diff options
Diffstat (limited to 'docs/3_Developer_Guides/2_Application_Framework_Binder/2_How_to_write_a_binding.md')
| -rw-r--r-- | docs/3_Developer_Guides/2_Application_Framework_Binder/2_How_to_write_a_binding.md | 444 |
1 files changed, 444 insertions, 0 deletions
diff --git a/docs/3_Developer_Guides/2_Application_Framework_Binder/2_How_to_write_a_binding.md b/docs/3_Developer_Guides/2_Application_Framework_Binder/2_How_to_write_a_binding.md new file mode 100644 index 0000000..d739167 --- /dev/null +++ b/docs/3_Developer_Guides/2_Application_Framework_Binder/2_How_to_write_a_binding.md @@ -0,0 +1,444 @@ +--- +title: How to write a binding? +--- + +# Overview of the bindings + +The ***binder*** serves files through HTTP protocol and offers developers the capability to offer application API methods through HTTP or +WebSocket protocol. + +The ***bindings*** are used to add **API** to ***binders***. +This part describes how to write a ***binding*** for ***binder*** +or in other words how to add a new **API** to the system. + +This section target developers. + +This section shortly explain how to write a binding +using the C programming language. + +It is convenient to install the ***binder*** on the +desktop used for writing the binding. +It allows for easy debug and test. + +## Nature of a binding + +A ***binding*** is an independent piece of software compiled as a shared +library and dynamically loaded by a ***binder***. +It is intended to provide one **API** (**A**pplication **P**rogramming +**I**nterface). + +The **API** is designated and accessed through its name. +It contains several **verbs** that implement the ***binding*** +functionalities. +Each of these **verbs** is a **method** that +processes requests of applications and sends results. + +The ***binding***'s methods are invoked by HTTP or websocket +requests. + +The **methods** of the ***bindings*** are noted **api/verb** +where **api** is the **API** name of the binding and **verb** is +the **method**'s name within the **API**. +This notation comes from HTTP invocations that rely on URL path terminated +with **api/verb**. + +The name of an **API** can be made of any characters except: + +- the control characters (\u0000 .. \u001f) +- the characters of the set { ' ', '"', '#', '%', '&', + '\'', '/', '?', '`', '\x7f' } + +The names of the **verbs** can be any character. + +The binder makes no distinctions between upper case and lower case +latin letters. +So **API/VERB** matches **Api/Verb** or **api/verb**. + +## Versions of the bindings + +Since introduction of the binder, the way how bindings are written +evolved a little. While changing, attention was made to ensure binary +compatibility between the different versions. + +Actually it exists 3 ways of writing ***bindings***. +You can either write: + +- a binding version 1 (not more supported); +- a binding version 2 (not recommended); +- a binding version 3 (RECOMMENDED). + +A ***binder*** loads and runs any of these version in any combination. +This document explain how to write bindings version 3. + +## Sample binding: tuto-1 + +This is the code of the binding **tuto-1.c**: + +```C + 1 #define AFB_BINDING_VERSION 3 + 2 #include <afb/afb-binding.h> + 3 + 4 void hello(afb_req_t req) + 5 { + 6 AFB_REQ_DEBUG(req, "hello world"); + 7 afb_req_reply(req, NULL, NULL, "hello world"); + 8 } + 9 + 10 const afb_verb_t verbs[] = { + 11 { .verb="hello", .callback=hello }, + 12 { .verb=NULL } + 13 }; + 14 + 15 const afb_binding_t afbBindingExport = { + 16 .api = "tuto-1", + 17 .verbs = verbs + 18 }; +``` + +Compiling: + +```bash +gcc -fPIC -shared tuto-1.c -o tuto-1.so $(pkg-config --cflags-only-I afb-daemon) +``` + +> Note: the variable environment variable PKG_CONFIG_PATH might be necessary +> tuned to get **pkg-config** working properly + +Running: + +```bash +afb-daemon --binding ./tuto-1.so --port 3333 --token '' +``` + +At this point, afb-daemon has started, it loaded the binding tuto-1.so and now +listen at localhost on the port 3333. + +Testing using **curl**: + +```bash +$ curl http://localhost:3333/api/tuto-1/hello +{"jtype":"afb-reply","request":{"status":"success","info":"hello world","uuid":"1e587b54-900b-49ab-9940-46141bc2e1d6"}} +``` + +Testing using **afb-client-demo** (with option -H for +getting a human readable output): + +```bash +$ afb-client-demo -H ws://localhost:3333/api?token=x tuto-1 hello +ON-REPLY 1:tuto-1/hello: OK +{ + "jtype":"afb-reply", + "request":{ + "status":"success", + "info":"hello world", + "uuid":"03a84ad1-458a-4ace-af74-b1da917391b9" + } +} +``` + +This shows basic things: + +- The include to get for creating a binding +- How to declare the API offered by the binding +- How to handle requests made to the binding + +### Getting declarations for the binding + +The lines 1 and 2 show how to get the include file **afb-binding.h**. + +```C + 1 #define AFB_BINDING_VERSION 3 + 2 #include <afb/afb-binding.h> +``` + +You must define the version of ***binding*** that you are using. +This is done line 1 where we define that this is the version 3 (earlier +versions 1 and 2 are deprecated). + +If you don't define it, an error is reported and the compilation aborts. + +To include **afb-binding.h** successfully, the include search path +should be set correctly if needed (not needed only if installed in +/usr/include/afb directory that is the default). + +Setting the include path is easy using **pkg-config**: + +```bash +pkg-config --cflags-only-I afb-daemon +``` + +> Note for **C++** developers: +> +> The ***binder*** currently expose a draft version of **C++** api. +> To get it include the file <**afb/afb-binding**> (without **.h**). + + +### Declaring the API of the binding + +Lines 10 to 18 show the declaration of the ***binding***. + +The ***binder*** knows that this is a ***binding*** because +it finds the exported symbol **afbBindingExport** that is expected to be +a structure of type **afb_binding_t**. + +```C + 10 const afb_verb_t verbs[] = { + 11 { .verb="hello", .callback=hello }, + 12 { .verb=NULL } + 13 }; + 14 + 15 const afb_binding_t afbBindingExport = { + 16 .api = "tuto-1", + 17 .verbs = verbs + 18 }; +``` + +The structure **afbBindingExport** actually tells that: + +- the exported **API** name is **tuto-1** (line 16) +- the array of verbs is the above defined one + +The exported list of verb is specified by an array of structures of +type **afb_verb_t**, each describing a verb, ended with a verb NULL (line 12). + +The only defined verb here (line 11) is named **hello** (field **.verb**) +and the function that handle the related request is **hello** +(field **.callback**). + +### Handling binder's requests + +As shown above this is by default the common include directory where +the AGL stuff is installed. + +```C + 4 void hello(afb_req_t req) + 5 { + 6 AFB_REQ_DEBUG(req, "hello world"); + 7 afb_req_reply(req, NULL, NULL, "hello world"); + 8 } +``` + +When the ***binder*** receives a request for the verb **hello** of +of the api **tuto-1**, it invoke the callback **hello** of the **binding** +with the argument **req** that handles the client request. + +The callback has to treat synchronously or asynchronously the request and +should at the end emit a reply for the request. + +At the line 7, the callback for **tuto-1/hello** replies to the request **req**. +Parameters of the reply are: + + 1. The first parameter is the replied request + 2. The second parameter is a json object (here NULL) + 3. The third parameter is the error string indication (here NULL: no error) + 4. The fourth parameter is an informative string (that can be NULL) that can be used to provide meta data. + +The 3 last parameters are sent back to the client as the reply content. + +<!-- pagebreak --> + +## Sample binding: tuto-2 + +The second tutorial shows many important feature that can +commonly be used when writing a ***binding***: + +- initialization, getting arguments, sending replies, pushing events. + +This is the code of the binding **tuto-2.c**: + +```C + 1 #include <string.h> + 2 #include <json-c/json.h> + 3 + 4 #define AFB_BINDING_VERSION 3 + 5 #include <afb/afb-binding.h> + 6 + 7 afb_event_t event_login, event_logout; + 8 + 9 void login(afb_req_t req) + 10 { + 11 json_object *args, *user, *passwd; + 12 char *usr; + 13 + 14 args = afb_req_json(req); + 15 if (!json_object_object_get_ex(args, "user", &user) + 16 || !json_object_object_get_ex(args, "password", &passwd)) { + 17 AFB_REQ_ERROR(req, "login, bad request: %s", json_object_get_string(args)); + 18 afb_req_reply(req, NULL, "bad-request", NULL); + 19 } else if (afb_req_context_get(req)) { + 20 AFB_REQ_ERROR(req, "login, bad state, logout first"); + 21 afb_req_reply(req, NULL, "bad-state", NULL); + 22 } else if (strcmp(json_object_get_string(passwd), "please")) { + 23 AFB_REQ_ERROR(req, "login, unauthorized: %s", json_object_get_string(args)); + 24 afb_req_reply(req, NULL, "unauthorized", NULL); + 25 } else { + 26 usr = strdup(json_object_get_string(user)); + 27 AFB_REQ_NOTICE(req, "login user: %s", usr); + 28 afb_req_session_set_LOA(req, 1); + 29 afb_req_context_set(req, usr, free); + 30 afb_req_reply(req, NULL, NULL, NULL); + 31 afb_event_push(event_login, json_object_new_string(usr)); + 32 } + 33 } + 34 + 35 void action(afb_req_t req) + 36 { + 37 json_object *args, *val; + 38 char *usr; + 39 + 40 args = afb_req_json(req); + 41 usr = afb_req_context_get(req); + 42 AFB_REQ_NOTICE(req, "action for user %s: %s", usr, json_object_get_string(args)); + 43 if (json_object_object_get_ex(args, "subscribe", &val)) { + 44 if (json_object_get_boolean(val)) { + 45 AFB_REQ_NOTICE(req, "user %s subscribes to events", usr); + 46 afb_req_subscribe(req, event_login); + 47 afb_req_subscribe(req, event_logout); + 48 } else { + 49 AFB_REQ_NOTICE(req, "user %s unsubscribes to events", usr); + 50 afb_req_unsubscribe(req, event_login); + 51 afb_req_unsubscribe(req, event_logout); + 52 } + 53 } + 54 afb_req_reply(req, json_object_get(args), NULL, NULL); + 55 } + 56 + 57 void logout(afb_req_t req) + 58 { + 59 char *usr; + 60 + 61 usr = afb_req_context_get(req); + 62 AFB_REQ_NOTICE(req, "login user %s out", usr); + 63 afb_event_push(event_logout, json_object_new_string(usr)); + 64 afb_req_session_set_LOA(req, 0); + 65 afb_req_context_clear(req); + 66 afb_req_reply(req, NULL, NULL, NULL); + 67 } + 68 + 69 int preinit(afb_api_t api) + 70 { + 71 AFB_API_NOTICE(api, "preinit"); + 72 return 0; + 73 } + 74 + 75 int init(afb_api_t api) + 76 { + 77 AFB_API_NOTICE(api, "init"); + 78 event_login = afb_api_make_event(api, "login"); + 79 event_logout = afb_api_make_event(api, "logout"); + 80 if (afb_event_is_valid(event_login) && afb_event_is_valid(event_logout)) + 81 return 0; + 82 AFB_API_ERROR(api, "Can't create events"); + 83 return -1; + 84 } + 85 + 86 const afb_verb_t verbs[] = { + 87 { .verb="login", .callback=login }, + 88 { .verb="action", .callback=action, .session=AFB_SESSION_LOA_1 }, + 89 { .verb="logout", .callback=logout, .session=AFB_SESSION_LOA_1 }, + 90 { .verb=NULL } + 91 }; + 92 + 93 const afb_binding_t afbBindingExport = { + 94 .api = "tuto-2", + 95 .specification = NULL, + 96 .verbs = verbs, + 97 .preinit = preinit, + 98 .init = init, + 99 .noconcurrency = 0 + 100 }; +``` + +Compiling: + +```bash +gcc -fPIC -shared tuto-2.c -o tuto-2.so $(pkg-config --cflags --libs afb-daemon) +``` + +Running: + +```bash +afb-daemon --binding ./tuto-2.so --port 3333 --token '' +``` + +Testing: + +```bash +$ afb-client-demo -H localhost:3333/api?token=toto +tuto-2 login {"help":true} +ON-REPLY 1:tuto-2/login: ERROR +{ + "jtype":"afb-reply", + "request":{ + "status":"bad-request", + "uuid":"e2b24a13-fc43-487e-a5f4-9266dd1e60a9" + } +} +tuto-2 login {"user":"jose","password":"please"} +ON-REPLY 2:tuto-2/login: OK +{ + "jtype":"afb-reply", + "request":{ + "status":"success" + } +} +tuto-2 login {"user":"jobol","password":"please"} +ON-REPLY 3:tuto-2/login: ERROR +{ + "jtype":"afb-reply", + "request":{ + "status":"bad-state" + } +} +tuto-2 action {"subscribe":true} +ON-REPLY 4:tuto-2/action: OK +{ + "response":{ + "subscribe":true + }, + "jtype":"afb-reply", + "request":{ + "status":"success" + } +} +``` + +In another terminal: + +```bash +$ afb-client-demo -H localhost:3333/api?token=toto +tuto-2 login {"user":"jobol","password":"please"} +ON-REPLY 1:tuto-2/login: OK +{ + "jtype":"afb-reply", + "request":{ + "status":"success", + "uuid":"a09f55ff-0e89-4f4e-8415-c6e0e7f439be" + } +} +tuto-2 logout true +ON-REPLY 2:tuto-2/logout: OK +{ + "jtype":"afb-reply", + "request":{ + "status":"success" + } +} +``` + +It produced in the first terminal: + +```bash +ON-EVENT tuto-2/login: +{ + "event":"tuto-2\/login", + "data":"jobol", + "jtype":"afb-event" +} +ON-EVENT tuto-2/logout: +{ + "event":"tuto-2\/logout", + "data":"jobol", + "jtype":"afb-event" +} +``` |