diff --git a/lib/dalli/server.rb b/lib/dalli/server.rb
index 8e089a73..15ddd64f 100644
--- a/lib/dalli/server.rb
+++ b/lib/dalli/server.rb
@@ -583,7 +583,7 @@ def flush_response
     def write(bytes)
       begin
         @inprogress = true
-        result = @sock.write(bytes)
+        result = @sock.writefull(bytes)
         @inprogress = false
         result
       rescue SystemCallError, Timeout::Error => e
diff --git a/lib/dalli/socket.rb b/lib/dalli/socket.rb
index 13d2124b..04d4e0d2 100644
--- a/lib/dalli/socket.rb
+++ b/lib/dalli/socket.rb
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require 'resolv'
+
 module Dalli
   module Socket
     module InstanceMethods
@@ -21,6 +23,22 @@ def readfull(count)
         value
       end
 
+      def writefull(bytes)
+        offset = 0
+        while offset < bytes.bytesize
+          chunk = offset == 0 ? bytes : bytes.byteslice(offset..-1)
+          result = write_nonblock(chunk, exception: false)
+          if result == :wait_writable
+            raise Timeout::Error, "IO timeout: #{safe_options.inspect}" unless IO.select(nil, [self], nil, options[:socket_timeout])
+          elsif result == :wait_readable
+            raise Timeout::Error, "IO timeout: #{safe_options.inspect}" unless IO.select([self], nil, nil, options[:socket_timeout])
+          else
+            offset += result
+          end
+        end
+        offset
+      end
+
       def read_available
         value = +""
         loop do
@@ -43,35 +61,97 @@ def safe_options
       end
     end
 
-    class TCP < TCPSocket
+    class TCP < ::Socket
       include Dalli::Socket::InstanceMethods
       attr_accessor :options, :server
 
       def self.open(host, port, server, options = {})
-        Timeout.timeout(options[:socket_timeout]) do
-          sock = new(host, port)
-          sock.options = {host: host, port: port}.merge(options)
-          sock.server = server
-          sock.setsockopt(::Socket::IPPROTO_TCP, ::Socket::TCP_NODELAY, true)
-          sock.setsockopt(::Socket::SOL_SOCKET, ::Socket::SO_KEEPALIVE, true) if options[:keepalive]
-          sock.setsockopt(::Socket::SOL_SOCKET, ::Socket::SO_RCVBUF, options[:rcvbuf]) if options[:rcvbuf]
-          sock.setsockopt(::Socket::SOL_SOCKET, ::Socket::SO_SNDBUF, options[:sndbuf]) if options[:sndbuf]
-          sock
+        addr_info = resolve_address(host, options[:socket_timeout])
+        sock = new(addr_info[4], ::Socket::SOCK_STREAM, 0) # addr_info[4] == address family constant (e.g. AF_INET), expressed as an integer
+
+        sock.setsockopt(::Socket::IPPROTO_TCP, ::Socket::TCP_NODELAY, true)
+        sock.setsockopt(::Socket::SOL_SOCKET, ::Socket::SO_KEEPALIVE, true) if options[:keepalive]
+        sock.setsockopt(::Socket::SOL_SOCKET, ::Socket::SO_RCVBUF, options[:rcvbuf]) if options[:rcvbuf]
+        sock.setsockopt(::Socket::SOL_SOCKET, ::Socket::SO_SNDBUF, options[:sndbuf]) if options[:sndbuf]
+
+        sockaddr = ::Socket.pack_sockaddr_in(port, addr_info[3]) # addr_info[3] == IP address string (e.g. "192.168.1.1")
+        result = sock.connect_nonblock(sockaddr, exception: false)
+        if result == :wait_writable
+          unless IO.select(nil, [sock], nil, options[:socket_timeout])
+            raise Timeout::Error, "Connection timeout: #{host}:#{port}"
+          end
+          begin
+            sock.connect_nonblock(sockaddr)
+          rescue Errno::EISCONN
+            # already connected
+          end
         end
+
+        sock.options = { host: host, port: port }.merge(options)
+        sock.server = server
+        sock
+      rescue
+        sock&.close rescue nil
+        raise
+      end
+
+      # Resolve a hostname to structured address info with timeout protection.
+      # getaddrinfo(3) is a blocking C library call that can block indefinitely
+      # on unresponsive DNS. For IP addresses (the common case with memcached),
+      # getaddrinfo returns immediately without DNS and is safe to call directly.
+      # For hostnames, we use Ruby's Resolv library which is pure Ruby and
+      # supports timeouts, then pass the resolved IP to getaddrinfo for the
+      # structured address info the caller expects.
+      def self.resolve_address(host, timeout)
+        if ip_address?(host)
+          return ::Socket.getaddrinfo(host, nil, ::Socket::AF_UNSPEC, ::Socket::SOCK_STREAM).first
+        end
+
+        dns = Resolv::DNS.new
+        dns.timeouts = timeout
+        resolver = Resolv.new([Resolv::Hosts.new, dns])
+        resolved_ip = resolver.getaddress(host).to_s
+        ::Socket.getaddrinfo(resolved_ip, nil, ::Socket::AF_UNSPEC, ::Socket::SOCK_STREAM).first
+      rescue Resolv::ResolvError => e
+        raise SocketError, "getaddrinfo: Name or service not known - #{host} (#{e.message})"
+      ensure
+        dns&.close
       end
+      private_class_method :resolve_address
+
+      # Returns true if host is an IP address (v4 or v6) rather than a hostname.
+      def self.ip_address?(host)
+        host.match?(Resolv::IPv4::Regex) || host.include?(':')
+      end
+      private_class_method :ip_address?
     end
 
-    class UNIX < UNIXSocket
+    class UNIX < ::Socket
       include Dalli::Socket::InstanceMethods
       attr_accessor :options, :server
 
       def self.open(path, server, options = {})
-        Timeout.timeout(options[:socket_timeout]) do
-          sock = new(path)
-          sock.options = {path: path}.merge(options)
-          sock.server = server
-          sock
+        sock = new(::Socket::AF_UNIX, ::Socket::SOCK_STREAM, 0)
+        sockaddr = ::Socket.pack_sockaddr_un(path)
+
+        result = sock.connect_nonblock(sockaddr, exception: false)
+        if result == :wait_writable
+          unless IO.select(nil, [sock], nil, options[:socket_timeout])
+            raise Timeout::Error, "Connection timeout: #{path}"
+          end
+          begin
+            sock.connect_nonblock(sockaddr)
+          rescue Errno::EISCONN
+            # already connected
+          end
         end
+
+        sock.options = { path: path }.merge(options)
+        sock.server = server
+        sock
+      rescue
+        sock&.close rescue nil
+        raise
       end
     end
   end
diff --git a/test/test_socket.rb b/test/test_socket.rb
index ad2983a5..51c169cc 100644
--- a/test/test_socket.rb
+++ b/test/test_socket.rb
@@ -3,12 +3,14 @@
 
 class MockSocket
   include Dalli::Socket::InstanceMethods
-  attr_accessor :options, :read_results
+  attr_accessor :options, :read_results, :write_results
 
   def initialize(options = {})
     @options = options
     @read_results = []
+    @write_results = []
     @read_index = 0
+    @write_index = 0
   end
 
   def read_nonblock(_count, exception: true)
@@ -16,6 +18,12 @@ def read_nonblock(_count, exception: true)
     @read_index += 1
     result
   end
+
+  def write_nonblock(_bytes, exception: true)
+    result = @write_results[@write_index]
+    @write_index += 1
+    result
+  end
 end
 
 describe 'Dalli::Socket::InstanceMethods' do
@@ -81,6 +89,70 @@ def read_nonblock(_count, exception: true)
     end
   end
 
+  describe '#writefull' do
+    it 'writes all bytes in a single call' do
+      sock.write_results = [5]
+      assert_equal 5, sock.writefull("hello")
+    end
+
+    it 'handles partial writes across multiple calls' do
+      sock.write_results = [2, 3]
+      assert_equal 5, sock.writefull("hello")
+    end
+
+    it 'retries on :wait_writable when IO.select succeeds' do
+      sock.write_results = [:wait_writable, 5]
+      IO.stubs(:select).with(nil, [sock], nil, 1).returns([nil, [sock]])
+      assert_equal 5, sock.writefull("hello")
+    end
+
+    it 'retries on :wait_readable when IO.select succeeds' do
+      sock.write_results = [:wait_readable, 5]
+      IO.stubs(:select).with([sock], nil, nil, 1).returns([[sock]])
+      assert_equal 5, sock.writefull("hello")
+    end
+
+    it 'raises Timeout::Error on :wait_writable when IO.select times out' do
+      sock.write_results = [:wait_writable]
+      IO.stubs(:select).with(nil, [sock], nil, 1).returns(nil)
+      assert_raises(Timeout::Error) { sock.writefull("hello") }
+    end
+
+    it 'raises Timeout::Error on :wait_readable when IO.select times out' do
+      sock.write_results = [:wait_readable]
+      IO.stubs(:select).with([sock], nil, nil, 1).returns(nil)
+      assert_raises(Timeout::Error) { sock.writefull("hello") }
+    end
+
+    it 'delivers all bytes through a real socket pair' do
+      s1, s2 = Socket.pair(:UNIX, :STREAM, 0)
+      s1.extend(Dalli::Socket::InstanceMethods)
+      def s1.options; { socket_timeout: 5 }; end
+
+      data = "hello world"
+      result = s1.writefull(data)
+      s1.close
+
+      assert_equal data.bytesize, result
+      assert_equal data, s2.read
+    ensure
+      s1&.close rescue nil
+      s2&.close rescue nil
+    end
+
+    describe 'with credentials' do
+      let(:sock) { MockSocket.new(socket_timeout: 1, username: 'admin', password: 'secret') }
+
+      it 'excludes credentials from Timeout::Error message' do
+        sock.write_results = [:wait_writable]
+        IO.stubs(:select).with(nil, [sock], nil, 1).returns(nil)
+        error = assert_raises(Timeout::Error) { sock.writefull("hello") }
+        refute_match(/admin/, error.message)
+        refute_match(/secret/, error.message)
+      end
+    end
+  end
+
   describe '#read_available' do
     it 'reads all available data until :wait_readable' do
       sock.read_results = ["he", "llo", :wait_readable]
@@ -179,6 +251,19 @@ def read_nonblock(_count, exception: true)
     @sock = Dalli::Socket::TCP.open('127.0.0.1', @port, 'my_server', socket_timeout: 5)
     assert_equal 'my_server', @sock.server
   end
+
+  it 'raises SocketError for unresolvable hostname' do
+    assert_raises(SocketError) do
+      Dalli::Socket::TCP.open('this-host-does-not-exist.invalid', 11211, 'srv', socket_timeout: 1)
+    end
+  end
+
+  it 'includes hostname in SocketError message for unresolvable host' do
+    error = assert_raises(SocketError) do
+      Dalli::Socket::TCP.open('this-host-does-not-exist.invalid', 11211, 'srv', socket_timeout: 1)
+    end
+    assert_match(/this-host-does-not-exist\.invalid/, error.message)
+  end
 end
 
 describe 'Dalli::Socket::UNIX' do
@@ -212,4 +297,10 @@ def read_nonblock(_count, exception: true)
     @sock = Dalli::Socket::UNIX.open(@path, 'my_server', socket_timeout: 5)
     assert_equal 'my_server', @sock.server
   end
+
+  it 'raises Errno::ENOENT for non-existent socket path' do
+    assert_raises(Errno::ENOENT) do
+      Dalli::Socket::UNIX.open('/tmp/nonexistent_dalli_test_socket', 'srv', socket_timeout: 1)
+    end
+  end
 end