Selenium 4.x trying to POST CDP: "UnsupportedCommandException" - selenium

Question

I`m trying to execute some commands via CDP, however no matter what combination of Selenium/Driver/Chrome I use it's always the same result.
Last tested with:
Selenium 4.1.1
Chrome + Driver 96.0.4664.110
The project is made in C so I am posting manually to Selenium via CURL. Every other command besides CDP works fine.
I have checked Selenium, Chrome Driver; they both have the CDP support built in.
The URL's I tried to post to are:
- /session/id/goog/cdp/execute
- /session/id/{}/cdp/execute
The posted data format is: "cmd" + "params" (json object).
Both end in the same result: org.openqa.selenium.UnsupportedCommandException.
I also tried to run Selenium in different modes, standalone, hub/node, same result.
Can someone please advise what I am doing wrong? Or maybe I have misunderstood the usage?

Answer 1

Using chromedriver executable
This worked for me (Windows + Postman), but should also work with CURL Linux/Mac.
1 Download chromedriver: https://chromedriver.chromium.org/downloads for your chrome version.
2 Start chromedriver
start chromedriver.exe
output:
Starting ChromeDriver 97.0.4692.71 on port 9515...
3 Send requests to localhost:9515/
3.1 Create Session:
POST localhost:9515/session
request json body:
{"capabilities":{"goog:chromeOptions": {}}}
status 200
response:
"value": {
"capabilities": {
...
},
"sessionId": "b8ac49ce2203739fa0d32dfe8d1a23b5"
3.2 Navigate some url (optional, just check request by sessionId works):
POST localhost:9515/session/b8ac49ce2203739fa0d32dfe8d1a23b5/url
request json body:
{"url": "https://example.com"}
status 200
3.3 Execute CDP command (take screenshot):
POST localhost:9515/session/b8ac49ce2203739fa0d32dfe8d1a23b5/goog/cdp/execute
request json body:
{"cmd":"Page.captureScreenshot", "params":{}}
status 200
response:
{
"value": {
"data": "iVBORw0KGgoAAAANSUhEUgA...."
}
}
Allow remote connections
By default chromedriver allows only local connections.
To allow some remote IPs:
start chromedriver.exe --allowed-ips="some-remote-ip"
Reference: https://sites.google.com/a/chromium.org/chromedriver/security-considerations
Run CDP commands with Selenium Grid
Eventually, it started to work for me with
ChromeDriver 97.0.4692.71
selenium-server-4.1.1
Chrome 97.0.4692.71 (Official Build) (64-bit)
Note: Content-Type header should have charset=utf-8
Content-Type:application/json;charset=utf-8 for Selenium Grid HTTP requests.
Prerequisites
1 Download and run selenium server according to
https://www.selenium.dev/documentation/grid/getting_started/
java -jar selenium-server-<version>.jar standalone --driver-configuration display-name='Chrome' stereotype='{"browserName":"chrome"}'
2 Create Session:
POST localhost:4444/wd/hub/session
request json body:
{
"desiredCapabilities": {
"browserName": "chrome",
"goog:chromeOptions": {
"args": [
],
"extensions": [
]
}
},
"capabilities": {
"firstMatch": [
{
"browserName": "chrome",
"goog:chromeOptions": {
"args": [
],
"extensions": [
]
}
}
]
}
}
status 200
response:
{
"status": 0,
"sessionId": "69ac1c82306f72c7aaf53cfbb28a30e7",
...
}
}
3 Execute CDP command (take screenshot):
POST localhost:4444/wd/hub/session/69ac1c82306f72c7aaf53cfbb28a30e7/goog/cdp/execute
request json body:
{"cmd":"Page.captureScreenshot", "params":{}}
status 200
response:
{
"value": {
"data": "iVBORw0KGgoAAAANSUhEUgA...."
}
}