src/h3/qpack/decoder.rs

// Copyright (C) 2019, Cloudflare, Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright notice,
//       this list of conditions and the following disclaimer.
//
//     * Redistributions in binary form must reproduce the above copyright
//       notice, this list of conditions and the following disclaimer in the
//       documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
// THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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use crate::octets;

use super::Error;
use super::Result;

use crate::h3::Header;

use super::INDEXED;
use super::INDEXED_WITH_POST_BASE;
use super::LITERAL;
use super::LITERAL_WITH_NAME_REF;

#[derive(Clone, Copy, Debug, PartialEq)]
enum Representation {
    Indexed,
    IndexedWithPostBase,
    Literal,
    LiteralWithNameRef,
    LiteralWithPostBase,
}

impl Representation {
    pub fn from_byte(b: u8) -> Representation {
        if b & INDEXED == INDEXED {
            return Representation::Indexed;
        }

        if b & LITERAL_WITH_NAME_REF == LITERAL_WITH_NAME_REF {
            return Representation::LiteralWithNameRef;
        }

        if b & LITERAL == LITERAL {
            return Representation::Literal;
        }

        if b & INDEXED_WITH_POST_BASE == INDEXED_WITH_POST_BASE {
            return Representation::IndexedWithPostBase;
        }

        Representation::LiteralWithPostBase
    }
}

/// A QPACK decoder.
pub struct Decoder {}

impl Default for Decoder {
    fn default() -> Decoder {
        Decoder {}
    }
}

impl Decoder {
    /// Creates a new QPACK decoder.
    pub fn new() -> Decoder {
        Decoder::default()
    }

    /// Processes control instructions from the encoder.
    pub fn control(&mut self, _buf: &mut [u8]) -> Result<()> {
        // TODO: process control instructions
        Ok(())
    }

    /// Decodes a QPACK header block into a list of headers.
    pub fn decode(&mut self, buf: &[u8], max_size: u64) -> Result<Vec<Header>> {
        let mut b = octets::Octets::with_slice(buf);

        let mut out = Vec::new();

        let mut left = max_size;

        let req_insert_count = decode_int(&mut b, 8)?;
        let base = decode_int(&mut b, 7)?;

        trace!("Header count={} base={}", req_insert_count, base);

        while b.cap() > 0 {
            let first = b.peek_u8()?;

            match Representation::from_byte(first) {
                Representation::Indexed => {
                    const STATIC: u8 = 0x40;

                    let s = first & STATIC == STATIC;
                    let index = decode_int(&mut b, 6)?;

                    trace!("Indexed index={} static={}", index, s);

                    if !s {
                        // TODO: implement dynamic table
                        return Err(Error::InvalidHeaderValue);
                    }

                    let (name, value) = lookup_static(index)?;

                    left = left
                        .checked_sub((name.len() + value.len()) as u64)
                        .ok_or(Error::HeaderListTooLarge)?;

                    let hdr = Header::new(name, value);
                    out.push(hdr);
                },

                Representation::IndexedWithPostBase => {
                    let index = decode_int(&mut b, 4)?;

                    trace!("Indexed With Post Base index={}", index);

                    // TODO: implement dynamic table
                    return Err(Error::InvalidHeaderValue);
                },

                Representation::Literal => {
                    let name_huff = b.as_ref()[0] & 0x08 == 0x08;
                    let name_len = decode_int(&mut b, 3)? as usize;

                    let mut name = b.get_bytes(name_len)?;

                    let name = if name_huff {
                        let name = super::huffman::decode(&mut name, true)?;

                        String::from_utf8(name)
                            .map_err(|_| Error::InvalidHeaderValue)?
                    } else {
                        let name = std::str::from_utf8(name.as_ref())
                            .map_err(|_| Error::InvalidHeaderValue)?;

                        name.to_ascii_lowercase()
                    };

                    let value = decode_str(&mut b)?;

                    trace!(
                        "Literal Without Name Reference name={:?} value={:?}",
                        name,
                        value,
                    );

                    left = left
                        .checked_sub((name.len() + value.len()) as u64)
                        .ok_or(Error::HeaderListTooLarge)?;

                    // Instead of calling Header::new(), create Header directly
                    // from `name` and `value`, which are already String.
                    let hdr = Header(name, value);
                    out.push(hdr);
                },

                Representation::LiteralWithNameRef => {
                    const STATIC: u8 = 0x10;

                    let s = first & STATIC == STATIC;
                    let name_idx = decode_int(&mut b, 4)?;
                    let value = decode_str(&mut b)?;

                    trace!(
                        "Literal name_idx={} static={} value={:?}",
                        name_idx,
                        s,
                        value
                    );

                    if !s {
                        // TODO: implement dynamic table
                        return Err(Error::InvalidHeaderValue);
                    }

                    let (name, _) = lookup_static(name_idx)?;

                    left = left
                        .checked_sub((name.len() + value.len()) as u64)
                        .ok_or(Error::HeaderListTooLarge)?;

                    // Instead of calling Header::new(), create Header directly
                    // from `value`, which is already String, but clone `name`
                    // as it is just a reference.
                    let hdr = Header(name.to_string(), value);
                    out.push(hdr);
                },

                Representation::LiteralWithPostBase => {
                    trace!("Literal With Post Base");

                    // TODO: implement dynamic table
                    return Err(Error::InvalidHeaderValue);
                },
            }
        }

        Ok(out)
    }
}

fn lookup_static(idx: u64) -> Result<(&'static str, &'static str)> {
    if idx >= super::static_table::STATIC_TABLE.len() as u64 {
        return Err(Error::InvalidStaticTableIndex);
    }

    Ok(super::static_table::STATIC_TABLE[idx as usize])
}

fn decode_int(b: &mut octets::Octets, prefix: usize) -> Result<u64> {
    let mask = 2u64.pow(prefix as u32) - 1;

    let mut val = u64::from(b.get_u8()?);
    val &= mask;

    if val < mask {
        return Ok(val);
    }

    let mut shift = 0;

    while b.cap() > 0 {
        let byte = b.get_u8()?;

        let inc = u64::from(byte & 0x7f)
            .checked_shl(shift)
            .ok_or(Error::BufferTooShort)?;

        val = val.checked_add(inc).ok_or(Error::BufferTooShort)?;

        shift += 7;

        if byte & 0x80 == 0 {
            return Ok(val);
        }
    }

    Err(Error::BufferTooShort)
}

fn decode_str<'a>(b: &'a mut octets::Octets) -> Result<String> {
    let first = b.peek_u8()?;

    let huff = first & 0x80 == 0x80;

    let len = decode_int(b, 7)? as usize;

    let mut val = b.get_bytes(len)?;

    let val = if huff {
        super::huffman::decode(&mut val, false)?
    } else {
        val.to_vec()
    };

    let val = String::from_utf8(val).map_err(|_| Error::InvalidHeaderValue)?;
    Ok(val)
}

#[cfg(test)]
mod tests {
    use super::*;

    use crate::octets;

    #[test]
    fn decode_int1() {
        let mut encoded = [0b01010, 0x02];
        let mut b = octets::Octets::with_slice(&mut encoded);

        assert_eq!(decode_int(&mut b, 5), Ok(10));
    }

    #[test]
    fn decode_int2() {
        let mut encoded = [0b11111, 0b10011010, 0b00001010];
        let mut b = octets::Octets::with_slice(&mut encoded);

        assert_eq!(decode_int(&mut b, 5), Ok(1337));
    }

    #[test]
    fn decode_int3() {
        let mut encoded = [0b101010];
        let mut b = octets::Octets::with_slice(&mut encoded);

        assert_eq!(decode_int(&mut b, 8), Ok(42));
    }
}