fix(contexts): detect the browser's implicit context and create targets in it without id

CHANGELOG.md

@@ -23,6 +23,10 @@
   the browser; a failed `IO.close` is raised to the caller.
 
 ### Fixed
+- `create_page` raised `Failed to find browser context with id` against a browser that came up with its own startup
+  window (browserless). That window lives in the browser's implicit context, which Chrome below 145
+  won't address by id. Ferrum now detects it and exposes as `Ferrum::Context#implicit?`. It's never
+  disposed, so `#reset` won't clear such a browser. [#578] [#627]
 - Targets of a type `Ferrum::Contexts` doesn't track were left attached and paused by auto-attach for the lifetime
   of the browser; Chrome opens two `browser_ui` ones per browser context. They're now resumed and detached from
 - `Ferrum::Browser::Process` registered two `ObjectSpace` finalizers on the same object, a directory remover and

lib/ferrum/context.rb

@@ -15,14 +15,25 @@ class Context
 
     attr_reader :id, :targets
 
-    def initialize(client, contexts, id)
+    def initialize(client, contexts, id, implicit: false)
       @id = id
+      @implicit = implicit
       @client = client
       @contexts = contexts
       @targets = Concurrent::Map.new
       @pendings = Concurrent::Map.new
     end
 
+    # Whether this is the browser's implicit context, the one it puts its
+    # startup window in. We didn't create it, so we can't dispose it, and
+    # Chrome doesn't let us address it by id either: targets are created in
+    # it by omitting `browserContextId` altogether.
+    #
+    # @return [Boolean]
+    def implicit?
+      @implicit
+    end
+
     # The context's first known target, creating one via
     # `Target.createTarget` if none has attached yet.
     #
@@ -92,7 +103,8 @@ def create_page(**options)
     #
     # @raise [NoSuchTargetError]
     def create_target
-      target_id = @client.command("Target.createTarget", browserContextId: @id, url: "about:blank")["targetId"]
+      options = { browserContextId: @id } unless implicit?
+      target_id = @client.command("Target.createTarget", url: "about:blank", **Hash(options))["targetId"]
 
       new_pending = Concurrent::IVar.new
       pending = @pendings.put_if_absent(target_id, new_pending) || new_pending
@@ -184,9 +196,10 @@ def close_targets_connection
       end
     end
 
-    # Disposes this browser context and all of its targets.
+    # Disposes this browser context and all of its targets. The browser's
+    # implicit context cannot be disposed, see {#implicit?}.
     #
-    # @return [Boolean]
+    # @return [Boolean, nil]
     def dispose
       @contexts.dispose(@id)
     end

lib/ferrum/contexts.rb

@@ -22,6 +22,7 @@ def initialize(client)
       @client = client
       @contexts = Concurrent::Map.new
       @manually_attached = Concurrent::Map.new
+      @default_context = find_implicit_context
       subscribe
       auto_attach
       discover
@@ -33,7 +34,9 @@ def manually_attached(target_id)
       @manually_attached[target_id] = true
     end
 
-    # The browser's first context, created lazily.
+    # The context we work in unless told otherwise: the browser's implicit
+    # context when it came up with a startup window (see {#find_implicit_context}),
+    # otherwise one of our own, created lazily.
     #
     # @return [Context]
     def default_context
@@ -84,14 +87,16 @@ def create(**options)
       context
     end
 
-    # Disposes a browser context and all of its targets.
+    # Disposes a browser context and all of its targets. The browser's implicit
+    # context is not ours to dispose, see {Context#implicit?}.
     #
     # @param [String] context_id
     #
-    # @return [Boolean]
+    # @return [Boolean, nil]
     def dispose(context_id)
       context = @contexts[context_id]
       return unless context
+      return if context.implicit?
 
       context.close_targets_connection
       @client.command("Target.disposeBrowserContext", browserContextId: context.id)
@@ -251,9 +256,29 @@ def auto_attach
     def add_context(context_id)
       return if @contexts[context_id]
 
-      context = Context.new(@client, self, context_id)
-      @contexts[context_id] = context
-      @default_context ||= context # rubocop:disable Naming/MemoizedInstanceVariableName
+      @contexts[context_id] = Context.new(@client, self, context_id)
+    end
+
+    # The browser's implicit context, the context Chrome uses for its startup window.
+    # We register it so events for that window are routed to it.
+    # `Target.getBrowserContexts` reports every context created with
+    # `Target.createBrowserContext`, ours and those of anyone else driving the same
+    # browser, so the context holding targets that it doesn't report is the implicit
+    # one. Chrome also reports its id as `defaultBrowserContextId`, but only since
+    # 145 and only as an experimental field, so we don't rely on it.
+    #
+    # Returns nil if the browser has no startup window, which happens when it is
+    # launched with `--no-startup-window` (used for `incognito: true`). In that case,
+    # we create our own context instead.
+    #
+    # @return [Context, nil]
+    def find_implicit_context
+      created_ids = @client.command("Target.getBrowserContexts")["browserContextIds"]
+      target_infos = @client.command("Target.getTargets")["targetInfos"]
+      implicit_id = (target_infos.filter_map { |t| t["browserContextId"] } - created_ids).first
+      return unless implicit_id
+
+      @contexts[implicit_id] = Context.new(@client, self, implicit_id, implicit: true)
     end
   end
 end

sig/ferrum/context.rbs

@@ -6,13 +6,16 @@ module Ferrum
     attr_reader targets: ::Concurrent::Map[String, Target]
 
     @id: String
+    @implicit: bool
     @client: Client
     @contexts: Contexts
     @targets: ::Concurrent::Map[String, Target]
     @pendings: ::Concurrent::Map[String, ::Concurrent::IVar]
     @default_target: Target?
 
-    def initialize: (Client, Contexts, String) -> void
+    def initialize: (Client, Contexts, String, ?implicit: bool) -> void
+
+    def implicit?: () -> bool
 
     def default_target: () -> Target
 
@@ -42,7 +45,7 @@ module Ferrum
 
     def close_targets_connection: () -> void
 
-    def dispose: () -> bool
+    def dispose: () -> bool?
 
     def target?: (String target_id) -> bool
 

sig/ferrum/contexts.rbs

@@ -27,7 +27,7 @@ module Ferrum
 
     def create: (**untyped options) -> Context
 
-    def dispose: (String context_id) -> bool
+    def dispose: (String context_id) -> bool?
 
     def close_connections: () -> void
 
@@ -62,5 +62,7 @@ module Ferrum
     def auto_attach: () -> void
 
     def add_context: (String? context_id) -> Context?
+
+    def find_implicit_context: () -> Context?
   end
 end

spec/contexts_spec.rb

@@ -23,4 +23,49 @@
     browser.client.off("Target.attachedToTarget", attached_id)
     browser.client.off("Target.detachedFromTarget", detached_id)
   end
+
+  describe "#default_context" do
+    it "works in the browser's startup window when it came up with one" do
+      with_external_browser(incognito: false) do |url|
+        remote = Ferrum::Browser.new(url: url)
+
+        expect(remote.contexts.default_context).to be_implicit
+        expect { remote.create_page }.not_to raise_error
+      ensure
+        remote&.quit
+      end
+    end
+
+    it "creates a context of its own when the browser has no startup window" do
+      with_external_browser do |url|
+        remote = Ferrum::Browser.new(url: url)
+        remote.create_page
+
+        expect(remote.contexts.default_context).not_to be_implicit
+
+        remote.reset
+
+        expect(remote.contexts.size).to be_zero
+      ensure
+        remote&.quit
+      end
+    end
+
+    it "ignores contexts another client created in the same browser" do
+      with_external_browser do |url|
+        first = Ferrum::Browser.new(url: url)
+        context = first.contexts.create
+        context.create_page
+
+        second = Ferrum::Browser.new(url: url)
+
+        expect(second.contexts.default_context).not_to be_implicit
+        expect(second.contexts.default_context.id).not_to eq(context.id)
+        expect { second.create_page }.not_to raise_error
+      ensure
+        second&.quit
+        first&.quit
+      end
+    end
+  end
 end

spec/support/global_helpers.rb

@@ -44,8 +44,9 @@ def with_timeout(new_timeout)
     browser.timeout = old_timeout
   end
 
-  def with_external_browser(host: "127.0.0.1", port: 32_001)
-    options = Ferrum::Browser::Options.new(host: host, port: port, window_size: [1400, 1400], headless: true)
+  def with_external_browser(host: "127.0.0.1", port: 32_001, incognito: true)
+    options = Ferrum::Browser::Options.new(host: host, port: port, window_size: [1400, 1400],
+                                           headless: true, incognito: incognito)
     process = Ferrum::Browser::Process.new(options)
 
     begin