evrpc(3) | Library Functions Manual | evrpc(3)

# NAME

evrpc - This header files provides basic support for an RPC server and client.

# SYNOPSIS

#include <event2/rpc.h>

## Macros

#define EVRPC_GENERATE(rpcname, reqstruct, rplystruct)
Generates the code for receiving and sending an RPC message. #define EVRPC_HEADER(rpcname, reqstruct, rplystruct)
Creates the definitions and prototypes for an RPC. #define EVRPC_MAKE_CTX(rpcname, reqstruct, rplystruct, pool, request, reply, cb, cbarg)
Creates a context structure that contains rpc specific information. #define EVRPC_MAKE_REQUEST(name, pool, request, reply, cb, cbarg) evrpc_send_request_##name((pool), (request), (reply), (cb), (cbarg))
launches an RPC and sends it to the server #define EVRPC_REGISTER(base, name, request, reply, callback, cbarg)
register RPCs with the HTTP Server #define EVRPC_REQUEST_DONE(rpc_req)
Creates the reply to an RPC request. #define EVRPC_REQUEST_HTTP(rpc_req) (rpc_req)->http_req
Provides access to the HTTP request object underlying an RPC. #define EVRPC_STRUCT(rpcname) struct evrpc_req__##rpcname
The type of a specific RPC Message. #define EVRPC_UNREGISTER(base, name) evrpc_unregister_rpc((base), #name)
Unregisters an already registered RPC. #define EVTAG_ARRAY_ADD(msg, member) (*(msg)->base->member##_add)(msg)
Allocates a new entry in the array and returns it. #define EVTAG_ARRAY_ADD_VALUE(msg, member, value) (*(msg)->base->member##_add)((msg), (value))
Adds a value to an array. #define EVTAG_ARRAY_GET(msg, member, offset, pvalue) (*(msg)->base->member##_get)((msg), (offset), (pvalue))
Gets a variable at the specified offset from the array. #define EVTAG_ARRAY_LEN(msg, member) ((msg)->member##_length)
Returns the number of entries in the array. #define EVTAG_ASSIGN(msg, member, value) (*(msg)->base->member##_assign)((msg), (value))
Assigns a value to the member in the message. #define EVTAG_ASSIGN_WITH_LEN(msg, member, value, len) (*(msg)->base->member##_assign)((msg), (value), (len))
Assigns a value to the member in the message. #define EVTAG_GET(msg, member, pvalue) (*(msg)->base->member##_get)((msg), (pvalue))
Returns the value for a member. #define EVTAG_GET_WITH_LEN(msg, member, pvalue, plen) (*(msg)->base->member##_get)((msg), (pvalue), (plen))
Returns the value for a member. #define EVTAG_HAS(msg, member) ((msg)->member##_set == 1)
Determines if the member has been set in the message. #define INPUT EVRPC_INPUT
Deprecated alias for EVRPC_INPUT. #define OUTPUT EVRPC_OUTPUT
Deprecated alias for EVRPC_OUTPUT.

## Enumerations

enum EVRPC_HOOK_RESULT { EVRPC_TERMINATE = -1, EVRPC_CONTINUE = 0, EVRPC_PAUSE = 1 } Return value from hook processing functions. "
enum EVRPC_HOOK_TYPE { EVRPC_INPUT, EVRPC_OUTPUT } Hooks for changing the input and output of RPCs; this can be used to implement compression, authentication, encryption, ... "

## Functions

void * evrpc_add_hook (void *vbase, enum EVRPC_HOOK_TYPE hook_type, int(*cb)(void *, struct evhttp_request *, struct evbuffer *, void *), void *cb_arg)
adds a processing hook to either an rpc base or rpc pool void evrpc_free (struct evrpc_base *base)
Frees the evrpc base. void * evrpc_get_reply (struct evrpc_req_generic *req)
void * evrpc_get_request (struct evrpc_req_generic *req)
accessors for request and reply void evrpc_hook_add_meta (void *ctx, const char *key, const void *data, size_t data_size)
adds meta data to request int evrpc_hook_find_meta (void *ctx, const char *key, void **data, size_t *data_size)
retrieves meta data previously associated struct evhttp_connection * evrpc_hook_get_connection (void *ctx)
returns the connection object associated with the request struct evrpc_base * evrpc_init (struct evhttp *server)
Creates a new rpc base from which RPC requests can be received. int evrpc_make_request (struct evrpc_request_wrapper *ctx)
Makes an RPC request based on the provided context. struct evrpc_request_wrapper * evrpc_make_request_ctx (struct evrpc_pool *pool, void *request, void *reply, const char *rpcname, void(*req_marshal)(struct evbuffer *, void *), void(*rpl_clear)(void *), int(*rpl_unmarshal)(void *, struct evbuffer *), void(*cb)(struct evrpc_status *, void *, void *, void *), void *cbarg)
use EVRPC_GENERATE instead void evrpc_pool_add_connection (struct evrpc_pool *pool, struct evhttp_connection *evcon)
Adds a connection over which rpc can be dispatched to the pool. void evrpc_pool_free (struct evrpc_pool *pool)
frees an rpc connection pool struct evrpc_pool * evrpc_pool_new (struct event_base *base)
creates an rpc connection pool void evrpc_pool_remove_connection (struct evrpc_pool *pool, struct evhttp_connection *evcon)
Removes a connection from the pool. void evrpc_pool_set_timeout (struct evrpc_pool *pool, int timeout_in_secs)
Sets the timeout in secs after which a request has to complete. int evrpc_register_generic (struct evrpc_base *base, const char *name, void(*callback)(struct evrpc_req_generic *, void *), void *cbarg, void *(*req_new)(void *), void *req_new_arg, void(*req_free)(void *), int(*req_unmarshal)(void *, struct evbuffer *), void *(*rpl_new)(void *), void *rpl_new_arg, void(*rpl_free)(void *), int(*rpl_complete)(void *), void(*rpl_marshal)(struct evbuffer *, void *))
Function for registering a generic RPC with the RPC base. int evrpc_register_rpc (struct evrpc_base *, struct evrpc *, void(*)(struct evrpc_req_generic *, void *), void *)
Low level function for registering an RPC with a server. int evrpc_remove_hook (void *vbase, enum EVRPC_HOOK_TYPE hook_type, void *handle)
removes a previously added hook void evrpc_request_done (struct evrpc_req_generic *req)
completes the server response to an rpc request struct evrpc_pool * evrpc_request_get_pool (struct evrpc_request_wrapper *ctx)
accessors for obscure and undocumented functionality void evrpc_request_set_cb (struct evrpc_request_wrapper *ctx, void(*cb)(struct evrpc_status *, void *request, void *reply, void *arg), void *cb_arg)
void evrpc_request_set_pool (struct evrpc_request_wrapper *ctx, struct evrpc_pool *pool)
int evrpc_resume_request (void *vbase, void *ctx, enum EVRPC_HOOK_RESULT res)
resume a paused request int evrpc_send_request_generic (struct evrpc_pool *pool, void *request, void *reply, void(*cb)(struct evrpc_status *, void *, void *, void *), void *cb_arg, const char *rpcname, void(*req_marshal)(struct evbuffer *, void *), void(*rpl_clear)(void *), int(*rpl_unmarshal)(void *, struct evbuffer *))
Function for sending a generic RPC request. int evrpc_unregister_rpc (struct evrpc_base *base, const char *name)

# Detailed Description

This header files provides basic support for an RPC server and client.

To support RPCs in a server, every supported RPC command needs to be defined and registered.

EVRPC_HEADER(SendCommand, Request, Reply);

SendCommand is the name of the RPC command. Request is the name of a structure generated by event_rpcgen.py. It contains all parameters relating to the SendCommand RPC. The server needs to fill in the Reply structure. Reply is the name of a structure generated by event_rpcgen.py. It contains the answer to the RPC.

To register an RPC with an HTTP server, you need to first create an RPC base with:

struct evrpc_base *base = evrpc_init(http);

A specific RPC can then be registered with

EVRPC_REGISTER(base, SendCommand, Request, Reply, FunctionCB, arg);

when the server receives an appropriately formatted RPC, the user callback is invoked. The callback needs to fill in the reply structure.

void FunctionCB(EVRPC_STRUCT(SendCommand)* rpc, void *arg);

To send the reply, call EVRPC_REQUEST_DONE(rpc);

See the regression test for an example.

# Macro Definition Documentation

## #define EVRPC_GENERATE(rpcname, reqstruct, rplystruct)

Value:

    int evrpc_send_request_##rpcname(struct evrpc_pool *pool,         struct reqstruct *request, struct rplystruct *reply,            void (*cb)(struct evrpc_status *,                       struct reqstruct *, struct rplystruct *, void *cbarg),          void *cbarg) {                          return evrpc_send_request_generic(pool, request, reply,         (void (*)(struct evrpc_status *, void *, void *, void *))cb,         cbarg,                                  #rpcname,                                   (void (*)(struct evbuffer *, void *))reqstruct##_marshal,           (void (*)(void *))rplystruct##_clear,                   (int (*)(void *, struct evbuffer *))rplystruct##_unmarshal); }

Generates the code for receiving and sending an RPC message. EVRPC_GENERATE is used to create the code corresponding to sending and receiving a particular RPC message

Parameters:

rpcname the name of the RPC
reqstruct the name of the RPC request structure
replystruct the name of the RPC reply structure

See also:

EVRPC_HEADER()

## #define EVRPC_HEADER(rpcname, reqstruct, rplystruct)

Value:

    EVRPC_STRUCT(rpcname) {     struct evrpc_hook_meta *hook_meta;     struct reqstruct* request;     struct rplystruct* reply;     struct evrpc* rpc;     struct evhttp_request* http_req;     struct evbuffer* rpc_data; };                                   int evrpc_send_request_##rpcname(struct evrpc_pool *,     struct reqstruct *, struct rplystruct *,     void (*)(struct evrpc_status *,     struct reqstruct *, struct rplystruct *, void *cbarg),      void *);

Creates the definitions and prototypes for an RPC. You need to use EVRPC_HEADER to create structures and function prototypes needed by the server and client implementation. The structures have to be defined in an .rpc file and converted to source code via event_rpcgen.py

Parameters:

rpcname the name of the RPC
reqstruct the name of the RPC request structure
replystruct the name of the RPC reply structure

See also:

EVRPC_GENERATE()

## #define EVRPC_MAKE_CTX(rpcname, reqstruct, rplystruct, pool, request, reply, cb, cbarg)

Value:

    evrpc_make_request_ctx(pool, request, reply,                 #rpcname,                                   (void (*)(struct evbuffer *, void *))reqstruct##_marshal,           (void (*)(void *))rplystruct##_clear,                   (int (*)(void *, struct evbuffer *))rplystruct##_unmarshal,         (void (*)(struct evrpc_status *, void *, void *, void *))cb,         cbarg)

Creates a context structure that contains rpc specific information. EVRPC_MAKE_CTX is used to populate a RPC specific context that contains information about marshaling the RPC data types.

Parameters:

rpcname the name of the RPC
reqstruct the name of the RPC request structure
replystruct the name of the RPC reply structure
pool the evrpc_pool over which to make the request
request a pointer to the RPC request structure object
reply a pointer to the RPC reply structure object
cb the callback function to call when the RPC has completed
cbarg the argument to supply to the callback

## #define EVRPC_MAKE_REQUEST(name, pool, request, reply, cb, cbarg) evrpc_send_request_##name((pool), (request), (reply), (cb), (cbarg))

launches an RPC and sends it to the server EVRPC_MAKE_REQUEST() is used by the client to send an RPC to the server.

Parameters:

name the name of the RPC
pool the evrpc_pool that contains the connection objects over which the request should be sent.
request a pointer to the RPC request structure - it contains the data to be sent to the server.
reply a pointer to the RPC reply structure. It is going to be filled if the request was answered successfully
cb the callback to invoke when the RPC request has been answered
cbarg an additional argument to be passed to the client

Returns:

0 on success, -1 on failure

## #define EVRPC_REGISTER(base, name, request, reply, callback, cbarg)

Value:

    evrpc_register_generic(base, #name,                     (void (*)(struct evrpc_req_generic *, void *))callback, cbarg,         (void *(*)(void *))request##_new, NULL,                 (void (*)(void *))request##_free,                       (int (*)(void *, struct evbuffer *))request##_unmarshal,            (void *(*)(void *))reply##_new, NULL,                   (void (*)(void *))reply##_free,         (int (*)(void *))reply##_complete,         (void (*)(struct evbuffer *, void *))reply##_marshal)

register RPCs with the HTTP Server registers a new RPC with the HTTP server, each RPC needs to have a unique name under which it can be identified.

Parameters:

base the evrpc_base structure in which the RPC should be registered.
name the name of the RPC
request the name of the RPC request structure
reply the name of the RPC reply structure
callback the callback that should be invoked when the RPC is received. The callback has the following prototype void (callback)(EVRPC_STRUCT(Message) rpc, void *arg)
cbarg an additional parameter that can be passed to the callback. The parameter can be used to carry around state.

## #define EVRPC_REQUEST_DONE(rpc_req)

Value:

    do {   struct evrpc_req_generic *req_ = (struct evrpc_req_generic *)(rpc_req); \
      evrpc_request_done(req_);                 } while (0)

Creates the reply to an RPC request. EVRPC_REQUEST_DONE is used to answer a request; the reply is expected to have been filled in. The request and reply pointers become invalid after this call has finished.

Parameters:

rpc_req the rpc request structure provided to the server callback

## #define EVRPC_REQUEST_HTTP(rpc_req) (rpc_req)->http_req

Provides access to the HTTP request object underlying an RPC. Access to the underlying http object; can be used to look at headers or for getting the remote ip address

Parameters:

rpc_req the rpc request structure provided to the server callback

Returns:

an struct evhttp_request object that can be inspected for HTTP headers or sender information.

## #define EVRPC_STRUCT(rpcname) struct evrpc_req__##rpcname

The type of a specific RPC Message.

Parameters:

rpcname the name of the RPC message

## #define EVRPC_UNREGISTER(base, name) evrpc_unregister_rpc((base), #name)

Unregisters an already registered RPC.

Parameters:

base the evrpc_base object from which to unregister an RPC
name the name of the rpc to unregister

Returns:

-1 on error or 0 when successful.

See also:

EVRPC_REGISTER()

## #define EVTAG_ASSIGN(msg, member, value) (*(msg)->base->member##_assign)((msg), (value))

Assigns a value to the member in the message.

Parameters:

msg the message to which to assign a value
member the name of the member variable
value the value to assign

## #define EVTAG_ASSIGN_WITH_LEN(msg, member, value, len) (*(msg)->base->member##_assign)((msg), (value), (len))

Assigns a value to the member in the message.

Parameters:

msg the message to which to assign a value
member the name of the member variable
value the value to assign
len the length of the value

## #define EVTAG_GET(msg, member, pvalue) (*(msg)->base->member##_get)((msg), (pvalue))

Returns the value for a member.

Parameters:

msg the message from which to get the value
member the name of the member variable
pvalue a pointer to the variable to hold the value

Returns:

0 on success, -1 otherwise.

## #define EVTAG_GET_WITH_LEN(msg, member, pvalue, plen) (*(msg)->base->member##_get)((msg), (pvalue), (plen))

Returns the value for a member.

Parameters:

msg the message from which to get the value
member the name of the member variable
pvalue a pointer to the variable to hold the value
plen a pointer to the length of the value

Returns:

0 on success, -1 otherwise.

## #define EVTAG_HAS(msg, member) ((msg)->member##_set == 1)

Determines if the member has been set in the message.

Parameters:

msg the message to inspect
member the member variable to test for presences

Returns:

1 if it's present or 0 otherwise.

## #define INPUT EVRPC_INPUT

Deprecated alias for EVRPC_INPUT. Not available on windows, where it conflicts with platform headers.

## #define OUTPUT EVRPC_OUTPUT

Deprecated alias for EVRPC_OUTPUT. Not available on windows, where it conflicts with platform headers.

# Enumeration Type Documentation

## enum EVRPC_HOOK_RESULT

Return value from hook processing functions.

Enumerator

EVRPC_TERMINATE
  indicates the rpc should be terminated
EVRPC_CONTINUE
  continue processing the rpc
EVRPC_PAUSE
  pause processing request until resumed

## enum EVRPC_HOOK_TYPE

Hooks for changing the input and output of RPCs; this can be used to implement compression, authentication, encryption, ...

Enumerator

EVRPC_INPUT
  apply the function to an input hook
EVRPC_OUTPUT
  apply the function to an output hook

# Function Documentation

## void* evrpc_add_hook (void * vbase, enum EVRPC_HOOK_TYPE hook_type, int(*)(void *, struct evhttp_request *, struct evbuffer *, void *) cb, void * cb_arg)

adds a processing hook to either an rpc base or rpc pool If a hook returns TERMINATE, the processing is aborted. On CONTINUE, the request is immediately processed after the hook returns. If the hook returns PAUSE, request processing stops until evrpc_resume_request() has been called.

The add functions return handles that can be used for removing hooks.

Parameters:

vbase a pointer to either struct evrpc_base or struct evrpc_pool
hook_type either INPUT or OUTPUT
cb the callback to call when the hook is activated
cb_arg an additional argument for the callback

Returns:

a handle to the hook so it can be removed later

See also:

evrpc_remove_hook()

## void evrpc_free (struct evrpc_base * base)

Frees the evrpc base. For now, you are responsible for making sure that no rpcs are ongoing.

Parameters:

base the evrpc_base object to be freed

See also:

evrpc_init

## void evrpc_hook_add_meta (void * ctx, const char * key, const void * data, size_t data_size)

adds meta data to request evrpc_hook_add_meta() allows hooks to add meta data to a request. for a client request, the meta data can be inserted by an outgoing request hook and retrieved by the incoming request hook.

Parameters:

ctx the context provided to the hook call
key a NUL-terminated c-string
data the data to be associated with the key
data_size the size of the data

## int evrpc_hook_find_meta (void * ctx, const char * key, void ** data, size_t * data_size)

retrieves meta data previously associated evrpc_hook_find_meta() can be used to retrieve meta data associated to a request by a previous hook.

Parameters:

ctx the context provided to the hook call
key a NUL-terminated c-string
data pointer to a data pointer that will contain the retrieved data
data_size pointer to the size of the data

Returns:

0 on success or -1 on failure

## struct evhttp_connection* evrpc_hook_get_connection (void * ctx)

returns the connection object associated with the request

Parameters:

ctx the context provided to the hook call

Returns:

a pointer to the evhttp_connection object

## struct evrpc_base* evrpc_init (struct evhttp * server)

Creates a new rpc base from which RPC requests can be received.

Parameters:

server a pointer to an existing HTTP server

Returns:

a newly allocated evrpc_base struct

See also:

evrpc_free()

## int evrpc_make_request (struct evrpc_request_wrapper * ctx)

Makes an RPC request based on the provided context. This is a low-level function and should not be used directly unless a custom context object is provided. Use EVRPC_MAKE_REQUEST() instead.

Parameters:

ctx a context from EVRPC_MAKE_CTX()

Returns:

0 on success, -1 otherwise.

See also:

EVRPC_MAKE_REQUEST(), EVRPC_MAKE_CTX()

## void evrpc_pool_add_connection (struct evrpc_pool * pool, struct evhttp_connection * evcon)

Adds a connection over which rpc can be dispatched to the pool. The connection object must have been newly created.

Parameters:

pool the pool to which to add the connection
evcon the connection to add to the pool.

## void evrpc_pool_free (struct evrpc_pool * pool)

frees an rpc connection pool

Parameters:

pool a pointer to an evrpc_pool allocated via evrpc_pool_new()

See also:

evrpc_pool_new()

## struct evrpc_pool* evrpc_pool_new (struct event_base * base)

creates an rpc connection pool a pool has a number of connections associated with it. rpc requests are always made via a pool.

Parameters:

base a pointer to an struct event_based object; can be left NULL in singled-threaded applications

Returns:

a newly allocated struct evrpc_pool object

See also:

evrpc_pool_free()

## void evrpc_pool_remove_connection (struct evrpc_pool * pool, struct evhttp_connection * evcon)

Removes a connection from the pool. The connection object must have been newly created.

Parameters:

pool the pool from which to remove the connection
evcon the connection to remove from the pool.

## void evrpc_pool_set_timeout (struct evrpc_pool * pool, int timeout_in_secs)

Sets the timeout in secs after which a request has to complete. The RPC is completely aborted if it does not complete by then. Setting the timeout to 0 means that it never timeouts and can be used to implement callback type RPCs.

Any connection already in the pool will be updated with the new timeout. Connections added to the pool after set_timeout has be called receive the pool timeout only if no timeout has been set for the connection itself.

Parameters:

pool a pointer to a struct evrpc_pool object
timeout_in_secs the number of seconds after which a request should timeout and a failure be returned to the callback.

## int evrpc_register_generic (struct evrpc_base * base, const char * name, void(*)(struct evrpc_req_generic *, void *) callback, void * cbarg, void *(*)(void *) req_new, void * req_new_arg, void(*)(void *) req_free, int(*)(void *, struct evbuffer *) req_unmarshal, void *(*)(void *) rpl_new, void * rpl_new_arg, void(*)(void *) rpl_free, int(*)(void *) rpl_complete, void(*)(struct evbuffer *, void *) rpl_marshal)

Function for registering a generic RPC with the RPC base. Do not call this function directly, use EVRPC_REGISTER() instead.

See also:

EVRPC_REGISTER()

## int evrpc_register_rpc (struct evrpc_base *, struct evrpc *, void(*)(struct evrpc_req_generic *, void *), void *)

Low level function for registering an RPC with a server. Use EVRPC_REGISTER() instead.

See also:

EVRPC_REGISTER()

## int evrpc_remove_hook (void * vbase, enum EVRPC_HOOK_TYPE hook_type, void * handle)

removes a previously added hook

Parameters:

vbase a pointer to either struct evrpc_base or struct evrpc_pool
hook_type either INPUT or OUTPUT
handle a handle returned by evrpc_add_hook()

Returns:

1 on success or 0 on failure

See also:

evrpc_add_hook()

## int evrpc_resume_request (void * vbase, void * ctx, enum EVRPC_HOOK_RESULT res)

resume a paused request

Parameters:

vbase a pointer to either struct evrpc_base or struct evrpc_pool
ctx the context pointer provided to the original hook call

## int evrpc_send_request_generic (struct evrpc_pool * pool, void * request, void * reply, void(*)(struct evrpc_status *, void *, void *, void *) cb, void * cb_arg, const char * rpcname, void(*)(struct evbuffer *, void *) req_marshal, void(*)(void *) rpl_clear, int(*)(void *, struct evbuffer *) rpl_unmarshal)

Function for sending a generic RPC request. Do not call this function directly, use EVRPC_MAKE_REQUEST() instead.

See also:

EVRPC_MAKE_REQUEST()

# Author

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Tue Jan 31 2017 | libevent