/src/libserialize/json.rs

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// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

// Rust JSON serialization library
// Copyright (c) 2011 Google Inc.

#![forbid(non_camel_case_types)]
#![allow(missing_docs)]

//! JSON parsing and serialization
//!
//! # What is JSON?
//!
//! JSON (JavaScript Object Notation) is a way to write data in Javascript.
//! Like XML, it allows to encode structured data in a text format that can be easily read by humans
//! Its simple syntax and native compatibility with JavaScript have made it a widely used format.
//!
//! Data types that can be encoded are JavaScript types (see the `Json` enum for more details):
//!
//! * `Boolean`: equivalent to rust's `bool`
//! * `Number`: equivalent to rust's `f64`
//! * `String`: equivalent to rust's `String`
//! * `Array`: equivalent to rust's `Vec<T>`, but also allowing objects of different types in the
//!   same array
//! * `Object`: equivalent to rust's `BTreeMap<String, json::Json>`
//! * `Null`
//!
//! An object is a series of string keys mapping to values, in `"key": value` format.
//! Arrays are enclosed in square brackets ([ ... ]) and objects in curly brackets ({ ... }).
//! A simple JSON document encoding a person, their age, address and phone numbers could look like
//!
//! ```ignore
//! {
//!     "FirstName": "John",
//!     "LastName": "Doe",
//!     "Age": 43,
//!     "Address": {
//!         "Street": "Downing Street 10",
//!         "City": "London",
//!         "Country": "Great Britain"
//!     },
//!     "PhoneNumbers": [
//!         "+44 1234567",
//!         "+44 2345678"
//!     ]
//! }
//! ```
//!
//! # Rust Type-based Encoding and Decoding
//!
//! Rust provides a mechanism for low boilerplate encoding & decoding of values to and from JSON via
//! the serialization API.
//! To be able to encode a piece of data, it must implement the `serialize::RustcEncodable` trait.
//! To be able to decode a piece of data, it must implement the `serialize::RustcDecodable` trait.
//! The Rust compiler provides an annotation to automatically generate the code for these traits:
//! `#[derive(RustcDecodable, RustcEncodable)]`
//!
//! The JSON API provides an enum `json::Json` and a trait `ToJson` to encode objects.
//! The `ToJson` trait provides a `to_json` method to convert an object into a `json::Json` value.
//! A `json::Json` value can be encoded as a string or buffer using the functions described above.
//! You can also use the `json::Encoder` object, which implements the `Encoder` trait.
//!
//! When using `ToJson` the `RustcEncodable` trait implementation is not mandatory.
//!
//! # Examples of use
//!
//! ## Using Autoserialization
//!
//! Create a struct called `TestStruct` and serialize and deserialize it to and from JSON using the
//! serialization API, using the derived serialization code.
//!
//! ```rust
//! # #![feature(rustc_private)]
//! extern crate serialize as rustc_serialize; // for the deriving below
//! use rustc_serialize::json;
//!
//! // Automatically generate `Decodable` and `Encodable` trait implementations
//! #[derive(RustcDecodable, RustcEncodable)]
//! pub struct TestStruct  {
//!     data_int: u8,
//!     data_str: String,
//!     data_vector: Vec<u8>,
//! }
//!
//! fn main() {
//!     let object = TestStruct {
//!         data_int: 1,
//!         data_str: "homura".to_string(),
//!         data_vector: vec![2,3,4,5],
//!     };
//!
//!     // Serialize using `json::encode`
//!     let encoded = json::encode(&object).unwrap();
//!
//!     // Deserialize using `json::decode`
//!     let decoded: TestStruct = json::decode(&encoded[..]).unwrap();
//! }
//! ```
//!
//! ## Using the `ToJson` trait
//!
//! The examples above use the `ToJson` trait to generate the JSON string, which is required
//! for custom mappings.
//!
//! ### Simple example of `ToJson` usage
//!
//! ```rust
//! # #![feature(rustc_private)]
//! extern crate serialize;
//! use serialize::json::{self, ToJson, Json};
//!
//! // A custom data structure
//! struct ComplexNum {
//!     a: f64,
//!     b: f64,
//! }
//!
//! // JSON value representation
//! impl ToJson for ComplexNum {
//!     fn to_json(&self) -> Json {
//!         Json::String(format!("{}+{}i", self.a, self.b))
//!     }
//! }
//!
//! // Only generate `RustcEncodable` trait implementation
//! #[derive(Encodable)]
//! pub struct ComplexNumRecord {
//!     uid: u8,
//!     dsc: String,
//!     val: Json,
//! }
//!
//! fn main() {
//!     let num = ComplexNum { a: 0.0001, b: 12.539 };
//!     let data: String = json::encode(&ComplexNumRecord{
//!         uid: 1,
//!         dsc: "test".to_string(),
//!         val: num.to_json(),
//!     }).unwrap();
//!     println!("data: {}", data);
//!     // data: {"uid":1,"dsc":"test","val":"0.0001+12.539i"};
//! }
//! ```
//!
//! ### Verbose example of `ToJson` usage
//!
//! ```rust
//! # #![feature(rustc_private)]
//! extern crate serialize;
//! use std::collections::BTreeMap;
//! use serialize::json::{self, Json, ToJson};
//!
//! // Only generate `Decodable` trait implementation
//! #[derive(Decodable)]
//! pub struct TestStruct {
//!     data_int: u8,
//!     data_str: String,
//!     data_vector: Vec<u8>,
//! }
//!
//! // Specify encoding method manually
//! impl ToJson for TestStruct {
//!     fn to_json(&self) -> Json {
//!         let mut d = BTreeMap::new();
//!         // All standard types implement `to_json()`, so use it
//!         d.insert("data_int".to_string(), self.data_int.to_json());
//!         d.insert("data_str".to_string(), self.data_str.to_json());
//!         d.insert("data_vector".to_string(), self.data_vector.to_json());
//!         Json::Object(d)
//!     }
//! }
//!
//! fn main() {
//!     // Serialize using `ToJson`
//!     let input_data = TestStruct {
//!         data_int: 1,
//!         data_str: "madoka".to_string(),
//!         data_vector: vec![2,3,4,5],
//!     };
//!     let json_obj: Json = input_data.to_json();
//!     let json_str: String = json_obj.to_string();
//!
//!     // Deserialize like before
//!     let decoded: TestStruct = json::decode(&json_str).unwrap();
//! }
//! ```

use self::JsonEvent::*;
use self::ErrorCode::*;
use self::ParserError::*;
use self::DecoderError::*;
use self::ParserState::*;
use self::InternalStackElement::*;

use std::borrow::Cow;
use std::collections::{HashMap, BTreeMap};
use std::io::prelude::*;
use std::io;
use std::mem::swap;
use std::num::FpCategory as Fp;
use std::ops::Index;
use std::str::FromStr;
use std::string;
use std::{char, f64, fmt, str};
use std;

use Encodable;

/// Represents a json value
#[derive(Clone, PartialEq, PartialOrd, Debug)]
pub enum Json {
    I64(i64),
    U64(u64),
    F64(f64),
    String(string::String),
    Boolean(bool),
    Array(self::Array),
    Object(self::Object),
    Null,
}

pub type Array = Vec<Json>;
pub type Object = BTreeMap<string::String, Json>;

pub struct PrettyJson<'a> { inner: &'a Json }

pub struct AsJson<'a, T: 'a> { inner: &'a T }
pub struct AsPrettyJson<'a, T: 'a> { inner: &'a T, indent: Option<usize> }

/// The errors that can arise while parsing a JSON stream.
#[derive(Clone, Copy, PartialEq, Debug)]
pub enum ErrorCode {
    InvalidSyntax,
    InvalidNumber,
    EOFWhileParsingObject,
    EOFWhileParsingArray,
    EOFWhileParsingValue,
    EOFWhileParsingString,
    KeyMustBeAString,
    ExpectedColon,
    TrailingCharacters,
    TrailingComma,
    InvalidEscape,
    InvalidUnicodeCodePoint,
    LoneLeadingSurrogateInHexEscape,
    UnexpectedEndOfHexEscape,
    UnrecognizedHex,
    NotFourDigit,
    NotUtf8,
}

#[derive(Clone, PartialEq, Debug)]
pub enum ParserError {
    /// msg, line, col
    SyntaxError(ErrorCode, usize, usize),
    IoError(io::ErrorKind, String),
}

// Builder and Parser have the same errors.
pub type BuilderError = ParserError;

#[derive(Clone, PartialEq, Debug)]
pub enum DecoderError {
    ParseError(ParserError),
    ExpectedError(string::String, string::String),
    MissingFieldError(string::String),
    UnknownVariantError(string::String),
    ApplicationError(string::String)
}

#[derive(Copy, Clone, Debug)]
pub enum EncoderError {
    FmtError(fmt::Error),
    BadHashmapKey,
}

/// Returns a readable error string for a given error code.
pub fn error_str(error: ErrorCode) -> &'static str {
    match error {
        InvalidSyntax => "invalid syntax",
        InvalidNumber => "invalid number",
        EOFWhileParsingObject => "EOF While parsing object",
        EOFWhileParsingArray => "EOF While parsing array",
        EOFWhileParsingValue => "EOF While parsing value",
        EOFWhileParsingString => "EOF While parsing string",
        KeyMustBeAString => "key must be a string",
        ExpectedColon => "expected `:`",
        TrailingCharacters => "trailing characters",
        TrailingComma => "trailing comma",
        InvalidEscape => "invalid escape",
        UnrecognizedHex => "invalid \\u{ esc}ape (unrecognized hex)",
        NotFourDigit => "invalid \\u{ esc}ape (not four digits)",
        NotUtf8 => "contents not utf-8",
        InvalidUnicodeCodePoint => "invalid Unicode code point",
        LoneLeadingSurrogateInHexEscape => "lone leading surrogate in hex escape",
        UnexpectedEndOfHexEscape => "unexpected end of hex escape",
    }
}

/// Shortcut function to decode a JSON `&str` into an object
pub fn decode<T: ::Decodable>(s: &str) -> DecodeResult<T> {
    let json = match from_str(s) {
        Ok(x) => x,
        Err(e) => return Err(ParseError(e))
    };

    let mut decoder = Decoder::new(json);
    ::Decodable::decode(&mut decoder)
}

/// Shortcut function to encode a `T` into a JSON `String`
pub fn encode<T: ::Encodable>(object: &T) -> Result<string::String, EncoderError> {
    let mut s = String::new();
    {
        let mut encoder = Encoder::new(&mut s);
        object.encode(&mut encoder)?;
    }
    Ok(s)
}

impl fmt::Display for ErrorCode {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        error_str(*self).fmt(f)
    }
}

fn io_error_to_error(io: io::Error) -> ParserError {
    IoError(io.kind(), io.to_string())
}

impl fmt::Display for ParserError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        // FIXME this should be a nicer error
        fmt::Debug::fmt(self, f)
    }
}

impl fmt::Display for DecoderError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        // FIXME this should be a nicer error
        fmt::Debug::fmt(self, f)
    }
}

impl std::error::Error for DecoderError {
    fn description(&self) -> &str { "decoder error" }
}

impl fmt::Display for EncoderError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        // FIXME this should be a nicer error
        fmt::Debug::fmt(self, f)
    }
}

impl std::error::Error for EncoderError {
    fn description(&self) -> &str { "encoder error" }
}

impl From<fmt::Error> for EncoderError {
    fn from(err: fmt::Error) -> EncoderError { EncoderError::FmtError(err) }
}

pub type EncodeResult = Result<(), EncoderError>;
pub type DecodeResult<T> = Result<T, DecoderError>;

fn escape_str(wr: &mut fmt::Write, v: &str) -> EncodeResult {
    wr.write_str("\"")?;

    let mut start = 0;

    for (i, byte) in v.bytes().enumerate() {
        let escaped = match byte {
            b'"' => "\\\"",
            b'\\' => "\\\\",
            b'\x00' => "\\u0000",
            b'\x01' => "\\u0001",
            b'\x02' => "\\u0002",
            b'\x03' => "\\u0003",
            b'\x04' => "\\u0004",
            b'\x05' => "\\u0005",
            b'\x06' => "\\u0006",
            b'\x07' => "\\u0007",
            b'\x08' => "\\b",
            b'\t' => "\\t",
            b'\n' => "\\n",
            b'\x0b' => "\\u000b",
            b'\x0c' => "\\f",
            b'\r' => "\\r",
            b'\x0e' => "\\u000e",
            b'\x0f' => "\\u000f",
            b'\x10' => "\\u0010",
            b'\x11' => "\\u0011",
            b'\x12' => "\\u0012",
            b'\x13' => "\\u0013",
            b'\x14' => "\\u0014",
            b'\x15' => "\\u0015",
            b'\x16' => "\\u0016",
            b'\x17' => "\\u0017",
            b'\x18' => "\\u0018",
            b'\x19' => "\\u0019",
            b'\x1a' => "\\u001a",
            b'\x1b' => "\\u001b",
            b'\x1c' => "\\u001c",
            b'\x1d' => "\\u001d",
            b'\x1e' => "\\u001e",
            b'\x1f' => "\\u001f",
            b'\x7f' => "\\u007f",
            _ => { continue; }
        };

        if start < i {
            wr.write_str(&v[start..i])?;
        }

        wr.write_str(escaped)?;

        start = i + 1;
    }

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

    wr.write_str("\"")?;
    Ok(())
}

fn escape_char(writer: &mut fmt::Write, v: char) -> EncodeResult {
    escape_str(writer, v.encode_utf8(&mut [0; 4]))
}

fn spaces(wr: &mut fmt::Write, mut n: usize) -> EncodeResult {
    const BUF: &'static str = "                ";

    while n >= BUF.len() {
        wr.write_str(BUF)?;
        n -= BUF.len();
    }

    if n > 0 {
        wr.write_str(&BUF[..n])?;
    }
    Ok(())
}

fn fmt_number_or_null(v: f64) -> string::String {
    match v.classify() {
        Fp::Nan | Fp::Infinite => string::String::from("null"),
        _ if v.fract() != 0f64 => v.to_string(),
        _ => v.to_string() + ".0",
    }
}

/// A structure for implementing serialization to JSON.
pub struct Encoder<'a> {
    writer: &'a mut (fmt::Write+'a),
    is_emitting_map_key: bool,
}

impl<'a> Encoder<'a> {
    /// Creates a new JSON encoder whose output will be written to the writer
    /// specified.
    pub fn new(writer: &'a mut fmt::Write) -> Encoder<'a> {
        Encoder { writer: writer, is_emitting_map_key: false, }
    }
}

macro_rules! emit_enquoted_if_mapkey {
    ($enc:ident,$e:expr) => ({
        if $enc.is_emitting_map_key {
            write!($enc.writer, "\"{}\"", $e)?;
        } else {
            write!($enc.writer, "{}", $e)?;
        }
        Ok(())
    })
}

impl<'a> ::Encoder for Encoder<'a> {
    type Error = EncoderError;

    fn emit_nil(&mut self) -> EncodeResult {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        write!(self.writer, "null")?;
        Ok(())
    }

    fn emit_usize(&mut self, v: usize) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_u128(&mut self, v: u128) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_u64(&mut self, v: u64) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_u32(&mut self, v: u32) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_u16(&mut self, v: u16) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_u8(&mut self, v: u8) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }

    fn emit_isize(&mut self, v: isize) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_i128(&mut self, v: i128) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_i64(&mut self, v: i64) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_i32(&mut self, v: i32) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_i16(&mut self, v: i16) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_i8(&mut self, v: i8) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }

    fn emit_bool(&mut self, v: bool) -> EncodeResult {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        if v {
            write!(self.writer, "true")?;
        } else {
            write!(self.writer, "false")?;
        }
        Ok(())
    }

    fn emit_f64(&mut self, v: f64) -> EncodeResult {
        emit_enquoted_if_mapkey!(self, fmt_number_or_null(v))
    }
    fn emit_f32(&mut self, v: f32) -> EncodeResult {
        self.emit_f64(v as f64)
    }

    fn emit_char(&mut self, v: char) -> EncodeResult {
        escape_char(self.writer, v)
    }
    fn emit_str(&mut self, v: &str) -> EncodeResult {
        escape_str(self.writer, v)
    }

    fn emit_enum<F>(&mut self, _name: &str, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        f(self)
    }

    fn emit_enum_variant<F>(&mut self,
                            name: &str,
                            _id: usize,
                            cnt: usize,
                            f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        // enums are encoded as strings or objects
        // Bunny => "Bunny"
        // Kangaroo(34,"William") => {"variant": "Kangaroo", "fields": [34,"William"]}
        if cnt == 0 {
            escape_str(self.writer, name)
        } else {
            if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
            write!(self.writer, "{{\"variant\":")?;
            escape_str(self.writer, name)?;
            write!(self.writer, ",\"fields\":[")?;
            f(self)?;
            write!(self.writer, "]}}")?;
            Ok(())
        }
    }

    fn emit_enum_variant_arg<F>(&mut self, idx: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        if idx != 0 {
            write!(self.writer, ",")?;
        }
        f(self)
    }

    fn emit_enum_struct_variant<F>(&mut self,
                                   name: &str,
                                   id: usize,
                                   cnt: usize,
                                   f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        self.emit_enum_variant(name, id, cnt, f)
    }

    fn emit_enum_struct_variant_field<F>(&mut self,
                                         _: &str,
                                         idx: usize,
                                         f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        self.emit_enum_variant_arg(idx, f)
    }

    fn emit_struct<F>(&mut self, _: &str, _: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        write!(self.writer, "{{")?;
        f(self)?;
        write!(self.writer, "}}")?;
        Ok(())
    }

    fn emit_struct_field<F>(&mut self, name: &str, idx: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        if idx != 0 { write!(self.writer, ",")?; }
        escape_str(self.writer, name)?;
        write!(self.writer, ":")?;
        f(self)
    }

    fn emit_tuple<F>(&mut self, len: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        self.emit_seq(len, f)
    }
    fn emit_tuple_arg<F>(&mut self, idx: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        self.emit_seq_elt(idx, f)
    }

    fn emit_tuple_struct<F>(&mut self, _name: &str, len: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        self.emit_seq(len, f)
    }
    fn emit_tuple_struct_arg<F>(&mut self, idx: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        self.emit_seq_elt(idx, f)
    }

    fn emit_option<F>(&mut self, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        f(self)
    }
    fn emit_option_none(&mut self) -> EncodeResult {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        self.emit_nil()
    }
    fn emit_option_some<F>(&mut self, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        f(self)
    }

    fn emit_seq<F>(&mut self, _len: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        write!(self.writer, "[")?;
        f(self)?;
        write!(self.writer, "]")?;
        Ok(())
    }

    fn emit_seq_elt<F>(&mut self, idx: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        if idx != 0 {
            write!(self.writer, ",")?;
        }
        f(self)
    }

    fn emit_map<F>(&mut self, _len: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        write!(self.writer, "{{")?;
        f(self)?;
        write!(self.writer, "}}")?;
        Ok(())
    }

    fn emit_map_elt_key<F>(&mut self, idx: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        if idx != 0 { write!(self.writer, ",")? }
        self.is_emitting_map_key = true;
        f(self)?;
        self.is_emitting_map_key = false;
        Ok(())
    }

    fn emit_map_elt_val<F>(&mut self, _idx: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        write!(self.writer, ":")?;
        f(self)
    }
}

/// Another encoder for JSON, but prints out human-readable JSON instead of
/// compact data
pub struct PrettyEncoder<'a> {
    writer: &'a mut (fmt::Write+'a),
    curr_indent: usize,
    indent: usize,
    is_emitting_map_key: bool,
}

impl<'a> PrettyEncoder<'a> {
    /// Creates a new encoder whose output will be written to the specified writer
    pub fn new(writer: &'a mut fmt::Write) -> PrettyEncoder<'a> {
        PrettyEncoder {
            writer: writer,
            curr_indent: 0,
            indent: 2,
            is_emitting_map_key: false,
        }
    }

    /// Set the number of spaces to indent for each level.
    /// This is safe to set during encoding.
    pub fn set_indent(&mut self, indent: usize) {
        // self.indent very well could be 0 so we need to use checked division.
        let level = self.curr_indent.checked_div(self.indent).unwrap_or(0);
        self.indent = indent;
        self.curr_indent = level * self.indent;
    }
}

impl<'a> ::Encoder for PrettyEncoder<'a> {
    type Error = EncoderError;

    fn emit_nil(&mut self) -> EncodeResult {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        write!(self.writer, "null")?;
        Ok(())
    }

    fn emit_usize(&mut self, v: usize) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_u128(&mut self, v: u128) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_u64(&mut self, v: u64) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_u32(&mut self, v: u32) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_u16(&mut self, v: u16) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_u8(&mut self, v: u8) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }

    fn emit_isize(&mut self, v: isize) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_i128(&mut self, v: i128) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_i64(&mut self, v: i64) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_i32(&mut self, v: i32) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_i16(&mut self, v: i16) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
    fn emit_i8(&mut self, v: i8) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }

    fn emit_bool(&mut self, v: bool) -> EncodeResult {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        if v {
            write!(self.writer, "true")?;
        } else {
            write!(self.writer, "false")?;
        }
        Ok(())
    }

    fn emit_f64(&mut self, v: f64) -> EncodeResult {
        emit_enquoted_if_mapkey!(self, fmt_number_or_null(v))
    }
    fn emit_f32(&mut self, v: f32) -> EncodeResult {
        self.emit_f64(v as f64)
    }

    fn emit_char(&mut self, v: char) -> EncodeResult {
        escape_char(self.writer, v)
    }
    fn emit_str(&mut self, v: &str) -> EncodeResult {
        escape_str(self.writer, v)
    }

    fn emit_enum<F>(&mut self, _name: &str, f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        f(self)
    }

    fn emit_enum_variant<F>(&mut self,
                            name: &str,
                            _id: usize,
                            cnt: usize,
                            f: F)
                            -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if cnt == 0 {
            escape_str(self.writer, name)
        } else {
            if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
            write!(self.writer, "{{\n")?;
            self.curr_indent += self.indent;
            spaces(self.writer, self.curr_indent)?;
            write!(self.writer, "\"variant\": ")?;
            escape_str(self.writer, name)?;
            write!(self.writer, ",\n")?;
            spaces(self.writer, self.curr_indent)?;
            write!(self.writer, "\"fields\": [\n")?;
            self.curr_indent += self.indent;
            f(self)?;
            self.curr_indent -= self.indent;
            write!(self.writer, "\n")?;
            spaces(self.writer, self.curr_indent)?;
            self.curr_indent -= self.indent;
            write!(self.writer, "]\n")?;
            spaces(self.writer, self.curr_indent)?;
            write!(self.writer, "}}")?;
            Ok(())
        }
    }

    fn emit_enum_variant_arg<F>(&mut self, idx: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        if idx != 0 {
            write!(self.writer, ",\n")?;
        }
        spaces(self.writer, self.curr_indent)?;
        f(self)
    }

    fn emit_enum_struct_variant<F>(&mut self,
                                   name: &str,
                                   id: usize,
                                   cnt: usize,
                                   f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        self.emit_enum_variant(name, id, cnt, f)
    }

    fn emit_enum_struct_variant_field<F>(&mut self,
                                         _: &str,
                                         idx: usize,
                                         f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        self.emit_enum_variant_arg(idx, f)
    }


    fn emit_struct<F>(&mut self, _: &str, len: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        if len == 0 {
            write!(self.writer, "{{}}")?;
        } else {
            write!(self.writer, "{{")?;
            self.curr_indent += self.indent;
            f(self)?;
            self.curr_indent -= self.indent;
            write!(self.writer, "\n")?;
            spaces(self.writer, self.curr_indent)?;
            write!(self.writer, "}}")?;
        }
        Ok(())
    }

    fn emit_struct_field<F>(&mut self, name: &str, idx: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        if idx == 0 {
            write!(self.writer, "\n")?;
        } else {
            write!(self.writer, ",\n")?;
        }
        spaces(self.writer, self.curr_indent)?;
        escape_str(self.writer, name)?;
        write!(self.writer, ": ")?;
        f(self)
    }

    fn emit_tuple<F>(&mut self, len: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        self.emit_seq(len, f)
    }
    fn emit_tuple_arg<F>(&mut self, idx: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        self.emit_seq_elt(idx, f)
    }

    fn emit_tuple_struct<F>(&mut self, _: &str, len: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        self.emit_seq(len, f)
    }
    fn emit_tuple_struct_arg<F>(&mut self, idx: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        self.emit_seq_elt(idx, f)
    }

    fn emit_option<F>(&mut self, f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        f(self)
    }
    fn emit_option_none(&mut self) -> EncodeResult {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        self.emit_nil()
    }
    fn emit_option_some<F>(&mut self, f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        f(self)
    }

    fn emit_seq<F>(&mut self, len: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        if len == 0 {
            write!(self.writer, "[]")?;
        } else {
            write!(self.writer, "[")?;
            self.curr_indent += self.indent;
            f(self)?;
            self.curr_indent -= self.indent;
            write!(self.writer, "\n")?;
            spaces(self.writer, self.curr_indent)?;
            write!(self.writer, "]")?;
        }
        Ok(())
    }

    fn emit_seq_elt<F>(&mut self, idx: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        if idx == 0 {
            write!(self.writer, "\n")?;
        } else {
            write!(self.writer, ",\n")?;
        }
        spaces(self.writer, self.curr_indent)?;
        f(self)
    }

    fn emit_map<F>(&mut self, len: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        if len == 0 {
            write!(self.writer, "{{}}")?;
        } else {
            write!(self.writer, "{{")?;
            self.curr_indent += self.indent;
            f(self)?;
            self.curr_indent -= self.indent;
            write!(self.writer, "\n")?;
            spaces(self.writer, self.curr_indent)?;
            write!(self.writer, "}}")?;
        }
        Ok(())
    }

    fn emit_map_elt_key<F>(&mut self, idx: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        if idx == 0 {
            write!(self.writer, "\n")?;
        } else {
            write!(self.writer, ",\n")?;
        }
        spaces(self.writer, self.curr_indent)?;
        self.is_emitting_map_key = true;
        f(self)?;
        self.is_emitting_map_key = false;
        Ok(())
    }

    fn emit_map_elt_val<F>(&mut self, _idx: usize, f: F) -> EncodeResult where
        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
    {
        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
        write!(self.writer, ": ")?;
        f(self)
    }
}

impl Encodable for Json {
    fn encode<E: ::Encoder>(&self, e: &mut E) -> Result<(), E::Error> {
        match *self {
            Json::I64(v) => v.encode(e),
            Json::U64(v) => v.encode(e),
            Json::F64(v) => v.encode(e),
            Json::String(ref v) => v.encode(e),
            Json::Boolean(v) => v.encode(e),
            Json::Array(ref v) => v.encode(e),
            Json::Object(ref v) => v.encode(e),
            Json::Null => e.emit_nil(),
        }
    }
}

/// Create an `AsJson` wrapper which can be used to print a value as JSON
/// on-the-fly via `write!`
pub fn as_json<T>(t: &T) -> AsJson<T> {
    AsJson { inner: t }
}

/// Create an `AsPrettyJson` wrapper which can be used to print a value as JSON
/// on-the-fly via `write!`
pub fn as_pretty_json<T>(t: &T) -> AsPrettyJson<T> {
    AsPrettyJson { inner: t, indent: None }
}

impl Json {
    /// Borrow this json object as a pretty object to generate a pretty
    /// representation for it via `Display`.
    pub fn pretty(&self) -> PrettyJson {
        PrettyJson { inner: self }
    }

     /// If the Json value is an Object, returns the value associated with the provided key.
    /// Otherwise, returns None.
    pub fn find<'a>(&'a self, key: &str) -> Option<&'a Json>{
        match *self {
            Json::Object(ref map) => map.get(key),
            _ => None
        }
    }

    /// Attempts to get a nested Json Object for each key in `keys`.
    /// If any key is found not to exist, find_path will return None.
    /// Otherwise, it will return the Json value associated with the final key.
    pub fn find_path<'a>(&'a self, keys: &[&str]) -> Option<&'a Json>{
        let mut target = self;
        for key in keys {
            match target.find(*key) {
                Some(t) => { target = t; },
                None => return None
            }
        }
        Some(target)
    }

    /// If the Json value is an Object, performs a depth-first search until
    /// a value associated with the provided key is found. If no value is found
    /// or the Json value is not an Object, returns None.
    pub fn search<'a>(&'a self, key: &str) -> Option<&'a Json> {
        match self {
            &Json::Object(ref map) => {
                match map.get(key) {
                    Some(json_value) => Some(json_value),
                    None => {
                        for (_, v) in map {
                            match v.search(key) {
                                x if x.is_some() => return x,
                                _ => ()
                            }
                        }
                        None
                    }
                }
            },
            _ => None
        }
    }

    /// Returns true if the Json value is an Object. Returns false otherwise.
    pub fn is_object(&self) -> bool {
        self.as_object().is_some()
    }

    /// If the Json value is an Object, returns the associated BTreeMap.
    /// Returns None otherwise.
    pub fn as_object(&self) -> Option<&Object> {
        match *self {
            Json::Object(ref map) => Some(map),
            _ => None
        }
    }

    /// Returns true if the Json value is an Array. Returns false otherwise.
    pub fn is_array(&self) -> bool {
        self.as_array().is_some()
    }

    /// If the Json value is an Array, returns the associated vector.
    /// Returns None otherwise.
    pub fn as_array(&self) -> Option<&Array> {
        match *self {
            Json::Array(ref array) => Some(&*array),
            _ => None
        }
    }

    /// Returns true if the Json value is a String. Returns false otherwise.
    pub fn is_string(&self) -> bool {
        self.as_string().is_some()
    }

    /// If the Json value is a String, returns the associated str.
    /// Returns None otherwise.
    pub fn as_string(&self) -> Option<&str> {
        match *self {
            Json::String(ref s) => Some(&s[..]),
            _ => None
        }
    }

    /// Returns true if the Json value is a Number. Returns false otherwise.
    pub fn is_number(&self) -> bool {
        match *self {
            Json::I64(_) | Json::U64(_) | Json::F64(_) => true,
            _ => false,
        }
    }

    /// Returns true if the Json value is a i64. Returns false otherwise.
    pub fn is_i64(&self) -> bool {
        match *self {
            Json::I64(_) => true,
            _ => false,
        }
    }

    /// Returns true if the Json value is a u64. Returns false otherwise.
    pub fn is_u64(&self) -> bool {
        match *self {
            Json::U64(_) => true,
            _ => false,
        }
    }

    /// Returns true if the Json value is a f64. Returns false otherwise.
    pub fn is_f64(&self) -> bool {
        match *self {
            Json::F64(_) => true,
            _ => false,
        }
    }

    /// If the Json value is a number, return or cast it to a i64.
    /// Returns None otherwise.
    pub fn as_i64(&self) -> Option<i64> {
        match *self {
            Json::I64(n) => Some(n),
            Json::U64(n) => Some(n as i64),
            _ => None
        }
    }

    /// If the Json value is a number, return or cast it to a u64.
    /// Returns None otherwise.
    pub fn as_u64(&self) -> Option<u64> {
        match *self {
            Json::I64(n) => Some(n as u64),
            Json::U64(n) => Some(n),
            _ => None
        }
    }

    /// If the Json value is a number, return or cast it to a f64.
    /// Returns None otherwise.
    pub fn as_f64(&self) -> Option<f64> {
        match *self {
            Json::I64(n) => Some(n as f64),
            Json::U64(n) => Some(n as f64),
            Json::F64(n) => Some(n),
            _ => None
        }
    }

    /// Returns true if the Json value is a Boolean. Returns false otherwise.
    pub fn is_boolean(&self) -> bool {
        self.as_boolean().is_some()
    }

    /// If the Json value is a Boolean, returns the associated bool.
    /// Returns None otherwise.
    pub fn as_boolean(&self) -> Option<bool> {
        match *self {
            Json::Boolean(b) => Some(b),
            _ => None
        }
    }

    /// Returns true if the Json value is a Null. Returns false otherwise.
    pub fn is_null(&self) -> bool {
        self.as_null().is_some()
    }

    /// If the Json value is a Null, returns ().
    /// Returns None otherwise.
    pub fn as_null(&self) -> Option<()> {
        match *self {
            Json::Null => Some(()),
            _ => None
        }
    }
}

impl<'a> Index<&'a str>  for Json {
    type Output = Json;

    fn index(&self, idx: &'a str) -> &Json {
        self.find(idx).unwrap()
    }
}

impl Index<usize> for Json {
    type Output = Json;

    fn index(&self, idx: usize) -> &Json {
        match *self {
            Json::Array(ref v) => &v[idx],
            _ => panic!("can only index Json with usize if it is an array")
        }
    }
}

/// The output of the streaming parser.
#[derive(PartialEq, Clone, Debug)]
pub enum JsonEvent {
    ObjectStart,
    ObjectEnd,
    ArrayStart,
    ArrayEnd,
    BooleanValue(bool),
    I64Value(i64),
    U64Value(u64),
    F64Value(f64),
    StringValue(string::String),
    NullValue,
    Error(ParserError),
}

#[derive(PartialEq, Debug)]
enum ParserState {
    // Parse a value in an array, true means first element.
    ParseArray(bool),
    // Parse ',' or ']' after an element in an array.
    ParseArrayComma,
    // Parse a key:value in an object, true means first element.
    ParseObject(bool),
    // Parse ',' or ']' after an element in an object.
    ParseObjectComma,
    // Initial state.
    ParseStart,
    // Expecting the stream to end.
    ParseBeforeFinish,
    // Parsing can't continue.
    ParseFinished,
}

/// A Stack represents the current position of the parser in the logical
/// structure of the JSON stream.
/// For example foo.bar[3].x
pub struct Stack {
    stack: Vec<InternalStackElement>,
    str_buffer: Vec<u8>,
}

/// StackElements compose a Stack.
/// For example, StackElement::Key("foo"), StackElement::Key("bar"),
/// StackElement::Index(3) and StackElement::Key("x") are the
/// StackElements compositing the stack that represents foo.bar[3].x
#[derive(PartialEq, Clone, Debug)]
pub enum StackElement<'l> {
    Index(u32),
    Key(&'l str),
}

// Internally, Key elements are stored as indices in a buffer to avoid
// allocating a string for every member of an object.
#[derive(PartialEq, Clone, Debug)]
enum InternalStackElement {
    InternalIndex(u32),
    InternalKey(u16, u16), // start, size
}

impl Stack {
    pub fn new() -> Stack {
        Stack { stack: Vec::new(), str_buffer: Vec::new() }
    }

    /// Returns The number of elements in the Stack.
    pub fn len(&self) -> usize { self.stack.len() }

    /// Returns true if the stack is empty.
    pub fn is_empty(&self) -> bool { self.stack.is_empty() }

    /// Provides access to the StackElement at a given index.
    /// lower indices are at the bottom of the stack while higher indices are
    /// at the top.
    pub fn get(&self, idx: usize) -> StackElement {
        match self.stack[idx] {
            InternalIndex(i) => StackElement::Index(i),
            InternalKey(start, size) => {
                StackElement::Key(str::from_utf8(
                    &self.str_buffer[start as usize .. start as usize + size as usize])
                        .unwrap())
            }
        }
    }

    /// Compares this stack with an array of StackElements.
    pub fn is_equal_to(&self, rhs: &[StackElement]) -> bool {
        if self.stack.len() != rhs.len() { return false; }
        for (i, r) in rhs.iter().enumerate() {
            if self.get(i) != *r { return false; }
        }
        true
    }

    /// Returns true if the bottom-most elements of this stack are the same as
    /// the ones passed as parameter.
    pub fn starts_with(&self, rhs: &[StackElement]) -> bool {
        if self.stack.len() < rhs.len() { return false; }
        for (i, r) in rhs.iter().enumerate() {
            if self.get(i) != *r { return false; }
        }
        true
    }

    /// Returns true if the top-most elements of this stack are the same as
    /// the ones passed as parameter.
    pub fn ends_with(&self, rhs: &[StackElement]) -> bool {
        if self.stack.len() < rhs.len() { return false; }
        let offset = self.stack.len() - rhs.len();
        for (i, r) in rhs.iter().enumerate() {
            if self.get(i + offset) != *r { return false; }
        }
        true
    }

    /// Returns the top-most element (if any).
    pub fn top(&self) -> Option<StackElement> {
        match self.stack.last() {
            None => None,
            Some(&InternalIndex(i)) => Some(StackElement::Index(i)),
            Some(&InternalKey(start, size)) => {
                Some(StackElement::Key(str::from_utf8(
                    &self.str_buffer[start as usize .. (start+size) as usize]
                ).unwrap()))
            }
        }
    }

    // Used by Parser to insert StackElement::Key elements at the top of the stack.
    fn push_key(&mut self, key: string::String) {
        self.stack.push(InternalKey(self.str_buffer.len() as u16, key.len() as u16));
        for c in key.as_bytes() {
            self.str_buffer.push(*c);
        }
    }

    // Used by Parser to insert StackElement::Index elements at the top of the stack.
    fn push_index(&mut self, index: u32) {
        self.stack.push(InternalIndex(index));
    }

    // Used by Parser to remove the top-most element of the stack.
    fn pop(&mut self) {
        assert!(!self.is_empty());
        match *self.stack.last().unwrap() {
            InternalKey(_, sz) => {
                let new_size = self.str_buffer.len() - sz as usize;
                self.str_buffer.truncate(new_size);
            }
            InternalIndex(_) => {}
        }
        self.stack.pop();
    }

    // Used by Parser to test whether the top-most element is an index.
    fn last_is_index(&self) -> bool {
        if self.is_empty() { return false; }
        return match *self.stack.last().unwrap() {
            InternalIndex(_) => true,
            _ => false,
        }
    }

    // Used by Parser to increment the index of the top-most element.
    fn bump_index(&mut self) {
        let len = self.stack.len();
        let idx = match *self.stack.last().unwrap() {
            InternalIndex(i) => { i + 1 }
            _ => { panic!(); }
        };
        self.stack[len - 1] = InternalIndex(idx);
    }
}

/// A streaming JSON parser implemented as an iterator of JsonEvent, consuming
/// an iterator of char.
pub struct Parser<T> {
    rdr: T,
    ch: Option<char>,
    line: usize,
    col: usize,
    // We maintain a stack representing where we are in the logical structure
    // of the JSON stream.
    stack: Stack,
    // A state machine is kept to make it possible to interrupt and resume parsing.
    state: ParserState,
}

impl<T: Iterator<Item=char>> Iterator for Parser<T> {
    type Item = JsonEvent;

    fn next(&mut self) -> Option<JsonEvent> {
        if self.state == ParseFinished {
            return None;
        }

        if self.state == ParseBeforeFinish {
            self.parse_whitespace();
            // Make sure there is no trailing characters.
            if self.eof() {
                self.state = ParseFinished;
                return None;
            } else {
                return Some(self.error_event(TrailingCharacters));
            }
        }

        Some(self.parse())
    }
}

impl<T: Iterator<Item=char>> Parser<T> {
    /// Creates the JSON parser.
    pub fn new(rdr: T) -> Parser<T> {
        let mut p = Parser {
            rdr: rdr,
            ch: Some('\x00'),
            line: 1,
            col: 0,
            stack: Stack::new(),
            state: ParseStart,
        };
        p.bump();
        p
    }

    /// Provides access to the current position in the logical structure of the
    /// JSON stream.
    pub fn stack(&self) -> &Stack {
        &self.stack
    }

    fn eof(&self) -> bool { self.ch.is_none() }
    fn ch_or_null(&self) -> char { self.ch.unwrap_or('\x00') }
    fn bump(&mut self) {
        self.ch = self.rdr.next();

        if self.ch_is('\n') {
            self.line += 1;
            self.col = 1;
        } else {
            self.col += 1;
        }
    }

    fn next_char(&mut self) -> Option<char> {
        self.bump();
        self.ch
    }
    fn ch_is(&self, c: char) -> bool {
        self.ch == Some(c)
    }

    fn error<U>(&self, reason: ErrorCode) -> Result<U, ParserError> {
        Err(SyntaxError(reason, self.line, self.col))
    }

    fn parse_whitespace(&mut self) {
        while self.ch_is(' ') ||
              self.ch_is('\n') ||
              self.ch_is('\t') ||
              self.ch_is('\r') { self.bump(); }
    }

    fn parse_number(&mut self) -> JsonEvent {
        let mut neg = false;

        if self.ch_is('-') {
            self.bump();
            neg = true;
        }

        let res = match self.parse_u64() {
            Ok(res) => res,
            Err(e) => { return Error(e); }
        };

        if self.ch_is('.') || self.ch_is('e') || self.ch_is('E') {
            let mut res = res as f64;

            if self.ch_is('.') {
                res = match self.parse_decimal(res) {
                    Ok(res) => res,
                    Err(e) => { return Error(e); }
                };
            }

            if self.ch_is('e') || self.ch_is('E') {
                res = match self.parse_exponent(res) {
                    Ok(res) => res,
                    Err(e) => { return Error(e); }
                };
            }

            if neg {
                res *= -1.0;
            }

            F64Value(res)
        } else {
            if neg {
                let res = (res as i64).wrapping_neg();

                // Make sure we didn't underflow.
                if res > 0 {
                    Error(SyntaxError(InvalidNumber, self.line, self.col))
                } else {
                    I64Value(res)
                }
            } else {
                U64Value(res)
            }
        }
    }

    fn parse_u64(&mut self) -> Result<u64, ParserError> {
        let mut accum = 0u64;
        let last_accum = 0; // necessary to detect overflow.

        match self.ch_or_null() {
            '0' => {
                self.bump();

                // A leading '0' must be the only digit before the decimal …