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