rabbitmq-orders

RabbitMQ orders — Python produces, Node consumes

A Python producer publishes canonical BabelQueue envelopes to a RabbitMQ queue; a Node service reads the same queue and routes by URN. Same wire envelope, different languages, one broker — no PHP serialize(), no language-specific format. The Node consumer never knows which language wrote the message; it only sees the canonical envelope and meta.lang.

Each SDK uses the §2 RabbitMQ binding: the message body is the envelope JSON, and the contract fields are projected onto native AMQP 0-9-1 properties so a consumer routes without decoding the body — type = URN, correlation_id = trace_id, message_id = meta.id, app_id = babelqueue, plus the native-typed x-schema-version / x-source-lang / x-attempts headers (AMQP field-tables carry typed values — integers stay integers). Consume is basic.get + manual ack (at-least-once); routing reads properties.type. x-attempts is the authoritative attempt counter — RabbitMQ has no native delivery count for this transport, so attempts lives in the body.

The demo runs against a stock rabbitmq:3-management container, so it needs no managed broker. Point BROKER_URL at any RabbitMQ to run it there unchanged.

Run it

# 1) start RabbitMQ (AMQP on 5672, management UI on http://localhost:15672 — guest/guest)
docker compose up -d
# wait until healthy (~15-20s): docker compose ps

# 2) producer — Python   (needs babelqueue[amqp] from PyPI)
cd producer-python
python -m venv .venv && .venv/bin/pip install "babelqueue[amqp]"
.venv/bin/python produce.py

# 3) consumer — Node   (needs @babelqueue/rabbitmq ^1.0.0 + amqplib)
cd consumer-node
npm install
node consume.mjs

The Node consumer polls the orders queue and prints each order as it routes it by URN:

[node] consuming from 'orders' until 4 message(s) handled...
[node] orders:created  order_id=1001  amount=19.99  from lang=python  trace=b3e1d875-1be1-4ae4-9d9d-d2523910de27  attempts=0
[node] orders:created  order_id=1002  amount=39.98  from lang=python  trace=ca00b24c-5200-47fe-b995-333cb8a4eb3b  attempts=0
[node] orders:created  order_id=1003  amount=59.97  from lang=python  trace=8af7b35d-3a0f-4c95-a087-b8bf0cbce6f3  attempts=0
[node] orders:shipped  order_id=1002  carrier=DHL  from lang=python
[node] done — handled 4 message(s).

BROKER_URL (both sides, default amqp://guest:guest@localhost:5672/) and CONSUME_MESSAGES (consumer, default 4) are configurable via env vars.

What this proves

• One envelope, two languages. Python's PikaTransport and Node's RabbitMQConsumer agree on the byte-identical envelope body and the §2 AMQP property projection (Python → Node).
• URN routing without decoding. The consumer routes on properties.type (urn:babel:orders:created vs urn:babel:orders:shipped); it never parses a message it has no handler for.
• Trace propagation. Each message's trace_id (carried as correlation_id) survives the hop unchanged.
• attempts from the body. A first delivery reads attempts = 0 (RabbitMQ has no native delivery count for this transport; the body — mirrored to x-attempts — is the home).
• Manual ack (at-least-once). The Node consumer acks a message only after the handler returns.

Cleanup

docker compose down