---
name: "sd_bus_message_get_reply_cookie"
section: "3"
platform: "linux"
package: "libsystemd-dev"
version: "257.13-1~deb13u1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/sd_bus_message_get_cookie"
---

# sd\_bus\_message\_get\_reply\_cookie(3)

Returns the transaction cookie of a message

Part of [sd\_bus\_message\_get\_cookie(3)](/sd_bus_message_get_cookie/3.md).

## NAME

sd\_bus\_message\_get\_cookie, sd\_bus\_message\_get\_reply\_cookie - Returns the transaction cookie of a message

## SYNOPSIS

```
#include <systemd/sd-bus.h>
```

**int sd\_bus\_message\_get\_cookie(sd\_bus\_message \****message***, uint64\_t \****cookie***);**

**int sd\_bus\_message\_get\_reply\_cookie(sd\_bus\_message \****message***, uint64\_t \****cookie***);**

## DESCRIPTION

**sd\_bus\_message\_get\_cookie()** returns the transaction cookie of a message. The cookie uniquely identifies a message within each bus peer, but is not globally unique. It is assigned when a message is sent.

**sd\_bus\_message\_get\_reply\_cookie()** returns the transaction cookie of the message the specified message is a response to. When a reply message is generated for a method call message, its cookie is copied over into this field. Note that while every message that is transferred is identified by a cookie, only response messages carry a reply cookie field.

Both functions take a message object as first parameter and a place to store the 64-bit cookie in.

## RETURN VALUE

On success, these calls return 0 or a positive integer. On failure, they return a negative errno-style error code.

On success, the cookie/reply cookie is returned in the specified 64-bit unsigned integer variable.

### Errors

Returned errors may indicate the following problems:

**-EINVAL**

A specified parameter is invalid.

**-ENODATA**

No cookie has been assigned to this message. This either indicates that the message has not been sent yet and hence has no cookie assigned, or that the message is not a method response message and hence carries a reply cookie field.

## NOTES

Functions described here are available as a shared library, which can be compiled against and linked to with the **libsystemd** [**pkg-config**(1)](/pkg-config/1.md) file.

The code described here uses [**getenv**(3)](/getenv/3.md), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call [**setenv**(3)](/setenv/3.md) from a parallel thread. It is recommended to only do calls to **setenv()** from an early phase of the program when no other threads have been started.

## HISTORY

**sd\_bus\_message\_get\_cookie()** and **sd\_bus\_message\_get\_reply\_cookie()** were added in version 209.

## SEE ALSO

[**systemd**(1)](/systemd/1.md), [**sd-bus**(3)](/sd-bus/3.md), [**sd\_bus\_new**(3)](/sd_bus_new/3.md)