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| author | markus schnalke <meillo@marmaro.de> |
|---|---|
| date | Thu, 12 Jul 2012 11:50:32 +0200 |
| parents | 8c0d5bd92f0b |
| children | fead1fc981f0 |
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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 .[
30 gancarz unix philosophy
31 .]
32 MH follows this philosophy.
34 .U2 "History
35 .P
36 In 1977 at RAND Corporation, Norman Shapiro and Stockton Gaines
37 proposed the design
38 of a new mail handling system, called \fIMail Handler\fP (MH),
39 to superseed RAND's old monolithic \fIMail System\fP (MS).
40 .[
41 shapiro gaines mh proposal
42 .]
43 Two years later, in 1979, Bruce Borden took the proposal and implemented a
44 prototype of MH.
45 Before the prototype's existence, the concept was
46 believed to be practically unusable.
47 But the prototype proved successful and replaced MS thereafter.\&
48 .[
49 history of mh website
50 .]
51 .P
52 In the early eighties,
53 the University of California at Irvine (UCI) started to use MH.
54 Marshall T. Rose and John L. Romine then became the driving force.
55 They took over the development and pushed MH forward.
56 RAND had put the code into the public domain by then.
57 MH was developed at UCI at the time when the Internet appeared,
58 the University of California at Berkeley (UCB) added TCP/IP
59 networking to their distribution, and Eric Allman wrote Sendmail.
60 MH was extended as emailing became more featured.
61 The development of MH was closely related to the development of email
62 RFCs.
63 In the advent of the \fIMultipurpose Internet Mail Extensions\fP (MIME),
64 MH was one of the first implementations of the new email standard.
65 MH grew to provide anything necessary for emailing.
66 .P
67 In the nineties, the Internet became popular and in December 1996,
68 Richard Coleman initiated the \fINew Mail Handler\fP (nmh) project.
69 Nmh is a fork of MH 6.8.3 and bases strongly on the
70 \fILBL changes\fP by Van Jacobson, Mike Karels and Craig Leres.
71 .[
72 lbl changes
73 .]
74 Colman intended to modernize MH and improve its portability and
75 MIME handling capabilities.
76 This should be done openly within the Internet community.
77 The development of MH at UCI stopped after the 6.8.4 release in
78 February 1996, soon after the development of nmh had started.
79 Today, nmh has almost completely replaced the original MH.
80 Some systems might still provide old MH, but mainly for historical reasons.
81 .P
82 In the last years, the changes in nmh were mostly maintenance work.
83 However, the development was revived in December 2011
84 and stayed busy since then.
87 .U2 "Concepts
88 .P
89 MH consists of a set of tools, each covering a specific task of
90 email handling, like composing a message, replying to a message,
91 refiling a message to a different folder, listing the messages in a folder.
92 All of the programs operate on a common mail storage.
93 .P
94 The mail storage consists of \fImail folders\fP (directories) and
95 \fPmessages\fP (regular files).
96 Each message is stored in a separate file in the format it was
97 received (i.e. transfer format).
98 The files are named with ascending numbers in each folder.
99 The specific format of the mail storage characterizes MH in the same way
100 as the format of the file system characterizes Unix.
101 .P
102 MH tools maintain a \fIcontext\fP, which includes for instance the
103 current mail folder.
104 Processes in Unix have a similar context, containing the current working
105 directory, for instance. In contrast, the process context is maintained
106 by the Unix kernel automatically, whereas MH tools need to maintain the MH
107 context themselves.
108 The user can have one MH context or multiple ones; he can even share it
109 with others.
110 .P
111 Messages are named by their numeric filename,
112 but they can have symbolic names, as well.
113 These are either one of six system-controlled position names
114 or user-settable group names for arbitrary sets of messages.
115 These names are called sequences.
116 Automatically updated position names exist for the
117 first, last, previous, next, current message, and
118 for the number one beyond the last message.
119 (In mmh, the names of these sequences are abbreviated to the
120 first character.)
121 User-definded sequences can be bound to the folder containing the
122 messages (\fIpublic sequences\fP) or to the user's context
123 (\fIprivate sequences\fP).
124 .P
125 The user's \fIprofile\fP is the file that contains his MH configuration.
126 Default switches for the individual tools can be specified to
127 adjust them to the user's personal preferences.
128 These switches will be automatically supplied whenever the specific
129 tool is invoked.
130 Additionally, a single command can be linked under different names
131 with different default values.
132 Form templates for new messages and replies, as well as format files
133 to adjust the output of tools are easily exchanged in the profile.
134 .P
135 Switches consist of a single dash (`\fL-\fP') followed by a word.
136 To ease typing, the word can be abbreviated, given the remaining
137 prefix remains unambiguous.
138 If no other switch starts with the letter `t', then any of
139 .Cl "-truncate" ,
140 .Cl "-trunc" ,
141 .Cl "-tr" ,
142 and
143 .Cl "-t
144 is equal.
145 As a result, switches can neither be grouped (as in
146 .Cl "ls -ltr" )
147 nor can switch arguments be appended directly to the switch (as in
148 .Cl "sendmail -q30m" ).
149 Many switches have negating counter-parts, which start with `no'.
150 For example
151 .Cl "-notruncate
152 inverts the
153 .Cl "-truncate
154 switch.
155 They exist to override the effect of default switches in the profile.
156 .P
157 The system is well scriptable and extensible.
158 Almost every part of the system can be adjusted to personal preference.
159 New MH tools are built out of or on top of existing ones quickly.
160 Furthermore, MH encourages the user to tailor, extend, and automate
161 the system.
162 As the MH tool chest was modeled after the Unix tool chest, the
163 properties of the latter apply to the former as well.
167 .U2 "Using MH
168 .P
169 It is strongly recommended to have a look at the \fIMH Book\fP,
170 .[ [
171 peek mh book
172 .], Part II]
173 which introduces into using MH.
174 Rose and Romine provide a deeper and more technical,
175 though slightly outdated, introduction in only about two dozen pages.
176 .[
177 rose romine real work
178 .]
179 .P
180 Following here is an example mail handling session.
181 Although it uses mmh, it is mostly compatible with nmh and the
182 original MH.
183 Details might vary but the look and feel is the same.
185 .so input/mh-session
188 .H1 "nmh
189 .P
190 In order to understand the condition, goals and dynamics of a project,
191 one needs to know the reasons behind them.
192 This section explains the background.
193 .P
194 MH predates the Internet;
195 it comes from times before networking was universal,
196 it comes from times when emailing was small, short and simple.
197 Then it grew, spread and adapted to the changes email went through.
198 Its core-concepts, however, remained the same.
199 During the eighties, students at UCI actively worked on MH.
200 They added new features and optimized the code for the systems
201 popular at that time.
202 All this still was in times before POSIX and ANSI C.
203 As large parts of the code stem from this time, today's nmh source code
204 still contains many ancient parts.
205 BSD-specific code and constructs tailored for hardware of that time
206 are frequent.
207 .P
208 Nmh started about a decade after the POSIX and ANSI C standards were
209 established. A more modern coding style entered the code base, but still
210 a part of the developers came from ``the old days''. The developer
211 base became more diverse, thus broadening the range of different
212 coding styles.
213 Programming practices from different decades merged in the project.
214 As several peers added code, the system became more a conglomeration
215 of single tools rather than a homogeneous of-one-cast mail system.
216 Still, the existing basic concepts held it together.
217 They were mostly untouched throughout the years.
218 .P
219 Despite the separation of the tool chest approach at the surface
220 \(en a collection of small, separate programs \(en
221 on the source code level, it is much more interwoven.
222 Several separate components were compiled into one program
223 for efficiency reasons.
224 This led to intricate innards.
225 While clearly separated on the outside,
226 the programs turned out to be fairly interwoven inside.
227 .\" XXX FIXME rewrite...
228 .\" nicht zweimal ``interwoven''
229 .\" Unfortunately, the clear separation on the outside turned out to be
230 .\" fairly interwoven inside.
231 .P
232 The advent of MIME raised the complexity of email by a magnitude.
233 This is visible in nmh. The MIME-related parts are the most complex ones.
234 It is also visible that MIME support was added on top of the old MH core.
235 MH's tool chest style made this easily possible and encourages
236 such approaches, but unfortunately, it led to duplicated functions
237 and half-hearted implementation of the concepts.
238 .P
239 To provide backward-compatibility, it is a common understanding not to
240 change the default settings.
241 In consequence, the user needs to activate modern features explicitly
242 to be able to use them.
243 This puts a burden on new users, because out-of-the-box nmh remains
244 in the same ancient style.
245 If nmh is seen to be a back-end,
246 then this compatibility surely is important.
247 However, at the same time, new users have difficulties using nmh for
248 modern emailing.
249 The small but mature community around nmh needs little change
250 as they have had their convenient setups for decades.
251 .\" XXX Explain more
254 .H1 "mmh
255 .P
256 I started to work on my experimental version in October 2011,
257 basing my work on nmh version \fInmh-1.3-dev\fP.
258 At that time no more than three commits were made to nmh
259 since the beginning of the year, the latest one being
260 .Ci a01a41d031c796b526329a4170eb23f0ac93b949
261 on 2011-04-13.
262 In December, when I announced my work in progress on the
263 nmh-workers mailing list,
264 .[
265 nmh-workers mmh announce December
266 .]
267 nmh's community became active, all of a sudden.
268 This movement was heavily pushed by Paul Vixie's ``edginess'' comment.
269 .[
270 nmh-workers vixie edginess
271 .]
272 After long years of stagnation, nmh became actively developed again.
273 Hence, while I was working on mmh, the community was working on nmh,
274 in parallel.
275 .P
276 The name \fImmh\fP may stand for \fImodern mail handler\fP,
277 because the project tries to modernize nmh.
278 Personally however, I prefer to call mmh \fImeillo's mail handler\fP,
279 emphasizing that the project is my version of nmh,
280 following my visions and preferences.
281 (My login name is \fImeillo\fP.)
282 This project model was inspired by \fIdwm\fP,
283 .[
284 dwm website
285 .]
286 which is Anselm Garbe's personal window manager \(en
287 targeted to satisfy Garbe's personal needs whenever conflicts appear.
288 Dwm had retained its lean elegance and its focused character, whereas
289 its community-driven predecessor \fIwmii\fP
290 .[
291 wmii website
292 .]
293 had grown fat over time.
294 The development of mmh should remain focused.
297 .U2 "Motivation
298 .P
299 MH is the most important of very few email systems in a tool chest style.
300 Tool chests are powerful because they can be perfectly automated and
301 extended. They allow arbitrary kinds of front-ends to be
302 implemented on top of them quickly and without internal knowledge.
303 Additionally, tool chests are easier to maintain than monolithic
304 programs.
305 As there are few tool chests for emailing and as MH-like ones are the most
306 popular among them, they should be developed further.
307 This keeps their
308 conceptional elegance and unique scripting qualities available to users.
309 Mmh creates a modern and convenient entry point to MH-like systems
310 for new and interested users.
311 .P
312 The mmh project is motivated by deficits of nmh and
313 my wish for general changes, combined
314 with the nmh community's reluctancy to change.
315 .P
316 At that time, nmh had not adjusted to modern emailing needs well enough.
317 The default setup was completely unusable for modern emailing.
318 Too much setup work was required.
319 Several modern features were already available but the community
320 did not want to have them as default.
321 Mmh is a way to change this.
322 .P
323 In my eyes, MH's concepts could be exploited even better and
324 the style of the tools could be improved. Both would simplify
325 and generalize the system, providing cleaner interfaces and more
326 software leverage at the same time.
327 Mmh is a way to demonstrate this.
328 .P
329 In providing several parts of an email system, nmh can hardly
330 compete with the large specialized projects that focus
331 on only one of the components.
332 The situation can be improved by concentrating the development power
333 on the most unique part of MH and letting the user pick his preferred
334 set of other mail components.
335 Today's pre-packaged software components encourage this model.
336 Mmh is a way to go for this approach.
337 .P
338 It is worthwhile to fork nmh for the development of mmh,
339 because the two projects focus on different goals and differ in
340 fundamental questions.
341 The nmh community's reluctance regarding change conflicts
342 with my strong desire for it.
343 .[
344 nmh-workers schnalke understanding nmh
345 .]
346 In developing a separate experimental version new approaches can
347 easily be tried out without the need to discuss changes beforehand.
348 In fact, revolutionary changes are hardly possible otherwise.
349 .P
350 The mmh project provides the basis on which the aforementioned
351 ideas can be implemented and demonstrated,
352 without the need to change the nmh project or its community.
353 Of course, the results of the mmh project shall improve nmh, in the end.
354 By no means it is my intent to work against the nmh project.
357 .U2 "Target Field
358 .P
359 Any effort needs to be targeted towards a specific goal
360 in order to be successful.
361 Therefore, a description of an imagined typical mmh user follows.
362 Mmh should satisfy his needs.
363 Actually, as mmh is my personal version of MH, this is a description
364 of myself.
365 Writing software for oneself is a reliable way to produce software
366 that matches the user's desires.
367 .P
368 The target user of mmh likes Unix and its philosophy.
369 He appreciates to use programs that are conceptionally appealing.
370 He is familiar with the command line and enjoys its power.
371 He is capable of shell scripting and wants to improve his
372 productivity by scripting the mail system.
373 He uses modern email features, such as attachments,
374 non-ASCII text, digital signatures and message encryption in a natural way.
375 He is able to set up mail system components,
376 and like to have the choice to pick the ones he prefers.
377 He has a reasonably modern operating system that complies to the
378 POSIX and ANSI C standards.
379 .P
380 The typical user invokes mmh commands directly in an interactive
381 shell session, but he uses them to automate mail handling tasks as well.
382 Likely, he runs his mail setup on a server machine,
383 to which he connects via ssh.
384 He might also have a local mmh installation on his workstation.
385 Still, he tend to use mmh directly in the shell instead
386 of using graphical front-ends.
387 He definitely wants to be flexible and thus be able to change
388 his setup to suit his needs.
389 .P
390 The typical mmh user is a programmer.
391 He likes to, occasionally, take the opportunity of free software to put
392 hands on and get involved in the software he uses.
393 In consequence, he likes small and clean code bases and cares for
394 code quality.
395 In general, he believes that:
396 .BU
397 The elegance of source code is most important.
398 .BU
399 Concepts are more important than concrete implementations.
400 .BU
401 Code optimizations for anything but readability should be avoided.
402 .BU
403 Having a lot of choice is bad.
404 .BU
405 Removed code is debugged code.
408 .U2 "Goals
409 .P
410 The general goals for the mmh project are the following:
411 .IP "Streamlining
412 Mmh should be stripped down to its core, which is the user agent (MUA).
413 The feature set should be distilled to the indispensable ones,
414 effectively removing corner cases.
415 Parts that do not add to the main task of being a conceptionally
416 appealing user agent should be removed.
417 This includes the mail submission and mail retrieval facilities.
418 Choice should be reduced to the main options.
419 All tools should be tightly shaped.
420 .IP "Modernizing
421 Mmh's feature set needs to become more modern.
422 Better support for attachments, digital signatures and message encryption
423 should be added.
424 MIME support should be integrated deeper and more naturally.
425 The modern email features need to be readily available, out-of-the-box.
426 On the other hand,
427 bulletin board support and similar obsolete facilities can be dropped out.
428 Likewise, ancient technologies should not be supported any further.
429 The available concepts need to be expanded as far as possible.
430 A small set of concepts should recur consistently.
431 .IP "Styling
432 Mmh's source code needs to be updated to modern standards.
433 Standardized library functions should replace non-standard versions
434 whenever possible.
435 Code should be separated into distinct modules when feasible.
436 Time and space optimizations should to be replaced by
437 clear and readable code.
438 A uniform programming style should prevail.
439 The whole system should appear to be of-one-style;
440 it should feel like being cast as one.