2 title: How to write a binding?
5 # Overview of the bindings
7 The ***binder*** serves files through HTTP protocol and offers developers the capability to offer application API methods through HTTP or
10 The ***bindings*** are used to add **API** to ***binders***.
11 This part describes how to write a ***binding*** for ***binder***
12 or in other words how to add a new **API** to the system.
14 This section target developers.
16 This section shortly explain how to write a binding
17 using the C programming language.
19 It is convenient to install the ***binder*** on the
20 desktop used for writing the binding.
21 It allows for easy debug and test.
23 ## Nature of a binding
25 A ***binding*** is an independent piece of software compiled as a shared
26 library and dynamically loaded by a ***binder***.
27 It is intended to provide one **API** (**A**pplication **P**rogramming
30 The **API** is designated and accessed through its name.
31 It contains several **verbs** that implement the ***binding***
33 Each of these **verbs** is a **method** that
34 processes requests of applications and sends results.
36 The ***binding***'s methods are invoked 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 of the **verbs** can be any character.
53 The binder makes no distinctions between upper case and lower case
55 So **API/VERB** matches **Api/Verb** or **api/verb**.
57 ## Versions of the bindings
59 Since introduction of the binder, the way how bindings are written
60 evolved a little. While changing, attention was made to ensure binary
61 compatibility between the different versions.
63 Actually it exists 3 ways of writing ***bindings***.
66 - a binding version 1 (not more supported);
67 - a binding version 2 (not recommended);
68 - a binding version 3 (RECOMMENDED).
70 A ***binder*** loads and runs any of these version in any combination.
71 This document explain how to write bindings version 3.
73 ## Sample binding: tuto-1
75 This is the code of the binding **tuto-1.c**:
78 1 #define AFB_BINDING_VERSION 3
79 2 #include <afb/afb-binding.h>
81 4 void hello(afb_req_t req)
83 6 AFB_REQ_DEBUG(req, "hello world");
84 7 afb_req_reply(req, NULL, NULL, "hello world");
87 10 const afb_verb_t verbs[] = {
88 11 { .verb="hello", .callback=hello },
92 15 const afb_binding_t afbBindingExport = {
101 gcc -fPIC -shared tuto-1.c -o tuto-1.so $(pkg-config --cflags-only-I afb-daemon)
104 > Note: the variable environment variable PKG_CONFIG_PATH might be necessary
105 > tuned to get **pkg-config** working properly
110 afb-daemon --binding ./tuto-1.so --port 3333 --token ''
113 At this point, afb-daemon has started, it loaded the binding tuto-1.so and now
114 listen at localhost on the port 3333.
116 Testing using **curl**:
119 $ curl http://localhost:3333/api/tuto-1/hello
120 {"jtype":"afb-reply","request":{"status":"success","info":"hello world","uuid":"1e587b54-900b-49ab-9940-46141bc2e1d6"}}
123 Testing using **afb-client-demo** (with option -H for
124 getting a human readable output):
127 $ afb-client-demo -H ws://localhost:3333/api?token=x tuto-1 hello
128 ON-REPLY 1:tuto-1/hello: OK
133 "info":"hello world",
134 "uuid":"03a84ad1-458a-4ace-af74-b1da917391b9"
139 This shows basic things:
141 - The include to get for creating a binding
142 - How to declare the API offered by the binding
143 - How to handle requests made to the binding
145 ### Getting declarations for the binding
147 The lines 1 and 2 show how to get the include file **afb-binding.h**.
150 1 #define AFB_BINDING_VERSION 3
151 2 #include <afb/afb-binding.h>
154 You must define the version of ***binding*** that you are using.
155 This is done line 1 where we define that this is the version 3 (earlier
156 versions 1 and 2 are deprecated).
158 If you don't define it, an error is reported and the compilation aborts.
160 To include **afb-binding.h** successfully, the include search path
161 should be set correctly if needed (not needed only if installed in
162 /usr/include/afb directory that is the default).
164 Setting the include path is easy using **pkg-config**:
167 pkg-config --cflags-only-I afb-daemon
170 > Note for **C++** developers:
172 > The ***binder*** currently expose a draft version of **C++** api.
173 > To get it include the file <**afb/afb-binding**> (without **.h**).
176 ### Declaring the API of the binding
178 Lines 10 to 18 show the declaration of the ***binding***.
180 The ***binder*** knows that this is a ***binding*** because
181 it finds the exported symbol **afbBindingExport** that is expected to be
182 a structure of type **afb_binding_t**.
185 10 const afb_verb_t verbs[] = {
186 11 { .verb="hello", .callback=hello },
190 15 const afb_binding_t afbBindingExport = {
196 The structure **afbBindingExport** actually tells that:
198 - the exported **API** name is **tuto-1** (line 16)
199 - the array of verbs is the above defined one
201 The exported list of verb is specified by an array of structures of
202 type **afb_verb_t**, each describing a verb, ended with a verb NULL (line 12).
204 The only defined verb here (line 11) is named **hello** (field **.verb**)
205 and the function that handle the related request is **hello**
206 (field **.callback**).
208 ### Handling binder's requests
210 As shown above this is by default the common include directory where
211 the AGL stuff is installed.
214 4 void hello(afb_req_t req)
216 6 AFB_REQ_DEBUG(req, "hello world");
217 7 afb_req_reply(req, NULL, NULL, "hello world");
221 When the ***binder*** receives a request for the verb **hello** of
222 of the api **tuto-1**, it invoke the callback **hello** of the **binding**
223 with the argument **req** that handles the client request.
225 The callback has to treat synchronously or asynchronously the request and
226 should at the end emit a reply for the request.
228 At the line 7, the callback for **tuto-1/hello** replies to the request **req**.
229 Parameters of the reply are:
231 1. The first parameter is the replied request
232 2. The second parameter is a json object (here NULL)
233 3. The third parameter is the error string indication (here NULL: no error)
234 4. The fourth parameter is an informative string (that can be NULL) that can be used to provide meta data.
236 The 3 last parameters are sent back to the client as the reply content.
240 ## Sample binding: tuto-2
242 The second tutorial shows many important feature that can
243 commonly be used when writing a ***binding***:
245 - initialization, getting arguments, sending replies, pushing events.
247 This is the code of the binding **tuto-2.c**:
250 1 #include <string.h>
251 2 #include <json-c/json.h>
253 4 #define AFB_BINDING_VERSION 3
254 5 #include <afb/afb-binding.h>
256 7 afb_event_t event_login, event_logout;
258 9 void login(afb_req_t req)
260 11 json_object *args, *user, *passwd;
263 14 args = afb_req_json(req);
264 15 if (!json_object_object_get_ex(args, "user", &user)
265 16 || !json_object_object_get_ex(args, "password", &passwd)) {
266 17 AFB_REQ_ERROR(req, "login, bad request: %s", json_object_get_string(args));
267 18 afb_req_reply(req, NULL, "bad-request", NULL);
268 19 } else if (afb_req_context_get(req)) {
269 20 AFB_REQ_ERROR(req, "login, bad state, logout first");
270 21 afb_req_reply(req, NULL, "bad-state", NULL);
271 22 } else if (strcmp(json_object_get_string(passwd), "please")) {
272 23 AFB_REQ_ERROR(req, "login, unauthorized: %s", json_object_get_string(args));
273 24 afb_req_reply(req, NULL, "unauthorized", NULL);
275 26 usr = strdup(json_object_get_string(user));
276 27 AFB_REQ_NOTICE(req, "login user: %s", usr);
277 28 afb_req_session_set_LOA(req, 1);
278 29 afb_req_context_set(req, usr, free);
279 30 afb_req_reply(req, NULL, NULL, NULL);
280 31 afb_event_push(event_login, json_object_new_string(usr));
284 35 void action(afb_req_t req)
286 37 json_object *args, *val;
289 40 args = afb_req_json(req);
290 41 usr = afb_req_context_get(req);
291 42 AFB_REQ_NOTICE(req, "action for user %s: %s", usr, json_object_get_string(args));
292 43 if (json_object_object_get_ex(args, "subscribe", &val)) {
293 44 if (json_object_get_boolean(val)) {
294 45 AFB_REQ_NOTICE(req, "user %s subscribes to events", usr);
295 46 afb_req_subscribe(req, event_login);
296 47 afb_req_subscribe(req, event_logout);
298 49 AFB_REQ_NOTICE(req, "user %s unsubscribes to events", usr);
299 50 afb_req_unsubscribe(req, event_login);
300 51 afb_req_unsubscribe(req, event_logout);
303 54 afb_req_reply(req, json_object_get(args), NULL, NULL);
306 57 void logout(afb_req_t req)
310 61 usr = afb_req_context_get(req);
311 62 AFB_REQ_NOTICE(req, "login user %s out", usr);
312 63 afb_event_push(event_logout, json_object_new_string(usr));
313 64 afb_req_session_set_LOA(req, 0);
314 65 afb_req_context_clear(req);
315 66 afb_req_reply(req, NULL, NULL, NULL);
318 69 int preinit(afb_api_t api)
320 71 AFB_API_NOTICE(api, "preinit");
324 75 int init(afb_api_t api)
326 77 AFB_API_NOTICE(api, "init");
327 78 event_login = afb_api_make_event(api, "login");
328 79 event_logout = afb_api_make_event(api, "logout");
329 80 if (afb_event_is_valid(event_login) && afb_event_is_valid(event_logout))
331 82 AFB_API_ERROR(api, "Can't create events");
335 86 const afb_verb_t verbs[] = {
336 87 { .verb="login", .callback=login },
337 88 { .verb="action", .callback=action, .session=AFB_SESSION_LOA_1 },
338 89 { .verb="logout", .callback=logout, .session=AFB_SESSION_LOA_1 },
342 93 const afb_binding_t afbBindingExport = {
344 95 .specification = NULL,
346 97 .preinit = preinit,
348 99 .noconcurrency = 0
355 gcc -fPIC -shared tuto-2.c -o tuto-2.so $(pkg-config --cflags --libs afb-daemon)
361 afb-daemon --binding ./tuto-2.so --port 3333 --token ''
367 $ afb-client-demo -H localhost:3333/api?token=toto
368 tuto-2 login {"help":true}
369 ON-REPLY 1:tuto-2/login: ERROR
373 "status":"bad-request",
374 "uuid":"e2b24a13-fc43-487e-a5f4-9266dd1e60a9"
377 tuto-2 login {"user":"jose","password":"please"}
378 ON-REPLY 2:tuto-2/login: OK
385 tuto-2 login {"user":"jobol","password":"please"}
386 ON-REPLY 3:tuto-2/login: ERROR
393 tuto-2 action {"subscribe":true}
394 ON-REPLY 4:tuto-2/action: OK
409 $ afb-client-demo -H localhost:3333/api?token=toto
410 tuto-2 login {"user":"jobol","password":"please"}
411 ON-REPLY 1:tuto-2/login: OK
416 "uuid":"a09f55ff-0e89-4f4e-8415-c6e0e7f439be"
420 ON-REPLY 2:tuto-2/logout: OK
429 It produced in the first terminal:
432 ON-EVENT tuto-2/login:
434 "event":"tuto-2\/login",
438 ON-EVENT tuto-2/logout:
440 "event":"tuto-2\/logout",