2 Overview of the bindings
3 ========================
5 The ***binder*** serves files through HTTP protocol and offers to
6 developers the capability to offer application API methods through HTTP or
9 The ***bindings*** are used to add **API** to ***binders***.
10 This part describes how to write a ***binding*** for ***binder***
11 or in other words how to add a new **API** to the system.
13 Excepting this summary, this section target developers.
15 This section shortly explain how to write a binding
16 using the C programming language.
18 It is convenient to install the ***binder*** on the
19 desktop used for writing the binding. It allows easy
25 A ***binding*** is an independent piece of software compiled as a shared
26 library and dynamically loaded by a ***binder***.
28 It is intended to provide one **API** (**A**pplication **P**rogramming
31 The **API** is designated and accessed through its name.
32 It contains several **verbs** that implement the ***binding***
33 functionnalities. Each of these **verbs** is a **method** that
34 processes requests of applications and sends result.
36 The ***binding***'s methods is invoqued by HTTP or websocket
39 The **methods** of the ***bindings*** are noted **api/verb**
40 where **api** is the **API** name of the binding and **verb** is
41 the **method**'s name within the **API**.
42 This notation comes from HTTP invocations that rely on URL path terminated
45 The name of an **API** can be made of any characters except:
47 - the control characters (\u0000 .. \u001f)
48 - the characters of the set { ' ', '"', '#', '%', '&',
49 '\'', '/', '?', '`', '\x7f' }
51 The names if the **verbs** can be any character.
53 The binder mkes no distinctions between upper case and lower case
54 latin letters. So **API/VERB** matches **Api/Verb** or **api/verb**.
56 Actually it exists 2 ways of writing ***bindings***.
59 - a binding version 1 (not recommanded);
60 - a binding version 2 (RECOMMANDED).
62 A ***binder*** loads and runs any of these version
65 This document explain how to write bindings version 2.
68 Sample binding: tuto-1
69 ======================
71 This is the code of the binding **tuto-1.c**:
74 1 #define AFB_BINDING_VERSION 2
75 2 #include <afb/afb-binding.h>
77 4 void hello(afb_req req)
79 6 AFB_REQ_DEBUG(req, "hello world");
80 7 afb_req_success(req, NULL, "hello world");
83 10 const afb_verb_v2 verbs[] = {
84 11 { .verb="hello", .callback=hello },
88 15 const afb_binding_v2 afbBindingV2 = {
97 $ gcc -fPIC -shared tuto-1.c -o tuto-1.so $(pkg-config --cflags-only-I afb-daemon)
103 $ afb-daemon --binding tuto-1.so --port 3333 --token ''
106 Testing using **curl**:
109 $ curl http://localhost:3333/api/tuto-1/hello
110 {"jtype":"afb-reply","request":{"status":"success","info":"hello world","uuid":"1e587b54-900b-49ab-9940-46141bc2e1d6"}}
113 Testing using **afb-client-demo** (with option -H for
114 getting a human readable output):
117 $ afb-client-demo -H ws://localhost:3333/api?token=x tuto-1 hello
118 ON-REPLY 1:tuto-1/hello: OK
123 "info":"hello world",
124 "uuid":"03a84ad1-458a-4ace-af74-b1da917391b9"
129 This shows basic things:
131 - The include to get for creating a binding
132 - How to declare the API offered by the binding
133 - How to handle request made to the binding
136 ### Getting declarations for the binding
138 The lines 1 and 2 show how to get the include file **afb-binding.h**.
141 1 #define AFB_BINDING_VERSION 2
142 2 #include <afb/afb-binding.h>
145 You must define the version of ***binding*** that you are using.
146 This is done line 1 where we define that this is the version 2.
148 If you don't define it, a warning message is prompted by the compiler
149 and the version is switched to version 1. This behaviour is
150 temporarily and enables to continue to use previously written
151 ***binding*** without change but it will change in some future when
152 ***bindings*** V1 will become obsoletes.
154 To include **afb-binding.h** successfuly, the include search path
155 should be set correctly if needed (not needed only if installed in
156 /usr/include/afb directory that is the default).
158 Setting the include path is easy using **pkg-config**:
161 $ pkg-config --cflags-only-I afb-daemon
164 Note for **C++** developers: The ***binder*** currently expose
165 only **C** language **API**. The file **afb/afb-binding.h**
166 isn't **C++** ready. You should use the construct **extern "C"**
170 #define AFB_BINDING_VERSION 2
172 #include <afb/afb-binding.h>
176 Future version of the ***binder*** will include a **C++**
177 interface. Until it is available, please, use the above
180 ### Declaring the API of the binding
182 Lines 10 to 18 show the declaration of the ***binding***.
184 The ***binder*** knows that this is a ***binding*** version 2 because
185 it finds the exported symbol **afbBindingV2** that is expected to be
186 a structure of type **afb_binding_v2**.
189 10 const afb_verb_v2 verbs[] = {
190 11 { .verb="hello", .callback=hello },
194 15 const afb_binding_v2 afbBindingV2 = {
200 The structure **afbBindingV2** actually tells that:
202 - the exported **API** name is **tuto-1** (line 16)
203 - the array of verbs is the above defined one
205 The exported list of verb is specified by an array of structures,
206 each describing a verb, ended with a verb NULL (line 12).
208 The only defined verb here (line 11) is named **hello** (field **.verb**)
209 and the function that handle the related request is **hello**
210 (field **.callback**).
212 Note that you can explicitely mark the fact that these are
213 struct by typing the **struct** as below:
216 10 const struct afb_verb_v2 verbs[] = {
217 11 { .verb="hello", .callback=hello },
221 15 const struct afb_binding_v2 afbBindingV2 = {
227 ### Handling binder's requests
229 As shown above this is by default the common include directory where
230 the AGL stuff is installed.
233 4 void hello(afb_req req)
235 6 AFB_REQ_DEBUG(req, "hello world");
236 7 afb_req_success(req, NULL, "hello world");
240 When the ***binder*** receives a request for the verb **hello** of
241 of the api **tuto-1**, it invoque the callback **hello** of the **binding**
242 with the argument **req** that handles the client request.
244 The callback has to treat synchronously or asynchronously the request and
245 should at the end emit a reply for the request.
247 Here, the callback for **tuto-1/hello** replies a successful answer
248 (ligne 7) to the request **req**. The second parameter (here NULL)
249 is a json object that is sent to the client with the reply.
250 The third parameter is also sent with the reply and is a string
251 called info that can be used as some meta data.
253 Here again, you can explicitely mark the fact that
254 **afb_req** is a structure by declaring **hello** as below:
257 4 void hello(struct afb_req req)
260 Sample binding: tuto-2
261 ======================
263 The second tutorial shows many important feature that can
264 commonly be used when writting a ***binding***: initialisation,
265 getting arguments, sending replies, pushing events.
267 This is the code of the binding **tuto-2.c**:
270 1 #include <string.h>
271 2 #include <json-c/json.h>
273 4 #define AFB_BINDING_VERSION 2
274 5 #include <afb/afb-binding.h>
276 7 afb_event event_login, event_logout;
278 9 void login(afb_req req)
280 11 json_object *args, *user, *passwd;
283 14 args = afb_req_json(req);
284 15 if (!json_object_object_get_ex(args, "user", &user)
285 16 || !json_object_object_get_ex(args, "password", &passwd)) {
286 17 AFB_REQ_ERROR(req, "login, bad request: %s", json_object_get_string(args));
287 18 afb_req_fail(req, "bad-request", NULL);
288 19 } else if (afb_req_context_get(req)) {
289 20 AFB_REQ_ERROR(req, "login, bad state, logout first");
290 21 afb_req_fail(req, "bad-state", NULL);
291 22 } else if (strcmp(json_object_get_string(passwd), "please")) {
292 23 AFB_REQ_ERROR(req, "login, unauthorized: %s", json_object_get_string(args));
293 24 afb_req_fail(req, "unauthorized", NULL);
295 26 usr = strdup(json_object_get_string(user));
296 27 AFB_REQ_NOTICE(req, "login user: %s", usr);
297 28 afb_req_session_set_LOA(req, 1);
298 29 afb_req_context_set(req, usr, free);
299 30 afb_req_success(req, NULL, NULL);
300 31 afb_event_push(event_login, json_object_new_string(usr));
304 35 void action(afb_req req)
306 37 json_object *args, *val;
309 40 args = afb_req_json(req);
310 41 usr = afb_req_context_get(req);
311 42 AFB_REQ_NOTICE(req, "action for user %s: %s", usr, json_object_get_string(args));
312 43 if (json_object_object_get_ex(args, "subscribe", &val)) {
313 44 if (json_object_get_boolean(val)) {
314 45 AFB_REQ_NOTICE(req, "user %s subscribes to events", usr);
315 46 afb_req_subscribe(req, event_login);
316 47 afb_req_subscribe(req, event_logout);
318 49 AFB_REQ_NOTICE(req, "user %s unsubscribes to events", usr);
319 50 afb_req_unsubscribe(req, event_login);
320 51 afb_req_unsubscribe(req, event_logout);
323 54 afb_req_success(req, json_object_get(args), NULL);
326 57 void logout(afb_req req)
330 61 usr = afb_req_context_get(req);
331 62 AFB_REQ_NOTICE(req, "login user %s out", usr);
332 63 afb_event_push(event_logout, json_object_new_string(usr));
333 64 afb_req_session_set_LOA(req, 0);
334 65 afb_req_context_clear(req);
335 66 afb_req_success(req, NULL, NULL);
340 71 AFB_NOTICE("preinit");
346 77 AFB_NOTICE("init");
347 78 event_login = afb_daemon_make_event("login");
348 79 event_logout = afb_daemon_make_event("logout");
349 80 if (afb_event_is_valid(event_login) && afb_event_is_valid(event_logout))
351 82 AFB_ERROR("Can't create events");
355 86 const afb_verb_v2 verbs[] = {
356 87 { .verb="login", .callback=login },
357 88 { .verb="action", .callback=action, .session=AFB_SESSION_LOA_1 },
358 89 { .verb="logout", .callback=logout, .session=AFB_SESSION_LOA_1 },
362 93 const afb_binding_v2 afbBindingV2 = {
364 95 .specification = NULL,
366 97 .preinit = preinit,
368 99 .noconcurrency = 0
375 $ gcc -fPIC -shared tuto-2.c -o tuto-2.so $(pkg-config --cflags --libs afb-daemon)
381 $ afb-daemon --binding tuto-2.so --port 3333 --token ''
387 $ afb-client-demo -H localhost:3333/api?token=toto
388 tuto-2 login {"help":true}
389 ON-REPLY 1:tuto-2/login: ERROR
393 "status":"bad-request",
394 "uuid":"e2b24a13-fc43-487e-a5f4-9266dd1e60a9"
397 tuto-2 login {"user":"jose","password":"please"}
398 ON-REPLY 2:tuto-2/login: OK
405 tuto-2 login {"user":"jobol","password":"please"}
406 ON-REPLY 3:tuto-2/login: ERROR
413 tuto-2 action {"subscribe":true}
414 ON-REPLY 4:tuto-2/action: OK
426 In an other terminal:
429 $ afb-client-demo -H localhost:3333/api?token=toto
430 tuto-2 login {"user":"jobol","password":"please"}
431 ON-REPLY 1:tuto-2/login: OK
436 "uuid":"a09f55ff-0e89-4f4e-8415-c6e0e7f439be"
440 ON-REPLY 2:tuto-2/logout: OK
449 It produced in the first terminal:
452 ON-EVENT tuto-2/login:
454 "event":"tuto-2\/login",
458 ON-EVENT tuto-2/logout:
460 "event":"tuto-2\/logout",