



	    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
	     occurs 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 occurred 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 occurred, 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 occurred, 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 occurred.

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 occurred.


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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