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annotate intro.roff @ 207:e0e49a8bfbe8

Added refs.
author markus schnalke <meillo@marmaro.de>
date Thu, 12 Jul 2012 11:50:32 +0200
parents 8c0d5bd92f0b
children fead1fc981f0
rev   line source
meillo@39 1 .RN 1
meillo@197 2 .H0 "Introduction
meillo@197 3 .Id introduction
meillo@39 4
meillo@0 5 .P
meillo@53 6 MH is a set of mail handling tools with a common concept, similar to
meillo@53 7 the Unix tool chest, which is a set of file handling tools with a common
meillo@53 8 concept. \fInmh\fP is the currently most popular implementation of an
meillo@53 9 MH-like mail handling system.
meillo@53 10 This thesis describes an experimental version of nmh, named \fImmh\fP.
meillo@53 11 .P
meillo@32 12 This chapter introduces MH, its history, concepts and how it is used.
meillo@47 13 It describes nmh's code base and community to give the reader
meillo@106 14 a better understanding of the state of mmh when it started off.
meillo@181 15 Furthermore, this chapter outlines the mmh project itself,
meillo@47 16 describing the motivation for it and its goals.
meillo@8 17
meillo@0 18
meillo@28 19 .H1 "MH \(en the Mail Handler
meillo@197 20 .Id mh
meillo@0 21 .P
meillo@47 22 MH is a conceptual email system design and its concrete implementation.
meillo@47 23 Notably, MH had started as a design proposal at RAND Corporation,
meillo@47 24 where the first implementation followed later.
meillo@47 25 In spirit, MH is similar to Unix, which
meillo@42 26 influenced the world more in being a set of system design concepts
meillo@32 27 than in being a specific software product.
meillo@47 28 The ideas behind Unix are summarized in the \fIUnix philosophy\fP.
meillo@207 29 .[
meillo@207 30 gancarz unix philosophy
meillo@207 31 .]
meillo@42 32 MH follows this philosophy.
meillo@2 33
meillo@11 34 .U2 "History
meillo@2 35 .P
meillo@32 36 In 1977 at RAND Corporation, Norman Shapiro and Stockton Gaines
meillo@106 37 proposed the design
meillo@181 38 of a new mail handling system, called \fIMail Handler\fP (MH),
meillo@181 39 to superseed RAND's old monolithic \fIMail System\fP (MS).
meillo@207 40 .[
meillo@207 41 shapiro gaines mh proposal
meillo@207 42 .]
meillo@27 43 Two years later, in 1979, Bruce Borden took the proposal and implemented a
meillo@32 44 prototype of MH.
meillo@106 45 Before the prototype's existence, the concept was
meillo@47 46 believed to be practically unusable.
meillo@207 47 But the prototype proved successful and replaced MS thereafter.\&
meillo@207 48 .[
meillo@207 49 history of mh website
meillo@207 50 .]
meillo@2 51 .P
meillo@106 52 In the early eighties,
meillo@106 53 the University of California at Irvine (UCI) started to use MH.
meillo@106 54 Marshall T. Rose and John L. Romine then became the driving force.
meillo@57 55 They took over the development and pushed MH forward.
meillo@57 56 RAND had put the code into the public domain by then.
meillo@57 57 MH was developed at UCI at the time when the Internet appeared,
meillo@207 58 the University of California at Berkeley (UCB) added TCP/IP
meillo@207 59 networking to their distribution, and Eric Allman wrote Sendmail.
meillo@47 60 MH was extended as emailing became more featured.
meillo@32 61 The development of MH was closely related to the development of email
meillo@204 62 RFCs.
meillo@204 63 In the advent of the \fIMultipurpose Internet Mail Extensions\fP (MIME),
meillo@204 64 MH was one of the first implementations of the new email standard.
meillo@207 65 MH grew to provide anything necessary for emailing.
meillo@2 66 .P
meillo@117 67 In the nineties, the Internet became popular and in December 1996,
meillo@181 68 Richard Coleman initiated the \fINew Mail Handler\fP (nmh) project.
meillo@57 69 Nmh is a fork of MH 6.8.3 and bases strongly on the
meillo@47 70 \fILBL changes\fP by Van Jacobson, Mike Karels and Craig Leres.
meillo@207 71 .[
meillo@207 72 lbl changes
meillo@207 73 .]
meillo@32 74 Colman intended to modernize MH and improve its portability and
meillo@32 75 MIME handling capabilities.
meillo@32 76 This should be done openly within the Internet community.
meillo@47 77 The development of MH at UCI stopped after the 6.8.4 release in
meillo@47 78 February 1996, soon after the development of nmh had started.
meillo@57 79 Today, nmh has almost completely replaced the original MH.
meillo@47 80 Some systems might still provide old MH, but mainly for historical reasons.
meillo@47 81 .P
meillo@171 82 In the last years, the changes in nmh were mostly maintenance work.
meillo@117 83 However, the development was revived in December 2011
meillo@57 84 and stayed busy since then.
meillo@0 85
meillo@197 86
meillo@11 87 .U2 "Concepts
meillo@0 88 .P
meillo@53 89 MH consists of a set of tools, each covering a specific task of
meillo@53 90 email handling, like composing a message, replying to a message,
meillo@53 91 refiling a message to a different folder, listing the messages in a folder.
meillo@47 92 All of the programs operate on a common mail storage.
meillo@42 93 .P
meillo@32 94 The mail storage consists of \fImail folders\fP (directories) and
meillo@32 95 \fPmessages\fP (regular files).
meillo@106 96 Each message is stored in a separate file in the format it was
meillo@47 97 received (i.e. transfer format).
meillo@47 98 The files are named with ascending numbers in each folder.
meillo@47 99 The specific format of the mail storage characterizes MH in the same way
meillo@106 100 as the format of the file system characterizes Unix.
meillo@42 101 .P
meillo@164 102 MH tools maintain a \fIcontext\fP, which includes for instance the
meillo@164 103 current mail folder.
meillo@32 104 Processes in Unix have a similar context, containing the current working
meillo@32 105 directory, for instance. In contrast, the process context is maintained
meillo@32 106 by the Unix kernel automatically, whereas MH tools need to maintain the MH
meillo@32 107 context themselves.
meillo@106 108 The user can have one MH context or multiple ones; he can even share it
meillo@106 109 with others.
meillo@42 110 .P
meillo@164 111 Messages are named by their numeric filename,
meillo@207 112 but they can have symbolic names, as well.
meillo@207 113 These are either one of six system-controlled position names
meillo@32 114 or user-settable group names for arbitrary sets of messages.
meillo@32 115 These names are called sequences.
meillo@207 116 Automatically updated position names exist for the
meillo@207 117 first, last, previous, next, current message, and
meillo@207 118 for the number one beyond the last message.
meillo@207 119 (In mmh, the names of these sequences are abbreviated to the
meillo@207 120 first character.)
meillo@207 121 User-definded sequences can be bound to the folder containing the
meillo@207 122 messages (\fIpublic sequences\fP) or to the user's context
meillo@207 123 (\fIprivate sequences\fP).
meillo@2 124 .P
meillo@207 125 The user's \fIprofile\fP is the file that contains his MH configuration.
meillo@47 126 Default switches for the individual tools can be specified to
meillo@47 127 adjust them to the user's personal preferences.
meillo@207 128 These switches will be automatically supplied whenever the specific
meillo@207 129 tool is invoked.
meillo@164 130 Additionally, a single command can be linked under different names
meillo@207 131 with different default values.
meillo@207 132 Form templates for new messages and replies, as well as format files
meillo@207 133 to adjust the output of tools are easily exchanged in the profile.
meillo@42 134 .P
meillo@207 135 Switches consist of a single dash (`\fL-\fP') followed by a word.
meillo@207 136 To ease typing, the word can be abbreviated, given the remaining
meillo@102 137 prefix remains unambiguous.
meillo@207 138 If no other switch starts with the letter `t', then any of
meillo@102 139 .Cl "-truncate" ,
meillo@102 140 .Cl "-trunc" ,
meillo@102 141 .Cl "-tr" ,
meillo@102 142 and
meillo@102 143 .Cl "-t
meillo@207 144 is equal.
meillo@102 145 As a result, switches can neither be grouped (as in
meillo@102 146 .Cl "ls -ltr" )
meillo@102 147 nor can switch arguments be appended directly to the switch (as in
meillo@102 148 .Cl "sendmail -q30m" ).
meillo@102 149 Many switches have negating counter-parts, which start with `no'.
meillo@102 150 For example
meillo@102 151 .Cl "-notruncate
meillo@102 152 inverts the
meillo@102 153 .Cl "-truncate
meillo@102 154 switch.
meillo@207 155 They exist to override the effect of default switches in the profile.
meillo@207 156 .P
meillo@207 157 The system is well scriptable and extensible.
meillo@207 158 Almost every part of the system can be adjusted to personal preference.
meillo@207 159 New MH tools are built out of or on top of existing ones quickly.
meillo@207 160 Furthermore, MH encourages the user to tailor, extend, and automate
meillo@207 161 the system.
meillo@207 162 As the MH tool chest was modeled after the Unix tool chest, the
meillo@207 163 properties of the latter apply to the former as well.
meillo@102 164
meillo@102 165
meillo@102 166
meillo@54 167 .U2 "Using MH
meillo@53 168 .P
meillo@207 169 It is strongly recommended to have a look at the \fIMH Book\fP,
meillo@54 170 .[ [
meillo@54 171 peek mh book
meillo@54 172 .], Part II]
meillo@207 173 which introduces into using MH.
meillo@207 174 Rose and Romine provide a deeper and more technical,
meillo@207 175 though slightly outdated, introduction in only about two dozen pages.
meillo@54 176 .[
meillo@54 177 rose romine real work
meillo@54 178 .]
meillo@27 179 .P
meillo@207 180 Following here is an example mail handling session.
meillo@207 181 Although it uses mmh, it is mostly compatible with nmh and the
meillo@207 182 original MH.
meillo@106 183 Details might vary but the look and feel is the same.
meillo@82 184
meillo@202 185 .so input/mh-session
meillo@27 186
meillo@27 187
meillo@131 188 .H1 "nmh
meillo@2 189 .P
meillo@49 190 In order to understand the condition, goals and dynamics of a project,
meillo@106 191 one needs to know the reasons behind them.
meillo@53 192 This section explains the background.
meillo@53 193 .P
meillo@197 194 MH predates the Internet;
meillo@197 195 it comes from times before networking was universal,
meillo@49 196 it comes from times when emailing was small, short and simple.
meillo@106 197 Then it grew, spread and adapted to the changes email went through.
meillo@49 198 Its core-concepts, however, remained the same.
meillo@106 199 During the eighties, students at UCI actively worked on MH.
meillo@164 200 They added new features and optimized the code for the systems
meillo@164 201 popular at that time.
meillo@49 202 All this still was in times before POSIX and ANSI C.
meillo@49 203 As large parts of the code stem from this time, today's nmh source code
meillo@49 204 still contains many ancient parts.
meillo@51 205 BSD-specific code and constructs tailored for hardware of that time
meillo@49 206 are frequent.
meillo@2 207 .P
meillo@106 208 Nmh started about a decade after the POSIX and ANSI C standards were
meillo@49 209 established. A more modern coding style entered the code base, but still
meillo@49 210 a part of the developers came from ``the old days''. The developer
meillo@106 211 base became more diverse, thus broadening the range of different
meillo@106 212 coding styles.
meillo@49 213 Programming practices from different decades merged in the project.
meillo@51 214 As several peers added code, the system became more a conglomeration
meillo@51 215 of single tools rather than a homogeneous of-one-cast mail system.
meillo@49 216 Still, the existing basic concepts held it together.
meillo@8 217 They were mostly untouched throughout the years.
meillo@8 218 .P
meillo@106 219 Despite the separation of the tool chest approach at the surface
meillo@106 220 \(en a collection of small, separate programs \(en
meillo@171 221 on the source code level, it is much more interwoven.
meillo@49 222 Several separate components were compiled into one program
meillo@51 223 for efficiency reasons.
meillo@106 224 This led to intricate innards.
meillo@106 225 While clearly separated on the outside,
meillo@171 226 the programs turned out to be fairly interwoven inside.
meillo@106 227 .\" XXX FIXME rewrite...
meillo@171 228 .\" nicht zweimal ``interwoven''
meillo@106 229 .\" Unfortunately, the clear separation on the outside turned out to be
meillo@171 230 .\" fairly interwoven inside.
meillo@8 231 .P
meillo@106 232 The advent of MIME raised the complexity of email by a magnitude.
meillo@49 233 This is visible in nmh. The MIME-related parts are the most complex ones.
meillo@106 234 It is also visible that MIME support was added on top of the old MH core.
meillo@51 235 MH's tool chest style made this easily possible and encourages
meillo@106 236 such approaches, but unfortunately, it led to duplicated functions
meillo@49 237 and half-hearted implementation of the concepts.
meillo@49 238 .P
meillo@159 239 To provide backward-compatibility, it is a common understanding not to
meillo@49 240 change the default settings.
meillo@51 241 In consequence, the user needs to activate modern features explicitly
meillo@47 242 to be able to use them.
meillo@49 243 This puts a burden on new users, because out-of-the-box nmh remains
meillo@49 244 in the same ancient style.
meillo@171 245 If nmh is seen to be a back-end,
meillo@171 246 then this compatibility surely is important.
meillo@171 247 However, at the same time, new users have difficulties using nmh for
meillo@171 248 modern emailing.
meillo@173 249 The small but mature community around nmh needs little change
meillo@106 250 as they have had their convenient setups for decades.
meillo@159 251 .\" XXX Explain more
meillo@8 252
meillo@8 253
meillo@27 254 .H1 "mmh
meillo@28 255 .P
meillo@49 256 I started to work on my experimental version in October 2011,
meillo@197 257 basing my work on nmh version \fInmh-1.3-dev\fP.
meillo@197 258 At that time no more than three commits were made to nmh
meillo@197 259 since the beginning of the year, the latest one being
meillo@197 260 .Ci a01a41d031c796b526329a4170eb23f0ac93b949
meillo@197 261 on 2011-04-13.
meillo@53 262 In December, when I announced my work in progress on the
meillo@53 263 nmh-workers mailing list,
meillo@42 264 .[
meillo@51 265 nmh-workers mmh announce December
meillo@42 266 .]
meillo@197 267 nmh's community became active, all of a sudden.
meillo@49 268 This movement was heavily pushed by Paul Vixie's ``edginess'' comment.
meillo@42 269 .[
meillo@42 270 nmh-workers vixie edginess
meillo@42 271 .]
meillo@53 272 After long years of stagnation, nmh became actively developed again.
meillo@197 273 Hence, while I was working on mmh, the community was working on nmh,
meillo@197 274 in parallel.
meillo@28 275 .P
meillo@53 276 The name \fImmh\fP may stand for \fImodern mail handler\fP,
meillo@53 277 because the project tries to modernize nmh.
meillo@53 278 Personally however, I prefer to call mmh \fImeillo's mail handler\fP,
meillo@207 279 emphasizing that the project is my version of nmh,
meillo@207 280 following my visions and preferences.
meillo@42 281 (My login name is \fImeillo\fP.)
meillo@53 282 This project model was inspired by \fIdwm\fP,
meillo@207 283 .[
meillo@207 284 dwm website
meillo@207 285 .]
meillo@42 286 which is Anselm Garbe's personal window manager \(en
meillo@42 287 targeted to satisfy Garbe's personal needs whenever conflicts appear.
meillo@53 288 Dwm had retained its lean elegance and its focused character, whereas
meillo@207 289 its community-driven predecessor \fIwmii\fP
meillo@207 290 .[
meillo@207 291 wmii website
meillo@207 292 .]
meillo@207 293 had grown fat over time.
meillo@53 294 The development of mmh should remain focused.
meillo@27 295
meillo@45 296
meillo@27 297 .U2 "Motivation
meillo@27 298 .P
meillo@207 299 MH is the most important of very few email systems in a tool chest style.
meillo@51 300 Tool chests are powerful because they can be perfectly automated and
meillo@53 301 extended. They allow arbitrary kinds of front-ends to be
meillo@53 302 implemented on top of them quickly and without internal knowledge.
meillo@106 303 Additionally, tool chests are easier to maintain than monolithic
meillo@43 304 programs.
meillo@53 305 As there are few tool chests for emailing and as MH-like ones are the most
meillo@106 306 popular among them, they should be developed further.
meillo@53 307 This keeps their
meillo@43 308 conceptional elegance and unique scripting qualities available to users.
meillo@106 309 Mmh creates a modern and convenient entry point to MH-like systems
meillo@53 310 for new and interested users.
meillo@43 311 .P
meillo@51 312 The mmh project is motivated by deficits of nmh and
meillo@45 313 my wish for general changes, combined
meillo@45 314 with the nmh community's reluctancy to change.
meillo@45 315 .P
meillo@106 316 At that time, nmh had not adjusted to modern emailing needs well enough.
meillo@45 317 The default setup was completely unusable for modern emailing.
meillo@45 318 Too much setup work was required.
meillo@45 319 Several modern features were already available but the community
meillo@106 320 did not want to have them as default.
meillo@106 321 Mmh is a way to change this.
meillo@45 322 .P
meillo@45 323 In my eyes, MH's concepts could be exploited even better and
meillo@45 324 the style of the tools could be improved. Both would simplify
meillo@45 325 and generalize the system, providing cleaner interfaces and more
meillo@53 326 software leverage at the same time.
meillo@106 327 Mmh is a way to demonstrate this.
meillo@45 328 .P
meillo@45 329 In providing several parts of an email system, nmh can hardly
meillo@45 330 compete with the large specialized projects that focus
meillo@45 331 on only one of the components.
meillo@45 332 The situation can be improved by concentrating the development power
meillo@51 333 on the most unique part of MH and letting the user pick his preferred
meillo@45 334 set of other mail components.
meillo@45 335 Today's pre-packaged software components encourage this model.
meillo@106 336 Mmh is a way to go for this approach.
meillo@45 337 .P
meillo@197 338 It is worthwhile to fork nmh for the development of mmh,
meillo@197 339 because the two projects focus on different goals and differ in
meillo@197 340 fundamental questions.
meillo@106 341 The nmh community's reluctance regarding change conflicts
meillo@106 342 with my strong desire for it.
meillo@207 343 .[
meillo@207 344 nmh-workers schnalke understanding nmh
meillo@207 345 .]
meillo@43 346 In developing a separate experimental version new approaches can
meillo@43 347 easily be tried out without the need to discuss changes beforehand.
meillo@43 348 In fact, revolutionary changes are hardly possible otherwise.
meillo@43 349 .P
meillo@117 350 The mmh project provides the basis on which the aforementioned
meillo@117 351 ideas can be implemented and demonstrated,
meillo@164 352 without the need to change the nmh project or its community.
meillo@43 353 Of course, the results of the mmh project shall improve nmh, in the end.
meillo@159 354 By no means it is my intent to work against the nmh project.
meillo@117 355
meillo@27 356
meillo@27 357 .U2 "Target Field
meillo@27 358 .P
meillo@45 359 Any effort needs to be targeted towards a specific goal
meillo@45 360 in order to be successful.
meillo@197 361 Therefore, a description of an imagined typical mmh user follows.
meillo@197 362 Mmh should satisfy his needs.
meillo@48 363 Actually, as mmh is my personal version of MH, this is a description
meillo@48 364 of myself.
meillo@197 365 Writing software for oneself is a reliable way to produce software
meillo@197 366 that matches the user's desires.
meillo@45 367 .P
meillo@197 368 The target user of mmh likes Unix and its philosophy.
meillo@197 369 He appreciates to use programs that are conceptionally appealing.
meillo@197 370 He is familiar with the command line and enjoys its power.
meillo@197 371 He is capable of shell scripting and wants to improve his
meillo@27 372 productivity by scripting the mail system.
meillo@197 373 He uses modern email features, such as attachments,
meillo@169 374 non-ASCII text, digital signatures and message encryption in a natural way.
meillo@197 375 He is able to set up mail system components,
meillo@197 376 and like to have the choice to pick the ones he prefers.
meillo@197 377 He has a reasonably modern operating system that complies to the
meillo@164 378 POSIX and ANSI C standards.
meillo@27 379 .P
meillo@197 380 The typical user invokes mmh commands directly in an interactive
meillo@197 381 shell session, but he uses them to automate mail handling tasks as well.
meillo@197 382 Likely, he runs his mail setup on a server machine,
meillo@197 383 to which he connects via ssh.
meillo@197 384 He might also have a local mmh installation on his workstation.
meillo@197 385 Still, he tend to use mmh directly in the shell instead
meillo@117 386 of using graphical front-ends.
meillo@197 387 He definitely wants to be flexible and thus be able to change
meillo@197 388 his setup to suit his needs.
meillo@8 389 .P
meillo@197 390 The typical mmh user is a programmer.
meillo@197 391 He likes to, occasionally, take the opportunity of free software to put
meillo@197 392 hands on and get involved in the software he uses.
meillo@197 393 In consequence, he likes small and clean code bases and cares for
meillo@197 394 code quality.
meillo@197 395 In general, he believes that:
meillo@8 396 .BU
meillo@197 397 The elegance of source code is most important.
meillo@8 398 .BU
meillo@197 399 Concepts are more important than concrete implementations.
meillo@8 400 .BU
meillo@197 401 Code optimizations for anything but readability should be avoided.
meillo@8 402 .BU
meillo@45 403 Having a lot of choice is bad.
meillo@48 404 .BU
meillo@48 405 Removed code is debugged code.
meillo@8 406
meillo@197 407
meillo@48 408 .U2 "Goals
meillo@45 409 .P
meillo@45 410 The general goals for the mmh project are the following:
meillo@128 411 .IP "Streamlining
meillo@87 412 Mmh should be stripped down to its core, which is the user agent (MUA).
meillo@117 413 The feature set should be distilled to the indispensable ones,
meillo@171 414 effectively removing corner cases.
meillo@173 415 Parts that do not add to the main task of being a conceptionally
meillo@187 416 appealing user agent should be removed.
meillo@117 417 This includes the mail submission and mail retrieval facilities.
meillo@48 418 Choice should be reduced to the main options.
meillo@131 419 All tools should be tightly shaped.
meillo@48 420 .IP "Modernizing
meillo@48 421 Mmh's feature set needs to become more modern.
meillo@164 422 Better support for attachments, digital signatures and message encryption
meillo@164 423 should be added.
meillo@159 424 MIME support should be integrated deeper and more naturally.
meillo@48 425 The modern email features need to be readily available, out-of-the-box.
meillo@117 426 On the other hand,
meillo@117 427 bulletin board support and similar obsolete facilities can be dropped out.
meillo@131 428 Likewise, ancient technologies should not be supported any further.
meillo@131 429 The available concepts need to be expanded as far as possible.
meillo@131 430 A small set of concepts should recur consistently.
meillo@131 431 .IP "Styling
meillo@48 432 Mmh's source code needs to be updated to modern standards.
meillo@48 433 Standardized library functions should replace non-standard versions
meillo@48 434 whenever possible.
meillo@117 435 Code should be separated into distinct modules when feasible.
meillo@48 436 Time and space optimizations should to be replaced by
meillo@48 437 clear and readable code.
meillo@48 438 A uniform programming style should prevail.
meillo@117 439 The whole system should appear to be of-one-style;
meillo@117 440 it should feel like being cast as one.