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2 | |
3 | LOOKUPS | |
4 | ------- | |
5 | ||
6 | Each lookup type is implemented by 6 functions, xxx_open(), xxx_check(), | |
7 | xxx_find(), xxx_close(), xxx_tidy(), and xxx_quote(), where xxx is the name of | |
8 | the lookup type (e.g. lsearch, dbm, or whatever). | |
9 | ||
10 | The xxx_check(), xxx_close(), xxx_tidy(), and xxx_quote() functions need not | |
11 | exist. There is a table in drtables.c which links the lookup names to the | |
12 | various sets of functions, with NULL entries for any that don't exist. When | |
13 | the code for a lookup type is omitted from the binary, all its entries are | |
14 | NULL. | |
15 | ||
16 | One of the fields in the table contains flags describing the kind of lookup. | |
17 | These are | |
18 | ||
19 | lookup_querystyle | |
20 | ||
21 | This is a "query style" lookup without a file name, as opposed to the "single | |
22 | key" style, where the key is associated with a "file name". | |
23 | ||
24 | lookup_absfile | |
25 | ||
26 | For single key lookups, this means that the file name must be an absolute path. | |
27 | It is set for lsearch and dbm, but not for NIS, for example. | |
28 | ||
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29 | lookup_absfilequery |
30 | ||
31 | This is a query-style lookup that must start with an absolute file name. For | |
32 | example, the sqlite lookup is of this type. | |
33 | ||
34 | When a single-key or absfilequery lookup file is opened, the handle returned by | |
35 | the xxx_open() function is saved, along with the file name and lookup type, in | |
36 | a tree. The xxx_close() function is not called when the first lookup is | |
37 | completed. If there are subsequent lookups of the same type that quote the same | |
38 | file name, xxx_open() isn't called; instead the cached handle is re-used. | |
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39 | |
40 | Exim calls the function search_tidyup() at strategic points in its processing | |
41 | (e.g. after all routing and directing has been done) and this function walks | |
42 | the tree and calls the xxx_close() functions for all the cached handles. | |
43 | ||
44 | Query-style lookups don't have the concept of an open file that can be cached | |
45 | this way. Of course, the local code for the lookup can manage its own caching | |
46 | information in any way it pleases. This means that the xxx_close() | |
47 | function, even it it exists, is never called. However, if an xxx_tidy() | |
48 | function exists, it is called once whenever Exim calls search_tidyup(). | |
49 | ||
50 | A single-key lookup type may also have an xxx_tidy() function, which is called | |
51 | by search_tidyup() after all cached handles have been closed via the | |
52 | xxx_close() function. | |
53 | ||
54 | The lookup functions are wrapped into a special store pool (POOL_SEARCH). You | |
55 | can safely use store_get to allocate store for your handle caching. The store | |
56 | will be reset after all xxx_tidy() functions are called. | |
57 | ||
58 | The function interfaces are as follows: | |
59 | ||
60 | ||
61 | xxx_open() | |
62 | ---------- | |
63 | ||
64 | This function is called to initiate the lookup. For things that involve files | |
65 | it should do a real open; for other kinds of lookup it may do nothing at all. | |
66 | The arguments are: | |
67 | ||
68 | uschar *filename the name of the "file" to open, for non-query-style | |
69 | lookups; NULL for query-style lookups | |
70 | uschar **errmsg where to put an error message if there is a problem | |
71 | ||
72 | The yield of xxx_open() is a void * value representing the open file or | |
73 | database. For real files is is normally the FILE or DBM value. For other | |
74 | kinds of lookup, if there is no natural value to use, (-1) is recommended. | |
75 | The value should not be NULL (or 0) as that is taken to indicate failure of | |
76 | the xxx_open() function. For single-key lookups, the handle is cached along | |
77 | with the filename and type, and may be used for several lookups. | |
78 | ||
79 | ||
80 | xxx_check() | |
81 | ----------- | |
82 | ||
83 | If this function exists, it is called after a successful open to check on the | |
84 | ownership and mode of the file(s). The arguments are: | |
85 | ||
86 | void *handle the handle passed back from xxx_open() | |
87 | uschar *filename the filename passed to xxx_open() | |
88 | int modemask mode bits that must not be set | |
89 | int *owners permitted owners of the file(s) | |
90 | int *owngroups permitted group owners of the file(s) | |
91 | uschar **errmsg where to put an error message if there is a problem | |
92 | ||
93 | In the owners and owngroups vectors, the first element is the count of the | |
94 | remaining elements. There is a common function that can be called to check | |
95 | a file: | |
96 | ||
97 | int search_check_file(int fd, char *filename, int modemask, int *owners, | |
98 | int *owngroups, char *type, char **errmsg); | |
99 | ||
100 | If fd is >= 0, it is checked using fstat(), and filename is used only in | |
101 | error messages. If fd is < 0 then filename is checked using stat(). The yield | |
102 | is zero if all is well, +1 if the mode or uid or gid is wrong, or -1 if the | |
103 | stat() fails. | |
104 | ||
105 | The yield of xxx_check() is TRUE if all is well, FALSE otherwise. The | |
106 | function should not close the file(s) on failure. That is done from outside | |
107 | by calling the xxx_close() function. | |
108 | ||
109 | ||
110 | xxx_find() | |
111 | ---------- | |
112 | ||
113 | This is called to search an open file/database. The result is OK, FAIL, or | |
114 | DEFER. The arguments are: | |
115 | ||
116 | void *handle the handle passed back from xxx_open() | |
117 | uschar *filename the filename passed to xxx_open() (NULL for querystyle) | |
118 | uschar *keyquery the key to look up, or query to process, zero-terminated | |
119 | int length the length of the key | |
120 | uschar **result point to the yield, in dynamic store, on success | |
121 | uschar **errmsg where to put an error message on failure; | |
122 | this is initially set to "", and should be left | |
123 | as that for a standard "entry not found" error | |
124 | BOOL *do_cache the lookup should set this to FALSE when it changes data. | |
125 | This is TRUE by default. When set to FALSE the cache tree | |
126 | of the current search handle will be cleaned and the | |
127 | current result will NOT be cached. Currently the mysql | |
128 | and pgsql lookups use this when UPDATE/INSERT queries are | |
129 | executed. | |
130 | ||
131 | Even though the key is zero-terminated, the length is passed because in the | |
132 | common case it has been computed already and is often needed. | |
133 | ||
134 | ||
135 | xxx_close() | |
136 | ----------- | |
137 | ||
138 | This is called for single-key lookups when a file is finished with. There is no | |
139 | yield, and the only argument is the handle that was passed back from | |
140 | xxx_open(). It is not called for query style lookups. | |
141 | ||
142 | ||
143 | xxx_tidy() | |
144 | ---------- | |
145 | ||
146 | This function is called once at the end of search_tidyup() for every lookup | |
147 | type for which it exists. | |
148 | ||
149 | ||
150 | xxx_quote() | |
151 | ----------- | |
152 | ||
153 | This is called by the string expansion code for expansions of the form | |
154 | ${quote_xxx:<string>}, if it exists. If not, the expansion code makes no change | |
155 | to the string. The function must apply any quoting rules that are specific to | |
156 | the lookup, and return a pointer to the revised string. If quoting is not | |
157 | needed, it can return its single argument, which is a uschar *. This function | |
158 | does NOT use the POOL_SEARCH store, because it's usually never called from any | |
159 | lookup code. | |
160 | ||
161 | **** |