Allow integer map keys to accept string-encoded integers

src/de.rs

@@ -972,6 +972,160 @@ where
     }
 }
 
+// A wrapper around `visitor` to convert strings to integers. An version of this
+// struct is created for each integer type `$numtype` (e.g. u16). Any call to
+// `visit_str()` for this visitor will attempt to parse it to `$numtype` and pass
+// call `visit_$numtype()` on the wrapped visitor. Calls to `visit_$numtype()` are
+// passed through directly. All other visits result in an error.
+macro_rules! int_or_string_visitor {
+    ($visitor_name:ident, $visit:ident, $numtype:ty) => {
+        struct $visitor_name<'de, V: de::Visitor<'de>> {
+            inner_visitor: V,
+            _phantom_data: std::marker::PhantomData<&'de ()>,
+        }
+
+        impl<'de, V: de::Visitor<'de>> de::Visitor<'_> for $visitor_name<'de, V> {
+            type Value = V::Value;
+
+            fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
+                write!(formatter, "an integer or string-encoded integer key")
+            }
+
+            fn visit_str<E>(self, v: &str) -> std::result::Result<Self::Value, E>
+            where
+                E: de::Error,
+            {
+                let num = v.parse().map_err(|e| E::custom(e))?;
+                self.inner_visitor.$visit(num)
+            }
+
+            fn $visit<E>(self, v: $numtype) -> std::result::Result<Self::Value, E>
+            where
+                E: de::Error,
+            {
+                self.inner_visitor.$visit(v)
+            }
+        }
+    };
+}
+
+int_or_string_visitor!(IntOrStringVisitorI8, visit_i8, i8);
+int_or_string_visitor!(IntOrStringVisitorI16, visit_i16, i16);
+int_or_string_visitor!(IntOrStringVisitorI32, visit_i32, i32);
+int_or_string_visitor!(IntOrStringVisitorI64, visit_i64, i64);
+int_or_string_visitor!(IntOrStringVisitorU8, visit_u8, u8);
+int_or_string_visitor!(IntOrStringVisitorU16, visit_u16, u16);
+int_or_string_visitor!(IntOrStringVisitorU32, visit_u32, u32);
+int_or_string_visitor!(IntOrStringVisitorU64, visit_u64, u64);
+
+serde::serde_if_integer128! {
+    int_or_string_visitor!(IntOrStringVisitorI128, visit_i128, i128);
+    int_or_string_visitor!(IntOrStringVisitorU128, visit_u128, u128);
+}
+
+// A type that can deserialize strings of integers (e.g. "4") to integers.
+// This is necessary for compatibility with serde_json.
+struct MapKey<'a, R> {
+    de: &'a mut Deserializer<R>,
+}
+
+macro_rules! deserialize_integer_key {
+    ($visitor_name:ident, $method:ident) => {
+        fn $method<V>(self, visitor: V) -> Result<V::Value>
+        where
+            V: de::Visitor<'de>,
+        {
+            // Deserialize the next value, which should be either an integer
+            // of the type corresponding to $visitor_name, (e.g. u16), or it
+            // should be a string that can be parsed to that type.
+            self.de.deserialize_any($visitor_name {
+                inner_visitor: visitor,
+                _phantom_data: Default::default(),
+            })
+        }
+    };
+}
+
+impl<'de, 'a, R> de::Deserializer<'de> for MapKey<'a, R>
+where
+    R: Read<'de>,
+{
+    type Error = Error;
+
+    #[inline]
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.de.deserialize_any(visitor)
+    }
+
+    deserialize_integer_key!(IntOrStringVisitorI8, deserialize_i8);
+    deserialize_integer_key!(IntOrStringVisitorI16, deserialize_i16);
+    deserialize_integer_key!(IntOrStringVisitorI32, deserialize_i32);
+    deserialize_integer_key!(IntOrStringVisitorI64, deserialize_i64);
+    deserialize_integer_key!(IntOrStringVisitorU8, deserialize_u8);
+    deserialize_integer_key!(IntOrStringVisitorU16, deserialize_u16);
+    deserialize_integer_key!(IntOrStringVisitorU32, deserialize_u32);
+    deserialize_integer_key!(IntOrStringVisitorU64, deserialize_u64);
+
+    serde::serde_if_integer128! {
+        deserialize_integer_key!(IntOrStringVisitorI128, deserialize_i128);
+        deserialize_integer_key!(IntOrStringVisitorU128, deserialize_u128);
+    }
+
+    #[inline]
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        // Map keys cannot be null.
+        visitor.visit_some(self)
+    }
+
+    #[inline]
+    fn deserialize_newtype_struct<V>(self, _name: &'static str, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_newtype_struct(self)
+    }
+
+    #[inline]
+    fn deserialize_enum<V>(
+        self,
+        name: &'static str,
+        variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.de.deserialize_enum(name, variants, visitor)
+    }
+
+    #[inline]
+    fn deserialize_bytes<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.de.deserialize_bytes(visitor)
+    }
+
+    #[inline]
+    fn deserialize_byte_buf<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.de.deserialize_bytes(visitor)
+    }
+
+    serde::forward_to_deserialize_any! {
+        bool f32 f64 char str string unit unit_struct seq tuple tuple_struct map
+        struct identifier ignored_any
+    }
+}
+
 struct MapAccess<'a, R> {
     de: &'a mut Deserializer<R>,
     len: &'a mut usize,
@@ -1004,7 +1158,8 @@ where
             _ => {}
         };
 
-        let value = seed.deserialize(&mut *self.de)?;
+        let value = seed.deserialize(MapKey { de: &mut *self.de })?;
+
         Ok(Some(value))
     }
 

tests/de.rs

@@ -744,4 +744,77 @@ mod std_tests {
         let err = serde_cbor::from_slice::<serde_cbor::Value>(&input).expect_err("recursion limit");
         assert!(err.is_syntax());
     }
+
+    #[test]
+    fn test_int_as_string_map_keys() {
+        use std::collections::HashMap;
+
+        // Given a map with keys that are strings, but happen to be strings of integers
+        // e.g. "4", try to deserialize it into a HashMap<i32, ...>. This should
+        // work to have compatibility with serde_json.
+        let mut input = HashMap::<String, i32>::new();
+        input.insert("1".to_string(), 1);
+        input.insert("12345".to_string(), 2);
+        input.insert("-2".to_string(), 3);
+        let buf = to_vec(&input).unwrap();
+
+        let deserialized = from_slice::<HashMap<i16, i32>>(&buf).unwrap();
+
+        assert_eq!(deserialized.len(), 3);
+        assert_eq!(deserialized.get(&1), Some(&1));
+        assert_eq!(deserialized.get(&12345), Some(&2));
+        assert_eq!(deserialized.get(&-2), Some(&3));
+    }
+
+    #[test]
+    fn test_int_as_string_map_keys_unsigned_err() {
+        use std::collections::HashMap;
+
+        let mut input = HashMap::<String, i32>::new();
+        input.insert("1".to_string(), 1);
+        input.insert("-2".to_string(), 3);
+        let buf = to_vec(&input).unwrap();
+
+        // Should fail because key is negative.
+        from_slice::<HashMap<u16, i32>>(&buf).expect_err("");
+    }
+
+    #[test]
+    fn test_int_as_string_map_keys_out_of_range() {
+        use std::collections::HashMap;
+
+        let mut input = HashMap::<String, i32>::new();
+        input.insert("1".to_string(), 1);
+        input.insert("12345".to_string(), 2);
+        let buf = to_vec(&input).unwrap();
+
+        // Should fail because key is out of range.
+        from_slice::<HashMap<u8, i32>>(&buf).expect_err("");
+    }
+
+    #[test]
+    fn test_int_as_string_map_keys_empty() {
+        use std::collections::HashMap;
+
+        let mut input = HashMap::<String, i32>::new();
+        input.insert("1".to_string(), 1);
+        input.insert("".to_string(), 2);
+        let buf = to_vec(&input).unwrap();
+
+        // Should fail because key is empty
+        from_slice::<HashMap<u8, i32>>(&buf).expect_err("");
+    }
+
+    #[test]
+    fn test_int_as_string_map_keys_invalid() {
+        use std::collections::HashMap;
+
+        let mut input = HashMap::<String, i32>::new();
+        input.insert("1".to_string(), 1);
+        input.insert("12.5".to_string(), 2);
+        let buf = to_vec(&input).unwrap();
+
+        // Should fail because key is not an integer
+        from_slice::<HashMap<u8, i32>>(&buf).expect_err("");
+    }
 }