docs/master

annotate intro.roff @ 159:8b411125645d

Corrections and improvements by Kate, Phil, Matou, Michi, Lydi.
author markus schnalke <meillo@marmaro.de>
date Mon, 09 Jul 2012 11:16:30 +0200
parents 7c741bc8f719
children 5c01017be420
rev   line source
meillo@39 1 .RN 1
meillo@39 2
meillo@0 3 .H0 "Introduction
meillo@0 4 .P
meillo@53 5 MH is a set of mail handling tools with a common concept, similar to
meillo@53 6 the Unix tool chest, which is a set of file handling tools with a common
meillo@53 7 concept. \fInmh\fP is the currently most popular implementation of an
meillo@53 8 MH-like mail handling system.
meillo@53 9 This thesis describes an experimental version of nmh, named \fImmh\fP.
meillo@53 10 .P
meillo@32 11 This chapter introduces MH, its history, concepts and how it is used.
meillo@47 12 It describes nmh's code base and community to give the reader
meillo@106 13 a better understanding of the state of mmh when it started off.
meillo@47 14 Further more, this chapter outlines the mmh project itself,
meillo@47 15 describing the motivation for it and its goals.
meillo@8 16
meillo@0 17
meillo@28 18 .H1 "MH \(en the Mail Handler
meillo@0 19 .P
meillo@47 20 MH is a conceptual email system design and its concrete implementation.
meillo@47 21 Notably, MH had started as a design proposal at RAND Corporation,
meillo@159 22 .\" XXX ref to rand corp.
meillo@47 23 where the first implementation followed later.
meillo@47 24 In spirit, MH is similar to Unix, which
meillo@42 25 influenced the world more in being a set of system design concepts
meillo@32 26 than in being a specific software product.
meillo@47 27 The ideas behind Unix are summarized in the \fIUnix philosophy\fP.
meillo@42 28 MH follows this philosophy.
meillo@2 29
meillo@11 30 .U2 "History
meillo@2 31 .P
meillo@32 32 In 1977 at RAND Corporation, Norman Shapiro and Stockton Gaines
meillo@106 33 proposed the design
meillo@32 34 of a new mail handling system, called ``Mail Handler'' (MH),
meillo@32 35 to superseed RAND's old monolithic ``Mail System'' (MS).
meillo@27 36 Two years later, in 1979, Bruce Borden took the proposal and implemented a
meillo@32 37 prototype of MH.
meillo@106 38 Before the prototype's existence, the concept was
meillo@47 39 believed to be practically unusable.
meillo@106 40 But the prototype proved successful and replaced MS thereafter.
meillo@47 41 In replacing MS, MH grew to an all-in-one mail system.
meillo@2 42 .P
meillo@106 43 In the early eighties,
meillo@106 44 the University of California at Irvine (UCI) started to use MH.
meillo@106 45 Marshall T. Rose and John L. Romine then became the driving force.
meillo@57 46 They took over the development and pushed MH forward.
meillo@57 47 RAND had put the code into the public domain by then.
meillo@57 48 MH was developed at UCI at the time when the Internet appeared,
meillo@57 49 when UCB implemented the TCP/IP stack, and when Allman wrote Sendmail.
meillo@47 50 MH was extended as emailing became more featured.
meillo@32 51 The development of MH was closely related to the development of email
meillo@32 52 RFCs. In the advent of MIME, MH was the first implementation of this new
meillo@32 53 email standard.
meillo@2 54 .P
meillo@117 55 In the nineties, the Internet became popular and in December 1996,
meillo@47 56 Richard Coleman initiated the ``New Mail Handler'' (nmh) project.
meillo@57 57 Nmh is a fork of MH 6.8.3 and bases strongly on the
meillo@47 58 \fILBL changes\fP by Van Jacobson, Mike Karels and Craig Leres.
meillo@32 59 Colman intended to modernize MH and improve its portability and
meillo@32 60 MIME handling capabilities.
meillo@32 61 This should be done openly within the Internet community.
meillo@47 62 The development of MH at UCI stopped after the 6.8.4 release in
meillo@47 63 February 1996, soon after the development of nmh had started.
meillo@57 64 Today, nmh has almost completely replaced the original MH.
meillo@47 65 Some systems might still provide old MH, but mainly for historical reasons.
meillo@47 66 .P
meillo@47 67 In the last years, the work on nmh was mostly maintenance work.
meillo@117 68 However, the development was revived in December 2011
meillo@57 69 and stayed busy since then.
meillo@0 70
meillo@11 71 .U2 "Concepts
meillo@0 72 .P
meillo@53 73 MH consists of a set of tools, each covering a specific task of
meillo@53 74 email handling, like composing a message, replying to a message,
meillo@53 75 refiling a message to a different folder, listing the messages in a folder.
meillo@47 76 All of the programs operate on a common mail storage.
meillo@42 77 .P
meillo@32 78 The mail storage consists of \fImail folders\fP (directories) and
meillo@32 79 \fPmessages\fP (regular files).
meillo@106 80 Each message is stored in a separate file in the format it was
meillo@47 81 received (i.e. transfer format).
meillo@47 82 The files are named with ascending numbers in each folder.
meillo@47 83 The specific format of the mail storage characterizes MH in the same way
meillo@106 84 as the format of the file system characterizes Unix.
meillo@42 85 .P
meillo@47 86 MH tools maintain a \fIcontext\fP, which includes the current mail folder.
meillo@32 87 Processes in Unix have a similar context, containing the current working
meillo@32 88 directory, for instance. In contrast, the process context is maintained
meillo@32 89 by the Unix kernel automatically, whereas MH tools need to maintain the MH
meillo@32 90 context themselves.
meillo@106 91 The user can have one MH context or multiple ones; he can even share it
meillo@106 92 with others.
meillo@42 93 .P
meillo@47 94 Messages are named by their numeric filename, but they can have symbolic names,
meillo@47 95 too. These are either automatically updated
meillo@106 96 position names such as the next or the last message,
meillo@32 97 or user-settable group names for arbitrary sets of messages.
meillo@32 98 These names are called sequences.
meillo@47 99 Sequences can be bound to the containing folder or to the context.
meillo@2 100 .P
meillo@47 101 The user's \fIprofile\fP is a file that contains his MH configuration.
meillo@47 102 Default switches for the individual tools can be specified to
meillo@47 103 adjust them to the user's personal preferences.
meillo@47 104 Multiple versions of the same command with different
meillo@47 105 default values can also be created very easily.
meillo@51 106 Form templates for new messages or for replies are easily changeable,
meillo@47 107 and output is adjustable with format files.
meillo@47 108 Almost every part of the system can be adjusted to personal preference.
meillo@42 109 .P
meillo@51 110 The system is well scriptable and extensible.
meillo@47 111 New MH tools are built out of or on top of existing ones quickly.
meillo@51 112 Further more, MH encourages the user to tailor, extend and automate the system.
meillo@51 113 As the MH tool chest was modeled after the Unix tool chest, the
meillo@32 114 properties of the latter apply to the former as well.
meillo@8 115
meillo@102 116
meillo@102 117 .ig \"XXX
meillo@102 118
meillo@102 119 .P
meillo@102 120 To ease typing, the switches can be abbreviated as much as the remaining
meillo@102 121 prefix remains unambiguous.
meillo@102 122 If in our example no other switch would start with the letter `t', then
meillo@102 123 .Cl "-truncate" ,
meillo@102 124 .Cl "-trunc" ,
meillo@102 125 .Cl "-tr" ,
meillo@102 126 and
meillo@102 127 .Cl "-t
meillo@102 128 would all be the same.
meillo@102 129 As a result, switches can neither be grouped (as in
meillo@102 130 .Cl "ls -ltr" )
meillo@102 131 nor can switch arguments be appended directly to the switch (as in
meillo@102 132 .Cl "sendmail -q30m" ).
meillo@102 133 .P
meillo@102 134 Many switches have negating counter-parts, which start with `no'.
meillo@102 135 For example
meillo@102 136 .Cl "-notruncate
meillo@102 137 inverts the
meillo@102 138 .Cl "-truncate
meillo@102 139 switch.
meillo@102 140 They exist to undo the effect of default switches in the profile.
meillo@102 141 If the user has chosen to change the default behavior of some tool
meillo@102 142 by adding a default switch to the profile,
meillo@102 143 he can still undo this change in behavior by specifying the inverse
meillo@102 144 switch on the command line.
meillo@102 145
meillo@102 146 ..
meillo@102 147
meillo@102 148
meillo@54 149 .U2 "Using MH
meillo@53 150 .P
meillo@54 151 It is strongly recommended to have a look at the MH Book,
meillo@106 152 which offers a thorough introduction to using MH.
meillo@54 153 .[ [
meillo@54 154 peek mh book
meillo@54 155 .], Part II]
meillo@54 156 Rose and Romine provide a deeper and more technical
meillo@159 157 though slightly outdated introduction in only about two dozen pages.
meillo@54 158 .[
meillo@54 159 rose romine real work
meillo@54 160 .]
meillo@27 161 .P
meillo@53 162 Following is an example mail handling session.
meillo@53 163 It uses mmh but is mostly compatible with nmh and old MH.
meillo@106 164 Details might vary but the look and feel is the same.
meillo@82 165
meillo@83 166 .VF input/mh-session
meillo@27 167
meillo@27 168
meillo@131 169 .H1 "nmh
meillo@2 170 .P
meillo@49 171 In order to understand the condition, goals and dynamics of a project,
meillo@106 172 one needs to know the reasons behind them.
meillo@53 173 This section explains the background.
meillo@53 174 .P
meillo@106 175 MH predates the Internet; it comes from times before networking was universal,
meillo@49 176 it comes from times when emailing was small, short and simple.
meillo@106 177 Then it grew, spread and adapted to the changes email went through.
meillo@49 178 Its core-concepts, however, remained the same.
meillo@106 179 During the eighties, students at UCI actively worked on MH.
meillo@49 180 They added new features and optimized the code for the then popular systems.
meillo@49 181 All this still was in times before POSIX and ANSI C.
meillo@49 182 As large parts of the code stem from this time, today's nmh source code
meillo@49 183 still contains many ancient parts.
meillo@51 184 BSD-specific code and constructs tailored for hardware of that time
meillo@49 185 are frequent.
meillo@2 186 .P
meillo@106 187 Nmh started about a decade after the POSIX and ANSI C standards were
meillo@49 188 established. A more modern coding style entered the code base, but still
meillo@49 189 a part of the developers came from ``the old days''. The developer
meillo@106 190 base became more diverse, thus broadening the range of different
meillo@106 191 coding styles.
meillo@49 192 Programming practices from different decades merged in the project.
meillo@51 193 As several peers added code, the system became more a conglomeration
meillo@51 194 of single tools rather than a homogeneous of-one-cast mail system.
meillo@49 195 Still, the existing basic concepts held it together.
meillo@8 196 They were mostly untouched throughout the years.
meillo@8 197 .P
meillo@106 198 Despite the separation of the tool chest approach at the surface
meillo@106 199 \(en a collection of small, separate programs \(en
meillo@106 200 on the source code level, it is much more interweaved.
meillo@49 201 Several separate components were compiled into one program
meillo@51 202 for efficiency reasons.
meillo@106 203 This led to intricate innards.
meillo@106 204 While clearly separated on the outside,
meillo@106 205 the programs turned out to be fairly interweaved inside.
meillo@106 206 .\" XXX FIXME rewrite...
meillo@159 207 .\" nicht zweimal ``interweaved''
meillo@106 208 .\" Unfortunately, the clear separation on the outside turned out to be
meillo@106 209 .\" fairly interweaved inside.
meillo@8 210 .P
meillo@106 211 The advent of MIME raised the complexity of email by a magnitude.
meillo@49 212 This is visible in nmh. The MIME-related parts are the most complex ones.
meillo@106 213 It is also visible that MIME support was added on top of the old MH core.
meillo@51 214 MH's tool chest style made this easily possible and encourages
meillo@106 215 such approaches, but unfortunately, it led to duplicated functions
meillo@49 216 and half-hearted implementation of the concepts.
meillo@49 217 .P
meillo@159 218 To provide backward-compatibility, it is a common understanding not to
meillo@49 219 change the default settings.
meillo@51 220 In consequence, the user needs to activate modern features explicitly
meillo@47 221 to be able to use them.
meillo@49 222 This puts a burden on new users, because out-of-the-box nmh remains
meillo@49 223 in the same ancient style.
meillo@49 224 If nmh is seen to be a back-end, then this compatibility surely is important.
meillo@106 225 However, in the same go, new users have difficulties using nmh for modern
meillo@49 226 emailing.
meillo@106 227 The small but mature community around nmh needs few change
meillo@106 228 as they have had their convenient setups for decades.
meillo@159 229 .\" XXX Explain more
meillo@8 230
meillo@8 231
meillo@27 232 .H1 "mmh
meillo@28 233 .P
meillo@49 234 I started to work on my experimental version in October 2011,
meillo@106 235 at a time when there had been no more than three commits to nmh
meillo@53 236 since the beginning of the year.
meillo@53 237 In December, when I announced my work in progress on the
meillo@53 238 nmh-workers mailing list,
meillo@42 239 .[
meillo@51 240 nmh-workers mmh announce December
meillo@42 241 .]
meillo@53 242 nmh's community became active, too.
meillo@49 243 This movement was heavily pushed by Paul Vixie's ``edginess'' comment.
meillo@42 244 .[
meillo@42 245 nmh-workers vixie edginess
meillo@42 246 .]
meillo@53 247 After long years of stagnation, nmh became actively developed again.
meillo@106 248 Hence, while I was working on mmh, the community was once more working
meillo@106 249 on nmh, in parallel.
meillo@28 250 .P
meillo@53 251 The name \fImmh\fP may stand for \fImodern mail handler\fP,
meillo@53 252 because the project tries to modernize nmh.
meillo@53 253 Personally however, I prefer to call mmh \fImeillo's mail handler\fP,
meillo@53 254 emphasizing that the project follows my visions and preferences.
meillo@42 255 (My login name is \fImeillo\fP.)
meillo@53 256 This project model was inspired by \fIdwm\fP,
meillo@159 257 .\" XXX Ref
meillo@42 258 which is Anselm Garbe's personal window manager \(en
meillo@42 259 targeted to satisfy Garbe's personal needs whenever conflicts appear.
meillo@53 260 Dwm had retained its lean elegance and its focused character, whereas
meillo@53 261 its community-driven predecessor \fIwmii\fP had grown fat over time.
meillo@159 262 .\" XXX ref
meillo@53 263 The development of mmh should remain focused.
meillo@27 264
meillo@45 265
meillo@27 266 .U2 "Motivation
meillo@27 267 .P
meillo@51 268 MH is the most important of very few command line tool chest email systems.
meillo@51 269 Tool chests are powerful because they can be perfectly automated and
meillo@53 270 extended. They allow arbitrary kinds of front-ends to be
meillo@53 271 implemented on top of them quickly and without internal knowledge.
meillo@106 272 Additionally, tool chests are easier to maintain than monolithic
meillo@43 273 programs.
meillo@53 274 As there are few tool chests for emailing and as MH-like ones are the most
meillo@106 275 popular among them, they should be developed further.
meillo@53 276 This keeps their
meillo@43 277 conceptional elegance and unique scripting qualities available to users.
meillo@106 278 Mmh creates a modern and convenient entry point to MH-like systems
meillo@53 279 for new and interested users.
meillo@43 280 .P
meillo@51 281 The mmh project is motivated by deficits of nmh and
meillo@45 282 my wish for general changes, combined
meillo@45 283 with the nmh community's reluctancy to change.
meillo@45 284 .P
meillo@106 285 At that time, nmh had not adjusted to modern emailing needs well enough.
meillo@45 286 The default setup was completely unusable for modern emailing.
meillo@45 287 Too much setup work was required.
meillo@45 288 Several modern features were already available but the community
meillo@106 289 did not want to have them as default.
meillo@106 290 Mmh is a way to change this.
meillo@45 291 .P
meillo@45 292 In my eyes, MH's concepts could be exploited even better and
meillo@45 293 the style of the tools could be improved. Both would simplify
meillo@45 294 and generalize the system, providing cleaner interfaces and more
meillo@53 295 software leverage at the same time.
meillo@106 296 Mmh is a way to demonstrate this.
meillo@45 297 .P
meillo@45 298 In providing several parts of an email system, nmh can hardly
meillo@45 299 compete with the large specialized projects that focus
meillo@45 300 on only one of the components.
meillo@45 301 The situation can be improved by concentrating the development power
meillo@51 302 on the most unique part of MH and letting the user pick his preferred
meillo@45 303 set of other mail components.
meillo@45 304 Today's pre-packaged software components encourage this model.
meillo@106 305 Mmh is a way to go for this approach.
meillo@45 306 .P
meillo@106 307 It is worthwhile to fork nmh for the development of mmh, because
meillo@43 308 the two projects focus on different goals and differ in fundamental questions.
meillo@106 309 The nmh community's reluctance regarding change conflicts
meillo@106 310 with my strong desire for it.
meillo@43 311 In developing a separate experimental version new approaches can
meillo@43 312 easily be tried out without the need to discuss changes beforehand.
meillo@43 313 In fact, revolutionary changes are hardly possible otherwise.
meillo@43 314 .P
meillo@117 315 The mmh project provides the basis on which the aforementioned
meillo@117 316 ideas can be implemented and demonstrated,
meillo@106 317 without the need to change nmh or its community.
meillo@43 318 Of course, the results of the mmh project shall improve nmh, in the end.
meillo@159 319 By no means it is my intent to work against the nmh project.
meillo@117 320
meillo@27 321
meillo@27 322 .U2 "Target Field
meillo@27 323 .P
meillo@45 324 Any effort needs to be targeted towards a specific goal
meillo@45 325 in order to be successful.
meillo@117 326 Following is a description of imagined typical mmh users.
meillo@117 327 Mmh should satisfy their needs.
meillo@53 328 .\" XXX Remove the next sentence?
meillo@48 329 Actually, as mmh is my personal version of MH, this is a description
meillo@48 330 of myself.
meillo@45 331 .P
meillo@117 332 The target users of mmh like Unix and its philosophy.
meillo@117 333 They appreciate to use programs that are conceptionally appealing.
meillo@117 334 They are familiar with the command line and enjoy its power.
meillo@117 335 They are at least capable of shell scripting and want to improve their
meillo@27 336 productivity by scripting the mail system.
meillo@117 337 .\" XXX Naturally, he uses ...
meillo@117 338 They naturally use modern email features, such as attachments,
meillo@51 339 non-ASCII text, and digital cryptography.
meillo@117 340 They are able to setup email system components besides mmh,
meillo@117 341 and actually like to have the choice to pick the ones they prefer.
meillo@117 342 They have a reasonably modern operating system that complies to standards,
meillo@43 343 like POSIX and ANSI C.
meillo@27 344 .P
meillo@117 345 The typical users invoke mmh commands directly in an interactive
meillo@117 346 shell session, but they use them to automate mail handling tasks as well.
meillo@159 347 Likely, they run their mail setup on a server machine,
meillo@117 348 to which they connect via ssh.
meillo@117 349 They might also have local mmh installations on their workstations,
meillo@117 350 where they tend to work with mmh directly in the shell instead
meillo@117 351 of using graphical front-ends.
meillo@117 352 They definitely want to be flexible and thus be able to change
meillo@117 353 their setup to suit their needs.
meillo@8 354 .P
meillo@117 355 .\" XXX themself vs. themselves
meillo@117 356 Typical mmh users are programmers themselves.
meillo@117 357 They like to, occasionally, take the opportunity of Free Software to put
meillo@117 358 hands on and get involved in the software they use.
meillo@117 359 Hence, they like small and clean code bases and care for code quality.
meillo@117 360 In general, they believe that:
meillo@8 361 .BU
meillo@48 362 Elegance \(en i.e. simplicity, clarity and generality \(en
meillo@48 363 is most important.
meillo@8 364 .BU
meillo@48 365 Concepts are more important than the concrete implementation.
meillo@8 366 .BU
meillo@48 367 Code optimizations for anything but readability should be avoided
meillo@48 368 if possible.
meillo@8 369 .BU
meillo@45 370 Having a lot of choice is bad.
meillo@48 371 .BU
meillo@48 372 Removed code is debugged code.
meillo@8 373
meillo@48 374 .U2 "Goals
meillo@45 375 .P
meillo@45 376 The general goals for the mmh project are the following:
meillo@128 377 .IP "Streamlining
meillo@87 378 Mmh should be stripped down to its core, which is the user agent (MUA).
meillo@117 379 The feature set should be distilled to the indispensable ones,
meillo@48 380 effectively removing corner-cases.
meillo@53 381 Parts that don't add to the main task of being a conceptionally
meillo@53 382 appealing MUA should be removed.
meillo@117 383 This includes the mail submission and mail retrieval facilities.
meillo@48 384 Choice should be reduced to the main options.
meillo@131 385 All tools should be tightly shaped.
meillo@48 386 .IP "Modernizing
meillo@48 387 Mmh's feature set needs to become more modern.
meillo@117 388 Better support for attachment and digital cryptography should be added.
meillo@159 389 MIME support should be integrated deeper and more naturally.
meillo@48 390 The modern email features need to be readily available, out-of-the-box.
meillo@117 391 On the other hand,
meillo@117 392 bulletin board support and similar obsolete facilities can be dropped out.
meillo@131 393 Likewise, ancient technologies should not be supported any further.
meillo@131 394 The available concepts need to be expanded as far as possible.
meillo@131 395 A small set of concepts should recur consistently.
meillo@131 396 .IP "Styling
meillo@48 397 Mmh's source code needs to be updated to modern standards.
meillo@48 398 Standardized library functions should replace non-standard versions
meillo@48 399 whenever possible.
meillo@117 400 Code should be separated into distinct modules when feasible.
meillo@48 401 Time and space optimizations should to be replaced by
meillo@48 402 clear and readable code.
meillo@48 403 A uniform programming style should prevail.
meillo@117 404 The whole system should appear to be of-one-style;
meillo@117 405 it should feel like being cast as one.