# The Kamailio RPC Control Interface

## Overview of Operation

The RPC (Remote Procedure Call) interface is an interface for communicating with external applications. Using it an external application can call a function or procedure that will be executed inside Kamailio. Function parameters are supported as well as returning multiple values as results.

By itself RPC consists of two APIs, one for defining RPC functions in a transport independent way (called the rpc module api) and one for implementing RPC transports.

The RPC transports are implemented by writing a RPC transport module. The most used transport modules are ctl , xmlrpc and jsonrpc-s .

ctl implements a proprietary fast and space efficient RPC encoding over different protocols (unix sockets, UDP, TCP, fifo).

xmlrpc uses the de-facto XML-RPC standard encoding (over HTTP TCP or TLS).

jsonrpc-s uses the de-facto JSON-RPC standard encoding (over HTTP TCP or TLS).

For more information about the existing transport modules, please refer to their documentation.

When writing a RPC procedure or function, one needs only use the RPC API and it will work automatically with all the transports and encodings. One needs only to load the desired RPC transport module (e.g. xmlrpc).

The RPC interface (or API) was created in such a way that would allow supporting XML-RPC (because XML-RPC is a de-facto standard), while in the same time being very easy to use.

## Module API

Each module can export RPC functions just like it can export parameters and functions to be called from the script. Whenever &kamailio; receives an RPC request, it will search through the list of exported RPC functions and the function with matching name will be executed. A couple of essential RPC functions are also embedded into the SIP server core.

This section gives a detailed overview of the whole RPC API. describes the prototype and conventions used in RPC functions. gives a detailed overview of available data types that can be used in function parameters and return value. describes functions of the RPC API that can be used to retrieve parameters of the function, and finally describes functions of the API that can be used to build the result value that will be sent in the reply to the caller.

The whole RPC API is described in header file `kamailio/rpc.h`. This file defines the set of functions that must be implemented by RPC transport modules, as described in , prototypes of RPC functions and structures used for the communication between RPC transport modules and ordinary modules exporting RPC functions.

### RPC Functions

RPC functions are standard C functions with the following prototype:

    typedef void (*rpc_function_t)(rpc_t* rpc, void* ctx);

RPC functions take two parameters, first parameter is a pointer to rpc_t structure and the context. The rpc_t structure contains references to all API functions available to the RPC function as well as all data necessary to create the response. RPC functions do not return any value, instead the return value is created using functions from the context. The motivation for this decision is the fact that RPC functions should always return a response and even the API functions called from RPC functions should have the possibility to indicate an error (and should not rely on RPC functions doing so).

If no reply is sent explicitely, the RPC transport module will automatically send a "success" reply (e.g. 200 OK for XML-RPC) when the RPC function finishes. If no values are added to the response, the reponse will be an empty "success" reply (e.g. a 200 OK with empty body for XML-RPC). RPC API functions will automatically send an error reply upon a failure.

Each RPC function has associated an array of documentation strings. The purpose of the documentation strings is to give a short overview of the function, accepted parameters, and format of the reply. By convention the name of the documentation string array is same as the name of the function with "_doc" suffix.

Each module containing RPC functions has to export all the RPC functions to the &kamailio; core in order to make them visible to the RPC transport modules. The export process involves a rpc_export_t structure (either by itself or in an array):

    typedef struct rpc_export {
        const char* name;        /* Name of the RPC function (null terminated) */
        rpc_function_t function; /* Pointer to the function */
        const char** doc_str;    /* Documentation strings, method signature and description */
        unsigned int flags;      /* Various flags, reserved for future use */
    } rpc_export_t;

The `flags` attribute of the `rpc_export` structure is reserved for future use and is currently unused.

There are several ways of exporting the RPC functions to the &kamailio; core:

- register a null terminated array of rpc_export_t structures using the `rpc_register_array()` function (defined in rpc_lookup.h), from the module init function (mod_init()). This is the recommended method for all the new modules.

  #### usrloc RPC Exports Declaration

  The `rpc_export_t` array for the modules_s/usrloc module looks like:

      rpc_export_t ul_rpc[] = {
          {"usrloc.statistics",      rpc_stats,           rpc_stats_doc,          0},
          {"usrloc.delete_aor",      rpc_delete_aor,      rpc_delete_aor_doc,     0},
          {"usrloc.delete_contact",  rpc_delete_contact,  rpc_delete_contact_doc, 0},
          {"usrloc.dump",            rpc_dump,            rpc_dump_doc,           0},
          {"usrloc.flush",           rpc_flush,           rpc_flush_doc,          0},
          {"usrloc.add_contact",     rpc_add_contact,     rpc_add_contact_doc,    0},
          {"usrloc.show_contacts",   rpc_show_contacts,   rpc_show_contacts_doc,  0},
          {0, 0, 0, 0}
      };

  To register it from the module init function one would use something similar to:

      	if (rpc_register_array(ul_rpc) != 0) {
      		ERR("failed to register RPC commands\n");
      		return -1;
      	}

- register RPCs one by one using the `rpc_register_function()` (defined in rpc_lookup.h), from the module init function.

- register a null terminated array of rpc_export_t structures using the &kamailio; module interface SER_MOD_INTERFACE For this purpose, the `module_exports` structure of the &kamailio; module API contains a new attribute called `rpc_methods`:

      struct module_exports {
          char* name;                 /* null terminated module name */
          cmd_export_t* cmds;         /* null terminated array of the exported commands */
          rpc_export_t* rpc_methods;  /* null terminated array of exported rpc methods */
          param_export_t* params;     /* null terminated array of the exported module parameters */

          init_function init_f;         /* Initialization function */
          response_function response_f; /* function used for responses */
          destroy_function destroy_f;   /* function called upon shutdown */
          onbreak_function onbreak_f;
          child_init_function init_child_f;  /* function called by all processes after the fork */
      };

  `rpc_methods` is a pointer to an array of rpc_export_t structures. The last element of the array is a bumper containing zeroes in all the attributes of the structure. The following program listing shows the exported RPC functions of the modules_s/usrloc module, using the rpc_export_t array ul_rpc defined above, in the rpc_register_array() example:

  #### usrloc Module Exports Declaration

      struct module_exports exports = {
          "usrloc",
          cmds,      /* Exported functions */
          ul_rpc,    /* RPC methods */
          params,    /* Export parameters */
          mod_init,  /* Module initialization function */
          0,         /* Response function */
          destroy,   /* Destroy function */
          0,         /* OnCancel function */
          child_init /* Child initialization function */ };

  This mode works only with modules using the SER flavour module interface. It does not work for &kamailio; modules and it will probably not work for future sip-router modules. It is safer and recommended to use instead the `rpc_register_array()` function.

By convention the name of every exported function consists of two parts delimited by a dot. The first part is the name of the module or &kamailio; subsystem this function belongs to. The second part is the name of the function.

### Data Types

The RPC API defines several basic and one compound data type that can be used in communication with the caller of RPC functions. The RPC API uses formating strings to describe data types. Each data type is described by exactly one character in the formating string. For example, if an RPC function calls function `add` of the RPC API and it passes two parameters to it, the first one of type string and the second one of type integer, the function parameters will look like:

    add("sd", string_param, int_param);

Character "s" in the formating string tells to the function that the 2nd parameter should be interpreted as string, character "d" in the formating string tells to the function that the 3rd parameter should be interpreted as signed integer.

#### Integer

Integer type represents a signed 32-bit integer. Corresponding character in the formating string is "d". This parameter can be stored in C-style variable with type `int`.

#### Float

Float type represents a signed floating point number. Corresponding character in the formating string is "f". Data of this type can be stored in C-style variables of type `double`.

#### String

String type represents a string of characters. The string may contain zeroes. This data type is represented by two characters in the formatting string, either "s" or "S". "s" indicates to the conversion function that the result should be stored in a variable of type `char*` and it should be zero terminated. "S" indicates to the conversion function that the result will be stored in a variable of type `str` which contains both the pointer to the beginning of the string and its length.

#### Structure

Structure is the only compound data type currently defined in the API. A structure is a collection of attributes. Each attribute is identified using name (string) and each attribute can be one of the basic data types, that is integer, float, or string. Nesting of structures is not allowed (in other words, structure attributes cannot be of type struct again). Corresponding character in the formatting string is "{".

#### Optional parameters

Optional parameters can be used, but only in the `scan` function. For optional parameters the `scan` function will not automatically generate a rpc fault if the input ends. Note that in this case the `scan` will still return a negative value (minus the number of parameters successfully read). Optional parameters can be marked in the format string by preceding the first optional parameter type with a "*". All the parameters following a "*" are considered to be optional. For example for the format string "ds*dds", the last 3 parameters (2 ints and a string) are optional.

#### Data Type Overview

Name | Formating String Char | C-Style Variable
Integer | d | int
Float | f | double
String | s | char*
String | S | str*
Optional modifier | * | marks all further parameters as optional
Autoconvert modifier | . | requires auto-conversion for the next parameter

### Getting Parameters

Each RPC function call can contain parameters. Parameters have no name, their meaning is determined by their position in the parameter set.

You can pass all parameters to a function within a structure if you want to make them position independent. Then each parameter can be retrieved by its name regardless of its position.

There are two functions in the RPC API that can be used to obtain function call parameters: `scan` and `struct_scan`.

#### `scan`

Function `scan` can be used to retrieve parameters from the parameter set. The function accepts variable number of parameters. The first parameter is the formatting string that determines the type of the parameters to be retrieved. Each parameter is represented by exactly one parameter type character in the string. The variable part of parameters must contain as many pointers to C variables as there are formatting non-modifiers characters in the formatting string.

The function will crash if you fail to provide enough parameters.

Besides characters representing parameter types, the formatting string can contain two special modifiers: "*" and ".". The modifiers do not have a correspondent in the variable part of the parameters.

The meaning of "*" modifier is that any further parameters (defined by other type characters in the formatting string) are optional (they can be missing in the input and no rpc fault will automatically be generated).

The '.' modifiers turns on type autoconversion for the next parameter. This means that if the type of the next parameter differs from the type specified in the formatting string, the parameter will be automatically converted to the formatting string type (if possible) and if the automatic conversion succeeds, no fault will be generated.

The function returns the number of parameters read on success (a number greater or equal 0) and - (minus) the number of parameters read on error (for example for an error after reading 2 parameters it will return -2). When a failure occurs (incorrect parameter type or no more parameters in the parameter set) the function will return a negative number (- number of parameters read so far) and it will also automatically change the reply that will be sent to the caller to indicate that a failure has occurred on the server (unless the "*" is used and the error is lack of more parameters).

The prototype of the function is:

    int scan((void* ctx, char* fmt, ...)

It is possible to either call the function once to scan all the parameters:

    rpc->scan(ctx, "sdf", &string_val, &int_val, &double_val);

Or you can call the same function several times and it will continue where it left off previously:

    rpc->scan(ctx, "s", &string_val);
    rpc->scan(ctx, "d", &int_val);
    rpc->scan(ctx, "f", &double_val);

#### `struct_scan`

Function `struct_scan` can be used to retrieve named attributes from a parameter of type structure.

This function is obsolete and not implemented by all the rpc transports (e.g.: ctl / binrpc). Consider using the normal `scan` instead.

When retrieving a structure parameter from the parameter set:

    rpc->scan(ctx, "{", &handle);

The corresponding variable (named `handle` in the example above) will contain the index of the structure parameter within the parameter set, but the index cannot be used to retrieve the contents of the structure. To retrieve the contents of the structure you can use function `struct_scan`. The function gets the handle as the first parameter:

    rpc->struct_scan(handle, "sd", "str_attr", &str_val, "int_attr", &int_val);

The second parameter is the formatting string followed by pairs of parameters. First parameter in each pair is the name of the attribute to retrieve (string) and the second parameter in each pair is the pointer to the variable to store the value of the parameter. The function returns the number of parameters (name value pairs) read on success and - number of parameters read so far on an error (just like the `scan` function). The function also indicates an error if a requested attribute is missing in the structure.

#### Retrieving Parameters Example

##### Retrieving Parameters

    static void rpc_delete_contact(rpc_t* rpc, void* ctx)
    {
        str aor, contact;
        char* table;
        void *handle;
        int   expires;
        double q;

        if (rpc->scan(ctx, "sS{", &table, &aor, &handle) < 0) {
            /* Reply is set automatically by scan upon failure,
             * no need to do anything here
             */
            return;
        }

        if (rpc->struct_scan(handle, "Sdf", "Contact", &contact,
                                            "Expires", &expires,
                                            "Q",       &q        ) < 0) {
            /* Reply is set automatically by struct_scan upon failure,
             * no need to do anything here
             */
            return;
        }

        /* Process retrieved parameters here */
    }

    /* variable number of parameters:
       echo back all the parameters, string type required */
    static void core_prints(rpc_t* rpc, void* c)
    {
    	char* string = 0;
    	while((rpc->scan(c, "*s", &string)>0))
    		rpc->add(c, "s", string);
    }

    /* variable number of parameters and auto conversion:
       echo back all the parameters, works with any type (everything is
       internally converted to string, notice the '.' modifier) */
    static void core_echo(rpc_t* rpc, void* c)
    {
    	char* string = 0;
    	while((rpc->scan(c, "*.s", &string)>0))
    		rpc->add(c, "s", string);
    }

### Building Reply

The RPC API contains several functions that can be used to modify and/or send a reply. The functions use formatting strings and parameter lists just like functions described in .

Each RPC function call must return a reply. The reply can be either a failure reply or success reply. Failure replies contain only the status code and reason phrase. Success replies can have arbitrary amount of data attached to them. Status codes 3xx, 4xx, 5xx, and 6xx indicate failures. Status code 2xx indicates success.

The default reply is 200 OK with no data attached to it. This is what will be returned by the RPC transport module if you do not call any of the reply-related functions described in this section.

#### Sending default reply

    static void rpc_dummy(rpc_t* rpc, void *ctx)
    {
      /* 200 OK with no data will be returned */
    }

#### fault

You can use `fault` function to indicate that an error has occurred on the server to the caller. The function accepts two parameters. The first parameter is the status code and the second parameter is the reason phrase.

    static void rpc_my_function(rpc_t* rpc, void *ctx)
    {
        rpc->fault(ctx, 600, "Not Yet Implemented");
    }

If your function first creates some result using `add`, or `printf` functions then all the data will be lost once you call `fault` function. Failure replies must not contain any data:

    static void rpc_my_function(rpc_t* rpc, void *ctx)
    {
        rpc->add(ctx, "s", "result1");
        rpc->add(ctx, "d", variable);

        /* Reply created by previous functions will be
         * deleted and a failure reply 600 Not Yet Implemented
         * will be created instead
         */
        rpc->fault(ctx, 600, "Not Yet Implemented");

        /* You can also add data here, but that will have no
         * effect
         */
        rpc->add(ctx, "s", "result2");
    }

Similarly you can also call `add` or `printf` functions after calling `fault`, in this case they will have no effect:

    static void rpc_my_function(rpc_t* rpc, void *ctx)
    {
        rpc->fault(ctx, 600, "Not Yet Implemented");

        /* You can also add data here, but that will have no
         * effect and only 600 Not Yet Implemented will be returned
         */
        rpc->add(ctx, "s", "result2");
    }

#### send

RPC functions can use function `send` to explicitly send the reply. Each RPC function call generates exactly one reply. No reply will be sent after the function finishes if it already sent the reply using `send` function explicitly. This function is especially useful if the RPC function needs to perform some (potentially destructive) actions after the reply has been sent.

##### Kill the server

    static void core_kill(rpc_t* rpc, void *ctx)
    {
        int sig_no;

        if (rpc->scan(ctx, "d", &sig_no) < 0) return;
        rpc->send(ctx, );     /* First send a reply */
        kill(0, sig_no); /* Then kill the server */
    }

#### add

Function `add` can be used to add arbitrary data to the result set. Its parameters and use are analogical to `scan` function described in . The first parameter of the function is the formatting string that determines the types of additional parameters:

    static void rpc_func(rpc_t* rpc, void *ctx)
    {
        str str_result;
        int int_result;
        void *handle;
        double float_result;

        if (rpc->add(ctx, "Sdf{", &str_result, int_result, float_result, &handle) < 0) return;
    }

Naturally you can call this function several times, adding only one piece of data at a time. The function returns 0 on success and -1 on an error. In case of an error the reply is set automatically with corresponding error code and reason phrase.

The last character in the formatting string of the function above indicates that the last data to be added will be a structure. This deserves some clarification. In this case, the function will create an empty structure and the handle to the newly created structure will be stored in `handle` variable (hence the last parameter is pointer to an integer). In this particular example parameters `str_result`, `int_result`, and `float_result` will be used for reading while parameter `handle` will be used for writing by the function.

You can set the attributes of the newly created structure using `struct_add` function described in .

#### rpl_printf

`rpl_printf` is a convenience function. The function adds data of type string to the result set. The first parameter of the function is again a formatting string, but this time it is standard `printf`-like formatting string:

    if (rpc->rpl_printf(ctx, "Unable to delete %d entries from table %s", num_entries, table_name) < 0) return;

The return value of the function is the same as of `add` function.

#### struct_add

Function `struct_add` can be used to add attributes to a structure (created previously by `add` function). The first parameter of the function is handle obtained through `add` function, the second parameters is formatting string that determines the types of attributes to be added. There must be two parameters per each character in the formatting string, the first one is the name of the attribute, the second parameter is the value of the attribute. If a parameter with such a name already exist in the structure then it will be overwritten with the new value.

    static void rpc_func(rpc_t* rpc, void *ctx)
    {
        void *handle;

            /* Create empty structure and obtain its handle */
        if (rpc->add(ctx, "{", &handle) < 0) return;
            /* Fill-in the structure */
        if (rpc->struct_add(handle, "sd", "attr1", str_val,
                                          "attr2", int_val ) < 0)
            return;
    }

The function returns -1 on an error (and sets the status code and reason phrase of the reply accordingly) and 0 on success.

### Real World Example

The following example illustrates the use of most of the functions from the API together:

#### Real World Example RPC Function

    static void rpc_register(rpc_t* rpc, void *ctx)
    {
        char* domain;
        str aor;
        contact_t contact, new_contact;
        void *handle;

            /* Extract the domain, address of record from the request */
        if (rpc->scan(ctx, "sS{", &domain, &aor, &handle) < 0) return;
            /* Extract the structure describing the contact to be processed */
        if (rpc->struct_scan(handle, "Sdf", "Contact", &contact.c,
                                            "Expires", &contact.expires,
                                            "Q",       &contact.q       ) < 0)
            return;

            /* Process the contact, new_contact will contain updated value after processing */
        if (process_contact(domain, &aor, &new_contact, &contact) < 0) {
               /* Processing failed, indicate the failure to the caller */
            rpc->fault(ctx, 500, "Error While Processing Contact");
            return;
        }

            /* Return the domain and the address of record */
        rpc->add(ctx, "sS{", &domain, &aor, &handle) < 0) return;
            /* And also add the new values for contact, q, and expires parameters */
        rpc->struct_add(handle, "Sdf", "Contact", &new_contact.c,
                                       "Expires", &new_contact.expires,
                                       "Q",       &new_contact.q       );
    }

## Client Examples

- sercmd (C application that uses the binrpc interface implemented by the ctl module).

- ser_ctl (python application that uses the XML-RPC interface implemented by the xmlrpc module).

- serweb (php application that can use the XML-RPC interface to call ser functions).

## Implementing New Transports

Examples:

- ctl

- xmlrpc

## Examples using xmlrpc

See the `xmlrpc` module documentation: modules/xmlrpc/README.