Structured Data

Client libraries may provide tools to help receive structured data, like JSON. The core traffic to the NATS server will always be opaque byte arrays. The server does not process message payloads in any form. For libraries that don't provide helpers, you can always encode and decode data before sending the associated bytes to the NATS client.

For example, to receive JSON you could do:

Go
Java
JavaScript
Python
Ruby
TypeScript
C
Go
nc, err := nats.Connect("demo.nats.io",
nats.ErrorHandler(func(nc *nats.Conn, s *nats.Subscription, err error) {
if s != nil {
log.Printf("Async error in %q/%q: %v", s.Subject, s.Queue, err)
} else {
log.Printf("Async error outside subscription: %v", err)
}
}))
if err != nil {
log.Fatal(err)
}
defer nc.Close()
ec, err := nats.NewEncodedConn(nc, nats.JSON_ENCODER)
if err != nil {
log.Fatal(err)
}
defer ec.Close()
// Define the object
type stock struct {
Symbol string
Price int
}
wg := sync.WaitGroup{}
wg.Add(1)
// Subscribe
// Decoding errors will be passed to the function supplied via
// nats.ErrorHandler above, and the callback supplied here will
// not be invoked.
if _, err := ec.Subscribe("updates", func(s *stock) {
log.Printf("Stock: %s - Price: %v", s.Symbol, s.Price)
wg.Done()
}); err != nil {
log.Fatal(err)
}
// Wait for a message to come in
wg.Wait()
Java
class StockForJsonSub {
public String symbol;
public float price;
public String toString() {
return symbol + " is at " + price;
}
}
public class SubscribeJSON {
public static void main(String[] args) {
try {
Connection nc = Nats.connect("nats://demo.nats.io:4222");
// Use a latch to wait for 10 messages to arrive
CountDownLatch latch = new CountDownLatch(10);
// Create a dispatcher and inline message handler
Dispatcher d = nc.createDispatcher((msg) -> {
Gson gson = new Gson();
String json = new String(msg.getData(), StandardCharsets.UTF_8);
StockForJsonSub stk = gson.fromJson(json, StockForJsonSub.class);
// Use the object
System.out.println(stk);
latch.countDown();
});
// Subscribe
d.subscribe("updates");
// Wait for a message to come in
latch.await();
// Close the connection
nc.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
JavaScript
let nc = NATS.connect({
url: "nats://demo.nats.io:4222",
json: true
});
nc.subscribe('updates', (msg) => {
if(msg && msg.ticker === 'TSLA') {
t.log('got message:', msg);
}
});
Python
import asyncio
import json
from nats.aio.client import Client as NATS
from nats.aio.errors import ErrTimeout
async def run(loop):
nc = NATS()
await nc.connect(servers=["nats://127.0.0.1:4222"], loop=loop)
async def message_handler(msg):
data = json.loads(msg.data.decode())
print(data)
sid = await nc.subscribe("updates", cb=message_handler)
await nc.flush()
await nc.auto_unsubscribe(sid, 2)
await nc.publish("updates", json.dumps({"symbol": "GOOG", "price": 1200 }).encode())
await asyncio.sleep(1, loop=loop)
await nc.close()
Ruby
require 'nats/client'
require 'json'
NATS.start(servers:["nats://127.0.0.1:4222"]) do |nc|
nc.subscribe("updates") do |msg|
m = JSON.parse(msg)
# {"symbol"=>"GOOG", "price"=>12}
p m
end
end
TypeScript
let nc = await connect({
url: "nats://demo.nats.io:4222",
payload: Payload.JSON
});
nc.subscribe('updates', (err, msg) => {
t.log('got message:', msg.data ? msg.data : "no payload");
});
C
// Structured data is not configurable in C NATS Client.
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