Private serde fork (#390)

* Fork serde_urlencoded

* Apply enum PR https://github.com/nox/serde_urlencoded/pull/30

* Add test to verify enum in query

* Docs are updated to show example of how to use enum.

Cargo.toml

@@ -67,7 +67,6 @@ rand = "0.5"
 regex = "1.0"
 serde = "1.0"
 serde_json = "1.0"
-serde_urlencoded = "0.5"
 sha1 = "0.6"
 smallvec = "0.6"
 time = "0.1"
@@ -105,6 +104,10 @@ tokio-tls = { version="0.1", optional = true }
 openssl = { version="0.10", optional = true }
 tokio-openssl = { version="0.2", optional = true }
 
+# forked url_encoded
+itoa = "0.4"
+dtoa = "0.4"
+
 [dev-dependencies]
 env_logger = "0.5"
 serde_derive = "1.0"

src/extractor.rs

@@ -139,15 +139,24 @@ impl<T: fmt::Display> fmt::Display for Path<T> {
 /// #[macro_use] extern crate serde_derive;
 /// use actix_web::{App, Query, http};
 ///
-/// #[derive(Deserialize)]
+///
-/// struct Info {
+///#[derive(Debug, Deserialize)]
-///     username: String,
+///pub enum ResponseType {
-/// }
+///    Token,
+///    Code
+///}
+///
+///#[derive(Deserialize)]
+///pub struct AuthRequest {
+///    id: u64,
+///    response_type: ResponseType,
+///}
 ///
 /// // use `with` extractor for query info
 /// // this handler get called only if request's query contains `username` field
-/// fn index(info: Query<Info>) -> String {
+/// // The correct request for this handler would be `/index.html?id=64&response_type=Code"`
-///     format!("Welcome {}!", info.username)
+/// fn index(info: Query<AuthRequest>) -> String {
+///     format!("Authorization request for client with id={} and type={:?}!", info.id, info.response_type)
 /// }
 ///
 /// fn main() {

src/lib.rs

@@ -133,7 +133,6 @@ extern crate num_cpus;
 #[macro_use]
 extern crate percent_encoding;
 extern crate serde_json;
-extern crate serde_urlencoded;
 extern crate smallvec;
 #[macro_use]
 extern crate actix as actix_inner;
@@ -152,6 +151,7 @@ extern crate openssl;
 #[cfg(feature = "openssl")]
 extern crate tokio_openssl;
 
+mod serde_urlencoded;
 mod application;
 mod body;
 mod context;

src/serde_urlencoded/de.rs

@@ -0,0 +1,298 @@
+//! Deserialization support for the `application/x-www-form-urlencoded` format.
+
+use serde::de::{self, DeserializeSeed, EnumAccess, IntoDeserializer, VariantAccess, Visitor};
+use serde::de::Error as de_Error;
+
+use serde::de::value::MapDeserializer;
+use std::borrow::Cow;
+use std::io::Read;
+use url::form_urlencoded::Parse as UrlEncodedParse;
+use url::form_urlencoded::parse;
+
+#[doc(inline)]
+pub use serde::de::value::Error;
+
+/// Deserializes a `application/x-wwww-url-encoded` value from a `&[u8]`.
+///
+/// ```ignore
+/// let meal = vec![
+///     ("bread".to_owned(), "baguette".to_owned()),
+///     ("cheese".to_owned(), "comté".to_owned()),
+///     ("meat".to_owned(), "ham".to_owned()),
+///     ("fat".to_owned(), "butter".to_owned()),
+/// ];
+///
+/// assert_eq!(
+///     serde_urlencoded::from_bytes::<Vec<(String, String)>>(
+///         b"bread=baguette&cheese=comt%C3%A9&meat=ham&fat=butter"),
+///     Ok(meal));
+/// ```
+pub fn from_bytes<'de, T>(input: &'de [u8]) -> Result<T, Error>
+    where T: de::Deserialize<'de>,
+{
+    T::deserialize(Deserializer::new(parse(input)))
+}
+
+/// Deserializes a `application/x-wwww-url-encoded` value from a `&str`.
+///
+/// ```ignore
+/// let meal = vec![
+///     ("bread".to_owned(), "baguette".to_owned()),
+///     ("cheese".to_owned(), "comté".to_owned()),
+///     ("meat".to_owned(), "ham".to_owned()),
+///     ("fat".to_owned(), "butter".to_owned()),
+/// ];
+///
+/// assert_eq!(
+///     serde_urlencoded::from_str::<Vec<(String, String)>>(
+///         "bread=baguette&cheese=comt%C3%A9&meat=ham&fat=butter"),
+///     Ok(meal));
+/// ```
+pub fn from_str<'de, T>(input: &'de str) -> Result<T, Error>
+    where T: de::Deserialize<'de>,
+{
+    from_bytes(input.as_bytes())
+}
+
+#[allow(dead_code)]
+/// Convenience function that reads all bytes from `reader` and deserializes
+/// them with `from_bytes`.
+pub fn from_reader<T, R>(mut reader: R) -> Result<T, Error>
+    where T: de::DeserializeOwned,
+          R: Read,
+{
+    let mut buf = vec![];
+    reader.read_to_end(&mut buf)
+        .map_err(|e| {
+            de::Error::custom(format_args!("could not read input: {}", e))
+        })?;
+    from_bytes(&buf)
+}
+
+/// A deserializer for the `application/x-www-form-urlencoded` format.
+///
+/// * Supported top-level outputs are structs, maps and sequences of pairs,
+///   with or without a given length.
+///
+/// * Main `deserialize` methods defers to `deserialize_map`.
+///
+/// * Everything else but `deserialize_seq` and `deserialize_seq_fixed_size`
+///   defers to `deserialize`.
+pub struct Deserializer<'de> {
+    inner: MapDeserializer<'de, PartIterator<'de>, Error>,
+}
+
+impl<'de> Deserializer<'de> {
+    /// Returns a new `Deserializer`.
+    pub fn new(parser: UrlEncodedParse<'de>) -> Self {
+        Deserializer {
+            inner: MapDeserializer::new(PartIterator(parser)),
+        }
+    }
+}
+
+impl<'de> de::Deserializer<'de> for Deserializer<'de> {
+    type Error = Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where V: de::Visitor<'de>,
+    {
+        self.deserialize_map(visitor)
+    }
+
+    fn deserialize_map<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where V: de::Visitor<'de>,
+    {
+        visitor.visit_map(self.inner)
+    }
+
+    fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where V: de::Visitor<'de>,
+    {
+        visitor.visit_seq(self.inner)
+    }
+
+    fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where V:  de::Visitor<'de>,
+    {
+        self.inner.end()?;
+        visitor.visit_unit()
+    }
+
+    forward_to_deserialize_any! {
+        bool
+        u8
+        u16
+        u32
+        u64
+        i8
+        i16
+        i32
+        i64
+        f32
+        f64
+        char
+        str
+        string
+        option
+        bytes
+        byte_buf
+        unit_struct
+        newtype_struct
+        tuple_struct
+        struct
+        identifier
+        tuple
+        enum
+        ignored_any
+    }
+}
+
+struct PartIterator<'de>(UrlEncodedParse<'de>);
+
+impl<'de> Iterator for PartIterator<'de> {
+    type Item = (Part<'de>, Part<'de>);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.0.next().map(|(k, v)| (Part(k), Part(v)))
+    }
+}
+
+struct Part<'de>(Cow<'de, str>);
+
+impl<'de> IntoDeserializer<'de> for Part<'de>
+{
+    type Deserializer = Self;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        self
+    }
+}
+
+macro_rules! forward_parsed_value {
+    ($($ty:ident => $method:ident,)*) => {
+        $(
+            fn $method<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+                where V: de::Visitor<'de>
+            {
+                match self.0.parse::<$ty>() {
+                    Ok(val) => val.into_deserializer().$method(visitor),
+                    Err(e) => Err(de::Error::custom(e))
+                }
+            }
+        )*
+    }
+}
+
+impl<'de> de::Deserializer<'de> for Part<'de> {
+    type Error = Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where V: de::Visitor<'de>,
+    {
+        self.0.into_deserializer().deserialize_any(visitor)
+    }
+
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where V: de::Visitor<'de>,
+    {
+        visitor.visit_some(self)
+    }
+
+    fn deserialize_enum<V>(self, _name: &'static str, _variants: &'static [&'static str], visitor: V) -> Result<V::Value, Self::Error>
+        where V: de::Visitor<'de>,
+    {
+        visitor.visit_enum(ValueEnumAccess { value: self.0 })
+    }
+
+    forward_to_deserialize_any! {
+        char
+        str
+        string
+        unit
+        bytes
+        byte_buf
+        unit_struct
+        newtype_struct
+        tuple_struct
+        struct
+        identifier
+        tuple
+        ignored_any
+        seq
+        map
+    }
+
+    forward_parsed_value! {
+        bool => deserialize_bool,
+        u8 => deserialize_u8,
+        u16 => deserialize_u16,
+        u32 => deserialize_u32,
+        u64 => deserialize_u64,
+        i8 => deserialize_i8,
+        i16 => deserialize_i16,
+        i32 => deserialize_i32,
+        i64 => deserialize_i64,
+        f32 => deserialize_f32,
+        f64 => deserialize_f64,
+    }
+}
+
+/// Provides access to a keyword which can be deserialized into an enum variant. The enum variant
+/// must be a unit variant, otherwise deserialization will fail.
+struct ValueEnumAccess<'de> {
+    value: Cow<'de, str>,
+}
+
+impl<'de> EnumAccess<'de> for ValueEnumAccess<'de> {
+    type Error = Error;
+    type Variant = UnitOnlyVariantAccess;
+
+    fn variant_seed<V>(
+        self,
+        seed: V,
+    ) -> Result<(V::Value, Self::Variant), Self::Error>
+        where V: DeserializeSeed<'de>,
+    {
+        let variant = seed.deserialize(self.value.into_deserializer())?;
+        Ok((variant, UnitOnlyVariantAccess))
+    }
+}
+
+/// A visitor for deserializing the contents of the enum variant. As we only support
+/// `unit_variant`, all other variant types will return an error.
+struct UnitOnlyVariantAccess;
+
+impl<'de> VariantAccess<'de> for UnitOnlyVariantAccess {
+    type Error = Error;
+
+    fn unit_variant(self) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    fn newtype_variant_seed<T>(self, _seed: T) -> Result<T::Value, Self::Error>
+        where T: DeserializeSeed<'de>,
+    {
+        Err(Error::custom("expected unit variant"))
+    }
+
+    fn tuple_variant<V>(
+        self,
+        _len: usize,
+        _visitor: V,
+    ) -> Result<V::Value, Self::Error>
+        where V: Visitor<'de>,
+    {
+        Err(Error::custom("expected unit variant"))
+    }
+
+    fn struct_variant<V>(
+        self,
+        _fields: &'static [&'static str],
+        _visitor: V,
+    ) -> Result<V::Value, Self::Error>
+        where V: Visitor<'de>,
+    {
+        Err(Error::custom("expected unit variant"))
+    }
+}

src/serde_urlencoded/mod.rs

@@ -0,0 +1,114 @@
+//! `x-www-form-urlencoded` meets Serde
+
+extern crate itoa;
+extern crate dtoa;
+
+pub mod de;
+pub mod ser;
+
+#[doc(inline)]
+pub use self::de::{Deserializer, from_bytes, from_reader, from_str};
+#[doc(inline)]
+pub use self::ser::{Serializer, to_string};
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn deserialize_bytes() {
+        let result = vec![("first".to_owned(), 23), ("last".to_owned(), 42)];
+
+        assert_eq!(super::from_bytes(b"first=23&last=42"),
+                   Ok(result));
+    }
+
+    #[test]
+    fn deserialize_str() {
+        let result = vec![("first".to_owned(), 23), ("last".to_owned(), 42)];
+
+        assert_eq!(super::from_str("first=23&last=42"),
+                   Ok(result));
+    }
+
+    #[test]
+    fn deserialize_reader() {
+        let result = vec![("first".to_owned(), 23), ("last".to_owned(), 42)];
+
+        assert_eq!(super::from_reader(b"first=23&last=42" as &[_]),
+                   Ok(result));
+    }
+
+    #[test]
+    fn deserialize_option() {
+        let result = vec![
+            ("first".to_owned(), Some(23)),
+            ("last".to_owned(), Some(42)),
+        ];
+        assert_eq!(super::from_str("first=23&last=42"), Ok(result));
+    }
+
+    #[test]
+    fn deserialize_unit() {
+        assert_eq!(super::from_str(""), Ok(()));
+        assert_eq!(super::from_str("&"), Ok(()));
+        assert_eq!(super::from_str("&&"), Ok(()));
+        assert!(super::from_str::<()>("first=23").is_err());
+    }
+
+    #[derive(Serialize, Deserialize, Debug, PartialEq, Eq)]
+    enum X {
+        A,
+        B,
+        C,
+    }
+
+    #[test]
+    fn deserialize_unit_enum() {
+        let result = vec![
+            ("one".to_owned(), X::A),
+            ("two".to_owned(), X::B),
+            ("three".to_owned(), X::C)
+        ];
+
+        assert_eq!(super::from_str("one=A&two=B&three=C"), Ok(result));
+    }
+
+    #[test]
+    fn serialize_option_map_int() {
+        let params = &[("first", Some(23)), ("middle", None), ("last", Some(42))];
+
+        assert_eq!(super::to_string(params),
+                   Ok("first=23&last=42".to_owned()));
+    }
+
+    #[test]
+    fn serialize_option_map_string() {
+        let params =
+            &[("first", Some("hello")), ("middle", None), ("last", Some("world"))];
+
+        assert_eq!(super::to_string(params),
+                   Ok("first=hello&last=world".to_owned()));
+    }
+
+    #[test]
+    fn serialize_option_map_bool() {
+        let params = &[("one", Some(true)), ("two", Some(false))];
+
+        assert_eq!(super::to_string(params),
+                   Ok("one=true&two=false".to_owned()));
+    }
+
+    #[test]
+    fn serialize_map_bool() {
+        let params = &[("one", true), ("two", false)];
+
+        assert_eq!(super::to_string(params),
+                   Ok("one=true&two=false".to_owned()));
+    }
+
+    #[test]
+    fn serialize_unit_enum() {
+        let params = &[("one", X::A), ("two", X::B), ("three", X::C)];
+        assert_eq!(super::to_string(params),
+                   Ok("one=A&two=B&three=C".to_owned()));
+    }
+}

src/serde_urlencoded/ser/key.rs

@@ -0,0 +1,76 @@
+use super::super::ser::Error;
+use super::super::ser::part::Sink;
+use serde::Serialize;
+use std::borrow::Cow;
+use std::ops::Deref;
+
+pub enum Key<'key> {
+    Static(&'static str),
+    Dynamic(Cow<'key, str>),
+}
+
+impl<'key> Deref for Key<'key> {
+    type Target = str;
+
+    fn deref(&self) -> &str {
+        match *self {
+            Key::Static(key) => key,
+            Key::Dynamic(ref key) => key,
+        }
+    }
+}
+
+impl<'key> From<Key<'key>> for Cow<'static, str> {
+    fn from(key: Key<'key>) -> Self {
+        match key {
+            Key::Static(key) => key.into(),
+            Key::Dynamic(key) => key.into_owned().into(),
+        }
+    }
+}
+
+pub struct KeySink<End> {
+    end: End,
+}
+
+impl<End, Ok> KeySink<End>
+    where End: for<'key> FnOnce(Key<'key>) -> Result<Ok, Error>
+{
+    pub fn new(end: End) -> Self {
+        KeySink { end: end }
+    }
+}
+
+impl<End, Ok> Sink for KeySink<End>
+    where End: for<'key> FnOnce(Key<'key>) -> Result<Ok, Error>
+{
+    type Ok = Ok;
+
+    fn serialize_static_str(self,
+                            value: &'static str)
+                            -> Result<Ok, Error> {
+        (self.end)(Key::Static(value))
+    }
+
+    fn serialize_str(self, value: &str) -> Result<Ok, Error> {
+        (self.end)(Key::Dynamic(value.into()))
+    }
+
+    fn serialize_string(self, value: String) -> Result<Ok, Error> {
+        (self.end)(Key::Dynamic(value.into()))
+    }
+
+    fn serialize_none(self) -> Result<Ok, Error> {
+        Err(self.unsupported())
+    }
+
+    fn serialize_some<T: ?Sized + Serialize>(self,
+                                             _value: &T)
+                                             -> Result<Ok, Error> {
+        Err(self.unsupported())
+    }
+
+    fn unsupported(self) -> Error {
+        Error::Custom("unsupported key".into())
+    }
+}

src/serde_urlencoded/ser/mod.rs

@@ -0,0 +1,507 @@
+//! Serialization support for the `application/x-www-form-urlencoded` format.
+
+mod key;
+mod pair;
+mod part;
+mod value;
+
+use serde::ser;
+use std::borrow::Cow;
+use std::error;
+use std::fmt;
+use std::str;
+use url::form_urlencoded::Serializer as UrlEncodedSerializer;
+use url::form_urlencoded::Target as UrlEncodedTarget;
+
+/// Serializes a value into a `application/x-wwww-url-encoded` `String` buffer.
+///
+/// ```ignore
+/// let meal = &[
+///     ("bread", "baguette"),
+///     ("cheese", "comté"),
+///     ("meat", "ham"),
+///     ("fat", "butter"),
+/// ];
+///
+/// assert_eq!(
+///     serde_urlencoded::to_string(meal),
+///     Ok("bread=baguette&cheese=comt%C3%A9&meat=ham&fat=butter".to_owned()));
+/// ```
+pub fn to_string<T: ser::Serialize>(input: T) -> Result<String, Error> {
+    let mut urlencoder = UrlEncodedSerializer::new("".to_owned());
+    input.serialize(Serializer::new(&mut urlencoder))?;
+    Ok(urlencoder.finish())
+}
+
+/// A serializer for the `application/x-www-form-urlencoded` format.
+///
+/// * Supported top-level inputs are structs, maps and sequences of pairs,
+///   with or without a given length.
+///
+/// * Supported keys and values are integers, bytes (if convertible to strings),
+///   unit structs and unit variants.
+///
+/// * Newtype structs defer to their inner values.
+pub struct Serializer<'output, Target: 'output + UrlEncodedTarget> {
+    urlencoder: &'output mut UrlEncodedSerializer<Target>,
+}
+
+impl<'output, Target: 'output + UrlEncodedTarget> Serializer<'output, Target> {
+    /// Returns a new `Serializer`.
+    pub fn new(urlencoder: &'output mut UrlEncodedSerializer<Target>) -> Self {
+        Serializer { urlencoder: urlencoder }
+    }
+}
+
+/// Errors returned during serializing to `application/x-www-form-urlencoded`.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum Error {
+    Custom(Cow<'static, str>),
+    Utf8(str::Utf8Error),
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            Error::Custom(ref msg) => msg.fmt(f),
+            Error::Utf8(ref err) => write!(f, "invalid UTF-8: {}", err),
+        }
+    }
+}
+
+impl error::Error for Error {
+    fn description(&self) -> &str {
+        match *self {
+            Error::Custom(ref msg) => msg,
+            Error::Utf8(ref err) => error::Error::description(err),
+        }
+    }
+
+    /// The lower-level cause of this error, in the case of a `Utf8` error.
+    fn cause(&self) -> Option<&error::Error> {
+        match *self {
+            Error::Custom(_) => None,
+            Error::Utf8(ref err) => Some(err),
+        }
+    }
+}
+
+impl ser::Error for Error {
+    fn custom<T: fmt::Display>(msg: T) -> Self {
+        Error::Custom(format!("{}", msg).into())
+    }
+}
+
+/// Sequence serializer.
+pub struct SeqSerializer<'output, Target: 'output + UrlEncodedTarget> {
+    urlencoder: &'output mut UrlEncodedSerializer<Target>,
+}
+
+/// Tuple serializer.
+///
+/// Mostly used for arrays.
+pub struct TupleSerializer<'output, Target: 'output + UrlEncodedTarget> {
+    urlencoder: &'output mut UrlEncodedSerializer<Target>,
+}
+
+/// Tuple struct serializer.
+///
+/// Never instantiated, tuple structs are not supported.
+pub struct TupleStructSerializer<'output, T: 'output + UrlEncodedTarget> {
+    inner: ser::Impossible<&'output mut UrlEncodedSerializer<T>, Error>,
+}
+
+/// Tuple variant serializer.
+///
+/// Never instantiated, tuple variants are not supported.
+pub struct TupleVariantSerializer<'output, T: 'output + UrlEncodedTarget> {
+    inner: ser::Impossible<&'output mut UrlEncodedSerializer<T>, Error>,
+}
+
+/// Map serializer.
+pub struct MapSerializer<'output, Target: 'output + UrlEncodedTarget> {
+    urlencoder: &'output mut UrlEncodedSerializer<Target>,
+    key: Option<Cow<'static, str>>,
+}
+
+/// Struct serializer.
+pub struct StructSerializer<'output, Target: 'output + UrlEncodedTarget> {
+    urlencoder: &'output mut UrlEncodedSerializer<Target>,
+}
+
+/// Struct variant serializer.
+///
+/// Never instantiated, struct variants are not supported.
+pub struct StructVariantSerializer<'output, T: 'output + UrlEncodedTarget> {
+    inner: ser::Impossible<&'output mut UrlEncodedSerializer<T>, Error>,
+}
+
+impl<'output, Target> ser::Serializer for Serializer<'output, Target>
+    where Target: 'output + UrlEncodedTarget,
+{
+    type Ok = &'output mut UrlEncodedSerializer<Target>;
+    type Error = Error;
+    type SerializeSeq = SeqSerializer<'output, Target>;
+    type SerializeTuple = TupleSerializer<'output, Target>;
+    type SerializeTupleStruct = TupleStructSerializer<'output, Target>;
+    type SerializeTupleVariant = TupleVariantSerializer<'output, Target>;
+    type SerializeMap = MapSerializer<'output, Target>;
+    type SerializeStruct = StructSerializer<'output, Target>;
+    type SerializeStructVariant = StructVariantSerializer<'output, Target>;
+
+    /// Returns an error.
+    fn serialize_bool(self, _v: bool) -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_i8(self, _v: i8) -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_i16(self, _v: i16) -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_i32(self, _v: i32) -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_i64(self, _v: i64) -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_u8(self, _v: u8) -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_u16(self, _v: u16) -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_u32(self, _v: u32) -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_u64(self, _v: u64) -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_f32(self, _v: f32) -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_f64(self, _v: f64) -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_char(self, _v: char) -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_str(self, _value: &str) -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_bytes(self, _value: &[u8]) -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_unit(self) -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_unit_struct(self,
+                             _name: &'static str)
+                             -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_unit_variant(self,
+                              _name: &'static str,
+                              _variant_index: u32,
+                              _variant: &'static str)
+                              -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Serializes the inner value, ignoring the newtype name.
+    fn serialize_newtype_struct<T: ?Sized + ser::Serialize>
+        (self,
+         _name: &'static str,
+         value: &T)
+         -> Result<Self::Ok, Error> {
+        value.serialize(self)
+    }
+
+    /// Returns an error.
+    fn serialize_newtype_variant<T: ?Sized + ser::Serialize>
+        (self,
+         _name: &'static str,
+         _variant_index: u32,
+         _variant: &'static str,
+         _value: &T)
+         -> Result<Self::Ok, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns `Ok`.
+    fn serialize_none(self) -> Result<Self::Ok, Error> {
+        Ok(self.urlencoder)
+    }
+
+    /// Serializes the given value.
+    fn serialize_some<T: ?Sized + ser::Serialize>
+        (self,
+         value: &T)
+         -> Result<Self::Ok, Error> {
+        value.serialize(self)
+    }
+
+    /// Serialize a sequence, given length (if any) is ignored.
+    fn serialize_seq(self,
+                     _len: Option<usize>)
+                     -> Result<Self::SerializeSeq, Error> {
+        Ok(SeqSerializer { urlencoder: self.urlencoder })
+    }
+
+    /// Returns an error.
+    fn serialize_tuple(self,
+                       _len: usize)
+                       -> Result<Self::SerializeTuple, Error> {
+        Ok(TupleSerializer { urlencoder: self.urlencoder })
+    }
+
+    /// Returns an error.
+    fn serialize_tuple_struct(self,
+                              _name: &'static str,
+                              _len: usize)
+                              -> Result<Self::SerializeTupleStruct, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Returns an error.
+    fn serialize_tuple_variant
+        (self,
+         _name: &'static str,
+         _variant_index: u32,
+         _variant: &'static str,
+         _len: usize)
+         -> Result<Self::SerializeTupleVariant, Error> {
+        Err(Error::top_level())
+    }
+
+    /// Serializes a map, given length is ignored.
+    fn serialize_map(self,
+                     _len: Option<usize>)
+                     -> Result<Self::SerializeMap, Error> {
+        Ok(MapSerializer {
+            urlencoder: self.urlencoder,
+            key: None,
+        })
+    }
+
+    /// Serializes a struct, given length is ignored.
+    fn serialize_struct(self,
+                        _name: &'static str,
+                        _len: usize)
+                        -> Result<Self::SerializeStruct, Error> {
+        Ok(StructSerializer { urlencoder: self.urlencoder })
+    }
+
+    /// Returns an error.
+    fn serialize_struct_variant
+        (self,
+         _name: &'static str,
+         _variant_index: u32,
+         _variant: &'static str,
+         _len: usize)
+         -> Result<Self::SerializeStructVariant, Error> {
+        Err(Error::top_level())
+    }
+}
+
+impl<'output, Target> ser::SerializeSeq for SeqSerializer<'output, Target>
+    where Target: 'output + UrlEncodedTarget,
+{
+    type Ok = &'output mut UrlEncodedSerializer<Target>;
+    type Error = Error;
+
+    fn serialize_element<T: ?Sized + ser::Serialize>(&mut self,
+                                                     value: &T)
+                                                     -> Result<(), Error> {
+        value.serialize(pair::PairSerializer::new(self.urlencoder))
+    }
+
+    fn end(self) -> Result<Self::Ok, Error> {
+        Ok(self.urlencoder)
+    }
+}
+
+impl<'output, Target> ser::SerializeTuple for TupleSerializer<'output, Target>
+    where Target: 'output + UrlEncodedTarget,
+{
+    type Ok = &'output mut UrlEncodedSerializer<Target>;
+    type Error = Error;
+
+    fn serialize_element<T: ?Sized + ser::Serialize>(&mut self,
+                                                     value: &T)
+                                                     -> Result<(), Error> {
+        value.serialize(pair::PairSerializer::new(self.urlencoder))
+    }
+
+    fn end(self) -> Result<Self::Ok, Error> {
+        Ok(self.urlencoder)
+    }
+}
+
+impl<'output, Target> ser::SerializeTupleStruct
+    for
+    TupleStructSerializer<'output, Target>
+    where Target: 'output + UrlEncodedTarget,
+{
+    type Ok = &'output mut UrlEncodedSerializer<Target>;
+    type Error = Error;
+
+    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
+                                                   value: &T)
+                                                   -> Result<(), Error> {
+        self.inner.serialize_field(value)
+    }
+
+    fn end(self) -> Result<Self::Ok, Error> {
+        self.inner.end()
+    }
+}
+
+impl<'output, Target> ser::SerializeTupleVariant
+    for
+    TupleVariantSerializer<'output, Target>
+    where Target: 'output + UrlEncodedTarget,
+{
+    type Ok = &'output mut UrlEncodedSerializer<Target>;
+    type Error = Error;
+
+    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
+                                                   value: &T)
+                                                   -> Result<(), Error> {
+        self.inner.serialize_field(value)
+    }
+
+    fn end(self) -> Result<Self::Ok, Error> {
+        self.inner.end()
+    }
+}
+
+impl<'output, Target> ser::SerializeMap for MapSerializer<'output, Target>
+    where Target: 'output + UrlEncodedTarget,
+{
+    type Ok = &'output mut UrlEncodedSerializer<Target>;
+    type Error = Error;
+
+    fn serialize_entry<K: ?Sized + ser::Serialize, V: ?Sized + ser::Serialize>
+        (&mut self,
+         key: &K,
+         value: &V)
+         -> Result<(), Error> {
+        let key_sink = key::KeySink::new(|key| {
+            let value_sink = value::ValueSink::new(self.urlencoder, &key);
+            value.serialize(part::PartSerializer::new(value_sink))?;
+            self.key = None;
+            Ok(())
+        });
+        let entry_serializer = part::PartSerializer::new(key_sink);
+        key.serialize(entry_serializer)
+    }
+
+    fn serialize_key<T: ?Sized + ser::Serialize>(&mut self,
+                                                 key: &T)
+                                                 -> Result<(), Error> {
+        let key_sink = key::KeySink::new(|key| Ok(key.into()));
+        let key_serializer = part::PartSerializer::new(key_sink);
+        self.key = Some(key.serialize(key_serializer)?);
+        Ok(())
+    }
+
+    fn serialize_value<T: ?Sized + ser::Serialize>(&mut self,
+                                                   value: &T)
+                                                   -> Result<(), Error> {
+        {
+            let key = self.key.as_ref().ok_or_else(|| Error::no_key())?;
+            let value_sink = value::ValueSink::new(self.urlencoder, &key);
+            value.serialize(part::PartSerializer::new(value_sink))?;
+        }
+        self.key = None;
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok, Error> {
+        Ok(self.urlencoder)
+    }
+}
+
+impl<'output, Target> ser::SerializeStruct for StructSerializer<'output, Target>
+    where Target: 'output + UrlEncodedTarget,
+{
+    type Ok = &'output mut UrlEncodedSerializer<Target>;
+    type Error = Error;
+
+    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
+                                                   key: &'static str,
+                                                   value: &T)
+                                                   -> Result<(), Error> {
+        let value_sink = value::ValueSink::new(self.urlencoder, key);
+        value.serialize(part::PartSerializer::new(value_sink))
+    }
+
+    fn end(self) -> Result<Self::Ok, Error> {
+        Ok(self.urlencoder)
+    }
+}
+
+impl<'output, Target> ser::SerializeStructVariant
+    for
+    StructVariantSerializer<'output, Target>
+    where Target: 'output + UrlEncodedTarget,
+{
+    type Ok = &'output mut UrlEncodedSerializer<Target>;
+    type Error = Error;
+
+    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
+                                                   key: &'static str,
+                                                   value: &T)
+                                                   -> Result<(), Error> {
+        self.inner.serialize_field(key, value)
+    }
+
+    fn end(self) -> Result<Self::Ok, Error> {
+        self.inner.end()
+    }
+}
+
+impl Error {
+    fn top_level() -> Self {
+        let msg = "top-level serializer supports only maps and structs";
+        Error::Custom(msg.into())
+    }
+
+    fn no_key() -> Self {
+        let msg = "tried to serialize a value before serializing key";
+        Error::Custom(msg.into())
+    }
+}

src/serde_urlencoded/ser/pair.rs

@@ -0,0 +1,257 @@
+use super::super::ser::Error;
+use super::super::ser::key::KeySink;
+use super::super::ser::part::PartSerializer;
+use super::super::ser::value::ValueSink;
+use serde::ser;
+use std::borrow::Cow;
+use std::mem;
+use url::form_urlencoded::Serializer as UrlEncodedSerializer;
+use url::form_urlencoded::Target as UrlEncodedTarget;
+
+pub struct PairSerializer<'target, Target: 'target + UrlEncodedTarget> {
+    urlencoder: &'target mut UrlEncodedSerializer<Target>,
+    state: PairState,
+}
+
+impl<'target, Target> PairSerializer<'target, Target>
+    where Target: 'target + UrlEncodedTarget,
+{
+    pub fn new(urlencoder: &'target mut UrlEncodedSerializer<Target>) -> Self {
+        PairSerializer {
+            urlencoder: urlencoder,
+            state: PairState::WaitingForKey,
+        }
+    }
+}
+
+impl<'target, Target> ser::Serializer for PairSerializer<'target, Target>
+    where Target: 'target + UrlEncodedTarget,
+{
+    type Ok = ();
+    type Error = Error;
+    type SerializeSeq = ser::Impossible<(), Error>;
+    type SerializeTuple = Self;
+    type SerializeTupleStruct = ser::Impossible<(), Error>;
+    type SerializeTupleVariant = ser::Impossible<(), Error>;
+    type SerializeMap = ser::Impossible<(), Error>;
+    type SerializeStruct = ser::Impossible<(), Error>;
+    type SerializeStructVariant = ser::Impossible<(), Error>;
+
+    fn serialize_bool(self, _v: bool) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_i8(self, _v: i8) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_i16(self, _v: i16) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_i32(self, _v: i32) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_i64(self, _v: i64) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_u8(self, _v: u8) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_u16(self, _v: u16) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_u32(self, _v: u32) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_u64(self, _v: u64) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_f32(self, _v: f32) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_f64(self, _v: f64) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_char(self, _v: char) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_str(self, _value: &str) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_bytes(self, _value: &[u8]) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_unit(self) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_unit_variant(self,
+                              _name: &'static str,
+                              _variant_index: u32,
+                              _variant: &'static str)
+                              -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_newtype_struct<T: ?Sized + ser::Serialize>
+        (self,
+         _name: &'static str,
+         value: &T)
+         -> Result<(), Error> {
+        value.serialize(self)
+    }
+
+    fn serialize_newtype_variant<T: ?Sized + ser::Serialize>
+        (self,
+         _name: &'static str,
+         _variant_index: u32,
+         _variant: &'static str,
+         _value: &T)
+         -> Result<(), Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_none(self) -> Result<(), Error> {
+        Ok(())
+    }
+
+    fn serialize_some<T: ?Sized + ser::Serialize>(self,
+                                                  value: &T)
+                                                  -> Result<(), Error> {
+        value.serialize(self)
+    }
+
+    fn serialize_seq(self,
+                     _len: Option<usize>)
+                     -> Result<Self::SerializeSeq, Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_tuple(self, len: usize) -> Result<Self, Error> {
+        if len == 2 {
+            Ok(self)
+        } else {
+            Err(Error::unsupported_pair())
+        }
+    }
+
+    fn serialize_tuple_struct(self,
+                              _name: &'static str,
+                              _len: usize)
+                              -> Result<Self::SerializeTupleStruct, Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_tuple_variant
+        (self,
+         _name: &'static str,
+         _variant_index: u32,
+         _variant: &'static str,
+         _len: usize)
+         -> Result<Self::SerializeTupleVariant, Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_map(self,
+                     _len: Option<usize>)
+                     -> Result<Self::SerializeMap, Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_struct(self,
+                        _name: &'static str,
+                        _len: usize)
+                        -> Result<Self::SerializeStruct, Error> {
+        Err(Error::unsupported_pair())
+    }
+
+    fn serialize_struct_variant
+        (self,
+         _name: &'static str,
+         _variant_index: u32,
+         _variant: &'static str,
+         _len: usize)
+         -> Result<Self::SerializeStructVariant, Error> {
+        Err(Error::unsupported_pair())
+    }
+}
+
+impl<'target, Target> ser::SerializeTuple for PairSerializer<'target, Target>
+    where Target: 'target + UrlEncodedTarget,
+{
+    type Ok = ();
+    type Error = Error;
+
+    fn serialize_element<T: ?Sized + ser::Serialize>(&mut self,
+                                                     value: &T)
+                                                     -> Result<(), Error> {
+        match mem::replace(&mut self.state, PairState::Done) {
+            PairState::WaitingForKey => {
+                let key_sink = KeySink::new(|key| Ok(key.into()));
+                let key_serializer = PartSerializer::new(key_sink);
+                self.state = PairState::WaitingForValue {
+                    key: value.serialize(key_serializer)?,
+                };
+                Ok(())
+            },
+            PairState::WaitingForValue { key } => {
+                let result = {
+                    let value_sink = ValueSink::new(self.urlencoder, &key);
+                    let value_serializer = PartSerializer::new(value_sink);
+                    value.serialize(value_serializer)
+                };
+                if result.is_ok() {
+                    self.state = PairState::Done;
+                } else {
+                    self.state = PairState::WaitingForValue { key: key };
+                }
+                result
+            },
+            PairState::Done => Err(Error::done()),
+        }
+    }
+
+    fn end(self) -> Result<(), Error> {
+        if let PairState::Done = self.state {
+            Ok(())
+        } else {
+            Err(Error::not_done())
+        }
+    }
+}
+
+enum PairState {
+    WaitingForKey,
+    WaitingForValue { key: Cow<'static, str> },
+    Done,
+}
+
+impl Error {
+    fn done() -> Self {
+        Error::Custom("this pair has already been serialized".into())
+    }
+
+    fn not_done() -> Self {
+        Error::Custom("this pair has not yet been serialized".into())
+    }
+
+    fn unsupported_pair() -> Self {
+        Error::Custom("unsupported pair".into())
+    }
+}

src/serde_urlencoded/ser/part.rs

@@ -0,0 +1,222 @@
+use ::serde;
+
+use super::super::dtoa;
+use super::super::itoa;
+use super::super::ser::Error;
+use std::str;
+
+pub struct PartSerializer<S> {
+    sink: S,
+}
+
+impl<S: Sink> PartSerializer<S> {
+    pub fn new(sink: S) -> Self {
+        PartSerializer { sink: sink }
+    }
+}
+
+pub trait Sink: Sized {
+    type Ok;
+
+    fn serialize_static_str(self,
+                            value: &'static str)
+                            -> Result<Self::Ok, Error>;
+
+    fn serialize_str(self, value: &str) -> Result<Self::Ok, Error>;
+    fn serialize_string(self, value: String) -> Result<Self::Ok, Error>;
+    fn serialize_none(self) -> Result<Self::Ok, Error>;
+
+    fn serialize_some<T: ?Sized + serde::ser::Serialize>
+        (self,
+         value: &T)
+         -> Result<Self::Ok, Error>;
+
+    fn unsupported(self) -> Error;
+}
+
+impl<S: Sink> serde::ser::Serializer for PartSerializer<S> {
+    type Ok = S::Ok;
+    type Error = Error;
+    type SerializeSeq = serde::ser::Impossible<S::Ok, Error>;
+    type SerializeTuple = serde::ser::Impossible<S::Ok, Error>;
+    type SerializeTupleStruct = serde::ser::Impossible<S::Ok, Error>;
+    type SerializeTupleVariant = serde::ser::Impossible<S::Ok, Error>;
+    type SerializeMap = serde::ser::Impossible<S::Ok, Error>;
+    type SerializeStruct = serde::ser::Impossible<S::Ok, Error>;
+    type SerializeStructVariant = serde::ser::Impossible<S::Ok, Error>;
+
+    fn serialize_bool(self, v: bool) -> Result<S::Ok, Error> {
+        self.sink.serialize_static_str(if v { "true" } else { "false" })
+    }
+
+    fn serialize_i8(self, v: i8) -> Result<S::Ok, Error> {
+        self.serialize_integer(v)
+    }
+
+    fn serialize_i16(self, v: i16) -> Result<S::Ok, Error> {
+        self.serialize_integer(v)
+    }
+
+    fn serialize_i32(self, v: i32) -> Result<S::Ok, Error> {
+        self.serialize_integer(v)
+    }
+
+    fn serialize_i64(self, v: i64) -> Result<S::Ok, Error> {
+        self.serialize_integer(v)
+    }
+
+    fn serialize_u8(self, v: u8) -> Result<S::Ok, Error> {
+        self.serialize_integer(v)
+    }
+
+    fn serialize_u16(self, v: u16) -> Result<S::Ok, Error> {
+        self.serialize_integer(v)
+    }
+
+    fn serialize_u32(self, v: u32) -> Result<S::Ok, Error> {
+        self.serialize_integer(v)
+    }
+
+    fn serialize_u64(self, v: u64) -> Result<S::Ok, Error> {
+        self.serialize_integer(v)
+    }
+
+    fn serialize_f32(self, v: f32) -> Result<S::Ok, Error> {
+        self.serialize_floating(v)
+    }
+
+    fn serialize_f64(self, v: f64) -> Result<S::Ok, Error> {
+        self.serialize_floating(v)
+    }
+
+    fn serialize_char(self, v: char) -> Result<S::Ok, Error> {
+        self.sink.serialize_string(v.to_string())
+    }
+
+    fn serialize_str(self, value: &str) -> Result<S::Ok, Error> {
+        self.sink.serialize_str(value)
+    }
+
+    fn serialize_bytes(self, value: &[u8]) -> Result<S::Ok, Error> {
+        match str::from_utf8(value) {
+            Ok(value) => self.sink.serialize_str(value),
+            Err(err) => Err(Error::Utf8(err)),
+        }
+    }
+
+    fn serialize_unit(self) -> Result<S::Ok, Error> {
+        Err(self.sink.unsupported())
+    }
+
+    fn serialize_unit_struct(self, name: &'static str) -> Result<S::Ok, Error> {
+        self.sink.serialize_static_str(name.into())
+    }
+
+    fn serialize_unit_variant(self,
+                              _name: &'static str,
+                              _variant_index: u32,
+                              variant: &'static str)
+                              -> Result<S::Ok, Error> {
+        self.sink.serialize_static_str(variant.into())
+    }
+
+    fn serialize_newtype_struct<T: ?Sized + serde::ser::Serialize>
+        (self,
+         _name: &'static str,
+         value: &T)
+         -> Result<S::Ok, Error> {
+        value.serialize(self)
+    }
+
+    fn serialize_newtype_variant<T: ?Sized + serde::ser::Serialize>
+        (self,
+         _name: &'static str,
+         _variant_index: u32,
+         _variant: &'static str,
+         _value: &T)
+         -> Result<S::Ok, Error> {
+        Err(self.sink.unsupported())
+    }
+
+    fn serialize_none(self) -> Result<S::Ok, Error> {
+        self.sink.serialize_none()
+    }
+
+    fn serialize_some<T: ?Sized + serde::ser::Serialize>(self,
+                                                  value: &T)
+                                                  -> Result<S::Ok, Error> {
+        self.sink.serialize_some(value)
+    }
+
+    fn serialize_seq(self,
+                     _len: Option<usize>)
+                     -> Result<Self::SerializeSeq, Error> {
+        Err(self.sink.unsupported())
+    }
+
+    fn serialize_tuple(self,
+                       _len: usize)
+                       -> Result<Self::SerializeTuple, Error> {
+        Err(self.sink.unsupported())
+    }
+
+    fn serialize_tuple_struct(self,
+                              _name: &'static str,
+                              _len: usize)
+                              -> Result<Self::SerializeTuple, Error> {
+        Err(self.sink.unsupported())
+    }
+
+    fn serialize_tuple_variant
+        (self,
+         _name: &'static str,
+         _variant_index: u32,
+         _variant: &'static str,
+         _len: usize)
+         -> Result<Self::SerializeTupleVariant, Error> {
+        Err(self.sink.unsupported())
+    }
+
+    fn serialize_map(self,
+                     _len: Option<usize>)
+                     -> Result<Self::SerializeMap, Error> {
+        Err(self.sink.unsupported())
+    }
+
+    fn serialize_struct(self,
+                        _name: &'static str,
+                        _len: usize)
+                        -> Result<Self::SerializeStruct, Error> {
+        Err(self.sink.unsupported())
+    }
+
+    fn serialize_struct_variant
+        (self,
+         _name: &'static str,
+         _variant_index: u32,
+         _variant: &'static str,
+         _len: usize)
+         -> Result<Self::SerializeStructVariant, Error> {
+        Err(self.sink.unsupported())
+    }
+}
+
+impl<S: Sink> PartSerializer<S> {
+    fn serialize_integer<I>(self, value: I) -> Result<S::Ok, Error>
+        where I: itoa::Integer,
+    {
+        let mut buf = [b'\0'; 20];
+        let len = itoa::write(&mut buf[..], value).unwrap();
+        let part = unsafe { str::from_utf8_unchecked(&buf[0..len]) };
+        serde::ser::Serializer::serialize_str(self, part)
+    }
+
+    fn serialize_floating<F>(self, value: F) -> Result<S::Ok, Error>
+        where F: dtoa::Floating,
+    {
+        let mut buf = [b'\0'; 24];
+        let len = dtoa::write(&mut buf[..], value).unwrap();
+        let part = unsafe { str::from_utf8_unchecked(&buf[0..len]) };
+        serde::ser::Serializer::serialize_str(self, part)
+    }
+}

src/serde_urlencoded/ser/value.rs

@@ -0,0 +1,59 @@
+use super::super::ser::Error;
+use super::super::ser::part::{PartSerializer, Sink};
+use serde::ser::Serialize;
+use std::str;
+use url::form_urlencoded::Serializer as UrlEncodedSerializer;
+use url::form_urlencoded::Target as UrlEncodedTarget;
+
+pub struct ValueSink<'key, 'target, Target>
+    where Target: 'target + UrlEncodedTarget,
+{
+    urlencoder: &'target mut UrlEncodedSerializer<Target>,
+    key: &'key str,
+}
+
+impl<'key, 'target, Target> ValueSink<'key, 'target, Target>
+    where Target: 'target + UrlEncodedTarget,
+{
+    pub fn new(urlencoder: &'target mut UrlEncodedSerializer<Target>,
+               key: &'key str)
+               -> Self {
+        ValueSink {
+            urlencoder: urlencoder,
+            key: key,
+        }
+    }
+}
+
+impl<'key, 'target, Target> Sink for ValueSink<'key, 'target, Target>
+    where Target: 'target + UrlEncodedTarget,
+{
+    type Ok = ();
+
+    fn serialize_str(self, value: &str) -> Result<(), Error> {
+        self.urlencoder.append_pair(self.key, value);
+        Ok(())
+    }
+
+    fn serialize_static_str(self, value: &'static str) -> Result<(), Error> {
+        self.serialize_str(value)
+    }
+
+    fn serialize_string(self, value: String) -> Result<(), Error> {
+        self.serialize_str(&value)
+    }
+
+    fn serialize_none(self) -> Result<Self::Ok, Error> {
+        Ok(())
+    }
+
+    fn serialize_some<T: ?Sized + Serialize>(self,
+                                             value: &T)
+                                             -> Result<Self::Ok, Error> {
+        value.serialize(PartSerializer::new(self))
+    }
+
+    fn unsupported(self) -> Error {
+        Error::Custom("unsupported value".into())
+    }
+}

tests/test_handlers.rs

@@ -91,6 +91,48 @@ fn test_query_extractor() {
     assert_eq!(response.status(), StatusCode::BAD_REQUEST);
 }
 
+#[derive(Deserialize, Debug)]
+pub enum ResponseType {
+    Token,
+    Code
+}
+
+#[derive(Debug, Deserialize)]
+pub struct AuthRequest {
+    id: u64,
+    response_type: ResponseType,
+}
+
+#[test]
+fn test_query_enum_extractor() {
+    let mut srv = test::TestServer::new(|app| {
+        app.resource("/index.html", |r| {
+            r.with(|p: Query<AuthRequest>| format!("{:?}", p.into_inner()))
+        });
+    });
+
+    // client request
+    let request = srv
+        .get()
+        .uri(srv.url("/index.html?id=64&response_type=Code"))
+        .finish()
+        .unwrap();
+    let response = srv.execute(request.send()).unwrap();
+    assert!(response.status().is_success());
+
+    // read response
+    let bytes = srv.execute(response.body()).unwrap();
+    assert_eq!(bytes, Bytes::from_static(b"AuthRequest { id: 64, response_type: Code }"));
+
+    let request = srv.get().uri(srv.url("/index.html?id=64&response_type=Co")).finish().unwrap();
+    let response = srv.execute(request.send()).unwrap();
+    assert_eq!(response.status(), StatusCode::BAD_REQUEST);
+
+    let request = srv.get().uri(srv.url("/index.html?response_type=Code")).finish().unwrap();
+    let response = srv.execute(request.send()).unwrap();
+    assert_eq!(response.status(), StatusCode::BAD_REQUEST);
+}
+
 #[test]
 fn test_async_extractor_async() {
     let mut srv = test::TestServer::new(|app| {