1 Migration from binding V1 to binding V2
2 =======================================
4 The ***binding*** interface evolved from version 1 to version 2
5 for the following reasons:
7 - integration of the security requirements within the bindings
8 - simplification of the API (after developer feedbacks)
9 - removal of obscure features, cleanup
11 The ***binder*** can run ***bindings*** v1 and/or v2 in any combination.
12 Thus moving from v1 to v2 is not enforced, there is no real need.
14 More, it is possible to write a dual ***binding***:
16 - a ***binding*** that implements the version 1 and the version 2.
18 However, IT IS HIGHLY RECOMMENDED TO SWITCH TO ONLY VERSION 2:
20 - any new development SHOULD start using ***binding*** V2
21 - existing ***bindings*** SHOULD migrate to the version 2
23 This guide covers the migration of bindings from version 1 to version 2.
25 It also explains some of the rationale taken when migrating from version 1 to version 2.
27 In the future, if ***binding*** api evolves to fresh versions (3, 4, ...)
28 it might be necessarily to write bindings implementing more than
32 - a ***binding*** being v2 AND v3 will resolve the issue of running on older and newer version of AGL.
34 This should always be possible even if more complicated.
36 Important things to known when migrating
37 ----------------------------------------
39 One of the most important change when migrating from v1 to v2 is
40 that many functions use an hidden *common* variable.
41 This affects the functions of the following classes:
43 - functions of class **daemon**:
44 - functions starting with **afb_daemon_...**
45 - functions for logging: **ERROR**, **WARNING**, **NOTICE**, **INFO**, **DEBUG**
46 - functions of class **service**:
47 - functions starting with **afb_service_...**
49 - the register function (that is removed)
50 - the service init function
51 - the onevent function
53 For these functions, the first parameter is now implicit.
56 For ***binding*** v1 you had to write:
59 afb_daemon_broadcast_event(afbitf->daemon, reason, description);
62 For ***binding*** v2, you simply write:
65 afb_daemon_broadcast_event(reason, description);
68 This simplification is possible because the header files included for the bindings
69 now provide a common variable for storing the **daemon** and **service** data.
71 As a programmer, you shouldn't care much about that hidden variable.
72 It simplifies the job, that's all and that is the reason of the change.
74 An other important difference is between the version 1 and the version 2 is
75 on how the ***binding***'s **API** is documented.
76 The version 2 emphasis the **OpenAPI v3** description of the **API**.
77 For this reason, to avoid duplication of descriptions, only one description is expected:
79 - The **OpenAPI** one.
81 Task list for the migration
82 ---------------------------
86 1. Enforce use of binding v2 by setting **AFB_BINDING_VERSION**
87 1. Rewrite the main structure and the list of exported verbs
88 1. Adapt the init and callback functions
89 1. Removes the first parameter of functions of classes **daemon** and **service**
90 1. Consider where to emit logs for requests
91 1. Take care of store/unstore changes
92 1. Consider use of synchronous (sub)call requests
93 1. Optionally, removes explicit struct
95 The remaining chapters explain these task with more details.
97 Enforce use of binding v2 by setting AFB_BINDING_VERSION
98 --------------------------------------------------------
100 By defining **AFB_BINDING_VERSION** to **2** you switch to version 2.
101 This is done as below.
104 #define AFB_BINDING_VERSION 2
105 #include <afb/afb-binding.h>
108 After that you will get many errors when compiling.
110 Rewrite the main structures and the list of exported verbs
111 ---------------------------------------------------------
113 The structures describing the ***binding** changed from version 1 to version 2.
115 The structure for describing verbs changed to include security
121 struct afb_verb_desc_v1
123 const char *name; /* name of the verb */
124 enum afb_session_flags_v1 session; /* authorization and session requirements of the verb */
125 void (*callback)(struct afb_req req); /* callback function implementing the verb */
126 const char *info; /* textual description of the verb */
130 In version 2 it becomes:
135 const char *verb; /* name of the verb */
136 void (*callback)(struct afb_req req); /* callback function implementing the verb */
137 const struct afb_auth *auth; /* required authorization */
138 uint32_t session; /* authorization and session requirements of the verb */
143 The migration of instances of that structure requires the following actions:
145 - rename field **name** to **verb**
146 - remove field **info**
147 - adapt field **session** if needed
148 - set field **auth** to NULL
153 { .name= "new", .session= AFB_SESSION_NONE, .callback= new, .info= "Starts a new game" }
159 { .verb = "new", .session = AFB_SESSION_NONE, .callback = new, .auth = NULL }
162 The field **auth** can be set to a value describing the requested
165 The main describing structure also changed.
170 struct afb_binding_desc_v1
172 const char *info; /* textual information about the binding */
173 const char *prefix; /* required prefix name for the binding */
174 const struct afb_verb_desc_v1 *verbs; /* array of descriptions of verbs terminated by a NULL name */
178 In version 2 it becomes:
181 struct afb_binding_v2
183 const char *api; /* api name for the binding */
184 const char *specification; /* textual specification of the binding */
185 const struct afb_verb_v2 *verbs; /* array of descriptions of verbs terminated by a NULL name */
186 int (*preinit)(); /* callback at load of the binding */
187 int (*init)(); /* callback for starting the service */
188 void (*onevent)(const char *event, struct json_object *object); /* callback for handling events */
189 unsigned noconcurrency: 1; /* avoids concurrent requests to verbs */
193 The migration of instances of that structure requires the following actions:
195 - declare, explore, name the structure as ```const struct afb_binding_v2 afbBindingV2```
196 - rename the field **prefix** to **api**
197 - remove the field **info**
198 - setup the fields **preinit**, **init**, **onevent** according to the next section
199 - set the field **noconcurrency** to the right value:
200 - to 1 if you want to avoid concurrent calls to verbs.
201 - to 0 if you allow concurrent calls to verbs.
206 static const struct afb_binding plugin_desc = {
207 .type = AFB_BINDING_VERSION_1,
209 .info = "Minimal Hello World Sample",
218 const struct afb_binding_v2 afbBindingV2 = {
220 .specification = NULL,
227 The **binder** now relies only on the exported names
228 to deduce the type of the binding.
229 This make the main structure more simple.
231 Adapt the init and callback functions
232 -------------------------------------
234 The ***bindings*** version 1 defined 3 exported functions:
236 - **afbBindingV1Register**
237 - **afbBindingV1ServiceInit**
238 - **afbBindingV1ServiceEvent**
240 These function should not be exported any more and there definition changed.
242 The function **afbBindingV1Register** is no more used to describe the binding.
243 When a binding has to take actions when it is loaded, it must set the field
244 **preinit** of the structure **afbBindingV2**.
245 This field, this preinit, might be used to check features at load.
246 When it returns a negative number, the ***binder*** stops before initializing any ***binding***.
248 The function **afbBindingV1ServiceInit** is replaced by the field **init**
249 of the structure **afbBindingV2**.
250 The init function should return 0 in case of success or a negative error code
252 It is called during initialization of services.
254 The function **afbBindingV1ServiceEvent**is replaced by the field **onevent**
255 of the structure **afbBindingV2**.
257 The two functions **afbBindingV1Register** and **afbBindingV1ServiceInit**,
258 were taking as parameter the ***binder*** interface and the service interface respectively.
259 These interfaces are now managed hiddenly for the **binding** by the **binder**.
260 So the variable that ***bindings*** version used to store the ***binder*** interface
261 and the service interface are no more needed and can be removed.
266 const struct afb_binding_interface *interface;
267 struct afb_service service;
269 static const struct afb_binding plugin_desc = {
270 .type = AFB_BINDING_VERSION_1,
272 .info = "Minimal Hello World Sample",
278 const struct afb_binding *afbBindingV1Register (const struct afb_binding_interface *itf)
281 NOTICE(interface, "binding register");
285 int afbBindingV1ServiceInit(struct afb_service svc)
288 NOTICE(interface, "binding init");
292 void afbBindingV1ServiceEvent(const char *event, struct json_object *object)
294 NOTICE(interface, "onevent %s", event);
303 AFB_NOTICE("binding preinit (was register)");
309 AFB_NOTICE("binding init");
313 static void onevent(const char *event, struct json_object *object)
315 AFB_NOTICE("onevent %s", event);
318 const struct afb_binding_v2 afbBindingV2 = {
320 .specification = NULL,
328 The two functions **afbBindingV1Register** and **afbBindingV1ServiceInit**,
329 were taking as parameter the ***binder*** interface and the service interface respectively.
330 These interfaces are now managed hiddenly for the **binding** by the **binder**.
331 So the variable that ***bindings*** version used to store the ***binder*** interface
332 and the service interface are no more needed and can be removed.
334 On the above example the following lines were removed:
337 const struct afb_binding_interface *interface;
338 struct afb_service service;
345 Removes the first parameter of functions of classes **daemon** and **service**
346 ------------------------------------------------------------------------------
348 As explained before, many functions loose there first
349 arguments, this are the functions of the following classes:
351 - functions of class **daemon**:
352 - functions starting with **afb_daemon_...**
353 - functions for logging: **ERROR**, **WARNING**, **NOTICE**, **INFO**, **DEBUG**
354 - functions of class **service**:
355 - functions starting with **afb_service_...**
356 - callback functions:
357 - the register function (that is removed)
358 - the service init function
359 - the onevent function
361 For these functions, the first parameter is now implicit.
366 afb_daemon_broadcast_event(afbitf->daemon, reason, description);
372 afb_daemon_broadcast_event(reason, description);
375 Also, to avoid possible conflicts, we introduced prefixed logging functions:
384 have now a prefixed version:
392 It is now recommended to use the prefixed version.
397 NOTICE(interface, "hello plugin comes to live");
403 NOTICE("hello plugin comes to live");
409 AFB_NOTICE("hello plugin comes to live");
412 To remove definition of the un-prefixed versions of logging macros:
422 - **AFB_BINDING_PRAGMA_NO_VERBOSE_UNPREFIX**
424 before to include **afb/afb-binding.h**.
427 #define AFB_BINDING_PRAGMA_NO_VERBOSE_UNPREFIX
428 #define AFB_BINDING_VERSION 2
429 #include <afb/afb-binding.h>
432 Consider where to emit logs for requests
433 ----------------------------------------
435 The ***bindings*** v2 now allows to emit log messages associated to ***requests***.
436 This feature is valuable when debugging because it allows to return
437 side information associated to a ***request***.
439 The defined macros for logging to requests are:
442 - **AFB_REQ_WARNING**
447 We encourage the use of these new logging facilities everywhere it makes sense.
452 INFO(afbitf, "method 'new' called for boardid %d", board->id);
458 AFB_REQ_INFO(req, "method 'new' called for boardid %d", board->id);
461 Take care of store/unstore change
462 ---------------------------------
464 For efficiency, the version 2 redefined how storing/un-storing of
466 Storing request is needed for asynchronous handling of requests.
468 For ***bindings*** version, the signature of the functions were:
471 struct afb_req *afb_req_store(struct afb_req req);
472 struct afb_req afb_req_unstore(struct afb_req *req);
475 For version 2 it becomes
478 struct afb_stored_req *afb_req_store(struct afb_req req);
479 struct afb_req afb_req_unstore(struct afb_stored_req *sreq);
482 Where the structure ```struct afb_stored_req``` is opaque.
484 It should require few code change.
486 Also check the following chapter that explain that asynchronous (sub)calls
487 can be replaced by synchronous one, avoiding the need to store/unstore
490 Consider use of synchronous (sub)call requests
491 ----------------------------------------------
493 ***Bindings*** can emit requests for themselves (calls) or for
494 their clients (subcalls).
495 With ***bindings*** version 2 comes also synchronous requests for both cases.
497 So when migrating to bindings version 2, a developer can consider
498 to replace the asynchronous requests (with asynchronous call back)
501 See functions ***afb_service_call_sync*** and ***afb_req_subcall_sync***.
503 Optionally, removes explicit struct
504 -----------------------------------
506 The new definitions now includes **typedefs** for common
507 structures, as shown on below sample:
510 typedef struct afb_daemon afb_daemon;
511 typedef struct afb_event afb_event;
512 typedef struct afb_arg afb_arg;
513 typedef struct afb_req afb_req;
514 typedef struct afb_service afb_service;
517 So you can remove the keyword **struct** if it bores you.
522 static void verb(struct afb_req req)
531 static void verb(afb_req req)
540 The first ***binding*** that migrated from v1 to v2 was the sample **HelloWorld**.
541 Here is shown the differences between the version 1 and the version 2.
544 diff --git a/bindings/samples/HelloWorld.c b/bindings/samples/HelloWorld.c
545 index c6fa779..505aee3 100644
546 --- a/bindings/samples/HelloWorld.c
547 +++ b/bindings/samples/HelloWorld.c
550 #include <json-c/json.h>
552 +#define AFB_BINDING_VERSION 2
553 #include <afb/afb-binding.h>
555 -const struct afb_binding_interface *interface;
556 static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
559 @@ -79,7 +80,7 @@ static int event_add(const char *tag, const char *name)
563 - e->event = afb_daemon_make_event(interface->daemon, name);
564 + e->event = afb_daemon_make_event(name);
565 if (!e->event.closure) { free(e); return -1; }
568 @@ -140,7 +141,7 @@ static void pingBug (struct afb_req request)
569 static void pingEvent(struct afb_req request)
571 json_object *query = afb_req_json(request);
572 - afb_daemon_broadcast_event(interface->daemon, "event", json_object_get(query));
573 + afb_daemon_broadcast_event("event", json_object_get(query));
574 ping(request, json_object_get(query), "event");
577 @@ -288,38 +289,43 @@ static void exitnow (struct afb_req request)
581 +static int preinit()
583 + AFB_NOTICE("hello binding comes to live");
589 + AFB_NOTICE("hello binding starting");
593 // NOTE: this sample does not use session to keep test a basic as possible
594 // in real application most APIs should be protected with AFB_SESSION_CHECK
595 -static const struct afb_verb_desc_v1 verbs[]= {
596 - {"ping" , AFB_SESSION_NONE, pingSample , "Ping Application Framework"},
597 - {"pingfail" , AFB_SESSION_NONE, pingFail , "Fails"},
598 - {"pingnull" , AFB_SESSION_NONE, pingNull , "Return NULL"},
599 - {"pingbug" , AFB_SESSION_NONE, pingBug , "Do a Memory Violation"},
600 - {"pingJson" , AFB_SESSION_NONE, pingJson , "Return a JSON object"},
601 - {"pingevent", AFB_SESSION_NONE, pingEvent , "Send an event"},
602 - {"subcall", AFB_SESSION_NONE, subcall , "Call api/verb(args)"},
603 - {"subcallsync", AFB_SESSION_NONE, subcallsync , "Call api/verb(args)"},
604 - {"eventadd", AFB_SESSION_NONE, eventadd , "adds the event of 'name' for the 'tag'"},
605 - {"eventdel", AFB_SESSION_NONE, eventdel , "deletes the event of 'tag'"},
606 - {"eventsub", AFB_SESSION_NONE, eventsub , "subscribes to the event of 'tag'"},
607 - {"eventunsub",AFB_SESSION_NONE, eventunsub , "unsubscribes to the event of 'tag'"},
608 - {"eventpush", AFB_SESSION_NONE, eventpush , "pushs the event of 'tag' with the 'data'"},
609 - {"exit", AFB_SESSION_NONE, exitnow , "exits from afb-daemon"},
611 +static const struct afb_verb_v2 verbs[]= {
612 + { "ping" , pingSample , NULL, AFB_SESSION_NONE },
613 + { "pingfail" , pingFail , NULL, AFB_SESSION_NONE },
614 + { "pingnull" , pingNull , NULL, AFB_SESSION_NONE },
615 + { "pingbug" , pingBug , NULL, AFB_SESSION_NONE },
616 + { "pingJson" , pingJson , NULL, AFB_SESSION_NONE },
617 + { "pingevent", pingEvent , NULL, AFB_SESSION_NONE },
618 + { "subcall", subcall , NULL, AFB_SESSION_NONE },
619 + { "subcallsync", subcallsync, NULL, AFB_SESSION_NONE },
620 + { "eventadd", eventadd , NULL, AFB_SESSION_NONE },
621 + { "eventdel", eventdel , NULL, AFB_SESSION_NONE },
622 + { "eventsub", eventsub , NULL, AFB_SESSION_NONE },
623 + { "eventunsub", eventunsub , NULL, AFB_SESSION_NONE },
624 + { "eventpush", eventpush , NULL, AFB_SESSION_NONE },
625 + { "exit", exitnow , NULL, AFB_SESSION_NONE },
629 -static const struct afb_binding plugin_desc = {
630 - .type = AFB_BINDING_VERSION_1,
632 - .info = "Minimal Hello World Sample",
636 +const struct afb_binding_v2 afbBindingV2 = {
638 + .specification = NULL,
640 + .preinit = preinit,
644 -const struct afb_binding *afbBindingV1Register (const struct afb_binding_interface *itf)
647 - NOTICE(interface, "hello plugin comes to live");
648 - return &plugin_desc;