diff --git a/lib/rs/src/server/mod.rs b/lib/rs/src/server/mod.rs
index 21c392c..3d8ccb2 100644
--- a/lib/rs/src/server/mod.rs
+++ b/lib/rs/src/server/mod.rs
@@ -17,7 +17,8 @@
 
 //! Types used to implement a Thrift server.
 
-use protocol::{TInputProtocol, TOutputProtocol};
+use {ApplicationError, ApplicationErrorKind};
+use protocol::{TInputProtocol, TMessageIdentifier, TMessageType, TOutputProtocol};
 
 mod multiplexed;
 mod threaded;
@@ -93,3 +94,31 @@
     /// Returns `()` if the handler was executed; `Err` otherwise.
     fn process(&self, i: &mut TInputProtocol, o: &mut TOutputProtocol) -> ::Result<()>;
 }
+
+/// Convenience function used in generated `TProcessor` implementations to
+/// return an `ApplicationError` if thrift message processing failed.
+pub fn handle_process_result(
+    msg_ident: &TMessageIdentifier,
+    res: ::Result<()>,
+    o_prot: &mut TOutputProtocol,
+) -> ::Result<()> {
+    if let Err(e) = res {
+        let e = match e {
+            ::Error::Application(a) => a,
+            _ => ApplicationError::new(ApplicationErrorKind::Unknown, format!("{:?}", e)),
+        };
+
+        let ident = TMessageIdentifier::new(
+            msg_ident.name.clone(),
+            TMessageType::Exception,
+            msg_ident.sequence_number,
+        );
+
+        o_prot.write_message_begin(&ident)?;
+        ::Error::write_application_error_to_out_protocol(&e, o_prot)?;
+        o_prot.write_message_end()?;
+        o_prot.flush()
+    } else {
+        Ok(())
+    }
+}
diff --git a/lib/rs/src/server/multiplexed.rs b/lib/rs/src/server/multiplexed.rs
index b1243a8..a7f6d04 100644
--- a/lib/rs/src/server/multiplexed.rs
+++ b/lib/rs/src/server/multiplexed.rs
@@ -16,13 +16,17 @@
 // under the License.
 
 use std::collections::HashMap;
+use std::fmt;
+use std::fmt::{Debug, Formatter};
 use std::convert::Into;
 use std::sync::{Arc, Mutex};
 
-use {ApplicationErrorKind, new_application_error};
 use protocol::{TInputProtocol, TMessageIdentifier, TOutputProtocol, TStoredInputProtocol};
 
-use super::TProcessor;
+use super::{TProcessor, handle_process_result};
+
+const MISSING_SEPARATOR_AND_NO_DEFAULT: &'static str = "missing service separator and no default processor set";
+type ThreadSafeProcessor = Box<TProcessor + Send + Sync>;
 
 /// A `TProcessor` that can demux service calls to multiple underlying
 /// Thrift services.
@@ -34,57 +38,85 @@
 ///
 /// A `TMultiplexedProcessor` can only handle messages sent by a
 /// `TMultiplexedOutputProtocol`.
-// FIXME: implement Debug
+#[derive(Default)]
 pub struct TMultiplexedProcessor {
-    processors: Mutex<HashMap<String, Arc<Box<TProcessor>>>>,
+    stored: Mutex<StoredProcessors>,
+}
+
+#[derive(Default)]
+struct StoredProcessors {
+    processors: HashMap<String, Arc<ThreadSafeProcessor>>,
+    default_processor: Option<Arc<ThreadSafeProcessor>>,
 }
 
 impl TMultiplexedProcessor {
-    /// Register a service-specific `processor` for the service named
-    /// `service_name`.
-    ///
-    /// Return `true` if this is the first registration for `service_name`.
-    ///
-    /// Return `false` if a mapping previously existed (the previous mapping is
-    /// *not* overwritten).
-    #[cfg_attr(feature = "cargo-clippy", allow(map_entry))]
-    pub fn register_processor<S: Into<String>>(
-        &mut self,
-        service_name: S,
-        processor: Box<TProcessor>,
-    ) -> bool {
-        let mut processors = self.processors.lock().unwrap();
-
-        let name = service_name.into();
-        if processors.contains_key(&name) {
-            false
-        } else {
-            processors.insert(name, Arc::new(processor));
-            true
+    /// Create a new `TMultiplexedProcessor` with no registered service-specific
+    /// processors.
+    pub fn new() -> TMultiplexedProcessor {
+        TMultiplexedProcessor {
+            stored: Mutex::new(
+                StoredProcessors {
+                    processors: HashMap::new(),
+                    default_processor: None,
+                },
+            ),
         }
     }
-}
 
-impl TProcessor for TMultiplexedProcessor {
-    fn process(&self, i_prot: &mut TInputProtocol, o_prot: &mut TOutputProtocol) -> ::Result<()> {
-        let msg_ident = i_prot.read_message_begin()?;
-        let sep_index = msg_ident
-            .name
-            .find(':')
-            .ok_or_else(
-                || {
-                    new_application_error(
-                        ApplicationErrorKind::Unknown,
-                        "no service separator found in incoming message",
-                    )
-                },
-            )?;
+    /// Register a service-specific `processor` for the service named
+    /// `service_name`. This implementation is also backwards-compatible with
+    /// non-multiplexed clients. Set `as_default` to `true` to allow
+    /// non-namespaced requests to be dispatched to a default processor.
+    ///
+    /// Returns success if a new entry was inserted. Returns an error if:
+    /// * A processor exists for `service_name`
+    /// * You attempt to register a processor as default, and an existing default exists
+    #[cfg_attr(feature = "cargo-clippy", allow(map_entry))]
+    pub fn register<S: Into<String>>(
+        &mut self,
+        service_name: S,
+        processor: Box<TProcessor + Send + Sync>,
+        as_default: bool,
+    ) -> ::Result<()> {
+        let mut stored = self.stored.lock().unwrap();
 
-        let (svc_name, svc_call) = msg_ident.name.split_at(sep_index);
+        let name = service_name.into();
+        if !stored.processors.contains_key(&name) {
+            let processor = Arc::new(processor);
 
-        let processor: Option<Arc<Box<TProcessor>>> = {
-            let processors = self.processors.lock().unwrap();
-            processors.get(svc_name).cloned()
+            if as_default {
+                if stored.default_processor.is_none() {
+                    stored.processors.insert(name, processor.clone());
+                    stored.default_processor = Some(processor.clone());
+                    Ok(())
+                } else {
+                    Err("cannot reset default processor".into())
+                }
+            } else {
+                stored.processors.insert(name, processor);
+                Ok(())
+            }
+        } else {
+            Err(format!("cannot overwrite existing processor for service {}", name).into(),)
+        }
+    }
+
+    fn process_message(
+        &self,
+        msg_ident: &TMessageIdentifier,
+        i_prot: &mut TInputProtocol,
+        o_prot: &mut TOutputProtocol,
+    ) -> ::Result<()> {
+        let (svc_name, svc_call) = split_ident_name(&msg_ident.name);
+        debug!("routing svc_name {:?} svc_call {}", &svc_name, &svc_call);
+
+        let processor: Option<Arc<ThreadSafeProcessor>> = {
+            let stored = self.stored.lock().unwrap();
+            if let Some(name) = svc_name {
+                stored.processors.get(name).cloned()
+            } else {
+                stored.default_processor.clone()
+            }
         };
 
         match processor {
@@ -97,14 +129,216 @@
                 let mut proxy_i_prot = TStoredInputProtocol::new(i_prot, new_msg_ident);
                 (*arc).process(&mut proxy_i_prot, o_prot)
             }
-            None => {
-                Err(
-                    new_application_error(
-                        ApplicationErrorKind::Unknown,
-                        format!("no processor found for service {}", svc_name),
-                    ),
-                )
+            None => Err(missing_processor_message(svc_name).into()),
+        }
+    }
+}
+
+impl TProcessor for TMultiplexedProcessor {
+    fn process(&self, i_prot: &mut TInputProtocol, o_prot: &mut TOutputProtocol) -> ::Result<()> {
+        let msg_ident = i_prot.read_message_begin()?;
+
+        debug!("process incoming msg id:{:?}", &msg_ident);
+        let res = self.process_message(&msg_ident, i_prot, o_prot);
+
+        handle_process_result(&msg_ident, res, o_prot)
+    }
+}
+
+impl Debug for TMultiplexedProcessor {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        let stored = self.stored.lock().unwrap();
+        write!(
+            f,
+            "TMultiplexedProcess {{ registered_count: {:?} default: {:?} }}",
+            stored.processors.keys().len(),
+            stored.default_processor.is_some()
+        )
+    }
+}
+
+fn split_ident_name(ident_name: &str) -> (Option<&str>, &str) {
+    ident_name
+        .find(':')
+        .map(
+            |pos| {
+                let (svc_name, svc_call) = ident_name.split_at(pos);
+                let (_, svc_call) = svc_call.split_at(1); // remove colon from service call name
+                (Some(svc_name), svc_call)
+            },
+        )
+        .or_else(|| Some((None, ident_name)))
+        .unwrap()
+}
+
+fn missing_processor_message(svc_name: Option<&str>) -> String {
+    match svc_name {
+        Some(name) => format!("no processor found for service {}", name),
+        None => MISSING_SEPARATOR_AND_NO_DEFAULT.to_owned(),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::convert::Into;
+    use std::sync::Arc;
+    use std::sync::atomic::{AtomicBool, Ordering};
+
+    use {ApplicationError, ApplicationErrorKind};
+    use protocol::{TBinaryInputProtocol, TBinaryOutputProtocol, TMessageIdentifier, TMessageType};
+    use transport::{ReadHalf, TBufferChannel, TIoChannel, WriteHalf};
+
+    use super::*;
+
+    #[test]
+    fn should_split_name_into_proper_separator_and_service_call() {
+        let ident_name = "foo:bar_call";
+        let (serv, call) = split_ident_name(&ident_name);
+        assert_eq!(serv, Some("foo"));
+        assert_eq!(call, "bar_call");
+    }
+
+    #[test]
+    fn should_return_full_ident_if_no_separator_exists() {
+        let ident_name = "bar_call";
+        let (serv, call) = split_ident_name(&ident_name);
+        assert_eq!(serv, None);
+        assert_eq!(call, "bar_call");
+    }
+
+    #[test]
+    fn should_write_error_if_no_separator_found_and_no_default_processor_exists() {
+        let (mut i, mut o) = build_objects();
+
+        let sent_ident = TMessageIdentifier::new("foo", TMessageType::Call, 10);
+        o.write_message_begin(&sent_ident).unwrap();
+        o.flush().unwrap();
+        o.transport.copy_write_buffer_to_read_buffer();
+        o.transport.empty_write_buffer();
+
+        let p = TMultiplexedProcessor::new();
+        p.process(&mut i, &mut o).unwrap(); // at this point an error should be written out
+
+        i.transport
+            .set_readable_bytes(&o.transport.write_bytes());
+        let rcvd_ident = i.read_message_begin().unwrap();
+        let expected_ident = TMessageIdentifier::new("foo", TMessageType::Exception, 10);
+        assert_eq!(rcvd_ident, expected_ident);
+        let rcvd_err = ::Error::read_application_error_from_in_protocol(&mut i).unwrap();
+        let expected_err = ApplicationError::new(
+            ApplicationErrorKind::Unknown,
+            MISSING_SEPARATOR_AND_NO_DEFAULT,
+        );
+        assert_eq!(rcvd_err, expected_err);
+    }
+
+    #[test]
+    fn should_write_error_if_separator_exists_and_no_processor_found() {
+        let (mut i, mut o) = build_objects();
+
+        let sent_ident = TMessageIdentifier::new("missing:call", TMessageType::Call, 10);
+        o.write_message_begin(&sent_ident).unwrap();
+        o.flush().unwrap();
+        o.transport.copy_write_buffer_to_read_buffer();
+        o.transport.empty_write_buffer();
+
+        let p = TMultiplexedProcessor::new();
+        p.process(&mut i, &mut o).unwrap(); // at this point an error should be written out
+
+        i.transport
+            .set_readable_bytes(&o.transport.write_bytes());
+        let rcvd_ident = i.read_message_begin().unwrap();
+        let expected_ident = TMessageIdentifier::new("missing:call", TMessageType::Exception, 10);
+        assert_eq!(rcvd_ident, expected_ident);
+        let rcvd_err = ::Error::read_application_error_from_in_protocol(&mut i).unwrap();
+        let expected_err = ApplicationError::new(
+            ApplicationErrorKind::Unknown,
+            missing_processor_message(Some("missing")),
+        );
+        assert_eq!(rcvd_err, expected_err);
+    }
+
+    #[derive(Default)]
+    struct Service {
+        pub invoked: Arc<AtomicBool>,
+    }
+
+    impl TProcessor for Service {
+        fn process(&self, _: &mut TInputProtocol, _: &mut TOutputProtocol) -> ::Result<()> {
+            let res = self.invoked
+                .compare_and_swap(false, true, Ordering::Relaxed);
+            if res {
+                Ok(())
+            } else {
+                Err("failed swap".into())
             }
         }
     }
+
+    #[test]
+    fn should_route_call_to_correct_processor() {
+        let (mut i, mut o) = build_objects();
+
+        // build the services
+        let svc_1 = Service { invoked: Arc::new(AtomicBool::new(false)) };
+        let atm_1 = svc_1.invoked.clone();
+        let svc_2 = Service { invoked: Arc::new(AtomicBool::new(false)) };
+        let atm_2 = svc_2.invoked.clone();
+
+        // register them
+        let mut p = TMultiplexedProcessor::new();
+        p.register("service_1", Box::new(svc_1), false).unwrap();
+        p.register("service_2", Box::new(svc_2), false).unwrap();
+
+        // make the service call
+        let sent_ident = TMessageIdentifier::new("service_1:call", TMessageType::Call, 10);
+        o.write_message_begin(&sent_ident).unwrap();
+        o.flush().unwrap();
+        o.transport.copy_write_buffer_to_read_buffer();
+        o.transport.empty_write_buffer();
+
+        p.process(&mut i, &mut o).unwrap();
+
+        // service 1 should have been invoked, not service 2
+        assert_eq!(atm_1.load(Ordering::Relaxed), true);
+        assert_eq!(atm_2.load(Ordering::Relaxed), false);
+    }
+
+    #[test]
+    fn should_route_call_to_correct_processor_if_no_separator_exists_and_default_processor_set() {
+        let (mut i, mut o) = build_objects();
+
+        // build the services
+        let svc_1 = Service { invoked: Arc::new(AtomicBool::new(false)) };
+        let atm_1 = svc_1.invoked.clone();
+        let svc_2 = Service { invoked: Arc::new(AtomicBool::new(false)) };
+        let atm_2 = svc_2.invoked.clone();
+
+        // register them
+        let mut p = TMultiplexedProcessor::new();
+        p.register("service_1", Box::new(svc_1), false).unwrap();
+        p.register("service_2", Box::new(svc_2), true).unwrap(); // second processor is default
+
+        // make the service call (it's an old client, so we have to be backwards compatible)
+        let sent_ident = TMessageIdentifier::new("old_call", TMessageType::Call, 10);
+        o.write_message_begin(&sent_ident).unwrap();
+        o.flush().unwrap();
+        o.transport.copy_write_buffer_to_read_buffer();
+        o.transport.empty_write_buffer();
+
+        p.process(&mut i, &mut o).unwrap();
+
+        // service 2 should have been invoked, not service 1
+        assert_eq!(atm_1.load(Ordering::Relaxed), false);
+        assert_eq!(atm_2.load(Ordering::Relaxed), true);
+    }
+
+    fn build_objects()
+        -> (TBinaryInputProtocol<ReadHalf<TBufferChannel>>,
+            TBinaryOutputProtocol<WriteHalf<TBufferChannel>>)
+    {
+        let c = TBufferChannel::with_capacity(128, 128);
+        let (r_c, w_c) = c.split().unwrap();
+        (TBinaryInputProtocol::new(r_c, true), TBinaryOutputProtocol::new(w_c, true))
+    }
 }
diff --git a/lib/rs/src/server/threaded.rs b/lib/rs/src/server/threaded.rs
index a486c5a..66680b1 100644
--- a/lib/rs/src/server/threaded.rs
+++ b/lib/rs/src/server/threaded.rs
@@ -47,7 +47,8 @@
 /// use thrift::protocol::{TInputProtocolFactory, TOutputProtocolFactory};
 /// use thrift::protocol::{TBinaryInputProtocolFactory, TBinaryOutputProtocolFactory};
 /// use thrift::protocol::{TInputProtocol, TOutputProtocol};
-/// use thrift::transport::{TBufferedReadTransportFactory, TBufferedWriteTransportFactory, TReadTransportFactory, TWriteTransportFactory};
+/// use thrift::transport::{TBufferedReadTransportFactory, TBufferedWriteTransportFactory,
+///                         TReadTransportFactory, TWriteTransportFactory};
 /// use thrift::server::{TProcessor, TServer};
 ///
 /// //