xmpp-rs/src/util/macros.rs

// Copyright (c) 2017-2018 Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

macro_rules! get_attr {
    ($elem:ident, $attr:tt, $type:tt) => {
        get_attr!($elem, $attr, $type, value, value.parse()?)
    };
    ($elem:ident, $attr:tt, OptionEmpty, $value:ident, $func:expr) => {
        match $elem.attr($attr) {
            Some("") => None,
            Some($value) => Some($func),
            None => None,
        }
    };
    ($elem:ident, $attr:tt, Option, $value:ident, $func:expr) => {
        match $elem.attr($attr) {
            Some($value) => Some($func),
            None => None,
        }
    };
    ($elem:ident, $attr:tt, Required, $value:ident, $func:expr) => {
        match $elem.attr($attr) {
            Some($value) => $func,
            None => {
                return Err(crate::util::error::Error::ParseError(concat!(
                    "Required attribute '",
                    $attr,
                    "' missing."
                )));
            }
        }
    };
    ($elem:ident, $attr:tt, RequiredNonEmpty, $value:ident, $func:expr) => {
        match $elem.attr($attr) {
            Some("") => {
                return Err(crate::util::error::Error::ParseError(concat!(
                    "Required attribute '",
                    $attr,
                    "' must not be empty."
                )));
            },
            Some($value) => $func,
            None => {
                return Err(crate::util::error::Error::ParseError(concat!(
                    "Required attribute '",
                    $attr,
                    "' missing."
                )));
            }
        }
    };
    ($elem:ident, $attr:tt, Default, $value:ident, $func:expr) => {
        match $elem.attr($attr) {
            Some($value) => $func,
            None => ::std::default::Default::default(),
        }
    };
}

macro_rules! generate_attribute {
    ($(#[$meta:meta])* $elem:ident, $name:tt, {$($(#[$a_meta:meta])* $a:ident => $b:tt),+,}) => (
        generate_attribute!($(#[$meta])* $elem, $name, {$($(#[$a_meta])* $a => $b),+});
    );
    ($(#[$meta:meta])* $elem:ident, $name:tt, {$($(#[$a_meta:meta])* $a:ident => $b:tt),+,}, Default = $default:ident) => (
        generate_attribute!($(#[$meta])* $elem, $name, {$($(#[$a_meta])* $a => $b),+}, Default = $default);
    );
    ($(#[$meta:meta])* $elem:ident, $name:tt, {$($(#[$a_meta:meta])* $a:ident => $b:tt),+}) => (
        $(#[$meta])*
        #[derive(Debug, Clone, PartialEq)]
        pub enum $elem {
            $(
                $(#[$a_meta])*
                $a
            ),+
        }
        impl ::std::str::FromStr for $elem {
            type Err = crate::util::error::Error;
            fn from_str(s: &str) -> Result<$elem, crate::util::error::Error> {
                Ok(match s {
                    $($b => $elem::$a),+,
                    _ => return Err(crate::util::error::Error::ParseError(concat!("Unknown value for '", $name, "' attribute."))),
                })
            }
        }
        impl ::minidom::IntoAttributeValue for $elem {
            fn into_attribute_value(self) -> Option<String> {
                Some(String::from(match self {
                    $($elem::$a => $b),+
                }))
            }
        }
    );
    ($(#[$meta:meta])* $elem:ident, $name:tt, {$($(#[$a_meta:meta])* $a:ident => $b:tt),+}, Default = $default:ident) => (
        $(#[$meta])*
        #[derive(Debug, Clone, PartialEq)]
        pub enum $elem {
            $(
                $(#[$a_meta])*
                $a
            ),+
        }
        impl ::std::str::FromStr for $elem {
            type Err = crate::util::error::Error;
            fn from_str(s: &str) -> Result<$elem, crate::util::error::Error> {
                Ok(match s {
                    $($b => $elem::$a),+,
                    _ => return Err(crate::util::error::Error::ParseError(concat!("Unknown value for '", $name, "' attribute."))),
                })
            }
        }
        impl ::minidom::IntoAttributeValue for $elem {
            #[allow(unreachable_patterns)]
            fn into_attribute_value(self) -> Option<String> {
                Some(String::from(match self {
                    $elem::$default => return None,
                    $($elem::$a => $b),+
                }))
            }
        }
        impl ::std::default::Default for $elem {
            fn default() -> $elem {
                $elem::$default
            }
        }
    );
    ($(#[$meta:meta])* $elem:ident, $name:tt, ($(#[$meta_symbol:meta])* $symbol:ident => $value:tt)) => (
        $(#[$meta])*
        #[derive(Debug, Clone, PartialEq)]
        pub enum $elem {
            $(#[$meta_symbol])*
            $symbol,
            /// Value when absent.
            None,
        }
        impl ::std::str::FromStr for $elem {
            type Err = crate::util::error::Error;
            fn from_str(s: &str) -> Result<Self, crate::util::error::Error> {
                Ok(match s {
                    $value => $elem::$symbol,
                    _ => return Err(crate::util::error::Error::ParseError(concat!("Unknown value for '", $name, "' attribute."))),
                })
            }
        }
        impl ::minidom::IntoAttributeValue for $elem {
            fn into_attribute_value(self) -> Option<String> {
                match self {
                    $elem::$symbol => Some(String::from($value)),
                    $elem::None => None
                }
            }
        }
        impl ::std::default::Default for $elem {
            fn default() -> $elem {
                $elem::None
            }
        }
    );
    ($(#[$meta:meta])* $elem:ident, $name:tt, bool) => (
        $(#[$meta])*
        #[derive(Debug, Clone, PartialEq)]
        pub enum $elem {
            /// True value, represented by either 'true' or '1'.
            True,
            /// False value, represented by either 'false' or '0'.
            False,
        }
        impl ::std::str::FromStr for $elem {
            type Err = crate::util::error::Error;
            fn from_str(s: &str) -> Result<Self, crate::util::error::Error> {
                Ok(match s {
                    "true" | "1" => $elem::True,
                    "false" | "0" => $elem::False,
                    _ => return Err(crate::util::error::Error::ParseError(concat!("Unknown value for '", $name, "' attribute."))),
                })
            }
        }
        impl ::minidom::IntoAttributeValue for $elem {
            fn into_attribute_value(self) -> Option<String> {
                match self {
                    $elem::True => Some(String::from("true")),
                    $elem::False => None
                }
            }
        }
        impl ::std::default::Default for $elem {
            fn default() -> $elem {
                $elem::False
            }
        }
    );
    ($(#[$meta:meta])* $elem:ident, $name:tt, $type:tt, Default = $default:expr) => (
        $(#[$meta])*
        #[derive(Debug, Clone, PartialEq)]
        pub struct $elem(pub $type);
        impl ::std::str::FromStr for $elem {
            type Err = crate::util::error::Error;
            fn from_str(s: &str) -> Result<Self, crate::util::error::Error> {
                Ok($elem($type::from_str(s)?))
            }
        }
        impl ::minidom::IntoAttributeValue for $elem {
            fn into_attribute_value(self) -> Option<String> {
                match self {
                    $elem($default) => None,
                    $elem(value) => Some(format!("{}", value)),
                }
            }
        }
        impl ::std::default::Default for $elem {
            fn default() -> $elem {
                $elem($default)
            }
        }
    );
}

macro_rules! generate_element_enum {
    ($(#[$meta:meta])* $elem:ident, $name:tt, $ns:ident, {$($(#[$enum_meta:meta])* $enum:ident => $enum_name:tt),+,}) => (
        generate_element_enum!($(#[$meta])* $elem, $name, $ns, {$($(#[$enum_meta])* $enum => $enum_name),+});
    );
    ($(#[$meta:meta])* $elem:ident, $name:tt, $ns:ident, {$($(#[$enum_meta:meta])* $enum:ident => $enum_name:tt),+}) => (
        $(#[$meta])*
        #[derive(Debug, Clone, PartialEq)]
        pub enum $elem {
            $(
                $(#[$enum_meta])*
                $enum
            ),+
        }
        impl ::try_from::TryFrom<::minidom::Element> for $elem {
            type Err = crate::util::error::Error;
            fn try_from(elem: ::minidom::Element) -> Result<$elem, crate::util::error::Error> {
                check_ns_only!(elem, $name, $ns);
                check_no_children!(elem, $name);
                check_no_attributes!(elem, $name);
                Ok(match elem.name() {
                    $($enum_name => $elem::$enum,)+
                    _ => return Err(crate::util::error::Error::ParseError(concat!("This is not a ", $name, " element."))),
                })
            }
        }
        impl From<$elem> for ::minidom::Element {
            fn from(elem: $elem) -> ::minidom::Element {
                ::minidom::Element::builder(
                    match elem {
                        $($elem::$enum => $enum_name,)+
                    }
                )
                    .ns(crate::ns::$ns)
                    .build()
            }
        }
    );
}

macro_rules! generate_attribute_enum {
    ($(#[$meta:meta])* $elem:ident, $name:tt, $ns:ident, $attr:tt, {$($(#[$enum_meta:meta])* $enum:ident => $enum_name:tt),+,}) => (
        generate_attribute_enum!($(#[$meta])* $elem, $name, $ns, $attr, {$($(#[$enum_meta])* $enum => $enum_name),+});
    );
    ($(#[$meta:meta])* $elem:ident, $name:tt, $ns:ident, $attr:tt, {$($(#[$enum_meta:meta])* $enum:ident => $enum_name:tt),+}) => (
        $(#[$meta])*
        #[derive(Debug, Clone, PartialEq)]
        pub enum $elem {
            $(
                $(#[$enum_meta])*
                $enum
            ),+
        }
        impl ::try_from::TryFrom<::minidom::Element> for $elem {
            type Err = crate::util::error::Error;
            fn try_from(elem: ::minidom::Element) -> Result<$elem, crate::util::error::Error> {
                check_ns_only!(elem, $name, $ns);
                check_no_children!(elem, $name);
                check_no_unknown_attributes!(elem, $name, [$attr]);
                Ok(match get_attr!(elem, $attr, Required) {
                    $($enum_name => $elem::$enum,)+
                    _ => return Err(crate::util::error::Error::ParseError(concat!("Invalid ", $name, " ", $attr, " value."))),
                })
            }
        }
        impl From<$elem> for ::minidom::Element {
            fn from(elem: $elem) -> ::minidom::Element {
                ::minidom::Element::builder($name)
                    .ns(crate::ns::$ns)
                    .attr($attr, match elem {
                         $($elem::$enum => $enum_name,)+
                     })
                     .build()
            }
        }
    );
}

macro_rules! check_self {
    ($elem:ident, $name:tt, $ns:ident) => {
        check_self!($elem, $name, $ns, $name);
    };
    ($elem:ident, $name:tt, $ns:ident, $pretty_name:tt) => {
        if !$elem.is($name, crate::ns::$ns) {
            return Err(crate::util::error::Error::ParseError(concat!(
                "This is not a ",
                $pretty_name,
                " element."
            )));
        }
    };
}

macro_rules! check_ns_only {
    ($elem:ident, $name:tt, $ns:ident) => {
        if !$elem.has_ns(crate::ns::$ns) {
            return Err(crate::util::error::Error::ParseError(concat!(
                "This is not a ",
                $name,
                " element."
            )));
        }
    };
}

macro_rules! check_no_children {
    ($elem:ident, $name:tt) => {
        #[cfg(not(feature = "disable-validation"))]
        for _ in $elem.children() {
            return Err(crate::util::error::Error::ParseError(concat!(
                "Unknown child in ",
                $name,
                " element."
            )));
        }
    };
}

macro_rules! check_no_attributes {
    ($elem:ident, $name:tt) => {
        #[cfg(not(feature = "disable-validation"))]
        for _ in $elem.attrs() {
            return Err(crate::util::error::Error::ParseError(concat!(
                "Unknown attribute in ",
                $name,
                " element."
            )));
        }
    };
}

macro_rules! check_no_unknown_attributes {
    ($elem:ident, $name:tt, [$($attr:tt),*]) => (
        #[cfg(not(feature = "disable-validation"))]
        for (_attr, _) in $elem.attrs() {
            $(
                if _attr == $attr {
                    continue;
                }
            )*
            return Err(crate::util::error::Error::ParseError(concat!("Unknown attribute in ", $name, " element.")));
        }
    );
}

macro_rules! generate_empty_element {
    ($(#[$meta:meta])* $elem:ident, $name:tt, $ns:ident) => (
        $(#[$meta])*
        #[derive(Debug, Clone)]
        pub struct $elem;

        impl ::try_from::TryFrom<::minidom::Element> for $elem {
            type Err = crate::util::error::Error;

            fn try_from(elem: ::minidom::Element) -> Result<$elem, crate::util::error::Error> {
                check_self!(elem, $name, $ns);
                check_no_children!(elem, $name);
                check_no_attributes!(elem, $name);
                Ok($elem)
            }
        }

        impl From<$elem> for ::minidom::Element {
            fn from(_: $elem) -> ::minidom::Element {
                ::minidom::Element::builder($name)
                    .ns(crate::ns::$ns)
                    .build()
            }
        }
    );
}

macro_rules! generate_id {
    ($(#[$meta:meta])* $elem:ident) => (
        $(#[$meta])*
        #[derive(Debug, Clone, PartialEq, Eq, Hash)]
        pub struct $elem(pub String);
        impl ::std::str::FromStr for $elem {
            type Err = crate::util::error::Error;
            fn from_str(s: &str) -> Result<$elem, crate::util::error::Error> {
                // TODO: add a way to parse that differently when needed.
                Ok($elem(String::from(s)))
            }
        }
        impl ::minidom::IntoAttributeValue for $elem {
            fn into_attribute_value(self) -> Option<String> {
                Some(self.0)
            }
        }
    );
}

macro_rules! generate_elem_id {
    ($(#[$meta:meta])* $elem:ident, $name:tt, $ns:ident) => (
        $(#[$meta])*
        #[derive(Debug, Clone, PartialEq, Eq, Hash)]
        pub struct $elem(pub String);
        impl ::std::str::FromStr for $elem {
            type Err = crate::util::error::Error;
            fn from_str(s: &str) -> Result<$elem, crate::util::error::Error> {
                // TODO: add a way to parse that differently when needed.
                Ok($elem(String::from(s)))
            }
        }
        impl ::try_from::TryFrom<::minidom::Element> for $elem {
            type Err = crate::util::error::Error;
            fn try_from(elem: ::minidom::Element) -> Result<$elem, crate::util::error::Error> {
                check_self!(elem, $name, $ns);
                check_no_children!(elem, $name);
                check_no_attributes!(elem, $name);
                // TODO: add a way to parse that differently when needed.
                Ok($elem(elem.text()))
            }
        }
        impl From<$elem> for ::minidom::Element {
            fn from(elem: $elem) -> ::minidom::Element {
                ::minidom::Element::builder($name)
                    .ns(crate::ns::$ns)
                    .append(elem.0)
                    .build()
            }
        }
    );
}

macro_rules! decl_attr {
    (OptionEmpty, $type:ty) => (
        Option<$type>
    );
    (Option, $type:ty) => (
        Option<$type>
    );
    (Required, $type:ty) => (
        $type
    );
    (RequiredNonEmpty, $type:ty) => (
        $type
    );
    (Default, $type:ty) => (
        $type
    );
}

macro_rules! start_decl {
    (Vec, $type:ty) => (
        Vec<$type>
    );
    (Option, $type:ty) => (
        Option<$type>
    );
    (Required, $type:ty) => (
        $type
    );
}

macro_rules! start_parse_elem {
    ($temp:ident: Vec) => {
        let mut $temp = Vec::new();
    };
    ($temp:ident: Option) => {
        let mut $temp = None;
    };
    ($temp:ident: Required) => {
        let mut $temp = None;
    };
}

macro_rules! do_parse {
    ($elem:ident, Element) => {
        $elem.clone()
    };
    ($elem:ident, String) => {
        $elem.text()
    };
    ($elem:ident, $constructor:ident) => {
        $constructor::try_from($elem.clone())?
    };
}

macro_rules! do_parse_elem {
    ($temp:ident: Vec = $constructor:ident => $elem:ident, $name:tt, $parent_name:tt) => {
        $temp.push(do_parse!($elem, $constructor));
    };
    ($temp:ident: Option = $constructor:ident => $elem:ident, $name:tt, $parent_name:tt) => {
        if $temp.is_some() {
            return Err(crate::util::error::Error::ParseError(concat!(
                "Element ",
                $parent_name,
                " must not have more than one ",
                $name,
                " child."
            )));
        }
        $temp = Some(do_parse!($elem, $constructor));
    };
    ($temp:ident: Required = $constructor:ident => $elem:ident, $name:tt, $parent_name:tt) => {
        if $temp.is_some() {
            return Err(crate::util::error::Error::ParseError(concat!(
                "Element ",
                $parent_name,
                " must not have more than one ",
                $name,
                " child."
            )));
        }
        $temp = Some(do_parse!($elem, $constructor));
    };
}

macro_rules! finish_parse_elem {
    ($temp:ident: Vec = $name:tt, $parent_name:tt) => {
        $temp
    };
    ($temp:ident: Option = $name:tt, $parent_name:tt) => {
        $temp
    };
    ($temp:ident: Required = $name:tt, $parent_name:tt) => {
        $temp.ok_or(crate::util::error::Error::ParseError(concat!(
            "Missing child ",
            $name,
            " in ",
            $parent_name,
            " element."
        )))?
    };
}

macro_rules! generate_serialiser {
    ($parent:ident, $elem:ident, Required, String, ($name:tt, $ns:ident)) => {
        ::minidom::Element::builder($name)
            .ns(crate::ns::$ns)
            .append($parent.$elem)
            .build()
    };
    ($parent:ident, $elem:ident, Option, String, ($name:tt, $ns:ident)) => {
        $parent.$elem.map(|elem| {
            ::minidom::Element::builder($name)
                .ns(crate::ns::$ns)
                .append(elem)
                .build()
        })
    };
    ($parent:ident, $elem:ident, $_:ident, $constructor:ident, ($name:tt, $ns:ident)) => {
        $parent.$elem
    };
}

macro_rules! generate_element {
    ($(#[$meta:meta])* $elem:ident, $name:tt, $ns:ident, attributes: [$($(#[$attr_meta:meta])* $attr:ident: $attr_action:tt<$attr_type:ty> = $attr_name:tt),+,]) => (
        generate_element!($(#[$meta])* $elem, $name, $ns, attributes: [$($(#[$attr_meta])* $attr: $attr_action<$attr_type> = $attr_name),*], children: []);
    );
    ($(#[$meta:meta])* $elem:ident, $name:tt, $ns:ident, attributes: [$($(#[$attr_meta:meta])* $attr:ident: $attr_action:tt<$attr_type:ty> = $attr_name:tt),+]) => (
        generate_element!($(#[$meta])* $elem, $name, $ns, attributes: [$($(#[$attr_meta])* $attr: $attr_action<$attr_type> = $attr_name),*], children: []);
    );
    ($(#[$meta:meta])* $elem:ident, $name:tt, $ns:ident, children: [$($(#[$child_meta:meta])* $child_ident:ident: $coucou:tt<$child_type:ty> = ($child_name:tt, $child_ns:ident) => $child_constructor:ident),*]) => (
        generate_element!($(#[$meta])* $elem, $name, $ns, attributes: [], children: [$($(#[$child_meta])* $child_ident: $coucou<$child_type> = ($child_name, $child_ns) => $child_constructor),*]);
    );
    ($(#[$meta:meta])* $elem:ident, $name:tt, $ns:ident, attributes: [$($(#[$attr_meta:meta])* $attr:ident: $attr_action:tt<$attr_type:ty> = $attr_name:tt),*,], children: [$($(#[$child_meta:meta])* $child_ident:ident: $coucou:tt<$child_type:ty> = ($child_name:tt, $child_ns:ident) => $child_constructor:ident),*]) => (
        generate_element!($(#[$meta])* $elem, $name, $ns, attributes: [$($(#[$attr_meta])* $attr: $attr_action<$attr_type> = $attr_name),*], children: [$($(#[$child_meta])* $child_ident: $coucou<$child_type> = ($child_name, $child_ns) => $child_constructor),*]);
    );
    ($(#[$meta:meta])* $elem:ident, $name:tt, $ns:ident, text: ($(#[$text_meta:meta])* $text_ident:ident: $codec:ident < $text_type:ty >)) => (
        generate_element!($(#[$meta])* $elem, $name, $ns, attributes: [], children: [], text: ($(#[$text_meta])* $text_ident: $codec<$text_type>));
    );
    ($(#[$meta:meta])* $elem:ident, $name:tt, $ns:ident, attributes: [$($(#[$attr_meta:meta])* $attr:ident: $attr_action:tt<$attr_type:ty> = $attr_name:tt),+], text: ($(#[$text_meta:meta])* $text_ident:ident: $codec:ident < $text_type:ty >)) => (
        generate_element!($(#[$meta])* $elem, $name, $ns, attributes: [$($(#[$attr_meta])* $attr: $attr_action<$attr_type> = $attr_name),*], children: [], text: ($(#[$text_meta])* $text_ident: $codec<$text_type>));
    );
    ($(#[$meta:meta])* $elem:ident, $name:tt, $ns:ident, attributes: [$($(#[$attr_meta:meta])* $attr:ident: $attr_action:tt<$attr_type:ty> = $attr_name:tt),*], children: [$($(#[$child_meta:meta])* $child_ident:ident: $coucou:tt<$child_type:ty> = ($child_name:tt, $child_ns:ident) => $child_constructor:ident),*] $(, text: ($(#[$text_meta:meta])* $text_ident:ident: $codec:ident < $text_type:ty >))*) => (
        $(#[$meta])*
        #[derive(Debug, Clone)]
        pub struct $elem {
            $(
                $(#[$attr_meta])*
                pub $attr: decl_attr!($attr_action, $attr_type),
            )*
            $(
                $(#[$child_meta])*
                pub $child_ident: start_decl!($coucou, $child_type),
            )*
            $(
                $(#[$text_meta])*
                pub $text_ident: $text_type,
            )*
        }

        impl ::try_from::TryFrom<::minidom::Element> for $elem {
            type Err = crate::util::error::Error;

            fn try_from(elem: ::minidom::Element) -> Result<$elem, crate::util::error::Error> {
                check_self!(elem, $name, $ns);
                check_no_unknown_attributes!(elem, $name, [$($attr_name),*]);
                $(
                    start_parse_elem!($child_ident: $coucou);
                )*
                for _child in elem.children() {
                    $(
                    if _child.is($child_name, crate::ns::$child_ns) {
                        do_parse_elem!($child_ident: $coucou = $child_constructor => _child, $child_name, $name);
                        continue;
                    }
                    )*
                    return Err(crate::util::error::Error::ParseError(concat!("Unknown child in ", $name, " element.")));
                }
                Ok($elem {
                    $(
                        $attr: get_attr!(elem, $attr_name, $attr_action),
                    )*
                    $(
                        $child_ident: finish_parse_elem!($child_ident: $coucou = $child_name, $name),
                    )*
                    $(
                        $text_ident: $codec::decode(&elem.text())?,
                    )*
                })
            }
        }

        impl From<$elem> for ::minidom::Element {
            fn from(elem: $elem) -> ::minidom::Element {
                ::minidom::Element::builder($name)
                    .ns(crate::ns::$ns)
                    $(
                        .attr($attr_name, elem.$attr)
                    )*
                    $(
                        .append(generate_serialiser!(elem, $child_ident, $coucou, $child_constructor, ($child_name, $child_ns)))
                    )*
                    $(
                        .append($codec::encode(&elem.$text_ident))
                    )*
                    .build()
            }
        }
    );
}

#[cfg(test)]
macro_rules! assert_size (
    ($t:ty, $sz:expr) => (
        assert_eq!(::std::mem::size_of::<$t>(), $sz);
    );
);

// TODO: move that to src/pubsub/mod.rs, once we figure out how to use macros from there.
macro_rules! impl_pubsub_item {
    ($item:ident, $ns:ident) => {
        impl crate::TryFrom<crate::Element> for $item {
            type Err = Error;

            fn try_from(elem: crate::Element) -> Result<$item, Error> {
                check_self!(elem, "item", $ns);
                check_no_unknown_attributes!(elem, "item", ["id", "publisher"]);
                let mut payloads = elem.children().cloned().collect::<Vec<_>>();
                let payload = payloads.pop();
                if !payloads.is_empty() {
                    return Err(Error::ParseError(
                        "More than a single payload in item element.",
                    ));
                }
                Ok($item(crate::pubsub::Item {
                    id: get_attr!(elem, "id", Option),
                    publisher: get_attr!(elem, "publisher", Option),
                    payload,
                }))
            }
        }

        impl From<$item> for crate::Element {
            fn from(item: $item) -> crate::Element {
                crate::Element::builder("item")
                    .ns(ns::$ns)
                    .attr("id", item.0.id)
                    .attr("publisher", item.0.publisher)
                    .append(item.0.payload)
                    .build()
            }
        }

        impl ::std::ops::Deref for $item {
            type Target = crate::pubsub::Item;

            fn deref(&self) -> &Self::Target {
                &self.0
            }
        }

        impl ::std::ops::DerefMut for $item {
            fn deref_mut(&mut self) -> &mut Self::Target {
                &mut self.0
            }
        }
    }
}