KasmVNC has an API to make changes or get data via simple HTTPS API calls.

All API calls require owner credentials. The following command will create a user with the owner permission.

vncpasswd -u my_username -w -r -o

Here is an example of how to use curl to send an API call.

curl -u 'my_username:mypassword' https://localhost:6901/api/get_bottleneck_stats -k

This uses the curl -u option, however, you can also send the credentials in the Authorization header. See specifications on HTTP Basic Authorization for more details.

Returns CPU and Network bottleneck statistics. These metrics attempt to identify where performance issues may be occurring. The network and CPU stats each have two numbers. The first number is the current snapshot in time value and the second is averaged over time. Values range from 0 to 10 with 10 representing no constraints. When the frame rate drops, the bottleneck stats should help identify if the bottleneck is server side CPU or the network. The following is an example of what is returned

/api/get_bottleneck_stats

Example Returned JSON

{
    "myusername": {
         "71.61.88.0_1627638421.160028::websocket": [ 8.2, 9.6, 10.0, 9.4 ],
         "71.61.88.0_1627638469.484285::websocket": [ 8.2, 9.6, 2.6, 8.5 ]
    }
}

Because KasmVNC supports multiple users and each user can have multiple connections, the returned JSON contains a dict for each user, which contains an entry for each connection. Each connection has an array with the following contents in order:

CPU, CPU Average, Network, Network Average

In the above example, the second connection for shows that the network is not able to keep up with the frames being sent from the server. It also indicates some CPU constraints, meaning that the CPU is mostly keeping up with the changes to the screen but not at 100%.

The bottleneck stats are a quick way to determine whether the network or the server-side CPU is causing a bottleneck, however, it does not provide enough fidelity to make coding decisions. The frame stats API call returns timings for all major processes with respect to processing a single frame.

/api/get_frame_stats

client - Which client connection to return frame stats for auto - Return frame stats for the first connection for the owner all - Return frame stats for ALL client connections none - Return no client side statistics 71.61.88.0_1627638421.160028::websocket - Example of providing a specific connection

Example: /api/get_frame_stats?client=auto

Example Returned JSON

{
    "frame" : {
        "resx": 1680,     
        "resy": 971,      
        "changed": 60,    
        "server_time": 45 
    },
    "server_side" : [
        { "process_name": "Analysis", "time": 2 },
	{ "process_name": "Screenshot", "time": 3 },
	{ "process_name": "Encoding_total", "time": 25, "videoscaling": 17 },
	{ "process_name": "TightJPEGEncoder", "time": 3, "count": 1, "area": 786432 },
	{ "process_name": "TightWEBPEncoder", "time": 0, "count": 0, "area": 0 }
    ],
    "client_side" : [
        {
            "client": "71.61.88.0_1627638469.484285::websocket",
            "client_time": 1,
            "ping": 54,
            "processes" : [
                { "process_name": "scanRenderQ", "time": 0 }
            ]
         }
     ]
}

Since encoding in jpeg and webp is multi-threaded, the time specified in the process entries for JPEG and WEBP encoding is CPU time not wall clock time. The "Encoding_total" process logs the wall clock time for all encoding and also includes videoscaling time which only applies when in "video mode". Video mode scales image down in size, encodes, sends to client, and the client scales it back up. Video mode keeps aspect ratio. Video mode kicks in when screen change reaches a threshold for a period of time defined.

Get a screenshot of the current session. You can pass a height and width that do not match the current aspect ratio, it will return the requested width with the height adjusted to keep the aspect ratio.

/api/get_screenshot

width - defaults to actual remote screen width height - defaults to actual remote screen height quality - JPEG quality, defaults to 7 deduplicate - set to true if you want the API call to return nothing if the screenshot has not changed since the last request

Add another user to the session.

/api/create_user

name - the username password - the requested password write - set to 'true' if the user should have write permissions (control of mouse and keyboard) read - Should the user have read access (optional) owner - Should the owner be able to manage users

example: /api/create_user?name=fred&password=123&write=true

Create User can also be called as a POST with JSON data for bulk operations.

[
   { "user": "username1", "password": "password123", "write": true, "read": true, "owner": false },
   { "user": "username2", "password": "password123", "write": true, "read": true, "owner": false }
]

/api/update_user

name - The target username password - The password to update (optional) write - Set to true if the user should have write permission (control of mouse and keyboard) (optional) read - Should the user have read access (optional) owner - Should the owner be able to manage users

example: /api/update_user?name=fred&password=123&write=true

Update User can also be called as a POST with JSON data for bulk operations.

[
   { "user": "username1", "write": true, "read": true, "owner": false },
   { "user": "username2", "write": true, "read": true, "owner": false }
]

Remove a user from the KasmVNC session

/api/remove_user

name - username of the user to remove

example: /api/remove_user?name=fred

Remove User can also be called as a POST with JSON data for bulk operations.

[
   { "user": "username1" },
   { "user": "username2" }
]