Initial implementation extracted from async-io.

.editorconfig

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+root = true
+
+[*]
+indent_style = tab
+indent_size = 2

.github/workflows/coverage.yaml

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+name: Coverage
+
+on: [push, pull_request]
+
+permissions:
+  contents: read
+
+env:
+  CONSOLE_OUTPUT: XTerm
+  COVERAGE: PartialSummary
+
+jobs:
+  test:
+    name: ${{matrix.ruby}} on ${{matrix.os}}
+    runs-on: ${{matrix.os}}-latest
+
+    strategy:
+      matrix:
+        os:
+          - ubuntu
+          - macos
+
+        ruby:
+          - "3.2"
+
+    steps:
+    - uses: actions/checkout@v3
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{matrix.ruby}}
+        bundler-cache: true
+
+    - name: Run tests
+      timeout-minutes: 5
+      run: bundle exec bake test
+
+    - uses: actions/upload-artifact@v2
+      with:
+        name: coverage-${{matrix.os}}-${{matrix.ruby}}
+        path: .covered.db
+
+  validate:
+    needs: test
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v3
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: "3.2"
+        bundler-cache: true
+
+    - uses: actions/download-artifact@v3
+
+    - name: Validate coverage
+      timeout-minutes: 5
+      run: bundle exec bake covered:validate --paths */.covered.db \;

.github/workflows/documentation.yaml

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+name: Documentation
+
+on:
+  push:
+    branches:
+      - main
+
+    # Allows you to run this workflow manually from the Actions tab:
+    workflow_dispatch:
+
+# Sets permissions of the GITHUB_TOKEN to allow deployment to GitHub Pages:
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+# Allow one concurrent deployment:
+concurrency:
+  group: "pages"
+  cancel-in-progress: true
+
+env:
+  CONSOLE_OUTPUT: XTerm
+  BUNDLE_WITH: maintenance
+
+jobs:
+  generate:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v3
+
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: "3.2"
+        bundler-cache: true
+
+    - name: Installing packages
+      run: sudo apt-get install wget
+
+    - name: Generate documentation
+      timeout-minutes: 5
+      run: bundle exec bake utopia:project:static --force no
+
+    - name: Upload documentation artifact
+      uses: actions/upload-pages-artifact@v1
+      with:
+        path: docs
+
+  deploy:
+    runs-on: ubuntu-latest
+
+    environment:
+      name: github-pages
+      url: ${{steps.deployment.outputs.page_url}}
+
+    needs: generate
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v1

.github/workflows/test-external.yaml

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+name: Test External
+
+on: [push, pull_request]
+
+permissions:
+  contents: read
+
+env:
+  CONSOLE_OUTPUT: XTerm
+
+jobs:
+  test:
+    name: ${{matrix.ruby}} on ${{matrix.os}}
+    runs-on: ${{matrix.os}}-latest
+
+    strategy:
+      matrix:
+        os:
+          - ubuntu
+          - macos
+
+        ruby:
+          - "3.2"
+
+    steps:
+    - uses: actions/checkout@v3
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{matrix.ruby}}
+        bundler-cache: true
+
+    - name: Run tests
+      timeout-minutes: 10
+      run: bundle exec bake test:external

.github/workflows/test.yaml

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+name: Test
+
+on: [push, pull_request]
+
+permissions:
+  contents: read
+
+env:
+  CONSOLE_OUTPUT: XTerm
+
+jobs:
+  test:
+    name: ${{matrix.ruby}} on ${{matrix.os}}
+    runs-on: ${{matrix.os}}-latest
+    continue-on-error: ${{matrix.experimental}}
+
+    strategy:
+      matrix:
+        os:
+          - ubuntu
+          - macos
+
+        ruby:
+          - "3.2"
+
+        experimental: [false]
+
+        include:
+          - os: ubuntu
+            ruby: truffleruby
+            experimental: true
+          - os: ubuntu
+            ruby: jruby
+            experimental: true
+          - os: ubuntu
+            ruby: head
+            experimental: true
+
+    steps:
+    - uses: actions/checkout@v3
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{matrix.ruby}}
+        bundler-cache: true
+
+    - name: Run tests
+      timeout-minutes: 10
+      run: bundle exec bake test

.gitignore

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+/.bundle/
+/pkg/
+/gems.locked
+/.covered.db
+/external

fixtures/with_temporary_directory.rb

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+# frozen_string_literal: true
+
+# Released under the MIT License.
+# Copyright, 2023, by Samuel Williams.
+
+require 'tmpdir'
+
+module WithTemporaryDirectory
+	attr :temporary_directory
+
+	def around
+		Dir.mktmpdir do |temporary_directory|
+			@temporary_directory = temporary_directory
+			yield
+		end
+	end
+end

gems.rb

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+# frozen_string_literal: true
+
+# Released under the MIT License.
+# Copyright, 2023, by Samuel Williams.
+
+source 'https://rubygems.org'
+
+gemspec
+
+group :maintenance, optional: true do
+	gem "bake-modernize"
+	gem "bake-gem"
+
+	gem "utopia-project"
+end

io-endpoint.gemspec

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+# frozen_string_literal: true
+
+require_relative "lib/io/endpoint/version"
+
+Gem::Specification.new do |spec|
+	spec.name = "io-endpoint"
+	spec.version = IO::Endpoint::VERSION
+
+	spec.summary = "Provides a separation of concerns interface for IO endpoints."
+	spec.authors = ["Samuel Williams"]
+	spec.license = "MIT"
+
+	spec.cert_chain  = ['release.cert']
+	spec.signing_key = File.expand_path('~/.gem/release.pem')
+
+	spec.homepage = "https://github.com/socketry/io-endpoint"
+
+	spec.files = Dir.glob(['{lib}/**/*', '*.md'], File::FNM_DOTMATCH, base: __dir__)
+
+	spec.required_ruby_version = ">= 3.2"
+
+	spec.add_development_dependency "bake"
+	spec.add_development_dependency "covered"
+	spec.add_development_dependency "sus"
+end

lib/io/endpoint.rb

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+# frozen_string_literal: true
+
+# Released under the MIT License.
+# Copyright, 2023, by Samuel Williams.
+
+require_relative "endpoint/version"
+require_relative "endpoint/generic"
+
+module IO::Endpoint
+	def self.file_descriptor_limit
+		Process.getrlimit(Process::RLIMIT_NOFILE).first
+	end
+end

lib/io/endpoint/address_endpoint.rb

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+# frozen_string_literal: true
+
+# Released under the MIT License.
+# Copyright, 2023, by Samuel Williams.
+
+require 'socket'
+
+require_relative 'generic'
+require_relative 'wrapper'
+
+module IO::Endpoint
+	class AddressEndpoint < Generic
+		def initialize(address, **options)
+			super(**options)
+
+			@address = address
+		end
+
+		def to_s
+			"\#<#{self.class} #{@address.inspect}>"
+		end
+
+		attr :address
+
+		# Bind a socket to the given address. If a block is given, the socket will be automatically closed when the block exits.
+		# @yield [Socket] the bound socket
+		# @return [Socket] the bound socket
+		def bind(&block)
+			Wrapper.bind(@address, **@options, &block)
+		end
+
+		# Connects a socket to the given address. If a block is given, the socket will be automatically closed when the block exits.
+		# @return [Socket] the connected socket
+		def connect(&block)
+			Wrapper.connect(@address, **@options, &block)
+		end
+	end
+end

lib/io/endpoint/composite_endpoint.rb

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+# frozen_string_literal: true
+
+# Released under the MIT License.
+# Copyright, 2023, by Samuel Williams.
+
+require_relative 'generic'
+
+module IO::Endpoint
+	class CompositeEndpoint < Generic
+		def initialize(endpoints, **options)
+			super(**options)
+			@endpoints = endpoints
+		end
+
+		def each(&block)
+			@endpoints.each(&block)
+		end
+
+		def connect(&block)
+			last_error = nil
+
+			@endpoints.each do |endpoint|
+				begin
+					return endpoint.connect(&block)
+				rescue => last_error
+				end
+			end
+
+			raise last_error
+		end
+
+		def bind(&block)
+			@endpoints.map(&:bind)
+		end
+	end
+
+	class Endpoint
+		def self.composite(*endpoints, **options)
+			CompositeEndpoint.new(endpoints, **options)
+		end
+	end
+end