Services

The objective of this lesson is to study services in the context of the web.

Is studied :

• concurrent and parallel programming
• synchronous/asynchronous programs
• handling transactions

This repo gather the exercises (tp) of the lesson.

TP1 - Automaton as a service

The case study of this TP is to handle stateful and stateless services through the example of an automaton.

TP2 - Register as service

The case study of this TP is to optimist concurrency control through the example of an automaton.

Server without concurrency control

Server

- get(rep) & Ressource(x) -> rep(x) & Ressource(x)
- set(rep, y) & Ressource(x) -> rep(y) & Ressource(y)

Client

- get(lecture) // Etat initial
- lecture(x) -> set(ecriture, x + 1)
- ecriture(x) -> Affichage(x)

Server with concurrency control

- get(rep) & Ressource(x) & Version(n)
    -> rep(x, n) & Ressource(x) & Version(n)
// Ecriture réussie
- set(rep, y, n) & Ressource(x) & Version(n)
    -> rep(OK, y, n + 1) & Ressource(y) & Version(n + 1)
// Ecriture annulée
- set(rep, y, m) & Ressource(x) & Version(n) & (n != m)
    -> rep(KO, x, n) & Ressource(x) & Version(n)

Server with client cache

// Lecture à réaliser en cache
- get(rep, n) & Version(n)
    -> rep(CACHE, n) & Version(n)
// Lecture de la ressource
- get(rep, m) & Ressource(x) & Version(n) & (n != m)
    -> rep(x, n) & Ressource(x) & Version(n)
// Ecriture réussie
- set(rep, y, n) & Ressource(x) & Version(n)
    -> rep(OK, y, n + 1) & Ressource(y) & Version(n + 1)
// Ecriture annulée
- set(rep, y, m) & Ressource(x) & Version(n) & (n != m)
  -> rep(KO, x, n) & Ressource(x) & Version(n)

Client with cache

Client

// Etat initial
- getI(lecture)

// Incrémentation
- lecture(x) -> setI(ecriture, x + 1)
// Echec avec reprise
- ecriture(KO, x) -> setI(ecriture, x + 1)
// Succès
- ecriture(OK, x) -> Affichage(x)

Interceptor

// Etat initial
- Cache(NON_DEFINI, NON_DEFINI)

// Interception d'une requête en lecture
- getI(k) & Cache(x, n) -> get(lectureI, n) & Cache(x, n)
// Réponse demandant la lecture en cache
- lectureI(CACHE, n) & Cache(x, n) -> k(x) & Cache(x, n)
// Réponse transmettant le résultat et mise en cache
- lectureI(y, m) & Cache(x, n) -> k(y) & Cache(y, m)

// Interception d'une requête en écriture
- setI(k, y) & Cache(x, n) -> set(ecritureI, y, n) & Cache(x, n)
// Ecriture réussie avec mise à jour du cache
- ecritureI(OK, y, m) & Cache(x, n) -> k(OK, y) & Cache(y, m)
// Ecriture annulée avec mise à jour du cache
- ecritureI(KO, y, m) & Cache(x, n) -> k(KO, y) & Cache(y, m)

Client version management

Client GET request

The request needs contain the header if-none-match=[clientVersion].

Then there is 2 cases :

• either the client and the server version are the same, then return
  • code 200 with
  • header ETag=[currentVersion]
• either version are different, then return
  • code 304 (Not-Modified) with
  • header ETag=[clientVersion] and
  • header Content-Length=[0]

Client SET request

The request needs contain the header if-match=[clientVersion].

Then there is 3 cases :

• either request header if-match is missing, then return
  • code 428 (Precondition Required) with
  • header ETag=[clientVersion]
• either the client and the server version are the same, then return
  • code 200 with
  • header ETag=[newVersion]
• otherwise return
  • code 412 (Precondition Failed) with
  • header ETag=[currentVersion]

Server filters

Priority : 1 ----------------------------------------------------------------------> 5

|--> CompterRequetes --> InteragirAtomiquement --> Cacher --> RealiserEcritureOptimiste  -->|
|                                                                                           | Business
|                                                                                           | code
|<-- CompterReponse  <-- InteragirAtomiquement <-- AjouterVersionAuxReponses             <--|

Priority : 1 <---------------------------------------------------------------------- 5