diff --git a/src/dav/calencoder.rs b/src/dav/calencoder.rs
new file mode 100644
index 0000000..918083d
--- /dev/null
+++ b/src/dav/calencoder.rs
@@ -0,0 +1,100 @@
+use super::encoder::{QuickWritable, Context};
+use super::caltypes::*;
+use super::types::Extension;
+
+use quick_xml::Error as QError;
+use quick_xml::events::{Event, BytesEnd, BytesStart, BytesText};
+use quick_xml::writer::{ElementWriter, Writer};
+use quick_xml::name::PrefixDeclaration;
+use tokio::io::AsyncWrite;
+
+/*pub trait CalWriter<E: Extension>: DavWriter<E> {
+    fn create_cal_element(&mut self, name: &str) -> ElementWriter<impl AsyncWrite + Unpin>;
+}
+
+impl<'a, W: AsyncWrite+Unpin> DavWriter<CalExtension> for Writer<'a, W, CalExtension> {
+    fn create_dav_element(&mut self, name: &str) -> ElementWriter<impl AsyncWrite + Unpin> {
+        self.create_ns_element(name, Namespace::Dav)
+    }
+    fn child(w: &'a mut QWriter<W>) -> impl DavWriter<CalExtension> {
+        Self::child(w)
+    }
+    async fn error(&mut self, err: &Violation) -> Result<(), QError> {
+       err.write(self).await 
+    }
+}
+
+impl<'a, W: AsyncWrite+Unpin> CalWriter<CalExtension> for Writer<'a, W, CalExtension> {
+    fn create_cal_element(&mut self, name: &str) -> ElementWriter<impl AsyncWrite + Unpin> {
+        self.create_ns_element(name, Namespace::CalDav)
+    }
+}*/
+
+pub struct CalCtx {
+    root: bool
+}
+impl Context<CalExtension> for CalCtx {
+    fn child(&self) -> Self {
+        Self { root: false }
+    }
+    fn create_dav_element(&self, name: &str) -> BytesStart {
+        let mut start = BytesStart::new(format!("D:{}", name));
+        if self.root {
+            start.push_attribute(("xmlns:D", "DAV:"));
+            start.push_attribute(("xmlns:C", "urn:ietf:params:xml:ns:caldav"));
+        }
+        start
+    }
+
+    async fn hook_error(&self, err: &Violation, xml: &mut Writer<impl AsyncWrite+Unpin>) -> Result<(), QError> {
+        err.write(xml, self.child()).await
+    }
+}
+
+impl QuickWritable<CalExtension, CalCtx> for Violation {
+    async fn write(&self, xml: &mut Writer<impl AsyncWrite+Unpin>, _ctx: CalCtx) -> Result<(), QError> {
+        match self {
+            Self::SupportedFilter => xml
+                .create_element("supported-filter")
+                .write_empty_async().await?,
+        };
+        Ok(())
+    }
+}
+
+/*
+ <?xml version="1.0" encoding="utf-8" ?>
+   <D:error>
+     <C:supported-filter>
+       <C:prop-filter name="X-ABC-GUID"/>
+     </C:supported-filter>
+   </D:error>
+*/
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::dav::types::{Error, Violation as DavViolation};
+    use tokio::io::AsyncWriteExt;
+
+    #[tokio::test]
+    async fn test_violation() {
+        let mut buffer = Vec::new();
+        let mut tokio_buffer = tokio::io::BufWriter::new(&mut buffer);
+        let mut writer = Writer::new_with_indent(&mut tokio_buffer, b' ', 4);
+
+        let res: Error<CalExtension> = Error(vec![
+            DavViolation::Extension(Violation::SupportedFilter),
+        ]);
+
+        res.write(&mut writer, CalCtx{ root: true }).await.expect("xml serialization");
+        tokio_buffer.flush().await.expect("tokio buffer flush");
+
+        let expected = r#"<D:error xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav">
+    <C:supported-filter/>
+</D:error>"#;
+        let got = std::str::from_utf8(buffer.as_slice()).unwrap();
+
+        assert_eq!(got, expected);
+    }
+}
diff --git a/src/dav/caltypes.rs b/src/dav/caltypes.rs
new file mode 100644
index 0000000..ed8496a
--- /dev/null
+++ b/src/dav/caltypes.rs
@@ -0,0 +1,41 @@
+use super::types::*;
+
+pub enum Namespace {
+    Dav,
+    CalDav,
+}
+
+pub struct CalExtension {}
+impl Extension for CalExtension {
+    type Error = Violation;
+    type Namespace = Namespace;
+
+    fn namespaces() -> &'static [(&'static str, &'static str)] {
+        return &[ ("D", "DAV:"), ("C", "urn:ietf:params:xml:ns:caldav") ][..]
+    }
+
+    fn short_ns(ns: Self::Namespace) -> &'static str {
+        match ns {
+            Namespace::Dav => "D",
+            Namespace::CalDav => "C",
+        }
+    }
+}
+
+pub enum Violation {
+    /// (CALDAV:supported-filter): The CALDAV:comp-filter (see
+    /// Section 9.7.1), CALDAV:prop-filter (see Section 9.7.2), and
+    /// CALDAV:param-filter (see Section 9.7.3) XML elements used in the
+    /// CALDAV:filter XML element (see Section 9.7) in the REPORT request
+    /// only make reference to components, properties, and parameters for
+    /// which queries are supported by the server, i.e., if the CALDAV:
+    /// filter element attempts to reference an unsupported component,
+    /// property, or parameter, this precondition is violated.  Servers
+    /// SHOULD report the CALDAV:comp-filter, CALDAV:prop-filter, or
+    /// CALDAV:param-filter for which it does not provide support.
+    ///
+    /// <!ELEMENT supported-filter (comp-filter*,
+    ///                             prop-filter*,
+    ///                             param-filter*)>
+    SupportedFilter,
+}
diff --git a/src/dav/encoder.rs b/src/dav/encoder.rs
index 552f183..ddef533 100644
--- a/src/dav/encoder.rs
+++ b/src/dav/encoder.rs
@@ -1,61 +1,205 @@
 use std::io::Cursor;
 
-use futures::stream::{StreamExt, TryStreamExt};
-use quick_xml::Error;
+use quick_xml::Error as QError;
 use quick_xml::events::{Event, BytesEnd, BytesStart, BytesText};
 use quick_xml::writer::{ElementWriter, Writer};
 use quick_xml::name::PrefixDeclaration;
 use tokio::io::AsyncWrite;
 use super::types::*;
 
-//@FIXME a cleaner way to manager namespace would be great
-//but at the same time, the quick-xml library is not cooperating.
-//So instead of writing many cursed workarounds - I tried, I am just hardcoding the namespaces...
 
-pub trait Encode {
-    async fn write(&self, xml: &mut Writer<impl AsyncWrite + Unpin>) -> Result<(), Error>; 
+//-------------- TRAITS ----------------------
+/*pub trait DavWriter<E: Extension> {
+    fn create_dav_element(&mut self, name: &str) -> ElementWriter<impl AsyncWrite + Unpin>;
+    fn child(w: &mut QWriter<impl AsyncWrite + Unpin>) -> impl DavWriter<E>;
+    async fn error(&mut self, err: &E::Error) -> Result<(), QError>;
+}*/
+
+/// Basic encode trait to make a type encodable
+pub trait QuickWritable<E: Extension, C: Context<E>> {
+    async fn write(&self, xml: &mut Writer<impl AsyncWrite+Unpin>, ctx: C) -> Result<(), QError>; 
 }
 
-impl Encode for Href {
-    async fn write(&self, xml: &mut Writer<impl AsyncWrite + Unpin>) -> Result<(), Error> {
-        xml.create_element("D:href")
+pub trait Context<E: Extension> {
+    fn child(&self) -> Self;
+    fn create_dav_element(&self, name: &str) -> BytesStart;
+    async fn hook_error(&self, err: &E::Error, xml: &mut Writer<impl AsyncWrite+Unpin>) -> Result<(), QError>;
+}
+
+pub struct NoExtCtx {
+    root: bool
+}
+impl Context<NoExtension> for NoExtCtx {
+    fn child(&self) -> Self {
+        Self { root: false }
+    }
+    fn create_dav_element(&self, name: &str) -> BytesStart {
+        let mut start = BytesStart::new(format!("D:{}", name));
+        if self.root {
+            start.push_attribute(("xmlns:D", "DAV:"));
+        }
+        start
+    }
+    async fn hook_error(&self, err: &Disabled, xml: &mut Writer<impl AsyncWrite+Unpin>) -> Result<(), QError> {
+        unreachable!();
+    }
+}
+
+
+//--------------------- ENCODING --------------------
+
+// --- XML ROOTS
+impl<E: Extension, C: Context<E>> QuickWritable<E,C> for Multistatus<E> {
+    async fn write(&self, xml: &mut Writer<impl AsyncWrite+Unpin>, ctx: C) -> Result<(), QError> {
+        let start = ctx.create_dav_element("multistatus");
+        let end = start.to_end();
+
+        xml.write_event_async(Event::Start(start.clone())).await?;
+        for response in self.responses.iter() {
+            response.write(xml, ctx.child()).await?;
+        }
+        if let Some(description) = &self.responsedescription {
+            description.write(xml, ctx.child()).await?;
+        }
+
+        xml.write_event_async(Event::End(end)).await?;
+        Ok(())
+    }
+}
+
+
+// --- XML inner elements
+impl<E: Extension, C: Context<E>> QuickWritable<E,C> for Href {
+    async fn write(&self, xml: &mut Writer<impl AsyncWrite+Unpin>, _ctx: C) -> Result<(), QError> {
+        xml.create_element("href")
             .write_text_content_async(BytesText::new(&self.0))
             .await?;
         Ok(())
     }
 }
 
-impl<T> Encode for Multistatus<T> {
-    async fn write(&self, xml: &mut Writer<impl AsyncWrite + Unpin>) -> Result<(), Error> {
-        xml.create_element("D:multistatus")
-            .with_attribute(("xmlns:D", "DAV:"))
-            .write_inner_content_async::<_, _, quick_xml::Error>(|inner_xml| async move {
-                for response in self.responses.iter() {
-                    response.write(inner_xml).await?;
+impl<E: Extension, C: Context<E>> QuickWritable<E,C> for Response<E> {
+    async fn write(&self, xml: &mut Writer<impl AsyncWrite+Unpin>, ctx: C) -> Result<(), QError> {
+        xml.create_element("response")
+            .write_inner_content_async::<_, _, QError>(|inner_xml| async move {
+                self.href.write(inner_xml, ctx.child()).await?; 
+                self.status_or_propstat.write(inner_xml, ctx.child()).await?;
+                if let Some(error) = &self.error {
+                    error.write(inner_xml, ctx.child()).await?;
                 }
-                
-                if let Some(description) = &self.responsedescription {
-                    description.write(inner_xml).await?;
+                if let Some(responsedescription) = &self.responsedescription {
+                    responsedescription.write(inner_xml, ctx.child()).await?;
                 }
-                
+                if let Some(location) = &self.location {
+                    location.write(inner_xml, ctx.child()).await?;
+                }
+
                 Ok(inner_xml)
             })
+        .await?;
+
+        Ok(())
+    }
+}
+
+impl<E: Extension, C: Context<E>> QuickWritable<E,C> for StatusOrPropstat<E> {
+    async fn write(&self, xml: &mut Writer<impl AsyncWrite+Unpin>, ctx: C) -> Result<(), QError> {
+        match self {
+            Self::Status(status) => status.write(xml, ctx.child()).await,
+            Self::PropStat(propstat_list) => {
+                for propstat in propstat_list.iter() {
+                    propstat.write(xml, ctx.child()).await?;
+                }
+
+                Ok(())
+            }
+        }
+    }
+}
+
+impl<E: Extension, C: Context<E>> QuickWritable<E,C> for Status {
+    async fn write(&self, xml: &mut Writer<impl AsyncWrite+Unpin>, ctx: C) -> Result<(), QError> {
+        xml.create_element("status")
+            .write_text_content_async(
+                BytesText::new(&format!("HTTP/1.1 {} {}", self.0.as_str(), self.0.canonical_reason().unwrap_or("No reason")))
+            )
             .await?;
         Ok(())
     }
 }
 
-impl<T> Encode for Response<T> {
-    async fn write(&self, xml: &mut Writer<impl AsyncWrite + Unpin>) -> Result<(), Error> {
+impl<E: Extension, C: Context<E>> QuickWritable<E,C> for ResponseDescription {
+    async fn write(&self, xml: &mut Writer<impl AsyncWrite+Unpin>, ctx: C) -> Result<(), QError> {
+        let start = ctx.create_dav_element("responsedescription");
+        let end = start.to_end();
+
+        xml.write_event_async(Event::Start(start.clone())).await?;
+        xml.write_event_async(Event::Text(BytesText::new(&self.0))).await?;
+        xml.write_event_async(Event::End(end)).await?;
+
+        Ok(())
+    }
+}
+
+impl<E: Extension, C: Context<E>> QuickWritable<E,C> for Location {
+    async fn write(&self, xml: &mut Writer<impl AsyncWrite+Unpin>, ctx: C) -> Result<(), QError> {
         unimplemented!();
     }
 }
 
-impl Encode for ResponseDescription {
-    async fn write(&self, xml: &mut Writer<impl AsyncWrite + Unpin>) -> Result<(), Error> {
-        xml.create_element("D:responsedescription")
-            .write_text_content_async(BytesText::new(&self.0))
-            .await?;
+impl<E: Extension, C: Context<E>> QuickWritable<E,C> for PropStat<E> {
+    async fn write(&self, xml: &mut Writer<impl AsyncWrite+Unpin>, ctx: C) -> Result<(), QError> {
+        unimplemented!();
+    }
+}
+
+impl<E: Extension, C: Context<E>> QuickWritable<E,C> for Error<E> {
+    async fn write(&self, xml: &mut Writer<impl AsyncWrite+Unpin>, ctx: C) -> Result<(), QError> {
+        xml.create_element("error")
+            .write_inner_content_async::<_, _, QError>(|inner_xml| async move {
+                for violation in &self.0 {
+                    violation.write(inner_xml, ctx.child()).await?;
+                }
+
+                Ok(inner_xml)
+            })
+        .await?;
+
+        Ok(())
+    }
+}
+
+impl<E: Extension, C: Context<E>> QuickWritable<E,C> for Violation<E> {
+    async fn write(&self, xml: &mut Writer<impl AsyncWrite+Unpin>, ctx: C) -> Result<(), QError> {
+        match self {
+            Violation::LockTokenMatchesRequestUri => xml.create_element("lock-token-matches-request-uri").write_empty_async().await?, 
+            Violation::LockTokenSubmitted(hrefs) => xml
+                .create_element("lock-token-submitted")
+                .write_inner_content_async::<_, _, QError>(|inner_xml| async move {
+                    for href in hrefs {
+                        href.write(inner_xml, ctx.child()).await?;
+                    }
+                    Ok(inner_xml)
+                }
+            ).await?,
+            Violation::NoConflictingLock(hrefs) =>  xml
+                .create_element("no-conflicting-lock")
+                .write_inner_content_async::<_, _, QError>(|inner_xml| async move {
+                    for href in hrefs {
+                        href.write(inner_xml, ctx.child()).await?;
+                    }
+                    Ok(inner_xml)
+                }
+            ).await?,
+            Violation::NoExternalEntities => xml.create_element("no-external-entities").write_empty_async().await?,
+            Violation::PreservedLiveProperties => xml.create_element("preserved-live-properties").write_empty_async().await?,
+            Violation::PropfindFiniteDepth => xml.create_element("propfind-finite-depth").write_empty_async().await?,
+            Violation::CannotModifyProtectedProperty => xml.create_element("cannot-modify-protected-property").write_empty_async().await?,
+            Violation::Extension(inner) => {
+                ctx.hook_error(inner, xml).await?;
+                xml
+            },
+        };
         Ok(())
     }
 }
@@ -74,7 +218,8 @@ mod tests {
         let mut tokio_buffer = tokio::io::BufWriter::new(&mut buffer);
         let mut writer = Writer::new_with_indent(&mut tokio_buffer, b' ', 4);
 
-        Href("/SOGo/dav/so/".into()).write(&mut writer).await.expect("xml serialization");
+        let ctx = NoExtCtx{ root: true };
+        Href("/SOGo/dav/so/".into()).write(&mut writer, ctx).await.expect("xml serialization");
         tokio_buffer.flush().await.expect("tokio buffer flush");
 
         assert_eq!(buffer.as_slice(), &b"<D:href>/SOGo/dav/so/</D:href>"[..]);
@@ -87,8 +232,9 @@ mod tests {
         let mut tokio_buffer = tokio::io::BufWriter::new(&mut buffer);
         let mut writer = Writer::new_with_indent(&mut tokio_buffer, b' ', 4);
 
-        let xml: Multistatus<u64> = Multistatus { responses: vec![], responsedescription: Some(ResponseDescription("Hello world".into())) };
-        xml.write(&mut writer).await.expect("xml serialization");
+        let ctx = NoExtCtx{ root: true };
+        let xml: Multistatus<NoExtension> = Multistatus { responses: vec![], responsedescription: Some(ResponseDescription("Hello world".into())) };
+        xml.write(&mut writer, ctx).await.expect("xml serialization");
         tokio_buffer.flush().await.expect("tokio buffer flush");
 
         let expected = r#"<D:multistatus xmlns:D="DAV:">
diff --git a/src/dav/mod.rs b/src/dav/mod.rs
index a542bbb..98d6965 100644
--- a/src/dav/mod.rs
+++ b/src/dav/mod.rs
@@ -1,5 +1,7 @@
 mod types;
+mod caltypes;
 mod encoder;
+mod calencoder;
 
 use std::net::SocketAddr;
 
diff --git a/src/dav/types.rs b/src/dav/types.rs
index 7bbea8e..69ddf52 100644
--- a/src/dav/types.rs
+++ b/src/dav/types.rs
@@ -2,6 +2,34 @@
 
 use chrono::{DateTime,FixedOffset};
 
+/// Extension utilities
+pub struct Disabled(());
+pub trait Extension {
+    type Error;
+    type Namespace;
+
+    fn namespaces() -> &'static [(&'static str, &'static str)];
+    fn short_ns(ns: Self::Namespace) -> &'static str;
+}
+
+/// No extension
+pub struct NoExtension {}
+pub enum Namespace {
+    Dav
+}
+impl Extension for NoExtension {
+    type Error = Disabled;
+    type Namespace = Namespace;
+
+    fn namespaces() -> &'static [(&'static str, &'static str)] {
+        return &[ ("D", "DAV:") ][..]
+    }
+
+    fn short_ns(ns: Self::Namespace) -> &'static str {
+        "D"
+    }
+}
+
 /// 14.1.  activelock XML Element
 ///
 /// Name:   activelock
@@ -10,11 +38,11 @@ use chrono::{DateTime,FixedOffset};
 /// <!ELEMENT activelock (lockscope, locktype, depth, owner?, timeout?,
 ///           locktoken?, lockroot)>
 pub struct ActiveLock {
-    lockscope: u64,
-    locktype: u64,
+    lockscope: LockScope,
+    locktype: LockType,
     depth: Depth,
-    owner: Option<u64>,
-    timeout: Option<u64>,
+    owner: Option<Owner>,
+    timeout: Option<Timeout>,
 }
 
 /// 14.2 allprop XML Element
@@ -72,7 +100,8 @@ pub enum Depth {
 ///   postcondition code.  Unrecognized elements MUST be ignored.
 ///
 /// <!ELEMENT error ANY >
-pub enum Error<T> {
+pub struct Error<T: Extension>(pub Vec<Violation<T>>);
+pub enum Violation<T: Extension> {
     /// Name:  lock-token-matches-request-uri
     ///
     /// Use with:  409 Conflict
@@ -156,7 +185,7 @@ pub enum Error<T> {
     CannotModifyProtectedProperty,
 
     /// Specific errors
-    Extensions(T),
+    Extension(T::Error),
 }
 
 /// 14.6.  exclusive XML Element
@@ -312,7 +341,7 @@ pub enum LockType {
 /// response descriptions contained within the responses.
 ///
 /// <!ELEMENT multistatus (response*, responsedescription?)  >
-pub struct Multistatus<T> {
+pub struct Multistatus<T: Extension> {
     pub responses: Vec<Response<T>>,
     pub responsedescription: Option<ResponseDescription>,
 }
@@ -416,7 +445,7 @@ pub struct PropName {}
 /// the properties named in 'prop'.
 ///
 /// <!ELEMENT propstat (prop, status, error?, responsedescription?) >
-pub struct PropStat<T> {
+pub struct PropStat<T: Extension> {
     prop: Prop,
     status: Status,
     error: Option<Error<T>>,
@@ -460,13 +489,16 @@ pub struct Remove(Prop);
 ///
 /// <!ELEMENT response (href, ((href*, status)|(propstat+)),
 ///                     error?, responsedescription? , location?) >
-pub struct Response<T> {
-    href: Vec<Href>,
-    status: Status,
-    propstat: Vec<PropStat<T>>,
-    error: Option<Error<T>>,
-    responsedescription: Option<ResponseDescription>,
-    location: Option<u64>,
+pub enum StatusOrPropstat<T: Extension> {
+    Status(Status),
+    PropStat(Vec<PropStat<T>>),
+}
+pub struct Response<T: Extension> {
+    pub href: Href, // It's wrong according to the spec, but I don't understand why there is an href*
+    pub status_or_propstat: StatusOrPropstat<T>,
+    pub error: Option<Error<T>>,
+    pub responsedescription: Option<ResponseDescription>,
+    pub location: Option<Location>,
 }
 
 /// 14.25.  responsedescription XML Element
@@ -521,7 +553,7 @@ pub struct Shared {}
 /// 
 /// <!ELEMENT status (#PCDATA) >
 //@FIXME: Better typing is possible with an enum for example
-pub struct Status(http::status::StatusCode);
+pub struct Status(pub http::status::StatusCode);
 
 /// 14.29.  timeout XML Element
 ///
diff --git a/src/main.rs b/src/main.rs
index 5f5089f..4f874b9 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,4 @@
+#![feature(type_alias_impl_trait)]
 #![feature(async_fn_in_trait)]
 
 mod auth;