SWUpdate: API for external programs


SWUpdate contains an integrated web-server to allow remote updating. However, which protocols are involved during an update is project specific and differs significantly. Some projects can decide to use FTP to load an image from an external server, or using even a proprietary protocol. The integrated web-server uses this interface.

SWUpdate has a simple interface to let external programs to communicate with the installer. Clients can start an upgrade and stream an image to the installer, querying then for the status and the final result. The API is at the moment very simple, but it can easy be extended in the future if new use cases will arise.

API Description

The communication runs via UDS (Unix Domain Socket). The socket is created at startup by SWUpdate in /tmp/sockinstctrl as per default configuration. This socket should, however, not be used directly but instead by the Client Library explained below.

The exchanged packets are described in network_ipc.h

typedef struct {
        int magic;
        int type;
        msgdata data;
} ipc_message;

Where the fields have the meaning:

  • magic : a magic number as simple proof of the packet
  • msgdata : a buffer used by the client to send the image or by SWUpdate to report back notifications and status.

The client sends a REQ_INSTALL packet and waits for an answer. SWUpdate sends back ACK or NACK, if for example an update is already in progress.

After the ACK, the client sends the whole image as a stream. SWUpdate expects that all bytes after the ACK are part of the image to be installed. SWUpdate recognizes the size of the image from the CPIO header. Any error lets SWUpdate to leave the update state, and further packets will be ignored until a new REQ_INSTALL will be received.


Client Library

A library simplifies the usage of the IPC making available a way to start asynchronously an update.

The library consists of one function and several call-backs.

int swupdate_async_start(writedata wr_func, getstatus status_func,
        terminated end_func)
typedef int (*writedata)(char **buf, int *size);
typedef int (*getstatus)(ipc_message *msg);
typedef int (*terminated)(RECOVERY_STATUS status);

swupdate_async_start creates a new thread and start the communication with SWUpdate, triggering for a new update. The wr_func is called to get the image to be installed. It is responsibility of the callback to provide the buffer and the size of the chunk of data.

The getstatus call-back is called after the stream was downloaded to check how upgrade is going on. It can be omitted if only the result is required.

The terminated call-back is called when SWUpdate has finished with the result of the upgrade.

Example about using this library is in the examples/client directory.

API to the integrated Webserver

The integrated Webserver provides REST resources to push a SWU package and to get inform about the update process. This API is based on HTTP standards. There are to kind of interface:

  • Install API to push a SWU and to restart the device after update.
  • A WebSocket interface to send the status of the update process.

Install API

POST /upload

This initiates an update: the initiator sends the request and start to stream the SWU in the same way as described in API Description.

Restart API

POST /restart

If configured (see post update command), this request will restart the device.

WebSocket API

The integrated Webserver exposes a WebSocket API. The WebSocket protocol specification defines ws (WebSocket) and wss (WebSocket Secure) as two new uniform resource identifier (URI) schemes that are used for unencrypted and encrypted con nections, respectively and both of them are supported by SWUpdate. A WebSocket provides full-duplex communication but it is used in SWUpdate to send events to an external host after each change in the update process. The Webserver sends JSON formatted responses as results of internal events.

The response contains the field type, that defines which event is sent.

Event Type
type Description of event
status Event sent when SWUpdate’s internal state changes
source Event to inform from which interface an update is received
info Event with custom message to be passed to an external process
message Event that contains the error message in case of error
step Event to inform about the running update

Status Change Event

This event is sent when the internal SWUpdate status change. Following status are supported:



        "type": "status",
        "status": "SUCCESS"

Source Event

This event informs from which interface a SWU is loaded.

        "type": "source",
        "source": "WEBSERVER"

The field source can have one of the following values:


Info Event

This event forwards all internal logs sent with level=INFO.

        "type": "info",
        "source": < text message >

Message Event

This event contains the error message in case of failure.

Fields for message event
name Description
status “message”
level “3” in case of error, “6” as info
text Message associated to the event


        "type": "message",
        "level": "3",
        "text" : "[ERROR] : SWUPDATE failed [0] ERROR core/cpio_utils.c : ",

Step event

This event contains which is the current step running and which percentage of this step is currently installed.

Fields for step event
name Description
number total number of steps N for this update
step running step in range [1..N]
name filename of artefact to be installed
percent percentage of the running step


        "type": "step",
        "number": "7",
        "step": "2",
        "name": "rootfs.ext4.gz",
        "percent": "18"