1MAILDROPGDBM(7) Double Precision, Inc. MAILDROPGDBM(7)
2
6 maildropgdbm - GDBM/DB support in maildrop
7
9 gdbmopen(filename, mode)
10 gdbmclose
12 gdbmfetch(key [,default])
14 gdbmstore(key,value)
16
18 The gdbm family of functions provides access to the GDBM library - a
19 library of routines that manage simple database files. The library
20 provides a way of quickly storing and looking up key/data pairs.
21 GDBM support in maildrop is optional, and may not be available to you.
23 GDBM support in maildrop can optionally be implemented using the DB
25 library. This option is selected by the system administrator. If this
26 is the case, these functions still work exactly as described below,
27 except that they will operate on DB hash files, instead of GDBM files.
28 To see whether GDBM or DB support is used, run the command "maildrop
30 -v".
31 GDBM support is minimal, and simplistic. A filter file may have only
33 one gdbm file open at the same time. However, the filter file can close
34 the current gdbm file, and open another one. If another filter file is
35 included using the include statement, the included filter file may open
36 its own, separate, gdbm file.
37 A GDBM file contains a list of key/value pairs. All keys in the GDBM
39 file are unique. After storing an arbitrary key/value pair in the GDBM
40 file, the value associated with the given key can be quickly located
41 and retrieved.
42 gdbmclose - close gdbm file
44 gdbmclose
45 This function closes the current GDBM file.
47 gdbmfetch - retrieve data
49 gdbmfetch (key [, options] [, default])
50 This function retrieves the data for the given key. key is the key to
52 retrieve. The gdbmfetch function returns the data associated with this
53 key. If the key does not exist in the GDBM file, gdbmfetch returns the
54 default argument. If the default argument is not specified, gdbmfetch
55 returns empty text. Please note that the default argument is not
56 actually evaluated unless the key does not exist in the GDBM file.
57 The options argument specifies additional maildrop value-added
59 features. The following functionality is not available in the GDBM
60 library, but is rather provided by maildrop.
61 If the options argument is set to "D", and the key could not be found
63 in the GDBM database, and the key is of the form "user@domain",
64 maildrop will then attempt to look up the key "user@". If that key is
65 also not found, maildrop finally looks up the key "domain".
66 If "domain" is also not found, and domain is of the form "a.b.c.d.tld"
68 (with variable number of period-separated sections), maildrop then
69 attempts to look up the key "b.c.d.tld". If that key is not found,
70 maildrop tries "c.d.tld", and so on, until a key is found, or there are
71 no more subdomains to remove, at which point gdbmfetch will return
72 either the default argument, or empty text.
73 If the options argument is set to "D", and the key could not be found
75 in the GDBM database, and the key is of the form "a.b.c.d.tld" (with
76 variable number of period-separated sections), maildrop will also
77 attempt to look up keys for successive higher-level domains in the GDBM
78 database.
79 Note
81 GDBM databases are case sensitive. Make sure that the GDBM database
82 is created using lowercase letters only, and use the tolower[1]
83 function to convert the key to lowercase.
84 If the options argument is "I", and the key is not in the GDBM
86 database, and the key is of the form "w.x.y.z" (with variable number of
87 period-separated sections), maildrop then tries to look up the key
88 "w.x.y", then "w.x", until a key is found, or there are no more
89 sections to remove. Use this feature to look up IP-address based GDBM
90 lists.
91 Note
93 These features are implemented by brute force: if the query doesn't
94 succeed, try again. Take note of potential denial-of-service
95 attacks where key is set to a long text string consisting mostly of
96 periods, which will result in numerous GDBM queries that will take
97 an excessive amount of time to complete.
98 gdbmopen - open gdbm file
100 gdbmopen (file [, mode])
101 gdbmopen opens the indicated GDBM file. The optional second argument
103 specifies the following:
104 "R"
106 Open this GDBM file for reading.
107 "W"
109 Open this GDBM file for reading and writing.
110 "C"
112 Open this GDBM file for reading and writing. If the GBDM file
113 doesn't exist, create it.
114 "N"
116 Create a new GDBM file. If the file exists, the existing file is
117 deleted. The file is opened for reading and writing.
118 The mode argument defaults to "R" is used. In embedded mode, only "R"
120 is allowed.
121 The GDBM library allows multiple processes to read the same GDBM file
123 at the same time, but it does not allow multiple access when the GDBM
124 file is open for writing. Using flock[2] or dotlock[3] is highly
125 recommended.
126 In delivery mode, maildrop runs from the recipient's home directory.
128 Keep that in mind while specifying the filename.
129 The gdbmopen function returns 0 if the GDBM file was successfully
131 opened, non-zero otherwise.
132 gdbmstore - store data
134 gdbmstore(key, value)
135 key is the key value to store in the GDBM file. value is the value to
137 store. If key already exists in the GDBM file, value replacest the old
138 value. The gdbmstore function is only permitted if the GDBM file is
139 opened for writing. If gdbmopen opened the GDBM file for reading only,
140 gdbmstore will return -1. Otherwise, gdbmstore returns 0.
141
143 Sam Varshavchik
144 Author
145
147 1. tolower
148 http://www.courier-mta.org/maildrop/maildropfilter.html#tolower
149 2. flock
151 http://www.courier-mta.org/maildrop/maildropfilter.html#flock
152 3. dotlock
154 http://www.courier-mta.org/maildrop/maildropfilter.html#dotlock
155Courier Mail Server 06/20/2015 MAILDROPGDBM(7)