docs/master
view intro.roff @ 202:e417f510aaca
Reworked the MH example session.
| author | markus schnalke <meillo@marmaro.de> |
|---|---|
| date | Thu, 12 Jul 2012 09:04:13 +0200 |
| parents | 05a243dffaca |
| children | 8c0d5bd92f0b |
line source
1 .RN 1
2 .H0 "Introduction
3 .Id introduction
5 .P
6 MH is a set of mail handling tools with a common concept, similar to
7 the Unix tool chest, which is a set of file handling tools with a common
8 concept. \fInmh\fP is the currently most popular implementation of an
9 MH-like mail handling system.
10 This thesis describes an experimental version of nmh, named \fImmh\fP.
11 .P
12 This chapter introduces MH, its history, concepts and how it is used.
13 It describes nmh's code base and community to give the reader
14 a better understanding of the state of mmh when it started off.
15 Furthermore, this chapter outlines the mmh project itself,
16 describing the motivation for it and its goals.
19 .H1 "MH \(en the Mail Handler
20 .Id mh
21 .P
22 MH is a conceptual email system design and its concrete implementation.
23 Notably, MH had started as a design proposal at RAND Corporation,
24 where the first implementation followed later.
25 In spirit, MH is similar to Unix, which
26 influenced the world more in being a set of system design concepts
27 than in being a specific software product.
28 The ideas behind Unix are summarized in the \fIUnix philosophy\fP.
29 MH follows this philosophy.
31 .U2 "History
32 .P
33 In 1977 at RAND Corporation, Norman Shapiro and Stockton Gaines
34 proposed the design
35 of a new mail handling system, called \fIMail Handler\fP (MH),
36 to superseed RAND's old monolithic \fIMail System\fP (MS).
37 Two years later, in 1979, Bruce Borden took the proposal and implemented a
38 prototype of MH.
39 Before the prototype's existence, the concept was
40 believed to be practically unusable.
41 But the prototype proved successful and replaced MS thereafter.
42 In replacing MS, MH grew to provide anything necessary for emailing.
43 .P
44 In the early eighties,
45 the University of California at Irvine (UCI) started to use MH.
46 Marshall T. Rose and John L. Romine then became the driving force.
47 They took over the development and pushed MH forward.
48 RAND had put the code into the public domain by then.
49 MH was developed at UCI at the time when the Internet appeared,
50 when UCB implemented the TCP/IP stack, and when Allman wrote Sendmail.
51 MH was extended as emailing became more featured.
52 The development of MH was closely related to the development of email
53 RFCs. In the advent of MIME, MH was the first implementation of this new
54 email standard.
55 .P
56 In the nineties, the Internet became popular and in December 1996,
57 Richard Coleman initiated the \fINew Mail Handler\fP (nmh) project.
58 Nmh is a fork of MH 6.8.3 and bases strongly on the
59 \fILBL changes\fP by Van Jacobson, Mike Karels and Craig Leres.
60 Colman intended to modernize MH and improve its portability and
61 MIME handling capabilities.
62 This should be done openly within the Internet community.
63 The development of MH at UCI stopped after the 6.8.4 release in
64 February 1996, soon after the development of nmh had started.
65 Today, nmh has almost completely replaced the original MH.
66 Some systems might still provide old MH, but mainly for historical reasons.
67 .P
68 In the last years, the changes in nmh were mostly maintenance work.
69 However, the development was revived in December 2011
70 and stayed busy since then.
73 .U2 "Concepts
74 .P
75 MH consists of a set of tools, each covering a specific task of
76 email handling, like composing a message, replying to a message,
77 refiling a message to a different folder, listing the messages in a folder.
78 All of the programs operate on a common mail storage.
79 .P
80 The mail storage consists of \fImail folders\fP (directories) and
81 \fPmessages\fP (regular files).
82 Each message is stored in a separate file in the format it was
83 received (i.e. transfer format).
84 The files are named with ascending numbers in each folder.
85 The specific format of the mail storage characterizes MH in the same way
86 as the format of the file system characterizes Unix.
87 .P
88 MH tools maintain a \fIcontext\fP, which includes for instance the
89 current mail folder.
90 Processes in Unix have a similar context, containing the current working
91 directory, for instance. In contrast, the process context is maintained
92 by the Unix kernel automatically, whereas MH tools need to maintain the MH
93 context themselves.
94 The user can have one MH context or multiple ones; he can even share it
95 with others.
96 .P
97 Messages are named by their numeric filename,
98 but they can have symbolic names, too.
99 These are either automatically updated
100 position names such as the next or the last message,
101 or user-settable group names for arbitrary sets of messages.
102 These names are called sequences.
103 Sequences can be bound to the containing folder or to the context.
104 .P
105 The user's \fIprofile\fP is a file that contains his MH configuration.
106 Default switches for the individual tools can be specified to
107 adjust them to the user's personal preferences.
108 Additionally, a single command can be linked under different names
109 with different default values easily.
110 Form templates for new messages or for replies are easily changeable,
111 and output is adjustable with format files.
112 Almost every part of the system can be adjusted to personal preference.
113 .P
114 The system is well scriptable and extensible.
115 New MH tools are built out of or on top of existing ones quickly.
116 Furthermore, MH encourages the user to tailor, extend and automate the system.
117 As the MH tool chest was modeled after the Unix tool chest, the
118 properties of the latter apply to the former as well.
121 .ig \"XXX
123 .P
124 To ease typing, the switches can be abbreviated as much as the remaining
125 prefix remains unambiguous.
126 If in our example no other switch would start with the letter `t', then
127 .Cl "-truncate" ,
128 .Cl "-trunc" ,
129 .Cl "-tr" ,
130 and
131 .Cl "-t
132 would all be the same.
133 As a result, switches can neither be grouped (as in
134 .Cl "ls -ltr" )
135 nor can switch arguments be appended directly to the switch (as in
136 .Cl "sendmail -q30m" ).
137 .P
138 Many switches have negating counter-parts, which start with `no'.
139 For example
140 .Cl "-notruncate
141 inverts the
142 .Cl "-truncate
143 switch.
144 They exist to undo the effect of default switches in the profile.
145 If the user has chosen to change the default behavior of some tool
146 by adding a default switch to the profile,
147 he can still undo this change in behavior by specifying the inverse
148 switch on the command line.
150 ..
153 .U2 "Using MH
154 .P
155 It is strongly recommended to have a look at the MH Book,
156 which offers a thorough introduction to using MH.
157 .[ [
158 peek mh book
159 .], Part II]
160 Rose and Romine provide a deeper and more technical
161 though slightly outdated introduction in only about two dozen pages.
162 .[
163 rose romine real work
164 .]
165 .P
166 Following is an example mail handling session.
167 It uses mmh but is mostly compatible with nmh and old MH.
168 Details might vary but the look and feel is the same.
170 .so input/mh-session
173 .H1 "nmh
174 .P
175 In order to understand the condition, goals and dynamics of a project,
176 one needs to know the reasons behind them.
177 This section explains the background.
178 .P
179 MH predates the Internet;
180 it comes from times before networking was universal,
181 it comes from times when emailing was small, short and simple.
182 Then it grew, spread and adapted to the changes email went through.
183 Its core-concepts, however, remained the same.
184 During the eighties, students at UCI actively worked on MH.
185 They added new features and optimized the code for the systems
186 popular at that time.
187 All this still was in times before POSIX and ANSI C.
188 As large parts of the code stem from this time, today's nmh source code
189 still contains many ancient parts.
190 BSD-specific code and constructs tailored for hardware of that time
191 are frequent.
192 .P
193 Nmh started about a decade after the POSIX and ANSI C standards were
194 established. A more modern coding style entered the code base, but still
195 a part of the developers came from ``the old days''. The developer
196 base became more diverse, thus broadening the range of different
197 coding styles.
198 Programming practices from different decades merged in the project.
199 As several peers added code, the system became more a conglomeration
200 of single tools rather than a homogeneous of-one-cast mail system.
201 Still, the existing basic concepts held it together.
202 They were mostly untouched throughout the years.
203 .P
204 Despite the separation of the tool chest approach at the surface
205 \(en a collection of small, separate programs \(en
206 on the source code level, it is much more interwoven.
207 Several separate components were compiled into one program
208 for efficiency reasons.
209 This led to intricate innards.
210 While clearly separated on the outside,
211 the programs turned out to be fairly interwoven inside.
212 .\" XXX FIXME rewrite...
213 .\" nicht zweimal ``interwoven''
214 .\" Unfortunately, the clear separation on the outside turned out to be
215 .\" fairly interwoven inside.
216 .P
217 The advent of MIME raised the complexity of email by a magnitude.
218 This is visible in nmh. The MIME-related parts are the most complex ones.
219 It is also visible that MIME support was added on top of the old MH core.
220 MH's tool chest style made this easily possible and encourages
221 such approaches, but unfortunately, it led to duplicated functions
222 and half-hearted implementation of the concepts.
223 .P
224 To provide backward-compatibility, it is a common understanding not to
225 change the default settings.
226 In consequence, the user needs to activate modern features explicitly
227 to be able to use them.
228 This puts a burden on new users, because out-of-the-box nmh remains
229 in the same ancient style.
230 If nmh is seen to be a back-end,
231 then this compatibility surely is important.
232 However, at the same time, new users have difficulties using nmh for
233 modern emailing.
234 The small but mature community around nmh needs little change
235 as they have had their convenient setups for decades.
236 .\" XXX Explain more
239 .H1 "mmh
240 .P
241 I started to work on my experimental version in October 2011,
242 basing my work on nmh version \fInmh-1.3-dev\fP.
243 At that time no more than three commits were made to nmh
244 since the beginning of the year, the latest one being
245 .Ci a01a41d031c796b526329a4170eb23f0ac93b949
246 on 2011-04-13.
247 In December, when I announced my work in progress on the
248 nmh-workers mailing list,
249 .[
250 nmh-workers mmh announce December
251 .]
252 nmh's community became active, all of a sudden.
253 This movement was heavily pushed by Paul Vixie's ``edginess'' comment.
254 .[
255 nmh-workers vixie edginess
256 .]
257 After long years of stagnation, nmh became actively developed again.
258 Hence, while I was working on mmh, the community was working on nmh,
259 in parallel.
260 .P
261 The name \fImmh\fP may stand for \fImodern mail handler\fP,
262 because the project tries to modernize nmh.
263 Personally however, I prefer to call mmh \fImeillo's mail handler\fP,
264 emphasizing that the project follows my visions and preferences.
265 (My login name is \fImeillo\fP.)
266 This project model was inspired by \fIdwm\fP,
267 .\" XXX Ref
268 which is Anselm Garbe's personal window manager \(en
269 targeted to satisfy Garbe's personal needs whenever conflicts appear.
270 Dwm had retained its lean elegance and its focused character, whereas
271 its community-driven predecessor \fIwmii\fP had grown fat over time.
272 .\" XXX ref
273 The development of mmh should remain focused.
276 .U2 "Motivation
277 .P
278 MH is the most important of very few command line tool chest email systems.
279 Tool chests are powerful because they can be perfectly automated and
280 extended. They allow arbitrary kinds of front-ends to be
281 implemented on top of them quickly and without internal knowledge.
282 Additionally, tool chests are easier to maintain than monolithic
283 programs.
284 As there are few tool chests for emailing and as MH-like ones are the most
285 popular among them, they should be developed further.
286 This keeps their
287 conceptional elegance and unique scripting qualities available to users.
288 Mmh creates a modern and convenient entry point to MH-like systems
289 for new and interested users.
290 .P
291 The mmh project is motivated by deficits of nmh and
292 my wish for general changes, combined
293 with the nmh community's reluctancy to change.
294 .P
295 At that time, nmh had not adjusted to modern emailing needs well enough.
296 The default setup was completely unusable for modern emailing.
297 Too much setup work was required.
298 Several modern features were already available but the community
299 did not want to have them as default.
300 Mmh is a way to change this.
301 .P
302 In my eyes, MH's concepts could be exploited even better and
303 the style of the tools could be improved. Both would simplify
304 and generalize the system, providing cleaner interfaces and more
305 software leverage at the same time.
306 Mmh is a way to demonstrate this.
307 .P
308 In providing several parts of an email system, nmh can hardly
309 compete with the large specialized projects that focus
310 on only one of the components.
311 The situation can be improved by concentrating the development power
312 on the most unique part of MH and letting the user pick his preferred
313 set of other mail components.
314 Today's pre-packaged software components encourage this model.
315 Mmh is a way to go for this approach.
316 .P
317 It is worthwhile to fork nmh for the development of mmh,
318 because the two projects focus on different goals and differ in
319 fundamental questions.
320 The nmh community's reluctance regarding change conflicts
321 with my strong desire for it.
322 In developing a separate experimental version new approaches can
323 easily be tried out without the need to discuss changes beforehand.
324 In fact, revolutionary changes are hardly possible otherwise.
325 .P
326 The mmh project provides the basis on which the aforementioned
327 ideas can be implemented and demonstrated,
328 without the need to change the nmh project or its community.
329 Of course, the results of the mmh project shall improve nmh, in the end.
330 By no means it is my intent to work against the nmh project.
333 .U2 "Target Field
334 .P
335 Any effort needs to be targeted towards a specific goal
336 in order to be successful.
337 Therefore, a description of an imagined typical mmh user follows.
338 Mmh should satisfy his needs.
339 Actually, as mmh is my personal version of MH, this is a description
340 of myself.
341 Writing software for oneself is a reliable way to produce software
342 that matches the user's desires.
343 .P
344 The target user of mmh likes Unix and its philosophy.
345 He appreciates to use programs that are conceptionally appealing.
346 He is familiar with the command line and enjoys its power.
347 He is capable of shell scripting and wants to improve his
348 productivity by scripting the mail system.
349 He uses modern email features, such as attachments,
350 non-ASCII text, digital signatures and message encryption in a natural way.
351 He is able to set up mail system components,
352 and like to have the choice to pick the ones he prefers.
353 He has a reasonably modern operating system that complies to the
354 POSIX and ANSI C standards.
355 .P
356 The typical user invokes mmh commands directly in an interactive
357 shell session, but he uses them to automate mail handling tasks as well.
358 Likely, he runs his mail setup on a server machine,
359 to which he connects via ssh.
360 He might also have a local mmh installation on his workstation.
361 Still, he tend to use mmh directly in the shell instead
362 of using graphical front-ends.
363 He definitely wants to be flexible and thus be able to change
364 his setup to suit his needs.
365 .P
366 The typical mmh user is a programmer.
367 He likes to, occasionally, take the opportunity of free software to put
368 hands on and get involved in the software he uses.
369 In consequence, he likes small and clean code bases and cares for
370 code quality.
371 In general, he believes that:
372 .BU
373 The elegance of source code is most important.
374 .BU
375 Concepts are more important than concrete implementations.
376 .BU
377 Code optimizations for anything but readability should be avoided.
378 .BU
379 Having a lot of choice is bad.
380 .BU
381 Removed code is debugged code.
384 .U2 "Goals
385 .P
386 The general goals for the mmh project are the following:
387 .IP "Streamlining
388 Mmh should be stripped down to its core, which is the user agent (MUA).
389 The feature set should be distilled to the indispensable ones,
390 effectively removing corner cases.
391 Parts that do not add to the main task of being a conceptionally
392 appealing user agent should be removed.
393 This includes the mail submission and mail retrieval facilities.
394 Choice should be reduced to the main options.
395 All tools should be tightly shaped.
396 .IP "Modernizing
397 Mmh's feature set needs to become more modern.
398 Better support for attachments, digital signatures and message encryption
399 should be added.
400 MIME support should be integrated deeper and more naturally.
401 The modern email features need to be readily available, out-of-the-box.
402 On the other hand,
403 bulletin board support and similar obsolete facilities can be dropped out.
404 Likewise, ancient technologies should not be supported any further.
405 The available concepts need to be expanded as far as possible.
406 A small set of concepts should recur consistently.
407 .IP "Styling
408 Mmh's source code needs to be updated to modern standards.
409 Standardized library functions should replace non-standard versions
410 whenever possible.
411 Code should be separated into distinct modules when feasible.
412 Time and space optimizations should to be replaced by
413 clear and readable code.
414 A uniform programming style should prevail.
415 The whole system should appear to be of-one-style;
416 it should feel like being cast as one.