1 # Overview of the bindings
3 The ***binder*** serves files through HTTP protocol and offers to
4 developers the capability to offer application API methods through HTTP or
7 The ***bindings*** are used to add **API** to ***binders***.
8 This part describes how to write a ***binding*** for ***binder***
9 or in other words how to add a new **API** to the system.
11 Excepting this summary, this section target developers.
13 This section shortly explain how to write a binding
14 using the C programming language.
16 It is convenient to install the ***binder*** on the
17 desktop used for writing the binding.
18 It allows easy debug and test.
20 ## Nature of a binding
22 A ***binding*** is an independent piece of software compiled as a shared
23 library and dynamically loaded by a ***binder***.
24 It is intended to provide one **API** (**A**pplication **P**rogramming
27 The **API** is designated and accessed through its name.
28 It contains several **verbs** that implement the ***binding***
30 Each of these **verbs** is a **method** that
31 processes requests of applications and sends result.
33 The ***binding***'s methods are invoked by HTTP or websocket
36 The **methods** of the ***bindings*** are noted **api/verb**
37 where **api** is the **API** name of the binding and **verb** is
38 the **method**'s name within the **API**.
39 This notation comes from HTTP invocations that rely on URL path terminated
42 The name of an **API** can be made of any characters except:
44 - the control characters (\u0000 .. \u001f)
45 - the characters of the set { ' ', '"', '#', '%', '&',
46 '\'', '/', '?', '`', '\x7f' }
48 The names of the **verbs** can be any character.
50 The binder makes no distinctions between upper case and lower case
52 So **API/VERB** matches **Api/Verb** or **api/verb**.
54 ## Versions of the bindings
56 Since introduction of the binder, the way how bindings are written
57 evolved a little. While changing, attention was made to ensure binary
58 compatibility between the different versions.
60 Actually it exists 3 ways of writing ***bindings***.
63 - a binding version 1 (not more supported);
64 - a binding version 2 (not recommended);
65 - a binding version 3 (RECOMMENDED).
67 A ***binder*** loads and runs any of these version in any combination.
68 This document explain how to write bindings version 3.
72 ## Sample binding: tuto-1
74 This is the code of the binding **tuto-1.c**:
77 1 #define AFB_BINDING_VERSION 3
78 2 #include <afb/afb-binding.h>
80 4 void hello(afb_req_t req)
82 6 AFB_REQ_DEBUG(req, "hello world");
83 7 afb_req_reply(req, NULL, NULL, "hello world");
86 10 const afb_verb_t verbs[] = {
87 11 { .verb="hello", .callback=hello },
91 15 const afb_binding_t afbBindingExport = {
100 gcc -fPIC -shared tuto-1.c -o tuto-1.so $(pkg-config --cflags-only-I afb-daemon)
103 > Note: the variable environment variable PKG_CONFIG_PATH might be necessary
104 > tuned to get **pkg-config** working properly
109 afb-daemon --binding tuto-1.so --port 3333 --token ''
112 At this point, afb-daemon has started, it loaded the binding tuto-1.so and now
113 listen at localhost on the port 3333.
115 Testing using **curl**:
118 $ curl http://localhost:3333/api/tuto-1/hello
119 {"jtype":"afb-reply","request":{"status":"success","info":"hello world","uuid":"1e587b54-900b-49ab-9940-46141bc2e1d6"}}
122 Testing using **afb-client-demo** (with option -H for
123 getting a human readable output):
126 $ afb-client-demo -H ws://localhost:3333/api?token=x tuto-1 hello
127 ON-REPLY 1:tuto-1/hello: OK
132 "info":"hello world",
133 "uuid":"03a84ad1-458a-4ace-af74-b1da917391b9"
138 This shows basic things:
140 - The include to get for creating a binding
141 - How to declare the API offered by the binding
142 - How to handle request made to the binding
144 ### Getting declarations for the binding
146 The lines 1 and 2 show how to get the include file **afb-binding.h**.
149 1 #define AFB_BINDING_VERSION 3
150 2 #include <afb/afb-binding.h>
153 You must define the version of ***binding*** that you are using.
154 This is done line 1 where we define that this is the version 3 (earlier
155 versions 1 and 2 are deprecated).
157 If you don't define it, an error is reported and the compilation aborts.
159 To include **afb-binding.h** successfully, the include search path
160 should be set correctly if needed (not needed only if installed in
161 /usr/include/afb directory that is the default).
163 Setting the include path is easy using **pkg-config**:
166 pkg-config --cflags-only-I afb-daemon
169 > Note for **C++** developers:
171 > The ***binder*** currently expose a draft version of **C++** api.
172 > To get it include the file <**afb/afb-binding**> (without **.h**).
175 ### Declaring the API of the binding
177 Lines 10 to 18 show the declaration of the ***binding***.
179 The ***binder*** knows that this is a ***binding*** because
180 it finds the exported symbol **afbBindingExport** that is expected to be
181 a structure of type **afb_binding_t**.
184 10 const afb_verb_t verbs[] = {
185 11 { .verb="hello", .callback=hello },
189 15 const afb_binding_t afbBindingExport = {
195 The structure **afbBindingExport** actually tells that:
197 - the exported **API** name is **tuto-1** (line 16)
198 - the array of verbs is the above defined one
200 The exported list of verb is specified by an array of structures of
201 type **afb_verb_t**, each describing a verb, ended with a verb NULL (line 12).
203 The only defined verb here (line 11) is named **hello** (field **.verb**)
204 and the function that handle the related request is **hello**
205 (field **.callback**).
207 ### Handling binder's requests
209 As shown above this is by default the common include directory where
210 the AGL stuff is installed.
213 4 void hello(afb_req_t req)
215 6 AFB_REQ_DEBUG(req, "hello world");
216 7 afb_req_reply(req, NULL, NULL, "hello world");
220 When the ***binder*** receives a request for the verb **hello** of
221 of the api **tuto-1**, it invoke the callback **hello** of the **binding**
222 with the argument **req** that handles the client request.
224 The callback has to treat synchronously or asynchronously the request and
225 should at the end emit a reply for the request.
227 At the line 7, the callback for **tuto-1/hello** replies to the request **req**.
228 Parameters of the reply are:
230 1. The first parameter is the replied request
231 2. The second parameter is a json object (here NULL)
232 3. The third parameter is the error string indication (here NULL: no error)
233 4. The fourth parameter is an informative string (that can be NULL) that can be used to provide meta data.
235 The 3 last parameters are sent back to the client as the reply content.
239 ## Sample binding: tuto-2
241 The second tutorial shows many important feature that can
242 commonly be used when writing a ***binding***:
244 - initialization, getting arguments, sending replies, pushing events.
246 This is the code of the binding **tuto-2.c**:
249 1 #include <string.h>
250 2 #include <json-c/json.h>
252 4 #define AFB_BINDING_VERSION 3
253 5 #include <afb/afb-binding.h>
255 7 afb_event_t event_login, event_logout;
257 9 void login(afb_req_t req)
259 11 json_object *args, *user, *passwd;
262 14 args = afb_req_json(req);
263 15 if (!json_object_object_get_ex(args, "user", &user)
264 16 || !json_object_object_get_ex(args, "password", &passwd)) {
265 17 AFB_REQ_ERROR(req, "login, bad request: %s", json_object_get_string(args));
266 18 afb_req_reply(req, NULL, "bad-request", NULL);
267 19 } else if (afb_req_context_get(req)) {
268 20 AFB_REQ_ERROR(req, "login, bad state, logout first");
269 21 afb_req_reply(req, NULL, "bad-state", NULL);
270 22 } else if (strcmp(json_object_get_string(passwd), "please")) {
271 23 AFB_REQ_ERROR(req, "login, unauthorized: %s", json_object_get_string(args));
272 24 afb_req_reply(req, NULL, "unauthorized", NULL);
274 26 usr = strdup(json_object_get_string(user));
275 27 AFB_REQ_NOTICE(req, "login user: %s", usr);
276 28 afb_req_session_set_LOA(req, 1);
277 29 afb_req_context_set(req, usr, free);
278 30 afb_req_reply(req, NULL, NULL, NULL);
279 31 afb_event_push(event_login, json_object_new_string(usr));
283 35 void action(afb_req_t req)
285 37 json_object *args, *val;
288 40 args = afb_req_json(req);
289 41 usr = afb_req_context_get(req);
290 42 AFB_REQ_NOTICE(req, "action for user %s: %s", usr, json_object_get_string(args));
291 43 if (json_object_object_get_ex(args, "subscribe", &val)) {
292 44 if (json_object_get_boolean(val)) {
293 45 AFB_REQ_NOTICE(req, "user %s subscribes to events", usr);
294 46 afb_req_subscribe(req, event_login);
295 47 afb_req_subscribe(req, event_logout);
297 49 AFB_REQ_NOTICE(req, "user %s unsubscribes to events", usr);
298 50 afb_req_unsubscribe(req, event_login);
299 51 afb_req_unsubscribe(req, event_logout);
302 54 afb_req_reply(req, json_object_get(args), NULL, NULL);
305 57 void logout(afb_req_t req)
309 61 usr = afb_req_context_get(req);
310 62 AFB_REQ_NOTICE(req, "login user %s out", usr);
311 63 afb_event_push(event_logout, json_object_new_string(usr));
312 64 afb_req_session_set_LOA(req, 0);
313 65 afb_req_context_clear(req);
314 66 afb_req_reply(req, NULL, NULL, NULL);
317 69 int preinit(afb_api_t api)
319 71 AFB_API_NOTICE(api, "preinit");
323 75 int init(afb_api_t api)
325 77 AFB_API_NOTICE(api, "init");
326 78 event_login = afb_api_make_event(api, "login");
327 79 event_logout = afb_api_make_event(api, "logout");
328 80 if (afb_event_is_valid(event_login) && afb_event_is_valid(event_logout))
330 82 AFB_API_ERROR(api, "Can't create events");
334 86 const afb_verb_t verbs[] = {
335 87 { .verb="login", .callback=login },
336 88 { .verb="action", .callback=action, .session=AFB_SESSION_LOA_1 },
337 89 { .verb="logout", .callback=logout, .session=AFB_SESSION_LOA_1 },
341 93 const afb_binding_t afbBindingExport = {
343 95 .specification = NULL,
345 97 .preinit = preinit,
347 99 .noconcurrency = 0
354 gcc -fPIC -shared tuto-2.c -o tuto-2.so $(pkg-config --cflags --libs afb-daemon)
360 afb-daemon --binding tuto-2.so --port 3333 --token ''
366 $ afb-client-demo -H localhost:3333/api?token=toto
367 tuto-2 login {"help":true}
368 ON-REPLY 1:tuto-2/login: ERROR
372 "status":"bad-request",
373 "uuid":"e2b24a13-fc43-487e-a5f4-9266dd1e60a9"
376 tuto-2 login {"user":"jose","password":"please"}
377 ON-REPLY 2:tuto-2/login: OK
384 tuto-2 login {"user":"jobol","password":"please"}
385 ON-REPLY 3:tuto-2/login: ERROR
392 tuto-2 action {"subscribe":true}
393 ON-REPLY 4:tuto-2/action: OK
405 In an other terminal:
408 $ afb-client-demo -H localhost:3333/api?token=toto
409 tuto-2 login {"user":"jobol","password":"please"}
410 ON-REPLY 1:tuto-2/login: OK
415 "uuid":"a09f55ff-0e89-4f4e-8415-c6e0e7f439be"
419 ON-REPLY 2:tuto-2/logout: OK
428 It produced in the first terminal:
431 ON-EVENT tuto-2/login:
433 "event":"tuto-2\/login",
437 ON-EVENT tuto-2/logout:
439 "event":"tuto-2\/logout",