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Rework and extension of text from yesterday.
author markus schnalke <meillo@marmaro.de>
date Sat, 02 Jun 2012 10:32:26 +0200
parents abbaca05ee8e
children f80ced4e749b
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65:c8a760de091d 66:4c9f4d05d90e
35 35
36 .H2 "Removal of Mail Transfer Facilities 36 .H2 "Removal of Mail Transfer Facilities
37 .P 37 .P
38 In contrast to nmh, which also provides mail submission and mail retrieval 38 In contrast to nmh, which also provides mail submission and mail retrieval
39 facilities, mmh is a MUA only. 39 facilities, mmh is a MUA only.
40 .P 40 This general difference in the view on the character of nmh
41 The MSA is called ``Message Transfer Service'' (MTS) in nmh. 41 strongly supported the development of mmh.
42 Removing the mail transfer facilities had been the first work task
43 for the mmh project.
44 .P
45 The MSA is called \fIMessage Transfer Service\fP (MTS) in nmh.
42 The facility establishes TCP/IP connections and speaks SMTP to submit 46 The facility establishes TCP/IP connections and speaks SMTP to submit
43 messages for relay to the outside world. 47 messages for relay to the outside world.
44 This part is implemented in the 48 This part is implemented in the
45 .Pn post 49 .Pn post
46 command. 50 command.
76 Incorporate them with 80 Incorporate them with
77 .Pn inc 81 .Pn inc
78 from the system maildrop, or with 82 from the system maildrop, or with
79 .Pn rcvstore 83 .Pn rcvstore
80 from the standard input. 84 from the standard input.
81 .P 85 In consequence, mmh has not any longer networking code
82 In consequence, mmh includes neither networking nor SASL code anymore. 86 and thus does no more need to do transfer encryption and authentication.
83 Two large separate functional units are removed. 87 Two large functional units are removed.
84 They account for about XXX lines of code and XXX libraries.
85 .P 88 .P
86 With the removal of the MSA and MRA, mmh converted from an all-in-one 89 With the removal of the MSA and MRA, mmh converted from an all-in-one
87 mail system to the core: the MUA. 90 mail system to being only a MUA.
88 Following the Unix philosophy, it focuses on one job and to do that well. 91 Following the Unix philosophy, it focuses on one job and to do that well.
89 Now, of course, mmh depends on third-party software. 92 Now, of course, mmh depends on third-party software.
90 An external MTA/MSA is required to transfer mail to the outside world; 93 An external MTA/MSA is required to transfer mail to the outside world;
91 an external MRA is required to retrieve mail from remote machines. 94 an external MRA is required to retrieve mail from remote machines.
92 There exist excellent implementations of such software, 95 There exist excellent implementations of such software,
107 if projects become complex, split them. 110 if projects become complex, split them.
108 Complexity is demanded by the problem to solve. Decades ago, 111 Complexity is demanded by the problem to solve. Decades ago,
109 emailing had been small and simple. 112 emailing had been small and simple.
110 (Remember, 113 (Remember,
111 .Pn /bin/mail 114 .Pn /bin/mail
112 had once covered anything there was to email.) 115 had once covered anything there was to email and still had been small.)
113 As the complexity in emailing increased, MH remainded mostly unchanged. 116 As the complexity in emailing increased, MH remainded mostly unchanged.
114 Nontheless, in nmh the POP server, which the original MH had included, 117 Nontheless, in nmh the POP server, which the original MH had included,
115 was removed. Now is the time to take one step further and remove 118 was removed. Now is the time to take one step further and remove
116 the MSA and MRA. 119 the MSA and MRA.
117 Not only does it decrease the code amount of the project, 120 Not only does it decrease the code amount of the project,
118 but more important, it removes the whole field of message transfer 121 but more important, it removes the whole field of message transfer
119 with all its implications from the project. 122 with all its implications from the project.
120 .P 123 .P
121 Users of MH are usually able to set up an external MSA and MRA. 124 If a project needs some kind of function, there's always the choice
125 between implementing the the function in the project directly or
126 depending on a library that provides the function or depending on
127 a program that provides the function.
128 Whereas adding the function directly to the project increases the
129 code size most, it makes the project most independent.
130 On the other end, interfacing external programs keeps the interface
131 smallest, but the depencency highest.
132 Using a library is in the middle.
133 Adding the function directly to the project is a bad choice for
134 any function of higher complexity, unless it's not available in other ways.
135 Hence, the dependencies only change in kind, not in their existence.
136 In mmh, library dependencies on
137 .Pn libsasl2
138 and
139 .Pn libcrypto /\c
140 .Pn libssl
141 were treated against program dependencies on an MSA and an MRA.
142 Besides program dependencies providing the stronger separation
143 and being more flexible, they also allowed
144 over 6\|000 lines of code to be removed from mmh.
145 This made mmh's code base about 12\|% smaller.
146 Reducing the projects code size by such an amount without actually
147 losing function is a convincing argument.
148 .P
149 Users of MH should have not problem to set up an external MSA and MRA.
122 Also, the popular MSAs and MRAs have large communities and a lot 150 Also, the popular MSAs and MRAs have large communities and a lot
123 of documentation available. 151 of documentation available.
124 .P 152 .P
125 Choices for MSAs range from the full-featured 153 Choices for MSAs range from the full-featured
126 .I Postfix 154 .I Postfix
210 together with the truly obsolete code relicts 238 together with the truly obsolete code relicts
211 .Pn vmh 239 .Pn vmh
212 and 240 and
213 .Pn wmh , 241 .Pn wmh ,
214 saved more than 7\|000 lines of C code \(en 242 saved more than 7\|000 lines of C code \(en
215 about 15\|% of the project's source code amount. 243 about 15\|% of the project's original source code amount.
216 Having the same functionality in less code (with equal readability, 244 Having the same functionality in less code (with equal readability,
217 of course) is an advantage. 245 of course) is an advantage.
218 Less code means less bugs and less maintenance work. 246 Less code means less bugs and less maintenance work.
219 If 247 If
220 .Pn rcvtty 248 .Pn rcvtty