OpenBMC REST API

The primary management interface for OpenBMC is REST. This document provides some basic structure and usage examples for the REST interface.

The schema for the rest interface is directly defined by the OpenBMC D-Bus structure. Therefore, the objects, attributes and methods closely map to those in the D-Bus schema.

For a quick explanation of HTTP verbs and how they relate to a RESTful API, see http://www.restapitutorial.com/lessons/httpmethods.html.

Authentication

See the details on authentication at REST-cheatsheet.

This tutorial uses token based authentication method:

$ export bmc=xx.xx.xx.xx
$ export token=`curl -k -H "Content-Type: application/json" -X POST https://${bmc}/login -d '{"username" :  "root", "password" :  "0penBmc"}' | grep token | awk '{print $2;}' | tr -d '"'`
$ curl -k -H "X-Auth-Token: $token" https://${bmc}/xyz/openbmc_project/...

HTTP GET operations & URL structure

There are a few conventions on the URL structure of the OpenBMC rest interface. They are:

To query the attributes of an object, perform a GET request on the object name, with no trailing slash. For example:

$ curl -k -H "X-Auth-Token: $token" https://${bmc}/xyz/openbmc_project/inventory/system
{
"data": {
 "AssetTag": "",
 "BuildDate": "",
 "Cached": true,
 "FieldReplaceable": true,
 "Manufacturer": "",
 "Model": "",
 "PartNumber": "",
 "Present": true,
 "PrettyName": "",
 "SerialNumber": ""
 },
 "message": "200 OK",
 "status": "ok"
}

To query a single attribute, use the attr/<name> path. Using the system object from above, we can query just the Name value:

$ curl -k -H "X-Auth-Token: $token" https://${bmc}/xyz/openbmc_project/inventory/system/attr/Cached
{
 "data": true,
 "message": "200 OK",
 "status": "ok"
}

When a path has a trailing-slash, the response will list the sub objects of the URL. For example, using the same object path as above, but adding a slash:

$ curl -k -H "X-Auth-Token: $token" https://${bmc}/xyz/openbmc_project/
{
 "data": [
 "/xyz/openbmc_project/Chassis",
 "/xyz/openbmc_project/Hiomapd",
 "/xyz/openbmc_project/Ipmi",
 "/xyz/openbmc_project/certs",
 "/xyz/openbmc_project/console",
 "/xyz/openbmc_project/control",
 "/xyz/openbmc_project/dump",
 "/xyz/openbmc_project/events",
 "/xyz/openbmc_project/inventory",
 "/xyz/openbmc_project/ipmi",
 "/xyz/openbmc_project/led",
 "/xyz/openbmc_project/logging",
 "/xyz/openbmc_project/network",
 "/xyz/openbmc_project/object_mapper",
 "/xyz/openbmc_project/sensors",
 "/xyz/openbmc_project/software",
 "/xyz/openbmc_project/state",
 "/xyz/openbmc_project/time",
 "/xyz/openbmc_project/user"
     ],
     "message": "200 OK",
  "status": "ok"
}

This shows that there are 19 children of the openbmc_project/ object: dump, software, control, network, logging,etc. This can be used with the base REST URL (ie., http://${bmc}/), to discover all objects in the hierarchy.

Performing the same query with /list will list the child objects recursively.

$ curl -k -H "X-Auth-Token: $token" https://${bmc}/xyz/openbmc_project/network/list
{
 "data": [
 "/xyz/openbmc_project/network/config",
 "/xyz/openbmc_project/network/config/dhcp",
 "/xyz/openbmc_project/network/eth0",
 "/xyz/openbmc_project/network/eth0/ipv4",
 "/xyz/openbmc_project/network/eth0/ipv4/3b9faa36",
 "/xyz/openbmc_project/network/eth0/ipv6",
 "/xyz/openbmc_project/network/eth0/ipv6/ff81b6d6",
 "/xyz/openbmc_project/network/eth1",
 "/xyz/openbmc_project/network/eth1/ipv4",
 "/xyz/openbmc_project/network/eth1/ipv4/3b9faa36",
 "/xyz/openbmc_project/network/eth1/ipv4/66e63348",
 "/xyz/openbmc_project/network/eth1/ipv6",
 "/xyz/openbmc_project/network/eth1/ipv6/ff81b6d6",
 "/xyz/openbmc_project/network/host0",
 "/xyz/openbmc_project/network/host0/intf",
 "/xyz/openbmc_project/network/host0/intf/addr",
 "/xyz/openbmc_project/network/sit0",
 "/xyz/openbmc_project/network/snmp",
 "/xyz/openbmc_project/network/snmp/manager"
     ],
   "message": "200 OK",
   "status": "ok"
}

Adding /enumerate instead of /list will also include the attributes of the listed objects.

$ curl -k -H "X-Auth-Token: $token" https://${bmc}/xyz/openbmc_project/time/enumerate
{
 "data": {
 "/xyz/openbmc_project/time/bmc": {
   "Elapsed": 1563209492098739
 },
 "/xyz/openbmc_project/time/host": {
   "Elapsed": 1563209492101678
 },
 "/xyz/openbmc_project/time/owner": {
   "TimeOwner": "xyz.openbmc_project.Time.Owner.Owners.BMC"
 },
 "/xyz/openbmc_project/time/sync_method": {
   "TimeSyncMethod": "xyz.openbmc_project.Time.Synchronization.Method.NTP"
 }
 },
 "message": "200 OK",
 "status": "ok"
}

HTTP PUT operations

PUT operations are for updating an existing resource (an object or property), or for creating a new resource when the client already knows where to put it. These require a json formatted payload. To get an example of what that looks like:

$ curl -k -H "X-Auth-Token: $token" https://${bmc}/xyz/openbmc_project/state/host0 > host.json
$ cat host.json
{
  "data": {
    "AttemptsLeft": 3,
    "BootProgress": "xyz.openbmc_project.State.Boot.Progress.ProgressStages.Unspecified",
    "CurrentHostState": "xyz.openbmc_project.State.Host.HostState.Off",
    "OperatingSystemState": "xyz.openbmc_project.State.OperatingSystem.Status.OSStatus.Inactive",
    "RequestedHostTransition": "xyz.openbmc_project.State.Host.Transition.Off"
  },
  "message": "200 OK",
  "status": "ok"
}

$ curl -k -H "X-Auth-Token: $token" https://${bmc}/xyz/openbmc_project/state/host0/attr/RequestedHostTransition > requested_host.json
$ cat requested_host.json
{
  "data": "xyz.openbmc_project.State.Host.Transition.Off",
  "message": "200 OK",
  "status": "ok"
}

When turning around and sending these as requests, delete the message and status properties.

To make curl use the correct content type header use the -H option to specify that we're sending JSON data:

$ curl -k -H "X-Auth-Token: $token" -H "Content-Type: application/json" -X PUT -d <json> <url>

A PUT operation on an object requires a complete object. For partial updates there is PATCH but that is not implemented yet. As a workaround individual attributes are PUTable.

For example, make changes to the requested_host.json file and do a PUT (upload):

$ cat requested_host.json
{"data": "xyz.openbmc_project.State.Host.Transition.Off"}
$ curl -k -H "X-Auth-Token: $token" -H "Content-Type: application/json" -X PUT -T requested_host.json https://${bmc}/xyz/openbmc_project/state/host0/attr/RequestedHostTransition

Alternatively specify the json inline with -d:

$ curl -k -H "X-Auth-Token: $token" -H "Content-Type: application/json" -X PUT -d '{"data": "xyz.openbmc_project.State.Host.Transition.On"}' https://${bmc}/xyz/openbmc_project/state/host0/attr/RequestedHostTransition

When using '-d' just remember that json requires quoting.

HTTP POST operations

POST operations are for calling methods, but also for creating new resources when the client doesn't know where to put it. OpenBMC does not support creating new resources via REST so any attempt to create a new resource will result in a HTTP 403 (Forbidden). These also require a json formatted payload. To delete logging entries:

$ curl -k -H "X-Auth-Token: $token" -H 'Content-Type: application/json' -X POST -d '{"data":[]}' https://${bmc}/xyz/openbmc_project/logging/action/DeleteAll

To invoke a method without parameters (Factory Reset of BMC and Host):

$ curl -k -H "X-Auth-Token: $token" -H 'Content-Type: application/json' -X POST -d '{"data":[]}' https://${bmc}/xyz/openbmc_project/software/action/Reset

HTTP DELETE operations

DELETE operations are for removing instances. Only D-Bus objects (instances) can be removed. If the underlying D-Bus object implements the xyz.openbmc_project.Object.Delete interface the REST server will call it. If xyz.openbmc_project.Object.Delete is not implemented, the REST server will return a HTTP 403 (Forbidden) error.

For example, to delete a event record:

Display logging entries:

$ curl -k -H "X-Auth-Token: $token" -H "Content-Type: application/json" -X GET https://${bmc}/xyz/openbmc_project/logging/entry/enumerate

Then delete the event record with ID 1:

$ curl -k -H "X-Auth-Token: $token" -H "Content-Type: application/json" -X DELETE  https://${bmc}/xyz/openbmc_project/logging/entry/1

Uploading images

It is possible to upload software upgrade images (for example to upgrade the BMC or host software) via REST. The content-type should be set to "application/octet-stream".

For example, to upload an image:(the <file_to_upload> must be a tar ball)

$ curl -k -H "X-Auth-Token: $token" -H "Content-Type: application/octet-stream" -X POST -T <file_to_upload> https://${bmc}/upload/image

In above example, the filename on the BMC will be chosen by the REST server.

It is possible for the user to choose the uploaded file's remote name:

curl -k -H "X-Auth-Token: $token" -H "Content-Type: application/octet-stream" -X PUT -T foo https://${bmc}/upload/image/bar

In above example, the file foo will be saved with the name bar on the BMC.

The operation will either return the version id (hash) of the uploaded file on success:

{
  "data": "afb92384",
  "message": "200 OK",
  "status": "ok"
}

or an error message

{
    "data": {
        "description": "Version already exists or failed to be extracted"
    },
    "message": "400 Bad Request",
    "status": "error"
}

For more details on uploading and updating software, see: https://github.com/openbmc/docs/tree/master/architecture/code-update

Event subscription protocol

It is possible to subscribe to events, of interest, occurring on the BMC. The implementation on the BMC uses WebSockets for this purpose, so that clients don't have do employ polling. Instead, the rest server on the BMC can push data to clients over a websocket. The BMC can push out information pertaining to D-Bus InterfacesAdded and PropertiesChanged signals.

Following is a description of the event subscription protocol, with example JS code snippets denoting client-side code.

a) The client needs to have logged on to the BMC. b) The client needs to open a secure websocket with the URL /subscribe.

   var ws = new WebSocket("wss://<BMC IP>/subscribe")

c) The client needs to send, over the websocket, a JSON dictionary, comprising of key-value pairs. This dictionary serves as the "events filter". All the keys are optional, so the dictionary can be empty if no filtering is desired. The filters represented by each of the key-value pairs are ORed.

One of the supported keys is "paths". The corresponding value is an array of D-Bus paths. The InterfacesAdded and PropertiesChanged D-Bus signals emanating from any of these path(s) alone, and not from any other paths, will be included in the event message going out of the BMC.

The other supported key is "interfaces". The corresponding value is an array of D-Bus interfaces. The InterfacesAdded and PropertiesChanged D-Bus signal messages comprising of any of these interfaces will be included in the event message going out of the BMC.

All of the following are valid:

var data = JSON.stringify(
{
    "paths": ["/xyz/openbmc_project/logging", "/xyz/openbmc_project/sensors"],
    "interfaces": ["xyz.openbmc_project.Logging.Entry", "xyz.openbmc_project.Sensor.Value"]
});
ws.onopen = function() {
    ws.send(data);
};

var data = JSON.stringify(
{
    "paths": ["/xyz/openbmc_project/logging", "/xyz/openbmc_project/sensors"],
});
ws.onopen = function() {
    ws.send(data);
};

var data = JSON.stringify(
{
    "interfaces": ["xyz.openbmc_project.Logging.Entry", "xyz.openbmc_project.Sensor.Value"]
});
ws.onopen = function() {
    ws.send(data);
};

var data = JSON.stringify(
{
});
ws.onopen = function() {
    ws.send(data);
};

d) The rest server on the BMC will respond over the websocket when a D-Bus event occurs, considering the client supplied filters. The rest servers notifies about InterfacesAdded and PropertiesChanged events. The response is a JSON dictionary as follows :

InterfacesAdded

"event": InterfacesAdded
"path": <string : new D-Bus path that was created>
"interfaces": <dict : a dictionary of interfaces> (similar to org.freedesktop.DBus.ObjectManager.InterfacesAdded )

PropertiesChanged

"event": PropertiesChanged
"path": <string : D-Bus path whose property changed>
"interface": <string : D-Bus interface to which the changed property belongs>
"properties": <dict : a dictionary of properties> (similar to org.freedesktop.DBus.Properties.PropertiesChanged)