docs/master

annotate intro.roff @ 204:8c0d5bd92f0b

Added full names of abbreviations.
author markus schnalke <meillo@marmaro.de>
date Thu, 12 Jul 2012 09:42:56 +0200
parents e417f510aaca
children e0e49a8bfbe8
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@42 29 MH follows this philosophy.
meillo@2 30
meillo@11 31 .U2 "History
meillo@2 32 .P
meillo@32 33 In 1977 at RAND Corporation, Norman Shapiro and Stockton Gaines
meillo@106 34 proposed the design
meillo@181 35 of a new mail handling system, called \fIMail Handler\fP (MH),
meillo@181 36 to superseed RAND's old monolithic \fIMail System\fP (MS).
meillo@27 37 Two years later, in 1979, Bruce Borden took the proposal and implemented a
meillo@32 38 prototype of MH.
meillo@106 39 Before the prototype's existence, the concept was
meillo@47 40 believed to be practically unusable.
meillo@106 41 But the prototype proved successful and replaced MS thereafter.
meillo@164 42 In replacing MS, MH grew to provide anything necessary for emailing.
meillo@2 43 .P
meillo@106 44 In the early eighties,
meillo@106 45 the University of California at Irvine (UCI) started to use MH.
meillo@106 46 Marshall T. Rose and John L. Romine then became the driving force.
meillo@57 47 They took over the development and pushed MH forward.
meillo@57 48 RAND had put the code into the public domain by then.
meillo@57 49 MH was developed at UCI at the time when the Internet appeared,
meillo@204 50 when the University of California at Berkeley (UCB) implemented
meillo@204 51 the TCP/IP stack, and when Eric Allman wrote Sendmail.
meillo@47 52 MH was extended as emailing became more featured.
meillo@32 53 The development of MH was closely related to the development of email
meillo@204 54 RFCs.
meillo@204 55 In the advent of the \fIMultipurpose Internet Mail Extensions\fP (MIME),
meillo@204 56 MH was one of the first implementations of the new email standard.
meillo@2 57 .P
meillo@117 58 In the nineties, the Internet became popular and in December 1996,
meillo@181 59 Richard Coleman initiated the \fINew Mail Handler\fP (nmh) project.
meillo@57 60 Nmh is a fork of MH 6.8.3 and bases strongly on the
meillo@47 61 \fILBL changes\fP by Van Jacobson, Mike Karels and Craig Leres.
meillo@32 62 Colman intended to modernize MH and improve its portability and
meillo@32 63 MIME handling capabilities.
meillo@32 64 This should be done openly within the Internet community.
meillo@47 65 The development of MH at UCI stopped after the 6.8.4 release in
meillo@47 66 February 1996, soon after the development of nmh had started.
meillo@57 67 Today, nmh has almost completely replaced the original MH.
meillo@47 68 Some systems might still provide old MH, but mainly for historical reasons.
meillo@47 69 .P
meillo@171 70 In the last years, the changes in nmh were mostly maintenance work.
meillo@117 71 However, the development was revived in December 2011
meillo@57 72 and stayed busy since then.
meillo@0 73
meillo@197 74
meillo@11 75 .U2 "Concepts
meillo@0 76 .P
meillo@53 77 MH consists of a set of tools, each covering a specific task of
meillo@53 78 email handling, like composing a message, replying to a message,
meillo@53 79 refiling a message to a different folder, listing the messages in a folder.
meillo@47 80 All of the programs operate on a common mail storage.
meillo@42 81 .P
meillo@32 82 The mail storage consists of \fImail folders\fP (directories) and
meillo@32 83 \fPmessages\fP (regular files).
meillo@106 84 Each message is stored in a separate file in the format it was
meillo@47 85 received (i.e. transfer format).
meillo@47 86 The files are named with ascending numbers in each folder.
meillo@47 87 The specific format of the mail storage characterizes MH in the same way
meillo@106 88 as the format of the file system characterizes Unix.
meillo@42 89 .P
meillo@164 90 MH tools maintain a \fIcontext\fP, which includes for instance the
meillo@164 91 current mail folder.
meillo@32 92 Processes in Unix have a similar context, containing the current working
meillo@32 93 directory, for instance. In contrast, the process context is maintained
meillo@32 94 by the Unix kernel automatically, whereas MH tools need to maintain the MH
meillo@32 95 context themselves.
meillo@106 96 The user can have one MH context or multiple ones; he can even share it
meillo@106 97 with others.
meillo@42 98 .P
meillo@164 99 Messages are named by their numeric filename,
meillo@164 100 but they can have symbolic names, too.
meillo@164 101 These are either automatically updated
meillo@106 102 position names such as the next or the last message,
meillo@32 103 or user-settable group names for arbitrary sets of messages.
meillo@32 104 These names are called sequences.
meillo@47 105 Sequences can be bound to the containing folder or to the context.
meillo@2 106 .P
meillo@47 107 The user's \fIprofile\fP is a file that contains his MH configuration.
meillo@47 108 Default switches for the individual tools can be specified to
meillo@47 109 adjust them to the user's personal preferences.
meillo@164 110 Additionally, a single command can be linked under different names
meillo@164 111 with different default values easily.
meillo@51 112 Form templates for new messages or for replies are easily changeable,
meillo@47 113 and output is adjustable with format files.
meillo@47 114 Almost every part of the system can be adjusted to personal preference.
meillo@42 115 .P
meillo@51 116 The system is well scriptable and extensible.
meillo@47 117 New MH tools are built out of or on top of existing ones quickly.
meillo@181 118 Furthermore, MH encourages the user to tailor, extend and automate the system.
meillo@51 119 As the MH tool chest was modeled after the Unix tool chest, the
meillo@32 120 properties of the latter apply to the former as well.
meillo@8 121
meillo@102 122
meillo@102 123 .ig \"XXX
meillo@102 124
meillo@102 125 .P
meillo@102 126 To ease typing, the switches can be abbreviated as much as the remaining
meillo@102 127 prefix remains unambiguous.
meillo@102 128 If in our example no other switch would start with the letter `t', then
meillo@102 129 .Cl "-truncate" ,
meillo@102 130 .Cl "-trunc" ,
meillo@102 131 .Cl "-tr" ,
meillo@102 132 and
meillo@102 133 .Cl "-t
meillo@102 134 would all be the same.
meillo@102 135 As a result, switches can neither be grouped (as in
meillo@102 136 .Cl "ls -ltr" )
meillo@102 137 nor can switch arguments be appended directly to the switch (as in
meillo@102 138 .Cl "sendmail -q30m" ).
meillo@102 139 .P
meillo@102 140 Many switches have negating counter-parts, which start with `no'.
meillo@102 141 For example
meillo@102 142 .Cl "-notruncate
meillo@102 143 inverts the
meillo@102 144 .Cl "-truncate
meillo@102 145 switch.
meillo@102 146 They exist to undo the effect of default switches in the profile.
meillo@102 147 If the user has chosen to change the default behavior of some tool
meillo@102 148 by adding a default switch to the profile,
meillo@102 149 he can still undo this change in behavior by specifying the inverse
meillo@102 150 switch on the command line.
meillo@102 151
meillo@102 152 ..
meillo@102 153
meillo@102 154
meillo@54 155 .U2 "Using MH
meillo@53 156 .P
meillo@54 157 It is strongly recommended to have a look at the MH Book,
meillo@106 158 which offers a thorough introduction to using MH.
meillo@54 159 .[ [
meillo@54 160 peek mh book
meillo@54 161 .], Part II]
meillo@54 162 Rose and Romine provide a deeper and more technical
meillo@159 163 though slightly outdated introduction in only about two dozen pages.
meillo@54 164 .[
meillo@54 165 rose romine real work
meillo@54 166 .]
meillo@27 167 .P
meillo@53 168 Following is an example mail handling session.
meillo@53 169 It uses mmh but is mostly compatible with nmh and old MH.
meillo@106 170 Details might vary but the look and feel is the same.
meillo@82 171
meillo@202 172 .so input/mh-session
meillo@27 173
meillo@27 174
meillo@131 175 .H1 "nmh
meillo@2 176 .P
meillo@49 177 In order to understand the condition, goals and dynamics of a project,
meillo@106 178 one needs to know the reasons behind them.
meillo@53 179 This section explains the background.
meillo@53 180 .P
meillo@197 181 MH predates the Internet;
meillo@197 182 it comes from times before networking was universal,
meillo@49 183 it comes from times when emailing was small, short and simple.
meillo@106 184 Then it grew, spread and adapted to the changes email went through.
meillo@49 185 Its core-concepts, however, remained the same.
meillo@106 186 During the eighties, students at UCI actively worked on MH.
meillo@164 187 They added new features and optimized the code for the systems
meillo@164 188 popular at that time.
meillo@49 189 All this still was in times before POSIX and ANSI C.
meillo@49 190 As large parts of the code stem from this time, today's nmh source code
meillo@49 191 still contains many ancient parts.
meillo@51 192 BSD-specific code and constructs tailored for hardware of that time
meillo@49 193 are frequent.
meillo@2 194 .P
meillo@106 195 Nmh started about a decade after the POSIX and ANSI C standards were
meillo@49 196 established. A more modern coding style entered the code base, but still
meillo@49 197 a part of the developers came from ``the old days''. The developer
meillo@106 198 base became more diverse, thus broadening the range of different
meillo@106 199 coding styles.
meillo@49 200 Programming practices from different decades merged in the project.
meillo@51 201 As several peers added code, the system became more a conglomeration
meillo@51 202 of single tools rather than a homogeneous of-one-cast mail system.
meillo@49 203 Still, the existing basic concepts held it together.
meillo@8 204 They were mostly untouched throughout the years.
meillo@8 205 .P
meillo@106 206 Despite the separation of the tool chest approach at the surface
meillo@106 207 \(en a collection of small, separate programs \(en
meillo@171 208 on the source code level, it is much more interwoven.
meillo@49 209 Several separate components were compiled into one program
meillo@51 210 for efficiency reasons.
meillo@106 211 This led to intricate innards.
meillo@106 212 While clearly separated on the outside,
meillo@171 213 the programs turned out to be fairly interwoven inside.
meillo@106 214 .\" XXX FIXME rewrite...
meillo@171 215 .\" nicht zweimal ``interwoven''
meillo@106 216 .\" Unfortunately, the clear separation on the outside turned out to be
meillo@171 217 .\" fairly interwoven inside.
meillo@8 218 .P
meillo@106 219 The advent of MIME raised the complexity of email by a magnitude.
meillo@49 220 This is visible in nmh. The MIME-related parts are the most complex ones.
meillo@106 221 It is also visible that MIME support was added on top of the old MH core.
meillo@51 222 MH's tool chest style made this easily possible and encourages
meillo@106 223 such approaches, but unfortunately, it led to duplicated functions
meillo@49 224 and half-hearted implementation of the concepts.
meillo@49 225 .P
meillo@159 226 To provide backward-compatibility, it is a common understanding not to
meillo@49 227 change the default settings.
meillo@51 228 In consequence, the user needs to activate modern features explicitly
meillo@47 229 to be able to use them.
meillo@49 230 This puts a burden on new users, because out-of-the-box nmh remains
meillo@49 231 in the same ancient style.
meillo@171 232 If nmh is seen to be a back-end,
meillo@171 233 then this compatibility surely is important.
meillo@171 234 However, at the same time, new users have difficulties using nmh for
meillo@171 235 modern emailing.
meillo@173 236 The small but mature community around nmh needs little change
meillo@106 237 as they have had their convenient setups for decades.
meillo@159 238 .\" XXX Explain more
meillo@8 239
meillo@8 240
meillo@27 241 .H1 "mmh
meillo@28 242 .P
meillo@49 243 I started to work on my experimental version in October 2011,
meillo@197 244 basing my work on nmh version \fInmh-1.3-dev\fP.
meillo@197 245 At that time no more than three commits were made to nmh
meillo@197 246 since the beginning of the year, the latest one being
meillo@197 247 .Ci a01a41d031c796b526329a4170eb23f0ac93b949
meillo@197 248 on 2011-04-13.
meillo@53 249 In December, when I announced my work in progress on the
meillo@53 250 nmh-workers mailing list,
meillo@42 251 .[
meillo@51 252 nmh-workers mmh announce December
meillo@42 253 .]
meillo@197 254 nmh's community became active, all of a sudden.
meillo@49 255 This movement was heavily pushed by Paul Vixie's ``edginess'' comment.
meillo@42 256 .[
meillo@42 257 nmh-workers vixie edginess
meillo@42 258 .]
meillo@53 259 After long years of stagnation, nmh became actively developed again.
meillo@197 260 Hence, while I was working on mmh, the community was working on nmh,
meillo@197 261 in parallel.
meillo@28 262 .P
meillo@53 263 The name \fImmh\fP may stand for \fImodern mail handler\fP,
meillo@53 264 because the project tries to modernize nmh.
meillo@53 265 Personally however, I prefer to call mmh \fImeillo's mail handler\fP,
meillo@53 266 emphasizing that the project follows my visions and preferences.
meillo@42 267 (My login name is \fImeillo\fP.)
meillo@53 268 This project model was inspired by \fIdwm\fP,
meillo@159 269 .\" XXX Ref
meillo@42 270 which is Anselm Garbe's personal window manager \(en
meillo@42 271 targeted to satisfy Garbe's personal needs whenever conflicts appear.
meillo@53 272 Dwm had retained its lean elegance and its focused character, whereas
meillo@53 273 its community-driven predecessor \fIwmii\fP had grown fat over time.
meillo@159 274 .\" XXX ref
meillo@53 275 The development of mmh should remain focused.
meillo@27 276
meillo@45 277
meillo@27 278 .U2 "Motivation
meillo@27 279 .P
meillo@51 280 MH is the most important of very few command line tool chest email systems.
meillo@51 281 Tool chests are powerful because they can be perfectly automated and
meillo@53 282 extended. They allow arbitrary kinds of front-ends to be
meillo@53 283 implemented on top of them quickly and without internal knowledge.
meillo@106 284 Additionally, tool chests are easier to maintain than monolithic
meillo@43 285 programs.
meillo@53 286 As there are few tool chests for emailing and as MH-like ones are the most
meillo@106 287 popular among them, they should be developed further.
meillo@53 288 This keeps their
meillo@43 289 conceptional elegance and unique scripting qualities available to users.
meillo@106 290 Mmh creates a modern and convenient entry point to MH-like systems
meillo@53 291 for new and interested users.
meillo@43 292 .P
meillo@51 293 The mmh project is motivated by deficits of nmh and
meillo@45 294 my wish for general changes, combined
meillo@45 295 with the nmh community's reluctancy to change.
meillo@45 296 .P
meillo@106 297 At that time, nmh had not adjusted to modern emailing needs well enough.
meillo@45 298 The default setup was completely unusable for modern emailing.
meillo@45 299 Too much setup work was required.
meillo@45 300 Several modern features were already available but the community
meillo@106 301 did not want to have them as default.
meillo@106 302 Mmh is a way to change this.
meillo@45 303 .P
meillo@45 304 In my eyes, MH's concepts could be exploited even better and
meillo@45 305 the style of the tools could be improved. Both would simplify
meillo@45 306 and generalize the system, providing cleaner interfaces and more
meillo@53 307 software leverage at the same time.
meillo@106 308 Mmh is a way to demonstrate this.
meillo@45 309 .P
meillo@45 310 In providing several parts of an email system, nmh can hardly
meillo@45 311 compete with the large specialized projects that focus
meillo@45 312 on only one of the components.
meillo@45 313 The situation can be improved by concentrating the development power
meillo@51 314 on the most unique part of MH and letting the user pick his preferred
meillo@45 315 set of other mail components.
meillo@45 316 Today's pre-packaged software components encourage this model.
meillo@106 317 Mmh is a way to go for this approach.
meillo@45 318 .P
meillo@197 319 It is worthwhile to fork nmh for the development of mmh,
meillo@197 320 because the two projects focus on different goals and differ in
meillo@197 321 fundamental questions.
meillo@106 322 The nmh community's reluctance regarding change conflicts
meillo@106 323 with my strong desire for it.
meillo@43 324 In developing a separate experimental version new approaches can
meillo@43 325 easily be tried out without the need to discuss changes beforehand.
meillo@43 326 In fact, revolutionary changes are hardly possible otherwise.
meillo@43 327 .P
meillo@117 328 The mmh project provides the basis on which the aforementioned
meillo@117 329 ideas can be implemented and demonstrated,
meillo@164 330 without the need to change the nmh project or its community.
meillo@43 331 Of course, the results of the mmh project shall improve nmh, in the end.
meillo@159 332 By no means it is my intent to work against the nmh project.
meillo@117 333
meillo@27 334
meillo@27 335 .U2 "Target Field
meillo@27 336 .P
meillo@45 337 Any effort needs to be targeted towards a specific goal
meillo@45 338 in order to be successful.
meillo@197 339 Therefore, a description of an imagined typical mmh user follows.
meillo@197 340 Mmh should satisfy his needs.
meillo@48 341 Actually, as mmh is my personal version of MH, this is a description
meillo@48 342 of myself.
meillo@197 343 Writing software for oneself is a reliable way to produce software
meillo@197 344 that matches the user's desires.
meillo@45 345 .P
meillo@197 346 The target user of mmh likes Unix and its philosophy.
meillo@197 347 He appreciates to use programs that are conceptionally appealing.
meillo@197 348 He is familiar with the command line and enjoys its power.
meillo@197 349 He is capable of shell scripting and wants to improve his
meillo@27 350 productivity by scripting the mail system.
meillo@197 351 He uses modern email features, such as attachments,
meillo@169 352 non-ASCII text, digital signatures and message encryption in a natural way.
meillo@197 353 He is able to set up mail system components,
meillo@197 354 and like to have the choice to pick the ones he prefers.
meillo@197 355 He has a reasonably modern operating system that complies to the
meillo@164 356 POSIX and ANSI C standards.
meillo@27 357 .P
meillo@197 358 The typical user invokes mmh commands directly in an interactive
meillo@197 359 shell session, but he uses them to automate mail handling tasks as well.
meillo@197 360 Likely, he runs his mail setup on a server machine,
meillo@197 361 to which he connects via ssh.
meillo@197 362 He might also have a local mmh installation on his workstation.
meillo@197 363 Still, he tend to use mmh directly in the shell instead
meillo@117 364 of using graphical front-ends.
meillo@197 365 He definitely wants to be flexible and thus be able to change
meillo@197 366 his setup to suit his needs.
meillo@8 367 .P
meillo@197 368 The typical mmh user is a programmer.
meillo@197 369 He likes to, occasionally, take the opportunity of free software to put
meillo@197 370 hands on and get involved in the software he uses.
meillo@197 371 In consequence, he likes small and clean code bases and cares for
meillo@197 372 code quality.
meillo@197 373 In general, he believes that:
meillo@8 374 .BU
meillo@197 375 The elegance of source code is most important.
meillo@8 376 .BU
meillo@197 377 Concepts are more important than concrete implementations.
meillo@8 378 .BU
meillo@197 379 Code optimizations for anything but readability should be avoided.
meillo@8 380 .BU
meillo@45 381 Having a lot of choice is bad.
meillo@48 382 .BU
meillo@48 383 Removed code is debugged code.
meillo@8 384
meillo@197 385
meillo@48 386 .U2 "Goals
meillo@45 387 .P
meillo@45 388 The general goals for the mmh project are the following:
meillo@128 389 .IP "Streamlining
meillo@87 390 Mmh should be stripped down to its core, which is the user agent (MUA).
meillo@117 391 The feature set should be distilled to the indispensable ones,
meillo@171 392 effectively removing corner cases.
meillo@173 393 Parts that do not add to the main task of being a conceptionally
meillo@187 394 appealing user agent should be removed.
meillo@117 395 This includes the mail submission and mail retrieval facilities.
meillo@48 396 Choice should be reduced to the main options.
meillo@131 397 All tools should be tightly shaped.
meillo@48 398 .IP "Modernizing
meillo@48 399 Mmh's feature set needs to become more modern.
meillo@164 400 Better support for attachments, digital signatures and message encryption
meillo@164 401 should be added.
meillo@159 402 MIME support should be integrated deeper and more naturally.
meillo@48 403 The modern email features need to be readily available, out-of-the-box.
meillo@117 404 On the other hand,
meillo@117 405 bulletin board support and similar obsolete facilities can be dropped out.
meillo@131 406 Likewise, ancient technologies should not be supported any further.
meillo@131 407 The available concepts need to be expanded as far as possible.
meillo@131 408 A small set of concepts should recur consistently.
meillo@131 409 .IP "Styling
meillo@48 410 Mmh's source code needs to be updated to modern standards.
meillo@48 411 Standardized library functions should replace non-standard versions
meillo@48 412 whenever possible.
meillo@117 413 Code should be separated into distinct modules when feasible.
meillo@48 414 Time and space optimizations should to be replaced by
meillo@48 415 clear and readable code.
meillo@48 416 A uniform programming style should prevail.
meillo@117 417 The whole system should appear to be of-one-style;
meillo@117 418 it should feel like being cast as one.