src/protocol/wire_format.rs

// Copyright 2018 The ChromiumOS Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use std::fmt;
use std::io;
use std::io::ErrorKind;
use std::io::Read;
use std::io::Write;
use std::mem;
use std::ops::Deref;
use std::ops::DerefMut;
use std::string::String;
use std::vec::Vec;

/// A type that can be encoded on the wire using the 9P protocol.
pub trait WireFormat: std::marker::Sized {
    /// Returns the number of bytes necessary to fully encode `self`.
    fn byte_size(&self) -> u32;

    /// Encodes `self` into `writer`.
    fn encode<W: Write>(&self, writer: &mut W) -> io::Result<()>;

    /// Decodes `Self` from `reader`.
    fn decode<R: Read>(reader: &mut R) -> io::Result<Self>;
}

// This doesn't really _need_ to be a macro but unfortunately there is no trait bound to
// express "can be casted to another type", which means we can't write `T as u8` in a trait
// based implementation.  So instead we have this macro, which is implemented for all the
// stable unsigned types with the added benefit of not being implemented for the signed
// types which are not allowed by the protocol.
macro_rules! uint_wire_format_impl {
    ($Ty:ty) => {
        impl WireFormat for $Ty {
            fn byte_size(&self) -> u32 {
                mem::size_of::<$Ty>() as u32
            }

            fn encode<W: Write>(&self, writer: &mut W) -> io::Result<()> {
                let mut buf = [0u8; mem::size_of::<$Ty>()];

                // Encode the bytes into the buffer in little endian order.
                for idx in 0..mem::size_of::<$Ty>() {
                    buf[idx] = (self >> (8 * idx)) as u8;
                }

                writer.write_all(&buf)
            }

            fn decode<R: Read>(reader: &mut R) -> io::Result<Self> {
                let mut buf = [0u8; mem::size_of::<$Ty>()];
                reader.read_exact(&mut buf)?;

                // Read bytes from the buffer in little endian order.
                let mut result = 0;
                for idx in 0..mem::size_of::<$Ty>() {
                    result |= (buf[idx] as $Ty) << (8 * idx);
                }

                Ok(result)
            }
        }
    };
}
uint_wire_format_impl!(u8);
uint_wire_format_impl!(u16);
uint_wire_format_impl!(u32);
uint_wire_format_impl!(u64);

// The 9P protocol requires that strings are UTF-8 encoded.  The wire format is a u16
// count |N|, encoded in little endian, followed by |N| bytes of UTF-8 data.
impl WireFormat for String {
    fn byte_size(&self) -> u32 {
        (mem::size_of::<u16>() + self.len()) as u32
    }

    fn encode<W: Write>(&self, writer: &mut W) -> io::Result<()> {
        if self.len() > std::u16::MAX as usize {
            return Err(io::Error::new(
                ErrorKind::InvalidInput,
                "string is too long",
            ));
        }

        (self.len() as u16).encode(writer)?;
        writer.write_all(self.as_bytes())
    }

    fn decode<R: Read>(reader: &mut R) -> io::Result<Self> {
        let len: u16 = WireFormat::decode(reader)?;
        let mut result = String::with_capacity(len as usize);
        reader.take(len as u64).read_to_string(&mut result)?;
        Ok(result)
    }
}

// The wire format for repeated types is similar to that of strings: a little endian
// encoded u16 |N|, followed by |N| instances of the given type.
impl<T: WireFormat> WireFormat for Vec<T> {
    fn byte_size(&self) -> u32 {
        mem::size_of::<u16>() as u32 + self.iter().map(|elem| elem.byte_size()).sum::<u32>()
    }

    fn encode<W: Write>(&self, writer: &mut W) -> io::Result<()> {
        if self.len() > std::u16::MAX as usize {
            return Err(io::Error::new(
                ErrorKind::InvalidInput,
                "too many elements in vector",
            ));
        }

        (self.len() as u16).encode(writer)?;
        for elem in self {
            elem.encode(writer)?;
        }

        Ok(())
    }

    fn decode<R: Read>(reader: &mut R) -> io::Result<Self> {
        let len: u16 = WireFormat::decode(reader)?;
        let mut result = Vec::with_capacity(len as usize);

        for _ in 0..len {
            result.push(WireFormat::decode(reader)?);
        }

        Ok(result)
    }
}

/// A type that encodes an arbitrary number of bytes of data.  Typically used for Rread
/// Twrite messages.  This differs from a `Vec<u8>` in that it encodes the number of bytes
/// using a `u32` instead of a `u16`.
#[derive(PartialEq, Eq)]
pub struct Data(pub Vec<u8>);

// The maximum length of a data buffer that we support.  In practice the server's max message
// size should prevent us from reading too much data so this check is mainly to ensure a
// malicious client cannot trick us into allocating massive amounts of memory.
const MAX_DATA_LENGTH: u32 = 32 * 1024 * 1024;

impl fmt::Debug for Data {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        // There may be a lot of data and we don't want to spew it all out in a trace.  Instead
        // just print out the number of bytes in the buffer.
        write!(f, "Data({} bytes)", self.len())
    }
}

// Implement Deref and DerefMut so that we don't have to use self.0 everywhere.
impl Deref for Data {
    type Target = Vec<u8>;
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}
impl DerefMut for Data {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

// Same as Vec<u8> except that it encodes the length as a u32 instead of a u16.
impl WireFormat for Data {
    fn byte_size(&self) -> u32 {
        mem::size_of::<u32>() as u32 + self.iter().map(|elem| elem.byte_size()).sum::<u32>()
    }

    fn encode<W: Write>(&self, writer: &mut W) -> io::Result<()> {
        if self.len() > std::u32::MAX as usize {
            return Err(io::Error::new(ErrorKind::InvalidInput, "data is too large"));
        }
        (self.len() as u32).encode(writer)?;
        writer.write_all(self)
    }

    fn decode<R: Read>(reader: &mut R) -> io::Result<Self> {
        let len: u32 = WireFormat::decode(reader)?;
        if len > MAX_DATA_LENGTH {
            return Err(io::Error::new(
                ErrorKind::InvalidData,
                format!("data length ({} bytes) is too large", len),
            ));
        }

        let mut buf = Vec::with_capacity(len as usize);
        reader.take(len as u64).read_to_end(&mut buf)?;

        if buf.len() == len as usize {
            Ok(Data(buf))
        } else {
            Err(io::Error::new(
                ErrorKind::UnexpectedEof,
                format!(
                    "unexpected end of data: want: {} bytes, got: {} bytes",
                    len,
                    buf.len()
                ),
            ))
        }
    }
}

#[cfg(test)]
mod test {
    use std::io::Cursor;
    use std::mem;
    use std::string::String;

    use super::*;

    #[test]
    fn integer_byte_size() {
        assert_eq!(1, 0u8.byte_size());
        assert_eq!(2, 0u16.byte_size());
        assert_eq!(4, 0u32.byte_size());
        assert_eq!(8, 0u64.byte_size());
    }

    #[test]
    fn integer_decode() {
        let buf: [u8; 8] = [0xef, 0xbe, 0xad, 0xde, 0x0d, 0xf0, 0xad, 0x8b];

        assert_eq!(0xef_u8, WireFormat::decode(&mut Cursor::new(&buf)).unwrap());
        assert_eq!(0xbeef_u16, u16::decode(&mut Cursor::new(&buf)).unwrap());
        assert_eq!(0xdeadbeef_u32, u32::decode(&mut Cursor::new(&buf)).unwrap());
        assert_eq!(
            0x8bad_f00d_dead_beef_u64,
            u64::decode(&mut Cursor::new(&buf)).unwrap()
        );
    }

    #[test]
    fn integer_encode() {
        let value: u64 = 0x8bad_f00d_dead_beef;
        let expected: [u8; 8] = [0xef, 0xbe, 0xad, 0xde, 0x0d, 0xf0, 0xad, 0x8b];

        let mut buf = vec![0; 8];

        (value as u8).encode(&mut Cursor::new(&mut *buf)).unwrap();
        assert_eq!(expected[0..1], buf[0..1]);

        (value as u16).encode(&mut Cursor::new(&mut *buf)).unwrap();
        assert_eq!(expected[0..2], buf[0..2]);

        (value as u32).encode(&mut Cursor::new(&mut *buf)).unwrap();
        assert_eq!(expected[0..4], buf[0..4]);

        value.encode(&mut Cursor::new(&mut *buf)).unwrap();
        assert_eq!(expected[0..8], buf[0..8]);
    }

    #[test]
    fn string_byte_size() {
        let values = [
            String::from("Google Video"),
            String::from("网页 图片 资讯更多 »"),
            String::from("Παγκόσμιος Ιστός"),
            String::from("Поиск страниц на русском"),
            String::from("전체서비스"),
        ];

        let exp = values
            .iter()
            .map(|v| (mem::size_of::<u16>() + v.len()) as u32);

        for (value, expected) in values.iter().zip(exp) {
            assert_eq!(expected, value.byte_size());
        }
    }

    #[test]
    fn zero_length_string() {
        let s = String::from("");
        assert_eq!(s.byte_size(), mem::size_of::<u16>() as u32);

        let mut buf = [0xffu8; 4];

        s.encode(&mut Cursor::new(&mut buf[..]))
            .expect("failed to encode empty string");
        assert_eq!(&[0, 0, 0xff, 0xff], &buf);

        assert_eq!(
            s,
            <String as WireFormat>::decode(&mut Cursor::new(&[0, 0, 0x61, 0x61][..]))
                .expect("failed to decode empty string")
        );
    }

    #[test]
    fn string_encode() {
        let values = [
            String::from("Google Video"),
            String::from("网页 图片 资讯更多 »"),
            String::from("Παγκόσμιος Ιστός"),
            String::from("Поиск страниц на русском"),
            String::from("전체서비스"),
        ];

        let expected = values.iter().map(|v| {
            let len = v.as_bytes().len();
            let mut buf = Vec::with_capacity(len + mem::size_of::<u16>());

            buf.push(len as u8);
            buf.push((len >> 8) as u8);

            buf.extend_from_slice(v.as_bytes());

            buf
        });

        for (val, exp) in values.iter().zip(expected) {
            let mut buf = vec![0; exp.len()];

            WireFormat::encode(val, &mut Cursor::new(&mut *buf)).unwrap();
            assert_eq!(exp, buf);
        }
    }

    #[test]
    fn string_decode() {
        assert_eq!(
            String::from("Google Video"),
            <String as WireFormat>::decode(&mut Cursor::new(
                &[
                    0x0c, 0x00, 0x47, 0x6F, 0x6F, 0x67, 0x6C, 0x65, 0x20, 0x56, 0x69, 0x64, 0x65,
                    0x6F,
                ][..]
            ))
            .unwrap()
        );
        assert_eq!(
            String::from("网页 图片 资讯更多 »"),
            <String as WireFormat>::decode(&mut Cursor::new(
                &[
                    0x1d, 0x00, 0xE7, 0xBD, 0x91, 0xE9, 0xA1, 0xB5, 0x20, 0xE5, 0x9B, 0xBE, 0xE7,
                    0x89, 0x87, 0x20, 0xE8, 0xB5, 0x84, 0xE8, 0xAE, 0xAF, 0xE6, 0x9B, 0xB4, 0xE5,
                    0xA4, 0x9A, 0x20, 0xC2, 0xBB,
                ][..]
            ))
            .unwrap()
        );
        assert_eq!(
            String::from("Παγκόσμιος Ιστός"),
            <String as WireFormat>::decode(&mut Cursor::new(
                &[
                    0x1f, 0x00, 0xCE, 0xA0, 0xCE, 0xB1, 0xCE, 0xB3, 0xCE, 0xBA, 0xCF, 0x8C, 0xCF,
                    0x83, 0xCE, 0xBC, 0xCE, 0xB9, 0xCE, 0xBF, 0xCF, 0x82, 0x20, 0xCE, 0x99, 0xCF,
                    0x83, 0xCF, 0x84, 0xCF, 0x8C, 0xCF, 0x82,
                ][..]
            ))
            .unwrap()
        );
        assert_eq!(
            String::from("Поиск страниц на русском"),
            <String as WireFormat>::decode(&mut Cursor::new(
                &[
                    0x2d, 0x00, 0xD0, 0x9F, 0xD0, 0xBE, 0xD0, 0xB8, 0xD1, 0x81, 0xD0, 0xBA, 0x20,
                    0xD1, 0x81, 0xD1, 0x82, 0xD1, 0x80, 0xD0, 0xB0, 0xD0, 0xBD, 0xD0, 0xB8, 0xD1,
                    0x86, 0x20, 0xD0, 0xBD, 0xD0, 0xB0, 0x20, 0xD1, 0x80, 0xD1, 0x83, 0xD1, 0x81,
                    0xD1, 0x81, 0xD0, 0xBA, 0xD0, 0xBE, 0xD0, 0xBC,
                ][..]
            ))
            .unwrap()
        );
        assert_eq!(
            String::from("전체서비스"),
            <String as WireFormat>::decode(&mut Cursor::new(
                &[
                    0x0f, 0x00, 0xEC, 0xA0, 0x84, 0xEC, 0xB2, 0xB4, 0xEC, 0x84, 0x9C, 0xEB, 0xB9,
                    0x84, 0xEC, 0x8A, 0xA4,
                ][..]
            ))
            .unwrap()
        );
    }

    #[test]
    fn invalid_string_decode() {
        let _ = <String as WireFormat>::decode(&mut Cursor::new(&[
            0x06, 0x00, 0xed, 0xa0, 0x80, 0xed, 0xbf, 0xbf,
        ]))
        .expect_err("surrogate code point");

        let _ = <String as WireFormat>::decode(&mut Cursor::new(&[
            0x05, 0x00, 0xf8, 0x80, 0x80, 0x80, 0xbf,
        ]))
        .expect_err("overlong sequence");

        let _ =
            <String as WireFormat>::decode(&mut Cursor::new(&[0x04, 0x00, 0xf4, 0x90, 0x80, 0x80]))
                .expect_err("out of range");

        let _ =
            <String as WireFormat>::decode(&mut Cursor::new(&[0x04, 0x00, 0x63, 0x61, 0x66, 0xe9]))
                .expect_err("ISO-8859-1");

        let _ =
            <String as WireFormat>::decode(&mut Cursor::new(&[0x04, 0x00, 0xb0, 0xa1, 0xb0, 0xa2]))
                .expect_err("EUC-KR");
    }

    #[test]
    fn vector_encode() {
        let values: Vec<u32> = vec![291, 18_916, 2_497, 22, 797_162, 2_119_732, 3_213_929_716];
        let mut expected: Vec<u8> =
            Vec::with_capacity(values.len() * mem::size_of::<u32>() + mem::size_of::<u16>());
        expected.push(values.len() as u8);
        expected.push((values.len() >> 8) as u8);

        const MASK: u32 = 0xff;
        for val in &values {
            expected.push((val & MASK) as u8);
            expected.push(((val >> 8) & MASK) as u8);
            expected.push(((val >> 16) & MASK) as u8);
            expected.push(((val >> 24) & MASK) as u8);
        }

        let mut actual: Vec<u8> = vec![0; expected.len()];

        WireFormat::encode(&values, &mut Cursor::new(&mut *actual))
            .expect("failed to encode vector");
        assert_eq!(expected, actual);
    }

    #[test]
    fn vector_decode() {
        let expected: Vec<u32> = vec![
            2_498,
            24,
            897,
            4_097_789_579,
            8_498_119,
            684_279,
            961_189_198,
            7,
        ];
        let mut input: Vec<u8> =
            Vec::with_capacity(expected.len() * mem::size_of::<u32>() + mem::size_of::<u16>());
        input.push(expected.len() as u8);
        input.push((expected.len() >> 8) as u8);

        const MASK: u32 = 0xff;
        for val in &expected {
            input.push((val & MASK) as u8);
            input.push(((val >> 8) & MASK) as u8);
            input.push(((val >> 16) & MASK) as u8);
            input.push(((val >> 24) & MASK) as u8);
        }

        assert_eq!(
            expected,
            <Vec<u32> as WireFormat>::decode(&mut Cursor::new(&*input))
                .expect("failed to decode vector")
        );
    }

    #[test]
    fn data_encode() {
        let values = Data(vec![169, 155, 79, 67, 182, 199, 25, 73, 129, 200]);
        let mut expected: Vec<u8> =
            Vec::with_capacity(values.len() * mem::size_of::<u8>() + mem::size_of::<u32>());
        expected.push(values.len() as u8);
        expected.push((values.len() >> 8) as u8);
        expected.push((values.len() >> 16) as u8);
        expected.push((values.len() >> 24) as u8);
        expected.extend_from_slice(&values);

        let mut actual: Vec<u8> = vec![0; expected.len()];

        WireFormat::encode(&values, &mut Cursor::new(&mut *actual))
            .expect("failed to encode datar");
        assert_eq!(expected, actual);
    }

    #[test]
    fn data_decode() {
        let expected = Data(vec![219, 15, 8, 155, 194, 129, 79, 91, 46, 53, 173]);
        let mut input: Vec<u8> =
            Vec::with_capacity(expected.len() * mem::size_of::<u8>() + mem::size_of::<u32>());
        input.push(expected.len() as u8);
        input.push((expected.len() >> 8) as u8);
        input.push((expected.len() >> 16) as u8);
        input.push((expected.len() >> 24) as u8);
        input.extend_from_slice(&expected);

        assert_eq!(
            expected,
            <Data as WireFormat>::decode(&mut Cursor::new(&mut *input))
                .expect("failed to decode data")
        );
    }

    #[test]
    fn error_cases() {
        // string is too long.
        let mut long_str = String::with_capacity(std::u16::MAX as usize);
        while long_str.len() < std::u16::MAX as usize {
            long_str.push_str("long");
        }
        long_str.push('!');

        let count = long_str.len() + mem::size_of::<u16>();
        let mut buf = vec![0; count];

        long_str
            .encode(&mut Cursor::new(&mut *buf))
            .expect_err("long string");

        // vector is too long.
        let mut long_vec: Vec<u32> = Vec::with_capacity(std::u16::MAX as usize);
        while long_vec.len() < std::u16::MAX as usize {
            long_vec.push(0x8bad_f00d);
        }
        long_vec.push(0x00ba_b10c);

        let count = long_vec.len() * mem::size_of::<u32>();
        let mut buf = vec![0; count];

        WireFormat::encode(&long_vec, &mut Cursor::new(&mut *buf)).expect_err("long vector");
    }

    #[derive(Debug, PartialEq, P9WireFormat)]
    struct Item {
        a: u64,
        b: String,
        c: Vec<u16>,
        buf: Data,
    }

    #[test]
    fn struct_encode() {
        let item = Item {
            a: 0xdead_10cc_00ba_b10c,
            b: String::from("冻住，不许走!"),
            c: vec![359, 492, 8891],
            buf: Data(vec![254, 129, 0, 62, 49, 172]),
        };

        let mut expected: Vec<u8> = vec![0x0c, 0xb1, 0xba, 0x00, 0xcc, 0x10, 0xad, 0xde];
        let strlen = item.b.len() as u16;
        expected.push(strlen as u8);
        expected.push((strlen >> 8) as u8);
        expected.extend_from_slice(item.b.as_bytes());

        let veclen = item.c.len() as u16;
        expected.push(veclen as u8);
        expected.push((veclen >> 8) as u8);
        for val in &item.c {
            expected.push(*val as u8);
            expected.push((val >> 8) as u8);
        }

        let buflen = item.buf.len() as u32;
        expected.push(buflen as u8);
        expected.push((buflen >> 8) as u8);
        expected.push((buflen >> 16) as u8);
        expected.push((buflen >> 24) as u8);
        expected.extend_from_slice(&item.buf);

        let mut actual = vec![0; expected.len()];

        WireFormat::encode(&item, &mut Cursor::new(&mut *actual)).expect("failed to encode item");

        assert_eq!(expected, actual);
    }

    #[test]
    fn struct_decode() {
        let expected = Item {
            a: 0xface_b00c_0404_4b1d,
            b: String::from("Огонь по готовности!"),
            c: vec![20067, 32449, 549, 4972, 77, 1987],
            buf: Data(vec![126, 236, 79, 59, 6, 159]),
        };

        let mut input: Vec<u8> = vec![0x1d, 0x4b, 0x04, 0x04, 0x0c, 0xb0, 0xce, 0xfa];
        let strlen = expected.b.len() as u16;
        input.push(strlen as u8);
        input.push((strlen >> 8) as u8);
        input.extend_from_slice(expected.b.as_bytes());

        let veclen = expected.c.len() as u16;
        input.push(veclen as u8);
        input.push((veclen >> 8) as u8);
        for val in &expected.c {
            input.push(*val as u8);
            input.push((val >> 8) as u8);
        }

        let buflen = expected.buf.len() as u32;
        input.push(buflen as u8);
        input.push((buflen >> 8) as u8);
        input.push((buflen >> 16) as u8);
        input.push((buflen >> 24) as u8);
        input.extend_from_slice(&expected.buf);

        let actual: Item =
            WireFormat::decode(&mut Cursor::new(input)).expect("failed to decode item");

        assert_eq!(expected, actual);
    }

    #[derive(Debug, PartialEq, P9WireFormat)]
    struct Nested {
        item: Item,
        val: Vec<u64>,
    }

    #[allow(clippy::vec_init_then_push)]
    fn build_encoded_buffer(value: &Nested) -> Vec<u8> {
        let mut result: Vec<u8> = Vec::new();

        // encode a
        result.push(value.item.a as u8);
        result.push((value.item.a >> 8) as u8);
        result.push((value.item.a >> 16) as u8);
        result.push((value.item.a >> 24) as u8);
        result.push((value.item.a >> 32) as u8);
        result.push((value.item.a >> 40) as u8);
        result.push((value.item.a >> 48) as u8);
        result.push((value.item.a >> 56) as u8);

        // encode b
        result.push(value.item.b.len() as u8);
        result.push((value.item.b.len() >> 8) as u8);
        result.extend_from_slice(value.item.b.as_bytes());

        // encode c
        result.push(value.item.c.len() as u8);
        result.push((value.item.c.len() >> 8) as u8);
        for val in &value.item.c {
            result.push((val & 0xffu16) as u8);
            result.push(((val >> 8) & 0xffu16) as u8);
        }

        // encode buf
        result.push(value.item.buf.len() as u8);
        result.push((value.item.buf.len() >> 8) as u8);
        result.push((value.item.buf.len() >> 16) as u8);
        result.push((value.item.buf.len() >> 24) as u8);
        result.extend_from_slice(&value.item.buf);

        // encode val
        result.push(value.val.len() as u8);
        result.push((value.val.len() >> 8) as u8);
        for val in &value.val {
            result.push(*val as u8);
            result.push((val >> 8) as u8);
            result.push((val >> 16) as u8);
            result.push((val >> 24) as u8);
            result.push((val >> 32) as u8);
            result.push((val >> 40) as u8);
            result.push((val >> 48) as u8);
            result.push((val >> 56) as u8);
        }

        result
    }

    #[test]
    fn nested_encode() {
        let value = Nested {
            item: Item {
                a: 0xcafe_d00d_8bad_f00d,
                b: String::from("龍が我が敵を喰らう!"),
                c: vec![2679, 55_919, 44, 38_819, 792],
                buf: Data(vec![129, 55, 200, 93, 7, 68]),
            },
            val: vec![1954978, 59, 4519, 15679],
        };

        let expected = build_encoded_buffer(&value);

        let mut actual = vec![0; expected.len()];

        WireFormat::encode(&value, &mut Cursor::new(&mut *actual)).expect("failed to encode value");
        assert_eq!(expected, actual);
    }

    #[test]
    fn nested_decode() {
        let expected = Nested {
            item: Item {
                a: 0x0ff1ce,
                b: String::from("龍神の剣を喰らえ!"),
                c: vec![21687, 159, 55, 9217, 192],
                buf: Data(vec![189, 22, 7, 59, 235]),
            },
            val: vec![15679, 8619196, 319746, 123957, 77, 0, 492],
        };

        let input = build_encoded_buffer(&expected);

        assert_eq!(
            expected,
            <Nested as WireFormat>::decode(&mut Cursor::new(&*input))
                .expect("failed to decode value")
        );
    }
}