src/interchange/cjson.rs

use itoa;
use json;
use std::collections::BTreeMap;
use std::io;

pub fn canonicalize(jsn: &json::Value) -> Result<Vec<u8>, String> {
    let converted = convert(jsn)?;
    let mut buf = Vec::new();
    let _ = converted.write(&mut buf); // Vec<u8> impl always succeeds (or panics).
    Ok(buf)
}

enum Value {
    Array(Vec<Value>),
    Bool(bool),
    Null,
    Number(Number),
    Object(BTreeMap<String, Value>),
    String(String),
}

impl Value {
    fn write(&self, mut buf: &mut Vec<u8>) -> Result<(), String> {
        match self {
            &Value::Null => Ok(buf.extend(b"null")),
            &Value::Bool(true) => Ok(buf.extend(b"true")),
            &Value::Bool(false) => Ok(buf.extend(b"false")),
            &Value::Number(Number::I64(n)) => {
                itoa::write(buf, n).map(|_| ()).map_err(|err| {
                    format!("Write error: {}", err)
                })
            }
            &Value::Number(Number::U64(n)) => {
                itoa::write(buf, n).map(|_| ()).map_err(|err| {
                    format!("Write error: {}", err)
                })
            }
            &Value::String(ref s) => {
                escape_str(&mut buf, &s).map_err(|err| format!("Write error: {}", err))
            }
            &Value::Array(ref arr) => {
                buf.push(b'[');
                let mut first = true;
                for a in arr.iter() {
                    if !first {
                        buf.push(b',');
                    }
                    a.write(&mut buf)?;
                    first = false;
                }
                Ok(buf.push(b']'))
            }
            &Value::Object(ref obj) => {
                buf.push(b'{');
                let mut first = true;
                for (k, v) in obj.iter() {
                    if !first {
                        buf.push(b',');
                    }
                    first = false;
                    escape_str(&mut buf, &k).map_err(|err| {
                        format!("Write error: {}", err)
                    })?;
                    buf.push(b':');
                    v.write(&mut buf)?;
                }
                Ok(buf.push(b'}'))
            }
        }
    }
}

enum Number {
    I64(i64),
    U64(u64),
}

fn convert(jsn: &json::Value) -> Result<Value, String> {
    match jsn {
        &json::Value::Null => Ok(Value::Null),
        &json::Value::Bool(b) => Ok(Value::Bool(b)),
        &json::Value::Number(ref n) => {
            n.as_i64()
                .map(Number::I64)
                .or(n.as_u64().map(Number::U64))
                .map(Value::Number)
                .ok_or_else(|| String::from("only i64 and u64 are supported"))
        }
        &json::Value::Array(ref arr) => {
            let mut out = Vec::new();
            for res in arr.iter().map(|v| convert(v)) {
                out.push(res?)
            }
            Ok(Value::Array(out))
        }
        &json::Value::Object(ref obj) => {
            let mut out = BTreeMap::new();
            for (k, v) in obj.iter() {
                let _ = out.insert(k.clone(), convert(v)?);
            }
            Ok(Value::Object(out))
        }
        &json::Value::String(ref s) => Ok(Value::String(s.clone())),
    }
}

/// Serializes and escapes a `&str` into a JSON string.
fn escape_str<W>(wr: &mut W, value: &str) -> Result<(), io::Error>
where
    W: io::Write,
{
    let bytes = value.as_bytes();

    wr.write_all(b"\"")?;

    let mut start = 0;

    for (i, &byte) in bytes.iter().enumerate() {
        let escape = ESCAPE[byte as usize];
        if escape == 0 {
            continue;
        }

        if start < i {
            wr.write_all(&bytes[start..i])?;
        }

        wr.write_all(&[b'\\', escape])?;

        start = i + 1;
    }

    if start != bytes.len() {
        wr.write_all(&bytes[start..])?;
    }

    wr.write_all(b"\"")?;
    Ok(())
}

const QU: u8 = b'"'; // \x22
const BS: u8 = b'\\'; // \x5C

// Lookup table of escape sequences. A value of b'x' at index i means that byte
// i is escaped as "\x" in JSON. A value of 0 means that byte i is not escaped.
#[cfg_attr(rustfmt, rustfmt_skip)]
static ESCAPE: [u8; 256] = [
    //  1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, // 0
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, // 1
    0,  0, QU,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, // 2
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, // 3
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, // 4
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, BS,  0,  0,  0, // 5
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, // 6
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, // 7
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, // 8
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, // 9
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, // A
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, // B
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, // C
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, // D
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, // E
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, // F
];

#[cfg(test)]
mod test {
    use super::*;

    use std::fs::File;
    use std::io::Read;

    #[test]
    fn write_str() {
        let jsn = Value::String(String::from("wat"));
        let mut out = Vec::new();
        jsn.write(&mut out).expect("write failed");
        assert_eq!(&out, b"\"wat\"");
    }

    #[test]
    fn write_arr() {
        let jsn = Value::Array(vec![
            Value::String(String::from("wat")),
            Value::String(String::from("lol")),
            Value::String(String::from("no")),
        ]);
        let mut out = Vec::new();
        jsn.write(&mut out).expect("write failed");
        assert_eq!(&out, b"[\"wat\",\"lol\",\"no\"]");
    }

    #[test]
    fn write_obj() {
        let mut map = BTreeMap::new();
        let arr = Value::Array(vec![
            Value::String(String::from("haha")),
            Value::String(String::from("omg so tired")),
        ]);
        let _ = map.insert(String::from("lol"), arr);
        let jsn = Value::Object(map);
        let mut out = Vec::new();
        jsn.write(&mut out).expect("write failed");
        assert_eq!(&out, b"{\"lol\":[\"haha\",\"omg so tired\"]}");
    }

    #[test]
    fn root_json() {
        let mut file = File::open("./tests/cjson/root.json").expect("couldn't open root.json");
        let mut buf = String::new();
        file.read_to_string(&mut buf).expect(
            "couldn't read root.json",
        );

        let mut file = File::open("./tests/cjson/root.cjson").expect("couldn't open root.cjson");
        let mut cjsn = String::new();
        file.read_to_string(&mut cjsn).expect(
            "couldn't read root.cjson",
        );

        let ref jsn = json::from_str(&buf).expect("not json");
        let out = canonicalize(jsn).expect("couldn't canonicalize");
        let out = ::std::str::from_utf8(&out).expect("not utf-8");

        assert_eq!(out, cjsn);
    }
}