1 [LEGACY] Migration from binding V1 to binding V2
2 =======================================
4 > LEGACY!!! IT IS NOT EXPECTED THAT YOU STILL NEED THIS GUIDE.
6 > THIS GUIDE WILL BE REMOVED IN A NEAR FUTURE
9 The ***binding*** interface evolved from version 1 to version 2
10 for the following reasons:
12 - integration of the security requirements within the bindings
13 - simplification of the API (after developer feedbacks)
14 - removal of obscure features, cleanup
16 The ***binder*** can run ***bindings*** v1 and/or v2 in any combination.
17 Thus moving from v1 to v2 is not enforced, there is no real need.
19 More, it is possible to write a dual ***binding***:
21 - a ***binding*** that implements the version 1 and the version 2.
23 However, IT IS HIGHLY RECOMMENDED TO SWITCH TO ONLY VERSION 2:
25 - any new development SHOULD start using ***binding*** V2
26 - existing ***bindings*** SHOULD migrate to the version 2
28 This guide covers the migration of bindings from version 1 to version 2.
30 It also explains some of the rationale taken when migrating from version 1 to version 2.
32 In the future, if ***binding*** api evolves to fresh versions (3, 4, ...)
33 it might be necessarily to write bindings implementing more than
37 - a ***binding*** being v2 AND v3 will resolve the issue of running on older and newer version of AGL.
39 This should always be possible even if more complicated.
41 Important things to known when migrating
42 ----------------------------------------
44 One of the most important change when migrating from v1 to v2 is
45 that many functions use an hidden *common* variable.
46 This affects the functions of the following classes:
48 - functions of class **daemon**:
49 - functions starting with **afb_daemon_...**
50 - functions for logging: **ERROR**, **WARNING**, **NOTICE**, **INFO**, **DEBUG**
51 - functions of class **service**:
52 - functions starting with **afb_service_...**
54 - the register function (that is removed)
55 - the service init function
56 - the onevent function
58 For these functions, the first parameter is now implicit.
61 For ***binding*** v1 you had to write:
64 afb_daemon_broadcast_event(afbitf->daemon, reason, description);
67 For ***binding*** v2, you simply write:
70 afb_daemon_broadcast_event(reason, description);
73 This simplification is possible because the header files included for the bindings
74 now provide a common variable for storing the **daemon** and **service** data.
76 As a programmer, you shouldn't care much about that hidden variable.
77 It simplifies the job, that's all and that is the reason of the change.
79 An other important difference is between the version 1 and the version 2 is
80 on how the ***binding***'s **API** is documented.
81 The version 2 emphasis the **OpenAPI v3** description of the **API**.
82 For this reason, to avoid duplication of descriptions, only one description is expected:
84 - The **OpenAPI** one.
86 Task list for the migration
87 ---------------------------
91 1. Enforce use of binding v2 by setting **AFB_BINDING_VERSION**
92 1. Rewrite the main structure and the list of exported verbs
93 1. Adapt the init and callback functions
94 1. Removes the first parameter of functions of classes **daemon** and **service**
95 1. Consider where to emit logs for requests
96 1. Take care of store/unstore changes
97 1. Consider use of synchronous (sub)call requests
98 1. Optionally, removes explicit struct
100 The remaining chapters explain these task with more details.
102 Enforce use of binding v2 by setting AFB_BINDING_VERSION
103 --------------------------------------------------------
105 By defining **AFB_BINDING_VERSION** to **2** you switch to version 2.
106 This is done as below.
109 #define AFB_BINDING_VERSION 2
110 #include <afb/afb-binding.h>
113 After that you will get many errors when compiling.
115 Rewrite the main structures and the list of exported verbs
116 ---------------------------------------------------------
118 The structures describing the ***binding** changed from version 1 to version 2.
120 The structure for describing verbs changed to include security
126 struct afb_verb_desc_v1
128 const char *name; /* name of the verb */
129 enum afb_session_flags_v1 session; /* authorization and session requirements of the verb */
130 void (*callback)(struct afb_req req); /* callback function implementing the verb */
131 const char *info; /* textual description of the verb */
135 In version 2 it becomes:
140 const char *verb; /* name of the verb */
141 void (*callback)(struct afb_req req); /* callback function implementing the verb */
142 const struct afb_auth *auth; /* required authorization */
143 uint32_t session; /* authorization and session requirements of the verb */
148 The migration of instances of that structure requires the following actions:
150 - rename field **name** to **verb**
151 - remove field **info**
152 - adapt field **session** if needed
153 - set field **auth** to NULL
158 { .name= "new", .session= AFB_SESSION_NONE, .callback= new, .info= "Starts a new game" }
164 { .verb = "new", .session = AFB_SESSION_NONE, .callback = new, .auth = NULL }
167 The field **auth** can be set to a value describing the requested
170 The main describing structure also changed.
175 struct afb_binding_desc_v1
177 const char *info; /* textual information about the binding */
178 const char *prefix; /* required prefix name for the binding */
179 const struct afb_verb_desc_v1 *verbs; /* array of descriptions of verbs terminated by a NULL name */
183 In version 2 it becomes:
186 struct afb_binding_v2
188 const char *api; /* api name for the binding */
189 const char *specification; /* textual specification of the binding */
190 const struct afb_verb_v2 *verbs; /* array of descriptions of verbs terminated by a NULL name */
191 int (*preinit)(); /* callback at load of the binding */
192 int (*init)(); /* callback for starting the service */
193 void (*onevent)(const char *event, struct json_object *object); /* callback for handling events */
194 unsigned noconcurrency: 1; /* avoids concurrent requests to verbs */
198 The migration of instances of that structure requires the following actions:
200 - declare, explore, name the structure as ```const struct afb_binding_v2 afbBindingV2```
201 - rename the field **prefix** to **api**
202 - remove the field **info**
203 - setup the fields **preinit**, **init**, **onevent** according to the next section
204 - set the field **noconcurrency** to the right value:
205 - to 1 if you want to avoid concurrent calls to verbs.
206 - to 0 if you allow concurrent calls to verbs.
211 static const struct afb_binding plugin_desc = {
212 .type = AFB_BINDING_VERSION_1,
214 .info = "Minimal Hello World Sample",
223 const struct afb_binding_v2 afbBindingV2 = {
225 .specification = NULL,
232 The **binder** now relies only on the exported names
233 to deduce the type of the binding.
234 This make the main structure more simple.
236 Adapt the init and callback functions
237 -------------------------------------
239 The ***bindings*** version 1 defined 3 exported functions:
241 - **afbBindingV1Register**
242 - **afbBindingV1ServiceInit**
243 - **afbBindingV1ServiceEvent**
245 These function should not be exported any more and there definition changed.
247 The function **afbBindingV1Register** is no more used to describe the binding.
248 When a binding has to take actions when it is loaded, it must set the field
249 **preinit** of the structure **afbBindingV2**.
250 This field, this preinit, might be used to check features at load.
251 When it returns a negative number, the ***binder*** stops before initializing any ***binding***.
253 The function **afbBindingV1ServiceInit** is replaced by the field **init**
254 of the structure **afbBindingV2**.
255 The init function should return 0 in case of success or a negative error code
257 It is called during initialization of services.
259 The function **afbBindingV1ServiceEvent**is replaced by the field **onevent**
260 of the structure **afbBindingV2**.
262 The two functions **afbBindingV1Register** and **afbBindingV1ServiceInit**,
263 were taking as parameter the ***binder*** interface and the service interface respectively.
264 These interfaces are now managed hiddenly for the **binding** by the **binder**.
265 So the variable that ***bindings*** version used to store the ***binder*** interface
266 and the service interface are no more needed and can be removed.
271 const struct afb_binding_interface *interface;
272 struct afb_service service;
274 static const struct afb_binding plugin_desc = {
275 .type = AFB_BINDING_VERSION_1,
277 .info = "Minimal Hello World Sample",
283 const struct afb_binding *afbBindingV1Register (const struct afb_binding_interface *itf)
286 NOTICE(interface, "binding register");
290 int afbBindingV1ServiceInit(struct afb_service svc)
293 NOTICE(interface, "binding init");
297 void afbBindingV1ServiceEvent(const char *event, struct json_object *object)
299 NOTICE(interface, "onevent %s", event);
308 AFB_NOTICE("binding preinit (was register)");
314 AFB_NOTICE("binding init");
318 static void onevent(const char *event, struct json_object *object)
320 AFB_NOTICE("onevent %s", event);
323 const struct afb_binding_v2 afbBindingV2 = {
325 .specification = NULL,
333 The two functions **afbBindingV1Register** and **afbBindingV1ServiceInit**,
334 were taking as parameter the ***binder*** interface and the service interface respectively.
335 These interfaces are now managed hiddenly for the **binding** by the **binder**.
336 So the variable that ***bindings*** version used to store the ***binder*** interface
337 and the service interface are no more needed and can be removed.
339 On the above example the following lines were removed:
342 const struct afb_binding_interface *interface;
343 struct afb_service service;
350 Removes the first parameter of functions of classes **daemon** and **service**
351 ------------------------------------------------------------------------------
353 As explained before, many functions loose there first
354 arguments, this are the functions of the following classes:
356 - functions of class **daemon**:
357 - functions starting with **afb_daemon_...**
358 - functions for logging: **ERROR**, **WARNING**, **NOTICE**, **INFO**, **DEBUG**
359 - functions of class **service**:
360 - functions starting with **afb_service_...**
361 - callback functions:
362 - the register function (that is removed)
363 - the service init function
364 - the onevent function
366 For these functions, the first parameter is now implicit.
371 afb_daemon_broadcast_event(afbitf->daemon, reason, description);
377 afb_daemon_broadcast_event(reason, description);
380 Also, to avoid possible conflicts, we introduced prefixed logging functions:
389 have now a prefixed version:
397 It is now recommended to use the prefixed version.
402 NOTICE(interface, "hello plugin comes to live");
408 NOTICE("hello plugin comes to live");
414 AFB_NOTICE("hello plugin comes to live");
417 To remove definition of the un-prefixed versions of logging macros:
427 - **AFB_BINDING_PRAGMA_NO_VERBOSE_UNPREFIX**
429 before to include **afb/afb-binding.h**.
432 #define AFB_BINDING_PRAGMA_NO_VERBOSE_UNPREFIX
433 #define AFB_BINDING_VERSION 2
434 #include <afb/afb-binding.h>
437 Consider where to emit logs for requests
438 ----------------------------------------
440 The ***bindings*** v2 now allows to emit log messages associated to ***requests***.
441 This feature is valuable when debugging because it allows to return
442 side information associated to a ***request***.
444 The defined macros for logging to requests are:
447 - **AFB_REQ_WARNING**
452 We encourage the use of these new logging facilities everywhere it makes sense.
457 INFO(afbitf, "method 'new' called for boardid %d", board->id);
463 AFB_REQ_INFO(req, "method 'new' called for boardid %d", board->id);
466 Take care of store/unstore change
467 ---------------------------------
469 For efficiency, the version 2 redefined how storing/un-storing of
471 Storing request is needed for asynchronous handling of requests.
473 For ***bindings*** version, the signature of the functions were:
476 struct afb_req *afb_req_store(struct afb_req req);
477 struct afb_req afb_req_unstore(struct afb_req *req);
480 For version 2 it becomes
483 struct afb_stored_req *afb_req_store(struct afb_req req);
484 struct afb_req afb_req_unstore(struct afb_stored_req *sreq);
487 Where the structure ```struct afb_stored_req``` is opaque.
489 It should require few code change.
491 Also check the following chapter that explain that asynchronous (sub)calls
492 can be replaced by synchronous one, avoiding the need to store/unstore
495 Consider use of synchronous (sub)call requests
496 ----------------------------------------------
498 ***Bindings*** can emit requests for themselves (calls) or for
499 their clients (subcalls).
500 With ***bindings*** version 2 comes also synchronous requests for both cases.
502 So when migrating to bindings version 2, a developer can consider
503 to replace the asynchronous requests (with asynchronous call back)
506 See functions ***afb_service_call_sync*** and ***afb_req_subcall_sync***.
508 Optionally, removes explicit struct
509 -----------------------------------
511 The new definitions now includes **typedefs** for common
512 structures, as shown on below sample:
515 typedef struct afb_daemon afb_daemon;
516 typedef struct afb_event afb_event;
517 typedef struct afb_arg afb_arg;
518 typedef struct afb_req afb_req;
519 typedef struct afb_service afb_service;
522 So you can remove the keyword **struct** if it bores you.
527 static void verb(struct afb_req req)
536 static void verb(afb_req req)
545 The first ***binding*** that migrated from v1 to v2 was the sample **HelloWorld**.
546 Here is shown the differences between the version 1 and the version 2.
549 diff --git a/bindings/samples/HelloWorld.c b/bindings/samples/HelloWorld.c
550 index c6fa779..505aee3 100644
551 --- a/bindings/samples/HelloWorld.c
552 +++ b/bindings/samples/HelloWorld.c
555 #include <json-c/json.h>
557 +#define AFB_BINDING_VERSION 2
558 #include <afb/afb-binding.h>
560 -const struct afb_binding_interface *interface;
561 static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
564 @@ -79,7 +80,7 @@ static int event_add(const char *tag, const char *name)
568 - e->event = afb_daemon_make_event(interface->daemon, name);
569 + e->event = afb_daemon_make_event(name);
570 if (!e->event.closure) { free(e); return -1; }
573 @@ -140,7 +141,7 @@ static void pingBug (struct afb_req request)
574 static void pingEvent(struct afb_req request)
576 json_object *query = afb_req_json(request);
577 - afb_daemon_broadcast_event(interface->daemon, "event", json_object_get(query));
578 + afb_daemon_broadcast_event("event", json_object_get(query));
579 ping(request, json_object_get(query), "event");
582 @@ -288,38 +289,43 @@ static void exitnow (struct afb_req request)
586 +static int preinit()
588 + AFB_NOTICE("hello binding comes to live");
594 + AFB_NOTICE("hello binding starting");
598 // NOTE: this sample does not use session to keep test a basic as possible
599 // in real application most APIs should be protected with AFB_SESSION_CHECK
600 -static const struct afb_verb_desc_v1 verbs[]= {
601 - {"ping" , AFB_SESSION_NONE, pingSample , "Ping Application Framework"},
602 - {"pingfail" , AFB_SESSION_NONE, pingFail , "Fails"},
603 - {"pingnull" , AFB_SESSION_NONE, pingNull , "Return NULL"},
604 - {"pingbug" , AFB_SESSION_NONE, pingBug , "Do a Memory Violation"},
605 - {"pingJson" , AFB_SESSION_NONE, pingJson , "Return a JSON object"},
606 - {"pingevent", AFB_SESSION_NONE, pingEvent , "Send an event"},
607 - {"subcall", AFB_SESSION_NONE, subcall , "Call api/verb(args)"},
608 - {"subcallsync", AFB_SESSION_NONE, subcallsync , "Call api/verb(args)"},
609 - {"eventadd", AFB_SESSION_NONE, eventadd , "adds the event of 'name' for the 'tag'"},
610 - {"eventdel", AFB_SESSION_NONE, eventdel , "deletes the event of 'tag'"},
611 - {"eventsub", AFB_SESSION_NONE, eventsub , "subscribes to the event of 'tag'"},
612 - {"eventunsub",AFB_SESSION_NONE, eventunsub , "unsubscribes to the event of 'tag'"},
613 - {"eventpush", AFB_SESSION_NONE, eventpush , "pushs the event of 'tag' with the 'data'"},
614 - {"exit", AFB_SESSION_NONE, exitnow , "exits from afb-daemon"},
616 +static const struct afb_verb_v2 verbs[]= {
617 + { "ping" , pingSample , NULL, AFB_SESSION_NONE },
618 + { "pingfail" , pingFail , NULL, AFB_SESSION_NONE },
619 + { "pingnull" , pingNull , NULL, AFB_SESSION_NONE },
620 + { "pingbug" , pingBug , NULL, AFB_SESSION_NONE },
621 + { "pingJson" , pingJson , NULL, AFB_SESSION_NONE },
622 + { "pingevent", pingEvent , NULL, AFB_SESSION_NONE },
623 + { "subcall", subcall , NULL, AFB_SESSION_NONE },
624 + { "subcallsync", subcallsync, NULL, AFB_SESSION_NONE },
625 + { "eventadd", eventadd , NULL, AFB_SESSION_NONE },
626 + { "eventdel", eventdel , NULL, AFB_SESSION_NONE },
627 + { "eventsub", eventsub , NULL, AFB_SESSION_NONE },
628 + { "eventunsub", eventunsub , NULL, AFB_SESSION_NONE },
629 + { "eventpush", eventpush , NULL, AFB_SESSION_NONE },
630 + { "exit", exitnow , NULL, AFB_SESSION_NONE },
634 -static const struct afb_binding plugin_desc = {
635 - .type = AFB_BINDING_VERSION_1,
637 - .info = "Minimal Hello World Sample",
641 +const struct afb_binding_v2 afbBindingV2 = {
643 + .specification = NULL,
645 + .preinit = preinit,
649 -const struct afb_binding *afbBindingV1Register (const struct afb_binding_interface *itf)
652 - NOTICE(interface, "hello plugin comes to live");
653 - return &plugin_desc;