$Cambridge: exim/src/src/lookups/README,v 1.1 2004/10/07 13:10:01 ph10 Exp $ LOOKUPS ------- Each lookup type is implemented by 6 functions, xxx_open(), xxx_check(), xxx_find(), xxx_close(), xxx_tidy(), and xxx_quote(), where xxx is the name of the lookup type (e.g. lsearch, dbm, or whatever). The xxx_check(), xxx_close(), xxx_tidy(), and xxx_quote() functions need not exist. There is a table in drtables.c which links the lookup names to the various sets of functions, with NULL entries for any that don't exist. When the code for a lookup type is omitted from the binary, all its entries are NULL. One of the fields in the table contains flags describing the kind of lookup. These are lookup_querystyle This is a "query style" lookup without a file name, as opposed to the "single key" style, where the key is associated with a "file name". lookup_absfile For single key lookups, this means that the file name must be an absolute path. It is set for lsearch and dbm, but not for NIS, for example. When a single-key lookup file is opened, the handle returned by the xxx_open() function is saved, along with the file name and lookup type, in a tree. The xxx_close() function is not called when the first lookup is completed. If there are subsequent lookups of the same type that quote the same file name, xxx_open() isn't called; instead the cached handle is re-used. Exim calls the function search_tidyup() at strategic points in its processing (e.g. after all routing and directing has been done) and this function walks the tree and calls the xxx_close() functions for all the cached handles. Query-style lookups don't have the concept of an open file that can be cached this way. Of course, the local code for the lookup can manage its own caching information in any way it pleases. This means that the xxx_close() function, even it it exists, is never called. However, if an xxx_tidy() function exists, it is called once whenever Exim calls search_tidyup(). A single-key lookup type may also have an xxx_tidy() function, which is called by search_tidyup() after all cached handles have been closed via the xxx_close() function. The lookup functions are wrapped into a special store pool (POOL_SEARCH). You can safely use store_get to allocate store for your handle caching. The store will be reset after all xxx_tidy() functions are called. The function interfaces are as follows: xxx_open() ---------- This function is called to initiate the lookup. For things that involve files it should do a real open; for other kinds of lookup it may do nothing at all. The arguments are: uschar *filename the name of the "file" to open, for non-query-style lookups; NULL for query-style lookups uschar **errmsg where to put an error message if there is a problem The yield of xxx_open() is a void * value representing the open file or database. For real files is is normally the FILE or DBM value. For other kinds of lookup, if there is no natural value to use, (-1) is recommended. The value should not be NULL (or 0) as that is taken to indicate failure of the xxx_open() function. For single-key lookups, the handle is cached along with the filename and type, and may be used for several lookups. xxx_check() ----------- If this function exists, it is called after a successful open to check on the ownership and mode of the file(s). The arguments are: void *handle the handle passed back from xxx_open() uschar *filename the filename passed to xxx_open() int modemask mode bits that must not be set int *owners permitted owners of the file(s) int *owngroups permitted group owners of the file(s) uschar **errmsg where to put an error message if there is a problem In the owners and owngroups vectors, the first element is the count of the remaining elements. There is a common function that can be called to check a file: int search_check_file(int fd, char *filename, int modemask, int *owners, int *owngroups, char *type, char **errmsg); If fd is >= 0, it is checked using fstat(), and filename is used only in error messages. If fd is < 0 then filename is checked using stat(). The yield is zero if all is well, +1 if the mode or uid or gid is wrong, or -1 if the stat() fails. The yield of xxx_check() is TRUE if all is well, FALSE otherwise. The function should not close the file(s) on failure. That is done from outside by calling the xxx_close() function. xxx_find() ---------- This is called to search an open file/database. The result is OK, FAIL, or DEFER. The arguments are: void *handle the handle passed back from xxx_open() uschar *filename the filename passed to xxx_open() (NULL for querystyle) uschar *keyquery the key to look up, or query to process, zero-terminated int length the length of the key uschar **result point to the yield, in dynamic store, on success uschar **errmsg where to put an error message on failure; this is initially set to "", and should be left as that for a standard "entry not found" error BOOL *do_cache the lookup should set this to FALSE when it changes data. This is TRUE by default. When set to FALSE the cache tree of the current search handle will be cleaned and the current result will NOT be cached. Currently the mysql and pgsql lookups use this when UPDATE/INSERT queries are executed. Even though the key is zero-terminated, the length is passed because in the common case it has been computed already and is often needed. xxx_close() ----------- This is called for single-key lookups when a file is finished with. There is no yield, and the only argument is the handle that was passed back from xxx_open(). It is not called for query style lookups. xxx_tidy() ---------- This function is called once at the end of search_tidyup() for every lookup type for which it exists. xxx_quote() ----------- This is called by the string expansion code for expansions of the form ${quote_xxx:}, if it exists. If not, the expansion code makes no change to the string. The function must apply any quoting rules that are specific to the lookup, and return a pointer to the revised string. If quoting is not needed, it can return its single argument, which is a uschar *. This function does NOT use the POOL_SEARCH store, because it's usually never called from any lookup code. ****