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diff --git a/docs/afb-migration-v1-to-v2.md b/docs/afb-migration-v1-to-v2.md new file mode 100644 index 00000000..487c259d --- /dev/null +++ b/docs/afb-migration-v1-to-v2.md @@ -0,0 +1,611 @@ +Migration from binding V1 to binding V2 +======================================= + +The ***binding*** interface evolved from version 1 to version 2 +for the following reasons: + + - integration of the security requirements within the bindings + - simplification of the API (after developer feedbacks) + - removal of obscur features, cleanup + +The ***binder*** can run ***bindings*** v1 and/or v2 in any combination. +Thus moving from v1 to v2 is not enforced. There is no real need. + +More, it is possible to write a dual ***binding***: a ***binding*** that +implements the version 1 AND the version 2. + +However, IT IS HIGHLY RECOMMANDED TO SWITCH TO ONLY VERSION 2: + + - any new developement SHOULD start using ***binding*** V2 + - existing ***bindings*** SHOULD migrate to the version 2 + +This guide covers the migration of bindings from version 1 to version 2. + +It also explains some of the rationale taken when migrating from version 1 to version 2. + +In the future, if ***binding*** api evolves to fresh versions (3, 4, ...) +it might be necessarily to write bindings implementing more than +just one version. For example, a ***binding*** being v2 AND v3 will resolve +the issue of running on older AND newer version of AGL. This should always +be possible even if more complicated. + +Important things to known when migrating +---------------------------------------- + +One of the most important change when migrating from v1 to v2 is +that many functions use an hidden *common* variable. +This affects the functions of the following classes: + + - functions of class **daemon**: + * functions starting with **afb_daemon_...** + * functions for logging: **ERROR**, **WARNING**, **NOTICE**, **INFO**, **DEBUG** + - functions of class **service**: + * functions starting with **afb_service_...** + - callback functions: + * the register function (that is removed) + * the service init function + * the onevent function + +For these functions, the first parameter is now implicit. + +Let takes an example. For ***binding*** v1 you had to write: + +```C + afb_daemon_broadcast_event(afbitf->daemon, reason, description); +``` + +For ***binding*** v2, you simply write: + +```C + afb_daemon_broadcast_event(reason, description); +``` + +This simplification is possible because the header files included for the bindings +now provide a common variable for storing the **daemon** and **service** data. + +As a programmer, you shouldn't care much about that hidden variable. +It simplifies the job, that's all and that is the reason of the change. + +An other important difference is between the version 1 and the version 2 is +on how the ***binding***'s **API** is documented. The version 2 enphasis the +**OpenAPI v3** description of the **API**. For this reason, to avoid +duplication of descriptions, only one description is expected: the **OpenAPI** one. + +Task list for the migration +--------------------------- + +This task list is: + + 1. Enforce use of binding v2 by setting **AFB_BINDING_VERSION** + 2. Rewrite the main structure and the list of exported verbs + 3. Adapt the init and callback functions + 4. Removes the first parameter of functions of classes **daemon** + and **service** + 5. Consider where to emit logs for requests + 6. Take care of store/unstore changes + 7. Consider use of synchronous (sub)call requests + 8. Optionnaly, removes explicit struct + +The remaining chapters explain these task with more details. + +Enforce use of binding v2 by setting AFB_BINDING_VERSION +-------------------------------------------------------- + +By defining **AFB_BINDING_VERSION** to **2** you switch to version 2. +This is done as below. + +```C +#define AFB_BINDING_VERSION 2 +#include <afb/afb-binding.h> +``` + +After that you will get many errors when compiling. + +Rewrite the main structures and the list of exported verbs +--------------------------------------------------------- + +The structures describing the ***binding** changed from version 1 to version 2. + +The structure for describing verbs changed to include security +requirements. In version 1 it was: + +```C +struct afb_verb_desc_v1 +{ + const char *name; /* name of the verb */ + enum afb_session_flags_v1 session; /* authorisation and session requirements of the verb */ + void (*callback)(struct afb_req req); /* callback function implementing the verb */ + const char *info; /* textual description of the verb */ +}; +``` + +In version 2 it becomes: + +```C +struct afb_verb_v2 +{ + const char *verb; /* name of the verb */ + void (*callback)(struct afb_req req); /* callback function implementing the verb */ + const struct afb_auth *auth; /* required authorisation */ + uint32_t session; /* authorisation and session requirements of the verb */ +}; + +``` + +The migration of instances of that structure requires the following actions: + + - rename field **name** to **verb** + - remove field **info** + - adapt field **session** if needed + - set field **auth** to NULL + +Example: + +```C + { .name= "new", .session= AFB_SESSION_NONE, .callback= new, .info= "Starts a new game" } +``` + +Becomes + +```C + { .verb = "new", .session = AFB_SESSION_NONE, .callback = new, .auth = NULL } +``` + +The field **auth** can be set to a value describing the requested +authorisation. + +The main describing structure also changed. In version 1 it was: + +```C +struct afb_binding_desc_v1 +{ + const char *info; /* textual information about the binding */ + const char *prefix; /* required prefix name for the binding */ + const struct afb_verb_desc_v1 *verbs; /* array of descriptions of verbs terminated by a NULL name */ +}; +``` + +In version 2 it becomes: + +```C +struct afb_binding_v2 +{ + const char *api; /* api name for the binding */ + const char *specification; /* textual specification of the binding */ + const struct afb_verb_v2 *verbs; /* array of descriptions of verbs terminated by a NULL name */ + int (*preinit)(); /* callback at load of the binding */ + int (*init)(); /* callback for starting the service */ + void (*onevent)(const char *event, struct json_object *object); /* callback for handling events */ + unsigned noconcurrency: 1; /* avoids concurrent requests to verbs */ +}; +``` + +The migration of instances of that structure requires the following actions: + + - declare, expore, name the structure as ```const struct afb_binding_v2 afbBindingV2``` + - rename the field **prefix** to **api** + - remove the field **info** + - setup the fields **preinit**, **init**, **onevent** accordling to the next section + - set the field **noconcurrency** to the right value: + * to 1 if you want to avoid concurrent calls to verbs. + * to 0 if you allow concurrent calls to verbs. + +Example: + +```C +static const struct afb_binding plugin_desc = { + .type = AFB_BINDING_VERSION_1, + .v1 = { + .info = "Minimal Hello World Sample", + .prefix = "hello", + .verbs = verbs + } +``` +Becomes: + +```C +const struct afb_binding_v2 afbBindingV2 = { + .api = "hello", + .specification = NULL, + .verbs = verbs, + .preinit = preinit, + .init = init +}; +``` + +The **binder** now relies only on the exported names +to deduce the type of the binding. This make the main +structure more simple. + +Adapt the init and callback functions +------------------------------------- + +The ***bindings*** version 1 defined 3 exported functions: + + - **afbBindingV1Register** + - **afbBindingV1ServiceInit** + - **afbBindingV1ServiceEvent** + +These function should not be exported any more and there definition changed. + +The function **afbBindingV1Register** is no more used to describe the binding. +When a binding has to take actions when it is loaded, it must set the field +**preinit** of the structure **afbBindingV2**. This field, this preinit, might +be used to check features at load. When it returns a negative number, the +***binder*** stops before initializing any ***binding***. + +The function **afbBindingV1ServiceInit** is replaced by the field **init** +of the structure **afbBindingV2**. The init function should return 0 in case +of success or a negative error code in case of problem. It is called during +initialisation of services. + +The function **afbBindingV1ServiceEvent**is replaced by the field **onevent** +of the structure **afbBindingV2**. + +The two functions **afbBindingV1Register** and **afbBindingV1ServiceInit**, +were taking as parameter the ***binder*** interface and the service interface respectively. +These interfaces are now managed hiddenly for the **binding** by the **binder**. +So the variable that ***bindings*** version used to store the ***binder*** interface +and the service interface are no more needed and can be removed. + +Example: + +```C +const struct afb_binding_interface *interface; +struct afb_service service; + +static const struct afb_binding plugin_desc = { + .type = AFB_BINDING_VERSION_1, + .v1 = { + .info = "Minimal Hello World Sample", + .prefix = "hello", + .verbs = verbs + } +} + +const struct afb_binding *afbBindingV1Register (const struct afb_binding_interface *itf) +{ + interface = itf; + NOTICE(interface, "binding register"); + return &plugin_desc; +} + +int afbBindingV1ServiceInit(struct afb_service svc) +{ + service = svc; + NOTICE(interface, "binding init"); + return 0; +} + +void afbBindingV1ServiceEvent(const char *event, struct json_object *object) +{ + NOTICE(interface, "onevent %s", event); +} +``` + +Becomes: + +```C +static int preinit() +{ + AFB_NOTICE("binding preinit (was register)"); + return 0; +} + +static int init() +{ + AFB_NOTICE("binding init"); + return 0; +} + +static void onevent(const char *event, struct json_object *object) +{ + AFB_NOTICE("onevent %s", event); +} + +const struct afb_binding_v2 afbBindingV2 = { + .api = "hello", + .specification = NULL, + .verbs = verbs, + .preinit = preinit, + .init = init, + .onevent = onevent +}; +``` + +The two functions **afbBindingV1Register** and **afbBindingV1ServiceInit**, +were taking as parameter the ***binder*** interface and the service interface respectively. +These interfaces are now managed hiddenly for the **binding** by the **binder**. +So the variable that ***bindings*** version used to store the ***binder*** interface +and the service interface are no more needed and can be removed. + +On the above example the folowing lines were removed: +```C +const struct afb_binding_interface *interface; +struct afb_service service; + + interface = itf; + + service = svc; +``` + + + +Removes the first parameter of functions of classes **daemon** and **service** +------------------------------------------------------------------------------ + +As explained before, many functions loose there first +arguments, this are the functions of the following classes: + + - functions of class **daemon**: + * functions starting with **afb_daemon_...** + * functions for logging: **ERROR**, **WARNING**, **NOTICE**, **INFO**, **DEBUG** + - functions of class **service**: + * functions starting with **afb_service_...** + - callback functions: + * the register function (that is removed) + * the service init function + * the onevent function + +For these functions, the first parameter is now implicit. + +Example: + +```C + afb_daemon_broadcast_event(afbitf->daemon, reason, description); +``` + +Becomes: + +```C + afb_daemon_broadcast_event(reason, description); +``` + +Also, to avoid possible conflicts, we introduced prefixed logging functions: +the macros **ERROR**, **WARNING**, **NOTICE**, **INFO**, **DEBUG** have now +a prefixed version: **AFB\_ERROR**, **AFB\_WARNING**, **AFB\_NOTICE**, +**AFB\_INFO**, **AFB\_DEBUG**. It is now recommanded to use the prefixed version. + +Example: + +```C + NOTICE(interface, "hello plugin comes to live"); +``` + +Become: + +```C + NOTICE("hello plugin comes to live"); +``` + +or, better: + +```C + AFB_NOTICE("hello plugin comes to live"); +``` + +To remove definition of the unprefixed versions of logging macros **ERROR**, **WARNING**, +**NOTICE**, **INFO**, **DEBUG** and just define **AFB_BINDING_PRAGMA_NO_VERBOSE_UNPREFIX** +before to include **afb/afb-binding.h**. + +```C +#define AFB_BINDING_PRAGMA_NO_VERBOSE_UNPREFIX +#define AFB_BINDING_VERSION 2 +#include <afb/afb-binding.h> +``` + +Consider where to emit logs for requests +---------------------------------------- + +The ***bindings*** v2 now allows to emit log messages associated to ***requests***. +This feature is valuable when debugging because it allows to return +side informations associated to a ***request***. + +The defined macros for logging to requests are: **AFB_REQ_ERROR**, +**AFB_REQ_WARNING**, **AFB_REQ_NOTICE**, **AFB_REQ_INFO**, **AFB_REQ_DEBUG**. + +We encourage the use of these new logging facilities everywhere it makes sense. + +Example: + +```C + INFO(afbitf, "method 'new' called for boardid %d", board->id); +``` + +Might become: + +```C + AFB_REQ_INFO(req, "method 'new' called for boardid %d", board->id); +``` + +Take care of store/unstore change +--------------------------------- + +For efficiency, the version 2 redefined how storing/unstoring of +requests works. Storing request is needed for asynchronous handling +of requests. + +For ***bindings*** version, the signature of the functions were: + +```C +struct afb_req *afb_req_store(struct afb_req req); +struct afb_req afb_req_unstore(struct afb_req *req); +``` + +For version 2 it becomes + +```C +struct afb_stored_req *afb_req_store(struct afb_req req); +struct afb_req afb_req_unstore(struct afb_stored_req *sreq); +``` + +Where the structure ```struct afb_stored_req``` is opaque. + +It should require few code change. + +Also check the following chapter that explain that asynchronous (sub)calls +can be replaced by synchronous one, avoiding the need to store/unstore +requests. + +Consider use of synchronous (sub)call requests +---------------------------------------------- + +***Bindings*** can emit requests for themselves (calls) or for +their clients (subcalls). With ***bindings*** version 2 comes +also synchronous requests for both cases. + +So when migrating to bindings version 2, a developper can consider +to replace the asynchronous requests (with asynchronous call back) +by synchronous ones. + +See functions ***afb_service_call_sync*** and ***afb_req_subcall_sync***. + +Optionnaly, removes explicit struct +----------------------------------- + +The new definitions now includes **typedefs** for common +structures, as shown on below sample: + +```C +typedef struct afb_daemon afb_daemon; +typedef struct afb_event afb_event; +typedef struct afb_arg afb_arg; +typedef struct afb_req afb_req; +typedef struct afb_service afb_service; +``` + +So you can remove the keyword **struct** if it bores you. + +Example: + +```C +static void verb(struct afb_req req) +{ + ... +} +``` + +Might become: + +```C +static void verb(afb_req req) +{ + ... +} +``` + +Example of migration +-------------------- + +The first ***binding*** that migrated from v1 to v2 was +the sample **HelloWorld**. Here is shown the differences between +the version 1 and the version 2. + +```diff +diff --git a/bindings/samples/HelloWorld.c b/bindings/samples/HelloWorld.c +index c6fa779..505aee3 100644 +--- a/bindings/samples/HelloWorld.c ++++ b/bindings/samples/HelloWorld.c +@@ -21,9 +21,9 @@ + + #include <json-c/json.h> + ++#define AFB_BINDING_VERSION 2 + #include <afb/afb-binding.h> + +-const struct afb_binding_interface *interface; + static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; + + struct event +@@ -79,7 +80,7 @@ static int event_add(const char *tag, const char *name) + strcpy(e->tag, tag); + + /* make the event */ +- e->event = afb_daemon_make_event(interface->daemon, name); ++ e->event = afb_daemon_make_event(name); + if (!e->event.closure) { free(e); return -1; } + + /* link */ +@@ -140,7 +141,7 @@ static void pingBug (struct afb_req request) + static void pingEvent(struct afb_req request) + { + json_object *query = afb_req_json(request); +- afb_daemon_broadcast_event(interface->daemon, "event", json_object_get(query)); ++ afb_daemon_broadcast_event("event", json_object_get(query)); + ping(request, json_object_get(query), "event"); + } + +@@ -288,38 +289,43 @@ static void exitnow (struct afb_req request) + exit(0); + } + ++static int preinit() ++{ ++ AFB_NOTICE("hello binding comes to live"); ++ return 0; ++} ++ ++static int init() ++{ ++ AFB_NOTICE("hello binding starting"); ++ return 0; ++} ++ + // NOTE: this sample does not use session to keep test a basic as possible + // in real application most APIs should be protected with AFB_SESSION_CHECK +-static const struct afb_verb_desc_v1 verbs[]= { +- {"ping" , AFB_SESSION_NONE, pingSample , "Ping Application Framework"}, +- {"pingfail" , AFB_SESSION_NONE, pingFail , "Fails"}, +- {"pingnull" , AFB_SESSION_NONE, pingNull , "Return NULL"}, +- {"pingbug" , AFB_SESSION_NONE, pingBug , "Do a Memory Violation"}, +- {"pingJson" , AFB_SESSION_NONE, pingJson , "Return a JSON object"}, +- {"pingevent", AFB_SESSION_NONE, pingEvent , "Send an event"}, +- {"subcall", AFB_SESSION_NONE, subcall , "Call api/verb(args)"}, +- {"subcallsync", AFB_SESSION_NONE, subcallsync , "Call api/verb(args)"}, +- {"eventadd", AFB_SESSION_NONE, eventadd , "adds the event of 'name' for the 'tag'"}, +- {"eventdel", AFB_SESSION_NONE, eventdel , "deletes the event of 'tag'"}, +- {"eventsub", AFB_SESSION_NONE, eventsub , "subscribes to the event of 'tag'"}, +- {"eventunsub",AFB_SESSION_NONE, eventunsub , "unsubscribes to the event of 'tag'"}, +- {"eventpush", AFB_SESSION_NONE, eventpush , "pushs the event of 'tag' with the 'data'"}, +- {"exit", AFB_SESSION_NONE, exitnow , "exits from afb-daemon"}, +- {NULL} ++static const struct afb_verb_v2 verbs[]= { ++ { "ping" , pingSample , NULL, AFB_SESSION_NONE }, ++ { "pingfail" , pingFail , NULL, AFB_SESSION_NONE }, ++ { "pingnull" , pingNull , NULL, AFB_SESSION_NONE }, ++ { "pingbug" , pingBug , NULL, AFB_SESSION_NONE }, ++ { "pingJson" , pingJson , NULL, AFB_SESSION_NONE }, ++ { "pingevent", pingEvent , NULL, AFB_SESSION_NONE }, ++ { "subcall", subcall , NULL, AFB_SESSION_NONE }, ++ { "subcallsync", subcallsync, NULL, AFB_SESSION_NONE }, ++ { "eventadd", eventadd , NULL, AFB_SESSION_NONE }, ++ { "eventdel", eventdel , NULL, AFB_SESSION_NONE }, ++ { "eventsub", eventsub , NULL, AFB_SESSION_NONE }, ++ { "eventunsub", eventunsub , NULL, AFB_SESSION_NONE }, ++ { "eventpush", eventpush , NULL, AFB_SESSION_NONE }, ++ { "exit", exitnow , NULL, AFB_SESSION_NONE }, ++ { NULL} + }; + +-static const struct afb_binding plugin_desc = { +- .type = AFB_BINDING_VERSION_1, +- .v1 = { +- .info = "Minimal Hello World Sample", +- .prefix = "hello", +- .verbs = verbs +- } ++const struct afb_binding_v2 afbBindingV2 = { ++ .api = "hello", ++ .specification = NULL, ++ .verbs = verbs, ++ .preinit = preinit, ++ .init = init + }; + +-const struct afb_binding *afbBindingV1Register (const struct afb_binding_interface *itf) +-{ +- interface = itf; +- NOTICE(interface, "hello plugin comes to live"); +- return &plugin_desc; +-} +```
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