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MAILDROPGDBM(7) Double Precision, Inc. MAILDROPGDBM(7)
NAME
maildropgdbm - GDBM/DB support in maildrop
SYNOPSIS
gdbmopen(filename, mode)
gdbmclose
gdbmfetch(key [,default])
gdbmstore(key,value)
DESCRIPTION
The gdbm family of functions provides access to the GDBM library - a library of routines
that manage simple database files. The library provides a way of quickly storing and
looking up key/data pairs.
GDBM support in maildrop is optional, and may not be available to you.
GDBM support in maildrop can optionally be implemented using the DB library. This option
is selected by the system administrator. If this is the case, these functions still work
exactly as described below, except that they will operate on DB hash files, instead of
GDBM files.
To see whether GDBM or DB support is used, run the command "maildrop -v".
GDBM support is minimal, and simplistic. A filter file may have only one gdbm file open at
the same time. However, the filter file can close the current gdbm file, and open another
one. If another filter file is included using the include statement, the included filter
file may open its own, separate, gdbm file.
A GDBM file contains a list of key/value pairs. All keys in the GDBM file are unique.
After storing an arbitrary key/value pair in the GDBM file, the value associated with the
given key can be quickly located and retrieved.
gdbmclose - close gdbm file
gdbmclose
This function closes the current GDBM file.
gdbmfetch - retrieve data
gdbmfetch (key [, options] [, default])
This function retrieves the data for the given key. key is the key to retrieve. The
gdbmfetch function returns the data associated with this key. If the key does not exist in
the GDBM file, gdbmfetch returns the default argument. If the default argument is not
specified, gdbmfetch returns empty text. Please note that the default argument is not
actually evaluated unless the key does not exist in the GDBM file.
The options argument specifies additional maildrop value-added features. The following
functionality is not available in the GDBM library, but is rather provided by maildrop.
If the options argument is set to "D", and the key could not be found in the GDBM
database, and the key is of the form "user@domain", maildrop will then attempt to look up
the key "user@". If that key is also not found, maildrop finally looks up the key
"domain".
If "domain" is also not found, and domain is of the form "a.b.c.d.tld" (with variable
number of period-separated sections), maildrop then attempts to look up the key
"b.c.d.tld". If that key is not found, maildrop tries "c.d.tld", and so on, until a key is
found, or there are no more subdomains to remove, at which point gdbmfetch will return
either the default argument, or empty text.
If the options argument is set to "D", and the key could not be found in the GDBM
database, and the key is of the form "a.b.c.d.tld" (with variable number of
period-separated sections), maildrop will also attempt to look up keys for successive
higher-level domains in the GDBM database.
Note
GDBM databases are case sensitive. Make sure that the GDBM database is created using
lowercase letters only, and use the tolower[1] function to convert the key to
lowercase.
If the options argument is "I", and the key is not in the GDBM database, and the key is of
the form "w.x.y.z" (with variable number of period-separated sections), maildrop then
tries to look up the key "w.x.y", then "w.x", until a key is found, or there are no more
sections to remove. Use this feature to look up IP-address based GDBM lists.
Note
These features are implemented by brute force: if the query doesn't succeed, try
again. Take note of potential denial-of-service attacks where key is set to a long
text string consisting mostly of periods, which will result in numerous GDBM queries
that will take an excessive amount of time to complete.
gdbmopen - open gdbm file
gdbmopen (file [, mode])
gdbmopen opens the indicated GDBM file. The optional second argument specifies the
following:
"R"
Open this GDBM file for reading.
"W"
Open this GDBM file for reading and writing.
"C"
Open this GDBM file for reading and writing. If the GBDM file doesn't exist, create
it.
"N"
Create a new GDBM file. If the file exists, the existing file is deleted. The file is
opened for reading and writing.
The mode argument defaults to "R" is used. In embedded mode, only "R" is allowed.
The GDBM library allows multiple processes to read the same GDBM file at the same time,
but it does not allow multiple access when the GDBM file is open for writing. Using
flock[2] or dotlock[3] is highly recommended.
In delivery mode, maildrop runs from the recipient's home directory. Keep that in mind
while specifying the filename.
The gdbmopen function returns 0 if the GDBM file was successfully opened, non-zero
otherwise.
gdbmstore - store data
gdbmstore(key, value)
key is the key value to store in the GDBM file. value is the value to store. If key
already exists in the GDBM file, value replacest the old value. The gdbmstore function is
only permitted if the GDBM file is opened for writing. If gdbmopen opened the GDBM file
for reading only, gdbmstore will return -1. Otherwise, gdbmstore returns 0.
AUTHOR
Sam Varshavchik
Author
NOTES
1. tolower
http://www.courier-mta.org/maildrop/maildropfilter.html#tolower
2. flock
http://www.courier-mta.org/maildrop/maildropfilter.html#flock
3. dotlock
http://www.courier-mta.org/maildrop/maildropfilter.html#dotlock
Courier Mail Server 06/20/2015 MAILDROPGDBM(7)
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On Apache
Under GNU General Public License
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