docs/master

annotate ch03.roff @ 62:24aabbfe5794

Minor rework of larger text areas.
author markus schnalke <meillo@marmaro.de>
date Fri, 01 Jun 2012 17:15:38 +0200
parents 6a92e0208de0
children abbaca05ee8e
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@58 6
meillo@58 7
meillo@58 8
meillo@58 9
meillo@58 10 .H1 "Stream-lining
meillo@58 11
meillo@0 12 .P
meillo@58 13 MH had been considered an all-in-one system for mail handling.
meillo@58 14 The community around nmh has a similar understanding.
meillo@58 15 In fundamental difference, I believe that mmh should be a MUA but
meillo@58 16 nothing more. I believe that all-in-one mail systems are not the way
meillo@58 17 to go. There are excellent specialized MTAs, like Postfix;
meillo@58 18 there are specialized MDAs, like Procmail; there are specialized
meillo@58 19 MRAs, like Fetchmail. I believe it's best to use them instead of
meillo@58 20 providing the same function ourselves. Doing something well requires to
meillo@58 21 focus on this particular aspect or a small set of aspects. The more
meillo@58 22 it is possible to focus, the better the result in this particular
meillo@58 23 area will be. The limiting resource in Free Software community development
meillo@58 24 usually is human power. If the low development power is even parted
meillo@58 25 into multiple development areas, it will hardly be possible to
meillo@58 26 compete with the specialists in the various fields. This is even
meillo@58 27 increased, given the small community \(en developers and users \(en
meillo@58 28 that MH-based mail systems have. In consequence, I believe that the
meillo@58 29 available resources should be concentrated at the point where MH is
meillo@58 30 most unique. This is clearly the MUA part.
meillo@58 31 .P
meillo@60 32 The goal for mmh was to remove peripheral parts and stream-line
meillo@60 33 it for the MUA task.
meillo@60 34
meillo@60 35
meillo@60 36 .H2 "Removal of Mail Transfer Facilities
meillo@60 37 .P
meillo@60 38 In contrast to nmh, which also provides mail submission and mail retrieval
meillo@60 39 facilities, mmh is a MUA only.
meillo@60 40 .P
meillo@60 41 The MSA is called ``Message Transfer Service'' (MTS) in nmh.
meillo@60 42 The facility establishes TCP/IP connections and speaks SMTP to submit
meillo@60 43 messages for relay to the outside world.
meillo@60 44 This part is implemented in the
meillo@60 45 .Pn post
meillo@60 46 command.
meillo@60 47 Demanded by the changes in
meillo@60 48 emailing, this part of nmh required changes in the last years.
meillo@60 49 Encrypted connections needed to be supported, hence SASL was introduced
meillo@60 50 into nmh. This added complexity to the nmh without improving it in
meillo@60 51 its core functions. Also, keeping up with recent developments in
meillo@60 52 this field needs requires development power and specialists.
meillo@60 53 Mmh cuts this whole facility off and depends on an external MTA instead.
meillo@60 54 The only outgoing interface available to mmh is the
meillo@60 55 .Pn sendmail
meillo@60 56 command.
meillo@60 57 Almost any MTA provides a
meillo@60 58 .Pn sendmail
meillo@60 59 command.
meillo@60 60 It not, any program can be substituted if it reads the
meillo@60 61 message from the standard input, extracts the recipient addresses
meillo@60 62 from the message header and does not conflict
meillo@60 63 with sendmail-specific command line arguments.
meillo@60 64 .P
meillo@60 65 To retrieve mail, the
meillo@60 66 .Pn inc
meillo@60 67 command in nmh has the ability to establish TCP/IP connections
meillo@60 68 and speaks POP3 to retrieve mail from remote servers.
meillo@60 69 As with mail submission, here encrypted connections are required
meillo@60 70 today, thus SASL support was added.
meillo@60 71 As POP3 is superseded by IMAP more and more, support for message
meillo@60 72 retrieval through IMAP will become necessary to be added soon.
meillo@60 73 Mmh has no support for retrieving mail from remote locations.
meillo@60 74 It depends on an external tool to cover this task.
meillo@60 75 There are two ways for messages to enter mmh's mail storage:
meillo@60 76 Incorporate them with
meillo@60 77 .Pn inc
meillo@60 78 from the system maildrop, or with
meillo@60 79 .Pn rcvstore
meillo@60 80 from the standard input.
meillo@60 81 .P
meillo@60 82 In consequence, mmh includes neither networking nor SASL code anymore.
meillo@60 83 Two large separate functional units are removed.
meillo@60 84 They account for about XXX lines of code and XXX libraries.
meillo@60 85 .P
meillo@60 86 With the removal of the MSA and MRA, mmh converted from an all-in-one
meillo@60 87 mail system to the core: the MUA.
meillo@60 88 Following the Unix philosophy, it focuses on one job and to do that well.
meillo@60 89 Now, of course, mmh depends on third-party software.
meillo@60 90 An external MTA/MSA is required to transfer mail to the outside world;
meillo@60 91 an external MRA is required to retrieve mail from remote machines.
meillo@60 92 There exist excellent implementations of such software,
meillo@60 93 which do this specific task likely much better than the internal
meillo@60 94 versions of nmh do it. Also, this provides the choice for the best
meillo@60 95 suiting one of the available implementation.
meillo@60 96 .P
meillo@60 97 As it had already been possible to use an external MSA or MRA,
meillo@60 98 why not keep the internal version for convenience?
meillo@60 99 If this would question the sense in having a fall-back pager in all
meillo@60 100 the command line tools, in case
meillo@60 101 .Pn more
meillo@60 102 or
meillo@60 103 .Pn less
meillo@60 104 wouldn't be available, the answer is intuitively seen.
meillo@60 105 Now, an MSA or MRA is clearly more complex than a text pager, but
meillo@60 106 still the concept holds: If programs become complex, split them;
meillo@60 107 if projects become complex, split them.
meillo@60 108 Complexity is demanded by the problem to solve. Decades ago,
meillo@60 109 emailing had been small and simple.
meillo@60 110 (Remember,
meillo@60 111 .Pn /bin/mail
meillo@60 112 had once covered anything there was to email.)
meillo@60 113 As the complexity in emailing increased, MH remainded mostly unchanged.
meillo@60 114 Nontheless, in nmh the POP server, which the original MH had included,
meillo@60 115 was removed. Now is the time to take one step further and remove
meillo@60 116 the MSA and MRA.
meillo@60 117 Not only does it decrease the code amount of the project,
meillo@60 118 but more important, it removes the whole field of message transfer
meillo@60 119 with all its implications from the project.
meillo@60 120 .P
meillo@60 121 Users of MH are usually able to set up an external MSA and MRA.
meillo@60 122 Also, the popular MSAs and MRAs have large communities and a lot
meillo@60 123 of documentation available.
meillo@60 124 .P
meillo@60 125 Choices for MSAs range from the full-featured
meillo@60 126 .I Postfix
meillo@60 127 over mid-size solutions like
meillo@60 128 .I masqmail
meillo@60 129 and
meillo@60 130 .I dma
meillo@60 131 to small forwarders like
meillo@60 132 .I ssmtp
meillo@60 133 and
meillo@60 134 .I nullmailer .
meillo@60 135 Choices for MRAs include
meillo@60 136 .I fetchmail ,
meillo@60 137 .I getmail ,
meillo@60 138 .I mpop
meillo@60 139 and
meillo@60 140 .I fdm .
meillo@60 141
meillo@60 142
meillo@60 143 .H2 "Removal of non-MUA Tools
meillo@60 144 .P
meillo@62 145 Some of nmh's tools were removed from mmh because they didn't
meillo@58 146 match the main focus of adding to the MUA's task.
meillo@62 147 .BU
meillo@58 148 .Pn conflict
meillo@58 149 was removed because it is a mail system maintenance tool.
meillo@62 150 Besides, it even checks
meillo@58 151 .Fn /etc/passwd
meillo@58 152 and
meillo@58 153 .Fn /etc/group
meillo@62 154 for consistency, which has nothing at all to do with emailing.
meillo@58 155 The tool might be useful, but it should not be shipped with mmh.
meillo@62 156 .BU
meillo@58 157 .Pn rcvtty
meillo@58 158 was removed because its usecase of writing to the user's terminal
meillo@58 159 on receiving of mail is hardly wanted today. If users like to be
meillo@58 160 informed of new mail, then using the shell's
meillo@58 161 .Ev MAILPATH
meillo@62 162 variable or graphical notifications are likely more
meillo@62 163 appealing.
meillo@62 164 Writing directly to a terminals is hardly ever wanted today.
meillo@62 165 If though one wants to have it this way, the standard tool
meillo@58 166 .Pn write
meillo@58 167 can be used in a way similar to:
meillo@58 168 .DS
meillo@58 169 scan -file - | write `id -un`
meillo@58 170 .DE
meillo@62 171 .BU
meillo@58 172 .Pn viamail
meillo@62 173 was removed when the new attachment system was introduced, because
meillo@58 174 .Pn forw
meillo@62 175 could can now the task itself.
meillo@62 176 The program
meillo@58 177 .Pn sendfiles
meillo@62 178 was rewritten as a shell script wrapper around
meillo@58 179 .Pn forw .
meillo@62 180 .BU
meillo@58 181 .Pn msgchk
meillo@62 182 was removed, because it lost its usefulness when POP support was removed.
meillo@58 183 .Pn msgchk
meillo@62 184 provides hardly more information than:
meillo@58 185 .DS
meillo@58 186 ls -l /var/mail/meillo
meillo@58 187 .DE
meillo@62 188 It does separate between old and new mail, but that's merely a detail
meillo@62 189 and can be done with
meillo@58 190 .Pn stat (1)
meillo@62 191 too.
meillo@62 192 A very small shell script could be written to output the information
meillo@62 193 in a convenient way, if truly necessary.
meillo@58 194 As mmh's inc only incorporates mail from the user's local maildrop
meillo@62 195 and thus no data transfers over slow networks are involved,
meillo@62 196 there's hardly need to check for new mail before incorporating it.
meillo@62 197 .BU
meillo@58 198 .Pn msh
meillo@62 199 was removed because the tool was in conflict with the
meillo@58 200 philosophy of MH. It provided an interactive shell to access the
meillo@58 201 features of MH. One major feature of MH is being a tool chest.
meillo@58 202 .Pn msh
meillo@58 203 wouldn't be just another shell, tailored to the needs of mail
meillo@58 204 handling, but one large program to have the MH tools built in.
meillo@58 205 It's main use was for accessing Bulletin Boards, which have seized to
meillo@62 206 be popular.
meillo@62 207 .P
meillo@62 208 XXX discuss
meillo@62 209 .P
meillo@62 210 Removing
meillo@58 211 .Pn msh ,
meillo@62 212 together with the truly obsolete code relicts
meillo@58 213 .Pn vmh
meillo@58 214 and
meillo@58 215 .Pn wmh ,
meillo@62 216 saved more than 7\|000 lines of C code \(en
meillo@62 217 that's about 15\|% less code in the project.
meillo@0 218
meillo@58 219
meillo@62 220 .H2 "Merge of \f(CWshow\fP and \f(CWmhshow\fP
meillo@58 221 .P
meillo@58 222 Since the very beginning, already in the first concept paper,
meillo@58 223 .Pn show
meillo@62 224 had been MH's message display program.
meillo@58 225 .Pn show
meillo@58 226 found out which pathnames the relevant messages had and invoked
meillo@58 227 .Pn mhl
meillo@62 228 then to have the content formated.
meillo@58 229 With the advent of MIME, this approach wasn't sufficient anymore.
meillo@58 230 MIME messages can consist of multiple parts, some of which aren't
meillo@62 231 directly displayable, and text content might be encoded in
meillo@58 232 foreign charsets.
meillo@58 233 .Pn show 's
meillo@58 234 simple approach and
meillo@58 235 .Pn mhl 's
meillo@58 236 limited display facilities couldn't cope with the task any longer.
meillo@62 237 .P
meillo@58 238 Instead of extending these tools, new ones were written from scratch
meillo@58 239 and then added to the MH tool chest. Doing so is encouraged by the
meillo@58 240 tool chest approach. The new tools could be added without interfering
meillo@62 241 with the existing ones. This is great. The ease of adding new tools
meillo@62 242 even made MH the first MUA to implement MIME.
meillo@58 243 .P
meillo@62 244 First, the new MIME features were added in form of the single program
meillo@58 245 .Pn mhn .
meillo@58 246 The command
meillo@62 247 .Cl "mhn \-show 42
meillo@58 248 would show the MIME message numbered 42.
meillo@58 249 With the 1.0 release of nmh in February 1999, Richard Coleman finished
meillo@58 250 the split of
meillo@58 251 .Pn mhn
meillo@58 252 into a set of specialized programs, which together covered the
meillo@62 253 multiple aspects of MIME. One of these resulting tools was
meillo@58 254 .Pn mhshow .
meillo@62 255 .Pn mhshow
meillo@62 256 resembled the
meillo@62 257 .Cl "mhn \-show
meillo@62 258 call.
meillo@62 259 .P
meillo@58 260
meillo@58 261
meillo@58 262 .H2 "Removal of Configure Options
meillo@58 263 .P
meillo@58 264
meillo@58 265 .H2 "Removal of switches
meillo@58 266 .P
meillo@58 267
meillo@58 268
meillo@58 269
meillo@58 270
meillo@58 271 .H1 "Moderizing
meillo@58 272
meillo@58 273
meillo@58 274 .H2 "Removal of Code Relicts
meillo@0 275 .P
meillo@51 276 The code base of mmh originates from the late Seventies,
meillo@51 277 had been extensively
meillo@51 278 worked on in the mid Eighties, and had been partly reorganized and extended
meillo@51 279 in the Nineties. Relicts of all those times had gathered in the code base.
meillo@12 280 My goal was to remove any ancient code parts. One part of the task was
meillo@12 281 converting obsolete code constructs to standard constructs, the other part
meillo@12 282 was dropping obsolete functions.
meillo@12 283 .P
meillo@12 284 As I'm not even thirty years old and have no more than seven years of
meillo@51 285 Unix experience, I needed to learn about the history in retrospective.
meillo@51 286 Older people likely have used those ancient constructs themselves
meillo@51 287 and have suffered from their incompatibilities and have longed for
meillo@12 288 standardization. Unfortunately, I have only read that others had done so.
meillo@12 289 This put me in a much more difficult positions when working on the old
meillo@12 290 code. I needed to recherche what other would have known by heart from
meillo@12 291 experience. All my programming experience comes from a time past ANSI C
meillo@12 292 and past POSIX. Although I knew about the times before, I took the
meillo@51 293 current state implicitly for granted most of the time.
meillo@12 294 .P
meillo@12 295 Being aware of
meillo@12 296 these facts, I rather let people with more historic experience solve the
meillo@12 297 task of converting the ancient code constructs to standardized ones.
meillo@12 298 Luckily, Lyndon Nerenberg focused on this task at the nmh project.
meillo@12 299 He converted large parts of the code to POSIX constructs, removing
meillo@12 300 the conditionals compilation for now standardized features.
meillo@12 301 I'm thankful for this task being solved. I only pulled the changes into
meillo@12 302 mmh.
meillo@12 303 .P
meillo@20 304 The other task \(en dropping ancient functionality to remove old code \(en
meillo@12 305 I did myself, though. My position to strip mmh to the bare minimum of
meillo@12 306 frequently used features is much more revolutional than the nmh community
meillo@20 307 likes it. Without the need to justify my decisions, I was able to quickly
meillo@20 308 remove functionality I considered ancient.
meillo@20 309 The need to discuss my decisions with
meillo@20 310 peers likely would have slowed this process down. Of course, I researched
meillo@12 311 if a particular feature really should be dropped. Having not had any
meillo@12 312 contact to this feature within my computer life was a first indicator to
meillo@12 313 drop it, but I also asked others and searched the literature for modern
meillo@12 314 usage of the feature. If it appeared to be truly ancient, I dropped it.
meillo@12 315 The reason for dropping is always part of the commit message in the
meillo@12 316 version control system. Thus, it is easy for others to check their
meillo@12 317 view on the topic with mine and possibly to argue for reinclusion.
meillo@12 318
meillo@12 319 .U2 "MMDF maildrop support
meillo@12 320 .P
meillo@12 321 I did drop any support for the MMDF maildrop format. This type of format
meillo@12 322 is conceptionally similar to the mbox format, but uses four bytes with
meillo@12 323 value 1 (\fL^A^A^A^A\fP) as message delimiter,
meillo@18 324 instead of the string ``\fLFrom\ \fP''.
meillo@12 325 Due to the similarity and mbox being the de-facto standard maildrop
meillo@12 326 format on Unix, but also due to the larger influence of Sendmail than MMDF,
meillo@12 327 the MMDF maildrop format had vanished.
meillo@12 328 .P
meillo@12 329 The simplifications within the code were only moderate. Switches could
meillo@12 330 be removed from tools like
meillo@12 331 .L packf ,
meillo@12 332 which generate packed mailboxes. Only one packed mailbox format remained:
meillo@12 333 mbox.
meillo@12 334 The most important changes affect the equally named mail parsing routine in
meillo@12 335 .L sbr/m_getfld.c .
meillo@12 336 The direct MMDF code had been removed, but as now only one packed mailbox
meillo@12 337 format is left, code structure simplifications are likely possible.
meillo@12 338 The reason why they are still outstanding is the heavily optimized code
meillo@18 339 of
meillo@18 340 .Fu m_getfld() .
meillo@18 341 Changes beyond a small local scope \(en
meillo@12 342 which restructuring in its core is \(en cause a high risk of damaging
meillo@12 343 the intricate workings of the optimized code. This problem is know
meillo@12 344 to the developers of nmh, too. They also avoid touching this minefield
meillo@12 345 if possible.
meillo@12 346
meillo@12 347 .U2 "UUCP Bang Paths
meillo@12 348 .P
meillo@12 349 More questionably than the former topic is the removal of support for the
meillo@12 350 UUCP bang path address style. However, the user may translate the bang
meillo@12 351 paths on retrieval to Internet addresses and the other way on posting
meillo@12 352 messages. The former can be done my an MDA like procmail; the latter
meillo@12 353 by a sendmail wrapper. This would ensure that any address handling would
meillo@12 354 work as expected. However, it might just work well without any
meillo@12 355 such modifications, as mmh does not touch addresses much, in general.
meillo@12 356 But I can't ensure as I have never used an environment with bang paths.
meillo@12 357 Also, the behavior might break at any point in further development.
meillo@12 358
meillo@12 359 .U2 "Hardcopy terminal support
meillo@12 360 .P
meillo@12 361 More of a funny anecdote is the remaining of a check for printing to a
meillo@12 362 hardcopy terminal until Spring 2012, when I finally removed it.
meillo@12 363 I surely would be very happy to see such a terminal in action, maybe
meillo@12 364 actually being able to work on it, but I fear my chances are null.
meillo@12 365 .P
meillo@12 366 The check only prevented a pager to be placed between the outputting
meillo@18 367 program (\c
meillo@18 368 .Pn mhl )
meillo@18 369 and the terminal. This could have been ensured with
meillo@18 370 the
meillo@18 371 .Sw \-nomoreproc
meillo@18 372 at the command line statically, too.
meillo@12 373
meillo@12 374 .U2 "Removed support for header fields
meillo@12 375 .P
meillo@12 376 The `Encrypted' header had been introduced by RFC\^822, but already
meillo@12 377 marked legacy in RFC 2822. It was superseded by FIXME.
meillo@12 378 Mmh does no more support this header.
meillo@12 379 .P
meillo@21 380 Native support for `Face' headers
meillo@21 381 had been removed, as well.
meillo@21 382 The feature is similar to the `X-Face' header in its intent,
meillo@21 383 but takes a different approach to store the image.
meillo@21 384 Instead of encoding the image data directly into the header,
meillo@21 385 the the header contains the hostname and UDP port where the image
meillo@21 386 date could be retrieved.
meillo@21 387 Neither `X-Face' nor the here described `Face' system
meillo@21 388 \**
meillo@21 389 .FS
meillo@21 390 There is also a newer but different system, invented 2005,
meillo@21 391 using `Face' headers.
meillo@21 392 It is the successor of `X-Face' providing colored PNG images.
meillo@21 393 .FE
meillo@21 394 became well used in the large scale.
meillo@21 395 It's still possible to use a Face systems,
meillo@21 396 although mmh does not provide support for any of the different systems
meillo@21 397 anymore. It's fairly easy to write a small shell script to
meillo@21 398 extract the embedded or fetch the external Face data and display the image.
meillo@21 399 Own Face headers can be added into the draft template files.
meillo@21 400 .P
meillo@12 401 `Content-MD5' headers were introduced by RFC\^1864. They provide only
meillo@12 402 a verification of data corruption during the transfer. By no means can
meillo@12 403 they ensure verbatim end-to-end delivery of the contents. This is clearly
meillo@12 404 stated in the RFC. The proper approach to provide verificationability
meillo@12 405 of content in an end-to-end relationship is the use of digital cryptography
meillo@12 406 (RFCs FIXME). On the other hand, transfer protocols should ensure the
meillo@12 407 integrity of the transmission. In combinations these two approaches
meillo@12 408 make the `Content-MD5' header field useless. In consequence, I removed
meillo@12 409 the support for it. By this removal, MD5 computation is not needed
meillo@12 410 anywhere in mmh. Hence, over 500 lines of code were removed by this one
meillo@12 411 change. Even if the `Content-MD5' header field is useful sometimes,
meillo@12 412 I value its usefulnes less than the improvement in maintainability, caused
meillo@12 413 by the removal.
meillo@12 414
meillo@20 415 .U2 "Prompter's Control Keys
meillo@20 416 .P
meillo@20 417 The program
meillo@20 418 .Pn prompter
meillo@20 419 queries the user to fill in a message form. When used by
meillo@20 420 .Pn comp
meillo@20 421 as:
meillo@20 422 .DS
meillo@20 423 comp \-editor prompter
meillo@20 424 .DE
meillo@20 425 the resulting behavior is similar to
meillo@20 426 .Pn mailx .
meillo@51 427 Apparently,
meillo@20 428 .Pn prompter
meillo@20 429 hadn't been touched lately. Otherwise it's hardly explainable why it
meillo@20 430 still offered the switches
meillo@20 431 .Sn \-erase \fUchr\fP
meillo@20 432 and
meillo@20 433 .Sn \-kill \fUchr\fP
meillo@20 434 to name the characters for command line editing.
meillo@21 435 The times when this had been necessary are long time gone.
meillo@20 436 Today these things work out-of-the-box, and if not, are configured
meillo@20 437 with the standard tool
meillo@20 438 .Pn stty .
meillo@20 439
meillo@21 440 .U2 "Vfork and Retry Loops
meillo@21 441 .P
meillo@51 442 MH creates many processes, which is a consequence of the tool chest approach.
meillo@21 443 In earlier times
meillo@21 444 .Fu fork()
meillo@21 445 had been an expensive system call, as the process's whole image needed
meillo@21 446 to be duplicated. One common case is replacing the image with
meillo@21 447 .Fu exec()
meillo@21 448 right after having forked the child process.
meillo@21 449 To speed up this case, the
meillo@21 450 .Fu vfork()
meillo@21 451 system call was invented at Berkeley. It completely omits copying the
meillo@21 452 image. If the image gets replaced right afterwards then unnecessary
meillo@21 453 work is omited. On old systems this results in large speed ups.
meillo@21 454 MH uses
meillo@21 455 .Fu vfork()
meillo@21 456 whenever possible.
meillo@21 457 .P
meillo@21 458 Memory management units that support copy-on-write semantics make
meillo@21 459 .Fu fork()
meillo@21 460 almost as fast as
meillo@21 461 .Fu vfork()
meillo@21 462 in the cases when they can be exchanged.
meillo@21 463 With
meillo@21 464 .Fu vfork()
meillo@51 465 being more error-prone and hardly faster, it's preferable to simply
meillo@21 466 use
meillo@21 467 .Fu fork()
meillo@21 468 instead.
meillo@21 469 .P
meillo@21 470 Related to the costs of
meillo@21 471 .Fu fork()
meillo@21 472 is the probability of its success.
meillo@21 473 Today on modern systems, the system call will succeed almost always.
meillo@51 474 In the Eighties on heavy loaded systems, as they were common at
meillo@21 475 universities, this had been different. Thus, many of the
meillo@21 476 .Fu fork()
meillo@21 477 calls were wrapped into loops to retry to fork several times in
meillo@21 478 short intervals, in case of previous failure.
meillo@21 479 In mmh, the program aborts at once if the fork failed.
meillo@21 480 The user can reexecute the command then. This is expected to be a
meillo@21 481 very rare case on modern systems, especially personal ones, which are
meillo@21 482 common today.
meillo@21 483
meillo@12 484
meillo@58 485 .H2 "Attachments
meillo@22 486 .P
meillo@58 487 MIME
meillo@58 488
meillo@58 489
meillo@58 490 .H2 "Digital Cryptography
meillo@22 491 .P
meillo@58 492 Signing and encryption.
meillo@58 493
meillo@58 494
meillo@58 495 .H2 "Good Defaults
meillo@22 496 .P
meillo@58 497 foo
meillo@58 498
meillo@58 499
meillo@58 500
meillo@58 501
meillo@58 502 .H1 "Code style
meillo@22 503 .P
meillo@58 504 foo
meillo@58 505
meillo@58 506
meillo@58 507 .H2 "Standard Code
meillo@22 508 .P
meillo@58 509 POSIX
meillo@22 510
meillo@22 511
meillo@58 512 .H2 "Separation
meillo@14 513
meillo@58 514 .U2 "MH Directory Split
meillo@0 515 .P
meillo@19 516 In MH and nmh, a personal setup had consisted of two parts:
meillo@19 517 The MH profile, named
meillo@19 518 .Fn \&.mh_profile
meillo@19 519 and being located directly in the user's home directory.
meillo@19 520 And the MH directory, where all his mail messages and also his personal
meillo@19 521 forms, scan formats, other configuration files are stored. The location
meillo@19 522 of this directory could be user-chosen. The default was to name it
meillo@19 523 .Fn Mail
meillo@19 524 and have it directly in the home directory.
meillo@19 525 .P
meillo@19 526 I've never liked the data storage and the configuration to be intermixed.
meillo@19 527 They are different kinds of data. One part, are the messages,
meillo@19 528 which are the data to operate on. The other part, are the personal
meillo@19 529 configuration files, which are able to change the behavior of the operations.
meillo@19 530 The actual operations are defined in the profile, however.
meillo@19 531 .P
meillo@19 532 When storing data, one should try to group data by its type.
meillo@19 533 There's sense in the Unix file system hierarchy, where configuration
meillo@19 534 file are stored separate (\c
meillo@19 535 .Fn /etc )
meillo@19 536 to the programs (\c
meillo@19 537 .Fn /bin
meillo@19 538 and
meillo@19 539 .Fn /usr/bin )
meillo@19 540 to their sources (\c
meillo@19 541 .Fn /usr/src ).
meillo@19 542 Such separation eases the backup management, for instance.
meillo@19 543 .P
meillo@19 544 In mmh, I've reorganized the file locations.
meillo@19 545 Still there are two places:
meillo@19 546 There's the mail storage directory, which, like in MH, contains all the
meillo@19 547 messages, but, unlike in MH, nothing else.
meillo@19 548 Its location still is user-chosen, with the default name
meillo@19 549 .Fn Mail ,
meillo@19 550 in the user's home directory. This is much similar to the case in nmh.
meillo@19 551 The configuration files, however, are grouped together in the new directory
meillo@19 552 .Fn \&.mmh
meillo@19 553 in the user's home directory.
meillo@19 554 The user's profile now is a file, named
meillo@19 555 .Fn profile ,
meillo@19 556 in this mmh directory.
meillo@19 557 Consistently, the context file and all the personal forms, scan formats,
meillo@19 558 and the like, are also there.
meillo@19 559 .P
meillo@19 560 The naming changed with the relocation.
meillo@19 561 The directory where everything, except the profile, had been stored (\c
meillo@19 562 .Fn $HOME/Mail ),
meillo@19 563 used to be called \fIMH directory\fP. Now, this directory is called the
meillo@19 564 user's \fImail storage\fP. The name \fImmh directory\fP is now given to
meillo@19 565 the new directory
meillo@19 566 (\c
meillo@19 567 .Fn $HOME/.mmh ),
meillo@19 568 containing all the personal configuration files.
meillo@19 569 .P
meillo@19 570 The separation of the files by type of content is logical and convenient.
meillo@19 571 There are no functional differences as any possible setup known to me
meillo@19 572 can be implemented with both approaches, although likely a bit easier
meillo@19 573 with the new approach. The main goal of the change had been to provide
meillo@19 574 sensible storage locations for any type of personal mmh file.
meillo@19 575 .P
meillo@19 576 In order for one user to have multiple MH setups, he can use the
meillo@19 577 environment variable
meillo@19 578 .Ev MH
meillo@19 579 the point to a different profile file.
meillo@19 580 The MH directory (mail storage plus personal configuration files) is
meillo@19 581 defined by the
meillo@19 582 .Pe Path
meillo@19 583 profile entry.
meillo@19 584 The context file could be defined by the
meillo@19 585 .Pe context
meillo@19 586 profile entry or by the
meillo@19 587 .Ev MHCONTEXT
meillo@19 588 environment variable.
meillo@19 589 The latter is useful to have a distinct context (e.g. current folders)
meillo@19 590 in each terminal window, for instance.
meillo@19 591 In mmh, there are three environment variables now.
meillo@19 592 .Ev MMH
meillo@19 593 may be used to change the location of the mmh directory.
meillo@19 594 .Ev MMHP
meillo@19 595 and
meillo@19 596 .Ev MMHC
meillo@19 597 change the profile and context files, respectively.
meillo@19 598 Besides providing a more consistent feel (which simply is the result
meillo@19 599 of being designed anew), the set of personal configuration files can
meillo@19 600 be chosen independently from the profile (including mail storage location)
meillo@19 601 and context, now. Being it relevant for practical use or not, it
meillo@19 602 de-facto is an improvement. However, the main achievement is the
meillo@19 603 split between mail storage and personal configuration files.
meillo@17 604
meillo@0 605
meillo@58 606 .H2 "Modularization
meillo@0 607 .P
meillo@58 608 whatnowproc
meillo@0 609 .P
meillo@49 610 The \fIMH library\fP
meillo@49 611 .Fn libmh.a
meillo@49 612 collects a bunch of standard functions that many of the MH tools need,
meillo@49 613 like reading the profile or context files.
meillo@49 614 This doesn't hurt the separation.
meillo@49 615
meillo@58 616
meillo@58 617 .H2 "Style
meillo@58 618 .P
meillo@58 619 Code layout, goto, ...
meillo@58 620
meillo@58 621
meillo@58 622
meillo@58 623
meillo@58 624 .H1 "Concept Exploitation/Homogeniety
meillo@58 625
meillo@58 626
meillo@58 627 .H2 "Draft Folder
meillo@58 628 .P
meillo@58 629 Historically, MH provided exactly one draft message, named
meillo@58 630 .Fn draft
meillo@58 631 and
meillo@58 632 being located in the MH directory. When starting to compose another message
meillo@58 633 before the former one was sent, the user had been questioned whether to use,
meillo@58 634 refile or replace the old draft. Working on multiple drafts at the same time
meillo@58 635 was impossible. One could only work on them in alteration by refiling the
meillo@58 636 previous one to some directory and fetching some other one for reediting.
meillo@58 637 This manual draft management needed to be done each time the user wanted
meillo@58 638 to switch between editing one draft to editing another.
meillo@58 639 .P
meillo@58 640 To allow true parallel editing of drafts, in a straight forward way, the
meillo@58 641 draft folder facility exists. It had been introduced already in July 1984
meillo@58 642 by Marshall T. Rose. The facility was deactivated by default.
meillo@58 643 Even in nmh, the draft folder facility remained deactivated by default.
meillo@58 644 At least, Richard Coleman added the man page
meillo@58 645 .Mp mh-draft(5)
meillo@58 646 to document
meillo@58 647 the feature well.
meillo@58 648 .P
meillo@58 649 The only advantage of not using the draft folder facility is the static
meillo@58 650 name of the draft file. This could be an issue for MH frontends like mh-e.
meillo@58 651 But as they likely want to provide working on multiple drafts in parallel,
meillo@58 652 the issue is only concerning compatibility. The aim of nmh to stay compatible
meillo@58 653 prevented the default activation of the draft folder facility.
meillo@58 654 .P
meillo@58 655 On the other hand, a draft folder is the much more natural concept than
meillo@58 656 a draft message. MH's mail storage consists of folders and messages,
meillo@58 657 the messages named with ascending numbers. A draft message breaks with this
meillo@58 658 concept by introducing a message in a file named
meillo@58 659 .Fn draft .
meillo@58 660 This draft
meillo@58 661 message is special. It can not be simply listed with the available tools,
meillo@58 662 but instead requires special switches. I.e. corner-cases were
meillo@58 663 introduced. A draft folder, in contrast, does not introduce such
meillo@58 664 corner-cases. The available tools can operate on the messages within that
meillo@58 665 folder like on any messages within any mail folders. The only difference
meillo@58 666 is the fact that the default folder for
meillo@58 667 .Pn send
meillo@58 668 is the draft folder,
meillo@58 669 instead of the current folder, like for all other tools.
meillo@58 670 .P
meillo@58 671 The trivial part of the change was activating the draft folder facility
meillo@58 672 by default and setting a default name for this folder. Obviously, I chose
meillo@58 673 the name
meillo@58 674 .Fn +drafts .
meillo@58 675 This made the
meillo@58 676 .Sw \-draftfolder
meillo@58 677 and
meillo@58 678 .Sw \-draftmessage
meillo@58 679 switches useless, and I could remove them.
meillo@58 680 The more difficult but also the part that showed the real improvement,
meillo@58 681 was updating the tools to the new concept.
meillo@58 682 .Sw \-draft
meillo@58 683 switches could
meillo@58 684 be dropped, as operating on a draft message became indistinguishable to
meillo@58 685 operating on any other message for the tools.
meillo@58 686 .Pn comp
meillo@58 687 still has its
meillo@58 688 .Sw \-use
meillo@58 689 switch for switching between its two modes: (1) Compose a new
meillo@58 690 draft, possibly by taking some existing message as a form. (2) Modify
meillo@58 691 an existing draft. In either case, the behavior of
meillo@58 692 .Pn comp is
meillo@58 693 deterministic. There is no more need to query the user. I consider this
meillo@58 694 a major improvement. By making
meillo@58 695 .Pn send
meillo@58 696 simply operate on the current
meillo@58 697 message in the draft folder by default, with message and folder both
meillo@58 698 overridable by specifying them on the command line, it is now possible
meillo@58 699 to send a draft anywhere within the storage by simply specifying its folder
meillo@58 700 and name.
meillo@58 701 .P
meillo@58 702 All theses changes converted special cases to regular cases, thus
meillo@58 703 simplifying the tools and increasing the flexibility.
meillo@58 704
meillo@58 705
meillo@58 706 .H2 "Trash Folder
meillo@58 707 .P
meillo@58 708 Similar to the situation for drafts is the situation for removed messages.
meillo@58 709 Historically, a message was deleted by renaming. A specific
meillo@58 710 \fIbackup prefix\fP, often comma (\c
meillo@58 711 .Fn , )
meillo@58 712 or hash (\c
meillo@58 713 .Fn # ),
meillo@58 714 being prepended to the file name. Thus, MH wouldn't recognize the file
meillo@58 715 as a message anymore, as only files whose name consists of digits only
meillo@58 716 are treated as messages. The removed messages remained as files in the
meillo@58 717 same directory and needed some maintenance job to truly delete them after
meillo@58 718 some grace time. Usually, by running a command similar to
meillo@58 719 .DS
meillo@58 720 find /home/user/Mail \-ctime +7 \-name ',*' | xargs rm
meillo@58 721 .DE
meillo@58 722 in a cron job. Within the grace time interval
meillo@58 723 the original message could be restored by stripping the
meillo@58 724 the backup prefix from the file name. If however, the last message of
meillo@58 725 a folder is been removed \(en say message
meillo@58 726 .Fn 6
meillo@58 727 becomes file
meillo@58 728 .Fn ,6
meillo@58 729 \(en and a new message enters the same folder, thus the same
meillo@58 730 numbered being given again \(en in our case
meillo@58 731 .Fn 6
meillo@58 732 \(en, if that one
meillo@58 733 is removed too, then the backup of the former message gets overwritten.
meillo@58 734 Thus, the ability to restore removed messages does not only depend on
meillo@58 735 the ``sweeping cron job'' but also on the removing of further messages.
meillo@58 736 This is undesirable, because the real mechanism is hidden from the user
meillo@58 737 and the consequences of further removals are not always obvious.
meillo@58 738 Further more, the backup files are scattered within the whole mail
meillo@58 739 storage, instead of being collected at one place.
meillo@58 740 .P
meillo@58 741 To improve the situation, the profile entry
meillo@58 742 .Pe rmmproc
meillo@58 743 (previously named
meillo@58 744 .Pe Delete-Prog )
meillo@58 745 was introduced, very early.
meillo@58 746 It could be set to any command, which would care for the mail removal
meillo@58 747 instead of taking the default action, described above.
meillo@58 748 Refiling the to-be-removed files to some garbage folder was a common
meillo@58 749 example. Nmh's man page
meillo@58 750 .Mp rmm(1)
meillo@58 751 proposes
meillo@58 752 .Cl "refile +d
meillo@58 753 to move messages to the garbage folder and
meillo@58 754 .Cl "rm `mhpath +d all`
meillo@58 755 the empty the garbage folder.
meillo@58 756 Managing the message removal this way is a sane approach. It keeps
meillo@58 757 the removed messages in one place, makes it easy to remove the backup
meillo@58 758 files, and, most important, enables the user to use the tools of MH
meillo@58 759 itself to operate on the removed messages. One can
meillo@58 760 .Pn scan
meillo@58 761 them,
meillo@58 762 .Pn show
meillo@58 763 them, and restore them with
meillo@58 764 .Pn refile .
meillo@58 765 There's no more
meillo@58 766 need to use
meillo@58 767 .Pn mhpath
meillo@58 768 to switch over from MH tools to Unix tools \(en MH can do it all itself.
meillo@58 769 .P
meillo@58 770 This approach matches perfect with the concepts of MH, thus making
meillo@58 771 it powerful. Hence, I made it the default. And even more, I also
meillo@58 772 removed the old backup prefix approach, as it is clearly less powerful.
meillo@58 773 Keeping unused alternative in the code is a bad choice as they likely
meillo@58 774 gather bugs, by not being constantly tested. Also, the increased code
meillo@58 775 size and more conditions crease the maintenance costs. By strictly
meillo@58 776 converting to the trash folder approach, I simplified the code base.
meillo@58 777 .Pn rmm
meillo@58 778 calls
meillo@58 779 .Pn refile
meillo@58 780 internally to move the to-be-removed
meillo@58 781 message to the trash folder (\c
meillo@58 782 .Fn +trash
meillo@58 783 by default). Messages
meillo@58 784 there can be operated on like on any other message in the storage.
meillo@58 785 The sweep clean, one can use
meillo@58 786 .Cl "rmm \-unlink +trash a" ,
meillo@58 787 where the
meillo@58 788 .Sw \-unlink
meillo@58 789 switch causes the files to be truly unliked instead
meillo@58 790 of moved to the trash folder.
meillo@58 791
meillo@58 792
meillo@58 793 .H2 "Path Notations
meillo@58 794 .P
meillo@58 795 foo
meillo@58 796
meillo@58 797
meillo@58 798 .H2 "MIME Integration
meillo@58 799 .P
meillo@58 800 user-visible access to whole messages and MIME parts are inherently
meillo@58 801 different
meillo@58 802
meillo@58 803
meillo@58 804 .H2 "Of One Cast
meillo@58 805 .P