---
name: "sd_bus_message_get_type"
section: "3"
platform: "linux"
package: "systemd-libs"
version: "262.1-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/sd_bus_message_get_type"
---

# sd\_bus\_message\_get\_type(3)

Query bus message addressing/credentials metadata

## NAME

sd\_bus\_message\_get\_type, sd\_bus\_message\_get\_error, sd\_bus\_message\_get\_errno, sd\_bus\_message\_get\_creds, sd\_bus\_message\_is\_signal, sd\_bus\_message\_is\_method\_call, sd\_bus\_message\_is\_method\_error - Query bus message addressing/credentials metadata

## SYNOPSIS

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

**int sd\_bus\_message\_get\_type(sd\_bus\_message \****m***, uint8\_t \****type***);**

**sd\_bus\_error\* sd\_bus\_message\_get\_error(sd\_bus\_message \****m***);**

**int sd\_bus\_message\_get\_errno(sd\_bus\_message \****m***);**

**sd\_bus\_creds\* sd\_bus\_message\_get\_creds(sd\_bus\_message \****m***);**

**int sd\_bus\_message\_is\_signal(sd\_bus\_message \****m***, const char \****interface***, const char \****member***);**

**int sd\_bus\_message\_is\_method\_call(sd\_bus\_message \****m***, const char \****interface***, const char \****member***);**

**int sd\_bus\_message\_is\_method\_error(sd\_bus\_message \****m***, const char \****name***);**

## DESCRIPTION

**sd\_bus\_message\_get\_type()** returns the type of a message in the output parameter *type*, one of **SD\_BUS\_MESSAGE\_METHOD\_CALL**, **SD\_BUS\_MESSAGE\_METHOD\_RETURN**, **SD\_BUS\_MESSAGE\_METHOD\_ERROR**, **SD\_BUS\_MESSAGE\_SIGNAL**. This type is either specified as a parameter when the message is created using [**sd\_bus\_message\_new**(3)](/sd_bus_message_new/3.md), or is set automatically when the message is created using [**sd\_bus\_message\_new\_signal**(3)](/sd_bus_message_new_signal/3.md), [**sd\_bus\_message\_new\_method\_call**(3)](/sd_bus_message_new_method_call/3.md), [**sd\_bus\_message\_new\_method\_error**(3)](/sd_bus_message_new_method_error/3.md) and similar functions.

**sd\_bus\_message\_get\_error()** returns the error stored in the message *m*, if there is any. Otherwise, it returns **NULL**. **sd\_bus\_message\_get\_errno()** returns the error stored in the message *m* as a positive errno-style value, if there is any. Otherwise, it returns zero. Errors are mapped to errno values according to the default and any additional registered error mappings. See [**sd-bus-errors**(3)](/sd-bus-errors/3.md) and [**sd\_bus\_error\_add\_map**(3)](/sd_bus_error_add_map/3.md).

**sd\_bus\_message\_get\_creds()** returns the message credentials attached to the message *m*. If no credentials are attached to the message, it returns **NULL**. Ownership of the credentials instance is not transferred to the caller and hence should not be freed.

**sd\_bus\_message\_is\_signal()** checks if message *m* is a signal message. If *interface* is non-null, it also checks if the message has the same interface set. If *member* is non-null, it also checks if the message has the same member set. Also see [**sd\_bus\_message\_new\_signal**(3)](/sd_bus_message_new_signal/3.md). It returns true when all checks pass.

**sd\_bus\_message\_is\_method\_call()** checks if message *m* is a method call message. If *interface* is non-null, it also checks if the message has the same interface set. If *member* is non-null, it also checks if the message has the same member set. Also see [**sd\_bus\_message\_new\_method\_call**(3)](/sd_bus_message_new_method_call/3.md). It returns true when all checks pass.

**sd\_bus\_message\_is\_method\_error()** checks if message *m* is an error reply message. If *name* is non-null, it also checks if the message has the same error identifier set. Also see [**sd\_bus\_message\_new\_method\_error**(3)](/sd_bus_message_new_method_error/3.md). It returns true when all checks pass.

## RETURN VALUE

On success, these functions (except **sd\_bus\_message\_get\_error()** and **sd\_bus\_message\_get\_creds()**) return a non-negative integer. On failure, they return a negative errno-style error code. **sd\_bus\_message\_get\_errno()** always returns a non-negative integer, even on failure.

### Errors

Returned errors may indicate the following problems:

**-EINVAL**

The message parameter *m* or an output parameter is **NULL**.

## 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.

All functions listed here are thread-agnostic and only a single thread may operate on a given object at any given time. Different threads may access the same object at different times. Multiple independent objects may be used from different threads in parallel.

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\_type()**, **sd\_bus\_message\_is\_signal()**, **sd\_bus\_message\_is\_method\_call()**, and **sd\_bus\_message\_is\_method\_error()** were added in version 240.

**sd\_bus\_message\_get\_error()**, **sd\_bus\_message\_get\_errno()**, and **sd\_bus\_message\_get\_creds()** were added in version 246.

## SEE ALSO

[**systemd**(1)](/systemd/1.md), [**sd-bus**(3)](/sd-bus/3.md), [**sd\_bus\_message\_new**(3)](/sd_bus_message_new/3.md), [**sd\_bus\_message\_set\_destination**(3)](/sd_bus_message_set_destination/3.md), [**sd-bus-errors**(3)](/sd-bus-errors/3.md), [**sd\_bus\_error\_add\_map**(3)](/sd_bus_error_add_map/3.md)