docs/master
view ch01.roff @ 92:e6f95015ba61
Added a grap diagram. Needed to adjust the makefile (soelim, grap, pic).
| author | markus schnalke <meillo@marmaro.de> |
|---|---|
| date | Fri, 15 Jun 2012 21:43:04 +0200 |
| parents | 99ab58dc891f |
| children | a782488c85f5 |
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.
115 .U2 "Using MH
116 .P
117 It is strongly recommended to have a look at the MH Book,
118 which introduces well into using MH.
119 .[ [
120 peek mh book
121 .], Part II]
122 Rose and Romine provide a deeper and more technical
123 though slightly outdated introduction in only about two dozens pages.
124 .[
125 rose romine real work
126 .]
127 .P
128 Following is an example mail handling session.
129 It uses mmh but is mostly compatible with nmh and old MH.
130 Details might vary but the look'n'feel is the same.
132 .VF input/mh-session
135 .H1 "nmh: Code and Community
136 .P
137 In order to understand the condition, goals and dynamics of a project,
138 one needs to know the reasons.
139 This section explains the background.
140 .P
141 MH predates the Internet, it comes from times before networking was universal,
142 it comes from times when emailing was small, short and simple.
143 Then it grew, spread and adopted to the changes email went through.
144 Its core-concepts, however, remained the same.
145 During the Eighties students at UCI actively worked on MH.
146 They added new features and optimized the code for the then popular systems.
147 All this still was in times before POSIX and ANSI C.
148 As large parts of the code stem from this time, today's nmh source code
149 still contains many ancient parts.
150 BSD-specific code and constructs tailored for hardware of that time
151 are frequent.
152 .P
153 Nmh started about a decade after the POSIX and ANSI C standards had been
154 established. A more modern coding style entered the code base, but still
155 a part of the developers came from ``the old days''. The developer
156 base became more diverse and thus resulted in code of different style.
157 Programming practices from different decades merged in the project.
158 As several peers added code, the system became more a conglomeration
159 of single tools rather than a homogeneous of-one-cast mail system.
160 Still, the existing basic concepts held it together.
161 They were mostly untouched throughout the years.
162 .P
163 Despite the tool chest approach at the surface \(en a collection
164 of separate small programs \(en on the source code level
165 it is much more interweaved.
166 Several separate components were compiled into one program
167 for efficiency reasons.
168 This lead to intricate innards.
169 Unfortunately, the clear separation on the outside appeared as being
170 pretty interweaved inside.
171 .P
172 The advent of MIME rose the complexity of email by a magnitude.
173 This is visible in nmh. The MIME-related parts are the most complex ones.
174 It's also visible that MIME support had been added on top of the old MH core.
175 MH's tool chest style made this easily possible and encourages
176 such approaches, but unfortunately, it lead to duplicated functions
177 and half-hearted implementation of the concepts.
178 .P
179 To provide backward-compatibility, it is a common understanding to not
180 change the default settings.
181 In consequence, the user needs to activate modern features explicitly
182 to be able to use them.
183 This puts a burden on new users, because out-of-the-box nmh remains
184 in the same ancient style.
185 If nmh is seen to be a back-end, then this compatibility surely is important.
186 However, in the same go, new users have difficulties to use nmh for modern
187 emailing.
188 The small but matured community around nmh hardly needs much change
189 as they have their convenient setups since decades.
192 .H1 "mmh
193 .P
194 I started to work on my experimental version in October 2011,
195 at a time when there were no more than three commits to nmh
196 since the beginning of the year.
197 In December, when I announced my work in progress on the
198 nmh-workers mailing list,
199 .[
200 nmh-workers mmh announce December
201 .]
202 nmh's community became active, too.
203 This movement was heavily pushed by Paul Vixie's ``edginess'' comment.
204 .[
205 nmh-workers vixie edginess
206 .]
207 After long years of stagnation, nmh became actively developed again.
208 Hence, while I was working on mmh, the community was working on nmh,
209 in parallel.
210 .P
211 The name \fImmh\fP may stand for \fImodern mail handler\fP,
212 because the project tries to modernize nmh.
213 Personally however, I prefer to call mmh \fImeillo's mail handler\fP,
214 emphasizing that the project follows my visions and preferences.
215 (My login name is \fImeillo\fP.)
216 This project model was inspired by \fIdwm\fP,
217 which is Anselm Garbe's personal window manager \(en
218 targeted to satisfy Garbe's personal needs whenever conflicts appear.
219 Dwm had retained its lean elegance and its focused character, whereas
220 its community-driven predecessor \fIwmii\fP had grown fat over time.
221 The development of mmh should remain focused.
224 .U2 "Motivation
225 .P
226 MH is the most important of very few command line tool chest email systems.
227 Tool chests are powerful because they can be perfectly automated and
228 extended. They allow arbitrary kinds of front-ends to be
229 implemented on top of them quickly and without internal knowledge.
230 Additionally, tool chests are much better to maintain than monolithic
231 programs.
232 As there are few tool chests for emailing and as MH-like ones are the most
233 popular among them they should be developed further.
234 This keeps their
235 conceptional elegance and unique scripting qualities available to users.
236 Mmh will create a modern and convenient entry point to MH-like systems
237 for new and interested users.
238 .P
239 The mmh project is motivated by deficits of nmh and
240 my wish for general changes, combined
241 with the nmh community's reluctancy to change.
242 .P
243 nmh hadn't adjusted to modern emailing needs well enough.
244 The default setup was completely unusable for modern emailing.
245 Too much setup work was required.
246 Several modern features were already available but the community
247 didn't wanted to have them as default.
248 mmh is a way to change this.
249 .P
250 In my eyes, MH's concepts could be exploited even better and
251 the style of the tools could be improved. Both would simplify
252 and generalize the system, providing cleaner interfaces and more
253 software leverage at the same time.
254 mmh is a way to demonstrate this.
255 .P
256 In providing several parts of an email system, nmh can hardly
257 compete with the large specialized projects that focus
258 on only one of the components.
259 The situation can be improved by concentrating the development power
260 on the most unique part of MH and letting the user pick his preferred
261 set of other mail components.
262 Today's pre-packaged software components encourage this model.
263 mmh is a way to go for this approach.
264 .P
265 It's worthwhile to fork nmh for the development of mmh, because
266 the two projects focus on different goals and differ in fundamental questions.
267 The nmh community's reluctance to change conflicts
268 with my strong will to change.
269 In developing a separate experimental version new approaches can
270 easily be tried out without the need to discuss changes beforehand.
271 In fact, revolutionary changes are hardly possible otherwise.
272 .P
273 The mmh project provides the basis to implemented and demonstrated
274 the listed ideas without the need to change nmh or its community.
275 Of course, the results of the mmh project shall improve nmh, in the end.
277 .U2 "Target Field
278 .P
279 Any effort needs to be targeted towards a specific goal
280 in order to be successful.
281 Following is a description of the imagined typical mmh user.
282 mmh should satisfy his needs.
283 .\" XXX Remove the next sentence?
284 Actually, as mmh is my personal version of MH, this is a description
285 of myself.
286 .P
287 The target user of mmh likes Unix and its philosophy.
288 He likes to use programs that are conceptionally appealing.
289 He's familiar with the command line and enjoys its power.
290 He is at least capable of shell scripting and wants to improve his
291 productivity by scripting the mail system.
292 He naturally uses modern email features, like attachments,
293 non-ASCII text, and digital cryptography.
294 He is able to setup email system components besides mmh,
295 and actually likes the choice to pick the ones he prefers.
296 He has a reasonably modern system that complies to standards,
297 like POSIX and ANSI C.
298 .P
299 The typical user invokes mmh commands directly in an interactive
300 shell session, but as well, he uses them to automate mail handling tasks.
301 Likely, he runs his mail setup on a server machine, to which he connects
302 via ssh. He might also have local mmh installations on his workstations,
303 but does rather not rely on graphical front-ends. He definitely wants
304 to be flexible and thus be able to change his setup to suite his needs.
305 .P
306 The typical mmh user is a programmer himself.
307 He likes to, occasionally, take the opportunity of Free Software to put
308 hands on and get involved in the software he uses.
309 Hence, he likes small and clean code bases and he cares for code quality.
310 In general, he believes that:
311 .BU
312 Elegance \(en i.e. simplicity, clarity and generality \(en
313 is most important.
314 .BU
315 Concepts are more important than the concrete implementation.
316 .BU
317 Code optimizations for anything but readability should be avoided
318 if possible.
319 .BU
320 Having a lot of choice is bad.
321 .BU
322 Removed code is debugged code.
324 .U2 "Goals
325 .P
326 The general goals for the mmh project are the following:
327 .IP "Stream-lining
328 Mmh should be stripped down to its core, which is the user agent (MUA).
329 The feature set should be distilled to the ones really needed,
330 effectively removing corner-cases.
331 Parts that don't add to the main task of being a conceptionally
332 appealing MUA should be removed.
333 This includes, the mail submission and mail retrieval facilities.
334 Choice should be reduced to the main options.
335 .IP "Modernizing
336 Mmh's feature set needs to become more modern.
337 Better support for attachment and digital cryptography needs to be added.
338 MIME support needs to be integrated deeper and more naturally.
339 The modern email features need to be readily available, out-of-the-box.
340 And on the other hand,
341 bulletin board support and similar obsolete facilities need to be dropped
342 out.
343 Likewise, ancient technologies, like hardcopy terminals, should not
344 be supported any further.
345 .IP "Code style
346 Mmh's source code needs to be updated to modern standards.
347 Standardized library functions should replace non-standard versions
348 whenever possible.
349 Code should be separated into distinct modules when possible.
350 Time and space optimizations should to be replaced by
351 clear and readable code.
352 A uniform programming style should prevail.
353 .IP "Homogeneity
354 The available concepts need to be expanded as far as possible.
355 A small set of concepts should prevail thoroughly throughout the system.
356 The whole system should appear to be of-one-style.
357 It should feel like being cast as one.