HtmlUnit Remote is a driver service for HtmlUnitDriver that enables you to acquire driver sessions from Selenium 4 Grid.
To eliminate behavioral differences between local and remote configurations, the Selenium Foundation framework always acquires browser sessions from a Grid instance, managing its own local grid instance when not configured to use an existing instance. Selenium 3 Grid could be configured to supply HtmlUnitDriver sessions, supported by special-case handling within the Node server itself. This handling was not carried over into Selenium 4 Grid, which was completely re-engineered with new architecture and vastly expanded capabilities.
The lack of HtmlUnitDriver support in Selenium 4 Grid necessitated reconfiguring the Selenium Foundation project unit tests from using this Java-only managed artifact to using a standard browser like Chrome, an external dependency that requires additional resources and imposes additional risks of failure.
The driver service implemented by HtmlUnit Remote enables Selenium 4 Grid to supply HtmlUnitDriver sessions.
HtmlUnit Remote provides the following elements:
- HtmlUnitDriverInfo - This class informs Selenium 4 Grid that HtmlUnitDriver is available and provides a method to create new driver instances.
- HtmlUnitDriverService - This class manages a server that hosts instances of HtmlUnitDriver.
- HtmlUnitDriverServer - This is the server class that hosts HtmlUnitDriver instances. It implements the W3C WebDriver protocol:
- Create new driver sessions
- Route driver commands to specified driver sessions
- Package driver method results into HTTP responses
In operation, HtmlUnitDriverService is instantiated by Selenium 4 Grid node servers that are configured to support HtmlUnitDriver. Unlike other driver services, which launch a new process for each created driver session, HtmlUnitDriverService starts a single in-process server that hosts all of the driver sessions it creates.
[node]
detect-drivers = false
[[node.driver-configuration]]
display-name = "HtmlUnit"
stereotype = "{\"browserName\": \"htmlunit\"}"
[distributor]
slot-matcher = "org.openqa.selenium.htmlunit.remote.HtmlUnitSlotMatcher"
The selenium-server JAR doesn't include the HtmlUnitDriver artifacts; these need to be specified as extensions to the grid class path via the --ext option:
java -jar selenium-server-<version>.jar --ext htmlunit-remote-<version>-grid-extension.jar standalone --config htmlunit.toml
The grid-extension artifact provides all of the specifications and service providers required to enable Selenium 4 Grid to supply remote sessions of HtmlUnitDriver. This artifact combines htmlunit-remote with htmlunit3-driver, htmlunit, and all of their unique dependencies.
In HtmlUnit Driver, you can use the standard browserVersion capability to select a specific browser emulation profile. This works as expected in local operation but will cause driver acquisition to fail in remote configurations. The reason for this is that browserVersion is an identity value that the Selenium Grid distributor expects to match against the stereotype of a compatible node. In HtmlUnit Driver, browserVersion is a configuration value, so this capability should not be considered for slot matching.
HtmlUnit Remote adds a vendor-specific capability for selecting a specific browser emulation profile: garg:browserVersion. If you use the standard HtmlUnitDriverOptions class to build your driver specification, this issue is handled for you automatically. If you specify driver capabilities directly, be sure to use this new vendor-specific capability name.
{"browserName": "htmlunit", "garg:browserVersion": "firefox-115"}
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