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 ported author's original MySQL code to the PostgreSQL module. ---------------------------------------------------------------------------