montpelliermaalsi2024/rabbit/modeles_msg.md

Bien sûr ! RabbitMQ supporte plusieurs modèles d'échange (exchange types) qui déterminent comment les messages sont routés vers les files d'attente. Voici les principaux modèles d'échange et des exemples pour chacun :

### 1. Direct Exchange

Un **Direct Exchange** route les messages vers les files d'attente dont la clé de routage (routing key) correspond exactement à la clé de routage du message.

#### Exemple

**Producer**:
```python
import pika

connection = pika.BlockingConnection(pika.ConnectionParameters('localhost'))
channel = connection.channel()

channel.exchange_declare(exchange='direct_logs', exchange_type='direct')

severity = "info"
message = "Hello World!"
channel.basic_publish(
    exchange='direct_logs',
    routing_key=severity,
    body=message,
)
print(f" [x] Sent {severity}:{message}")

connection.close()
```

**Consumer**:
```python
import pika

connection = pika.BlockingConnection(pika.ConnectionParameters('localhost'))
channel = connection.channel()

channel.exchange_declare(exchange='direct_logs', exchange_type='direct')

result = channel.queue_declare(queue='', exclusive=True)
queue_name = result.method.queue

severity = "info"
channel.queue_bind(
    exchange='direct_logs',
    queue=queue_name,
    routing_key=severity
)

def callback(ch, method, properties, body):
    print(f" [x] {method.routing_key}:{body}")

channel.basic_consume(
    queue=queue_name,
    on_message_callback=callback,
    auto_ack=True,
)

print(' [*] Waiting for logs. To exit press CTRL+C')
channel.start_consuming()
```

### 2. Fanout Exchange

Un **Fanout Exchange** route les messages à toutes les files d'attente qui sont liées à cet échange, indépendamment de la clé de routage.

#### Exemple

**Producer**:
```python
import pika

connection = pika.BlockingConnection(pika.ConnectionParameters('localhost'))
channel = connection.channel()

channel.exchange_declare(exchange='logs', exchange_type='fanout')

message = "Hello World!"
channel.basic_publish(
    exchange='logs',
    routing_key='',
    body=message,
)
print(f" [x] Sent {message}")

connection.close()
```

**Consumer**:
```python
import pika

connection = pika.BlockingConnection(pika.ConnectionParameters('localhost'))
channel = connection.channel()

channel.exchange_declare(exchange='logs', exchange_type='fanout')

result = channel.queue_declare(queue='', exclusive=True)
queue_name = result.method.queue

channel.queue_bind(exchange='logs', queue=queue_name)

def callback(ch, method, properties, body):
    print(f" [x] {body}")

channel.basic_consume(
    queue=queue_name,
    on_message_callback=callback,
    auto_ack=True,
)

print(' [*] Waiting for logs. To exit press CTRL+C')
channel.start_consuming()
```

### 3. Topic Exchange

Un **Topic Exchange** route les messages vers les files d'attente dont la clé de routage correspond à un motif (pattern) spécifique. Les clés de routage peuvent contenir des caractères génériques (`*` pour un seul mot et `#` pour zéro ou plusieurs mots).

#### Exemple

**Producer**:
```python
import pika

connection = pika.BlockingConnection(pika.ConnectionParameters('localhost'))
channel = connection.channel()

channel.exchange_declare(exchange='topic_logs', exchange_type='topic')

routing_key = "kern.critical"
message = "A critical kernel error"
channel.basic_publish(
    exchange='topic_logs',
    routing_key=routing_key,
    body=message,
)
print(f" [x] Sent {routing_key}:{message}")

connection.close()
```

**Consumer**:
```python
import pika

connection = pika.BlockingConnection(pika.ConnectionParameters('localhost'))
channel = connection.channel()

channel.exchange_declare(exchange='topic_logs', exchange_type='topic')

result = channel.queue_declare(queue='', exclusive=True)
queue_name = result.method.queue

binding_keys = ["kern.*", "*.critical"]
for binding_key in binding_keys:
    channel.queue_bind(
        exchange='topic_logs',
        queue=queue_name,
        routing_key=binding_key
    )

def callback(ch, method, properties, body):
    print(f" [x] {method.routing_key}:{body}")

channel.basic_consume(
    queue=queue_name,
    on_message_callback=callback,
    auto_ack=True,
)

print(' [*] Waiting for logs. To exit press CTRL+C')
channel.start_consuming()
```

### 4. RPC (Remote Procedure Call)

Le modèle RPC permet à un client d'appeler une fonction sur un serveur et d'obtenir une réponse. Ce modèle est souvent utilisé pour des opérations synchrones où le client attend une réponse avant de continuer.

#### Exemple

**Client (RPC Client)**:
```python
import pika
import uuid

class FibonacciRpcClient(object):
    def __init__(self):
        self.connection = pika.BlockingConnection(pika.ConnectionParameters(host='localhost'))
        self.channel = self.connection.channel()

        result = self.channel.queue_declare(queue='', exclusive=True)
        self.callback_queue = result.method.queue

        self.channel.basic_consume(
            queue=self.callback_queue,
            on_message_callback=self.on_response,
            auto_ack=True)

    def on_response(self, ch, method, props, body):
        if self.corr_id == props.correlation_id:
            self.response = body

    def call(self, n):
        self.response = None
        self.corr_id = str(uuid.uuid4())
        self.channel.basic_publish(
            exchange='',
            routing_key='rpc_queue',
            properties=pika.BasicProperties(
                reply_to=self.callback_queue,
                correlation_id=self.corr_id,
            ),
            body=str(n))
        while self.response is None:
            self.connection.process_data_events()
        return int(self.response)

fibonacci_rpc = FibonacciRpcClient()

print(" [x] Requesting fib(30)")
response = fibonacci_rpc.call(30)
print(" [.] Got %r" % response)
```

**Server (RPC Server)**:
```python
import pika

connection = pika.BlockingConnection(pika.ConnectionParameters(host='localhost'))
channel = connection.channel()

channel.queue_declare(queue='rpc_queue')

def fib(n):
    if n == 0:
        return 0
    elif n == 1:
        return 1
    else:
        return fib(n-1) + fib(n-2)

def on_request(ch, method, props, body):
    n = int(body)

    print(f" [.] fib({n})")
    response = fib(n)

    ch.basic_publish(
        exchange='',
        routing_key=props.reply_to,
        properties=pika.BasicProperties(correlation_id=props.correlation_id),
        body=str(response))
    ch.basic_ack(delivery_tag=method.delivery_tag)

channel.basic_qos(prefetch_count=1)
channel.basic_consume(queue='rpc_queue', on_message_callback=on_request)

print(" [x] Awaiting RPC requests")
channel.start_consuming()
```

### Explication

- **Direct Exchange**: Utilisé pour le routage direct où la clé de routage doit correspondre exactement.
- **Fanout Exchange**: Utilisé pour diffuser des messages à toutes les files d'attente liées.
- **Topic Exchange**: Utilisé pour le routage basé sur des motifs de clé de routage.
- **RPC**: Utilisé pour des appels de procédure à distance où le client attend une réponse du serveur.

Ces modèles d'échange permettent de gérer différents types de communication et de routage de messages dans RabbitMQ, offrant ainsi une grande flexibilité pour diverses architectures de micro-services.