jsony 0.1.10

An experimental fast compiling serialization and deserialization library for JSON like formats.
Documentation 
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use crate::{MaybeJson, json::DecodeError, parser::InnerParser, text::Ctx};

use crate::{FromJson, JsonError, JsonParserConfig, from_json_with_config};

static OBJECT_INDEX_ERROR: DecodeError = DecodeError {
    message: "Object Key Index Error",
};

static ARRAY_INDEX_ERROR_0: DecodeError = DecodeError {
    message: "Array Index of 0 is out of range",
};
static ARRAY_INDEX_ERROR_1: DecodeError = DecodeError {
    message: "Array Index of 1 is out of range",
};
static ARRAY_INDEX_ERROR_2: DecodeError = DecodeError {
    message: "Array Index of 2 is out of range",
};
static ARRAY_INDEX_ERROR_N: DecodeError = DecodeError {
    message: "Array Index out of range",
};

impl std::ops::Index<&'static &'static str> for MaybeJson {
    type Output = MaybeJson;

    /// If the current value is an object, get the value of the corresponding key
    fn index(&self, key: &'static &'static str) -> &Self::Output {
        if self.is_error() {
            return self;
        }
        let mut parser = InnerParser {
            index: 0,
            ctx: Ctx::new(&self.raw),
            config: Default::default(),
        };
        match parser.index_object(key) {
            // SAFETY: `parser.ctx.input` came from `self.raw`, which is valid
            // UTF-8. Parser indices are kept at ASCII token boundaries, so this
            // suffix starts on a UTF-8 boundary.
            Ok(true) => MaybeJson::new(unsafe {
                std::str::from_utf8_unchecked(&parser.ctx.input[parser.index..])
            }),
            Ok(false) => MaybeJson::from_object_index_error(key),
            Err(err) => MaybeJson::from_decode_error(err),
        }
    }
}

impl std::ops::Index<&str> for MaybeJson {
    type Output = MaybeJson;

    /// If the current value is an object, get the value of the corresponding key
    fn index(&self, key: &str) -> &Self::Output {
        if self.is_error() {
            return self;
        }
        let mut parser = InnerParser {
            index: 0,
            ctx: Ctx::new(&self.raw),
            config: Default::default(),
        };
        match parser.index_object(key) {
            // SAFETY: `parser.ctx.input` came from `self.raw`, which is valid
            // UTF-8. Parser indices are kept at ASCII token boundaries, so this
            // suffix starts on a UTF-8 boundary.
            Ok(true) => MaybeJson::new(unsafe {
                std::str::from_utf8_unchecked(&parser.ctx.input[parser.index..])
            }),
            Ok(false) => MaybeJson::from_decode_error(&OBJECT_INDEX_ERROR),
            Err(err) => MaybeJson::from_decode_error(err),
        }
    }
}

impl std::ops::Index<usize> for MaybeJson {
    type Output = MaybeJson;

    /// If the current value is an array, get the value of the corresponding index
    fn index(&self, index: usize) -> &Self::Output {
        if self.is_error() {
            return self;
        }
        let mut parser = InnerParser {
            index: 0,
            ctx: Ctx::new(&self.raw),
            config: Default::default(),
        };
        match parser.index_array(index) {
            // SAFETY: `parser.ctx.input` came from `self.raw`, which is valid
            // UTF-8. Parser indices are kept at ASCII token boundaries, so this
            // suffix starts on a UTF-8 boundary.
            Ok(true) => MaybeJson::new(unsafe {
                std::str::from_utf8_unchecked(&parser.ctx.input[parser.index..])
            }),
            Ok(false) => MaybeJson::from_decode_error(match index {
                0 => &ARRAY_INDEX_ERROR_0,
                1 => &ARRAY_INDEX_ERROR_1,
                2 => &ARRAY_INDEX_ERROR_2,
                _ => &ARRAY_INDEX_ERROR_N,
            }),
            Err(err) => MaybeJson::from_decode_error(err),
        }
    }
}

impl std::fmt::Debug for MaybeJson {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        if let Some(error) = self.decode_error() {
            let mut builder = f.debug_struct("MaybeJson");
            builder.field("error", error);
            if let Some(key) = self.key_error() {
                builder.field("key", &key);
            }
            builder.finish()
        } else {
            f.debug_struct("MaybeJson")
                .field("raw", &&self.raw)
                .finish()
        }
    }
}

impl MaybeJson {
    pub fn from_object_index_error(key: &'static &'static str) -> &'static MaybeJson {
        let ptr = (key as *const &'static str as *const u8).expose_provenance();
        let ptr = std::ptr::with_exposed_provenance::<u8>(ptr | 1);
        // SAFETY: `MaybeJson` is `repr(transparent)` over `str`. A zero-length
        // `str` may use a non-null dangling data pointer; here the pointer is
        // tagged with bit 0 to encode the missing-key state and is never
        // dereferenced as string data.
        unsafe { &*(core::ptr::slice_from_raw_parts(ptr, 0) as *const MaybeJson) }
    }
    pub fn from_decode_error(decode_error: &'static DecodeError) -> &'static MaybeJson {
        // We use exposed provenance here, so we can use
        // `with_exposed_provenance` when casting back the error. A zero-length
        // `str` reference does not carry a usable Stacked Borrows tag for
        // reading the stored static pointer back directly.
        let decode_error = (decode_error as *const DecodeError).expose_provenance();
        // SAFETY: `MaybeJson` is `repr(transparent)` over `str`, and a
        // zero-length `str` may use a non-null dangling data pointer. The data
        // pointer stores the exposed address of a `'static DecodeError` and is
        // recognized by `is_error` before any string access.
        unsafe {
            &*(core::ptr::slice_from_raw_parts(
                std::ptr::with_exposed_provenance::<u8>(decode_error),
                0,
            ) as *const MaybeJson)
        }
    }
    pub const fn const_from_decode_error(decode_error: &'static DecodeError) -> &'static MaybeJson {
        // SAFETY: same zero-length `MaybeJson` error representation as
        // `from_decode_error`. This const path cannot use exposed-provenance
        // helpers, but it stores a pointer to a `'static DecodeError` and never
        // dereferences it as string data.
        unsafe {
            &*(core::ptr::slice_from_raw_parts(decode_error as *const _ as *const u8, 0)
                as *const MaybeJson)
        }
    }
    pub fn parse<'a, T: FromJson<'a>>(&'a self) -> Result<T, JsonError> {
        if let Some(error) = self.json_error() {
            return Err(error);
        }
        from_json_with_config::<'a, T>(
            &self.raw,
            JsonParserConfig {
                recursion_limit: 128,
                allow_trailing_commas: false,
                allow_comments: false,
                allow_unquoted_field_keys: false,
                allow_trailing_data: true,
            },
        )
    }

    pub fn json_error(&self) -> Option<JsonError> {
        let Some(error) = self.decode_error() else {
            return None;
        };
        let mut context: Option<String> = None;
        if error == &OBJECT_INDEX_ERROR {
            if let Some(key) = self.key_error() {
                context = Some(format!("Object key not found: {key:?}"));
            }
        }
        Some(JsonError::new(error, context))
    }

    pub fn decode_error(&self) -> Option<&'static DecodeError> {
        if !self.is_error() {
            return None;
        }
        let tagged = self.raw.as_ptr() as usize;
        if tagged & 0b1 == 1 {
            Some(&OBJECT_INDEX_ERROR)
        } else {
            // SAFETY: non-key error values are created by `from_decode_error`,
            // which stores the exposed address of a `'static DecodeError` in
            // the zero-length string data pointer.
            Some(unsafe { &*(std::ptr::with_exposed_provenance(self.raw.as_ptr().addr())) })
        }
    }

    /// If the value is currently a MissingObjectKey get the key that causes
    /// error is possible.
    pub fn key_error(&self) -> Option<&'static str> {
        if !self.is_error() {
            return None;
        }
        let tagged = self.raw.as_ptr() as usize;
        if tagged & 0b1 == 1 {
            let ptr = std::ptr::with_exposed_provenance(self.raw.as_ptr().addr() & !0b1);
            // SAFETY: key-error values are created by
            // `from_object_index_error`, which stores the address of a
            // `&'static str` slot with bit 0 set. Clearing the tag recovers the
            // original aligned address.
            Some(unsafe { *(ptr as *const &'static str) })
        } else {
            None
        }
    }

    pub fn is_error(&self) -> bool {
        self.raw.is_empty()
    }

    pub fn null() -> &'static MaybeJson {
        MaybeJson::new("null")
    }

    pub fn new(raw: &str) -> &MaybeJson {
        if raw.is_empty() {
            MaybeJson::from_decode_error(&DecodeError {
                message: "Empty object is not valid JSON",
            })
        } else {
            // SAFETY: `MaybeJson` is `repr(transparent)` over `str`, so a
            // non-empty `&str` has the same reference layout. Non-empty strings
            // are not used for the tagged error representation.
            unsafe { &*(raw as *const str as *const MaybeJson) }
        }
    }
}

#[cfg(test)]
mod test {
    use super::*;
    #[test]
    fn keys_with_escapes() {
        let input = r#"{"v\r\f\n\t\"\\": 23, "\u0031\u0032\u0033": 41}"#;
        let json = MaybeJson::new(input);
        assert_eq!(23u32, json["v\r\x0C\n\t\"\\"].parse().unwrap());
        assert_eq!(41u32, json["123"].parse().unwrap());
    }

    #[test]
    fn arrays() {
        let value = MaybeJson::new(stringify!([
            {
                "inner": [42, "nice"]
            },
            "wow",
            false,
            true,
            -123.456,
            null
        ]));
        assert_eq!(42u64, value[0]["inner"][0].parse::<u64>().unwrap());
        assert_eq!("nice", value[0]["inner"][1].parse::<String>().unwrap());
        assert_eq!("wow", value[1].parse::<String>().unwrap());
        assert!(!value[2].parse::<bool>().unwrap());
        assert!(value[3].parse::<bool>().unwrap());
        assert_eq!(-123.456, value[4].parse::<f64>().unwrap());
        assert_eq!(None::<u32>, value[5].parse::<Option<u32>>().unwrap());
    }

    #[test]
    fn errors() {
        let value = MaybeJson::new(stringify!({
            "hello": 124,
            "nice": {"inner": [1,2,3]}
        }));
        assert_eq!(value["nice"]["inner"][0].parse::<u64>().unwrap(), 1);
        assert!(MaybeJson::new("[]")[0].decode_error().is_some());
        assert!(value["nice"]["inner"][5].decode_error().is_some());

        assert_eq!(value[&"nice"][&"not_inner"].key_error(), Some("not_inner"));

        assert!(value["nice"]["not_inner"].decode_error().is_some());

        assert!(value[0].decode_error().is_some());

        assert!(
            value["nice"]["inner"]["key_for_array"]
                .decode_error()
                .is_some()
        );
    }
}