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Developer Notes for courier-imap-myownquery.patch
document version: 1.03
author: Pawel Wilk
0 What's that?
1 Modifications overview
2 Definitions
3 New data types
3.1 struct var_data
3.2 typedef size_t (*parsefunc)
4 New functions
4.1 get_variable
4.2 parse_core
4.3 ParsePlugin_counter
4.4 ParsePlugin_builder
4.5 parse_string
4.6 validate_password
4.7 get_localpart
4.8 get_domain
4.9 parse_select_clause
4.10 parse_chpass_clause
5 Ideas and TODO
6 Thanks
*-----------------------
0 What's that?
*-----------------------
Courier-imap-myownquery.patch allows administrator to set own SQL queries
used by authdaemon to authenticate user (including fetchig credentials) and to
change user's password. It allows to construct SELECT or UPDATE clause in the
configuration file (authmysqlrc or authpgsqlrc) by adding two new configuration
variables: MYSQL_SELECT_CLAUSE or PGSQL_SELECT_CLAUSE and MYSQL_CHPASS_CLAUSE
or PGSQL_CHPASS_CLAUSE. It may be useful in the mail environments where there
is such a need to have different database structure and/or tables scheme than
expected by authmysql or authpgsql module.
It also implements a small parsing engine for substitution variables which
may appear in the clauses and are used to put informations like username
or domain into the right place of a query.
This patch was created using `diff -Nur` on courier-imap-1.3.12 source.
*-----------------------
1 Modifications overview
*-----------------------
Modified files: authmysqllib.c authmysqlrc authpgsqllib.c authpgsqlrc
Each modified set of instructions is marked by my e-mail address:
siefca@pld.org.pl (for MySQL files) or tom@minnesota.com (for PostgreSQL files)
Changes in the current source code are related to:
- sections where the queries are constructed
(including memory allocation for the buffers)
when MYSQL_SELECT_CLAUSE or MYSQL_CHPASS_CLAUSE or
PGSQL_SELECT_CLAUSE or PGSQL_CHPASS_CLAUSE is
used then the query goes through the parsing functions
passing over current memory allocation and query construction
subroutines
- section where the configuration file is read
i've had to modify read_env() function to allow line breaks
- now each sequence of the backslash as a first character and
newline as the second is replaced by two whitespaces while
putting into the buffer
- sections where the query is constructed
selection is made, depending on configuration variables which
are set or not - if own query is used
*-----------------------
2 Definitions
*-----------------------
#define MAX_SUBSTITUTION_LEN 32
#define SV_BEGIN_MARK "$("
#define SV_END_MARK ")"
#define SV_BEGIN_LEN ((sizeof(SV_BEGIN_MARK))-1)
#define SV_END_LEN ((sizeof(SV_END_MARK))-1)
These definitions allows to change substitution marks in an easy way.
SV_BEGIN_MARK refers to sequence of characters treated as a prefix of
each substitution variable and SV_END_MARK refers to string which is
a closing suffix. If the expected substitution variable is called
'local_part' (without apostrophes) then '$(local_part)' is a valid
string representation for SV_BEGIN_MARK set to "$(" and SV_END_MARK to ")".
MAX_SUBSTITUTION_LEN defines maximal length of a substitution variable's
identifier (name).
The last two definitions are just for code simplification.
*-----------------------
3 New data types
*-----------------------
This section describes new data type definitions and variables.
3.1 struct var_data
struct var_data {
const char *name;
const char *value;
const size_t size;
size_t value_length;
} ;
This structure holds information needed by parsing routines.
Using var_data array you may specify a set of string substitutions
which should be done while parsing a query. Last element in array
should have all fields set to zero (null).
name field - should contain substituted variable name
value - should contain string which replaces it
size - should contain string size including the last zero byte ('\0')
value_length - should be set to zero - it is used as a value size cache
explanation: size is used to increase speed of calculation proccess
value_length is used to cache length of a value during the
parsing subroutines - it helps when substitution variable
occures more than once within the query
Example:
struct var_data vdt[] = {
{"some", "replacement", sizeof("some"), 0},
{"anotha", NULL, sizeof("anotha"), 0},
{NULL, NULL, 0, 0}
};
In this example we've declared that $(some) in the query should be
replaced by 'replacement' text, and replacement for $(anotha) will
be defined in the code before passing on the array pointer to
the paring function.
3.2 typedef size_t (*parsefunc)
typedef int (*parsefunc)(const char *, size_t, void *);
This type definition refers to the function pointer, which is used
to pass plugin functions into the core parsing subroutine. This definition
is included to simplify the declaration of the parse_core() function.
*-----------------------
4 New functions
*-----------------------
This section describes added functions.
4.1 get_variable
NAME
get_variable
SYNOPSIS
static const struct var_data *get_variable (const char *begin,
size_t len,
struct var_data *vdt);
DESCRIPTION
This function searches an array pointed by vdt and tries to find
the substitution variable, which name is identified with begin
pointer and length of len bytes long.
This function is also responsible for updating length cache field
of vdt elements and validating requested variables.
This function repports errors by sending human readable
messages to the standard error stream.
RETURN VALUE
This function returns a pointer to the array element which is
structure of var_data type, which contains variable definition
of a given name. It returns NULL on error or failure.
4.2 parse_core
NAME
parse_core
SYNOPSIS
static int parse_core (const char *source, struct var_data *vdt,
parsefunc outfn, void *result);
DESCRIPTION
This is the parsing routine for query strings containing the
substitution variables. It reads the string pointed with source
and tries to catch a valid substitution variables or parts which
are plain text blocks. The main purpose of using this function
it to split source string into parts and for each part call
outfn() function. Those parts are substrings identified by
pointer to some element of the source string and size.
Those elements are the result of splitting source string into
logical parts: plain text substrings and substitution variables'
values. To get the values of any found substitution variables
parse_core() uses get_variable() function. To find places
where substitution variables occurs it uses strstr() function
in conjunction with SV_BEGIN_MARK and SV_END_MARK definitions.
It passes vdt structure pointer to get_variable() function is
it calls it.
outfn() function should be passed by its pointer which
refers to declaration:
int (*outfn) (const char *begin,
size_t string_length,
void *void_pointer);
Each time outfn() is called the result argument of parse_core()
is passed to the outfn() as a last argument (void_pointer).
Example:
Example string "$(local_part) AND $(domain)" will cause the
outfn() to be called 3 times. First time for a value of
$(local_part) substitution variable, second time
for " AND " string, and the last time for $(domain) variable's
value. Variables are passed to outfn() by their (found) values,
plain text blocks are passed as they appear.
This function repports errors by sending human readable
messages to the standard error stream.
RETURN VALUE
This function returns -1 if an error has occured and 0 if
everything went good.
4.3 ParsePlugin_counter
NAME
ParsePlugin_counter
SYNOPSIS
int ParsePlugin_counter (const char *begin, size_t len,
void *vp);
DESCRIPTION
This is parsing plugin function. It simply increments the value
found in the memory area pointed by vp. It assumes that
the memory area is allocated for the variable of size_t
type and that area was passed by (size_t *) pointer.
The value is incremented by len argument. Begin argument
is not used.
This function repports errors by sending human readable
messages to the standard error stream.
RETURN VALUE
This function returns the variable size or -1 if an error
has occured, 0 if everything went good.
4.4 ParsePlugin_builder
NAME
ParsePlugin_builder
SYNOPSIS
int ParsePlugin_builder (const char *begin, size_t len,
void *vp);
DESCRIPTION
This is parsing plugin function. It simply copies len bytes
of a string pointed by begin to the end of memory area pointed by
vp. It assumes that the area pointed by vp is passed by (char **)
type pointer and refers to the (char *) pointer variable.
After each call it shifts the value of pointer variable (char *)
incrementing it by len bytes. Be careful when using this function
- its changes the given pointer value. Always operate on an
additional pointer type variable when passing it as the third
argument.
RETURN VALUE
This function returns the variable size or -1 if an error
has occured, 0 if everything went good.
4.5 parse_string
NAME
parse_string
SYNOPSIS
static char *parse_string (const char *source, struct var_data *vdt);
DESCRIPTION
This function parses the string pointed with source according to the
replacement instructions set in var_data array, which is passed with
its pointer vdt. It produces changed string located in newly allocated
memory area.
This function calls parse_core() function with various parsing
subroutines passed as function pointers.
1. It uses parse_core() with ParsePlugin_counter to obtain the
total amount of memory needed for the output string.
2. It allocates the memory.
3. It uses parse_core() with ParsePlugin_builder to build the
output string.
This function repports errors by sending human readable
messages to the standard error stream.
RETURN VALUE
Function returns pointer to the result buffer or NULL
if an error has occured.
WARNINGS
This function allocates some amount of memory using standard
ANSI C routines. Memory allocated by this function should be
freed with free().
4.6 validate_password
NAME
validate_password
SYNOPSIS
static const char *validate_password (const char *password);
DESCRIPTION
This function checks whether password string does contain
any dangerous characters, which may be used to pass command
strings to the database connection stream. If it founds one
it replaces it by the backslash character.
RETURN VALUE
It returns a pointer to the static buffer which contains
validated password string or NULL if an error has occured.
4.7 get_localpart
NAME
get_localpart
SYNOPSIS
static const char *get_localpart (const char *username);
DESCRIPTION
This function detaches local part of an e-mail address
from string pointed with username and puts it to the
buffer of the fixed length. All necessary cleaning is
made on the result string.
RETURN VALUE
Pointer to the static buffer containing local part or
NULL if there was some error.
4.8 get_domain
NAME
get_domain
SYNOPSIS
static const char *get_domain (const char *username,
const char *defdomain);
DESCRIPTION
This function detaches domain part of an e-mail address
from string pointed with username and puts it to the
buffer of the fixed length. All necessary cleaning is
made on the result string. If function cannot find domain
part in the string the string pointed by defdomain is
used instead.
RETURN VALUE
Pointer to the static buffer containing domain name or
NULL if there was some error.
4.9 parse_select_clause
NAME
parse_select_clause
SYNOPSIS
static char *parse_select_clause (const char *clause,
const char *username,
const char *defdomain);
DESCRIPTION
This function is a simple wrapper to the parse_string()
function. It parses a query pointed by caluse. username
and defdomain strings are used to replace corresponding
substitution strings if present in the query: $(local_part)
and $(domain).
RETURN VALUE
Same as parse_string().
4.10 parse_chpass_clause
NAME
parse_chpass_clause
SYNOPSIS
static char *parse_chpass_clause (const char *clause,
const char *username,
const char *defdomain,
const char *newpass,
const char *newpass_crypt);
DESCRIPTION
This function is a simple wrapper to the parse_string()
function. It parses a query pointed by caluse. username,
defdomain, newpass and newpass_crypt strings are used to
replace corresponding substitution strings if present in
the query: $(local_part), $(domain), $(newpass),
$(newpass_crypt).
RETURN VALUE
Same as parse_string().
*------------------------
5 Ideas and TODO
*------------------------
- solve problem with fixed buffer length of local part and the domain part
strings after split (problem?)
- allow admin to set a group name instead of numerical group id
- allow admin to set a username instead of numerical user id
- add clauses:
- MYSQL_PRESELECT_CLAUSE (query which comes before MYSQL_SELECT_CLAUSE)
- MYSQL_POSTSELECT_CLAUSE (query which comes after MYSQL_SELECT_CLAUSE)
- PGSQL_PRESELECT_CLAUSE (query which comes before PGSQL_SELECT_CLAUSE)
- PGSQL_POSTSELECT_CLAUSE (query which comes after PGSQL_SELECT_CLAUSE)
*------------------------
6 Thanks
*------------------------
At the beginning this patch was messy indeed. :> I would like to thank
Sam Varshavchik for pointing me a lot how to make it more fast and solid.
I would also thank Philip Hazel, Chris Lightfoot and Mike Bremford which
by their software capabilities inspired me to write it.
Thomas T. Thai <tom@minnesota.com> ported author's original MySQL code
to the PostgreSQL module.
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