Overview of the bindings ======================== The ***binder*** serves files through HTTP protocol and offers to 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. Excepting this summary, 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 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 result. 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 if 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**. Actually it exists 2 ways of writing ***bindings***. You can either write: - a binding version 1 (not recommended); - a binding version 2 (RECOMMENDED). A ***binder*** loads and runs any of these version in any combination. This document explain how to write bindings version 2. Sample binding: tuto-1 ====================== This is the code of the binding **tuto-1.c**: ```C 1 #define AFB_BINDING_VERSION 2 2 #include 3 4 void hello(afb_req req) 5 { 6 AFB_REQ_DEBUG(req, "hello world"); 7 afb_req_success(req, NULL, "hello world"); 8 } 9 10 const afb_verb_v2 verbs[] = { 11 { .verb="hello", .callback=hello }, 12 { .verb=NULL } 13 }; 14 15 const afb_binding_v2 afbBindingV2 = { 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) ``` Running: ```bash $ afb-daemon --binding tuto-1.so --port 3333 --token '' ``` 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 request 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 2 2 #include ``` You must define the version of ***binding*** that you are using. This is done line 1 where we define that this is the version 2. If you don't define it, a warning message is prompted by the compiler and the version is switched to version 1. This behaviour is temporarily and enables to continue to use previously written ***binding*** without change but it will change in some future when ***bindings*** V1 will become obsoletes. 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 only **C** language **API**. The file **afb/afb-binding.h** isn't **C++** ready. You should use the construct **extern "C"** as below: ```C #define AFB_BINDING_VERSION 2 extern "C" { #include } ``` Future version of the ***binder*** will include a **C++** interface. Until it is available, please, use the above construct. ### Declaring the API of the binding Lines 10 to 18 show the declaration of the ***binding***. The ***binder*** knows that this is a ***binding*** version 2 because it finds the exported symbol **afbBindingV2** that is expected to be a structure of type **afb_binding_v2**. ```C 10 const afb_verb_v2 verbs[] = { 11 { .verb="hello", .callback=hello }, 12 { .verb=NULL } 13 }; 14 15 const afb_binding_v2 afbBindingV2 = { 16 .api = "tuto-1", 17 .verbs = verbs 18 }; ``` The structure **afbBindingV2** 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, 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**). Note that you can explicitly mark the fact that these are struct by typing the **struct** as below: ```C 10 const struct afb_verb_v2 verbs[] = { 11 { .verb="hello", .callback=hello }, 12 { .verb=NULL } 13 }; 14 15 const struct afb_binding_v2 afbBindingV2 = { 16 .api = "tuto-1", 17 .verbs = verbs 18 }; ``` ### 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 req) 5 { 6 AFB_REQ_DEBUG(req, "hello world"); 7 afb_req_success(req, 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. Here, the callback for **tuto-1/hello** replies a successful answer (line 7) to the request **req**. The second parameter (here NULL) is a json object that is sent to the client with the reply. The third parameter is also sent with the reply and is a string called info that can be used as some meta data. Here again, you can explicitly mark the fact that **afb_req** is a structure by declaring **hello** as below: ```C 4 void hello(struct afb_req req) ``` 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 2 #include 3 4 #define AFB_BINDING_VERSION 2 5 #include 6 7 afb_event event_login, event_logout; 8 9 void login(afb_req 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_fail(req, "bad-request", NULL); 19 } else if (afb_req_context_get(req)) { 20 AFB_REQ_ERROR(req, "login, bad state, logout first"); 21 afb_req_fail(req, "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_fail(req, "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_success(req, NULL, NULL); 31 afb_event_push(event_login, json_object_new_string(usr)); 32 } 33 } 34 35 void action(afb_req 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_success(req, json_object_get(args), NULL); 55 } 56 57 void logout(afb_req 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_success(req, NULL, NULL); 67 } 68 69 int preinit() 70 { 71 AFB_NOTICE("preinit"); 72 return 0; 73 } 74 75 int init() 76 { 77 AFB_NOTICE("init"); 78 event_login = afb_daemon_make_event("login"); 79 event_logout = afb_daemon_make_event("logout"); 80 if (afb_event_is_valid(event_login) && afb_event_is_valid(event_logout)) 81 return 0; 82 AFB_ERROR("Can't create events"); 83 return -1; 84 } 85 86 const afb_verb_v2 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_v2 afbBindingV2 = { 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 an other 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" } ```