fix: Support IPv6 bind addresses in http_server helper

CHANGELOG.md

@@ -1,3 +1,15 @@
+# v1.20
+
+## Release v1.20.0 - TBD
+
+### Bug fix
+
+* http_server helper: Fix IPv6 bind address support in URI construction
+  * Fixed `URI::InvalidURIError` when binding to IPv6 addresses (e.g., `::`, `::1`)
+  * IPv6 addresses are now properly bracketed in URIs per RFC 3986 (e.g., `http://[::]:24231`)
+  * Handles pre-bracketed addresses correctly to avoid double-bracketing
+  * Affects all plugins using http_server helper with IPv6 bind addresses
+
 # v1.19
 
 ## Release v1.19.1 - 2025/11/06

lib/fluent/plugin_helper/http_server/server.rb

@@ -31,13 +31,26 @@ class Server
         # @param default_app [Object] This method must have #call.
         # @param tls_context [OpenSSL::SSL::SSLContext]
         def initialize(addr:, port:, logger:, default_app: nil, tls_context: nil)
-          @addr = addr
+          # Normalize the address: strip brackets if present
+          # Brackets are only for URI formatting, not for socket binding
+          @addr = if addr.start_with?('[') && addr.end_with?(']')
+                    addr[1..-2]  # Remove surrounding brackets
+                  else
+                    addr
+                  end
           @port = port
           @logger = logger
 
           # TODO: support http2
           scheme = tls_context ? 'https' : 'http'
-          @uri = URI("#{scheme}://#{@addr}:#{@port}").to_s
+          # Handle IPv6 addresses properly in URI construction per RFC 3986
+          # Add brackets to IPv6 addresses for URI compliance (ip-literal per RFC 3986)
+          ip_literal = if @addr.include?(":")
+                         "[#{@addr}]"  # IPv6 address - add brackets
+                       else
+                         @addr         # IPv4 or hostname - use directly
+                       end
+          @uri = URI("#{scheme}://#{ip_literal}:#{@port}").to_s
           @router = Router.new(default_app)
           @server_task = nil
           Console.logger = Fluent::Log::ConsoleAdapter.wrap(@logger)

test/helper.rb

@@ -161,9 +161,16 @@ def ipv6_enabled?
   require 'socket'
 
   begin
-    TCPServer.open("::1", 0)
+    # Try to actually bind to an IPv6 address to verify it works
+    sock = Socket.new(Socket::AF_INET6, Socket::SOCK_STREAM, 0)
+    sock.bind(Socket.sockaddr_in(0, '::1'))
+    sock.close
+
+    # Also test that we can resolve IPv6 addresses
+    # This is needed because some systems can bind but can't connect
+    Socket.getaddrinfo('::1', nil, Socket::AF_INET6)
     true
-  rescue
+  rescue Errno::EADDRNOTAVAIL, Errno::EAFNOSUPPORT, SocketError
     false
   end
 end

test/plugin_helper/test_http_server_helper.rb

@@ -363,6 +363,28 @@ def start_https_request(addr, port, verify: true, cert_path: nil, selfsigned: tr
         end
       end
     end
+
+    data(
+      'IPv6 loopback ::1' => [:ipv6_loopback_test, '::1', '::1'],
+      'IPv6 any address ::' => [:ipv6_any_test, '::', '::1'],
+      'pre-bracketed IPv6 [::1]' => [:ipv6_bracketed_test, '[::1]', '::1']
+    )
+    test 'http_server can bind and serve on IPv6 address' do |data|
+      return unless ipv6_enabled?
+
+      test_name, bind_addr, connect_addr = data
+
+      on_driver do |driver|
+        driver.http_server_create_http_server(test_name, addr: bind_addr, port: @port, logger: NULL_LOGGER) do |s|
+          s.get('/test') { [200, { 'Content-Type' => 'text/plain' }, 'OK'] }
+        end
+
+        http = Net::HTTP.new(connect_addr, @port)
+        response = http.get('/test')
+        assert_equal('200', response.code)
+        assert_equal('OK', response.body)
+      end
+    end
 
     test 'must be called #start and #stop' do
       on_driver do |driver|