Implement consumer queue boilerplate

epics-writer/epics-writer/start.py

@@ -1,35 +1,73 @@
 import json
 
-from pika import BlockingConnection, ConnectionParameters
+from pika import BlockingConnection, ConnectionParameters, BasicProperties
+
+REQUEST_EXCHANGE = "request"
+STATUS_EXCHANGE = "status"
+QUEUE_NAME = "epics"
+OUTPUT_FILE_SUFFIX = ".epics.h5"
+
+
+def update_status(channel, body, action, file, message=None):
+
+    status_header = {
+        "action": action,
+        "source": "epics-writer",
+        "routing_key": QUEUE_NAME,
+        "file": file,
+        "message": message
+    }
+
+    channel.basic_publish(exchange=STATUS_EXCHANGE,
+                          properties=BasicProperties(
+                              headers=status_header),
+                          routing_key="",
+                          body=body)
 
 
 def on_message(channel, method_frame, header_frame, body):
-    request = json.loads(body.decode())
-    epics_pvs = request.get("epics_pvs")
 
-    if not epics_pvs:
+    try:
+        request = json.loads(body.decode())
+        output_prefix = request["output_prefix"]
+        start_pulse_id = 1
+        stop_pulse_id = 10
+        metadata = request["metadata"]
+        epics_pvs = request["epics_pvs"]
+
+        output_file = output_prefix + OUTPUT_FILE_SUFFIX
+
+        update_status(channel, body, "write_start", output_file)
+
+    except Exception as e:
         channel.basic_reject(delivery_tag=method_frame.delivery_tag,
                              requeue=False)
 
-        # TODO: Send to status exchange.
+        update_status(channel, body, "write_rejected", str(e))
+
+    else:
+        channel.basic_ack(delivery_tag=method_frame.delivery_tag)
+        update_status(channel, body, "write_finished", output_file)
 
 
-    channel.basic_ack(delivery_tag=method_frame.delivery_tag)
-
-
-def connect_to_broker(broker_url, exchange_name, queue_name):
+def connect_to_broker(broker_url):
     connection = BlockingConnection(ConnectionParameters(broker_url))
     channel = connection.channel()
 
-    channel.exchange_declare(exchange=exchange_name,
+    channel.exchange_declare(exchange=REQUEST_EXCHANGE,
                              exchange_type="topic")
 
-    channel.queue_declare(queue=queue_name, auto_delete=True)
-    channel.queue_bind(queue=queue_name,
-                       exchange=exchange_name,
-                       routing_key="*.%s.*" % queue_name)
+    channel.exchange_declare(exchange=STATUS_EXCHANGE,
+                             exchange_type="fanout")
 
-    channel.basic_consume(queue_name, on_message)
+    channel.queue_declare(queue=QUEUE_NAME, auto_delete=True)
+    channel.queue_bind(queue=QUEUE_NAME,
+                       exchange=REQUEST_EXCHANGE,
+                       routing_key="*.%s.*" % QUEUE_NAME,
+                       auto_detele=True)
+
+    channel.basic_qos(prefetch_count=1)
+    channel.basic_consume(QUEUE_NAME, on_message)
 
     try:
         channel.start_consuming()
@@ -37,29 +75,19 @@ def connect_to_broker(broker_url, exchange_name, queue_name):
         channel.stop_consuming()
 
 
-BROKER_URL = "127.0.0.1"
-EXCHANGE_NAME = "request"
-QUEUE_NAME = "epics"
+DEFAULT_BROKER_URL = "127.0.0.1"
 
 
 def main():
     import argparse
     parser = argparse.ArgumentParser(description='Epics HDF5 writer')
     parser.add_argument('--broker_url', dest='broker_url',
-                        default=BROKER_URL,
+                        default=DEFAULT_BROKER_URL,
                         help='RabbitMQ broker URL')
-    parser.add_argument('--exchange_name', dest='exchange_name',
-                        default=EXCHANGE_NAME,
-                        help='Name of the request exchange.')
-    parser.add_argument('--queue_name', dest='queue_name',
-                        default=QUEUE_NAME,
-                        help='Name of the queue to connect to')
 
     args = parser.parse_args()
 
-    connect_to_broker(broker_url=args.broker_url,
-                      exchange_name=args.exchange_name,
-                      queue_name=args.queue_name)
+    connect_to_broker(broker_url=args.broker_url)
 
 
 if __name__ == '__main__':