use std::convert::TryInto;
use std::io;
pub const MAGIC_NUM: u32 = 0xFD2F_B528;
pub const MIN_WINDOW_SIZE: u64 = 1024;
pub const MAX_WINDOW_SIZE: u64 = (1 << 41) + 7 * (1 << 38);
pub struct Frame {
magic_num: u32,
pub header: FrameHeader,
}
pub struct FrameHeader {
pub descriptor: FrameDescriptor,
window_descriptor: u8,
dict_id: Vec<u8>,
frame_content_size: Vec<u8>,
}
pub struct FrameDescriptor(u8);
#[derive(Debug, thiserror::Error)]
#[non_exhaustive]
pub enum FrameDescriptorError {
#[error("Invalid Frame_Content_Size_Flag; Is: {got}, Should be one of: 0, 1, 2, 3")]
InvalidFrameContentSizeFlag { got: u8 },
}
impl FrameDescriptor {
pub fn frame_content_size_flag(&self) -> u8 {
self.0 >> 6
}
pub fn reserved_flag(&self) -> bool {
((self.0 >> 3) & 0x1) == 1
}
pub fn single_segment_flag(&self) -> bool {
((self.0 >> 5) & 0x1) == 1
}
pub fn content_checksum_flag(&self) -> bool {
((self.0 >> 2) & 0x1) == 1
}
pub fn dict_id_flag(&self) -> u8 {
self.0 & 0x3
}
pub fn frame_content_size_bytes(&self) -> Result<u8, FrameDescriptorError> {
match self.frame_content_size_flag() {
0 => {
if self.single_segment_flag() {
Ok(1)
} else {
Ok(0)
}
}
1 => Ok(2),
2 => Ok(4),
3 => Ok(8),
other => Err(FrameDescriptorError::InvalidFrameContentSizeFlag { got: other }),
}
}
pub fn dictionary_id_bytes(&self) -> Result<u8, FrameDescriptorError> {
match self.dict_id_flag() {
0 => Ok(0),
1 => Ok(1),
2 => Ok(2),
3 => Ok(4),
other => Err(FrameDescriptorError::InvalidFrameContentSizeFlag { got: other }),
}
}
}
#[derive(Debug, thiserror::Error)]
#[non_exhaustive]
pub enum FrameHeaderError {
#[error("window_size bigger than allowed maximum. Is: {got}, Should be lower than: {MAX_WINDOW_SIZE}")]
WindowTooBig { got: u64 },
#[error("window_size smaller than allowed minimum. Is: {got}, Should be greater than: {MIN_WINDOW_SIZE}")]
WindowTooSmall { got: u64 },
#[error(transparent)]
FrameDescriptorError(#[from] FrameDescriptorError),
#[error("Not enough bytes in dict_id. Is: {got}, Should be: {expected}")]
DictIdTooSmall { got: usize, expected: usize },
#[error("frame_content_size does not have the right length. Is: {got}, Should be: {expected}")]
MismatchedFrameSize { got: usize, expected: u8 },
#[error("frame_content_size was zero")]
FrameSizeIsZero,
#[error("Invalid frame_content_size. Is: {got}, Should be one of 1, 2, 4, 8 bytes")]
InvalidFrameSize { got: u8 },
}
impl FrameHeader {
pub fn window_size(&self) -> Result<u64, FrameHeaderError> {
if self.descriptor.single_segment_flag() {
self.frame_content_size()
} else {
let exp = self.window_descriptor >> 3;
let mantissa = self.window_descriptor & 0x7;
let window_log = 10 + u64::from(exp);
let window_base = 1 << window_log;
let window_add = (window_base / 8) * u64::from(mantissa);
let window_size = window_base + window_add;
if window_size >= MIN_WINDOW_SIZE {
if window_size < MAX_WINDOW_SIZE {
Ok(window_size)
} else {
Err(FrameHeaderError::WindowTooBig { got: window_size })
}
} else {
Err(FrameHeaderError::WindowTooSmall { got: window_size })
}
}
}
pub fn dictionary_id(&self) -> Result<Option<u32>, FrameHeaderError> {
if self.descriptor.dict_id_flag() == 0 {
Ok(None)
} else {
let bytes = self.descriptor.dictionary_id_bytes()?;
if self.dict_id.len() != bytes as usize {
Err(FrameHeaderError::DictIdTooSmall {
got: self.dict_id.len(),
expected: bytes as usize,
})
} else {
let mut value: u32 = 0;
let mut shift = 0;
for x in &self.dict_id {
value |= u32::from(*x) << shift;
shift += 8;
}
Ok(Some(value))
}
}
}
pub fn frame_content_size(&self) -> Result<u64, FrameHeaderError> {
let bytes = self.descriptor.frame_content_size_bytes()?;
if self.frame_content_size.len() != (bytes as usize) {
return Err(FrameHeaderError::MismatchedFrameSize {
got: self.frame_content_size.len(),
expected: bytes,
});
}
match bytes {
0 => Err(FrameHeaderError::FrameSizeIsZero),
1 => Ok(u64::from(self.frame_content_size[0])),
2 => {
let val = (u64::from(self.frame_content_size[1]) << 8)
+ (u64::from(self.frame_content_size[0]));
Ok(val + 256) }
4 => {
let val = self.frame_content_size[..4]
.try_into()
.expect("optimized away");
let val = u32::from_le_bytes(val);
Ok(u64::from(val))
}
8 => {
let val = self.frame_content_size[..8]
.try_into()
.expect("optimized away");
let val = u64::from_le_bytes(val);
Ok(val)
}
other => Err(FrameHeaderError::InvalidFrameSize { got: other }),
}
}
}
#[derive(Debug, thiserror::Error)]
#[non_exhaustive]
pub enum FrameCheckError {
#[error("magic_num wrong. Is: {got}. Should be: {MAGIC_NUM}")]
WrongMagicNum { got: u32 },
#[error("Reserved Flag set. Must be zero")]
ReservedFlagSet,
#[error(transparent)]
FrameHeaderError(#[from] FrameHeaderError),
}
impl Frame {
pub fn check_valid(&self) -> Result<(), FrameCheckError> {
if self.magic_num != MAGIC_NUM {
Err(FrameCheckError::WrongMagicNum {
got: self.magic_num,
})
} else if self.header.descriptor.reserved_flag() {
Err(FrameCheckError::ReservedFlagSet)
} else {
self.header.dictionary_id()?;
self.header.window_size()?;
if self.header.descriptor.single_segment_flag() {
self.header.frame_content_size()?;
}
Ok(())
}
}
}
#[derive(Debug, thiserror::Error)]
#[non_exhaustive]
pub enum ReadFrameHeaderError {
#[error("Error while reading magic number: {0}")]
MagicNumberReadError(#[source] io::Error),
#[error("Error while reading frame descriptor: {0}")]
FrameDescriptorReadError(#[source] io::Error),
#[error(transparent)]
InvalidFrameDescriptor(#[from] FrameDescriptorError),
#[error("Error while reading window descriptor: {0}")]
WindowDescriptorReadError(#[source] io::Error),
#[error("Error while reading dictionary id: {0}")]
DictionaryIdReadError(#[source] io::Error),
#[error("Error while reading frame content size: {0}")]
FrameContentSizeReadError(#[source] io::Error),
#[error("SkippableFrame encountered with MagicNumber 0x{0:X} and length {1} bytes")]
SkipFrame(u32, u32),
}
use std::io::Read;
pub fn read_frame_header(mut r: impl Read) -> Result<(Frame, u8), ReadFrameHeaderError> {
use ReadFrameHeaderError as err;
let mut buf = [0u8; 4];
r.read_exact(&mut buf).map_err(err::MagicNumberReadError)?;
let magic_num = u32::from_le_bytes(buf);
if (0x184D2A50..=0x184D2A5F).contains(&magic_num) {
r.read_exact(&mut buf)
.map_err(err::FrameDescriptorReadError)?;
let skip_size = u32::from_le_bytes(buf);
return Err(ReadFrameHeaderError::SkipFrame(magic_num, skip_size));
}
let mut bytes_read = 4;
r.read_exact(&mut buf[0..1])
.map_err(err::FrameDescriptorReadError)?;
let desc = FrameDescriptor(buf[0]);
bytes_read += 1;
let mut frame_header = FrameHeader {
descriptor: FrameDescriptor(desc.0),
dict_id: vec![0; desc.dictionary_id_bytes()? as usize],
frame_content_size: vec![0; desc.frame_content_size_bytes()? as usize],
window_descriptor: 0,
};
if !desc.single_segment_flag() {
r.read_exact(&mut buf[0..1])
.map_err(err::WindowDescriptorReadError)?;
frame_header.window_descriptor = buf[0];
bytes_read += 1;
}
if !frame_header.dict_id.is_empty() {
r.read_exact(frame_header.dict_id.as_mut_slice())
.map_err(err::DictionaryIdReadError)?;
bytes_read += frame_header.dict_id.len();
}
if !frame_header.frame_content_size.is_empty() {
r.read_exact(frame_header.frame_content_size.as_mut_slice())
.map_err(err::FrameContentSizeReadError)?;
bytes_read += frame_header.frame_content_size.len();
}
let frame: Frame = Frame {
magic_num,
header: frame_header,
};
Ok((frame, bytes_read as u8))
}