could hardly be overviewed.
meillo@85	592 By having POP support togglable a second code base had been created,
meillo@85	593 one that needed to be tested.
meillo@85	594 This situation is basically similar for the conditional TLS and SASL
meillo@85	595 code, but there the changes are minor and can yet be overviewed.
meillo@85	596 Still, conditional compilation of a code base creates variations
meillo@85	597 of the original program.
meillo@85	598 More variations require more testing and maintenance work.
meillo@85	599 .P
meillo@85	600 Two other options only specified default configuration values:
meillo@85	601 .Sw --with-mts=[smtp\|sendmail]
meillo@85	602 defined the default transport service.
meillo@85	603 In mmh this fixed to
meillo@85	604 .Ar sendmail .
meillo@85	605 .Ci f6aa95b724fd8c791164abe7ee5468bf5c34f226
meillo@85	606 With
meillo@85	607 .Sw --with-smtpservers=[server1...]
meillo@85	608 default SMTP servers for the
meillo@85	609 .Ar smtp
meillo@85	610 transport service could be specified.
meillo@72	611 .Ci 128545e06224233b7e91fc4c83f8830252fe16c9
meillo@85	612 Both of them became irrelevant.
meillo@72	613
meillo@74	614 .U3 "Backup Prefix
meillo@74	615 .P
meillo@76	616 The backup prefix is the string that was prepended to message
meillo@76	617 filenames to tag them as deleted.
meillo@76	618 By default it had been the comma character `\f(CW,\fP'.
meillo@78	619 In July 2000, Kimmo Suominen introduced
meillo@78	620 the configure option
meillo@78	621 .Sw --with-hash-backup
meillo@78	622 to change the default to the hash symbol `\f(CW#\fP'.
meillo@78	623 The choice was probably personal preference, because first, the
meillo@78	624 option was named
meillo@78	625 .Sw --with-backup-prefix.
meillo@78	626 and had the prefix symbol as argument.
meillo@78	627 Because giving the hash symbol as argument caused to many problems
meillo@78	628 for configure,
meillo@78	629 the option was limited to use the hash symbol as the default prefix.
meillo@78	630 This makes me believe, that the choice for the hash was personal preference.
meillo@78	631 Being it related or not, words that start with the hash symbol
meillo@78	632 introduce a comment in the Unix shell.
meillo@72	633 Thus, the command line
meillo@72	634 .Cl "rm #13 #15
meillo@72	635 calls
meillo@72	636 .Pn rm
meillo@72	637 without arguments because the first hash symbol starts the comment
meillo@72	638 that reaches until the end of the line.
meillo@72	639 To delete the backup files,
meillo@72	640 .Cl "rm ./#13 ./#15"
meillo@72	641 needs to be used.
meillo@78	642 Using the hash as backup prefix can be seen as a precaution agains
meillo@78	643 data loss.
meillo@78	644 .P
meillo@72	645 I removed the configure option but added the profile entry
meillo@72	646 .Pe backup-prefix ,
meillo@72	647 which allows to specify an arbitrary string as backup prefix.
meillo@72	648 .Ci 6c40d481d661d532dd527eaf34cebb6d3f8ed086
meillo@76	649 Profile entries are the common method to change mmh's behavior.
meillo@76	650 This change did not remove the choice but moved it to a location where
meillo@72	651 it suited better.
meillo@76	652 .P
meillo@78	653 Eventually, however, the new trash folder concept
meillo@78	654 .Cf "Sec. XXX
meillo@78	655 obsoleted the concept of the backup prefix completely.
meillo@78	656 .Ci 8edc5aaf86f9f77124664f6801bc6c6cdf258173
meillo@72	657 (Well, there still are corner-cases to remove until the backup
meillo@89	658 prefix can be laid to rest, eventually.)
meillo@72	659 .\" FIXME: Do this work in the code!
meillo@76	660
meillo@76	661 .U3 "Editor and Pager
meillo@74	662 .P
meillo@74	663 The two configure options
meillo@74	664 .CW --with-editor=EDITOR
meillo@74	665 .CW --with-pager=PAGER
meillo@74	666 were used to specify the default editor and pager at configure time.
meillo@74	667 Doing so at configure time made sense in the Eighties,
meillo@76	668 when the set of available editors and pagers varied much across
meillo@76	669 different systems.
meillo@89	670 Today, the situation is more homogeneous.
meillo@74	671 The programs
meillo@74	672 .Pn vi
meillo@74	673 and
meillo@74	674 .Pn more
meillo@76	675 can be expected to be available on every Unix system,
meillo@74	676 as they are specified by POSIX since two decades.
meillo@74	677 (The specifications for
meillo@74	678 .Pn vi
meillo@74	679 and
meillo@74	680 .Pn more
meillo@74	681 appeared in
meillo@74	682 .[
meillo@74	683 posix 1987
meillo@74	684 .]
meillo@74	685 and,
meillo@74	686 .[
meillo@74	687 posix 1992
meillo@74	688 .]
meillo@74	689 respectively.)
meillo@74	690 As a first step, these two tools were hard-coded as defaults.
meillo@74	691 .Ci 5d43a99db70c12a673028c7758c20cbe3e13ef5f
meillo@74	692 Not changed were the
meillo@74	693 .Pe editor
meillo@74	694 and
meillo@74	695 .Pe moreproc
meillo@76	696 profile entries, which allowed the user to override the system defaults.
meillo@74	697 Later, the concept was reworked to respect the standard environment
meillo@74	698 variables
meillo@74	699 .Ev VISUAL
meillo@74	700 and
meillo@74	701 .Ev PAGER
meillo@76	702 if they are set.
meillo@74	703 Today, mmh determines the editor to use in the following order,
meillo@74	704 taking the first available and non-empty item:
meillo@74	705 .IP (1)
meillo@74	706 Environment variable
meillo@74	707 .Ev MMHEDITOR
meillo@74	708 .IP (2)
meillo@74	709 Profile entry
meillo@74	710 .Pe Editor
meillo@74	711 .IP (3)
meillo@74	712 Environment variable
meillo@74	713 .Ev VISUAL
meillo@74	714 .IP (4)
meillo@74	715 Environment variable
meillo@74	716 .Ev EDITOR
meillo@74	717 .IP (5)
meillo@74	718 Command
meillo@74	719 .Pn vi .
meillo@74	720 .P
meillo@76	721 .Ci f85f4b7ae62e3d05a945dcd46ead51f0a2a89a9b
meillo@76	722 .P
meillo@89	723 The pager to use is determined in a similar order,
meillo@74	724 also taking the first available and non-empty item:
meillo@74	725 .IP (1)
meillo@74	726 Environment variable
meillo@74	727 .Ev MMHPAGER
meillo@74	728 .IP (2)
meillo@74	729 Profile entry
meillo@74	730 .Pe Pager
meillo@74	731 (replaces
meillo@74	732 .Pe moreproc )
meillo@74	733 .IP (3)
meillo@74	734 Environment variable
meillo@74	735 .Ev PAGER
meillo@74	736 .IP (4)
meillo@74	737 Command
meillo@74	738 .Pn more .
meillo@74	739 .P
meillo@74	740 .Ci 0c4214ea2aec6497d0d67b436bbee9bc1d225f1e
meillo@74	741 .P
meillo@76	742 By respecting the
meillo@74	743 .Ev VISUAL /\c
meillo@74	744 .Ev EDITOR
meillo@74	745 and
meillo@74	746 .Ev PAGER
meillo@76	747 environment variables,
meillo@76	748 the new behavior confirms better to the common style on Unix systems.
meillo@76	749 Additionally, the new approach is more uniform and clearer to users.
meillo@72	750
meillo@74	751 .U3 "Locale
meillo@74	752 .P
meillo@74	753 The configure option
meillo@74	754 .Sw --disable-locale
meillo@85	755 was removed because POSIX provides locale support and there's
meillo@85	756 hardly any need to disable locale support.
meillo@74	757 .Ci ccf4f175ef4c4e7522f9510a4a1149c15d810dd9
meillo@72	758
meillo@76	759 .U3 "ndbm
meillo@72	760 .P
meillo@74	761 .Pn slocal
meillo@78	762 used to depend on
meillo@74	763 .I ndbm ,
meillo@74	764 a database library.
meillo@76	765 The database is used to store the `\fLMessage-ID\fP's of all
meillo@76	766 messages delivered.
meillo@74	767 This enables
meillo@74	768 .Pn slocal
meillo@74	769 to suppress delivering the same message to the same user twice.
meillo@74	770 (This features was enabled by the
meillo@74	771 .Sw -suppressdup
meillo@74	772 switch.)
meillo@74	773 .P
meillo@74	774 A variety of version of the database library exist.
meillo@78	775 .[
meillo@78	776 wolter unix incompat notes dbm
meillo@78	777 .]
meillo@74	778 Complicated autoconf code was needed to detect them correctly.
meillo@74	779 Further more, the configure switches
meillo@74	780 .Sw --with-ndbm=ARG
meillo@74	781 and
meillo@74	782 .Sw --with-ndbmheader=ARG
meillo@74	783 were added to help with difficult setups that would
meillo@78	784 not be detected automatically or correctly.
meillo@74	785 .P
meillo@74	786 By removing the suppress duplicates feature of
meillo@74	787 .Pn slocal ,
meillo@74	788 the dependency on
meillo@74	789 .I ndbm
meillo@78	790 vanished and 120 lines of complex autoconf code could be saved.
meillo@74	791 .Ci ecd6d6a20cb7a1507e3a20d6c4cb3a1cf14c6bbf
meillo@89	792 The change removed functionality too, but that is minor to the
meillo@78	793 improvement by dropping the dependency and the complex autoconf code.
meillo@72	794
meillo@74	795 .U3 "mh-e Support
meillo@72	796 .P
meillo@74	797 The configure option
meillo@74	798 .Sw --disable-mhe
meillo@74	799 was removed when the mh-e support was reworked.
meillo@74	800 Mh-e is the Emacs front-end to MH.
meillo@76	801 It requires MH to provide minor additional functions.
meillo@76	802 The
meillo@76	803 .Sw --disable-mhe
meillo@76	804 configure option could switch these extensions off.
meillo@76	805 After removing the support for old versions of mh-e,
meillo@74	806 only the
meillo@74	807 .Sw -build
meillo@76	808 switches of
meillo@74	809 .Pn forw
meillo@74	810 and
meillo@74	811 .Pn repl
meillo@76	812 are left to be mh-e extensions.
meillo@76	813 They are now always built in because they add little code and complexity.
meillo@76	814 In consequence, the
meillo@74	815 .Sw --disable-mhe
meillo@76	816 configure option was removed
meillo@72	817 .Ci a7ce7b4a580d77b6c2c4d980812beb589aa4c643
meillo@74	818 Removing the option removed a second code setup that would have
meillo@74	819 needed to be tested.
meillo@76	820 This change was first done in nmh and thereafter merged into mmh.
meillo@76	821 .P
meillo@76	822 The interface changes in mmh require mh-e to be adjusted in order
meillo@76	823 to be able to use mmh as back-end.
meillo@76	824 This will require minor changes to mh-e, but removing the
meillo@76	825 .Sw -build
meillo@76	826 switches would require more rework.
meillo@72	827
meillo@74	828 .U3 "Masquerading
meillo@72	829 .P
meillo@74	830 The configure option
meillo@74	831 .Sw --enable-masquerade
meillo@76	832 could take up to three arguments:
meillo@76	833 `draft_from', `mmailid', and `username_extension'.
meillo@74	834 They activated different types of address masquerading.
meillo@74	835 All of them were implemented in the SMTP-speaking
meillo@74	836 .Pn post
meillo@76	837 command, which provided an MSA.
meillo@76	838 Address masquerading is an MTA's task and mmh does not cover
meillo@76	839 this field anymore.
meillo@76	840 Hence, true masquerading needs to be implemented in the external MTA.
meillo@74	841 .P
meillo@74	842 The
meillo@74	843 .I mmailid
meillo@74	844 masquerading type is the oldest one of the three and the only one
meillo@74	845 available in the original MH.
meillo@74	846 It provided a
meillo@74	847 .I username
meillo@74	848 to
meillo@74	849 .I fakeusername
meillo@76	850 mapping, based on the password file's GECOS field.
meillo@74	851 The man page
meillo@74	852 .Mp mh-tailor(5)
meillo@74	853 described the use case as being the following:
meillo@74	854 .QP
meillo@74	855 This is useful if you want the messages you send to always
meillo@74	856 appear to come from the name of an MTA alias rather than your
meillo@74	857 actual account name. For instance, many organizations set up
meillo@74	858 `First.Last' sendmail aliases for all users. If this is
meillo@74	859 the case, the GECOS field for each user should look like:
meillo@74	860 ``First [Middle] Last <First.Last>''
meillo@74	861 .P
meillo@74	862 As mmh sends outgoing mail via the local MTA only,
meillo@76	863 the best location to do such global rewrites is there.
meillo@74	864 Besides, the MTA is conceptionally the right location because it
meillo@74	865 does the reverse mapping for incoming mail (aliasing), too.
meillo@76	866 Further more, masquerading set up there is readily available for all
meillo@74	867 mail software on the system.
meillo@76	868 Hence, mmailid masquerading was removed.
meillo@74	869 .Ci 0836c8000ccb34b59410ef1c15b1b7feac70ce5f
meillo@74	870 .P
meillo@74	871 The
meillo@74	872 .I username_extension
meillo@76	873 masquerading type did not replace the username but would append a suffix,
meillo@76	874 specified by the
meillo@74	875 .Ev USERNAME_EXTENSION
meillo@76	876 environment variable, to it.
meillo@76	877 This provided support for the
meillo@74	878 .I user-extension
meillo@74	879 feature of qmail and the similar
meillo@74	880 .I "plussed user
meillo@74	881 processing of sendmail.
meillo@74	882 The decision to remove this username_extension masquerading was
meillo@74	883 motivated by the fact that
meillo@74	884 .Pn spost
meillo@76	885 hadn't supported it already.
meillo@76	886 .Ci 2abae0bfd0ad5bf898461e50aa4b466d641f23d9
meillo@76	887 Username extensions are possible in mmh, but less convenient to use.
meillo@76	888 .\" XXX format file %(getenv USERNAME_EXTENSION)
meillo@74	889 .P
meillo@74	890 The
meillo@74	891 .I draft_from
meillo@74	892 masquerading type instructed
meillo@74	893 .Pn post
meillo@84	894 to use the value of the
meillo@84	895 .Hd From
meillo@84	896 header field as SMTP envelope sender.
meillo@76	897 Sender addresses could be replaced completely.
meillo@74	898 .Ci b14ea6073f77b4359aaf3fddd0e105989db9
meillo@76	899 Mmh offers a kind of masquerading similar in effect, but
meillo@74	900 with technical differences.
meillo@76	901 As mmh does not transfer messages itself, the local MTA has final control
meillo@76	902 over the sender's address. Any masquerading mmh introduces may be reverted
meillo@76	903 by the MTA.
meillo@76	904 In times of pedantic spam checking, an MTA will take care to use
meillo@76	905 sensible envelope sender addresses to keep its own reputation up.
meillo@84	906 Nonetheless, the MUA can set the
meillo@84	907 .Hd From
meillo@84	908 header field and thereby propose
meillo@76	909 a sender address to the MTA.
meillo@74	910 The MTA may then decide to take that one or generate the canonical sender
meillo@74	911 address for use as envelope sender address.
meillo@74	912 .P
meillo@74	913 In mmh, the MTA will always extract the recipient and sender from the
meillo@84	914 message header (\c
meillo@74	915 .Pn sendmail 's
meillo@74	916 .Sw -t
meillo@74	917 switch).
meillo@84	918 The
meillo@84	919 .Hd From
meillo@84	920 header field of the draft may be set arbitrary by the user.
meillo@74	921 If it is missing, the canonical sender address will be generated by the MTA.
meillo@74	922
meillo@74	923 .U3 "Remaining Options
meillo@74	924 .P
meillo@74	925 Two configure options remain in mmh.
meillo@74	926 One is the locking method to use:
meillo@74	927 .Sw --with-locking=[dot\|fcntl\|flock\|lockf] .
meillo@76	928 The idea of removing all methods except the portable dot locking
meillo@76	929 and having that one as the default is appealing, but this change
meillo@76	930 requires deeper technical investigation into the topic.
meillo@76	931 The other option,
meillo@74	932 .Sw --enable-debug ,
meillo@74	933 compiles the programs with debugging symbols and does not strip them.
meillo@74	934 This option is likely to stay.
meillo@72	935
meillo@72	936
meillo@58	937
meillo@63	938
meillo@58	939 .H2 "Removal of switches
meillo@58	940 .P
meillo@58	941
meillo@58	942
meillo@58	943
meillo@58	944
meillo@74	945 .H1 "Modernizing
meillo@58	946
meillo@58	947
meillo@58	948 .H2 "Removal of Code Relicts
meillo@0	949 .P
meillo@51	950 The code base of mmh originates from the late Seventies,
meillo@51	951 had been extensively
meillo@51	952 worked on in the mid Eighties, and had been partly reorganized and extended
meillo@51	953 in the Nineties. Relicts of all those times had gathered in the code base.
meillo@12	954 My goal was to remove any ancient code parts. One part of the task was
meillo@12	955 converting obsolete code constructs to standard constructs, the other part
meillo@12	956 was dropping obsolete functions.
meillo@12	957 .P
meillo@12	958 As I'm not even thirty years old and have no more than seven years of
meillo@51	959 Unix experience, I needed to learn about the history in retrospective.
meillo@51	960 Older people likely have used those ancient constructs themselves
meillo@51	961 and have suffered from their incompatibilities and have longed for
meillo@12	962 standardization. Unfortunately, I have only read that others had done so.
meillo@12	963 This put me in a much more difficult positions when working on the old
meillo@12	964 code. I needed to recherche what other would have known by heart from
meillo@12	965 experience. All my programming experience comes from a time past ANSI C
meillo@12	966 and past POSIX. Although I knew about the times before, I took the
meillo@51	967 current state implicitly for granted most of the time.
meillo@12	968 .P
meillo@12	969 Being aware of
meillo@12	970 these facts, I rather let people with more historic experience solve the
meillo@12	971 task of converting the ancient code constructs to standardized ones.
meillo@12	972 Luckily, Lyndon Nerenberg focused on this task at the nmh project.
meillo@12	973 He converted large parts of the code to POSIX constructs, removing
meillo@12	974 the conditionals compilation for now standardized features.
meillo@12	975 I'm thankful for this task being solved. I only pulled the changes into
meillo@12	976 mmh.
meillo@12	977 .P
meillo@20	978 The other task \(en dropping ancient functionality to remove old code \(en
meillo@12	979 I did myself, though. My position to strip mmh to the bare minimum of
meillo@12	980 frequently used features is much more revolutional than the nmh community
meillo@20	981 likes it. Without the need to justify my decisions, I was able to quickly
meillo@20	982 remove functionality I considered ancient.
meillo@20	983 The need to discuss my decisions with
meillo@20	984 peers likely would have slowed this process down. Of course, I researched
meillo@12	985 if a particular feature really should be dropped. Having not had any
meillo@12	986 contact to this feature within my computer life was a first indicator to
meillo@12	987 drop it, but I also asked others and searched the literature for modern
meillo@12	988 usage of the feature. If it appeared to be truly ancient, I dropped it.
meillo@12	989 The reason for dropping is always part of the commit message in the
meillo@12	990 version control system. Thus, it is easy for others to check their
meillo@12	991 view on the topic with mine and possibly to argue for reinclusion.
meillo@12	992
meillo@12	993 .U2 "MMDF maildrop support
meillo@12	994 .P
meillo@12	995 I did drop any support for the MMDF maildrop format. This type of format
meillo@12	996 is conceptionally similar to the mbox format, but uses four bytes with
meillo@12	997 value 1 (\fL^A^A^A^A\fP) as message delimiter,
meillo@18	998 instead of the string ``\fLFrom\ \fP''.
meillo@12	999 Due to the similarity and mbox being the de-facto standard maildrop
meillo@12	1000 format on Unix, but also due to the larger influence of Sendmail than MMDF,
meillo@12	1001 the MMDF maildrop format had vanished.
meillo@12	1002 .P
meillo@12	1003 The simplifications within the code were only moderate. Switches could
meillo@12	1004 be removed from tools like
meillo@12	1005 .L packf ,
meillo@12	1006 which generate packed mailboxes. Only one packed mailbox format remained:
meillo@12	1007 mbox.
meillo@12	1008 The most important changes affect the equally named mail parsing routine in
meillo@12	1009 .L sbr/m_getfld.c .
meillo@12	1010 The direct MMDF code had been removed, but as now only one packed mailbox
meillo@12	1011 format is left, code structure simplifications are likely possible.
meillo@12	1012 The reason why they are still outstanding is the heavily optimized code
meillo@18	1013 of
meillo@18	1014 .Fu m_getfld() .
meillo@18	1015 Changes beyond a small local scope \(en
meillo@12	1016 which restructuring in its core is \(en cause a high risk of damaging
meillo@12	1017 the intricate workings of the optimized code. This problem is know
meillo@12	1018 to the developers of nmh, too. They also avoid touching this minefield
meillo@12	1019 if possible.
meillo@12	1020
meillo@12	1021 .U2 "UUCP Bang Paths
meillo@12	1022 .P
meillo@12	1023 More questionably than the former topic is the removal of support for the
meillo@12	1024 UUCP bang path address style. However, the user may translate the bang
meillo@12	1025 paths on retrieval to Internet addresses and the other way on posting
meillo@12	1026 messages. The former can be done my an MDA like procmail; the latter
meillo@12	1027 by a sendmail wrapper. This would ensure that any address handling would
meillo@12	1028 work as expected. However, it might just work well without any
meillo@12	1029 such modifications, as mmh does not touch addresses much, in general.
meillo@12	1030 But I can't ensure as I have never used an environment with bang paths.
meillo@12	1031 Also, the behavior might break at any point in further development.
meillo@12	1032
meillo@12	1033 .U2 "Hardcopy terminal support
meillo@12	1034 .P
meillo@12	1035 More of a funny anecdote is the remaining of a check for printing to a
meillo@12	1036 hardcopy terminal until Spring 2012, when I finally removed it.
meillo@12	1037 I surely would be very happy to see such a terminal in action, maybe
meillo@12	1038 actually being able to work on it, but I fear my chances are null.
meillo@12	1039 .P
meillo@12	1040 The check only prevented a pager to be placed between the outputting
meillo@18	1041 program (\c
meillo@18	1042 .Pn mhl )
meillo@18	1043 and the terminal. This could have been ensured with
meillo@18	1044 the
meillo@82	1045 .Sw -nomoreproc
meillo@18	1046 at the command line statically, too.
meillo@12	1047
meillo@12	1048 .U2 "Removed support for header fields
meillo@12	1049 .P
meillo@84	1050 The
meillo@84	1051 .Hd Encrypted
meillo@84	1052 header field had been introduced by RFC\^822, but already
meillo@12	1053 marked legacy in RFC 2822. It was superseded by FIXME.
meillo@84	1054 Mmh does no more support this header field.
meillo@12	1055 .P
meillo@84	1056 Native support for
meillo@84	1057 .Hd Face
meillo@84	1058 header fields had been removed, as well.
meillo@84	1059 The feature is similar to the
meillo@84	1060 .Hd X-Face
meillo@84	1061 header field in its intent,
meillo@21	1062 but takes a different approach to store the image.
meillo@84	1063 Instead of encoding the image data directly into the header field,
meillo@84	1064 the it contains the hostname and UDP port where the image
meillo@21	1065 date could be retrieved.
meillo@84	1066 Neither
meillo@84	1067 .Hd X-Face
meillo@84	1068 nor the here described
meillo@84	1069 .Hd Face
meillo@84	1070 system
meillo@21	1071 \**
meillo@21	1072 .FS
meillo@21	1073 There is also a newer but different system, invented 2005,
meillo@84	1074 using
meillo@84	1075 .Hd Face
meillo@84	1076 headers.
meillo@84	1077 It is the successor of
meillo@84	1078 .Hd X-Face
meillo@84	1079 providing colored PNG images.
meillo@21	1080 .FE
meillo@21	1081 became well used in the large scale.
meillo@21	1082 It's still possible to use a Face systems,
meillo@21	1083 although mmh does not provide support for any of the different systems
meillo@21	1084 anymore. It's fairly easy to write a small shell script to
meillo@21	1085 extract the embedded or fetch the external Face data and display the image.
meillo@84	1086 Own
meillo@84	1087 .Hd Face
meillo@84	1088 header field can be added into the draft template files.
meillo@21	1089 .P
meillo@84	1090 .Hd Content-MD5
meillo@84	1091 header fields were introduced by RFC\^1864. They provide only
meillo@12	1092 a verification of data corruption during the transfer. By no means can
meillo@12	1093 they ensure verbatim end-to-end delivery of the contents. This is clearly
meillo@12	1094 stated in the RFC. The proper approach to provide verificationability
meillo@12	1095 of content in an end-to-end relationship is the use of digital cryptography
meillo@12	1096 (RFCs FIXME). On the other hand, transfer protocols should ensure the
meillo@12	1097 integrity of the transmission. In combinations these two approaches
meillo@84	1098 make the
meillo@84	1099 .Hd Content-MD5
meillo@84	1100 header field useless. In consequence, I removed
meillo@12	1101 the support for it. By this removal, MD5 computation is not needed
meillo@12	1102 anywhere in mmh. Hence, over 500 lines of code were removed by this one
meillo@84	1103 change. Even if the
meillo@84	1104 .Hd Content-MD5
meillo@84	1105 header field is useful sometimes,
meillo@89	1106 I value its usefulness less than the improvement in maintainability, caused
meillo@12	1107 by the removal.
meillo@12	1108
meillo@20	1109 .U2 "Prompter's Control Keys
meillo@20	1110 .P
meillo@20	1111 The program
meillo@20	1112 .Pn prompter
meillo@20	1113 queries the user to fill in a message form. When used by
meillo@20	1114 .Pn comp
meillo@20	1115 as:
meillo@82	1116 .VS
meillo@82	1117 comp -editor prompter
meillo@82	1118 VE
meillo@20	1119 the resulting behavior is similar to
meillo@20	1120 .Pn mailx .
meillo@51	1121 Apparently,
meillo@20	1122 .Pn prompter
meillo@20	1123 hadn't been touched lately. Otherwise it's hardly explainable why it
meillo@20	1124 still offered the switches
meillo@84	1125 .Sw -erase
meillo@84	1126 .Ar chr
meillo@20	1127 and
meillo@84	1128 .Sw -kill
meillo@84	1129 .Ar chr
meillo@20	1130 to name the characters for command line editing.
meillo@21	1131 The times when this had been necessary are long time gone.
meillo@20	1132 Today these things work out-of-the-box, and if not, are configured
meillo@20	1133 with the standard tool
meillo@20	1134 .Pn stty .
meillo@20	1135
meillo@21	1136 .U2 "Vfork and Retry Loops
meillo@21	1137 .P
meillo@51	1138 MH creates many processes, which is a consequence of the tool chest approach.
meillo@21	1139 In earlier times
meillo@21	1140 .Fu fork()
meillo@21	1141 had been an expensive system call, as the process's whole image needed
meillo@21	1142 to be duplicated. One common case is replacing the image with
meillo@21	1143 .Fu exec()
meillo@21	1144 right after having forked the child process.
meillo@21	1145 To speed up this case, the
meillo@21	1146 .Fu vfork()
meillo@21	1147 system call was invented at Berkeley. It completely omits copying the
meillo@21	1148 image. If the image gets replaced right afterwards then unnecessary
meillo@21	1149 work is omited. On old systems this results in large speed ups.
meillo@21	1150 MH uses
meillo@21	1151 .Fu vfork()
meillo@21	1152 whenever possible.
meillo@21	1153 .P
meillo@21	1154 Memory management units that support copy-on-write semantics make
meillo@21	1155 .Fu fork()
meillo@21	1156 almost as fast as
meillo@21	1157 .Fu vfork()
meillo@21	1158 in the cases when they can be exchanged.
meillo@21	1159 With
meillo@21	1160 .Fu vfork()
meillo@51	1161 being more error-prone and hardly faster, it's preferable to simply
meillo@21	1162 use
meillo@21	1163 .Fu fork()
meillo@21	1164 instead.
meillo@21	1165 .P
meillo@21	1166 Related to the costs of
meillo@21	1167 .Fu fork()
meillo@21	1168 is the probability of its success.
meillo@21	1169 Today on modern systems, the system call will succeed almost always.
meillo@51	1170 In the Eighties on heavy loaded systems, as they were common at
meillo@21	1171 universities, this had been different. Thus, many of the
meillo@21	1172 .Fu fork()
meillo@21	1173 calls were wrapped into loops to retry to fork several times in
meillo@21	1174 short intervals, in case of previous failure.
meillo@21	1175 In mmh, the program aborts at once if the fork failed.
meillo@21	1176 The user can reexecute the command then. This is expected to be a
meillo@21	1177 very rare case on modern systems, especially personal ones, which are
meillo@21	1178 common today.
meillo@21	1179
meillo@12	1180
meillo@58	1181 .H2 "Attachments
meillo@22	1182 .P
meillo@58	1183 MIME
meillo@58	1184
meillo@58	1185
meillo@58	1186 .H2 "Digital Cryptography
meillo@22	1187 .P
meillo@58	1188 Signing and encryption.
meillo@58	1189
meillo@58	1190
meillo@58	1191 .H2 "Good Defaults
meillo@22	1192 .P
meillo@58	1193 foo
meillo@58	1194
meillo@58	1195
meillo@58	1196
meillo@58	1197
meillo@58	1198 .H1 "Code style
meillo@22	1199 .P
meillo@58	1200 foo
meillo@58	1201
meillo@58	1202
meillo@58	1203 .H2 "Standard Code
meillo@22	1204 .P
meillo@58	1205 POSIX
meillo@22	1206
meillo@22	1207
meillo@58	1208 .H2 "Separation
meillo@14	1209
meillo@58	1210 .U2 "MH Directory Split
meillo@0	1211 .P
meillo@19	1212 In MH and nmh, a personal setup had consisted of two parts:
meillo@19	1213 The MH profile, named
meillo@19	1214 .Fn \&.mh_profile
meillo@19	1215 and being located directly in the user's home directory.
meillo@19	1216 And the MH directory, where all his mail messages and also his personal
meillo@19	1217 forms, scan formats, other configuration files are stored. The location
meillo@19	1218 of this directory could be user-chosen. The default was to name it
meillo@19	1219 .Fn Mail
meillo@19	1220 and have it directly in the home directory.
meillo@19	1221 .P
meillo@19	1222 I've never liked the data storage and the configuration to be intermixed.
meillo@19	1223 They are different kinds of data. One part, are the messages,
meillo@19	1224 which are the data to operate on. The other part, are the personal
meillo@19	1225 configuration files, which are able to change the behavior of the operations.
meillo@19	1226 The actual operations are defined in the profile, however.
meillo@19	1227 .P
meillo@19	1228 When storing data, one should try to group data by its type.
meillo@19	1229 There's sense in the Unix file system hierarchy, where configuration
meillo@19	1230 file are stored separate (\c
meillo@19	1231 .Fn /etc )
meillo@19	1232 to the programs (\c
meillo@19	1233 .Fn /bin
meillo@19	1234 and
meillo@19	1235 .Fn /usr/bin )
meillo@19	1236 to their sources (\c
meillo@19	1237 .Fn /usr/src ).
meillo@19	1238 Such separation eases the backup management, for instance.
meillo@19	1239 .P
meillo@19	1240 In mmh, I've reorganized the file locations.
meillo@19	1241 Still there are two places:
meillo@19	1242 There's the mail storage directory, which, like in MH, contains all the
meillo@19	1243 messages, but, unlike in MH, nothing else.
meillo@19	1244 Its location still is user-chosen, with the default name
meillo@19	1245 .Fn Mail ,
meillo@19	1246 in the user's home directory. This is much similar to the case in nmh.
meillo@19	1247 The configuration files, however, are grouped together in the new directory
meillo@19	1248 .Fn \&.mmh
meillo@19	1249 in the user's home directory.
meillo@19	1250 The user's profile now is a file, named
meillo@19	1251 .Fn profile ,
meillo@19	1252 in this mmh directory.
meillo@19	1253 Consistently, the context file and all the personal forms, scan formats,
meillo@19	1254 and the like, are also there.
meillo@19	1255 .P
meillo@19	1256 The naming changed with the relocation.
meillo@19	1257 The directory where everything, except the profile, had been stored (\c
meillo@19	1258 .Fn $HOME/Mail ),
meillo@19	1259 used to be called \fIMH directory\fP. Now, this directory is called the
meillo@19	1260 user's \fImail storage\fP. The name \fImmh directory\fP is now given to
meillo@19	1261 the new directory
meillo@19	1262 (\c
meillo@19	1263 .Fn $HOME/.mmh ),
meillo@19	1264 containing all the personal configuration files.
meillo@19	1265 .P
meillo@19	1266 The separation of the files by type of content is logical and convenient.
meillo@19	1267 There are no functional differences as any possible setup known to me
meillo@19	1268 can be implemented with both approaches, although likely a bit easier
meillo@19	1269 with the new approach. The main goal of the change had been to provide
meillo@19	1270 sensible storage locations for any type of personal mmh file.
meillo@19	1271 .P
meillo@19	1272 In order for one user to have multiple MH setups, he can use the
meillo@19	1273 environment variable
meillo@19	1274 .Ev MH
meillo@19	1275 the point to a different profile file.
meillo@19	1276 The MH directory (mail storage plus personal configuration files) is
meillo@19	1277 defined by the
meillo@19	1278 .Pe Path
meillo@19	1279 profile entry.
meillo@19	1280 The context file could be defined by the
meillo@19	1281 .Pe context
meillo@19	1282 profile entry or by the
meillo@19	1283 .Ev MHCONTEXT
meillo@19	1284 environment variable.
meillo@19	1285 The latter is useful to have a distinct context (e.g. current folders)
meillo@19	1286 in each terminal window, for instance.
meillo@19	1287 In mmh, there are three environment variables now.
meillo@19	1288 .Ev MMH
meillo@19	1289 may be used to change the location of the mmh directory.
meillo@19	1290 .Ev MMHP
meillo@19	1291 and
meillo@19	1292 .Ev MMHC
meillo@19	1293 change the profile and context files, respectively.
meillo@19	1294 Besides providing a more consistent feel (which simply is the result
meillo@19	1295 of being designed anew), the set of personal configuration files can
meillo@19	1296 be chosen independently from the profile (including mail storage location)
meillo@19	1297 and context, now. Being it relevant for practical use or not, it
meillo@19	1298 de-facto is an improvement. However, the main achievement is the
meillo@19	1299 split between mail storage and personal configuration files.
meillo@17	1300
meillo@0	1301
meillo@58	1302 .H2 "Modularization
meillo@0	1303 .P
meillo@58	1304 whatnowproc
meillo@0	1305 .P
meillo@49	1306 The \fIMH library\fP
meillo@49	1307 .Fn libmh.a
meillo@49	1308 collects a bunch of standard functions that many of the MH tools need,
meillo@49	1309 like reading the profile or context files.
meillo@49	1310 This doesn't hurt the separation.
meillo@49	1311
meillo@58	1312
meillo@58	1313 .H2 "Style
meillo@58	1314 .P
meillo@58	1315 Code layout, goto, ...
meillo@58	1316
meillo@58	1317
meillo@58	1318
meillo@58	1319
meillo@89	1320 .H1 "Concept Exploitation/Homogeneity
meillo@58	1321
meillo@58	1322
meillo@58	1323 .H2 "Draft Folder
meillo@58	1324 .P
meillo@58	1325 Historically, MH provided exactly one draft message, named
meillo@58	1326 .Fn draft
meillo@58	1327 and
meillo@58	1328 being located in the MH directory. When starting to compose another message
meillo@58	1329 before the former one was sent, the user had been questioned whether to use,
meillo@58	1330 refile or replace the old draft. Working on multiple drafts at the same time
meillo@58	1331 was impossible. One could only work on them in alteration by refiling the
meillo@58	1332 previous one to some directory and fetching some other one for reediting.
meillo@58	1333 This manual draft management needed to be done each time the user wanted
meillo@58	1334 to switch between editing one draft to editing another.
meillo@58	1335 .P
meillo@58	1336 To allow true parallel editing of drafts, in a straight forward way, the
meillo@58	1337 draft folder facility exists. It had been introduced already in July 1984
meillo@58	1338 by Marshall T. Rose. The facility was deactivated by default.
meillo@58	1339 Even in nmh, the draft folder facility remained deactivated by default.
meillo@58	1340 At least, Richard Coleman added the man page
meillo@58	1341 .Mp mh-draft(5)
meillo@58	1342 to document
meillo@58	1343 the feature well.
meillo@58	1344 .P
meillo@58	1345 The only advantage of not using the draft folder facility is the static
meillo@89	1346 name of the draft file. This could be an issue for MH front-ends like mh-e.
meillo@58	1347 But as they likely want to provide working on multiple drafts in parallel,
meillo@58	1348 the issue is only concerning compatibility. The aim of nmh to stay compatible
meillo@58	1349 prevented the default activation of the draft folder facility.
meillo@58	1350 .P
meillo@58	1351 On the other hand, a draft folder is the much more natural concept than
meillo@58	1352 a draft message. MH's mail storage consists of folders and messages,
meillo@58	1353 the messages named with ascending numbers. A draft message breaks with this
meillo@58	1354 concept by introducing a message in a file named
meillo@58	1355 .Fn draft .
meillo@58	1356 This draft
meillo@58	1357 message is special. It can not be simply listed with the available tools,
meillo@58	1358 but instead requires special switches. I.e. corner-cases were
meillo@58	1359 introduced. A draft folder, in contrast, does not introduce such
meillo@58	1360 corner-cases. The available tools can operate on the messages within that
meillo@58	1361 folder like on any messages within any mail folders. The only difference
meillo@58	1362 is the fact that the default folder for
meillo@58	1363 .Pn send
meillo@58	1364 is the draft folder,
meillo@58	1365 instead of the current folder, like for all other tools.
meillo@58	1366 .P
meillo@58	1367 The trivial part of the change was activating the draft folder facility
meillo@58	1368 by default and setting a default name for this folder. Obviously, I chose
meillo@58	1369 the name
meillo@58	1370 .Fn +drafts .
meillo@58	1371 This made the
meillo@82	1372 .Sw -draftfolder
meillo@58	1373 and
meillo@82	1374 .Sw -draftmessage
meillo@58	1375 switches useless, and I could remove them.
meillo@58	1376 The more difficult but also the part that showed the real improvement,
meillo@58	1377 was updating the tools to the new concept.
meillo@82	1378 .Sw -draft
meillo@58	1379 switches could
meillo@58	1380 be dropped, as operating on a draft message became indistinguishable to
meillo@58	1381 operating on any other message for the tools.
meillo@58	1382 .Pn comp
meillo@58	1383 still has its
meillo@82	1384 .Sw -use
meillo@58	1385 switch for switching between its two modes: (1) Compose a new
meillo@58	1386 draft, possibly by taking some existing message as a form. (2) Modify
meillo@58	1387 an existing draft. In either case, the behavior of
meillo@58	1388 .Pn comp is
meillo@58	1389 deterministic. There is no more need to query the user. I consider this
meillo@58	1390 a major improvement. By making
meillo@58	1391 .Pn send
meillo@58	1392 simply operate on the current
meillo@58	1393 message in the draft folder by default, with message and folder both
meillo@58	1394 overridable by specifying them on the command line, it is now possible
meillo@58	1395 to send a draft anywhere within the storage by simply specifying its folder
meillo@58	1396 and name.
meillo@58	1397 .P
meillo@58	1398 All theses changes converted special cases to regular cases, thus
meillo@58	1399 simplifying the tools and increasing the flexibility.
meillo@58	1400
meillo@58	1401
meillo@58	1402 .H2 "Trash Folder
meillo@58	1403 .P
meillo@58	1404 Similar to the situation for drafts is the situation for removed messages.
meillo@58	1405 Historically, a message was deleted by renaming. A specific
meillo@58	1406 \fIbackup prefix\fP, often comma (\c
meillo@58	1407 .Fn , )
meillo@58	1408 or hash (\c
meillo@58	1409 .Fn # ),
meillo@58	1410 being prepended to the file name. Thus, MH wouldn't recognize the file
meillo@58	1411 as a message anymore, as only files whose name consists of digits only
meillo@58	1412 are treated as messages. The removed messages remained as files in the
meillo@58	1413 same directory and needed some maintenance job to truly delete them after
meillo@58	1414 some grace time. Usually, by running a command similar to
meillo@82	1415 .VS
meillo@82	1416 find /home/user/Mail -ctime +7 -name ',*' \| xargs rm
meillo@82	1417 VE
meillo@58	1418 in a cron job. Within the grace time interval
meillo@58	1419 the original message could be restored by stripping the
meillo@58	1420 the backup prefix from the file name. If however, the last message of
meillo@58	1421 a folder is been removed \(en say message
meillo@58	1422 .Fn 6
meillo@58	1423 becomes file
meillo@58	1424 .Fn ,6
meillo@58	1425 \(en and a new message enters the same folder, thus the same
meillo@58	1426 numbered being given again \(en in our case
meillo@58	1427 .Fn 6
meillo@58	1428 \(en, if that one
meillo@58	1429 is removed too, then the backup of the former message gets overwritten.
meillo@58	1430 Thus, the ability to restore removed messages does not only depend on
meillo@58	1431 the ``sweeping cron job'' but also on the removing of further messages.
meillo@58	1432 This is undesirable, because the real mechanism is hidden from the user
meillo@58	1433 and the consequences of further removals are not always obvious.
meillo@58	1434 Further more, the backup files are scattered within the whole mail
meillo@58	1435 storage, instead of being collected at one place.
meillo@58	1436 .P
meillo@58	1437 To improve the situation, the profile entry
meillo@58	1438 .Pe rmmproc
meillo@58	1439 (previously named
meillo@58	1440 .Pe Delete-Prog )
meillo@58	1441 was introduced, very early.
meillo@58	1442 It could be set to any command, which would care for the mail removal
meillo@58	1443 instead of taking the default action, described above.
meillo@58	1444 Refiling the to-be-removed files to some garbage folder was a common
meillo@58	1445 example. Nmh's man page
meillo@58	1446 .Mp rmm(1)
meillo@58	1447 proposes
meillo@58	1448 .Cl "refile +d
meillo@58	1449 to move messages to the garbage folder and
meillo@58	1450 .Cl "rm `mhpath +d all`
meillo@58	1451 the empty the garbage folder.
meillo@58	1452 Managing the message removal this way is a sane approach. It keeps
meillo@58	1453 the removed messages in one place, makes it easy to remove the backup
meillo@58	1454 files, and, most important, enables the user to use the tools of MH
meillo@58	1455 itself to operate on the removed messages. One can
meillo@58	1456 .Pn scan
meillo@58	1457 them,
meillo@58	1458 .Pn show
meillo@58	1459 them, and restore them with
meillo@58	1460 .Pn refile .
meillo@58	1461 There's no more
meillo@58	1462 need to use
meillo@58	1463 .Pn mhpath
meillo@58	1464 to switch over from MH tools to Unix tools \(en MH can do it all itself.
meillo@58	1465 .P
meillo@58	1466 This approach matches perfect with the concepts of MH, thus making
meillo@58	1467 it powerful. Hence, I made it the default. And even more, I also
meillo@58	1468 removed the old backup prefix approach, as it is clearly less powerful.
meillo@58	1469 Keeping unused alternative in the code is a bad choice as they likely
meillo@58	1470 gather bugs, by not being constantly tested. Also, the increased code
meillo@58	1471 size and more conditions crease the maintenance costs. By strictly
meillo@58	1472 converting to the trash folder approach, I simplified the code base.
meillo@58	1473 .Pn rmm
meillo@58	1474 calls
meillo@58	1475 .Pn refile
meillo@58	1476 internally to move the to-be-removed
meillo@58	1477 message to the trash folder (\c
meillo@58	1478 .Fn +trash
meillo@58	1479 by default). Messages
meillo@58	1480 there can be operated on like on any other message in the storage.
meillo@58	1481 The sweep clean, one can use
meillo@82	1482 .Cl "rmm -unlink +trash a" ,
meillo@58	1483 where the
meillo@82	1484 .Sw -unlink
meillo@58	1485 switch causes the files to be truly unliked instead
meillo@58	1486 of moved to the trash folder.
meillo@58	1487
meillo@58	1488
meillo@58	1489 .H2 "Path Notations
meillo@58	1490 .P
meillo@58	1491 foo
meillo@58	1492
meillo@58	1493
meillo@58	1494 .H2 "MIME Integration
meillo@58	1495 .P
meillo@58	1496 user-visible access to whole messages and MIME parts are inherently
meillo@58	1497 different
meillo@58	1498
meillo@58	1499
meillo@58	1500 .H2 "Of One Cast
meillo@58	1501 .P