DEBUG-3700 agentless settings resolver

lib/datadog/core/configuration/agentless_settings_resolver.rb

@@ -0,0 +1,176 @@
+# frozen_string_literal: true
+
+# rubocop:disable Style/*
+
+require 'uri'
+
+require_relative 'agent_settings_resolver'
+
+module Datadog
+  module Core
+    module Configuration
+      # Agent settings resolver for agentless operations (currently, telemetry
+      # in agentless mode).
+      #
+      # The terminology gets a little confusing here, but transports communicate
+      # with servers which are - for most components in the tracer - the
+      # (local) agent. Hence, "agent settings" to refer to where the server
+      # is located. Telemetry supports sending to the local agent but also
+      # implements agentless mode where it sends directly to Datadog intake
+      # endpoints. The agentless mode is configured using different settings,
+      # and this class produces AgentSettings instances when in agentless mode.
+      #
+      # Agentless settings resolver uses the following configuration sources:
+      #
+      # 1. url_override constructor parameter, if provided
+      # 2. Built-in default host/port/TLS settings for the backend
+      #    intake endpoint
+      #
+      # The agentless resolver does NOT use agent settings (since it is
+      # for agentless operation), specifically it ignores:
+      #
+      # - c.agent.host
+      # - DD_AGENT_HOST
+      # - c.agent.port
+      # - DD_AGENT_PORT
+      #
+      # However, agentless resolver does respect the timeout specified via
+      # c.agent.timeout_seconds or DD_TRACE_AGENT_TIMEOUT_SECONDS.
+      class AgentlessSettingsResolver < AgentSettingsResolver
+        # To avoid coupling this class to telemetry, the URL override is
+        # taken here as a parameter instead of being read out of
+        # c.telemetry.agentless_url_override. For the same reason, the
+        # +url_override_source+ parameter should be set to the string
+        # "c.telemetry.agentless_url_override".
+        def self.call(settings, host_prefix:, url_override: nil, url_override_source: nil, logger: Datadog.logger)
+          new(
+            settings,
+            host_prefix: host_prefix,
+            url_override: url_override,
+            url_override_source: url_override_source,
+            logger: logger
+          ).send(:call)
+        end
+
+        private
+
+        attr_reader \
+          :host_prefix,
+          :url_override,
+          :url_override_source
+
+        def initialize(settings, host_prefix:, url_override: nil, url_override_source: nil, logger: Datadog.logger)
+          if url_override && url_override_source.nil?
+            raise ArgumentError, 'url_override_source must be provided when url_override is provided'
+          end
+
+          super(settings, logger: logger)
+
+          @host_prefix = host_prefix
+          @url_override = url_override
+          @url_override_source = url_override_source
+        end
+
+        def hostname
+          if should_use_uds?
+            nil
+          else
+            configured_hostname || "#{host_prefix}.#{settings.site}"
+          end
+        end
+
+        def configured_hostname
+          return @configured_hostname if defined?(@configured_hostname)
+
+          if should_use_uds?
+            nil
+          else
+            @configured_hostname = (parsed_url.hostname if parsed_url)
+          end
+        end
+
+        def configured_port
+          return @configured_port if defined?(@configured_port)
+
+          @configured_port = (parsed_url.port if parsed_url)
+        end
+
+        # Note that this method should always return true or false
+        def ssl?
+          if configured_hostname
+            configured_ssl || false
+          else
+            if should_use_uds?
+              false
+            else
+              # If no hostname is specified, we are communicating with the
+              # default Datadog intake, which uses TLS.
+              true
+            end
+          end
+        end
+
+        # Note that this method can return nil
+        def configured_ssl
+          return @configured_ssl if defined?(@configured_ssl)
+
+          @configured_ssl = (parsed_url_ssl? if parsed_url)
+        end
+
+        def port
+          if configured_port
+            configured_port
+          else
+            if should_use_uds?
+              nil
+            else
+              # If no hostname is specified, we are communicating with the
+              # default Datadog intake, which exists on port 443.
+              443
+            end
+          end
+        end
+
+        def mixed_http_and_uds
+          false
+        end
+
+        def configured_uds_path
+          return @configured_uds_path if defined?(@configured_uds_path)
+
+          parsed_url_uds_path
+        end
+
+        def can_use_uds?
+          # While in theory agentless transport could communicate via UDS,
+          # in practice "agentless" means we are communicating with Datadog
+          # infrastructure which is always remote.
+          # Permit UDS for proxy usage?
+          !configured_uds_path.nil?
+        end
+
+        def parsed_url
+          return @parsed_url if defined?(@parsed_url)
+
+          @parsed_url =
+            if @url_override
+              parsed = URI.parse(@url_override)
+
+              # Agentless URL should never refer to a UDS?
+              if http_scheme?(parsed) || unix_scheme?(parsed)
+                parsed
+              else
+                log_warning(
+                  "Invalid URI scheme '#{parsed.scheme}' for #{url_override_source}. " \
+                  "Ignoring the contents of #{url_override_source}."
+                )
+                nil
+              end
+            end
+        end
+      end
+    end
+  end
+end
+
+# rubocop:enable Style/*

sig/datadog/core/configuration/agentless_settings_resolver.rbs

@@ -0,0 +1,50 @@
+module Datadog
+  module Core
+    module Configuration
+      class AgentlessSettingsResolver < AgentSettingsResolver
+        @host_prefix: untyped
+
+        @url_override: untyped
+
+        @url_override_source: untyped
+
+        @configured_hostname: untyped
+
+        @configured_port: untyped
+
+        @configured_ssl: untyped
+
+        @parsed_url: untyped
+        def self.call: (untyped settings, host_prefix: untyped, ?url_override: untyped?, ?url_override_source: untyped?, ?logger: untyped) -> untyped
+
+        private
+
+        attr_reader host_prefix: untyped
+
+        attr_reader url_override: untyped
+
+        attr_reader url_override_source: untyped
+
+        def initialize: (untyped settings, host_prefix: untyped, ?url_override: untyped?, ?url_override_source: untyped?, ?logger: untyped) -> void
+
+        def hostname: () -> (nil | untyped)
+
+        def configured_hostname: () -> untyped
+
+        def configured_port: () -> untyped
+        def ssl?: () -> (untyped | false | true)
+        def configured_ssl: () -> untyped
+
+        def port: () -> (untyped | nil | 443)
+
+        def mixed_http_and_uds: () -> false
+
+        def configured_uds_path: () -> untyped
+
+        def can_use_uds?: () -> untyped
+
+        def parsed_url: () -> untyped
+      end
+    end
+  end
+end