//! `bincode` is a crate for encoding and decoding using a tiny binary
//! serialization strategy.
//!
//! There are simple functions for encoding to `Vec<u8>` and decoding from
//! `&[u8]`, but the meat of the library is the `encode_into` and `decode_from`
//! functions which respectively allow encoding into a `std::io::Writer`
//! and decoding from a `std::io::Buffer`.
//!
//! ### Using Basic Functions
//!
//! ```rust
//! #![allow(unstable)]
//! extern crate bincode;
//! fn main() {
//!     // The object that we will serialize.
//!     let target = Some("hello world".to_string());
//!     // The maximum size of the encoded message.
//!     let limit = bincode::SizeLimit::Bounded(20);
//!
//!     let encoded: Vec<u8> = bincode::encode(&target, limit).unwrap();
//!     let (decoded, len): (Option<String>, u64) = bincode::decode(&encoded[..]).unwrap();
//!     assert_eq!(target, decoded);
//! }
//! ```

#![crate_name = "bincode"]
#![crate_type = "rlib"]
#![crate_type = "dylib"]

#![doc(html_logo_url = "./icon.png")]
//`#![feature(unicode)]

extern crate rustc_serialize;
extern crate byteorder;

use rustc_serialize::{Encodable, Decodable};

pub use refbox::{RefBox, StrBox, SliceBox};
pub use writer::{EncoderWriter, EncodingResult, EncodingError};
pub use reader::{DecoderReader, DecodingResult, DecodingError};
use writer::SizeChecker;

use std::io::{Write, Read};

mod writer;
mod reader;
mod refbox;
#[cfg(test)] mod test;

/// A limit on the amount of bytes that can be read or written.
///
/// Size limits are an incredibly important part of both encoding and decoding.
///
/// In order to prevent DOS attacks on a decoder, it is important to limit the
/// amount of bytes that a single encoded message can be; otherwise, if you
/// are decoding bytes right off of a TCP stream for example, it would be
/// possible for an attacker to flood your server with a 3TB vec, causing the
/// decoder to run out of memory and crash your application!
/// Because of this, you can provide a maximum-number-of-bytes that can be read
/// during decoding, and the decoder will explicitly fail if it has to read
/// any more than that.
///
/// On the other side, you want to make sure that you aren't encoding a message
/// that is larger than your decoder expects.  By supplying a size limit to an
/// encoding function, the encoder will verify that the structure can be encoded
/// within that limit.  This verification occurs before any bytes are written to
/// the Writer, so recovering from an the error is easy.
#[derive(Clone, Copy, Debug, Hash, Eq, PartialEq, Ord, PartialOrd)]
pub enum SizeLimit {
    Infinite,
    Bounded(u64)
}

/// Encodes an encodable object into a `Vec` of bytes.
///
/// If the encoding would take more bytes than allowed by `size_limit`,
/// an error is returned.
pub fn encode<T: Encodable>(t: &T, size_limit: SizeLimit) -> EncodingResult<Vec<u8>> {
    // Since we are putting values directly into a vector, we can do size
    // computation out here and pre-allocate a buffer of *exactly*
    // the right size.
    let mut w = if let SizeLimit::Bounded(l) = size_limit {
        let actual_size = encoded_size_bounded(t, l);
        let actual_size = try!(actual_size.ok_or(EncodingError::SizeLimit));
        Vec::with_capacity(actual_size as usize)
    } else {
        vec![]
    };

    match encode_into(t, &mut w, SizeLimit::Infinite) {
        Ok(()) => Ok(w),
        Err(e) => Err(e)
    }
}

/// Decodes a slice of bytes into an object.
///
/// If successful, this function returns the decoded object along with the number
/// of bytes that were read.
///
/// This method does not have a size-limit because with all the bytes contiguous
/// in memory, then nothing is gained by having a limiter.
pub fn decode<T: Decodable>(b: &[u8]) -> DecodingResult<(T, u64)> {
    let mut b = b;
    decode_from(&mut b, SizeLimit::Infinite)
}

/// Encodes an object directly into a `Writer`.
///
/// If the encoding would take more bytes than allowed by `size_limit`, an error
/// is returned and *no bytes* will be written into the `Writer`.
///
/// If this returns an `EncodingError` (other than SizeLimit), assume that the
/// writer is in an invalid state, as writing could bail out in the middle of
/// encoding.
pub fn encode_into<T: Encodable, W: Write>(t: &T,
                                           w: &mut W,
                                           size_limit: SizeLimit)
                                           -> EncodingResult<()> {
    try!(match size_limit {
        SizeLimit::Infinite => Ok(()),
        SizeLimit::Bounded(x) => {
            let mut size_checker = SizeChecker::new(x);
            t.encode(&mut size_checker)
        }
    });

    t.encode(&mut writer::EncoderWriter::new(w))
}

/// Decodes an object directly from a `Read`er.  If successful, returns the
/// decoded object and the number of bytes read out of the `Read`er.
///
/// If the provided `SizeLimit` is reached, the decode will bail immediately.
/// A SizeLimit can help prevent an attacker from flooding your server with
/// a neverending stream of values that runs your server out of memory.
///
/// If this returns an `DecodingError`, assume that the buffer that you passed
/// in is in an invalid state, as the error could be returned during any point
/// in the reading.
pub fn decode_from<R: Read, T: Decodable>(r: &mut R, size_limit: SizeLimit) -> DecodingResult<(T, u64)> {
    let mut decoder_reader = reader::DecoderReader::new(r, size_limit);
    let value = try!(Decodable::decode(&mut decoder_reader));
    let bytes_read = decoder_reader.bytes_read();
    Ok((value, bytes_read))
}


/// Returns the size that an object would be if encoded using bincode.
///
/// This is used internally as part of the check for encode_into, but it can
/// be useful for preallocating buffers if thats your style.
pub fn encoded_size<T: Encodable>(t: &T) -> u64 {
    use std::u64::MAX;
    let mut size_checker = SizeChecker::new(MAX);
    t.encode(&mut size_checker).ok();
    size_checker.written
}

/// Given a maximum size limit, check how large an object would be if it
/// were to be encoded.
///
/// If it can be encoded in `max` or fewer bytes, that number will be returned
/// inside `Some`.  If it goes over bounds, then None is returned.
pub fn encoded_size_bounded<T: Encodable>(t: &T, max: u64) -> Option<u64> {
    let mut size_checker = SizeChecker::new(max);
    t.encode(&mut size_checker).ok().map(|_| size_checker.written)
}