# Replying to a Message

Incoming messages have an optional reply-to field. If that field is set, it will contain a subject to which a reply is expected.

For example, the following code will listen for that request and respond with the time.

{% tabs %}
{% tab title="Go" %}

```go
nc, err := nats.Connect("demo.nats.io")
if err != nil {
    log.Fatal(err)
}
defer nc.Close()

// Subscribe
sub, err := nc.SubscribeSync("time")
if err != nil {
    log.Fatal(err)
}

// Read a message
msg, err := sub.NextMsg(10 * time.Second)
if err != nil {
    log.Fatal(err)
}

// Get the time
timeAsBytes := []byte(time.Now().String())

// Send the time as the response.
msg.Respond(timeAsBytes)
```

{% endtab %}

{% tab title="Java" %}

```java
Connection nc = Nats.connect("nats://demo.nats.io:4222");

// Subscribe to the "time" subject and reply with the current time
Subscription sub = nc.subscribe("time");

// Read a message
Message msg = sub.nextMessage(Duration.ZERO);

// Get the time
Calendar cal = Calendar.getInstance();
SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
byte[] timeAsBytes = sdf.format(cal.getTime()).getBytes(StandardCharsets.UTF_8);

// Send the time to the reply to subject
nc.publish(msg.getReplyTo(), timeAsBytes);

// Flush and close the connection
nc.flush(Duration.ZERO);
nc.close();
```

{% endtab %}

{% tab title="JavaScript" %}

```javascript
const sc = StringCodec();
// set up a subscription to process a request
const sub = nc.subscribe("time");
for await (const m of sub) {
  m.respond(sc.encode(new Date().toLocaleDateString()));
}
```

{% endtab %}

{% tab title="Python" %}

```python
nc = NATS()

await nc.connect(servers=["nats://demo.nats.io:4222"])

future = asyncio.Future()

async def cb(msg):
  nonlocal future
  future.set_result(msg)

await nc.subscribe("time", cb=cb)

await nc.publish_request("time", new_inbox(), b'What is the time?')
await nc.flush()

# Read the message
msg = await asyncio.wait_for(future, 1)

# Send the time
time_as_bytes = "{}".format(datetime.now()).encode()
await nc.publish(msg.reply, time_as_bytes)
```

{% endtab %}

{% tab title="C#" %}

```csharp
// dotnet add package NATS.Net
using NATS.Net;

await using var client = new NatsClient();

// Subscribe to the "time" subject and reply with the current time
await foreach (var msg in client.SubscribeAsync<string>("time"))
{
    await msg.ReplyAsync(DateTime.Now);
}
```

{% endtab %}

{% tab title="Ruby" %}

```ruby
require 'nats/client'
require 'fiber'

NATS.start(servers:["nats://127.0.0.1:4222"]) do |nc|
  Fiber.new do
    f = Fiber.current

    nc.subscribe("time") do |msg, reply|
      f.resume Time.now
    end

    nc.publish("time", 'What is the time?', NATS.create_inbox)

    # Use the response
    msg = Fiber.yield
    puts "Reply: #{msg}"

  end.resume
end
```

{% endtab %}

{% tab title="C" %}

```c
natsConnection      *conn      = NULL;
natsSubscription    *sub       = NULL;
natsMsg             *msg       = NULL;
natsStatus          s          = NATS_OK;

s = natsConnection_ConnectTo(&conn, NATS_DEFAULT_URL);

// Subscribe
if (s == NATS_OK)
    s = natsConnection_SubscribeSync(&sub, conn, "time");

// Wait for messages
if (s == NATS_OK)
    s = natsSubscription_NextMsg(&msg, sub, 10000);

if (s == NATS_OK)
{
    char buf[64];

    snprintf(buf, sizeof(buf), "%lld", nats_Now());

    // Send the time as a response
    s = natsConnection_Publish(conn, natsMsg_GetReply(msg), buf, (int) strlen(buf));

    // Destroy message that was received
    natsMsg_Destroy(msg);
}

(...)

// Destroy objects that were created
natsSubscription_Destroy(sub);
natsConnection_Destroy(conn);
```

{% endtab %}
{% endtabs %}


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.nats.io/using-nats/developer/receiving/reply.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.