Ensure, that map keys are non-complex types that would not break XML markup

Author: Mingun

Changelog.md

@@ -17,6 +17,7 @@
 ### Misc Changes
 
 - [#468]: Content of `DeError::Unsupported` changed from `&'static str` to `Cow<'static, str>`
+- [#468]: Ensure, that map keys could only types that serialized as primitives only
 
 [#468]: https://github.com/tafia/quick-xml/pull/468
 

src/errors.rs

@@ -294,4 +294,11 @@ pub mod serialize {
             Self::InvalidFloat(e)
         }
     }
+
+    impl From<fmt::Error> for DeError {
+        #[inline]
+        fn from(e: fmt::Error) -> Self {
+            Self::Custom(e.to_string())
+        }
+    }
 }

src/se/key.rs

@@ -0,0 +1,297 @@
+use crate::errors::serialize::DeError;
+use serde::ser::{Impossible, Serialize, Serializer};
+use serde::serde_if_integer128;
+use std::fmt::Write;
+
+/// A serializer, that ensures, that only plain types can be serialized,
+/// so result can be used as an XML tag or attribute name.
+///
+/// This serializer does not check that name does not contain characters that
+/// [not allowed] in XML names, because in some cases it should pass names
+/// that would be filtered on higher level.
+///
+/// [not allowed]: https://www.w3.org/TR/REC-xml/#sec-common-syn
+pub struct XmlNameSerializer<W: Write> {
+    /// Writer to which this serializer writes content
+    pub writer: W,
+}
+
+impl<W: Write> XmlNameSerializer<W> {
+    #[inline]
+    fn write_str(&mut self, value: &str) -> Result<(), DeError> {
+        Ok(self.writer.write_str(value)?)
+    }
+}
+
+impl<W: Write> Serializer for XmlNameSerializer<W> {
+    type Ok = W;
+    type Error = DeError;
+
+    type SerializeSeq = Impossible<Self::Ok, Self::Error>;
+    type SerializeTuple = Impossible<Self::Ok, Self::Error>;
+    type SerializeTupleStruct = Impossible<Self::Ok, Self::Error>;
+    type SerializeTupleVariant = Impossible<Self::Ok, Self::Error>;
+    type SerializeMap = Impossible<Self::Ok, Self::Error>;
+    type SerializeStruct = Impossible<Self::Ok, Self::Error>;
+    type SerializeStructVariant = Impossible<Self::Ok, Self::Error>;
+
+    write_primitive!();
+
+    fn serialize_str(mut self, value: &str) -> Result<Self::Ok, Self::Error> {
+        self.write_str(value)?;
+        Ok(self.writer)
+    }
+
+    /// We cannot store anything, so the absence of a unit and presence of it
+    /// does not differ, so serialization of unit returns `Err(Unsupported)`
+    fn serialize_unit(self) -> Result<Self::Ok, Self::Error> {
+        Err(DeError::Unsupported(
+            "unit type `()` cannot be serialized as an XML tag name".into(),
+        ))
+    }
+
+    /// We cannot store both a variant discriminant and a variant value,
+    /// so serialization of enum newtype variant returns `Err(Unsupported)`
+    fn serialize_newtype_variant<T: ?Sized + Serialize>(
+        self,
+        name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        _value: &T,
+    ) -> Result<Self::Ok, DeError> {
+        Err(DeError::Unsupported(
+            format!(
+                "enum newtype variant `{}::{}` cannot be serialized as an XML tag name",
+                name, variant
+            )
+            .into(),
+        ))
+    }
+
+    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq, Self::Error> {
+        Err(DeError::Unsupported(
+            "sequence cannot be serialized as an XML tag name".into(),
+        ))
+    }
+
+    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple, Self::Error> {
+        Err(DeError::Unsupported(
+            "tuple cannot be serialized as an XML tag name".into(),
+        ))
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleStruct, Self::Error> {
+        Err(DeError::Unsupported(
+            format!(
+                "tuple struct `{}` cannot be serialized as an XML tag name",
+                name
+            )
+            .into(),
+        ))
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleVariant, Self::Error> {
+        Err(DeError::Unsupported(
+            format!(
+                "enum tuple variant `{}::{}` cannot be serialized as an XML tag name",
+                name, variant
+            )
+            .into(),
+        ))
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap, Self::Error> {
+        Err(DeError::Unsupported(
+            "map cannot be serialized as an XML tag name".into(),
+        ))
+    }
+
+    fn serialize_struct(
+        self,
+        name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStruct, Self::Error> {
+        Err(DeError::Unsupported(
+            format!("struct `{}` cannot be serialized as an XML tag name", name).into(),
+        ))
+    }
+
+    fn serialize_struct_variant(
+        self,
+        name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant, Self::Error> {
+        Err(DeError::Unsupported(
+            format!(
+                "enum struct variant `{}::{}` cannot be serialized as an XML tag name",
+                name, variant
+            )
+            .into(),
+        ))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::utils::Bytes;
+    use pretty_assertions::assert_eq;
+    use serde::Serialize;
+    use std::collections::BTreeMap;
+
+    #[derive(Debug, Serialize, PartialEq)]
+    struct Unit;
+
+    #[derive(Debug, Serialize, PartialEq)]
+    #[serde(rename = "<\"&'>")]
+    struct UnitEscaped;
+
+    #[derive(Debug, Serialize, PartialEq)]
+    struct Newtype(bool);
+
+    #[derive(Debug, Serialize, PartialEq)]
+    struct Tuple(&'static str, usize);
+
+    #[derive(Debug, Serialize, PartialEq)]
+    struct Struct {
+        key: &'static str,
+        val: usize,
+    }
+
+    #[derive(Debug, Serialize, PartialEq)]
+    enum Enum {
+        Unit,
+        #[serde(rename = "<\"&'>")]
+        UnitEscaped,
+        Newtype(bool),
+        Tuple(&'static str, usize),
+        Struct {
+            key: &'static str,
+            val: usize,
+        },
+    }
+
+    /// Checks that given `$data` successfully serialized as `$expected`
+    macro_rules! serialize_as {
+        ($name:ident: $data:expr => $expected:literal) => {
+            #[test]
+            fn $name() {
+                let ser = XmlNameSerializer {
+                    writer: String::new(),
+                };
+
+                let buffer = $data.serialize(ser).unwrap();
+                assert_eq!(buffer, $expected);
+            }
+        };
+    }
+
+    /// Checks that attempt to serialize given `$data` results to a
+    /// serialization error `$kind` with `$reason`
+    macro_rules! err {
+        ($name:ident: $data:expr => $kind:ident($reason:literal)) => {
+            #[test]
+            fn $name() {
+                let mut buffer = String::new();
+                let ser = XmlNameSerializer {
+                    writer: &mut buffer,
+                };
+
+                match $data.serialize(ser).unwrap_err() {
+                    DeError::$kind(e) => assert_eq!(e, $reason),
+                    e => panic!(
+                        "Expected `{}({})`, found `{:?}`",
+                        stringify!($kind),
+                        $reason,
+                        e
+                    ),
+                }
+                assert_eq!(buffer, "");
+            }
+        };
+    }
+
+    serialize_as!(false_: false => "false");
+    serialize_as!(true_:  true  => "true");
+
+    serialize_as!(i8_:    -42i8                => "-42");
+    serialize_as!(i16_:   -4200i16             => "-4200");
+    serialize_as!(i32_:   -42000000i32         => "-42000000");
+    serialize_as!(i64_:   -42000000000000i64   => "-42000000000000");
+    serialize_as!(isize_: -42000000000000isize => "-42000000000000");
+
+    serialize_as!(u8_:    42u8                => "42");
+    serialize_as!(u16_:   4200u16             => "4200");
+    serialize_as!(u32_:   42000000u32         => "42000000");
+    serialize_as!(u64_:   42000000000000u64   => "42000000000000");
+    serialize_as!(usize_: 42000000000000usize => "42000000000000");
+
+    serde_if_integer128! {
+        serialize_as!(i128_: -420000000000000000000000000000i128 => "-420000000000000000000000000000");
+        serialize_as!(u128_:  420000000000000000000000000000u128 => "420000000000000000000000000000");
+    }
+
+    serialize_as!(f32_: 4.2f32 => "4.2");
+    serialize_as!(f64_: 4.2f64 => "4.2");
+
+    serialize_as!(char_non_escaped: 'h' => "h");
+    serialize_as!(char_lt:   '<' => "<");
+    serialize_as!(char_gt:   '>' => ">");
+    serialize_as!(char_amp:  '&' => "&");
+    serialize_as!(char_apos: '\'' => "'");
+    serialize_as!(char_quot: '"' => "\"");
+
+    serialize_as!(str_valid_name: "valid-name" => "valid-name");
+    serialize_as!(str_space: "string with spaces" => "string with spaces");
+    serialize_as!(str_lt:   "string<" => "string<");
+    serialize_as!(str_gt:   "string>" => "string>");
+    serialize_as!(str_amp:  "string&" => "string&");
+    serialize_as!(str_apos: "string'" => "string'");
+    serialize_as!(str_quot: "string\"" => "string\"");
+
+    err!(bytes: Bytes(b"<\"escaped & bytes'>")
+        => Unsupported("`serialize_bytes` not supported yet"));
+
+    serialize_as!(option_none: Option::<&str>::None => "");
+    serialize_as!(option_some: Some("non-escaped-string") => "non-escaped-string");
+
+    err!(unit: ()
+        => Unsupported("unit type `()` cannot be serialized as an XML tag name"));
+    serialize_as!(unit_struct: Unit => "Unit");
+    serialize_as!(unit_struct_escaped: UnitEscaped => "<\"&'>");
+
+    serialize_as!(enum_unit: Enum::Unit => "Unit");
+    serialize_as!(enum_unit_escaped: Enum::UnitEscaped => "<\"&'>");
+
+    serialize_as!(newtype: Newtype(true) => "true");
+    err!(enum_newtype: Enum::Newtype(false)
+        => Unsupported("enum newtype variant `Enum::Newtype` cannot be serialized as an XML tag name"));
+
+    err!(seq: vec![1, 2, 3]
+        => Unsupported("sequence cannot be serialized as an XML tag name"));
+    err!(tuple: ("<\"&'>", "with\t\r\n spaces", 3usize)
+        => Unsupported("tuple cannot be serialized as an XML tag name"));
+    err!(tuple_struct: Tuple("first", 42)
+        => Unsupported("tuple struct `Tuple` cannot be serialized as an XML tag name"));
+    err!(enum_tuple: Enum::Tuple("first", 42)
+        => Unsupported("enum tuple variant `Enum::Tuple` cannot be serialized as an XML tag name"));
+
+    err!(map: BTreeMap::from([("_1", 2), ("_3", 4)])
+        => Unsupported("map cannot be serialized as an XML tag name"));
+    err!(struct_: Struct { key: "answer", val: 42 }
+        => Unsupported("struct `Struct` cannot be serialized as an XML tag name"));
+    err!(enum_struct: Enum::Struct { key: "answer", val: 42 }
+        => Unsupported("enum struct variant `Enum::Struct` cannot be serialized as an XML tag name"));
+}