--- /dev/null
+---
+edit_link: ''
+title: How to write a binding ?
+origin_url: >-
+ https://git.automotivelinux.org/src/app-framework-binder/plain/docs/afb-binding-writing.md?h=master
+---
+
+<!-- WARNING: This file is generated by fetch_docs.js using /home/boron/Documents/AGL/docs-webtemplate/site/_data/tocs/apis_services/master/app-framework-binder-developer-guides-api-services-book.yml -->
+
+# 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.
+
+<!-- pagebreak -->
+
+## 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"
+}
+```
Code Review / AGL / documentation.git / blobdiff