//!

//! # Overview

//!

//! The `tor-bytes` crate is part of

//! [Arti](https://gitlab.torproject.org/tpo/core/arti/), a project to

//! implement [Tor](https://www.torproject.org/) in Rust.

//! Other crates in Arti use it to build and handle all the byte-encoded

//! objects from the Tor protocol.  For textual directory items, see

//! the [`tor-netdoc`] crate.

//!

//! This crate is generally useful for encoding and decoding

//! byte-oriented formats that are not regular enough to qualify for

//! serde, and not complex enough to need a full meta-language.  It is

//! probably not suitable for handling anything bigger than a few

//! kilobytes in size.

//!

//! ## Alternatives

//!

//! The Reader/Writer traits in std::io are more appropriate for

//! operations that can fail because of some IO problem.  This crate

//! can't handle that: it is for handling things that are already in

//! memory.

//!

//! TODO: Look into using the "bytes" crate more here.

//!

//! TODO: The "untrusted" crate has similar goals to our [`Reader`],

//! but takes more steps to make sure it can never panic. Perhaps we

//! should see if we can learn any tricks from it.

//!

//! TODO: Do we really want to keep `Reader` as a struct and

//! `Writer` as a trait?

//!

//! # Contents and concepts

//!

//! This crate is structured around four key types:

//!

//! * [`Reader`]: A view of a byte slice, from which data can be decoded.

//! * [`Writer`]: Trait to represent a growable buffer of bytes.

//!   (Vec<u8> and [`bytes::BytesMut`] implement this.)

//! * [`Writeable`]: Trait for an object that can be encoded onto a [`Writer`]

//! * [`Readable`]: Trait for an object that can be decoded from a [`Reader`].

//!

//! Every object you want to encode or decode should implement

//! [`Writeable`] or [`Readable`] respectively.

//!

//! Once you implement these traits, you can use Reader and Writer to

//! handle your type, and other types that are built around it.

#![deny(missing_docs)]

#![warn(noop_method_call)]

#![deny(unreachable_pub)]

#![warn(clippy::all)]

#![deny(clippy::await_holding_lock)]

#![deny(clippy::cargo_common_metadata)]

#![deny(clippy::cast_lossless)]

#![deny(clippy::checked_conversions)]

#![warn(clippy::cognitive_complexity)]

#![deny(clippy::debug_assert_with_mut_call)]

#![deny(clippy::exhaustive_enums)]

#![deny(clippy::exhaustive_structs)]

#![deny(clippy::expl_impl_clone_on_copy)]

#![deny(clippy::fallible_impl_from)]

#![deny(clippy::implicit_clone)]

#![deny(clippy::large_stack_arrays)]

#![warn(clippy::manual_ok_or)]

#![deny(clippy::missing_docs_in_private_items)]

#![deny(clippy::missing_panics_doc)]

#![warn(clippy::needless_borrow)]

#![warn(clippy::needless_pass_by_value)]

#![warn(clippy::option_option)]

#![warn(clippy::rc_buffer)]

#![deny(clippy::ref_option_ref)]

#![warn(clippy::semicolon_if_nothing_returned)]

#![warn(clippy::trait_duplication_in_bounds)]

#![deny(clippy::unnecessary_wraps)]

#![warn(clippy::unseparated_literal_suffix)]

#![deny(clippy::unwrap_used)]

mod err;

mod impls;

mod reader;

mod writer;

pub use err::Error;

pub use reader::Reader;

pub use writer::Writer;

use arrayref::array_ref;

/// Result type returned by this crate.

pub type Result<T> = std::result::Result<T, Error>;

/// Trait for an object that can be encoded onto a Writer by reference.

///

/// Implement this trait in order to make an object writeable.

///

/// Most code won't need to call this directly, but will instead use

/// it implicitly via the Writer::write() method.

///

/// # Example

///

/// ```

/// use tor_bytes::{Writeable, Writer};

/// #[derive(Debug, Eq, PartialEq)]

/// struct Message {

///   flags: u32,

///   cmd: u8

/// }

///

/// impl Writeable for Message {

///     fn write_onto<B:Writer+?Sized>(&self, b: &mut B) {

///         // We'll say that a "Message" is encoded as flags, then command.

///         b.write_u32(self.flags);

///         b.write_u8(self.cmd);

///     }

/// }

///

/// let msg = Message { flags: 0x43, cmd: 0x07 };

/// let mut writer: Vec<u8> = Vec::new();

/// writer.write(&msg);

/// assert_eq!(writer, &[0x00, 0x00, 0x00, 0x43, 0x07 ]);

/// ```

pub trait Writeable {

    /// Encode this object into the writer `b`.

    fn write_onto<B: Writer + ?Sized>(&self, b: &mut B);

}

/// Trait for an object that can be encoded and consumed by a Writer.

///

/// Implement this trait in order to make an object that can be

/// written more efficiently by absorbing it into the writer.

///

/// Most code won't need to call this directly, but will instead use

/// it implicitly via the Writer::write_and_consume() method.

pub trait WriteableOnce {

    /// Encode this object into the writer `b`, and consume it.

    fn write_into<B: Writer + ?Sized>(self, b: &mut B);

}

impl<W: Writeable> WriteableOnce for W {

}

// ----------------------------------------------------------------------

/// Trait for an object that can be extracted from a Reader.

///

/// Implement this trait in order to make an object that can (maybe)

/// be decoded from a reader.

//

/// Most code won't need to call this directly, but will instead use

/// it implicitly via the Reader::extract() method.

///

/// # Example

///

/// ```

/// use tor_bytes::{Readable,Reader,Result};

/// #[derive(Debug, Eq, PartialEq)]

/// struct Message {

///   flags: u32,

///   cmd: u8

/// }

///

/// impl Readable for Message {

///     fn take_from(r: &mut Reader<'_>) -> Result<Self> {

///         // A "Message" is encoded as flags, then command.

///         let flags = r.take_u32()?;

///         let cmd = r.take_u8()?;

///         Ok(Message{ flags, cmd })

///     }

/// }

///

/// let encoded = [0x00, 0x00, 0x00, 0x43, 0x07 ];

/// let mut reader = Reader::from_slice(&encoded);

/// let m: Message = reader.extract()?;

/// assert_eq!(m, Message { flags: 0x43, cmd: 0x07 });

/// reader.should_be_exhausted()?; // make sure there are no bytes left over

/// # Result::Ok(())

/// ```

pub trait Readable: Sized {

    /// Try to extract an object of this type from a Reader.

    ///

    /// Implementations should generally try to be efficient: this is

    /// not the right place to check signatures or perform expensive

    /// operations.  If you have an object that must not be used until

    /// it is finally validated, consider making this function return

    /// a wrapped type that can be unwrapped later on once it gets

    /// checked.

    fn take_from(b: &mut Reader<'_>) -> Result<Self>;

}

// ----------------------------------------------------------------------

#[cfg(test)]

mod test {

    use super::*;

    #[test]

    fn writer() {

        let mut v: Vec<u8> = Vec::new();

        v.write_u8(0x57);

        v.write_u16(0x6520);

        v.write_u32(0x68617665);

        v.write_u64(0x2061206d61636869);

        v.write_all(b"ne in a plexiglass dome");

        v.write_zeros(3);

        assert_eq!(&v[..], &b"We have a machine in a plexiglass dome\0\0\0"[..]);

    }

}