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feat(readme): adds example with multiples RPC requests #15

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feat(readme): adds example with multiples RPC requests #15

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43 changes: 43 additions & 0 deletions README.md
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Expand Up @@ -157,6 +157,49 @@ except socket.timeout:
print('No reply :(')
```

Multiples requests can be done throughout same client. To distinguish which reply is related to each request, you can use the `correlation_id`. This attribute is always set when a `Message` is published containing `reply_to` parameter, which means that it was a RPC request. Example below shows how to deal with it.

```python
from __future__ import print_function
from is_wire.core import Channel, Message, Subscription
from google.protobuf.struct_pb2 import Struct
import socket

channel = Channel("amqp://guest:guest@localhost:5672")
subscription = Subscription(channel)

# Prepare first request
struct = Struct()
struct.fields["value"].number_value = 1.0
request_1 = Message(content=struct, reply_to=subscription)

# Prepare second request
struct = Struct()
struct.fields["value"].number_value = 2.0
request_2 = Message(content=struct, reply_to=subscription)

# Make requests
channel.publish(request_1, topic="MyService.Increment")
channel.publish(request_2, topic="MyService.Increment")

# Wait for replies with 1.0 seconds timeout
n_replies = 0
while n_replies < 2:
try:
reply = channel.consume(timeout=1.0)
struct = reply.unpack(Struct)
if reply.correlation_id == request_1.correlation_id:
n_replies += 1
print('First Request\nRPC Status:', reply.status, '\nReply:', struct)
elif reply.correlation_id == request_2.correlation_id:
n_replies += 1
print('Second Request\nRPC Status:', reply.status, '\nReply:', struct)
else:
print('Unexpected message')
except socket.timeout:
print('No reply :(')
```

### Tracing messages

This middleware uses [opencensus](https://github.com/census-instrumentation/opencensus-python) as instrumentation library. Latest versions of opencensus released separate packages to integrate with different frameworks and tracing collector tools. When interacting with services implemented with either the C++ or Python of is-wire, we recommend to use [Zipkin](https://zipkin.apache.org/) to collect the tracing data. To do so, use the latest version of [OpenCensus Zipkin Exporter](https://github.com/census-instrumentation/opencensus-python/tree/master/contrib/opencensus-ext-zipkin).
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