docs/master
view ch01.roff @ 105:9ff356d84c57
Added reference to Allman to the text; added missing reference to ML.
| author | markus schnalke <meillo@marmaro.de> |
|---|---|
| date | Thu, 21 Jun 2012 08:58:56 +0200 |
| parents | 7d5b180de542 |
| children | 3c4e5f0a7e7b |
line source
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 from which mmh 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 where the first implementation followed later.
23 In spirit, MH is similar to Unix, which
24 influenced the world more in being a set of system design concepts
25 than in being a specific software product.
26 The ideas behind Unix are summarized in the \fIUnix philosophy\fP.
27 MH follows this philosophy.
29 .U2 "History
30 .P
31 In 1977 at RAND Corporation, Norman Shapiro and Stockton Gaines
32 had proposed the design
33 of a new mail handling system, called ``Mail Handler'' (MH),
34 to superseed RAND's old monolithic ``Mail System'' (MS).
35 Two years later, in 1979, Bruce Borden took the proposal and implemented a
36 prototype of MH.
37 Before the prototype had been available, the concept was
38 believed to be practically unusable.
39 But the prototype had proven successful and replaced MS thereafter.
40 In replacing MS, MH grew to an all-in-one mail system.
41 .P
42 In the early Eighties,
43 the University of California at Irvine (UCI) had started to use MH.
44 Marshall T. Rose and John L. Romine became the driving force then.
45 They took over the development and pushed MH forward.
46 RAND had put the code into the public domain by then.
47 MH was developed at UCI at the time when the Internet appeared,
48 when UCB implemented the TCP/IP stack, and when Allman wrote Sendmail.
49 MH was extended as emailing became more featured.
50 The development of MH was closely related to the development of email
51 RFCs. In the advent of MIME, MH was the first implementation of this new
52 email standard.
53 .P
54 In the Nineties, the Internet had become popular and in December 1996,
55 Richard Coleman initiated the ``New Mail Handler'' (nmh) project.
56 Nmh is a fork of MH 6.8.3 and bases strongly on the
57 \fILBL changes\fP by Van Jacobson, Mike Karels and Craig Leres.
58 Colman intended to modernize MH and improve its portability and
59 MIME handling capabilities.
60 This should be done openly within the Internet community.
61 The development of MH at UCI stopped after the 6.8.4 release in
62 February 1996, soon after the development of nmh had started.
63 Today, nmh has almost completely replaced the original MH.
64 Some systems might still provide old MH, but mainly for historical reasons.
65 .P
66 In the last years, the work on nmh was mostly maintenance work.
67 However, the development revived in December 2011
68 and stayed busy since then.
70 .U2 "Concepts
71 .P
72 MH consists of a set of tools, each covering a specific task of
73 email handling, like composing a message, replying to a message,
74 refiling a message to a different folder, listing the messages in a folder.
75 All of the programs operate on a common mail storage.
76 .P
77 The mail storage consists of \fImail folders\fP (directories) and
78 \fPmessages\fP (regular files).
79 Each message is stored in a separate file in the format it had been
80 received (i.e. transfer format).
81 The files are named with ascending numbers in each folder.
82 The specific format of the mail storage characterizes MH in the same way
83 like the format of the file system characterizes Unix.
84 .P
85 MH tools maintain a \fIcontext\fP, which includes the current mail folder.
86 Processes in Unix have a similar context, containing the current working
87 directory, for instance. In contrast, the process context is maintained
88 by the Unix kernel automatically, whereas MH tools need to maintain the MH
89 context themselves.
90 The user can have one MH context or multiple ones, he can even share it
91 with other users.
92 .P
93 Messages are named by their numeric filename, but they can have symbolic names,
94 too. These are either automatically updated
95 position names like being the next or the last message,
96 or user-settable group names for arbitrary sets of messages.
97 These names are called sequences.
98 Sequences can be bound to the containing folder or to the context.
99 .P
100 The user's \fIprofile\fP is a file that contains his MH configuration.
101 Default switches for the individual tools can be specified to
102 adjust them to the user's personal preferences.
103 Multiple versions of the same command with different
104 default values can also be created very easily.
105 Form templates for new messages or for replies are easily changeable,
106 and output is adjustable with format files.
107 Almost every part of the system can be adjusted to personal preference.
108 .P
109 The system is well scriptable and extensible.
110 New MH tools are built out of or on top of existing ones quickly.
111 Further more, MH encourages the user to tailor, extend and automate the system.
112 As the MH tool chest was modeled after the Unix tool chest, the
113 properties of the latter apply to the former as well.
116 .ig \"XXX
118 .P
119 To ease typing, the switches can be abbreviated as much as the remaining
120 prefix remains unambiguous.
121 If in our example no other switch would start with the letter `t', then
122 .Cl "-truncate" ,
123 .Cl "-trunc" ,
124 .Cl "-tr" ,
125 and
126 .Cl "-t
127 would all be the same.
128 As a result, switches can neither be grouped (as in
129 .Cl "ls -ltr" )
130 nor can switch arguments be appended directly to the switch (as in
131 .Cl "sendmail -q30m" ).
132 .P
133 Many switches have negating counter-parts, which start with `no'.
134 For example
135 .Cl "-notruncate
136 inverts the
137 .Cl "-truncate
138 switch.
139 They exist to undo the effect of default switches in the profile.
140 If the user has chosen to change the default behavior of some tool
141 by adding a default switch to the profile,
142 he can still undo this change in behavior by specifying the inverse
143 switch on the command line.
145 ..
148 .U2 "Using MH
149 .P
150 It is strongly recommended to have a look at the MH Book,
151 which introduces well into using MH.
152 .[ [
153 peek mh book
154 .], Part II]
155 Rose and Romine provide a deeper and more technical
156 though slightly outdated introduction in only about two dozens pages.
157 .[
158 rose romine real work
159 .]
160 .P
161 Following is an example mail handling session.
162 It uses mmh but is mostly compatible with nmh and old MH.
163 Details might vary but the look'n'feel is the same.
165 .VF input/mh-session
168 .H1 "nmh: Code and Community
169 .P
170 In order to understand the condition, goals and dynamics of a project,
171 one needs to know the reasons.
172 This section explains the background.
173 .P
174 MH predates the Internet, it comes from times before networking was universal,
175 it comes from times when emailing was small, short and simple.
176 Then it grew, spread and adopted to the changes email went through.
177 Its core-concepts, however, remained the same.
178 During the Eighties students at UCI actively worked on MH.
179 They added new features and optimized the code for the then popular systems.
180 All this still was in times before POSIX and ANSI C.
181 As large parts of the code stem from this time, today's nmh source code
182 still contains many ancient parts.
183 BSD-specific code and constructs tailored for hardware of that time
184 are frequent.
185 .P
186 Nmh started about a decade after the POSIX and ANSI C standards had been
187 established. A more modern coding style entered the code base, but still
188 a part of the developers came from ``the old days''. The developer
189 base became more diverse and thus resulted in code of different style.
190 Programming practices from different decades merged in the project.
191 As several peers added code, the system became more a conglomeration
192 of single tools rather than a homogeneous of-one-cast mail system.
193 Still, the existing basic concepts held it together.
194 They were mostly untouched throughout the years.
195 .P
196 Despite the tool chest approach at the surface \(en a collection
197 of separate small programs \(en on the source code level
198 it is much more interweaved.
199 Several separate components were compiled into one program
200 for efficiency reasons.
201 This lead to intricate innards.
202 Unfortunately, the clear separation on the outside appeared as being
203 pretty interweaved inside.
204 .P
205 The advent of MIME rose the complexity of email by a magnitude.
206 This is visible in nmh. The MIME-related parts are the most complex ones.
207 It's also visible that MIME support had been added on top of the old MH core.
208 MH's tool chest style made this easily possible and encourages
209 such approaches, but unfortunately, it lead to duplicated functions
210 and half-hearted implementation of the concepts.
211 .P
212 To provide backward-compatibility, it is a common understanding to not
213 change the default settings.
214 In consequence, the user needs to activate modern features explicitly
215 to be able to use them.
216 This puts a burden on new users, because out-of-the-box nmh remains
217 in the same ancient style.
218 If nmh is seen to be a back-end, then this compatibility surely is important.
219 However, in the same go, new users have difficulties to use nmh for modern
220 emailing.
221 The small but matured community around nmh hardly needs much change
222 as they have their convenient setups since decades.
225 .H1 "mmh
226 .P
227 I started to work on my experimental version in October 2011,
228 at a time when there were no more than three commits to nmh
229 since the beginning of the year.
230 In December, when I announced my work in progress on the
231 nmh-workers mailing list,
232 .[
233 nmh-workers mmh announce December
234 .]
235 nmh's community became active, too.
236 This movement was heavily pushed by Paul Vixie's ``edginess'' comment.
237 .[
238 nmh-workers vixie edginess
239 .]
240 After long years of stagnation, nmh became actively developed again.
241 Hence, while I was working on mmh, the community was working on nmh,
242 in parallel.
243 .P
244 The name \fImmh\fP may stand for \fImodern mail handler\fP,
245 because the project tries to modernize nmh.
246 Personally however, I prefer to call mmh \fImeillo's mail handler\fP,
247 emphasizing that the project follows my visions and preferences.
248 (My login name is \fImeillo\fP.)
249 This project model was inspired by \fIdwm\fP,
250 which is Anselm Garbe's personal window manager \(en
251 targeted to satisfy Garbe's personal needs whenever conflicts appear.
252 Dwm had retained its lean elegance and its focused character, whereas
253 its community-driven predecessor \fIwmii\fP had grown fat over time.
254 The development of mmh should remain focused.
257 .U2 "Motivation
258 .P
259 MH is the most important of very few command line tool chest email systems.
260 Tool chests are powerful because they can be perfectly automated and
261 extended. They allow arbitrary kinds of front-ends to be
262 implemented on top of them quickly and without internal knowledge.
263 Additionally, tool chests are much better to maintain than monolithic
264 programs.
265 As there are few tool chests for emailing and as MH-like ones are the most
266 popular among them they should be developed further.
267 This keeps their
268 conceptional elegance and unique scripting qualities available to users.
269 Mmh will create a modern and convenient entry point to MH-like systems
270 for new and interested users.
271 .P
272 The mmh project is motivated by deficits of nmh and
273 my wish for general changes, combined
274 with the nmh community's reluctancy to change.
275 .P
276 nmh hadn't adjusted to modern emailing needs well enough.
277 The default setup was completely unusable for modern emailing.
278 Too much setup work was required.
279 Several modern features were already available but the community
280 didn't wanted to have them as default.
281 mmh is a way to change this.
282 .P
283 In my eyes, MH's concepts could be exploited even better and
284 the style of the tools could be improved. Both would simplify
285 and generalize the system, providing cleaner interfaces and more
286 software leverage at the same time.
287 mmh is a way to demonstrate this.
288 .P
289 In providing several parts of an email system, nmh can hardly
290 compete with the large specialized projects that focus
291 on only one of the components.
292 The situation can be improved by concentrating the development power
293 on the most unique part of MH and letting the user pick his preferred
294 set of other mail components.
295 Today's pre-packaged software components encourage this model.
296 mmh is a way to go for this approach.
297 .P
298 It's worthwhile to fork nmh for the development of mmh, because
299 the two projects focus on different goals and differ in fundamental questions.
300 The nmh community's reluctance to change conflicts
301 with my strong will to change.
302 In developing a separate experimental version new approaches can
303 easily be tried out without the need to discuss changes beforehand.
304 In fact, revolutionary changes are hardly possible otherwise.
305 .P
306 The mmh project provides the basis to implemented and demonstrated
307 the listed ideas without the need to change nmh or its community.
308 Of course, the results of the mmh project shall improve nmh, in the end.
310 .U2 "Target Field
311 .P
312 Any effort needs to be targeted towards a specific goal
313 in order to be successful.
314 Following is a description of the imagined typical mmh user.
315 mmh should satisfy his needs.
316 .\" XXX Remove the next sentence?
317 Actually, as mmh is my personal version of MH, this is a description
318 of myself.
319 .P
320 The target user of mmh likes Unix and its philosophy.
321 He likes to use programs that are conceptionally appealing.
322 He's familiar with the command line and enjoys its power.
323 He is at least capable of shell scripting and wants to improve his
324 productivity by scripting the mail system.
325 He naturally uses modern email features, like attachments,
326 non-ASCII text, and digital cryptography.
327 He is able to setup email system components besides mmh,
328 and actually likes the choice to pick the ones he prefers.
329 He has a reasonably modern system that complies to standards,
330 like POSIX and ANSI C.
331 .P
332 The typical user invokes mmh commands directly in an interactive
333 shell session, but as well, he uses them to automate mail handling tasks.
334 Likely, he runs his mail setup on a server machine, to which he connects
335 via ssh. He might also have local mmh installations on his workstations,
336 but does rather not rely on graphical front-ends. He definitely wants
337 to be flexible and thus be able to change his setup to suite his needs.
338 .P
339 The typical mmh user is a programmer himself.
340 He likes to, occasionally, take the opportunity of Free Software to put
341 hands on and get involved in the software he uses.
342 Hence, he likes small and clean code bases and he cares for code quality.
343 In general, he believes that:
344 .BU
345 Elegance \(en i.e. simplicity, clarity and generality \(en
346 is most important.
347 .BU
348 Concepts are more important than the concrete implementation.
349 .BU
350 Code optimizations for anything but readability should be avoided
351 if possible.
352 .BU
353 Having a lot of choice is bad.
354 .BU
355 Removed code is debugged code.
357 .U2 "Goals
358 .P
359 The general goals for the mmh project are the following:
360 .IP "Stream-lining
361 Mmh should be stripped down to its core, which is the user agent (MUA).
362 The feature set should be distilled to the ones really needed,
363 effectively removing corner-cases.
364 Parts that don't add to the main task of being a conceptionally
365 appealing MUA should be removed.
366 This includes, the mail submission and mail retrieval facilities.
367 Choice should be reduced to the main options.
368 .IP "Modernizing
369 Mmh's feature set needs to become more modern.
370 Better support for attachment and digital cryptography needs to be added.
371 MIME support needs to be integrated deeper and more naturally.
372 The modern email features need to be readily available, out-of-the-box.
373 And on the other hand,
374 bulletin board support and similar obsolete facilities need to be dropped
375 out.
376 Likewise, ancient technologies, like hardcopy terminals, should not
377 be supported any further.
378 .IP "Code style
379 Mmh's source code needs to be updated to modern standards.
380 Standardized library functions should replace non-standard versions
381 whenever possible.
382 Code should be separated into distinct modules when possible.
383 Time and space optimizations should to be replaced by
384 clear and readable code.
385 A uniform programming style should prevail.
386 .IP "Homogeneity
387 The available concepts need to be expanded as far as possible.
388 A small set of concepts should prevail thoroughly throughout the system.
389 The whole system should appear to be of-one-style.
390 It should feel like being cast as one.