diff --git a/src/main/java/dev.toad/ClientObserveStream.java b/src/main/java/dev.toad/ClientObserveStream.java
index 7eee837..d816baf 100644
--- a/src/main/java/dev.toad/ClientObserveStream.java
+++ b/src/main/java/dev.toad/ClientObserveStream.java
@@ -15,13 +15,13 @@ public class ClientObserveStream {
   public ClientObserveStream(Client client, Message message) {
     this.state = State.OPEN;
     this.client = client;
-    this.message = message.modify().option(Observe.REGISTER).build();
+    this.message = message.buildCopy().option(Observe.REGISTER).build();
     this.buffered = Optional.of(client.send(this.message));
   }
 
   public CompletableFuture<Void> close() {
     return this.client.send(
-        this.message.modify().option(Observe.DEREGISTER).unsetId().build()
+        this.message.buildCopy().option(Observe.DEREGISTER).unsetId().build()
       )
       .thenAccept(m -> {
         this.state = State.CLOSED;
@@ -29,7 +29,7 @@ public class ClientObserveStream {
   }
 
   public CompletableFuture<Message> next() {
-    if (this.state == State.CLOSED) {
+    if (State.eq.test(State.CLOSED, this.state)) {
       throw new RuntimeException(
         "ClientObserveStream.next() invoked after .close()"
       );
@@ -47,6 +47,8 @@ public class ClientObserveStream {
 
   public static final class State {
 
+    public static final Eq<State> eq = Eq.int_.contramap((State s) -> s.state);
+
     public static final State OPEN = new State(0);
     public static final State CLOSED = new State(1);
 
@@ -56,14 +58,10 @@ public class ClientObserveStream {
       this.state = state;
     }
 
-    public boolean equals(State other) {
-      return this.state == other.state;
-    }
-
     @Override
     public boolean equals(Object other) {
       return switch (other) {
-        case State s -> this.equals(s);
+        case State s -> State.eq.test(this, s);
         default -> false;
       };
     }
diff --git a/src/main/java/dev.toad/Eq.java b/src/main/java/dev.toad/Eq.java
new file mode 100644
index 0000000..ebb26c9
--- /dev/null
+++ b/src/main/java/dev.toad/Eq.java
@@ -0,0 +1,87 @@
+package dev.toad;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.function.BiFunction;
+import java.util.function.Function;
+
+public final class Eq<T> {
+
+  public static final Eq<Short> short_ = new Eq<>((a, b) -> a == b);
+  public static final Eq<Integer> int_ = new Eq<>((a, b) -> a == b);
+  public static final Eq<Long> long_ = new Eq<>((a, b) -> a == b);
+  public static final Eq<String> string = new Eq<>((a, b) ->
+    (a != null && b != null && a.equals(b)) || (a == null && b == null)
+  );
+  public static final Eq<byte[]> byteArray = new Eq<>((a, b) ->
+    Arrays.equals(a, b)
+  );
+
+  public static final Eq<java.net.InetSocketAddress> socketAddress = new Eq<>(
+      (a, b) ->
+    a.equals(b)
+  );
+
+  public static <T> Eq<T> all(List<Eq<T>> eqs) {
+    return new Eq<>((a, b) -> eqs.stream().allMatch(eq -> eq.test(a, b)));
+  }
+
+  public static <T> Eq<Optional<T>> optional(Eq<T> eq) {
+    return new Eq<>((a, b) -> {
+      if (!a.isEmpty() && !b.isEmpty()) {
+        return eq.test(a.get(), b.get());
+      } else {
+        return a.isEmpty() && b.isEmpty();
+      }
+    });
+  }
+
+  public static <K, V> Eq<Map<K, V>> map(Eq<V> eq) {
+    return new Eq<>((a, b) -> {
+      if (a.entrySet().size() != b.entrySet().size()) {
+        return false;
+      }
+
+      for (var ent : a.entrySet()) {
+        var val = b.get(ent.getKey());
+        if (val == null || !eq.test(val, ent.getValue())) {
+          return false;
+        }
+      }
+
+      return true;
+    });
+  }
+
+  public static <T> Eq<List<T>> list(Eq<T> eq) {
+    return new Eq<>((a, b) -> {
+      if (a.size() != b.size()) {
+        return false;
+      }
+
+      for (int i = 0; i < a.size(); i++) {
+        if (!eq.test(a.get(i), b.get(i))) {
+          return false;
+        }
+      }
+
+      return true;
+    });
+  }
+
+  final BiFunction<T, T, Boolean> eq;
+
+  public Eq(BiFunction<T, T, Boolean> eq) {
+    this.eq = eq;
+  }
+
+  public boolean test(T a, T b) {
+    return this.eq.apply(a, b);
+  }
+
+  public <U> Eq<U> contramap(Function<U, T> from) {
+    return new Eq<>((a, b) -> this.test(from.apply(a), from.apply(b)));
+  }
+}
diff --git a/src/main/java/dev.toad/Server.java b/src/main/java/dev.toad/Server.java
index 3916281..13a8389 100644
--- a/src/main/java/dev.toad/Server.java
+++ b/src/main/java/dev.toad/Server.java
@@ -110,9 +110,7 @@ public final class Server {
       CompletableFuture.completedFuture(Optional.empty());
 
     public static final Function<Message, Result> notFound = m -> {
-      return Middleware.respond(
-        m.modify().unsetId().code(Code.NOT_FOUND).build()
-      );
+      return Middleware.respond(m.buildResponse().code(Code.NOT_FOUND).build());
     };
 
     public static final BiFunction<Message, Throwable, Result> debugExceptionHandler =
@@ -126,8 +124,7 @@ public final class Server {
           );
 
         var rep = m
-          .modify()
-          .unsetId()
+          .buildResponse()
           .code(Code.INTERNAL_SERVER_ERROR)
           .payload(Payload.text(e.toString()))
           .build();
@@ -144,7 +141,7 @@ public final class Server {
             String.format("while handling %s", m.toDebugString()),
             e
           );
-        var rep = m.modify().unsetId().code(Code.INTERNAL_SERVER_ERROR).build();
+        var rep = m.buildResponse().code(Code.INTERNAL_SERVER_ERROR).build();
         return Middleware.respond(rep);
       };
 
@@ -358,8 +355,11 @@ public final class Server {
     public Builder put(String path, Function<Message, Middleware.Result> f) {
       return this.when(
           m ->
-            m.code().equals(Code.PUT) &&
-            m.getPath().map(p -> p.matches(path)).orElse(path == ""),
+            Code.eq.test(m.code(), Code.PUT) &&
+            m
+              .getPath()
+              .map(p -> p.matches(path))
+              .orElse(path == null || path.isEmpty()),
           f
         );
     }
@@ -367,8 +367,11 @@ public final class Server {
     public Builder post(String path, Function<Message, Middleware.Result> f) {
       return this.when(
           m ->
-            m.code().equals(Code.POST) &&
-            m.getPath().map(p -> p.matches(path)).orElse(path == ""),
+            Code.eq.test(m.code(), Code.POST) &&
+            m
+              .getPath()
+              .map(p -> p.matches(path))
+              .orElse(path == null || path.isEmpty()),
           f
         );
     }
@@ -376,8 +379,11 @@ public final class Server {
     public Builder delete(String path, Function<Message, Middleware.Result> f) {
       return this.when(
           m ->
-            m.code().equals(Code.DELETE) &&
-            m.getPath().map(p -> p.matches(path)).orElse(path == ""),
+            Code.eq.test(m.code(), Code.DELETE) &&
+            m
+              .getPath()
+              .map(p -> p.matches(path))
+              .orElse(path == null || path.isEmpty()),
           f
         );
     }
@@ -385,7 +391,7 @@ public final class Server {
     public Builder get(String path, Function<Message, Middleware.Result> f) {
       return this.when(
           m ->
-            m.code().equals(Code.GET) &&
+            Code.eq.test(m.code(), Code.GET) &&
             m
               .getPath()
               .map(p -> p.matches(path))
diff --git a/src/main/java/dev.toad/Toad.java b/src/main/java/dev.toad/Toad.java
index ee31d56..ea58e8b 100644
--- a/src/main/java/dev.toad/Toad.java
+++ b/src/main/java/dev.toad/Toad.java
@@ -208,7 +208,8 @@ public final class Toad implements AutoCloseable {
     @Override
     public boolean equals(Object other) {
       return switch (other) {
-        case Config o -> o.concurrency == this.concurrency && o.msg == this.msg;
+        case Config o -> o.concurrency.equals(this.concurrency) &&
+        o.msg.equals(this.msg);
         default -> false;
       };
     }
@@ -258,11 +259,11 @@ public final class Toad implements AutoCloseable {
       @Override
       public boolean equals(Object other) {
         return switch (other) {
-          case Msg o -> o.tokenSeed == this.tokenSeed &&
-          o.probingRateBytesPerSecond == this.probingRateBytesPerSecond &&
-          o.multicastResponseLeisure == this.multicastResponseLeisure &&
-          o.con == this.con &&
-          o.non == this.non;
+          case Msg o -> o.tokenSeed.equals(this.tokenSeed) &&
+          o.probingRateBytesPerSecond.equals(this.probingRateBytesPerSecond) &&
+          o.multicastResponseLeisure.equals(this.multicastResponseLeisure) &&
+          o.con.equals(this.con) &&
+          o.non.equals(this.non);
           default -> false;
         };
       }
@@ -362,9 +363,11 @@ public final class Toad implements AutoCloseable {
         @Override
         public boolean equals(Object other) {
           return switch (other) {
-            case Con o -> this.ackedRetryStrategy == o.ackedRetryStrategy &&
-            this.unackedRetryStrategy == o.unackedRetryStrategy &&
-            this.maxAttempts == o.maxAttempts;
+            case Con o -> this.ackedRetryStrategy.equals(
+                o.ackedRetryStrategy
+              ) &&
+            this.unackedRetryStrategy.equals(o.unackedRetryStrategy) &&
+            this.maxAttempts.equals(o.maxAttempts);
             default -> false;
           };
         }
@@ -435,8 +438,8 @@ public final class Toad implements AutoCloseable {
         @Override
         public boolean equals(Object other) {
           return switch (other) {
-            case Non o -> this.retryStrategy == o.retryStrategy &&
-            this.maxAttempts == o.maxAttempts;
+            case Non o -> this.retryStrategy.equals(o.retryStrategy) &&
+            this.maxAttempts.equals(o.maxAttempts);
             default -> false;
           };
         }
diff --git a/src/main/java/dev.toad/msg/Code.java b/src/main/java/dev.toad/msg/Code.java
index 4ff4c8a..49c0898 100644
--- a/src/main/java/dev.toad/msg/Code.java
+++ b/src/main/java/dev.toad/msg/Code.java
@@ -1,13 +1,22 @@
 package dev.toad.msg;
 
 import dev.toad.Debug;
+import dev.toad.Eq;
 import dev.toad.ffi.u8;
+import java.util.List;
 
 public final class Code implements Debug {
 
   final u8 clazz;
   final u8 detail;
 
+  public static Eq<Code> eq = Eq.all(
+    List.of(
+      Eq.short_.contramap(Code::codeClass),
+      Eq.short_.contramap(Code::codeDetail)
+    )
+  );
+
   public static final Code EMPTY = new Code(0, 0);
 
   public static final Code GET = new Code(0, 1);
@@ -112,17 +121,10 @@ public final class Code implements Debug {
     return this.toString();
   }
 
-  public boolean equals(Code other) {
-    return (
-      this.codeClass() == other.codeClass() &&
-      this.codeDetail() == other.codeDetail()
-    );
-  }
-
   @Override
   public boolean equals(Object other) {
     return switch (other) {
-      case Code c -> c.equals(this);
+      case Code c -> Code.eq.test(c, this);
       default -> false;
     };
   }
diff --git a/src/main/java/dev.toad/msg/Id.java b/src/main/java/dev.toad/msg/Id.java
index c8c6d9d..130480c 100644
--- a/src/main/java/dev.toad/msg/Id.java
+++ b/src/main/java/dev.toad/msg/Id.java
@@ -1,12 +1,15 @@
 package dev.toad.msg;
 
 import dev.toad.Debug;
+import dev.toad.Eq;
 import dev.toad.ffi.u16;
 
 public final class Id implements Debug {
 
   public static native Id defaultId();
 
+  public static final Eq<Id> eq = Eq.int_.contramap(Id::toInt);
+
   final u16 id;
 
   public Id(int id) {
@@ -17,6 +20,14 @@ public final class Id implements Debug {
     return this.id.intValue();
   }
 
+  @Override
+  public boolean equals(Object other) {
+    return switch (other) {
+      case Id i -> Id.eq.test(this, i);
+      default -> false;
+    };
+  }
+
   @Override
   public String toDebugString() {
     return String.format("Id(%d)", this.toInt());
diff --git a/src/main/java/dev.toad/msg/Message.java b/src/main/java/dev.toad/msg/Message.java
index 0ae8737..2ed0d0e 100644
--- a/src/main/java/dev.toad/msg/Message.java
+++ b/src/main/java/dev.toad/msg/Message.java
@@ -1,6 +1,7 @@
 package dev.toad.msg;
 
 import dev.toad.Debug;
+import dev.toad.Eq;
 import dev.toad.msg.option.Accept;
 import dev.toad.msg.option.ContentFormat;
 import dev.toad.msg.option.Host;
@@ -35,8 +36,12 @@ public interface Message extends Debug {
 
   public byte[] toBytes();
 
-  public default dev.toad.msg.build.Message modify() {
-    return dev.toad.msg.build.Message.from(this);
+  public default dev.toad.msg.build.Message buildCopy() {
+    return dev.toad.msg.build.Message.copyOf(this);
+  }
+
+  public default dev.toad.msg.build.MessageNeeds.Code buildResponse() {
+    return dev.toad.msg.build.Message.respondTo(this);
   }
 
   public default Optional<Option> getOption(long number) {
@@ -91,17 +96,24 @@ public interface Message extends Debug {
     }
   }
 
-  public default boolean equals(Message o) {
-    return (
-      this.addr().equals(o.addr()) &&
-      this.options().equals(o.options()) &&
-      this.id().equals(o.id()) &&
-      this.token().equals(o.token()) &&
-      this.type().equals(o.type()) &&
-      this.payload().equals(o.payload())
+  public static Eq<Message> eq() {
+    return Eq.all(
+      List.of(
+        Eq.optional(Eq.socketAddress).contramap(m -> m.addr()),
+        Eq.list(Option.eq()).contramap(m -> m.options()),
+        Code.eq.contramap(m -> m.code()),
+        Id.eq.contramap(m -> m.id()),
+        Token.eq.contramap(m -> m.token()),
+        Type.eq.contramap(m -> m.type()),
+        Payload.eq.contramap(m -> m.payload())
+      )
     );
   }
 
+  public default boolean equals(Message m) {
+    return Message.eq().test(this, m);
+  }
+
   @Override
   public default String toDebugString() {
     return (
diff --git a/src/main/java/dev.toad/msg/Option.java b/src/main/java/dev.toad/msg/Option.java
index 2976a8d..084f718 100644
--- a/src/main/java/dev.toad/msg/Option.java
+++ b/src/main/java/dev.toad/msg/Option.java
@@ -1,6 +1,7 @@
 package dev.toad.msg;
 
 import dev.toad.Debug;
+import dev.toad.Eq;
 import dev.toad.msg.option.*;
 import java.util.List;
 import java.util.stream.Collectors;
@@ -10,8 +11,17 @@ public interface Option extends Debug {
 
   public List<OptionValue> values();
 
+  public static Eq<Option> eq() {
+    return Eq.all(
+      List.of(
+        Eq.long_.contramap(o -> o.number()),
+        Eq.list(OptionValue.eq()).contramap(Option::values)
+      )
+    );
+  }
+
   public default boolean equals(Option o) {
-    return this.number() == o.number() && this.values().equals(o.values());
+    return Option.eq().test(this, o);
   }
 
   @Override
diff --git a/src/main/java/dev.toad/msg/OptionValue.java b/src/main/java/dev.toad/msg/OptionValue.java
index 5cd9dff..0b79705 100644
--- a/src/main/java/dev.toad/msg/OptionValue.java
+++ b/src/main/java/dev.toad/msg/OptionValue.java
@@ -1,6 +1,7 @@
 package dev.toad.msg;
 
 import dev.toad.Debug;
+import dev.toad.Eq;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -11,6 +12,10 @@ public interface OptionValue extends Debug {
 
   public dev.toad.msg.owned.OptionValue toOwned();
 
+  public static Eq<OptionValue> eq() {
+    return Eq.byteArray.contramap(OptionValue::asBytes);
+  }
+
   public default boolean equals(OptionValue o) {
     return this.asBytes().equals(o.asBytes());
   }
diff --git a/src/main/java/dev.toad/msg/Payload.java b/src/main/java/dev.toad/msg/Payload.java
index d761d4a..ba96b9f 100644
--- a/src/main/java/dev.toad/msg/Payload.java
+++ b/src/main/java/dev.toad/msg/Payload.java
@@ -1,9 +1,12 @@
 package dev.toad.msg;
 
 import dev.toad.Debug;
+import dev.toad.Eq;
 import dev.toad.msg.option.ContentFormat;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
 import java.util.Optional;
 
 public final class Payload implements Debug {
@@ -11,6 +14,19 @@ public final class Payload implements Debug {
   final byte[] bytes;
   final Optional<ContentFormat> contentFormat;
 
+  public static final Eq<Payload> eq = Eq.all(
+    List.of(
+      Eq.optional(ContentFormat.eq).contramap(Payload::contentFormat),
+      Eq.byteArray.contramap(Payload::bytes)
+    )
+  );
+
+  public static boolean equals(Payload a, Payload b) {
+    return (
+      Arrays.equals(a.bytes, b.bytes) && a.contentFormat.equals(b.contentFormat)
+    );
+  }
+
   public Payload() {
     this.contentFormat = Optional.empty();
     this.bytes = new byte[] {};
@@ -63,6 +79,14 @@ public final class Payload implements Debug {
     return new Payload(ContentFormat.OCTET_STREAM, bytes);
   }
 
+  @Override
+  public boolean equals(Object other) {
+    return switch (other) {
+      case Payload p -> Payload.eq.test(this, p);
+      default -> false;
+    };
+  }
+
   @Override
   public String toDebugString() {
     if (this.contentFormat.map(ContentFormat::isUtf8Text).orElse(false)) {
diff --git a/src/main/java/dev.toad/msg/Token.java b/src/main/java/dev.toad/msg/Token.java
index c040f2d..4457ff7 100644
--- a/src/main/java/dev.toad/msg/Token.java
+++ b/src/main/java/dev.toad/msg/Token.java
@@ -1,12 +1,16 @@
 package dev.toad.msg;
 
 import dev.toad.Debug;
+import dev.toad.Eq;
 import java.util.ArrayList;
+import java.util.Arrays;
 
 public final class Token implements Debug {
 
   public static native Token defaultToken();
 
+  public static final Eq<Token> eq = Eq.byteArray.contramap(Token::toBytes);
+
   final byte[] bytes;
 
   public Token(byte[] bytes) {
@@ -30,7 +34,7 @@ public final class Token implements Debug {
   @Override
   public boolean equals(Object other) {
     return switch (other) {
-      case Token t -> t.bytes.equals(this.bytes);
+      case Token t -> Token.eq.test(this, t);
       default -> false;
     };
   }
diff --git a/src/main/java/dev.toad/msg/Type.java b/src/main/java/dev.toad/msg/Type.java
index 3234af1..64801cb 100644
--- a/src/main/java/dev.toad/msg/Type.java
+++ b/src/main/java/dev.toad/msg/Type.java
@@ -1,6 +1,7 @@
 package dev.toad.msg;
 
 import dev.toad.Debug;
+import dev.toad.Eq;
 
 public enum Type implements Debug {
   CON(1),
@@ -8,6 +9,8 @@ public enum Type implements Debug {
   ACK(3),
   RESET(4);
 
+  public static final Eq<Type> eq = new Eq<>((a, b) -> a == b);
+
   private Type(int val) {}
 
   public String toString() {
diff --git a/src/main/java/dev.toad/msg/build/Message.java b/src/main/java/dev.toad/msg/build/Message.java
index ce78704..3c90634 100644
--- a/src/main/java/dev.toad/msg/build/Message.java
+++ b/src/main/java/dev.toad/msg/build/Message.java
@@ -35,30 +35,48 @@ public final class Message
 
   Message() {}
 
-  public static Message from(dev.toad.msg.Message other) {
+  public static MessageNeeds.Code respondTo(dev.toad.msg.Message other) {
+    return Message.respondTo(other, false);
+  }
+
+  public static MessageNeeds.Code respondTo(
+    dev.toad.msg.Message other,
+    boolean conResponseToNonRequest
+  ) {
+    // prettier-ignore
+    Type type = Type.eq.test(other.type(), Type.CON) ? Type.ACK
+              : conResponseToNonRequest              ? Type.CON
+              : Type.NON;
+
+    return Message.copyOf(other).unsetId().type(type);
+  }
+
+  public static Message copyOf(dev.toad.msg.Message other) {
     var builder = new Message();
 
-    Function<dev.toad.msg.Option, Long> key = o -> o.number();
-    Function<dev.toad.msg.Option, ArrayList<dev.toad.msg.owned.OptionValue>> value =
+    Function<dev.toad.msg.Option, Long> key;
+    Function<dev.toad.msg.Option, ArrayList<dev.toad.msg.owned.OptionValue>> value;
+    BinaryOperator<ArrayList<dev.toad.msg.owned.OptionValue>> merge;
+
+    key = o -> o.number();
+    value =
       o ->
         o
           .values()
           .stream()
-          .map(v -> v.toOwned())
+          .map(dev.toad.msg.OptionValue::toOwned)
           .collect(Collectors.toCollection(ArrayList::new));
-    BinaryOperator<ArrayList<dev.toad.msg.owned.OptionValue>> merge = (
-      a,
-      b
-    ) -> {
-      a.addAll(b);
-      return a;
-    };
+    merge =
+      (a, b) -> {
+        a.addAll(b);
+        return a;
+      };
 
     builder.options =
       other
         .options()
         .stream()
-        .collect(Collectors.toMap(key, value, merge, () -> new HashMap<>()));
+        .collect(Collectors.toMap(key, value, merge, HashMap::new));
     builder.id = Optional.of(other.id());
     builder.code = Optional.of(other.code());
     builder.token = Optional.of(other.token());
@@ -73,15 +91,17 @@ public final class Message
     return new Message();
   }
 
-  public MessageNeeds.Type uri(String uriStr)
+  public Message uri(String uriStr)
     throws URISyntaxException, UnknownHostException {
     var uri = new URI(uriStr);
     var addr = InetAddress.getByName(uri.getHost());
-    var port = uri.getPort() > 0
-      ? uri.getPort()
-      : uri.getScheme() != null && uri.getScheme().equals("coaps")
-        ? 5684
-        : 5683;
+    var secure = uri.getScheme() != null && uri.getScheme().equals("coaps");
+
+    // prettier-ignore
+    var port = uri.getPort() > 0 ? uri.getPort()
+             : secure ? 5684
+             : 5683;
+
     this.addr = Optional.of(new InetSocketAddress(addr, port));
 
     this.option(new Host(addr.getHostAddress()));
@@ -97,12 +117,12 @@ public final class Message
     return this;
   }
 
-  public MessageNeeds.Type addr(InetSocketAddress addr) {
+  public Message addr(InetSocketAddress addr) {
     this.addr = Optional.of(addr);
     return this;
   }
 
-  public MessageNeeds.Code type(Type type) {
+  public Message type(Type type) {
     this.type = Optional.of(type);
     return this;
   }
diff --git a/src/main/java/dev.toad/msg/option/Accept.java b/src/main/java/dev.toad/msg/option/Accept.java
index 791cec9..f515040 100644
--- a/src/main/java/dev.toad/msg/option/Accept.java
+++ b/src/main/java/dev.toad/msg/option/Accept.java
@@ -1,5 +1,6 @@
 package dev.toad.msg.option;
 
+import dev.toad.Eq;
 import dev.toad.ffi.u16;
 import dev.toad.msg.Option;
 import dev.toad.msg.OptionValue;
@@ -11,6 +12,7 @@ import java.util.stream.Collectors;
 public final class Accept extends ContentFormat implements Option {
 
   public static final long number = 17;
+  public static final Eq<Accept> eq = Eq.int_.contramap(Accept::value);
 
   public static final Accept TEXT = new Accept(ContentFormat.TEXT);
   public static final Accept LINK_FORMAT = new Accept(
@@ -46,7 +48,7 @@ public final class Accept extends ContentFormat implements Option {
           o
             .values()
             .stream()
-            .map(v -> v.asString())
+            .map(OptionValue::asString)
             .collect(Collectors.toList())
         )
       );
diff --git a/src/main/java/dev.toad/msg/option/ContentFormat.java b/src/main/java/dev.toad/msg/option/ContentFormat.java
index b65c425..74f0698 100644
--- a/src/main/java/dev.toad/msg/option/ContentFormat.java
+++ b/src/main/java/dev.toad/msg/option/ContentFormat.java
@@ -1,5 +1,6 @@
 package dev.toad.msg.option;
 
+import dev.toad.Eq;
 import dev.toad.ffi.u16;
 import dev.toad.msg.Option;
 import dev.toad.msg.OptionValue;
@@ -13,6 +14,9 @@ public sealed class ContentFormat implements Option permits Accept {
 
   protected u16 value;
 
+  public static final Eq<ContentFormat> eq = Eq.int_.contramap(
+    ContentFormat::value
+  );
   public static final long number = 12;
 
   public ContentFormat(Option o) {
@@ -76,48 +80,37 @@ public sealed class ContentFormat implements Option permits Accept {
 
   public boolean isUtf8Text() {
     return (
-      this.value() == ContentFormat.TEXT.value() ||
-      this.value() == ContentFormat.CSS.value() ||
-      this.value() == ContentFormat.JSON.value() ||
-      this.value() == ContentFormat.XML.value() ||
-      this.value() == ContentFormat.JAVASCRIPT.value() ||
-      this.value() == ContentFormat.LINK_FORMAT.value() ||
-      this.value() == ContentFormat.IMAGE_SVG.value()
+      this.equals(ContentFormat.TEXT) ||
+      this.equals(ContentFormat.CSS) ||
+      this.equals(ContentFormat.JSON) ||
+      this.equals(ContentFormat.XML) ||
+      this.equals(ContentFormat.JAVASCRIPT) ||
+      this.equals(ContentFormat.LINK_FORMAT) ||
+      this.equals(ContentFormat.IMAGE_SVG)
     );
   }
 
   public String toMimeType() {
     // https://www.iana.org/assignments/core-parameters/core-parameters.xhtml#content-formats
-    return this.value() == ContentFormat.TEXT.value()
-      ? "text/plain; charset=utf-8"
-      : this.value() == ContentFormat.CSS.value()
-        ? "text/css"
-        : this.value() == ContentFormat.JSON.value()
-          ? "application/json"
-          : this.value() == ContentFormat.XML.value()
-            ? "application/xml"
-            : this.value() == ContentFormat.EXI.value()
-              ? "application/exi"
-              : this.value() == ContentFormat.CBOR.value()
-                ? "application/cbor"
-                : this.value() == ContentFormat.JAVASCRIPT.value()
-                  ? "application/javascript"
-                  : this.value() == ContentFormat.OCTET_STREAM.value()
-                    ? "application/octet-stream"
-                    : this.value() == ContentFormat.LINK_FORMAT.value()
-                      ? "application/link-format"
-                      : this.value() == ContentFormat.IMAGE_GIF.value()
-                        ? "image/gif"
-                        : this.value() == ContentFormat.IMAGE_JPG.value()
-                          ? "image/jpeg"
-                          : this.value() == ContentFormat.IMAGE_PNG.value()
-                            ? "image/png"
-                            : this.value() == ContentFormat.IMAGE_SVG.value()
-                              ? "image/svg+xml"
-                              : String.format(
-                                "ContentFormat(%d)",
-                                this.value()
-                              );
+    // prettier-ignore
+    return this.equals(ContentFormat.TEXT)         ? "text/plain; charset=utf-8"
+         : this.equals(ContentFormat.CSS)          ? "text/css"
+         : this.equals(ContentFormat.JSON)         ? "application/json"
+         : this.equals(ContentFormat.XML)          ? "application/xml"
+         : this.equals(ContentFormat.EXI)          ? "application/exi"
+         : this.equals(ContentFormat.CBOR)         ? "application/cbor"
+         : this.equals(ContentFormat.JAVASCRIPT)   ? "application/javascript"
+         : this.equals(ContentFormat.OCTET_STREAM) ? "application/octet-stream"
+         : this.equals(ContentFormat.LINK_FORMAT)  ? "application/link-format"
+         : this.equals(ContentFormat.IMAGE_GIF)    ? "image/gif"
+         : this.equals(ContentFormat.IMAGE_JPG)    ? "image/jpeg"
+         : this.equals(ContentFormat.IMAGE_PNG)    ? "image/png"
+         : this.equals(ContentFormat.IMAGE_SVG)    ? "image/svg+xml"
+         : String.format("ContentFormat(%d)", this.value());
+  }
+
+  public boolean equals(ContentFormat cf) {
+    return ContentFormat.eq.test(this, cf);
   }
 
   @Override
@@ -128,10 +121,6 @@ public sealed class ContentFormat implements Option permits Accept {
     };
   }
 
-  public boolean equals(ContentFormat other) {
-    return this.value() == other.value();
-  }
-
   public String toString() {
     return String.format("ContentFormat(%d)", this.value());
   }
diff --git a/src/main/java/dev.toad/msg/option/Host.java b/src/main/java/dev.toad/msg/option/Host.java
index f0f846a..78cca86 100644
--- a/src/main/java/dev.toad/msg/option/Host.java
+++ b/src/main/java/dev.toad/msg/option/Host.java
@@ -1,5 +1,6 @@
 package dev.toad.msg.option;
 
+import dev.toad.Eq;
 import dev.toad.msg.Option;
 import dev.toad.msg.OptionValue;
 import java.util.ArrayList;
@@ -12,6 +13,7 @@ public final class Host implements Option {
   final String host;
 
   public static final long number = 3;
+  public static final Eq<Host> eq = Eq.string.contramap(Host::toString);
 
   public Host(Option o) {
     if (o.number() != Host.number) {
@@ -58,7 +60,7 @@ public final class Host implements Option {
   @Override
   public boolean equals(Object other) {
     return switch (other) {
-      case Host h -> this.toString().equals(h.toString());
+      case Host h -> Host.eq.test(this, h);
       default -> false;
     };
   }
diff --git a/src/main/java/dev.toad/msg/option/Path.java b/src/main/java/dev.toad/msg/option/Path.java
index cdee29d..e618778 100644
--- a/src/main/java/dev.toad/msg/option/Path.java
+++ b/src/main/java/dev.toad/msg/option/Path.java
@@ -1,5 +1,6 @@
 package dev.toad.msg.option;
 
+import dev.toad.Eq;
 import dev.toad.msg.Option;
 import dev.toad.msg.OptionValue;
 import java.util.ArrayList;
@@ -12,6 +13,9 @@ public final class Path implements Option {
   final ArrayList<String> segments;
 
   public static final long number = 11;
+  public static final Eq<Path> eq = Eq
+    .list(Eq.string)
+    .contramap(Path::segments);
 
   public Path(Option o) {
     if (o.number() != Path.number) {
@@ -40,10 +44,6 @@ public final class Path implements Option {
     }
   }
 
-  public boolean equals(Path other) {
-    return this.segments == other.segments;
-  }
-
   public List<String> segments() {
     return this.segments;
   }
@@ -73,4 +73,12 @@ public final class Path implements Option {
       .map(s -> new dev.toad.msg.owned.OptionValue(s))
       .collect(Collectors.toList());
   }
+
+  @Override
+  public boolean equals(Object other) {
+    return switch (other) {
+      case Path p -> Path.eq.test(this, p);
+      default -> false;
+    };
+  }
 }
diff --git a/src/main/java/dev.toad/msg/option/Query.java b/src/main/java/dev.toad/msg/option/Query.java
index cc67a66..b7057cc 100644
--- a/src/main/java/dev.toad/msg/option/Query.java
+++ b/src/main/java/dev.toad/msg/option/Query.java
@@ -1,5 +1,6 @@
 package dev.toad.msg.option;
 
+import dev.toad.Eq;
 import dev.toad.msg.Option;
 import dev.toad.msg.OptionValue;
 import java.util.ArrayList;
@@ -17,6 +18,9 @@ public final class Query implements Option {
 
   final ArrayList<String> query;
   public static final long number = 15;
+  public static final Eq<Query> eq = Eq
+    .<String, List<Value>>map(Eq.list(Value.eq))
+    .contramap(Query::toMap);
 
   public Query(Option o) {
     if (o.number() != Query.number) {
@@ -90,12 +94,24 @@ public final class Query implements Option {
     return String.format("Uri-Query: %s", this.toString());
   }
 
+  @Override
+  public boolean equals(Object other) {
+    return switch (other) {
+      case Query q -> Query.eq.test(this, q);
+      default -> false;
+    };
+  }
+
   public static final class Value {
 
+    public static final Eq<Value> eq = Eq
+      .optional(Eq.string)
+      .contramap(Value::value);
+
     final Optional<String> val;
 
     public Value(String val) {
-      if (val == null || val == "") {
+      if (val == null || val.isEmpty()) {
         this.val = Optional.empty();
       } else {
         this.val = Optional.of(val);
@@ -119,14 +135,10 @@ public final class Query implements Option {
       }
     }
 
-    public boolean equals(Value other) {
-      return this.toString().equals(other.toString());
-    }
-
     @Override
     public boolean equals(Object other) {
       return switch (other) {
-        case Value v -> this.equals(v);
+        case Value v -> Value.eq.test(this, v);
         default -> false;
       };
     }
diff --git a/src/test/scala/E2E.scala b/src/test/scala/E2E.scala
index 1646273..c5ea4ad 100644
--- a/src/test/scala/E2E.scala
+++ b/src/test/scala/E2E.scala
@@ -14,36 +14,29 @@ import java.util.concurrent.TimeUnit
 import java.net.InetAddress
 
 class E2E extends munit.FunSuite {
-  test("minimal client and server") {
+  test("little baby server") {
     Toad.loadNativeLib()
 
-    val serverThread = Thread((() => {
-      Toad.builder
-        .port(10102)
-        .logLevel(Level.INFO)
-        .server
-        .post(
-          "exit",
-          _msg => {
-            Server.Middleware.exit
-          }
-        )
-        .get(
-          "hello",
-          msg => {
-            val name = msg.payload.toString
-            val rep = msg.modify.unsetId
-              .`type`(Type.NON)
-              .code(Code.OK_CONTENT)
-              .payload(Payload.text(s"Hello, $name!"))
-              .build
-            Server.Middleware.respond(rep)
-          }
-        )
-        .build
-        .run
-    }): java.lang.Runnable)
+    val server = Toad.builder
+      .port(10102)
+      .logLevel(Level.INFO)
+      .server
+      .post("exit", _msg => Server.Middleware.exit)
+      .get(
+        "hello",
+        msg => {
+          val rep = msg.buildResponse
+            .code(Code.OK_CONTENT)
+            .`type`(Type.NON)
+            .payload(Payload.text(s"Hello, ${msg.payload.toString}!"))
+            .build
 
+          Server.Middleware.respond(rep)
+        }
+      )
+      .build;
+
+    val serverThread = Thread((() => server.run()): java.lang.Runnable)
     serverThread.start()
 
     val req = Message.builder
@@ -68,6 +61,6 @@ class E2E extends munit.FunSuite {
       client.sendNoResponse(exit)
     }
 
-    serverThread.join
+    serverThread.join()
   }
 }
diff --git a/src/test/scala/Eq.scala b/src/test/scala/Eq.scala
new file mode 100644
index 0000000..537481f
--- /dev/null
+++ b/src/test/scala/Eq.scala
@@ -0,0 +1,126 @@
+import scala.jdk.CollectionConverters.*
+import dev.toad.*
+import dev.toad.msg.*
+import dev.toad.msg.option.*
+
+class Eq extends munit.FunSuite {
+  test("byteArray") {
+    assert(dev.toad.Eq.byteArray.test(Array[Byte](), Array[Byte]()))
+    assert(dev.toad.Eq.byteArray.test(Array[Byte](1), Array[Byte](1)))
+    assert(dev.toad.Eq.byteArray.test(Array[Byte](1, 2), Array[Byte](1, 2)))
+    assert(!dev.toad.Eq.byteArray.test(Array[Byte](1), Array[Byte]()))
+  }
+
+  test("int, short, long") {
+    assert(dev.toad.Eq.int_.test(0, 0))
+    assert(dev.toad.Eq.int_.test(1, 1))
+    assert(dev.toad.Eq.long_.test(1, 1))
+    assert(dev.toad.Eq.short_.test(1.shortValue, 1.shortValue))
+    assert(!dev.toad.Eq.int_.test(1, 0))
+    assert(!dev.toad.Eq.long_.test(1, 0))
+    assert(!dev.toad.Eq.short_.test(1.shortValue, 0.shortValue))
+  }
+
+  test("String") {
+    assert(dev.toad.Eq.string.test(null, null))
+    assert(dev.toad.Eq.string.test("a", "a"))
+    assert(!dev.toad.Eq.string.test("", null))
+    assert(!dev.toad.Eq.string.test("", "a"))
+  }
+
+  test("contramap") {
+    class Foo(val bar: String)
+
+    val a = Foo("baz")
+    val b = Foo("bingo")
+
+    val eq = dev.toad.Eq.string.contramap((foo: Foo) => foo.bar)
+
+    assert(eq.test(a, a))
+    assert(!eq.test(a, b))
+  }
+
+  test("contramap + all") {
+    class Foo(val bar: String, val baz: String)
+
+    val a = Foo("a", "b")
+    val b = Foo("b", "c")
+    val c = Foo("a", "c")
+
+    val eq = dev.toad.Eq.all(
+      Seq(
+        dev.toad.Eq.string.contramap((f: Foo) => f.bar),
+        dev.toad.Eq.string.contramap((f: Foo) => f.baz)
+      ).asJava
+    )
+
+    assert(eq.test(a, a))
+    assert(eq.test(b, b))
+    assert(!eq.test(a, b))
+    assert(!eq.test(a, c))
+  }
+
+  test("Map") {
+    val map = dev.toad.Eq.map[String, String](dev.toad.Eq.string)
+    assert(map.test(Map().asJava, Map().asJava))
+    assert(
+      map.test(
+        Map("a" -> "a", "foo" -> "bar").asJava,
+        Map("a" -> "a", "foo" -> "bar").asJava
+      )
+    )
+    assert(
+      !map.test(
+        Map("foo" -> "bar").asJava,
+        Map("a" -> "a", "foo" -> "bar").asJava
+      )
+    )
+    assert(!map.test(Map().asJava, Map("a" -> "a", "foo" -> "bar").asJava))
+  }
+
+  test("List") {
+    val list = dev.toad.Eq.list(dev.toad.Eq.string)
+    assert(list.test(Seq("a", "b").asJava, Seq("a", "b").asJava))
+    assert(!list.test(Seq("b", "b").asJava, Seq("a", "b").asJava))
+  }
+
+  test("Id") {
+    assert(Id.eq.test(Id(1), Id(1)))
+    assert(!Id.eq.test(Id(0), Id(1)))
+  }
+
+  test("Token") {
+    assert(
+      Token.eq.test(Token(Array[Byte](1, 2, 3)), Token(Array[Byte](1, 2, 3)))
+    )
+    assert(
+      !Token.eq.test(Token(Array[Byte](2, 2, 3)), Token(Array[Byte](1, 2, 3)))
+    )
+  }
+
+  test("Code") {
+    assert(Code.eq.test(Code.OK_CONTENT, Code.OK_CONTENT))
+    assert(!Code.eq.test(Code.GET, Code.OK_CONTENT))
+  }
+
+  test("Message") {
+    val a = Message.builder
+      .uri("coap://localhost:1234/a/b/c")
+      .`type`(Type.CON)
+      .code(Code.GET)
+      .id(Id(0))
+      .token(Token(Array[Byte](1, 2, 3)))
+      .payload(Payload.text("foo"))
+      .build
+    assert(Message.eq.test(a, a))
+    assert(!Message.eq.test(a, a.buildCopy.`type`(Type.NON).build))
+    assert(!Message.eq.test(a, a.buildCopy.option(Path("b/c")).build))
+    assert(!Message.eq.test(a, a.buildCopy.code(Code.PUT).build))
+    assert(!Message.eq.test(a, a.buildCopy.id(Id(1)).build))
+    assert(!Message.eq.test(a, a.buildCopy.token(Token(Array[Byte](2))).build))
+    assert(
+      !Message.eq.test(a, a.buildCopy.uri("coap://google.com:1234/a/b/c").build)
+    )
+    assert(!Message.eq.test(a, a.buildCopy.payload(Payload.json("foo")).build))
+  }
+}
diff --git a/src/test/scala/Glue.scala b/src/test/scala/Glue.scala
index 6d933f1..a917f62 100644
--- a/src/test/scala/Glue.scala
+++ b/src/test/scala/Glue.scala
@@ -2,10 +2,10 @@ import sys.process._
 
 class Glue extends munit.FunSuite {
   test("cargo test") {
-    // Seq(
-    //   "sh",
-    //   "-c",
-    //   "cd glue; RUST_BACKTRACE=full cargo test --quiet --features e2e"
-    // ).!!
+    Seq(
+      "sh",
+      "-c",
+      "cd glue; RUST_BACKTRACE=full cargo test --quiet --features e2e"
+    ).!!
   }
 }
diff --git a/src/test/scala/Message.scala b/src/test/scala/Message.scala
index 93d66f5..8f45563 100644
--- a/src/test/scala/Message.scala
+++ b/src/test/scala/Message.scala
@@ -15,7 +15,54 @@ class MessageBuilder extends munit.FunSuite {
       .payload(Payload.json("[\"fart\"]"))
       .build
 
-    assertEquals(msg, dev.toad.msg.build.Message.from(msg).build)
+    assertEquals(msg, dev.toad.msg.build.Message.copyOf(msg).build)
+  }
+
+  test("respondTo(Message) unsets Id") {
+    val msg = dev.toad.msg.build.Message
+      .builder()
+      .uri("coap://localhost")
+      .`type`(Type.NON)
+      .code(Code.GET)
+      .payload(Payload.json("[\"fart\"]"))
+      .build
+
+    val rep =
+      dev.toad.msg.build.Message.respondTo(msg).code(Code.OK_CONTENT).build
+
+    assertEquals(rep.id, Id(0))
+  }
+
+  test("respondTo(Message) copies token") {
+    val msg = dev.toad.msg.build.Message
+      .builder()
+      .uri("coap://localhost")
+      .`type`(Type.NON)
+      .code(Code.GET)
+      .token(Token(Array[Byte](4, 5, 6)))
+      .payload(Payload.json("[\"fart\"]"))
+      .build
+
+    val rep =
+      dev.toad.msg.build.Message.respondTo(msg).code(Code.OK_CONTENT).build
+
+    assertEquals(rep.token, Token(Array[Byte](4, 5, 6)))
+  }
+
+  test("respondTo(Message) sets type to ACK on CON response") {
+    val msg = dev.toad.msg.build.Message
+      .builder()
+      .uri("coap://localhost")
+      .`type`(Type.CON)
+      .code(Code.GET)
+      .token(Token(Array[Byte](4, 5, 6)))
+      .payload(Payload.json("[\"fart\"]"))
+      .build
+
+    val rep =
+      dev.toad.msg.build.Message.respondTo(msg).code(Code.OK_CONTENT).build
+
+    assertEquals(rep.`type`(), Type.ACK)
   }
 
   test("payload(Payload) sets content format to ContentFormat.JSON") {