SeleniumHQ/selenium · error · ArgumentError

incompatible proxy type #{type.inspect} (already set to #{@t

Error message

incompatible proxy type #{type.inspect} (already set to #{@type.inspect})

What it means

Raised by Selenium::WebDriver::Proxy#type= when a proxy attribute setter implicitly forces a proxy type that conflicts with the type already established by a previous setter. The Proxy object enforces a single proxyType across all attributes: :direct, :manual, :pac, :auto_detect, :system. Each attribute setter (http=, ssl=, socks=, socks_version=, etc.) calls self.type = :manual, while pac= sets :pac and auto_detect= sets :auto_detect. Once one type is set, mixing attributes from a different type family triggers this ArgumentError.

Source

Thrown at rb/lib/selenium/webdriver/common/proxy.rb:130

      def socks_password=(value)
        self.type = :manual
        @socks_password = value
      end

      def socks_version=(value)
        self.type = :manual
        @socks_version = value
      end

      def type=(type)
        unless TYPES.key? type
          raise ArgumentError,
                "invalid proxy type: #{type.inspect}, expected one of #{TYPES.keys.inspect}"
        end

        if defined?(@type) && type != @type
          raise ArgumentError, "incompatible proxy type #{type.inspect} (already set to #{@type.inspect})"
        end

        @type = type
      end

      def as_json(*)
        json_result = {
          'proxyType' => TYPES[type].downcase,
          'httpProxy' => http,
          'noProxy' => no_proxy.is_a?(String) ? no_proxy.split(',').map(&:strip).reject(&:empty?) : no_proxy,
          'proxyAutoconfigUrl' => pac,
          'sslProxy' => ssl,
          'autodetect' => auto_detect,
          'socksProxy' => socks,
          'socksUsername' => socks_username,
          'socksPassword' => socks_password,
          'socksVersion' => socks_version
        }.compact

View on GitHub (pinned to aa36b38e69)

Solutions

Use only one proxy type family: either manual settings (http, ssl, socks, no_proxy, socks_username, socks_password, socks_version) OR pac URL OR auto_detect OR direct OR system.
If switching proxy modes at runtime, create a new Proxy instance instead of reusing the same one.
Inspect your options Hash before passing it to Proxy.new and remove keys belonging to a different type family.
Set the type explicitly via proxy.type = :manual (or :pac) once, then only set attributes consistent with that type.

Example fix

// before
proxy = Selenium::WebDriver::Proxy.new(
  pac: 'http://internal.corp/proxy.pac',
  http: 'proxy.corp:8080'  # conflicts: forces :manual, but :pac already set
)

// after
proxy = Selenium::WebDriver::Proxy.new(
  pac: 'http://internal.corp/proxy.pac'
)
# or, for manual:
proxy = Selenium::WebDriver::Proxy.new(
  http: 'proxy.corp:8080',
  ssl: 'proxy.corp:8080'
)

Defensive patterns

Strategy: validation

Validate before calling

# Validate proxy options before constructing Proxy
VALID_PROXY_KEYS = {
  manual: %i[http no_proxy ssl socks socks_username socks_password socks_version],
  pac: %i[pac],
  auto_detect: %i[auto_detect]
}.freeze

def safe_proxy(opts)
  detected_types = VALID_PROXY_KEYS.select { |_type, keys| (opts.keys & keys).any? }.keys
  if detected_types.size > 1
    raise ArgumentError, "Conflicting proxy types detected: #{detected_types}. Use only one type family."
  end
  Selenium::WebDriver::Proxy.new(opts)
end

Try / catch

begin
  proxy = Selenium::WebDriver::Proxy.new(proxy_opts)
rescue ArgumentError => e
  raise if e.message !~ /incompatible proxy type/
  # log and fall back to a single-type proxy
  puts "Proxy config conflict: #{e.message}. Using manual proxy only."
  proxy = Selenium::WebDriver::Proxy.new(http: proxy_opts[:http], ssl: proxy_opts[:ssl])
end

Prevention

Decide on a single proxy mode (manual, pac, auto_detect, system, direct) before building the options hash.
Document the allowed key sets per proxy type in your config schema.
Use a config validation layer (e.g., dry-validation, dry-schema) to catch conflicting keys before passing to Selenium.

When it happens

Trigger: Calling proxy.pac = 'http://...' (sets :pac) followed by proxy.http = 'host:8080' (sets :manual) raises this. Or passing a Hash to Proxy.new that includes both :pac and :http keys (each setter fires during initialize, so the second conflicting one fails). Setting socks_version= after pac= also conflicts (:manual vs :pac).

Common situations: Migrating from a manual proxy config to a PAC URL but leaving http/ssl keys in the options hash. Copying proxy examples from different blog posts that use different proxy modes. Building a Proxy from user-supplied config where the user mixes PAC and manual settings.

Related errors

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/31ba2f801f18e0bd. Report an issue: GitHub.