nushell/crates/nu-json/src/de.rs

//! Hjson Deserialization
//!
//! This module provides for Hjson deserialization with the type `Deserializer`.

use std::char;
use std::io;
use std::marker::PhantomData;
use std::str;

use serde::de;

use super::error::{Error, ErrorCode, Result};
use super::util::StringReader;
use super::util::{Number, ParseNumber};

enum State {
    Normal,
    Root,
    Keyname,
}

/// A structure that deserializes Hjson into Rust values.
pub struct Deserializer<Iter: Iterator<Item = u8>> {
    rdr: StringReader<Iter>,
    str_buf: Vec<u8>,
    state: State,
}

// macro_rules! try_or_invalid {
//     ($self_:expr, $e:expr) => {
//         match $e {
//             Some(v) => v,
//             None => { return Err($self_.error(ErrorCode::InvalidNumber)); }
//         }
//     }
// }

impl<Iter> Deserializer<Iter>
where
    Iter: Iterator<Item = u8>,
{
    /// Creates the Hjson parser from an `std::iter::Iterator`.
    #[inline]
    pub fn new(rdr: Iter) -> Deserializer<Iter> {
        Deserializer {
            rdr: StringReader::new(rdr),
            str_buf: Vec::with_capacity(128),
            state: State::Normal,
        }
    }

    /// Creates the Hjson parser from an `std::iter::Iterator`.
    #[inline]
    pub fn new_for_root(rdr: Iter) -> Deserializer<Iter> {
        let mut res = Deserializer::new(rdr);
        res.state = State::Root;
        res
    }

    /// The `Deserializer::end` method should be called after a value has been fully deserialized.
    /// This allows the `Deserializer` to validate that the input stream is at the end or that it
    /// only has trailing whitespace.
    #[inline]
    pub fn end(&mut self) -> Result<()> {
        self.rdr.parse_whitespace()?;
        if self.rdr.eof()? {
            Ok(())
        } else {
            Err(self.rdr.error(ErrorCode::TrailingCharacters))
        }
    }

    fn is_punctuator_char(&mut self, ch: u8) -> bool {
        matches!(ch, b'{' | b'}' | b'[' | b']' | b',' | b':')
    }

    fn parse_keyname<V>(&mut self, mut visitor: V) -> Result<V::Value>
    where
        V: de::Visitor,
    {
        // quotes for keys are optional in Hjson
        // unless they include {}[],: or whitespace.
        // assume whitespace was already eaten

        self.str_buf.clear();

        let mut space: Option<usize> = None;
        loop {
            let ch = self.rdr.next_char_or_null()?;

            if ch == b':' {
                if self.str_buf.is_empty() {
                    return Err(self.rdr.error(ErrorCode::Custom(
                        "Found ':' but no key name (for an empty key name use quotes)".to_string(),
                    )));
                } else if space.is_some()
                    && space.expect("Internal error: json parsing") != self.str_buf.len()
                {
                    return Err(self.rdr.error(ErrorCode::Custom(
                        "Found whitespace in your key name (use quotes to include)".to_string(),
                    )));
                }
                self.rdr.uneat_char(ch);
                let s = str::from_utf8(&self.str_buf).expect("Internal error: json parsing");
                return visitor.visit_str(s);
            } else if ch <= b' ' {
                if ch == 0 {
                    return Err(self.rdr.error(ErrorCode::EOFWhileParsingObject));
                } else if space.is_none() {
                    space = Some(self.str_buf.len());
                }
            } else if self.is_punctuator_char(ch) {
                return Err(self.rdr.error(ErrorCode::Custom("Found a punctuator where a key name was expected (check your syntax or use quotes if the key name includes {}[],: or whitespace)".to_string())));
            } else {
                self.str_buf.push(ch);
            }
        }
    }

    fn parse_value<V>(&mut self, mut visitor: V) -> Result<V::Value>
    where
        V: de::Visitor,
    {
        self.rdr.parse_whitespace()?;

        if self.rdr.eof()? {
            return Err(self.rdr.error(ErrorCode::EOFWhileParsingValue));
        }

        match self.state {
            State::Keyname => {
                self.state = State::Normal;
                return self.parse_keyname(visitor);
            }
            State::Root => {
                self.state = State::Normal;
                return visitor.visit_map(MapVisitor::new(self, true));
            }
            _ => {}
        }

        let value = match self.rdr.peek_or_null()? {
            /*
            b'-' => {
                self.rdr.eat_char();
                self.parse_integer(false, visitor)
            }
            b'0' ..= b'9' => {
                self.parse_integer(true, visitor)
            }
            */
            b'"' => {
                self.rdr.eat_char();
                self.parse_string()?;
                let s = str::from_utf8(&self.str_buf).expect("Internal error: json parsing");
                visitor.visit_str(s)
            }
            b'[' => {
                self.rdr.eat_char();
                visitor.visit_seq(SeqVisitor::new(self))
            }
            b'{' => {
                self.rdr.eat_char();
                visitor.visit_map(MapVisitor::new(self, false))
            }
            b'\x00' => Err(self.rdr.error(ErrorCode::ExpectedSomeValue)),
            _ => self.parse_tfnns(visitor),
        };

        match value {
            Ok(value) => Ok(value),
            Err(Error::Syntax(code, _, _)) => Err(self.rdr.error(code)),
            Err(err) => Err(err),
        }
    }

    fn parse_ident(&mut self, ident: &[u8]) -> Result<()> {
        for c in ident {
            if Some(*c) != self.rdr.next_char()? {
                return Err(self.rdr.error(ErrorCode::ExpectedSomeIdent));
            }
        }

        Ok(())
    }

    fn parse_tfnns<V>(&mut self, mut visitor: V) -> Result<V::Value>
    where
        V: de::Visitor,
    {
        // Hjson strings can be quoteless
        // returns string, true, false, or null.
        self.str_buf.clear();

        let first = self.rdr.peek()?.expect("Internal error: json parsing");

        if self.is_punctuator_char(first) {
            return Err(self.rdr.error(ErrorCode::PunctuatorInQlString));
        }

        loop {
            let ch = self.rdr.next_char_or_null()?;

            let is_eol = ch == b'\r' || ch == b'\n' || ch == b'\x00';
            let is_comment = ch == b'#'
                || if ch == b'/' {
                    let next = self.rdr.peek_or_null()?;
                    next == b'/' || next == b'*'
                } else {
                    false
                };
            if is_eol || is_comment || ch == b',' || ch == b'}' || ch == b']' {
                let chf = self.str_buf[0];
                match chf {
                    b'f' => {
                        if str::from_utf8(&self.str_buf)
                            .expect("Internal error: json parsing")
                            .trim()
                            == "false"
                        {
                            self.rdr.uneat_char(ch);
                            return visitor.visit_bool(false);
                        }
                    }
                    b'n' => {
                        if str::from_utf8(&self.str_buf)
                            .expect("Internal error: json parsing")
                            .trim()
                            == "null"
                        {
                            self.rdr.uneat_char(ch);
                            return visitor.visit_unit();
                        }
                    }
                    b't' => {
                        if str::from_utf8(&self.str_buf)
                            .expect("Internal error: json parsing")
                            .trim()
                            == "true"
                        {
                            self.rdr.uneat_char(ch);
                            return visitor.visit_bool(true);
                        }
                    }
                    _ => {
                        if chf == b'-' || (b'0'..=b'9').contains(&chf) {
                            let mut pn = ParseNumber::new(self.str_buf.iter().cloned());
                            match pn.parse(false) {
                                Ok(Number::F64(v)) => {
                                    self.rdr.uneat_char(ch);
                                    return visitor.visit_f64(v);
                                }
                                Ok(Number::U64(v)) => {
                                    self.rdr.uneat_char(ch);
                                    return visitor.visit_u64(v);
                                }
                                Ok(Number::I64(v)) => {
                                    self.rdr.uneat_char(ch);
                                    return visitor.visit_i64(v);
                                }
                                Err(_) => {} // not a number, continue
                            }
                        }
                    }
                }
                if is_eol {
                    // remove any whitespace at the end (ignored in quoteless strings)
                    return visitor.visit_str(
                        str::from_utf8(&self.str_buf)
                            .expect("Internal error: json parsing")
                            .trim(),
                    );
                }
            }
            self.str_buf.push(ch);

            if self.str_buf == vec![b'\''; 3] {
                return self.parse_ml_string(visitor);
            }
        }
    }

    fn decode_hex_escape(&mut self) -> Result<u16> {
        let mut i = 0;
        let mut n = 0u16;
        while i < 4 && !(self.rdr.eof()?) {
            n = match self.rdr.next_char_or_null()? {
                c @ b'0'..=b'9' => n * 16_u16 + ((c as u16) - (b'0' as u16)),
                b'a' | b'A' => n * 16_u16 + 10_u16,
                b'b' | b'B' => n * 16_u16 + 11_u16,
                b'c' | b'C' => n * 16_u16 + 12_u16,
                b'd' | b'D' => n * 16_u16 + 13_u16,
                b'e' | b'E' => n * 16_u16 + 14_u16,
                b'f' | b'F' => n * 16_u16 + 15_u16,
                _ => {
                    return Err(self.rdr.error(ErrorCode::InvalidEscape));
                }
            };

            i += 1;
        }

        // Error out if we didn't parse 4 digits.
        if i != 4 {
            return Err(self.rdr.error(ErrorCode::InvalidEscape));
        }

        Ok(n)
    }

    fn ml_skip_white(&mut self) -> Result<bool> {
        match self.rdr.peek_or_null()? {
            b' ' | b'\t' | b'\r' => {
                self.rdr.eat_char();
                Ok(true)
            }
            _ => Ok(false),
        }
    }

    fn ml_skip_indent(&mut self, indent: usize) -> Result<()> {
        let mut skip = indent;
        while self.ml_skip_white()? && skip > 0 {
            skip -= 1;
        }
        Ok(())
    }

    fn parse_ml_string<V>(&mut self, mut visitor: V) -> Result<V::Value>
    where
        V: de::Visitor,
    {
        self.str_buf.clear();

        // Parse a multiline string value.
        let mut triple = 0;

        // we are at ''' +1 - get indent
        let (_, col) = self.rdr.pos();
        let indent = col - 4;

        // skip white/to (newline)
        while self.ml_skip_white()? {}
        if self.rdr.peek_or_null()? == b'\n' {
            self.rdr.eat_char();
            self.ml_skip_indent(indent)?;
        }

        // When parsing multiline string values, we must look for ' characters.
        loop {
            if self.rdr.eof()? {
                return Err(self.rdr.error(ErrorCode::EOFWhileParsingString));
            } // todo error("Bad multiline string");
            let ch = self.rdr.next_char_or_null()?;

            if ch == b'\'' {
                triple += 1;
                if triple == 3 {
                    if self.str_buf.last() == Some(&b'\n') {
                        self.str_buf.pop();
                    }
                    let res = str::from_utf8(&self.str_buf).expect("Internal error: json parsing");
                    //todo if (self.str_buf.slice(-1) === '\n') self.str_buf=self.str_buf.slice(0, -1); // remove last EOL
                    return visitor.visit_str(res);
                } else {
                    continue;
                }
            }

            while triple > 0 {
                self.str_buf.push(b'\'');
                triple -= 1;
            }

            if ch != b'\r' {
                self.str_buf.push(ch);
            }
            if ch == b'\n' {
                self.ml_skip_indent(indent)?;
            }
        }
    }

    fn parse_string(&mut self) -> Result<()> {
        self.str_buf.clear();

        loop {
            let ch = match self.rdr.next_char()? {
                Some(ch) => ch,
                None => {
                    return Err(self.rdr.error(ErrorCode::EOFWhileParsingString));
                }
            };

            match ch {
                b'"' => {
                    return Ok(());
                }
                b'\\' => {
                    let ch = match self.rdr.next_char()? {
                        Some(ch) => ch,
                        None => {
                            return Err(self.rdr.error(ErrorCode::EOFWhileParsingString));
                        }
                    };

                    match ch {
                        b'"' => self.str_buf.push(b'"'),
                        b'\\' => self.str_buf.push(b'\\'),
                        b'/' => self.str_buf.push(b'/'),
                        b'b' => self.str_buf.push(b'\x08'),
                        b'f' => self.str_buf.push(b'\x0c'),
                        b'n' => self.str_buf.push(b'\n'),
                        b'r' => self.str_buf.push(b'\r'),
                        b't' => self.str_buf.push(b'\t'),
                        b'u' => {
                            let c = match self.decode_hex_escape()? {
                                0xDC00..=0xDFFF => {
                                    return Err(self
                                        .rdr
                                        .error(ErrorCode::LoneLeadingSurrogateInHexEscape));
                                }

                                // Non-BMP characters are encoded as a sequence of
                                // two hex escapes, representing UTF-16 surrogates.
                                n1 @ 0xD800..=0xDBFF => {
                                    match (self.rdr.next_char()?, self.rdr.next_char()?) {
                                        (Some(b'\\'), Some(b'u')) => (),
                                        _ => {
                                            return Err(self
                                                .rdr
                                                .error(ErrorCode::UnexpectedEndOfHexEscape));
                                        }
                                    }

                                    let n2 = self.decode_hex_escape()?;

                                    if !(0xDC00..=0xDFFF).contains(&n2) {
                                        return Err(self
                                            .rdr
                                            .error(ErrorCode::LoneLeadingSurrogateInHexEscape));
                                    }

                                    let n = (((n1 - 0xD800) as u32) << 10 | (n2 - 0xDC00) as u32)
                                        + 0x1_0000;

                                    match char::from_u32(n as u32) {
                                        Some(c) => c,
                                        None => {
                                            return Err(self
                                                .rdr
                                                .error(ErrorCode::InvalidUnicodeCodePoint));
                                        }
                                    }
                                }

                                n => match char::from_u32(n as u32) {
                                    Some(c) => c,
                                    None => {
                                        return Err(self
                                            .rdr
                                            .error(ErrorCode::InvalidUnicodeCodePoint));
                                    }
                                },
                            };

                            // FIXME: this allocation is required in order to be compatible with stable
                            // rust, which doesn't support encoding a `char` into a stack buffer.
                            let mut buf = String::new();
                            buf.push(c);
                            self.str_buf.extend(buf.bytes());
                        }
                        _ => {
                            return Err(self.rdr.error(ErrorCode::InvalidEscape));
                        }
                    }
                }
                ch => {
                    self.str_buf.push(ch);
                }
            }
        }
    }

    fn parse_object_colon(&mut self) -> Result<()> {
        self.rdr.parse_whitespace()?;

        match self.rdr.next_char()? {
            Some(b':') => Ok(()),
            Some(_) => Err(self.rdr.error(ErrorCode::ExpectedColon)),
            None => Err(self.rdr.error(ErrorCode::EOFWhileParsingObject)),
        }
    }
}

impl<Iter> de::Deserializer for Deserializer<Iter>
where
    Iter: Iterator<Item = u8>,
{
    type Error = Error;

    #[inline]
    fn deserialize<V>(&mut self, visitor: V) -> Result<V::Value>
    where
        V: de::Visitor,
    {
        self.parse_value(visitor)
    }

    /// Parses a `null` as a None, and any other values as a `Some(...)`.
    #[inline]
    fn deserialize_option<V>(&mut self, mut visitor: V) -> Result<V::Value>
    where
        V: de::Visitor,
    {
        self.rdr.parse_whitespace()?;

        match self.rdr.peek_or_null()? {
            b'n' => {
                self.rdr.eat_char();
                self.parse_ident(b"ull")?;
                visitor.visit_none()
            }
            _ => visitor.visit_some(self),
        }
    }

    /// Parses a newtype struct as the underlying value.
    #[inline]
    fn deserialize_newtype_struct<V>(&mut self, _name: &str, mut visitor: V) -> Result<V::Value>
    where
        V: de::Visitor,
    {
        visitor.visit_newtype_struct(self)
    }

    forward_to_deserialize! {
        deserialize_bool();
        deserialize_usize();
        deserialize_u8();
        deserialize_u16();
        deserialize_u32();
        deserialize_u64();
        deserialize_isize();
        deserialize_i8();
        deserialize_i16();
        deserialize_i32();
        deserialize_i64();
        deserialize_f32();
        deserialize_f64();
        deserialize_char();
        deserialize_str();
        deserialize_string();
        deserialize_unit();
        deserialize_seq();
        deserialize_seq_fixed_size(len: usize);
        deserialize_bytes();
        deserialize_map();
        deserialize_unit_struct(name: &'static str);
        deserialize_tuple_struct(name: &'static str, len: usize);
        deserialize_struct(name: &'static str, fields: &'static [&'static str]);
        deserialize_struct_field();
        deserialize_tuple(len: usize);
        deserialize_enum(name: &'static str, variants: &'static [&'static str]);
        deserialize_ignored_any();
    }
}

struct SeqVisitor<'a, Iter: 'a + Iterator<Item = u8>> {
    de: &'a mut Deserializer<Iter>,
}

impl<'a, Iter: Iterator<Item = u8>> SeqVisitor<'a, Iter> {
    fn new(de: &'a mut Deserializer<Iter>) -> Self {
        SeqVisitor { de }
    }
}

impl<'a, Iter> de::SeqVisitor for SeqVisitor<'a, Iter>
where
    Iter: Iterator<Item = u8>,
{
    type Error = Error;

    fn visit<T>(&mut self) -> Result<Option<T>>
    where
        T: de::Deserialize,
    {
        self.de.rdr.parse_whitespace()?;

        match self.de.rdr.peek()? {
            Some(b']') => {
                return Ok(None);
            }
            Some(_) => {}
            None => {
                return Err(self.de.rdr.error(ErrorCode::EOFWhileParsingList));
            }
        }

        let value = de::Deserialize::deserialize(self.de)?;

        // in Hjson the comma is optional and trailing commas are allowed
        self.de.rdr.parse_whitespace()?;
        if self.de.rdr.peek()? == Some(b',') {
            self.de.rdr.eat_char();
            self.de.rdr.parse_whitespace()?;
        }

        Ok(Some(value))
    }

    fn end(&mut self) -> Result<()> {
        self.de.rdr.parse_whitespace()?;

        match self.de.rdr.next_char()? {
            Some(b']') => Ok(()),
            Some(_) => Err(self.de.rdr.error(ErrorCode::TrailingCharacters)),
            None => Err(self.de.rdr.error(ErrorCode::EOFWhileParsingList)),
        }
    }
}

struct MapVisitor<'a, Iter: 'a + Iterator<Item = u8>> {
    de: &'a mut Deserializer<Iter>,
    first: bool,
    root: bool,
}

impl<'a, Iter: Iterator<Item = u8>> MapVisitor<'a, Iter> {
    fn new(de: &'a mut Deserializer<Iter>, root: bool) -> Self {
        MapVisitor {
            de,
            first: true,
            root,
        }
    }
}

impl<'a, Iter> de::MapVisitor for MapVisitor<'a, Iter>
where
    Iter: Iterator<Item = u8>,
{
    type Error = Error;

    fn visit_key<K>(&mut self) -> Result<Option<K>>
    where
        K: de::Deserialize,
    {
        self.de.rdr.parse_whitespace()?;

        if self.first {
            self.first = false;
        } else if self.de.rdr.peek()? == Some(b',') {
            // in Hjson the comma is optional and trailing commas are allowed
            self.de.rdr.eat_char();
            self.de.rdr.parse_whitespace()?;
        }

        match self.de.rdr.peek()? {
            Some(b'}') => return Ok(None), // handled later for root
            Some(_) => {}
            None => {
                if self.root {
                    return Ok(None);
                } else {
                    return Err(self.de.rdr.error(ErrorCode::EOFWhileParsingObject));
                }
            }
        }

        match self.de.rdr.peek()? {
            Some(ch) => {
                self.de.state = if ch == b'"' {
                    State::Normal
                } else {
                    State::Keyname
                };
                Ok(Some(de::Deserialize::deserialize(self.de)?))
            }
            None => Err(self.de.rdr.error(ErrorCode::EOFWhileParsingValue)),
        }
    }

    fn visit_value<V>(&mut self) -> Result<V>
    where
        V: de::Deserialize,
    {
        self.de.parse_object_colon()?;

        de::Deserialize::deserialize(self.de)
    }

    fn end(&mut self) -> Result<()> {
        self.de.rdr.parse_whitespace()?;

        match self.de.rdr.next_char()? {
            Some(b'}') => {
                if !self.root {
                    Ok(())
                } else {
                    Err(self.de.rdr.error(ErrorCode::TrailingCharacters))
                } // todo
            }
            Some(_) => Err(self.de.rdr.error(ErrorCode::TrailingCharacters)),
            None => {
                if self.root {
                    Ok(())
                } else {
                    Err(self.de.rdr.error(ErrorCode::EOFWhileParsingObject))
                }
            }
        }
    }

    fn missing_field<V>(&mut self, field: &'static str) -> Result<V>
    where
        V: de::Deserialize,
    {
        struct MissingFieldDeserializer(&'static str);

        impl de::Deserializer for MissingFieldDeserializer {
            type Error = de::value::Error;

            fn deserialize<V>(&mut self, _visitor: V) -> std::result::Result<V::Value, Self::Error>
            where
                V: de::Visitor,
            {
                let &mut MissingFieldDeserializer(field) = self;
                Err(de::value::Error::MissingField(field))
            }

            fn deserialize_option<V>(
                &mut self,
                mut visitor: V,
            ) -> std::result::Result<V::Value, Self::Error>
            where
                V: de::Visitor,
            {
                visitor.visit_none()
            }

            forward_to_deserialize! {
                deserialize_bool();
                deserialize_usize();
                deserialize_u8();
                deserialize_u16();
                deserialize_u32();
                deserialize_u64();
                deserialize_isize();
                deserialize_i8();
                deserialize_i16();
                deserialize_i32();
                deserialize_i64();
                deserialize_f32();
                deserialize_f64();
                deserialize_char();
                deserialize_str();
                deserialize_string();
                deserialize_unit();
                deserialize_seq();
                deserialize_seq_fixed_size(len: usize);
                deserialize_bytes();
                deserialize_map();
                deserialize_unit_struct(name: &'static str);
                deserialize_newtype_struct(name: &'static str);
                deserialize_tuple_struct(name: &'static str, len: usize);
                deserialize_struct(name: &'static str, fields: &'static [&'static str]);
                deserialize_struct_field();
                deserialize_tuple(len: usize);
                deserialize_enum(name: &'static str, variants: &'static [&'static str]);
                deserialize_ignored_any();
            }
        }

        let mut de = MissingFieldDeserializer(field);
        Ok(de::Deserialize::deserialize(&mut de)?)
    }
}

impl<Iter> de::VariantVisitor for Deserializer<Iter>
where
    Iter: Iterator<Item = u8>,
{
    type Error = Error;

    fn visit_variant<V>(&mut self) -> Result<V>
    where
        V: de::Deserialize,
    {
        let val = de::Deserialize::deserialize(self)?;
        self.parse_object_colon()?;
        Ok(val)
    }

    fn visit_unit(&mut self) -> Result<()> {
        de::Deserialize::deserialize(self)
    }

    fn visit_newtype<T>(&mut self) -> Result<T>
    where
        T: de::Deserialize,
    {
        de::Deserialize::deserialize(self)
    }

    fn visit_tuple<V>(&mut self, _len: usize, visitor: V) -> Result<V::Value>
    where
        V: de::Visitor,
    {
        de::Deserializer::deserialize(self, visitor)
    }

    fn visit_struct<V>(&mut self, _fields: &'static [&'static str], visitor: V) -> Result<V::Value>
    where
        V: de::Visitor,
    {
        de::Deserializer::deserialize(self, visitor)
    }
}

//////////////////////////////////////////////////////////////////////////////

/// Iterator that deserializes a stream into multiple Hjson values.
pub struct StreamDeserializer<T, Iter>
where
    Iter: Iterator<Item = u8>,
    T: de::Deserialize,
{
    deser: Deserializer<Iter>,
    _marker: PhantomData<T>,
}

impl<T, Iter> StreamDeserializer<T, Iter>
where
    Iter: Iterator<Item = u8>,
    T: de::Deserialize,
{
    /// Returns an `Iterator` of decoded Hjson values from an iterator over
    /// `Iterator<Item=u8>`.
    pub fn new(iter: Iter) -> StreamDeserializer<T, Iter> {
        StreamDeserializer {
            deser: Deserializer::new(iter),
            _marker: PhantomData,
        }
    }
}

impl<T, Iter> Iterator for StreamDeserializer<T, Iter>
where
    Iter: Iterator<Item = u8>,
    T: de::Deserialize,
{
    type Item = Result<T>;

    fn next(&mut self) -> Option<Result<T>> {
        // skip whitespaces, if any
        // this helps with trailing whitespaces, since whitespaces between
        // values are handled for us.
        if let Err(e) = self.deser.rdr.parse_whitespace() {
            return Some(Err(e));
        };

        match self.deser.rdr.eof() {
            Ok(true) => None,
            Ok(false) => match de::Deserialize::deserialize(&mut self.deser) {
                Ok(v) => Some(Ok(v)),
                Err(e) => Some(Err(e)),
            },
            Err(e) => Some(Err(e)),
        }
    }
}

//////////////////////////////////////////////////////////////////////////////

/// Decodes a Hjson value from an iterator over an iterator
/// `Iterator<Item=u8>`.
pub fn from_iter<I, T>(iter: I) -> Result<T>
where
    I: Iterator<Item = io::Result<u8>>,
    T: de::Deserialize,
{
    let fold: io::Result<Vec<_>> = iter.collect();
    if let Err(e) = fold {
        return Err(Error::Io(e));
    }

    let bytes = fold.expect("Internal error: json parsing");

    // deserialize tries first to decode with legacy support (new_for_root)
    // and then with the standard method if this fails.
    // todo: add compile switch

    // deserialize and make sure the whole stream has been consumed
    let mut de = Deserializer::new_for_root(bytes.iter().cloned());
    let value = match de::Deserialize::deserialize(&mut de).and_then(|x| {
        de.end()?;
        Ok(x)
    }) {
        Ok(v) => Ok(v),
        Err(_) => {
            let mut de2 = Deserializer::new(bytes.iter().cloned());
            match de::Deserialize::deserialize(&mut de2).and_then(|x| {
                de2.end()?;
                Ok(x)
            }) {
                Ok(v) => Ok(v),
                Err(e) => Err(e),
            }
        }
    };

    /* without legacy support:
    // deserialize and make sure the whole stream has been consumed
    let mut de = Deserializer::new(bytes.iter().map(|b| *b));
    let value = match de::Deserialize::deserialize(&mut de)
        .and_then(|x| { de.end()); Ok(x) })
    {
        Ok(v) => Ok(v),
        Err(e) => Err(e),
    };
    */

    value
}

/// Decodes a Hjson value from a `std::io::Read`.
pub fn from_reader<R, T>(rdr: R) -> Result<T>
where
    R: io::Read,
    T: de::Deserialize,
{
    from_iter(rdr.bytes())
}

/// Decodes a Hjson value from a byte slice `&[u8]`.
pub fn from_slice<T>(v: &[u8]) -> Result<T>
where
    T: de::Deserialize,
{
    from_iter(v.iter().map(|byte| Ok(*byte)))
}

/// Decodes a Hjson value from a `&str`.
pub fn from_str<T>(s: &str) -> Result<T>
where
    T: de::Deserialize,
{
    from_slice(s.as_bytes())
}