docs/master

annotate intro.roff @ 148:e042616ad3a2

future/summary: Added more notes.
author markus schnalke <meillo@marmaro.de>
date Thu, 05 Jul 2012 20:33:04 +0200
parents 76c440261ebb
children 8b411125645d
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@47 22 where the first implementation followed later.
meillo@47 23 In spirit, MH is similar to Unix, which
meillo@42 24 influenced the world more in being a set of system design concepts
meillo@32 25 than in being a specific software product.
meillo@47 26 The ideas behind Unix are summarized in the \fIUnix philosophy\fP.
meillo@42 27 MH follows this philosophy.
meillo@2 28
meillo@11 29 .U2 "History
meillo@2 30 .P
meillo@32 31 In 1977 at RAND Corporation, Norman Shapiro and Stockton Gaines
meillo@106 32 proposed the design
meillo@32 33 of a new mail handling system, called ``Mail Handler'' (MH),
meillo@32 34 to superseed RAND's old monolithic ``Mail System'' (MS).
meillo@27 35 Two years later, in 1979, Bruce Borden took the proposal and implemented a
meillo@32 36 prototype of MH.
meillo@106 37 Before the prototype's existence, the concept was
meillo@47 38 believed to be practically unusable.
meillo@106 39 But the prototype proved successful and replaced MS thereafter.
meillo@47 40 In replacing MS, MH grew to an all-in-one mail system.
meillo@2 41 .P
meillo@106 42 In the early eighties,
meillo@106 43 the University of California at Irvine (UCI) started to use MH.
meillo@106 44 Marshall T. Rose and John L. Romine then became the driving force.
meillo@57 45 They took over the development and pushed MH forward.
meillo@57 46 RAND had put the code into the public domain by then.
meillo@57 47 MH was developed at UCI at the time when the Internet appeared,
meillo@57 48 when UCB implemented the TCP/IP stack, and when Allman wrote Sendmail.
meillo@47 49 MH was extended as emailing became more featured.
meillo@32 50 The development of MH was closely related to the development of email
meillo@32 51 RFCs. In the advent of MIME, MH was the first implementation of this new
meillo@32 52 email standard.
meillo@2 53 .P
meillo@117 54 In the nineties, the Internet became popular and in December 1996,
meillo@47 55 Richard Coleman initiated the ``New Mail Handler'' (nmh) project.
meillo@57 56 Nmh is a fork of MH 6.8.3 and bases strongly on the
meillo@47 57 \fILBL changes\fP by Van Jacobson, Mike Karels and Craig Leres.
meillo@32 58 Colman intended to modernize MH and improve its portability and
meillo@32 59 MIME handling capabilities.
meillo@32 60 This should be done openly within the Internet community.
meillo@47 61 The development of MH at UCI stopped after the 6.8.4 release in
meillo@47 62 February 1996, soon after the development of nmh had started.
meillo@57 63 Today, nmh has almost completely replaced the original MH.
meillo@47 64 Some systems might still provide old MH, but mainly for historical reasons.
meillo@47 65 .P
meillo@47 66 In the last years, the work on nmh was mostly maintenance work.
meillo@117 67 However, the development was revived in December 2011
meillo@57 68 and stayed busy since then.
meillo@0 69
meillo@11 70 .U2 "Concepts
meillo@0 71 .P
meillo@53 72 MH consists of a set of tools, each covering a specific task of
meillo@53 73 email handling, like composing a message, replying to a message,
meillo@53 74 refiling a message to a different folder, listing the messages in a folder.
meillo@47 75 All of the programs operate on a common mail storage.
meillo@42 76 .P
meillo@32 77 The mail storage consists of \fImail folders\fP (directories) and
meillo@32 78 \fPmessages\fP (regular files).
meillo@106 79 Each message is stored in a separate file in the format it was
meillo@47 80 received (i.e. transfer format).
meillo@47 81 The files are named with ascending numbers in each folder.
meillo@47 82 The specific format of the mail storage characterizes MH in the same way
meillo@106 83 as the format of the file system characterizes Unix.
meillo@42 84 .P
meillo@47 85 MH tools maintain a \fIcontext\fP, which includes the current mail folder.
meillo@32 86 Processes in Unix have a similar context, containing the current working
meillo@32 87 directory, for instance. In contrast, the process context is maintained
meillo@32 88 by the Unix kernel automatically, whereas MH tools need to maintain the MH
meillo@32 89 context themselves.
meillo@106 90 The user can have one MH context or multiple ones; he can even share it
meillo@106 91 with others.
meillo@42 92 .P
meillo@47 93 Messages are named by their numeric filename, but they can have symbolic names,
meillo@47 94 too. These are either automatically updated
meillo@106 95 position names such as the next or the last message,
meillo@32 96 or user-settable group names for arbitrary sets of messages.
meillo@32 97 These names are called sequences.
meillo@47 98 Sequences can be bound to the containing folder or to the context.
meillo@2 99 .P
meillo@47 100 The user's \fIprofile\fP is a file that contains his MH configuration.
meillo@47 101 Default switches for the individual tools can be specified to
meillo@47 102 adjust them to the user's personal preferences.
meillo@47 103 Multiple versions of the same command with different
meillo@47 104 default values can also be created very easily.
meillo@51 105 Form templates for new messages or for replies are easily changeable,
meillo@47 106 and output is adjustable with format files.
meillo@47 107 Almost every part of the system can be adjusted to personal preference.
meillo@42 108 .P
meillo@51 109 The system is well scriptable and extensible.
meillo@47 110 New MH tools are built out of or on top of existing ones quickly.
meillo@51 111 Further more, MH encourages the user to tailor, extend and automate the system.
meillo@51 112 As the MH tool chest was modeled after the Unix tool chest, the
meillo@32 113 properties of the latter apply to the former as well.
meillo@8 114
meillo@102 115
meillo@102 116 .ig \"XXX
meillo@102 117
meillo@102 118 .P
meillo@102 119 To ease typing, the switches can be abbreviated as much as the remaining
meillo@102 120 prefix remains unambiguous.
meillo@102 121 If in our example no other switch would start with the letter `t', then
meillo@102 122 .Cl "-truncate" ,
meillo@102 123 .Cl "-trunc" ,
meillo@102 124 .Cl "-tr" ,
meillo@102 125 and
meillo@102 126 .Cl "-t
meillo@102 127 would all be the same.
meillo@102 128 As a result, switches can neither be grouped (as in
meillo@102 129 .Cl "ls -ltr" )
meillo@102 130 nor can switch arguments be appended directly to the switch (as in
meillo@102 131 .Cl "sendmail -q30m" ).
meillo@102 132 .P
meillo@102 133 Many switches have negating counter-parts, which start with `no'.
meillo@102 134 For example
meillo@102 135 .Cl "-notruncate
meillo@102 136 inverts the
meillo@102 137 .Cl "-truncate
meillo@102 138 switch.
meillo@102 139 They exist to undo the effect of default switches in the profile.
meillo@102 140 If the user has chosen to change the default behavior of some tool
meillo@102 141 by adding a default switch to the profile,
meillo@102 142 he can still undo this change in behavior by specifying the inverse
meillo@102 143 switch on the command line.
meillo@102 144
meillo@102 145 ..
meillo@102 146
meillo@102 147
meillo@54 148 .U2 "Using MH
meillo@53 149 .P
meillo@54 150 It is strongly recommended to have a look at the MH Book,
meillo@106 151 which offers a thorough introduction to using MH.
meillo@54 152 .[ [
meillo@54 153 peek mh book
meillo@54 154 .], Part II]
meillo@54 155 Rose and Romine provide a deeper and more technical
meillo@54 156 though slightly outdated introduction in only about two dozens pages.
meillo@54 157 .[
meillo@54 158 rose romine real work
meillo@54 159 .]
meillo@27 160 .P
meillo@53 161 Following is an example mail handling session.
meillo@53 162 It uses mmh but is mostly compatible with nmh and old MH.
meillo@106 163 Details might vary but the look and feel is the same.
meillo@82 164
meillo@83 165 .VF input/mh-session
meillo@27 166
meillo@27 167
meillo@131 168 .H1 "nmh
meillo@2 169 .P
meillo@49 170 In order to understand the condition, goals and dynamics of a project,
meillo@106 171 one needs to know the reasons behind them.
meillo@53 172 This section explains the background.
meillo@53 173 .P
meillo@106 174 MH predates the Internet; it comes from times before networking was universal,
meillo@49 175 it comes from times when emailing was small, short and simple.
meillo@106 176 Then it grew, spread and adapted to the changes email went through.
meillo@49 177 Its core-concepts, however, remained the same.
meillo@106 178 During the eighties, students at UCI actively worked on MH.
meillo@49 179 They added new features and optimized the code for the then popular systems.
meillo@49 180 All this still was in times before POSIX and ANSI C.
meillo@49 181 As large parts of the code stem from this time, today's nmh source code
meillo@49 182 still contains many ancient parts.
meillo@51 183 BSD-specific code and constructs tailored for hardware of that time
meillo@49 184 are frequent.
meillo@2 185 .P
meillo@106 186 Nmh started about a decade after the POSIX and ANSI C standards were
meillo@49 187 established. A more modern coding style entered the code base, but still
meillo@49 188 a part of the developers came from ``the old days''. The developer
meillo@106 189 base became more diverse, thus broadening the range of different
meillo@106 190 coding styles.
meillo@49 191 Programming practices from different decades merged in the project.
meillo@51 192 As several peers added code, the system became more a conglomeration
meillo@51 193 of single tools rather than a homogeneous of-one-cast mail system.
meillo@49 194 Still, the existing basic concepts held it together.
meillo@8 195 They were mostly untouched throughout the years.
meillo@8 196 .P
meillo@106 197 Despite the separation of the tool chest approach at the surface
meillo@106 198 \(en a collection of small, separate programs \(en
meillo@106 199 on the source code level, it is much more interweaved.
meillo@49 200 Several separate components were compiled into one program
meillo@51 201 for efficiency reasons.
meillo@106 202 This led to intricate innards.
meillo@106 203 While clearly separated on the outside,
meillo@106 204 the programs turned out to be fairly interweaved inside.
meillo@106 205 .\" XXX FIXME rewrite...
meillo@106 206 .\" Unfortunately, the clear separation on the outside turned out to be
meillo@106 207 .\" fairly interweaved inside.
meillo@8 208 .P
meillo@106 209 The advent of MIME raised the complexity of email by a magnitude.
meillo@49 210 This is visible in nmh. The MIME-related parts are the most complex ones.
meillo@106 211 It is also visible that MIME support was added on top of the old MH core.
meillo@51 212 MH's tool chest style made this easily possible and encourages
meillo@106 213 such approaches, but unfortunately, it led to duplicated functions
meillo@49 214 and half-hearted implementation of the concepts.
meillo@49 215 .P
meillo@49 216 To provide backward-compatibility, it is a common understanding to not
meillo@49 217 change the default settings.
meillo@51 218 In consequence, the user needs to activate modern features explicitly
meillo@47 219 to be able to use them.
meillo@49 220 This puts a burden on new users, because out-of-the-box nmh remains
meillo@49 221 in the same ancient style.
meillo@49 222 If nmh is seen to be a back-end, then this compatibility surely is important.
meillo@106 223 However, in the same go, new users have difficulties using nmh for modern
meillo@49 224 emailing.
meillo@106 225 The small but mature community around nmh needs few change
meillo@106 226 as they have had their convenient setups for decades.
meillo@8 227
meillo@8 228
meillo@27 229 .H1 "mmh
meillo@28 230 .P
meillo@49 231 I started to work on my experimental version in October 2011,
meillo@106 232 at a time when there had been no more than three commits to nmh
meillo@53 233 since the beginning of the year.
meillo@53 234 In December, when I announced my work in progress on the
meillo@53 235 nmh-workers mailing list,
meillo@42 236 .[
meillo@51 237 nmh-workers mmh announce December
meillo@42 238 .]
meillo@53 239 nmh's community became active, too.
meillo@49 240 This movement was heavily pushed by Paul Vixie's ``edginess'' comment.
meillo@42 241 .[
meillo@42 242 nmh-workers vixie edginess
meillo@42 243 .]
meillo@53 244 After long years of stagnation, nmh became actively developed again.
meillo@106 245 Hence, while I was working on mmh, the community was once more working
meillo@106 246 on nmh, in parallel.
meillo@28 247 .P
meillo@53 248 The name \fImmh\fP may stand for \fImodern mail handler\fP,
meillo@53 249 because the project tries to modernize nmh.
meillo@53 250 Personally however, I prefer to call mmh \fImeillo's mail handler\fP,
meillo@53 251 emphasizing that the project follows my visions and preferences.
meillo@42 252 (My login name is \fImeillo\fP.)
meillo@53 253 This project model was inspired by \fIdwm\fP,
meillo@42 254 which is Anselm Garbe's personal window manager \(en
meillo@42 255 targeted to satisfy Garbe's personal needs whenever conflicts appear.
meillo@53 256 Dwm had retained its lean elegance and its focused character, whereas
meillo@53 257 its community-driven predecessor \fIwmii\fP had grown fat over time.
meillo@53 258 The development of mmh should remain focused.
meillo@27 259
meillo@45 260
meillo@27 261 .U2 "Motivation
meillo@27 262 .P
meillo@51 263 MH is the most important of very few command line tool chest email systems.
meillo@51 264 Tool chests are powerful because they can be perfectly automated and
meillo@53 265 extended. They allow arbitrary kinds of front-ends to be
meillo@53 266 implemented on top of them quickly and without internal knowledge.
meillo@106 267 Additionally, tool chests are easier to maintain than monolithic
meillo@43 268 programs.
meillo@53 269 As there are few tool chests for emailing and as MH-like ones are the most
meillo@106 270 popular among them, they should be developed further.
meillo@53 271 This keeps their
meillo@43 272 conceptional elegance and unique scripting qualities available to users.
meillo@106 273 Mmh creates a modern and convenient entry point to MH-like systems
meillo@53 274 for new and interested users.
meillo@43 275 .P
meillo@51 276 The mmh project is motivated by deficits of nmh and
meillo@45 277 my wish for general changes, combined
meillo@45 278 with the nmh community's reluctancy to change.
meillo@45 279 .P
meillo@106 280 At that time, nmh had not adjusted to modern emailing needs well enough.
meillo@45 281 The default setup was completely unusable for modern emailing.
meillo@45 282 Too much setup work was required.
meillo@45 283 Several modern features were already available but the community
meillo@106 284 did not want to have them as default.
meillo@106 285 Mmh is a way to change this.
meillo@45 286 .P
meillo@45 287 In my eyes, MH's concepts could be exploited even better and
meillo@45 288 the style of the tools could be improved. Both would simplify
meillo@45 289 and generalize the system, providing cleaner interfaces and more
meillo@53 290 software leverage at the same time.
meillo@106 291 Mmh is a way to demonstrate this.
meillo@45 292 .P
meillo@45 293 In providing several parts of an email system, nmh can hardly
meillo@45 294 compete with the large specialized projects that focus
meillo@45 295 on only one of the components.
meillo@45 296 The situation can be improved by concentrating the development power
meillo@51 297 on the most unique part of MH and letting the user pick his preferred
meillo@45 298 set of other mail components.
meillo@45 299 Today's pre-packaged software components encourage this model.
meillo@106 300 Mmh is a way to go for this approach.
meillo@45 301 .P
meillo@106 302 It is worthwhile to fork nmh for the development of mmh, because
meillo@43 303 the two projects focus on different goals and differ in fundamental questions.
meillo@106 304 The nmh community's reluctance regarding change conflicts
meillo@106 305 with my strong desire for it.
meillo@43 306 In developing a separate experimental version new approaches can
meillo@43 307 easily be tried out without the need to discuss changes beforehand.
meillo@43 308 In fact, revolutionary changes are hardly possible otherwise.
meillo@43 309 .P
meillo@117 310 The mmh project provides the basis on which the aforementioned
meillo@117 311 ideas can be implemented and demonstrated,
meillo@106 312 without the need to change nmh or its community.
meillo@43 313 Of course, the results of the mmh project shall improve nmh, in the end.
meillo@117 314 By no means is my intend to work against the nmh project.
meillo@117 315
meillo@27 316
meillo@27 317 .U2 "Target Field
meillo@27 318 .P
meillo@45 319 Any effort needs to be targeted towards a specific goal
meillo@45 320 in order to be successful.
meillo@117 321 Following is a description of imagined typical mmh users.
meillo@117 322 Mmh should satisfy their needs.
meillo@53 323 .\" XXX Remove the next sentence?
meillo@48 324 Actually, as mmh is my personal version of MH, this is a description
meillo@48 325 of myself.
meillo@45 326 .P
meillo@117 327 The target users of mmh like Unix and its philosophy.
meillo@117 328 They appreciate to use programs that are conceptionally appealing.
meillo@117 329 They are familiar with the command line and enjoy its power.
meillo@117 330 They are at least capable of shell scripting and want to improve their
meillo@27 331 productivity by scripting the mail system.
meillo@117 332 .\" XXX Naturally, he uses ...
meillo@117 333 They naturally use modern email features, such as attachments,
meillo@51 334 non-ASCII text, and digital cryptography.
meillo@117 335 They are able to setup email system components besides mmh,
meillo@117 336 and actually like to have the choice to pick the ones they prefer.
meillo@117 337 They have a reasonably modern operating system that complies to standards,
meillo@43 338 like POSIX and ANSI C.
meillo@27 339 .P
meillo@117 340 The typical users invoke mmh commands directly in an interactive
meillo@117 341 shell session, but they use them to automate mail handling tasks as well.
meillo@117 342 Likely, they runs their mail setup on a server machine,
meillo@117 343 to which they connect via ssh.
meillo@117 344 They might also have local mmh installations on their workstations,
meillo@117 345 where they tend to work with mmh directly in the shell instead
meillo@117 346 of using graphical front-ends.
meillo@117 347 They definitely want to be flexible and thus be able to change
meillo@117 348 their setup to suit their needs.
meillo@8 349 .P
meillo@117 350 .\" XXX themself vs. themselves
meillo@117 351 Typical mmh users are programmers themselves.
meillo@117 352 They like to, occasionally, take the opportunity of Free Software to put
meillo@117 353 hands on and get involved in the software they use.
meillo@117 354 Hence, they like small and clean code bases and care for code quality.
meillo@117 355 In general, they believe that:
meillo@8 356 .BU
meillo@48 357 Elegance \(en i.e. simplicity, clarity and generality \(en
meillo@48 358 is most important.
meillo@8 359 .BU
meillo@48 360 Concepts are more important than the concrete implementation.
meillo@8 361 .BU
meillo@48 362 Code optimizations for anything but readability should be avoided
meillo@48 363 if possible.
meillo@8 364 .BU
meillo@45 365 Having a lot of choice is bad.
meillo@48 366 .BU
meillo@48 367 Removed code is debugged code.
meillo@8 368
meillo@48 369 .U2 "Goals
meillo@45 370 .P
meillo@45 371 The general goals for the mmh project are the following:
meillo@128 372 .IP "Streamlining
meillo@87 373 Mmh should be stripped down to its core, which is the user agent (MUA).
meillo@117 374 The feature set should be distilled to the indispensable ones,
meillo@48 375 effectively removing corner-cases.
meillo@53 376 Parts that don't add to the main task of being a conceptionally
meillo@53 377 appealing MUA should be removed.
meillo@117 378 This includes the mail submission and mail retrieval facilities.
meillo@48 379 Choice should be reduced to the main options.
meillo@131 380 All tools should be tightly shaped.
meillo@48 381 .IP "Modernizing
meillo@48 382 Mmh's feature set needs to become more modern.
meillo@117 383 Better support for attachment and digital cryptography should be added.
meillo@117 384 MIME support should to be integrated deeper and more naturally.
meillo@48 385 The modern email features need to be readily available, out-of-the-box.
meillo@117 386 On the other hand,
meillo@117 387 bulletin board support and similar obsolete facilities can be dropped out.
meillo@131 388 Likewise, ancient technologies should not be supported any further.
meillo@131 389 The available concepts need to be expanded as far as possible.
meillo@131 390 A small set of concepts should recur consistently.
meillo@131 391 .IP "Styling
meillo@48 392 Mmh's source code needs to be updated to modern standards.
meillo@48 393 Standardized library functions should replace non-standard versions
meillo@48 394 whenever possible.
meillo@117 395 Code should be separated into distinct modules when feasible.
meillo@48 396 Time and space optimizations should to be replaced by
meillo@48 397 clear and readable code.
meillo@48 398 A uniform programming style should prevail.
meillo@117 399 The whole system should appear to be of-one-style;
meillo@117 400 it should feel like being cast as one.