[Serusers] What has changed ???
Jan Janak
jan at iptel.org
Wed Mar 26 14:58:45 CET 2003
Hello,
Module interface has changed. There is now new flags field (the last
field in cmd_export_t structure) that specifies in which block your
function can be used.
This flag must be set to REQUEST_ROUTE if you want to use your function
in the main route block of your ser.cfg
I attached description of the new interface in plain-text, the
original can be found in sip_router/doc/sedev/modiface.sgml in docbook
format.
Jan.
On 26-03 13:44, Stephan Reiff-Marganiec wrote:
>
> I just updated ser from cvs and encounter the problem that ser will no
> longer start.
>
> I have my own module and a function (exec_pol) in that is started from
> ser.cfg in the route block.
>
> This used to work fine, but since the latest update from ser, ser just
> terminates saying "Parse Error: Command cannot be used in the block".
>
> I got this message after make all, make install and trying to start ser. I
> then realised that my module was not compiled anew because the find_export
> function now has more arguments (the NO_SCRIPT on, which it didn't need
> before). Having fixed this, things compile fine, but the error persists
> and I cannot start ser.
>
> Have I overseen an important change??
>
> thanks,
> Stephan
>
> --
> Dr Stephan Reiff-Marganiec
> Research Fellow
> Department of Computing Science; University of Stirling
> email: srm at cs.stir.ac.uk tel: 01786 46 7448
>
> --
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Table of Contents
1. Module Interface
1.1. Shared Objects
1.2. Exporting Functions
1.3. Exporting Parameters
1.4. Module Initialization
1.5. Module Clean-up
1.6. Module Callbacks
1.7. exports Structure - Assembling the Pieces Together
1.8. Example - Simple Module Interface
_________________________________________________________
Chapter 1. Module Interface
SIP Express Router features modular architecture which allows
us to split SIP Express Router's functionality across several
modules. This approach gives us greater flexibility, only
required set of functions can be loaded upon startup which
minimizes the server's memory footprint. Modules can be also
provided by 3rd party developers and distributed separately
from the main server. Most of the functionality that SIP
Express Router provides is available through modules, the core
itself contains only minimum set of functions that is
essential for proper server's behaviour or that is needed by
all modules.
This chapter provides detailed information on module interface
of SIP Express Router, which is used to pass information on
available functions and parameters from the modules to the
core.
_________________________________________________________
1.1. Shared Objects
First it would be good to know how SIP Express Router loads
and uses modules before we describe the module interface in
detail. This section gives a brief overview of SIP Express
Router's module subsystem.
SIP Express Router modules are compiled as "shared objects". A
file containing a shared object has usually .so suffix. All
modules (shared objects) will be stored in one directory after
installation. For example tm module, which contains code
essential for stateful processing, will be stored in file
named tm.so. By default these files are stored in
/usr/lib/ser/modules directory.
You can later load the modules using loadmodule command in
your configuration file. If you want to load previously
mentioned tm.so module, you can do it using loadmodule
"/usr/lib/ser/modules/tm.so" in your configuration file. This
command invokes dynamic linker provided by the operating
system which opens tm.so file, loads it into memory and
resolves all symbol dependencies (a module might require
symbols from the core, for example functions and variables).
As the last step of the module loading the core tries to find
variable named exports, which describes all functions and
parameters provided by the module. These functions and
parameters are later available to the server and can be used
either in the configuration file or by other modules.
_________________________________________________________
1.2. Exporting Functions
Each module can provide zero or more functions, which can be
used in the configuration file or by other modules internally.
This section gives a detailed description of structure
describing exported functions and passing this information to
the core through the module interface.
Each function exported by a module must be described by
cmd_export_t structure. Structures describing all exported
functions are arranged into an array and pointer to the array
is then passed to the core. The last element of the array must
contain 0 in all it's fields, this element serves as the mark
telling the core that this is the very last element and it
must stop scanning the array.
Each exported function is described by the following
structure:
struct cmd_export_ {
char* name; /* null terminated command name */
cmd_function function; /* pointer to the corresponding functio
n */
int param_no; /* number of parameters used by the fun
ction */
fixup_function fixup; /* pointer to the function called to "f
ix" the parameters */
int flags; /* Function flags */
};
typedef struct cmd_export_ cmd_export_t;
Meaning of the fileds:
* char* name
This is the name under which the function will be visible
to the core. Usually it is the same as the name of the
corresponding function.
* cmd_function function
cmd_function type is defined as follows:
typedef int (*cmd_function)(struct sip_msg*, char*, char*);
The first parameter is a SIP message being processed, the
other 2 parameters are given from the configuration file.
Note
From time to time you might need to export a function that has
different synopsis. This can happen if you export functions
that are supposed to be called by other modules only and must
not be called from the configuration script. In this case you
will have to do type-casting otherwise the compiler will
complain and will not compile your module.
Simply put (cmd_function) just before the function name, for
example (cmd_function)my_function. Don't use this unless you
know what are you doing ! The server might crash if you pass
wrong parameters to the function later !
* int param_no
Number of parameters of the function. It can be 0, 1 or 2.
The function will be not visible from the configuration
script if you use another value.
* fixup_function fixup
This is the function that will be used to "fixup" function
parameters. Set this field to 0 if you don't need this.
If you provide pointer to a fixup function in this field,
the fixup function will be called for each occurence of
the exported function in the configuration script.
The fixup function can be used to perform some operation
on the function parameters. For example, if one of the
parameters is a regular expression, you can use the fixup
to compile the regular expression. The fixup functions are
called only once - upon the server startup and so the
regular expression will be compiled before the server
starts processing messages. When the server calls the
exported function to process a SIP message, the function
will be given the already compiled regular expression and
doesn't have to compile it again. This is a significant
performance improvement.
Fixup functions can also be used to convert string to
integer. As you have might noticed, the exported functions
accept up to 2 parameters of type char*. Because of that
it is not possible to pass integer parameters from the
script files directly. If you want to pass an integer as a
parameter, you must pass it as string (i.e. enclosed in
quotes).
Fixup function can be used to convert the string back to
integer. Such a conversion should happend only once
because the string parameter doesn't change when the
server is running. Fixup is therefore ideal place for the
conversion, it will be converted upon the server startup
before the server starts processing SIP messages. After
the conversion the function will get directly the
converted value. See existing modules for example of such
a fixup function.
* int flags
Usage of each function can be restricted. You may want to
write a function that can be used by other modules but
cannot be called from the script. If you write a function
that is supposed to process SIP requests only, you may
want to restrict it so it will be never called for SIP
replies and vice versa. That's what is flags field for.
This field is OR value of different flags. Currently only
REQUEST_ROUTE and REPLY_ROUTE flags are defined and used
by the core. If you use REQUEST_ROUTE flag, then the
function can be called from the main route block. If you
use REPLY_ROUTE flag, then the function can be called from
reply route blocks (More on this in the SER User's Guide).
If this field is set to 0, then the function can be called
internally (i.e. from other modules) only. If you want to
make your function callable anywhere in the script, you
can use REQUEST_ROUTE | REPLY_ROUTE.
_________________________________________________________
1.3. Exporting Parameters
Each module can provide zero or more parameters, which can
affect the module's behaviour. This section gives a detailed
description of structures describing exported parameters and
passing this information to the core through the module
interface.
Each parameter exported by a module must be described by
param_export_t structure. Structures describing all exported
parameters are arranged into an array and pointer to the array
is then passed to the core. The last element of the array must
contain 0 in all it's fields, this element serves as the mark
telling the core that this is the very last element and it
must stop scanning the array (This is same as in array of
exported functions).
Each exported parameter is described by the following
structure:
struct param_export_ {
char* name; /* null terminated param. name */
modparam_t type; /* param. type */
void* param_pointer; /* pointer to the param. memory locatio
n */
};
typedef struct param_export_ param_export_t;
Meaning of the fields:
* char* name
This is null-terminated name of the parametes as it will
be used in the scripts. Usually this is the same as the
name of the variable holding the value.
* modparam_t type
Type of the parameter. Currently only two types are
defined. INT_PARAM for integer parameters (corresponding
variable must be of type int) and STR_PARAM for string
parameters (corresponding variable must be of type char*).
* void* param_pointer
Pointer to the corresponding variable (stored as void*
pointer, make sure that the variable has appropriate type
depending on the type of the parameter !).
_________________________________________________________
1.4. Module Initialization
If you need to initialize your module before the server starts
processing SIP messages, you should provide initialization
function. Each module can provide two initialization
functions, main initialization function and child-specific
initialization function. Fields holding pointers to both
initialization functions are in main export structure (will be
described later). Simply pass 0 instead of function pointer if
you don't need one or both initialization functions.
The main initialization function will be called before any
other function exported by the module. The function will be
called only once, before the main process forks. This function
is good for initialization that is common for all the children
(processes). The function should return 0 if everything went
OK and a negative error code otherwise. Server will abort if
the function returns a negative value.
Per-child initialization function will be called after the
main process forks. The function will be called for each child
separately. The function should perform initialization that is
specific for each child. For example each child process might
open it's own database connection to avoid locking of a single
connection shared by many processes. Such connections can be
opened in the per-child initialization function. The function
accepts one parameter which is rank (integer) of child for
which the function is being executed. This allows developers
to distinguish different children and perform different
initialization for each child. The meaning of return value is
same as in the main initialization function.
_________________________________________________________
1.5. Module Clean-up
A module can also export a clean-up function that will be
called by the main process when the server shuts down. The
function accepts no parameters and return no value.
_________________________________________________________
1.6. Module Callbacks
TBD.
_________________________________________________________
1.7. exports Structure - Assembling the Pieces Together
We have already described how a module can export functions
and parameters, but we haven't yet described how to pass this
information to the core. Each module must have variable named
exports which is structure module_exports. The variable will
be looked up by the core immediately after it loads the
module. The structure contains pointers to both arrays
(functions, parameters), pointers to both initialization
functions, destroy function and the callbacks. So the
structure contains everything the core will need.
The structure looks like the follows:
struct module_exports{
char* name; /* null terminated module name */
cmd_export_t* cmds; /* null terminated array of the exp
orted commands */
param_export_t* params; /* null terminated array of the exp
orted module parameters */
init_function init_f; /* Initilization function */
response_function response_f; /* function used for responses, ret
urns yes or no; can be null */
destroy_function destroy_f; /* function called when the module
should be "destroyed", e.g: on ser exit; can be null */
onbreak_function onbreak_f;
child_init_function init_child_f; /* function called by all proces
ses after the fork */
};
Field description:
* char* name
Null terminated name of the module
* cmd_exports* cmds
Pointer to the array of exported functions
* param_export_t* params
Pointer to the array of exported parameters
* init_function init_f
Pointer to the module initialization function
* response_function response_f
Pointer to function processing responses
* destroy_function destroy_f
Pointer to the module clean-up function
* onbreak_function onbreak_f
TBD
* child_init_function init_child_f
Pointer to the per-child initialization function
_________________________________________________________
1.8. Example - Simple Module Interface
Let's suppose that we are going to write a simple module. The
module will export two functions - foo_req which will be
processing SIP requests and foo_int which is an internal
function that can be called by other modules only. Both
functions will take 2 parameters.
/* Prototypes */
int foo_req(struct sip_msg* msg, char* param1, char* param2);
int foo_res(struct sip_msg* msg, char* param1, char* param2);
static cmd_export cmds[] = {
{"foo_req", foo_req, 2, 0, ROUTE_REQUEST},
{"foo_int", foo_int, 2, 0, 0 },
{0, 0, 0, 0}
};
The module will also have two parameters, foo_bar of type
integer and bar_foo of type string.
int foo_bar = 0;
char* bar_foo = "default value";
static param_export params[] = {
{"foo_bar", INT_PARAM, &foo_bar},
{"bar_foo", STR_PARAM, bar_foo },
{0, 0, 0}
};
We will also create both initialization functions and a
clean-up function:
static int mod_init(void)
{
printf("foo module initializing\n");
}
static int child_init(int rank)
{
printf("child nr. %d initializing\n", rank);
return 0;
}
static void destroy(void)
{
printf("foo module cleaning up\n");
}
And finally we put everything into the exports structure:
struct module_exports exports = {
"foobar", /* Module name */
cmds, /* Exported functions */
params, /* Exported parameters */
mod_init, /* Module initialization function */
0, /* Response function */
destroy, /* Clean-up function */
0, /* On Cancel function */
child_init /* Per-child init function */
};
And that's it.
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