diff --git a/glue/Cargo.lock b/glue/Cargo.lock
index a220312..dbafa35 100644
--- a/glue/Cargo.lock
+++ b/glue/Cargo.lock
@@ -504,9 +504,9 @@ checksum = "87cc5ceb3875bb20c2890005a4e226a4651264a5c75edb2421b52861a0a0cb50"
 
 [[package]]
 name = "toad"
-version = "0.17.4"
+version = "0.17.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4eeb47a7e30efe198acc91ee919d420b478d9874c9362611d61f2ad9a3d27848"
+checksum = "7a19447d2692bd6d8b1c0c10457f42394da7b3f633b96c8705825aca91c080ad"
 dependencies = [
  "embedded-time",
  "log",
@@ -582,9 +582,9 @@ dependencies = [
 
 [[package]]
 name = "toad-jni"
-version = "0.14.0"
+version = "0.14.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c0bdcbce1dfef5ac76668490d12944aec41816999b2bd6ab889a5afbcbf13eb5"
+checksum = "15d9feb2f3a24a6d67aa5672d37893d160a57b9dbbc62d09a0f243abaec6c11f"
 dependencies = [
  "embedded-time",
  "jni",
diff --git a/glue/Cargo.toml b/glue/Cargo.toml
index 8674be8..1284e93 100644
--- a/glue/Cargo.toml
+++ b/glue/Cargo.toml
@@ -14,8 +14,8 @@ e2e = []
 [dependencies]
 jni = "0.21.1"
 nb = "1"
-toad = "0.17.4"
-toad-jni = "0.14.0"
+toad = "0.17.5"
+toad-jni = "0.14.1"
 no-std-net = "0.6"
 toad-msg = "0.18.1"
 tinyvec = {version = "1.5", default_features = false, features = ["rustc_1_55"]}
diff --git a/glue/src/dev/toad/mod.rs b/glue/src/dev/toad/mod.rs
index bfd0e2f..7be8188 100644
--- a/glue/src/dev/toad/mod.rs
+++ b/glue/src/dev/toad/mod.rs
@@ -3,18 +3,21 @@ pub mod msg;
 
 mod retry_strategy;
 
-use jni::objects::{JClass, JObject};
+use jni::objects::{JClass, JObject, JThrowable};
 use jni::sys::jobject;
 pub use retry_strategy::RetryStrategy;
 use toad::net::Addrd;
-use toad::platform::Platform;
+use toad::platform::{Platform, PlatformError};
 use toad::retry::{Attempts, Strategy};
+use toad::step::Step;
 use toad::time::Millis;
+use toad_jni::java::io::IOException;
 use toad_jni::java::net::InetSocketAddress;
 use toad_jni::java::nio::channels::{DatagramChannel, PeekableDatagramChannel};
 use toad_jni::java::util::Optional;
-use toad_jni::java::{self, Object};
+use toad_jni::java::{self, Object, ResultYieldToJavaOrThrow};
 
+use self::ffi::Ptr;
 use crate::mem::{Shared, SharedMemoryRegion};
 use crate::Runtime;
 
@@ -38,11 +41,27 @@ impl Toad {
     CONFIG.invoke(e, self)
   }
 
+  pub fn ptr(&self, e: &mut java::Env) -> Ptr {
+    static PTR: java::Field<Toad, Ptr> = java::Field::new("ptr");
+    PTR.get(e, self)
+  }
+
   fn init_impl(e: &mut java::Env, cfg: Config, channel: PeekableDatagramChannel) -> i64 {
     let r = Runtime::new(&mut java::env(), cfg.log_level(e), cfg.to_toad(e), channel);
     unsafe { crate::mem::Shared::add_runtime(r).addr() as i64 }
   }
 
+  fn notify_impl(&self,
+                 e: &mut java::Env,
+                 path: impl AsRef<str> + Clone)
+                 -> Result<(), java::io::IOException> {
+    self.ptr(e)
+        .addr(e)
+        .map_err(|err| IOException::new_caused_by(e, "", err))
+        .map(|addr| unsafe { Shared::deref::<Runtime>(addr.inner(e)).as_ref().unwrap() })
+        .and_then(|r| r.notify(path).map_err(PlatformError::step))
+  }
+
   fn poll_req_impl(e: &mut java::Env, addr: i64) -> java::util::Optional<msg::ref_::Message> {
     let r = unsafe { Shared::deref::<Runtime>(addr).as_ref().unwrap() };
     match r.poll_req() {
@@ -375,6 +394,21 @@ pub extern "system" fn Java_dev_toad_Toad_pollResp<'local>(mut e: java::Env<'loc
   Toad::poll_resp_impl(e, addr, token, sock).yield_to_java(e)
 }
 
+#[no_mangle]
+pub extern "system" fn Java_dev_toad_Toad_notify<'local>(mut e: java::Env<'local>,
+                                                         toad: JObject<'local>,
+                                                         path: JObject<'local>)
+                                                         -> () {
+  let e = &mut e;
+  let toad = java::lang::Object::from_local(e, toad).upcast_to::<Toad>(e);
+  let path = java::lang::Object::from_local(e, path).upcast_to::<String>(e);
+
+  if let Err(err) = toad.notify_impl(e, path) {
+    let err = JThrowable::from(err.downcast(e).to_local(e));
+    e.throw(err).unwrap()
+  }
+}
+
 #[no_mangle]
 pub extern "system" fn Java_dev_toad_Toad_teardown<'local>(_: java::Env<'local>,
                                                            _: JClass<'local>)
diff --git a/glue/src/lib.rs b/glue/src/lib.rs
index 708a32b..af18af0 100644
--- a/glue/src/lib.rs
+++ b/glue/src/lib.rs
@@ -46,13 +46,16 @@ mod runtime {
                config: Config,
                channel: PeekableDatagramChannel)
                -> Self {
-      let handler = ConsoleHandler::new(e);
-      handler.set_level(e, log_level);
-
       let logger = Logger::get_logger(e, "dev.toad");
-      logger.use_parent_handlers(e, false);
-      logger.add_handler(e, handler.to_handler());
-      logger.set_level(e, log_level);
+
+      if logger.uses_parent_handlers(e) {
+        let handler = ConsoleHandler::new(e);
+        handler.set_level(e, log_level);
+
+        logger.use_parent_handlers(e, false);
+        logger.add_handler(e, handler.to_handler());
+        logger.set_level(e, log_level);
+      }
 
       Self { steps: Default::default(),
              config,
diff --git a/src/main/java/dev.toad/ClientObserveStream.java b/src/main/java/dev.toad/ClientObserveStream.java
index d816baf..e5fac4e 100644
--- a/src/main/java/dev.toad/ClientObserveStream.java
+++ b/src/main/java/dev.toad/ClientObserveStream.java
@@ -1,14 +1,16 @@
 package dev.toad;
 
 import dev.toad.msg.Message;
+import dev.toad.msg.Token;
 import dev.toad.msg.option.Observe;
 import java.util.Optional;
 import java.util.concurrent.CompletableFuture;
 
-public class ClientObserveStream {
+public class ClientObserveStream implements AutoCloseable {
 
   State state;
-  Optional<CompletableFuture<Message>> buffered;
+  CompletableFuture<Message> initial;
+  Optional<Token> token = Optional.empty();
   final Client client;
   final Message message;
 
@@ -16,16 +18,7 @@ public class ClientObserveStream {
     this.state = State.OPEN;
     this.client = client;
     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.buildCopy().option(Observe.DEREGISTER).unsetId().build()
-      )
-      .thenAccept(m -> {
-        this.state = State.CLOSED;
-      });
+    this.initial = client.send(this.message);
   }
 
   public CompletableFuture<Message> next() {
@@ -33,18 +26,31 @@ public class ClientObserveStream {
       throw new RuntimeException(
         "ClientObserveStream.next() invoked after .close()"
       );
-    } else if (this.buffered.isEmpty()) {
-      var buffered = this.buffered.get();
-      this.buffered = Optional.empty();
-      return buffered;
+    } else if (this.token.isEmpty()) {
+      return this.initial.whenComplete((rep, e) -> {
+          if (rep != null) {
+            this.token = Optional.of(rep.token());
+          }
+        });
     } else {
-      return this.client.awaitResponse(
-          this.message.token(),
-          this.message.addr().get()
+      return this.initial.thenCompose(_i ->
+          this.client.awaitResponse(this.token.get(), this.message.addr().get())
         );
     }
   }
 
+  @Override
+  public void close() {
+    try {
+      this.client.send(
+          this.message.buildCopy().option(Observe.DEREGISTER).unsetId().build()
+        )
+        .get();
+    } catch (Throwable t) {}
+
+    this.state = State.CLOSED;
+  }
+
   public static final class State {
 
     public static final Eq<State> eq = Eq.int_.contramap((State s) -> s.state);
diff --git a/src/main/java/dev.toad/Eq.java b/src/main/java/dev.toad/Eq.java
index ebb26c9..671fb99 100644
--- a/src/main/java/dev.toad/Eq.java
+++ b/src/main/java/dev.toad/Eq.java
@@ -9,6 +9,7 @@ import java.util.function.Function;
 
 public final class Eq<T> {
 
+  public static final Eq<Boolean> bool = new Eq<>((a, b) -> a == b);
   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);
diff --git a/src/main/java/dev.toad/Server.java b/src/main/java/dev.toad/Server.java
index 13a8389..87554e1 100644
--- a/src/main/java/dev.toad/Server.java
+++ b/src/main/java/dev.toad/Server.java
@@ -3,207 +3,305 @@ package dev.toad;
 import dev.toad.msg.Code;
 import dev.toad.msg.Message;
 import dev.toad.msg.Payload;
+import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Optional;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutionException;
 import java.util.function.BiFunction;
+import java.util.function.BiPredicate;
 import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.logging.Level;
 import java.util.logging.Level;
 
-public final class Server {
+public final class Server implements AutoCloseable {
 
+  boolean exit = false;
+  Optional<Thread> thread = Optional.empty();
   final Toad toad;
-  final ArrayList<Function<Message, Middleware.Result>> middlewares;
-  final Function<Message, Middleware.Result> notFoundHandler;
-  final BiFunction<Message, Throwable, Middleware.Result> exceptionHandler;
+  final ArrayList<Middleware> middlewares;
 
-  Server(
-    Toad toad,
-    ArrayList<Function<Message, Middleware.Result>> ms,
-    Function<Message, Middleware.Result> notFoundHandler,
-    BiFunction<Message, Throwable, Middleware.Result> exHandler
-  ) {
+  Server(Toad toad, ArrayList<Middleware> ms) {
     this.toad = toad;
     this.middlewares = ms;
-    this.notFoundHandler = notFoundHandler;
-    this.exceptionHandler = exHandler;
   }
 
-  public void run() {
-    while (true) {
+  public void exit() {
+    this.exit = true;
+  }
+
+  public void notify(String path) {
+    this.toad.notify(path);
+  }
+
+  public Thread run() {
+    if (!this.thread.isEmpty()) {
+      return this.thread.get();
+    }
+
+    var thread = new Thread(() -> {
       try {
-        dev.toad.msg.ref.Message req = Async
-          .pollCompletable(() -> this.toad.pollReq())
-          .get();
+        Toad
+          .logger()
+          .log(
+            Level.INFO,
+            String.format(
+              "Server listening on %s",
+              this.toad.localAddress().toString()
+            )
+          );
+      } catch (Throwable t) {}
 
-        Middleware.Result result = Middleware.next();
-        for (var f : this.middlewares) {
-          if (!result.shouldContinue()) {
-            break;
-          }
+      while (true) {
+        try {
+          dev.toad.msg.ref.Message req = Async
+            .pollCompletable(() -> {
+              if (this.exit) {
+                throw new Exit();
+              }
 
-          if (result.isAsync()) {
-            try {
-              result.response().get();
-            } catch (Throwable e) {
-              result = Middleware.error(e);
-              break;
-            }
-            // Toad.ack(req);
-          }
+              return this.toad.pollReq();
+            })
+            .get();
+          var addr = req.addr().get();
 
-          try {
-            result = f.apply(req);
-          } catch (Throwable e) {
-            result = Middleware.error(e);
-          }
-        }
-
-        switch (result) {
-          case Middleware.ResultExit e:
-            this.toad.close();
-            return;
-          case Middleware.ResultError e:
-            result = this.exceptionHandler.apply(req, e.error);
-            break;
-          case Middleware.ResultNextSync n:
-            result = this.notFoundHandler.apply(req);
-            break;
-          case Middleware.ResultNextAsync n:
-            result = this.notFoundHandler.apply(req);
-            break;
-          default:
-            break;
-        }
-
-        req.close();
-
-        var resp = result.response().get();
-        if (resp.isEmpty()) {
           Toad
             .logger()
             .log(
-              Level.SEVERE,
-              String.format(
-                "Server never generated response for message\n%s",
-                req.toDebugString()
-              )
+              Level.FINE,
+              String.format("<== %s\n%s", addr.toString(), req.toDebugString())
             );
-        } else {
-          Async
-            .pollCompletable(() -> this.toad.sendMessage(resp.get().toOwned()))
-            .get();
+
+          Middleware.Result result = Middleware.Result.next();
+          for (var m : this.middlewares) {
+            if (!m.shouldRun.test(result, req)) {
+              continue;
+            }
+
+            try {
+              if (result.isAsync()) {
+                result.response().get();
+                // Toad.ack(req);
+              }
+
+              result = m.run(result, req);
+            } catch (Throwable e) {
+              result = Middleware.Result.error(e);
+            }
+          }
+
+          var resp = result.response().get();
+          if (resp.isEmpty()) {
+            Toad
+              .logger()
+              .log(
+                Level.SEVERE,
+                String.format(
+                  "Server never generated response for message\n%s",
+                  req.toDebugString()
+                )
+              );
+          } else {
+            var resp_ = resp.get().toOwned();
+            Toad
+              .logger()
+              .log(
+                Level.FINE,
+                String.format("==> %s\n%s", addr, resp_.toDebugString())
+              );
+            Async.pollCompletable(() -> this.toad.sendMessage(resp_)).get();
+          }
+
+          req.close();
+        } catch (Throwable e) {
+          if (e.getCause() instanceof Exit || e instanceof Exit) {
+            return;
+          }
+
+          Toad.logger().log(Level.SEVERE, e.toString());
+          e.printStackTrace();
         }
-      } catch (Throwable e) {
-        Toad.logger().log(Level.SEVERE, e.toString());
       }
-    }
+    });
+
+    thread.start();
+
+    this.thread = Optional.of(thread);
+    return thread;
   }
 
+  @Override
+  public void close() {
+    this.toad.close();
+  }
+
+  static final class Exit extends RuntimeException {}
+
   public static final class Middleware {
 
-    public static final CompletableFuture<Optional<Message>> noop =
+    final BiPredicate<Result, Message> shouldRun;
+    final BiFunction<Result, Message, Result> fun;
+
+    static final CompletableFuture<Optional<Message>> noop =
       CompletableFuture.completedFuture(Optional.empty());
 
-    public static final Function<Message, Result> notFound = m -> {
-      return Middleware.respond(m.buildResponse().code(Code.NOT_FOUND).build());
-    };
+    public static final Middleware respondNotFound =
+      Middleware.requestHandler(m ->
+        Optional.of(m.buildResponse().code(Code.NOT_FOUND).build())
+      );
+
+    public static final Middleware handleException = new Middleware(
+      (r, _m) -> r instanceof ResultError,
+      (r, m) -> {
+        var e = ((ResultError) r).error;
 
-    public static final BiFunction<Message, Throwable, Result> debugExceptionHandler =
-      (m, e) -> {
         Toad
           .logger()
           .log(
             Level.SEVERE,
-            String.format("while handling %s", m.toDebugString()),
+            String.format(
+              "Exception thrown while handling:\n%s\nException:",
+              m.toDebugString()
+            ),
             e
           );
 
-        var rep = m
-          .buildResponse()
-          .code(Code.INTERNAL_SERVER_ERROR)
-          .payload(Payload.text(e.toString()))
-          .build();
+        return Middleware.Result.respond(
+          m.buildResponse().code(Code.INTERNAL_SERVER_ERROR).build()
+        );
+      }
+    );
 
-        return Middleware.respond(rep);
-      };
+    public static final Middleware handleExceptionDebug = new Middleware(
+      (r, _m) -> r instanceof ResultError,
+      (r, m) -> {
+        var e = ((ResultError) r).error;
 
-    public static final BiFunction<Message, Throwable, Result> exceptionHandler =
-      (m, e) -> {
         Toad
           .logger()
           .log(
             Level.SEVERE,
-            String.format("while handling %s", m.toDebugString()),
+            String.format(
+              "Exception thrown while handling:\n%s\nException:",
+              m.toDebugString()
+            ),
             e
           );
-        var rep = m.buildResponse().code(Code.INTERNAL_SERVER_ERROR).build();
-        return Middleware.respond(rep);
-      };
 
-    public static Result respond(Message m) {
-      return new ResultRespondSync(m);
+        return Middleware.Result.respond(
+          m
+            .buildResponse()
+            .code(Code.INTERNAL_SERVER_ERROR)
+            .payload(Payload.text(e.toString()))
+            .build()
+        );
+      }
+    );
+
+    public static Middleware requestHandler(
+      Function<Message, Optional<Message>> f
+    ) {
+      return new Middleware(
+        (r, _m) -> !r.isFinal(),
+        (_result, request) ->
+          f
+            .apply(request)
+            .map(Middleware.Result::respond)
+            .orElse(Middleware.Result.next())
+      );
     }
 
-    public static Result respond(CompletableFuture<Message> m) {
-      return new ResultRespondAsync(m);
+    public static Middleware requestHandlerAsync(
+      Function<Message, Optional<CompletableFuture<Message>>> f
+    ) {
+      return new Middleware(
+        (r, _m) -> !r.isFinal(),
+        (_result, request) ->
+          f
+            .apply(request)
+            .map(Middleware.Result::respond)
+            .orElse(Middleware.Result.next())
+      );
     }
 
-    public static Result error(Throwable e) {
-      return new ResultError(e);
+    public static Middleware responseConsumer(Consumer<Message> f) {
+      return new Middleware(
+        (r, _m) ->
+          r instanceof ResultRespondSync || r instanceof ResultRespondAsync,
+        (res, request) -> {
+          try {
+            var rep = res.response().get().get();
+            f.accept(rep);
+            return res;
+          } catch (Throwable e) {
+            throw new RuntimeException(e);
+          }
+        }
+      );
     }
 
-    public static Result exit() {
-      return new ResultExit();
+    public static Middleware exceptionHandler(Function<Throwable, Result> f) {
+      return new Middleware(
+        (r, _m) -> r instanceof ResultError,
+        (res, request) -> f.apply(((ResultError) res).error)
+      );
     }
 
-    public static Result next() {
-      return new ResultNextSync();
+    public Middleware(
+      BiPredicate<Result, Message> shouldRun,
+      BiFunction<Result, Message, Result> fun
+    ) {
+      this.fun = fun;
+      this.shouldRun = shouldRun;
     }
 
-    public static Result next(CompletableFuture<Void> work) {
-      return new ResultNextAsync(work);
+    public Result run(Result res, Message msg) {
+      return this.fun.apply(res, msg);
+    }
+
+    public Middleware filter(BiPredicate<Result, Message> f) {
+      return new Middleware(
+        (r, m) -> f.test(r, m) && this.shouldRun.test(r, m),
+        this.fun
+      );
     }
 
     public static sealed interface Result
       permits
-        ResultExit,
         ResultError,
         ResultNextSync,
         ResultNextAsync,
         ResultRespondSync,
         ResultRespondAsync {
-      public boolean shouldContinue();
+      public static Result respond(Message m) {
+        return new ResultRespondSync(m);
+      }
+
+      public static Result respond(CompletableFuture<Message> m) {
+        return new ResultRespondAsync(m);
+      }
+
+      public static Result error(Throwable e) {
+        return new ResultError(e);
+      }
+
+      public static Result next() {
+        return new ResultNextSync();
+      }
+
+      public static Result next(CompletableFuture<Void> work) {
+        return new ResultNextAsync(work);
+      }
+
+      public boolean isFinal();
 
       public boolean isAsync();
 
       public CompletableFuture<Optional<Message>> response();
     }
 
-    public static final class ResultExit implements Result {
-
-      public ResultExit() {}
-
-      @Override
-      public boolean shouldContinue() {
-        return false;
-      }
-
-      @Override
-      public boolean isAsync() {
-        return false;
-      }
-
-      @Override
-      public CompletableFuture<Optional<Message>> response() {
-        return Middleware.noop;
-      }
-    }
-
     public static final class ResultError implements Result {
 
       public final Throwable error;
@@ -213,8 +311,8 @@ public final class Server {
       }
 
       @Override
-      public boolean shouldContinue() {
-        return false;
+      public boolean isFinal() {
+        return true;
       }
 
       @Override
@@ -233,8 +331,8 @@ public final class Server {
       public ResultNextSync() {}
 
       @Override
-      public boolean shouldContinue() {
-        return true;
+      public boolean isFinal() {
+        return false;
       }
 
       @Override
@@ -257,8 +355,8 @@ public final class Server {
       }
 
       @Override
-      public boolean shouldContinue() {
-        return true;
+      public boolean isFinal() {
+        return false;
       }
 
       @Override
@@ -281,8 +379,8 @@ public final class Server {
       }
 
       @Override
-      public boolean shouldContinue() {
-        return false;
+      public boolean isFinal() {
+        return true;
       }
 
       @Override
@@ -305,8 +403,8 @@ public final class Server {
       }
 
       @Override
-      public boolean shouldContinue() {
-        return false;
+      public boolean isFinal() {
+        return true;
       }
 
       @Override
@@ -324,120 +422,104 @@ public final class Server {
   public static final class Builder {
 
     final Toad toad;
-    final ArrayList<Function<Message, Middleware.Result>> middlewares =
-      new ArrayList<>();
-    Function<Message, Middleware.Result> notFoundHandler = Middleware.notFound;
-    BiFunction<Message, Throwable, Middleware.Result> exceptionHandler =
-      Middleware.exceptionHandler;
+    final ArrayList<Middleware> middlewares = new ArrayList<>();
 
     Builder(Toad toad) {
       this.toad = toad;
     }
 
-    public Builder middleware(Function<Message, Middleware.Result> f) {
-      this.middlewares.add(f);
+    public Builder middleware(Middleware m) {
+      this.middlewares.add(m);
       return this;
     }
 
-    public Builder when(
-      Predicate<Message> pred,
-      Function<Message, Middleware.Result> f
-    ) {
-      return this.middleware(m -> {
-          if (pred.test(m)) {
-            return f.apply(m);
-          } else {
-            return Middleware.next();
-          }
-        });
+    public Builder put(String path, Function<Message, Optional<Message>> f) {
+      return this.put(path, Middleware.requestHandler(f));
     }
 
-    public Builder put(String path, Function<Message, Middleware.Result> f) {
-      return this.when(
-          m ->
-            Code.eq.test(m.code(), Code.PUT) &&
-            m
+    public Builder put(String path, Middleware m) {
+      return this.middleware(
+          m.filter((_r, req) ->
+            Code.eq.test(req.code(), Code.PUT) &&
+            req
               .getPath()
               .map(p -> p.matches(path))
-              .orElse(path == null || path.isEmpty()),
-          f
+              .orElse(path == null || path.isEmpty())
+          )
         );
     }
 
-    public Builder post(String path, Function<Message, Middleware.Result> f) {
-      return this.when(
-          m ->
-            Code.eq.test(m.code(), Code.POST) &&
-            m
+    public Builder post(String path, Function<Message, Optional<Message>> f) {
+      return this.post(path, Middleware.requestHandler(f));
+    }
+
+    public Builder post(String path, Middleware m) {
+      return this.middleware(
+          m.filter((_r, req) ->
+            Code.eq.test(req.code(), Code.POST) &&
+            req
               .getPath()
               .map(p -> p.matches(path))
-              .orElse(path == null || path.isEmpty()),
-          f
+              .orElse(path == null || path.isEmpty())
+          )
         );
     }
 
-    public Builder delete(String path, Function<Message, Middleware.Result> f) {
-      return this.when(
-          m ->
-            Code.eq.test(m.code(), Code.DELETE) &&
-            m
+    public Builder get(String path, Function<Message, Optional<Message>> f) {
+      return this.get(path, Middleware.requestHandler(f));
+    }
+
+    public Builder get(String path, Middleware m) {
+      return this.middleware(
+          m.filter((_r, req) ->
+            Code.eq.test(req.code(), Code.GET) &&
+            req
               .getPath()
               .map(p -> p.matches(path))
-              .orElse(path == null || path.isEmpty()),
-          f
+              .orElse(path == null || path.isEmpty())
+          )
         );
     }
 
-    public Builder get(String path, Function<Message, Middleware.Result> f) {
-      return this.when(
-          m ->
-            Code.eq.test(m.code(), Code.GET) &&
-            m
+    public Builder delete(String path, Function<Message, Optional<Message>> f) {
+      return this.delete(path, Middleware.requestHandler(f));
+    }
+
+    public Builder delete(String path, Middleware m) {
+      return this.middleware(
+          m.filter((_r, req) ->
+            Code.eq.test(req.code(), Code.DELETE) &&
+            req
               .getPath()
               .map(p -> p.matches(path))
-              .orElse(path == null || path.isEmpty()),
-          f
+              .orElse(path == null || path.isEmpty())
+          )
         );
     }
 
-    public Builder tap(Consumer<Message> f) {
-      return this.middleware(m -> {
-          f.accept(m);
-          return Middleware.next();
-        });
+    public Builder onRequest(Consumer<Message> f) {
+      return this.middleware(
+          Middleware.requestHandler(m -> {
+            f.accept(m);
+            return Optional.empty();
+          })
+        );
     }
 
-    public Builder tapAsync(Function<Message, CompletableFuture<?>> f) {
-      return this.middleware(m -> {
-          return Middleware.next(f.apply(m).thenAccept(_void -> {}));
-        });
+    public Builder onResponse(Consumer<Message> f) {
+      return this.middleware(Middleware.responseConsumer(f));
     }
 
-    public Builder debugExceptions() {
-      return this.exceptionHandler(Middleware.debugExceptionHandler);
-    }
-
-    public Builder exceptionHandler(
-      BiFunction<Message, Throwable, Middleware.Result> handler
-    ) {
-      this.exceptionHandler = handler;
-      return this;
-    }
-
-    public Builder notFoundHandler(
-      Function<Message, Middleware.Result> handler
-    ) {
-      this.notFoundHandler = handler;
-      return this;
+    public Server buildDebugExceptionHandler() {
+      this.middleware(Middleware.handleExceptionDebug);
+      this.middleware(Middleware.respondNotFound);
+      return new Server(this.toad, this.middlewares);
     }
 
     public Server build() {
-      return new Server(
-        this.toad,
-        this.middlewares,
-        this.notFoundHandler,
-        this.exceptionHandler
-      );
+      this.middleware(Middleware.handleException);
+      this.middleware(Middleware.respondNotFound);
+      return new Server(this.toad, this.middlewares);
     }
   }
 }
diff --git a/src/main/java/dev.toad/Toad.java b/src/main/java/dev.toad/Toad.java
index ea58e8b..dacf33f 100644
--- a/src/main/java/dev.toad/Toad.java
+++ b/src/main/java/dev.toad/Toad.java
@@ -17,7 +17,9 @@ public final class Toad implements AutoCloseable {
 
   public static Logger logger() {
     // Configured in `glue::Runtime::new()`
-    return Logger.getLogger("dev.toad");
+    var l = Logger.getLogger("dev.toad");
+    l.setUseParentHandlers(false);
+    return l;
   }
 
   static native Config defaultConfigImpl();
@@ -53,6 +55,8 @@ public final class Toad implements AutoCloseable {
     dev.toad.msg.owned.Message msg
   );
 
+  native void notify(String path);
+
   static native Optional<dev.toad.msg.ref.Message> pollReq(long ptr);
 
   static native Optional<dev.toad.msg.ref.Message> pollResp(
@@ -90,6 +94,10 @@ public final class Toad implements AutoCloseable {
     return this.config;
   }
 
+  public InetSocketAddress localAddress() throws IOException {
+    return (InetSocketAddress) this.channel.getLocalAddress();
+  }
+
   @Override
   public void close() {
     Toad.teardown();
diff --git a/src/main/java/dev.toad/msg/Code.java b/src/main/java/dev.toad/msg/Code.java
index 49c0898..2df2633 100644
--- a/src/main/java/dev.toad/msg/Code.java
+++ b/src/main/java/dev.toad/msg/Code.java
@@ -72,7 +72,7 @@ public final class Code implements Debug {
       };
     } else {
       var str = String.format(
-        "%d.%d",
+        "%d.%02d",
         this.clazz.shortValue(),
         this.detail.shortValue()
       );
diff --git a/src/main/java/dev.toad/msg/Message.java b/src/main/java/dev.toad/msg/Message.java
index 2ed0d0e..d5d0e52 100644
--- a/src/main/java/dev.toad/msg/Message.java
+++ b/src/main/java/dev.toad/msg/Message.java
@@ -72,8 +72,12 @@ public interface Message extends Debug {
     int port = this.addr().map(a -> a.getPort()).orElse(5683);
     String scheme = port == 5684 ? "coaps" : "coap";
     String hostAddr =
-      this.addr().map(a -> a.getAddress().toString()).orElse(null);
-    String host = this.getHost().map(h -> h.toString()).orElse(hostAddr);
+      this.addr().map(a -> a.getAddress().getHostAddress()).orElse(null);
+    String host =
+      this.getHost()
+        .map(h -> h.toString())
+        .filter(h -> h != null && !h.trim().isEmpty())
+        .orElse(hostAddr);
     String path =
       this.getPath()
         .map(p -> p.toString())
@@ -130,8 +134,8 @@ public interface Message extends Debug {
         .stream()
         .map(Debug::toDebugString)
         .reduce("", (b, a) -> b + "\n  " + a) +
-      "\n\n" +
-      this.payload().toDebugString()
+      "\n" +
+      (!this.payload().isEmpty() ? "\n" + this.payload().toDebugString() : "")
     );
   }
 }
diff --git a/src/main/java/dev.toad/msg/Option.java b/src/main/java/dev.toad/msg/Option.java
index 084f718..4c1b5c1 100644
--- a/src/main/java/dev.toad/msg/Option.java
+++ b/src/main/java/dev.toad/msg/Option.java
@@ -26,7 +26,9 @@ public interface Option extends Debug {
 
   @Override
   public default String toDebugString() {
-    if (this.number() == Path.number) {
+    if (this.number() == Observe.number) {
+      return new Observe(this).toDebugString();
+    } else if (this.number() == Path.number) {
       return new Path(this).toDebugString();
     } else if (this.number() == Host.number) {
       return new Host(this).toDebugString();
diff --git a/src/main/java/dev.toad/msg/Payload.java b/src/main/java/dev.toad/msg/Payload.java
index ba96b9f..a84aa91 100644
--- a/src/main/java/dev.toad/msg/Payload.java
+++ b/src/main/java/dev.toad/msg/Payload.java
@@ -42,6 +42,10 @@ public final class Payload implements Debug {
     this.bytes = bytes;
   }
 
+  public boolean isEmpty() {
+    return this.bytes.length == 0;
+  }
+
   @Override
   public String toString() {
     return new String(this.bytes, StandardCharsets.UTF_8);
diff --git a/src/main/java/dev.toad/msg/build/Message.java b/src/main/java/dev.toad/msg/build/Message.java
index 3c90634..5cb9e32 100644
--- a/src/main/java/dev.toad/msg/build/Message.java
+++ b/src/main/java/dev.toad/msg/build/Message.java
@@ -6,6 +6,7 @@ import dev.toad.msg.Payload;
 import dev.toad.msg.Token;
 import dev.toad.msg.Type;
 import dev.toad.msg.option.Host;
+import dev.toad.msg.option.Observe;
 import dev.toad.msg.option.Path;
 import dev.toad.msg.option.Query;
 import java.net.InetAddress;
@@ -48,7 +49,7 @@ public final class Message
               : conResponseToNonRequest              ? Type.CON
               : Type.NON;
 
-    return Message.copyOf(other).unsetId().type(type);
+    return Message.copyOf(other).unsetId().unsetOption(Observe.number).type(type);
   }
 
   public static Message copyOf(dev.toad.msg.Message other) {
diff --git a/src/main/java/dev.toad/msg/option/Observe.java b/src/main/java/dev.toad/msg/option/Observe.java
index 7d3262d..3a832da 100644
--- a/src/main/java/dev.toad/msg/option/Observe.java
+++ b/src/main/java/dev.toad/msg/option/Observe.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;
@@ -11,6 +12,8 @@ public final class Observe implements Option {
 
   final boolean register;
 
+  public static final Eq<Observe> eq = Eq.bool.contramap(Observe::isRegister);
+
   public static final Observe REGISTER = new Observe(true);
   public static final Observe DEREGISTER = new Observe(false);
 
@@ -41,13 +44,17 @@ public final class Observe implements Option {
     } else if (o.values().size() == 0) {
       this.register = false;
     } else {
-      this.register = o.values().get(0).asBytes()[0] == 1;
+      this.register = o.values().get(0).asBytes()[0] == 0;
     }
   }
 
   @Override
   public long number() {
-    return Host.number;
+    return Observe.number;
+  }
+
+  public boolean isRegister() {
+    return this.register;
   }
 
   @Override
@@ -68,9 +75,14 @@ public final class Observe implements Option {
     var list = new ArrayList<OptionValue>();
     list.add(
       new dev.toad.msg.owned.OptionValue(
-        new byte[] { this.register ? (byte) 1 : (byte) 0 }
+        new byte[] { this.register ? (byte) 0 : (byte) 1 }
       )
     );
     return list;
   }
+
+  @Override
+  public String toDebugString() {
+    return this.register ? "Observe: Register" : "Observe: Deregister";
+  }
 }
diff --git a/src/main/java/dev.toad/msg/ref/OptionValue.java b/src/main/java/dev.toad/msg/ref/OptionValue.java
index 36cbb4a..b23f2f6 100644
--- a/src/main/java/dev.toad/msg/ref/OptionValue.java
+++ b/src/main/java/dev.toad/msg/ref/OptionValue.java
@@ -1,6 +1,7 @@
 package dev.toad.msg.ref;
 
 import dev.toad.ffi.Ptr;
+import java.util.ArrayList;
 
 public final class OptionValue
   implements dev.toad.msg.OptionValue, AutoCloseable {
diff --git a/src/test/scala/E2E.scala b/src/test/scala/E2E.scala
index c5ea4ad..2b0a287 100644
--- a/src/test/scala/E2E.scala
+++ b/src/test/scala/E2E.scala
@@ -9,58 +9,149 @@ import java.net.InetSocketAddress
 import java.util.logging.Logger
 import java.util.logging.Level
 import java.util.ArrayList
+import java.util.Optional
 import java.nio.ByteBuffer
 import java.util.concurrent.TimeUnit
 import java.net.InetAddress
 
+val logLevel = Level.INFO;
+val serverPort = 10102;
+val clientPort = 10101;
+
 class E2E extends munit.FunSuite {
-  test("little baby server") {
-    Toad.loadNativeLib()
+  val client = new Fixture[Client]("client") {
+    private var client: Client = null;
 
-    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
+    def apply() = this.client
 
-          Server.Middleware.respond(rep)
-        }
-      )
-      .build;
-
-    val serverThread = Thread((() => server.run()): java.lang.Runnable)
-    serverThread.start()
-
-    val req = Message.builder
-      .uri("coap://localhost:10102/hello")
-      .`type`(Type.NON)
-      .code(Code.GET)
-      .payload(Payload.text("Fred"))
-      .build
-
-    val client = Toad.builder.port(10101).logLevel(Level.INFO).buildClient
-    val respFuture = client.send(req)
-
-    try {
-      val respActual = respFuture.get(1, TimeUnit.SECONDS)
-      assertNoDiff(respActual.payload.toString, "Hello, Fred!")
-    } finally {
-      val exit = Message.builder
-        .uri("coap://localhost:10102/exit")
-        .`type`(Type.NON)
-        .code(Code.POST)
-        .build
-      client.sendNoResponse(exit)
+    override def beforeAll(): Unit = {
+      this.client =
+        Toad.builder.port(clientPort.shortValue).logLevel(logLevel).buildClient
     }
 
-    serverThread.join()
+    override def afterAll(): Unit = {
+      this.client.close()
+      this.client = null
+    }
+  }
+
+  val server = new Fixture[Server]("server") {
+    private var thread: Thread = null;
+    private var server: Server = null;
+
+    def apply() = this.server
+
+    override def beforeAll(): Unit = {
+      Toad.loadNativeLib()
+
+      var counterN = 0
+      this.server = Toad.builder
+        .port(serverPort.shortValue)
+        .logLevel(logLevel)
+        .server
+        .put(
+          "failing",
+          _msg => {
+            throw java.lang.RuntimeException("fart")
+          }
+        )
+        .get(
+          "counter",
+          msg => {
+            counterN += 1
+            Optional.of(
+              msg.buildResponse
+                .code(Code.OK_CONTENT)
+                .payload(Payload.text(s"$counterN"))
+                .build
+            )
+          }
+        )
+        .get(
+          "greetings",
+          msg => {
+            Optional.of(
+              msg.buildResponse
+                .code(Code.OK_CONTENT)
+                .payload(Payload.text(s"Hello, ${msg.payload.toString}!"))
+                .build
+            )
+          }
+        )
+        .build
+
+      this.thread = this.server.run()
+    }
+
+    override def afterAll(): Unit = {
+      this.server.exit()
+      this.thread.join()
+      this.server.close()
+    }
+  }
+
+  override def munitFixtures = List(client, server)
+
+  test("server responds 2.05 Ok Content") {
+    server()
+
+    val rep = client()
+      .get(
+        Type.NON,
+        s"coap://localhost:$serverPort/greetings",
+        Payload.text("Fred")
+      )
+      .get()
+
+    assertNoDiff(
+      rep.payload.toString,
+      "Hello, Fred!"
+    )
+    assertEquals(
+      rep.code,
+      Code.OK_CONTENT
+    )
+  }
+
+  test(
+    "ClientObserveStream yields new resource states when server is notified of new state"
+  ) {
+    val stream =
+      client()
+        .observe(
+          Message.builder
+            .uri(s"coap://localhost:$serverPort/counter")
+            .`type`(Type.NON)
+            .code(Code.GET)
+            .build
+        );
+
+    try {
+      assertNoDiff(stream.next().get().payload.toString, "1")
+      server().notify("counter")
+      assertNoDiff(stream.next().get().payload.toString, "2")
+      server().notify("counter")
+      assertNoDiff(stream.next().get().payload.toString, "3")
+    } finally {
+      stream.close()
+    }
+  }
+
+  test("unregistered resource responds 4.04 Not Found") {
+    server()
+    val c = client()
+    assertEquals(
+      c.get(Type.NON, s"coap://localhost:$serverPort/not-found").get().code,
+      Code.NOT_FOUND
+    )
+  }
+
+  test("handler throwing exception responds 5.00 Internal Server Error") {
+    server()
+    val c = client()
+    assertEquals(
+      c.put(Type.NON, s"coap://localhost:$serverPort/failing").get().code,
+      Code.INTERNAL_SERVER_ERROR
+    )
   }
 }