rust/flexbuffers/src/reader/mod.rs - RealtimeRoboticsGroup/test - Gitiles

 // Copyright 2019 Google LLC
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 use crate::bitwidth::BitWidth;
 use crate::flexbuffer_type::FlexBufferType;
 use crate::Blob;
 use std::convert::{TryFrom, TryInto};
 use std::fmt;
 use std::ops::Rem;
 use std::str::FromStr;
 mod de;
 mod iter;
 mod map;
 mod vector;
 pub use de::DeserializationError;
 pub use iter::ReaderIterator;
 pub use map::{MapReader, MapReaderIndexer};
 pub use vector::VectorReader;

 /// All the possible errors when reading a flexbuffer.
 #[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize)]
 pub enum Error {
     /// One of the following data errors occured:
     ///
     /// *    The read flexbuffer had an offset that pointed outside the flexbuffer.
     /// *    The 'negative indicies' where length and map keys are stored were out of bounds
     /// *    The buffer was too small to contain a flexbuffer root.
     FlexbufferOutOfBounds,
     /// Failed to parse a valid FlexbufferType and Bitwidth from a type byte.
     InvalidPackedType,
     /// Flexbuffer type of the read data does not match function used.
     UnexpectedFlexbufferType {
         expected: FlexBufferType,
         actual: FlexBufferType,
     },
     /// BitWidth type of the read data does not match function used.
     UnexpectedBitWidth {
         expected: BitWidth,
         actual: BitWidth,
     },
     /// Read a flexbuffer offset or length that overflowed usize.
     ReadUsizeOverflowed,
     /// Tried to index a type that's not one of the Flexbuffer vector types.
     CannotIndexAsVector,
     /// Tried to index a Flexbuffer vector or map out of bounds.
     IndexOutOfBounds,
     /// A Map was indexed with a key that it did not contain.
     KeyNotFound,
     /// Failed to parse a Utf8 string.
     /// The Option will be `None` if and only if this Error was deserialized.
     // NOTE: std::str::Utf8Error does not implement Serialize, Deserialize, nor Default. We tell
     // serde to skip the field and default to None. We prefer to have the boxed error so it can be
     // used with std::error::Error::source, though another (worse) option could be to drop that
     // information.
     Utf8Error(#[serde(skip)] Option<Box<std::str::Utf8Error>>),
     /// get_slice failed because the given data buffer is misaligned.
     AlignmentError,
     InvalidRootWidth,
     InvalidMapKeysVectorWidth,
 }
 impl std::convert::From<std::str::Utf8Error> for Error {
     fn from(e: std::str::Utf8Error) -> Self {
         Self::Utf8Error(Some(Box::new(e)))
     }
 }
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             Self::UnexpectedBitWidth { expected, actual } => write!(
                 f,
                 "Error reading flexbuffer: Expected bitwidth: {:?}, found bitwidth: {:?}",
                 expected, actual
             ),
             Self::UnexpectedFlexbufferType { expected, actual } => write!(
                 f,
                 "Error reading flexbuffer: Expected type: {:?}, found type: {:?}",
                 expected, actual
             ),
             _ => write!(f, "Error reading flexbuffer: {:?}", self),
         }
     }
 }
 impl std::error::Error for Error {
     fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
         if let Self::Utf8Error(Some(e)) = self {
             Some(e)
         } else {
             None
         }
     }
 }

 pub trait ReadLE: crate::private::Sealed + std::marker::Sized {
     const VECTOR_TYPE: FlexBufferType;
     const WIDTH: BitWidth;
 }
 macro_rules! rle {
     ($T: ty, $VECTOR_TYPE: ident, $WIDTH: ident) => {
         impl ReadLE for $T {
             const VECTOR_TYPE: FlexBufferType = FlexBufferType::$VECTOR_TYPE;
             const WIDTH: BitWidth = BitWidth::$WIDTH;
         }
     };
 }
 rle!(u8, VectorUInt, W8);
 rle!(u16, VectorUInt, W16);
 rle!(u32, VectorUInt, W32);
 rle!(u64, VectorUInt, W64);
 rle!(i8, VectorInt, W8);
 rle!(i16, VectorInt, W16);
 rle!(i32, VectorInt, W32);
 rle!(i64, VectorInt, W64);
 rle!(f32, VectorFloat, W32);
 rle!(f64, VectorFloat, W64);

 macro_rules! as_default {
     ($as: ident, $get: ident, $T: ty) => {
         pub fn $as(&self) -> $T {
             self.$get().unwrap_or_default()
         }
     };
 }

 /// `Reader`s allow access to data stored in a Flexbuffer.
 ///
 /// Each reader represents a single address in the buffer so data is read lazily. Start a reader
 /// by calling `get_root` on your flexbuffer `&[u8]`.
 ///
 /// - The `get_T` methods return a `Result<T, Error>`. They return an OK value if and only if the
 /// flexbuffer type matches `T`. This is analogous to the behavior of Rust's json library, though
 /// with Result instead of Option.
 /// - The `as_T` methods will try their best to return to a value of type `T`
 /// (by casting or even parsing a string if necessary) but ultimately returns `T::default` if it
 /// fails. This behavior is analogous to that of flexbuffers C++.
 #[derive(Default, Clone)]
 pub struct Reader<'de> {
     fxb_type: FlexBufferType,
     width: BitWidth,
     address: usize,
     buffer: &'de [u8],
 }

 // manual implementation of Debug because buffer slice can't be automatically displayed
 impl<'de> std::fmt::Debug for Reader<'de> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         // skips buffer field
         f.debug_struct("Reader")
             .field("fxb_type", &self.fxb_type)
             .field("width", &self.width)
             .field("address", &self.address)
             .finish()
     }
 }


 macro_rules! try_cast_fn {
     ($name: ident, $full_width: ident, $Ty: ident) => {
         pub fn $name(&self) -> $Ty {
             self.$full_width().try_into().unwrap_or_default()
         }
     }
 }

 fn safe_sub(a: usize, b: usize) -> Result<usize, Error> {
     a.checked_sub(b).ok_or(Error::FlexbufferOutOfBounds)
 }

 fn deref_offset(buffer: &[u8], address: usize, width: BitWidth) -> Result<usize, Error> {
     let off = read_usize(buffer, address, width);
     safe_sub(address, off)
 }

 impl<'de> Reader<'de> {
     fn new(
         buffer: &'de [u8],
         mut address: usize,
         mut fxb_type: FlexBufferType,
         width: BitWidth,
         parent_width: BitWidth,
     ) -> Result<Self, Error> {
         if fxb_type.is_reference() {
             address = deref_offset(buffer, address, parent_width)?;
             // Indirects were dereferenced.
             if let Some(t) = fxb_type.to_direct() {
                 fxb_type = t;
             }
         }
         Ok(Reader {
             address,
             fxb_type,
             width,
             buffer,
         })
     }
     /// Parses the flexbuffer from the given buffer. Assumes the flexbuffer root is the last byte
     /// of the buffer.
     pub fn get_root(buffer: &'de [u8]) -> Result<Self, Error> {
         let end = buffer.len();
         if end < 3 {
             return Err(Error::FlexbufferOutOfBounds);
         }
         // Last byte is the root width.
         let root_width = BitWidth::from_nbytes(buffer[end - 1]).ok_or(Error::InvalidRootWidth)?;
         // Second last byte is root type.
         let (fxb_type, width) = unpack_type(buffer[end - 2])?;
         // Location of root data. (BitWidth bits before root type)
         let address = safe_sub(end - 2, root_width.n_bytes())?;
         Self::new(buffer, address, fxb_type, width, root_width)
     }
     /// Returns the FlexBufferType of this Reader.
     pub fn flexbuffer_type(&self) -> FlexBufferType {
         self.fxb_type
     }
     /// Returns the bitwidth of this Reader.
     pub fn bitwidth(&self) -> BitWidth {
         self.width
     }
     /// Returns the length of the Flexbuffer. If the type has no length, or if an error occurs,
     /// 0 is returned.
     pub fn length(&self) -> usize {
         if let Some(len) = self.fxb_type.fixed_length_vector_length() {
             len
         } else if self.fxb_type.has_length_slot() && self.address >= self.width.n_bytes() {
             read_usize(self.buffer, self.address - self.width.n_bytes(), self.width)
         } else {
             0
         }
     }
     /// Returns true if the flexbuffer is aligned to 8 bytes. This guarantees, for valid
     /// flexbuffers, that the data is correctly aligned in memory and slices can be read directly
     /// e.g. with `get_f64s` or `get_i16s`.
     pub fn is_aligned(&self) -> bool {
         (self.buffer.as_ptr() as usize).rem(8) == 0
     }
     as_default!(as_vector, get_vector, VectorReader<'de>);
     as_default!(as_map, get_map, MapReader<'de>);

     fn expect_type(&self, ty: FlexBufferType) -> Result<(), Error> {
         if self.fxb_type == ty {
             Ok(())
         } else {
             Err(Error::UnexpectedFlexbufferType {
                 expected: ty,
                 actual: self.fxb_type,
             })
         }
     }
     fn expect_bw(&self, bw: BitWidth) -> Result<(), Error> {
         if self.width == bw {
             Ok(())
         } else {
             Err(Error::UnexpectedBitWidth {
                 expected: bw,
                 actual: self.width,
             })
         }
     }
     /// Directly reads a slice of type `T`where `T` is one of `u8,u16,u32,u64,i8,i16,i32,i64,f32,f64`.
     /// Returns Err if the type, bitwidth, or memory alignment does not match. Since the bitwidth is
     /// dynamic, its better to use a VectorReader unless you know your data and performance is critical.
     #[cfg(target_endian = "little")]
     pub fn get_slice<T: ReadLE>(&self) -> Result<&'de [T], Error> {
         if self.flexbuffer_type().typed_vector_type() != T::VECTOR_TYPE.typed_vector_type() {
             self.expect_type(T::VECTOR_TYPE)?;
         }
         if self.bitwidth().n_bytes() != std::mem::size_of::<T>() {
             self.expect_bw(T::WIDTH)?;
         }
         let end = self.address + self.length() * std::mem::size_of::<T>();
         let slice = &self
             .buffer
             .get(self.address..end)
             .ok_or(Error::FlexbufferOutOfBounds)?;
         // `align_to` is required because the point of this function is to directly hand back a
         // slice of scalars. This can fail because Rust's default allocator is not 16byte aligned
         // (though in practice this only happens for small buffers).
         let (pre, mid, suf) = unsafe { slice.align_to::<T>() };
         if pre.is_empty() && suf.is_empty() {
             Ok(mid)
         } else {
             Err(Error::AlignmentError)
         }
     }

     pub fn get_bool(&self) -> Result<bool, Error> {
         self.expect_type(FlexBufferType::Bool)?;
         Ok(
             self.buffer[self.address..self.address + self.width.n_bytes()]
                 .iter()
                 .any(|&b| b != 0),
         )
     }
     pub fn get_key(&self) -> Result<&'de str, Error> {
         self.expect_type(FlexBufferType::Key)?;
         let (length, _) = self.buffer[self.address..]
             .iter()
             .enumerate()
             .find(|(_, &b)| b == b'\0')
             .unwrap_or((0, &0));
         let bytes = &self.buffer[self.address..self.address + length];
         Ok(std::str::from_utf8(bytes)?)
     }
     pub fn get_blob(&self) -> Result<Blob<'de>, Error> {
         self.expect_type(FlexBufferType::Blob)?;
         Ok(Blob(
             &self.buffer[self.address..self.address + self.length()],
         ))
     }
     pub fn as_blob(&self) -> Blob<'de> {
         self.get_blob().unwrap_or(Blob(&[]))
     }
     pub fn get_str(&self) -> Result<&'de str, Error> {
         self.expect_type(FlexBufferType::String)?;
         let bytes = &self.buffer[self.address..self.address + self.length()];
         Ok(std::str::from_utf8(bytes)?)
     }
     fn get_map_info(&self) -> Result<(usize, BitWidth), Error> {
         self.expect_type(FlexBufferType::Map)?;
         if 3 * self.width.n_bytes() >= self.address {
             return Err(Error::FlexbufferOutOfBounds);
         }
         let keys_offset_address = self.address - 3 * self.width.n_bytes();
         let keys_width = {
             let kw_addr = self.address - 2 * self.width.n_bytes();
             let kw = read_usize(self.buffer, kw_addr, self.width);
             BitWidth::from_nbytes(kw).ok_or(Error::InvalidMapKeysVectorWidth)
         }?;
         Ok((keys_offset_address, keys_width))
     }
     pub fn get_map(&self) -> Result<MapReader<'de>, Error> {
         let (keys_offset_address, keys_width) = self.get_map_info()?;
         let keys_address = deref_offset(self.buffer, keys_offset_address, self.width)?;
         // TODO(cneo): Check that vectors length equals keys length.
         Ok(MapReader {
             buffer: self.buffer,
             values_address: self.address,
             values_width: self.width,
             keys_address,
             keys_width,
             length: self.length(),
         })
     }
     /// Tries to read a FlexBufferType::UInt. Returns Err if the type is not a UInt or if the
     /// address is out of bounds.
     pub fn get_u64(&self) -> Result<u64, Error> {
         self.expect_type(FlexBufferType::UInt)?;
         let cursor = self
             .buffer
             .get(self.address..self.address + self.width.n_bytes());
         match self.width {
             BitWidth::W8 => cursor.map(|s| s[0] as u8).map(Into::into),
             BitWidth::W16 => cursor
                 .and_then(|s| s.try_into().ok())
                 .map(<u16>::from_le_bytes)
                 .map(Into::into),
             BitWidth::W32 => cursor
                 .and_then(|s| s.try_into().ok())
                 .map(<u32>::from_le_bytes)
                 .map(Into::into),
             BitWidth::W64 => cursor
                 .and_then(|s| s.try_into().ok())
                 .map(<u64>::from_le_bytes),
         }
         .ok_or(Error::FlexbufferOutOfBounds)
     }
     /// Tries to read a FlexBufferType::Int. Returns Err if the type is not a UInt or if the
     /// address is out of bounds.
     pub fn get_i64(&self) -> Result<i64, Error> {
         self.expect_type(FlexBufferType::Int)?;
         let cursor = self
             .buffer
             .get(self.address..self.address + self.width.n_bytes());
         match self.width {
             BitWidth::W8 => cursor.map(|s| s[0] as i8).map(Into::into),
             BitWidth::W16 => cursor
                 .and_then(|s| s.try_into().ok())
                 .map(<i16>::from_le_bytes)
                 .map(Into::into),
             BitWidth::W32 => cursor
                 .and_then(|s| s.try_into().ok())
                 .map(<i32>::from_le_bytes)
                 .map(Into::into),
             BitWidth::W64 => cursor
                 .and_then(|s| s.try_into().ok())
                 .map(<i64>::from_le_bytes),
         }
         .ok_or(Error::FlexbufferOutOfBounds)
     }
     /// Tries to read a FlexBufferType::Float. Returns Err if the type is not a UInt, if the
     /// address is out of bounds, or if its a f16 or f8 (not currently supported).
     pub fn get_f64(&self) -> Result<f64, Error> {
         self.expect_type(FlexBufferType::Float)?;
         let cursor = self
             .buffer
             .get(self.address..self.address + self.width.n_bytes());
         match self.width {
             BitWidth::W8 | BitWidth::W16 => return Err(Error::InvalidPackedType),
             BitWidth::W32 => cursor
                 .and_then(|s| s.try_into().ok())
                 .map(f32_from_le_bytes)
                 .map(Into::into),
             BitWidth::W64 => cursor
                 .and_then(|s| s.try_into().ok())
                 .map(f64_from_le_bytes),
         }
         .ok_or(Error::FlexbufferOutOfBounds)
     }
     pub fn as_bool(&self) -> bool {
         use FlexBufferType::*;
         match self.fxb_type {
             Bool => self.get_bool().unwrap_or_default(),
             UInt => self.as_u64() != 0,
             Int => self.as_i64() != 0,
             Float => self.as_f64().abs() > std::f64::EPSILON,
             String | Key => !self.as_str().is_empty(),
             Null => false,
             Blob => self.length() != 0,
             ty if ty.is_vector() => self.length() != 0,
             _ => unreachable!(),
         }
     }
     /// Returns a u64, casting if necessary. For Maps and Vectors, their length is
     /// returned. If anything fails, 0 is returned.
     pub fn as_u64(&self) -> u64 {
         match self.fxb_type {
             FlexBufferType::UInt => self.get_u64().unwrap_or_default(),
             FlexBufferType::Int => self
                 .get_i64()
                 .unwrap_or_default()
                 .try_into()
                 .unwrap_or_default(),
             FlexBufferType::Float => self.get_f64().unwrap_or_default() as u64,
             FlexBufferType::String => {
                 if let Ok(s) = self.get_str() {
                     if let Ok(f) = u64::from_str(s) {
                         return f;
                     }
                 }
                 0
             }
             _ if self.fxb_type.is_vector() => self.length() as u64,
             _ => 0,
         }
     }
     try_cast_fn!(as_u32, as_u64, u32);
     try_cast_fn!(as_u16, as_u64, u16);
     try_cast_fn!(as_u8, as_u64, u8);

     /// Returns an i64, casting if necessary. For Maps and Vectors, their length is
     /// returned. If anything fails, 0 is returned.
     pub fn as_i64(&self) -> i64 {
         match self.fxb_type {
             FlexBufferType::Int => self.get_i64().unwrap_or_default(),
             FlexBufferType::UInt => self
                 .get_u64()
                 .unwrap_or_default()
                 .try_into()
                 .unwrap_or_default(),
             FlexBufferType::Float => self.get_f64().unwrap_or_default() as i64,
             FlexBufferType::String => {
                 if let Ok(s) = self.get_str() {
                     if let Ok(f) = i64::from_str(s) {
                         return f;
                     }
                 }
                 0
             }
             _ if self.fxb_type.is_vector() => self.length() as i64,
             _ => 0,
         }
     }
     try_cast_fn!(as_i32, as_i64, i32);
     try_cast_fn!(as_i16, as_i64, i16);
     try_cast_fn!(as_i8, as_i64, i8);

     /// Returns an f64, casting if necessary. For Maps and Vectors, their length is
     /// returned. If anything fails, 0 is returned.
     pub fn as_f64(&self) -> f64 {
         match self.fxb_type {
             FlexBufferType::Int => self.get_i64().unwrap_or_default() as f64,
             FlexBufferType::UInt => self.get_u64().unwrap_or_default() as f64,
             FlexBufferType::Float => self.get_f64().unwrap_or_default(),
             FlexBufferType::String => {
                 if let Ok(s) = self.get_str() {
                     if let Ok(f) = f64::from_str(s) {
                         return f;
                     }
                 }
                 0.0
             }
             _ if self.fxb_type.is_vector() => self.length() as f64,
             _ => 0.0,
         }
     }
     pub fn as_f32(&self) -> f32 {
         self.as_f64() as f32
     }

     /// Returns empty string if you're not trying to read a string.
     pub fn as_str(&self) -> &'de str {
         match self.fxb_type {
             FlexBufferType::String => self.get_str().unwrap_or_default(),
             FlexBufferType::Key => self.get_key().unwrap_or_default(),
             _ => "",
         }
     }
     pub fn get_vector(&self) -> Result<VectorReader<'de>, Error> {
         if !self.fxb_type.is_vector() {
             self.expect_type(FlexBufferType::Vector)?;
         };
         Ok(VectorReader {
             reader: self.clone(),
             length: self.length(),
         })
     }
 }

 impl<'de> fmt::Display for Reader<'de> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         use FlexBufferType::*;
         match self.flexbuffer_type() {
             Null => write!(f, "null"),
             UInt => write!(f, "{}", self.as_u64()),
             Int => write!(f, "{}", self.as_i64()),
             Float => write!(f, "{}", self.as_f64()),
             Key | String => write!(f, "{:?}", self.as_str()),
             Bool => write!(f, "{}", self.as_bool()),
             Blob => write!(f, "blob"),
             Map => {
                 write!(f, "{{")?;
                 let m = self.as_map();
                 let mut pairs = m.iter_keys().zip(m.iter_values());
                 if let Some((k, v)) = pairs.next() {
                     write!(f, "{:?}: {}", k, v)?;
                     for (k, v) in pairs {
                         write!(f, ", {:?}: {}", k, v)?;
                     }
                 }
                 write!(f, "}}")
             }
             t if t.is_vector() => {
                 write!(f, "[")?;
                 let mut elems = self.as_vector().iter();
                 if let Some(first) = elems.next() {
                     write!(f, "{}", first)?;
                     for e in elems {
                         write!(f, ", {}", e)?;
                     }
                 }
                 write!(f, "]")
             }
             _ => unreachable!("Display not implemented for {:?}", self),
         }
     }
 }

 // TODO(cneo): Use <f..>::from_le_bytes when we move past rustc 1.39.
 fn f32_from_le_bytes(bytes: [u8; 4]) -> f32 {
     let bits = <u32>::from_le_bytes(bytes);
     <f32>::from_bits(bits)
 }
 fn f64_from_le_bytes(bytes: [u8; 8]) -> f64 {
     let bits = <u64>::from_le_bytes(bytes);
     <f64>::from_bits(bits)
 }

 fn read_usize(buffer: &[u8], address: usize, width: BitWidth) -> usize {
     let cursor = &buffer[address..];
     match width {
         BitWidth::W8 => cursor[0] as usize,
         BitWidth::W16 => cursor
             .get(0..2)
             .and_then(|s| s.try_into().ok())
             .map(<u16>::from_le_bytes)
             .unwrap_or_default() as usize,
         BitWidth::W32 => cursor
             .get(0..4)
             .and_then(|s| s.try_into().ok())
             .map(<u32>::from_le_bytes)
             .unwrap_or_default() as usize,
         BitWidth::W64 => cursor
             .get(0..8)
             .and_then(|s| s.try_into().ok())
             .map(<u64>::from_le_bytes)
             .unwrap_or_default() as usize,
     }
 }

 fn unpack_type(ty: u8) -> Result<(FlexBufferType, BitWidth), Error> {
     let w = BitWidth::try_from(ty & 3u8).map_err(|_| Error::InvalidPackedType)?;
     let t = FlexBufferType::try_from(ty >> 2).map_err(|_| Error::InvalidPackedType)?;
     Ok((t, w))
 }
	// Copyright 2019 Google LLC
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// https://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	use crate::bitwidth::BitWidth;
	use crate::flexbuffer_type::FlexBufferType;
	use crate::Blob;
	use std::convert::{TryFrom, TryInto};
	use std::fmt;
	use std::ops::Rem;
	use std::str::FromStr;
	mod de;
	mod iter;
	mod map;
	mod vector;
	pub use de::DeserializationError;
	pub use iter::ReaderIterator;
	pub use map::{MapReader, MapReaderIndexer};
	pub use vector::VectorReader;

	/// All the possible errors when reading a flexbuffer.
	#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize)]
	pub enum Error {
	/// One of the following data errors occured:
	///
	/// * The read flexbuffer had an offset that pointed outside the flexbuffer.
	/// * The 'negative indicies' where length and map keys are stored were out of bounds
	/// * The buffer was too small to contain a flexbuffer root.
	FlexbufferOutOfBounds,
	/// Failed to parse a valid FlexbufferType and Bitwidth from a type byte.
	InvalidPackedType,
	/// Flexbuffer type of the read data does not match function used.
	UnexpectedFlexbufferType {
	expected: FlexBufferType,
	actual: FlexBufferType,
	},
	/// BitWidth type of the read data does not match function used.
	UnexpectedBitWidth {
	expected: BitWidth,
	actual: BitWidth,
	},
	/// Read a flexbuffer offset or length that overflowed usize.
	ReadUsizeOverflowed,
	/// Tried to index a type that's not one of the Flexbuffer vector types.
	CannotIndexAsVector,
	/// Tried to index a Flexbuffer vector or map out of bounds.
	IndexOutOfBounds,
	/// A Map was indexed with a key that it did not contain.
	KeyNotFound,
	/// Failed to parse a Utf8 string.
	/// The Option will be `None` if and only if this Error was deserialized.
	// NOTE: std::str::Utf8Error does not implement Serialize, Deserialize, nor Default. We tell
	// serde to skip the field and default to None. We prefer to have the boxed error so it can be
	// used with std::error::Error::source, though another (worse) option could be to drop that
	// information.
	Utf8Error(#[serde(skip)] Option<Box<std::str::Utf8Error>>),
	/// get_slice failed because the given data buffer is misaligned.
	AlignmentError,
	InvalidRootWidth,
	InvalidMapKeysVectorWidth,
	}
	impl std::convert::From<std::str::Utf8Error> for Error {
	fn from(e: std::str::Utf8Error) -> Self {
	Self::Utf8Error(Some(Box::new(e)))
	}
	}
	impl fmt::Display for Error {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	match self {
	Self::UnexpectedBitWidth { expected, actual } => write!(
	f,
	"Error reading flexbuffer: Expected bitwidth: {:?}, found bitwidth: {:?}",
	expected, actual
	),
	Self::UnexpectedFlexbufferType { expected, actual } => write!(
	f,
	"Error reading flexbuffer: Expected type: {:?}, found type: {:?}",
	expected, actual
	),
	_ => write!(f, "Error reading flexbuffer: {:?}", self),
	}
	}
	}
	impl std::error::Error for Error {
	fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
	if let Self::Utf8Error(Some(e)) = self {
	Some(e)
	} else {
	None
	}
	}
	}

	pub trait ReadLE: crate::private::Sealed + std::marker::Sized {
	const VECTOR_TYPE: FlexBufferType;
	const WIDTH: BitWidth;
	}
	macro_rules! rle {
	($T: ty, $VECTOR_TYPE: ident, $WIDTH: ident) => {
	impl ReadLE for $T {
	const VECTOR_TYPE: FlexBufferType = FlexBufferType::$VECTOR_TYPE;
	const WIDTH: BitWidth = BitWidth::$WIDTH;
	}
	};
	}
	rle!(u8, VectorUInt, W8);
	rle!(u16, VectorUInt, W16);
	rle!(u32, VectorUInt, W32);
	rle!(u64, VectorUInt, W64);
	rle!(i8, VectorInt, W8);
	rle!(i16, VectorInt, W16);
	rle!(i32, VectorInt, W32);
	rle!(i64, VectorInt, W64);
	rle!(f32, VectorFloat, W32);
	rle!(f64, VectorFloat, W64);

	macro_rules! as_default {
	($as: ident, $get: ident, $T: ty) => {
	pub fn $as(&self) -> $T {
	self.$get().unwrap_or_default()
	}
	};
	}

	/// `Reader`s allow access to data stored in a Flexbuffer.
	///
	/// Each reader represents a single address in the buffer so data is read lazily. Start a reader
	/// by calling `get_root` on your flexbuffer `&[u8]`.
	///
	/// - The `get_T` methods return a `Result<T, Error>`. They return an OK value if and only if the
	/// flexbuffer type matches `T`. This is analogous to the behavior of Rust's json library, though
	/// with Result instead of Option.
	/// - The `as_T` methods will try their best to return to a value of type `T`
	/// (by casting or even parsing a string if necessary) but ultimately returns `T::default` if it
	/// fails. This behavior is analogous to that of flexbuffers C++.
	#[derive(Default, Clone)]
	pub struct Reader<'de> {
	fxb_type: FlexBufferType,
	width: BitWidth,
	address: usize,
	buffer: &'de [u8],
	}

	// manual implementation of Debug because buffer slice can't be automatically displayed
	impl<'de> std::fmt::Debug for Reader<'de> {
	fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
	// skips buffer field
	f.debug_struct("Reader")
	.field("fxb_type", &self.fxb_type)
	.field("width", &self.width)
	.field("address", &self.address)
	.finish()
	}
	}


	macro_rules! try_cast_fn {
	($name: ident, $full_width: ident, $Ty: ident) => {
	pub fn $name(&self) -> $Ty {
	self.$full_width().try_into().unwrap_or_default()
	}
	}
	}

	fn safe_sub(a: usize, b: usize) -> Result<usize, Error> {
	a.checked_sub(b).ok_or(Error::FlexbufferOutOfBounds)
	}

	fn deref_offset(buffer: &[u8], address: usize, width: BitWidth) -> Result<usize, Error> {
	let off = read_usize(buffer, address, width);
	safe_sub(address, off)
	}

	impl<'de> Reader<'de> {
	fn new(
	buffer: &'de [u8],
	mut address: usize,
	mut fxb_type: FlexBufferType,
	width: BitWidth,
	parent_width: BitWidth,
	) -> Result<Self, Error> {
	if fxb_type.is_reference() {
	address = deref_offset(buffer, address, parent_width)?;
	// Indirects were dereferenced.
	if let Some(t) = fxb_type.to_direct() {
	fxb_type = t;
	}
	}
	Ok(Reader {
	address,
	fxb_type,
	width,
	buffer,
	})
	}
	/// Parses the flexbuffer from the given buffer. Assumes the flexbuffer root is the last byte
	/// of the buffer.
	pub fn get_root(buffer: &'de [u8]) -> Result<Self, Error> {
	let end = buffer.len();
	if end < 3 {
	return Err(Error::FlexbufferOutOfBounds);
	}
	// Last byte is the root width.
	let root_width = BitWidth::from_nbytes(buffer[end - 1]).ok_or(Error::InvalidRootWidth)?;
	// Second last byte is root type.
	let (fxb_type, width) = unpack_type(buffer[end - 2])?;
	// Location of root data. (BitWidth bits before root type)
	let address = safe_sub(end - 2, root_width.n_bytes())?;
	Self::new(buffer, address, fxb_type, width, root_width)
	}
	/// Returns the FlexBufferType of this Reader.
	pub fn flexbuffer_type(&self) -> FlexBufferType {
	self.fxb_type
	}
	/// Returns the bitwidth of this Reader.
	pub fn bitwidth(&self) -> BitWidth {
	self.width
	}
	/// Returns the length of the Flexbuffer. If the type has no length, or if an error occurs,
	/// 0 is returned.
	pub fn length(&self) -> usize {
	if let Some(len) = self.fxb_type.fixed_length_vector_length() {
	len
	} else if self.fxb_type.has_length_slot() && self.address >= self.width.n_bytes() {
	read_usize(self.buffer, self.address - self.width.n_bytes(), self.width)
	} else {
	0
	}
	}
	/// Returns true if the flexbuffer is aligned to 8 bytes. This guarantees, for valid
	/// flexbuffers, that the data is correctly aligned in memory and slices can be read directly
	/// e.g. with `get_f64s` or `get_i16s`.
	pub fn is_aligned(&self) -> bool {
	(self.buffer.as_ptr() as usize).rem(8) == 0
	}
	as_default!(as_vector, get_vector, VectorReader<'de>);
	as_default!(as_map, get_map, MapReader<'de>);

	fn expect_type(&self, ty: FlexBufferType) -> Result<(), Error> {
	if self.fxb_type == ty {
	Ok(())
	} else {
	Err(Error::UnexpectedFlexbufferType {
	expected: ty,
	actual: self.fxb_type,
	})
	}
	}
	fn expect_bw(&self, bw: BitWidth) -> Result<(), Error> {
	if self.width == bw {
	Ok(())
	} else {
	Err(Error::UnexpectedBitWidth {
	expected: bw,
	actual: self.width,
	})
	}
	}
	/// Directly reads a slice of type `T`where `T` is one of `u8,u16,u32,u64,i8,i16,i32,i64,f32,f64`.
	/// Returns Err if the type, bitwidth, or memory alignment does not match. Since the bitwidth is
	/// dynamic, its better to use a VectorReader unless you know your data and performance is critical.
	#[cfg(target_endian = "little")]
	pub fn get_slice<T: ReadLE>(&self) -> Result<&'de [T], Error> {
	if self.flexbuffer_type().typed_vector_type() != T::VECTOR_TYPE.typed_vector_type() {
	self.expect_type(T::VECTOR_TYPE)?;
	}
	if self.bitwidth().n_bytes() != std::mem::size_of::<T>() {
	self.expect_bw(T::WIDTH)?;
	}
	let end = self.address + self.length() * std::mem::size_of::<T>();
	let slice = &self
	.buffer
	.get(self.address..end)
	.ok_or(Error::FlexbufferOutOfBounds)?;
	// `align_to` is required because the point of this function is to directly hand back a
	// slice of scalars. This can fail because Rust's default allocator is not 16byte aligned
	// (though in practice this only happens for small buffers).
	let (pre, mid, suf) = unsafe { slice.align_to::<T>() };
	if pre.is_empty() && suf.is_empty() {
	Ok(mid)
	} else {
	Err(Error::AlignmentError)
	}
	}

	pub fn get_bool(&self) -> Result<bool, Error> {
	self.expect_type(FlexBufferType::Bool)?;
	Ok(
	self.buffer[self.address..self.address + self.width.n_bytes()]
	.iter()
	.any(\|&b\| b != 0),
	)
	}
	pub fn get_key(&self) -> Result<&'de str, Error> {
	self.expect_type(FlexBufferType::Key)?;
	let (length, _) = self.buffer[self.address..]
	.iter()
	.enumerate()
	.find(\|(_, &b)\| b == b'\0')
	.unwrap_or((0, &0));
	let bytes = &self.buffer[self.address..self.address + length];
	Ok(std::str::from_utf8(bytes)?)
	}
	pub fn get_blob(&self) -> Result<Blob<'de>, Error> {
	self.expect_type(FlexBufferType::Blob)?;
	Ok(Blob(
	&self.buffer[self.address..self.address + self.length()],
	))
	}
	pub fn as_blob(&self) -> Blob<'de> {
	self.get_blob().unwrap_or(Blob(&[]))
	}
	pub fn get_str(&self) -> Result<&'de str, Error> {
	self.expect_type(FlexBufferType::String)?;
	let bytes = &self.buffer[self.address..self.address + self.length()];
	Ok(std::str::from_utf8(bytes)?)
	}
	fn get_map_info(&self) -> Result<(usize, BitWidth), Error> {
	self.expect_type(FlexBufferType::Map)?;
	if 3 * self.width.n_bytes() >= self.address {
	return Err(Error::FlexbufferOutOfBounds);
	}
	let keys_offset_address = self.address - 3 * self.width.n_bytes();
	let keys_width = {
	let kw_addr = self.address - 2 * self.width.n_bytes();
	let kw = read_usize(self.buffer, kw_addr, self.width);
	BitWidth::from_nbytes(kw).ok_or(Error::InvalidMapKeysVectorWidth)
	}?;
	Ok((keys_offset_address, keys_width))
	}
	pub fn get_map(&self) -> Result<MapReader<'de>, Error> {
	let (keys_offset_address, keys_width) = self.get_map_info()?;
	let keys_address = deref_offset(self.buffer, keys_offset_address, self.width)?;
	// TODO(cneo): Check that vectors length equals keys length.
	Ok(MapReader {
	buffer: self.buffer,
	values_address: self.address,
	values_width: self.width,
	keys_address,
	keys_width,
	length: self.length(),
	})
	}
	/// Tries to read a FlexBufferType::UInt. Returns Err if the type is not a UInt or if the
	/// address is out of bounds.
	pub fn get_u64(&self) -> Result<u64, Error> {
	self.expect_type(FlexBufferType::UInt)?;
	let cursor = self
	.buffer
	.get(self.address..self.address + self.width.n_bytes());
	match self.width {
	BitWidth::W8 => cursor.map(\|s\| s[0] as u8).map(Into::into),
	BitWidth::W16 => cursor
	.and_then(\|s\| s.try_into().ok())
	.map(<u16>::from_le_bytes)
	.map(Into::into),
	BitWidth::W32 => cursor
	.and_then(\|s\| s.try_into().ok())
	.map(<u32>::from_le_bytes)
	.map(Into::into),
	BitWidth::W64 => cursor
	.and_then(\|s\| s.try_into().ok())
	.map(<u64>::from_le_bytes),
	}
	.ok_or(Error::FlexbufferOutOfBounds)
	}
	/// Tries to read a FlexBufferType::Int. Returns Err if the type is not a UInt or if the
	/// address is out of bounds.
	pub fn get_i64(&self) -> Result<i64, Error> {
	self.expect_type(FlexBufferType::Int)?;
	let cursor = self
	.buffer
	.get(self.address..self.address + self.width.n_bytes());
	match self.width {
	BitWidth::W8 => cursor.map(\|s\| s[0] as i8).map(Into::into),
	BitWidth::W16 => cursor
	.and_then(\|s\| s.try_into().ok())
	.map(<i16>::from_le_bytes)
	.map(Into::into),
	BitWidth::W32 => cursor
	.and_then(\|s\| s.try_into().ok())
	.map(<i32>::from_le_bytes)
	.map(Into::into),
	BitWidth::W64 => cursor
	.and_then(\|s\| s.try_into().ok())
	.map(<i64>::from_le_bytes),
	}
	.ok_or(Error::FlexbufferOutOfBounds)
	}
	/// Tries to read a FlexBufferType::Float. Returns Err if the type is not a UInt, if the
	/// address is out of bounds, or if its a f16 or f8 (not currently supported).
	pub fn get_f64(&self) -> Result<f64, Error> {
	self.expect_type(FlexBufferType::Float)?;
	let cursor = self
	.buffer
	.get(self.address..self.address + self.width.n_bytes());
	match self.width {
	BitWidth::W8 \| BitWidth::W16 => return Err(Error::InvalidPackedType),
	BitWidth::W32 => cursor
	.and_then(\|s\| s.try_into().ok())
	.map(f32_from_le_bytes)
	.map(Into::into),
	BitWidth::W64 => cursor
	.and_then(\|s\| s.try_into().ok())
	.map(f64_from_le_bytes),
	}
	.ok_or(Error::FlexbufferOutOfBounds)
	}
	pub fn as_bool(&self) -> bool {
	use FlexBufferType::*;
	match self.fxb_type {
	Bool => self.get_bool().unwrap_or_default(),
	UInt => self.as_u64() != 0,
	Int => self.as_i64() != 0,
	Float => self.as_f64().abs() > std::f64::EPSILON,
	String \| Key => !self.as_str().is_empty(),
	Null => false,
	Blob => self.length() != 0,
	ty if ty.is_vector() => self.length() != 0,
	_ => unreachable!(),
	}
	}
	/// Returns a u64, casting if necessary. For Maps and Vectors, their length is
	/// returned. If anything fails, 0 is returned.
	pub fn as_u64(&self) -> u64 {
	match self.fxb_type {
	FlexBufferType::UInt => self.get_u64().unwrap_or_default(),
	FlexBufferType::Int => self
	.get_i64()
	.unwrap_or_default()
	.try_into()
	.unwrap_or_default(),
	FlexBufferType::Float => self.get_f64().unwrap_or_default() as u64,
	FlexBufferType::String => {
	if let Ok(s) = self.get_str() {
	if let Ok(f) = u64::from_str(s) {
	return f;
	}
	}
	0
	}
	_ if self.fxb_type.is_vector() => self.length() as u64,
	_ => 0,
	}
	}
	try_cast_fn!(as_u32, as_u64, u32);
	try_cast_fn!(as_u16, as_u64, u16);
	try_cast_fn!(as_u8, as_u64, u8);

	/// Returns an i64, casting if necessary. For Maps and Vectors, their length is
	/// returned. If anything fails, 0 is returned.
	pub fn as_i64(&self) -> i64 {
	match self.fxb_type {
	FlexBufferType::Int => self.get_i64().unwrap_or_default(),
	FlexBufferType::UInt => self
	.get_u64()
	.unwrap_or_default()
	.try_into()
	.unwrap_or_default(),
	FlexBufferType::Float => self.get_f64().unwrap_or_default() as i64,
	FlexBufferType::String => {
	if let Ok(s) = self.get_str() {
	if let Ok(f) = i64::from_str(s) {
	return f;
	}
	}
	0
	}
	_ if self.fxb_type.is_vector() => self.length() as i64,
	_ => 0,
	}
	}
	try_cast_fn!(as_i32, as_i64, i32);
	try_cast_fn!(as_i16, as_i64, i16);
	try_cast_fn!(as_i8, as_i64, i8);

	/// Returns an f64, casting if necessary. For Maps and Vectors, their length is
	/// returned. If anything fails, 0 is returned.
	pub fn as_f64(&self) -> f64 {
	match self.fxb_type {
	FlexBufferType::Int => self.get_i64().unwrap_or_default() as f64,
	FlexBufferType::UInt => self.get_u64().unwrap_or_default() as f64,
	FlexBufferType::Float => self.get_f64().unwrap_or_default(),
	FlexBufferType::String => {
	if let Ok(s) = self.get_str() {
	if let Ok(f) = f64::from_str(s) {
	return f;
	}
	}
	0.0
	}
	_ if self.fxb_type.is_vector() => self.length() as f64,
	_ => 0.0,
	}
	}
	pub fn as_f32(&self) -> f32 {
	self.as_f64() as f32
	}

	/// Returns empty string if you're not trying to read a string.
	pub fn as_str(&self) -> &'de str {
	match self.fxb_type {
	FlexBufferType::String => self.get_str().unwrap_or_default(),
	FlexBufferType::Key => self.get_key().unwrap_or_default(),
	_ => "",
	}
	}
	pub fn get_vector(&self) -> Result<VectorReader<'de>, Error> {
	if !self.fxb_type.is_vector() {
	self.expect_type(FlexBufferType::Vector)?;
	};
	Ok(VectorReader {
	reader: self.clone(),
	length: self.length(),
	})
	}
	}

	impl<'de> fmt::Display for Reader<'de> {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	use FlexBufferType::*;
	match self.flexbuffer_type() {
	Null => write!(f, "null"),
	UInt => write!(f, "{}", self.as_u64()),
	Int => write!(f, "{}", self.as_i64()),
	Float => write!(f, "{}", self.as_f64()),
	Key \| String => write!(f, "{:?}", self.as_str()),
	Bool => write!(f, "{}", self.as_bool()),
	Blob => write!(f, "blob"),
	Map => {
	write!(f, "{{")?;
	let m = self.as_map();
	let mut pairs = m.iter_keys().zip(m.iter_values());
	if let Some((k, v)) = pairs.next() {
	write!(f, "{:?}: {}", k, v)?;
	for (k, v) in pairs {
	write!(f, ", {:?}: {}", k, v)?;
	}
	}
	write!(f, "}}")
	}
	t if t.is_vector() => {
	write!(f, "[")?;
	let mut elems = self.as_vector().iter();
	if let Some(first) = elems.next() {
	write!(f, "{}", first)?;
	for e in elems {
	write!(f, ", {}", e)?;
	}
	}
	write!(f, "]")
	}
	_ => unreachable!("Display not implemented for {:?}", self),
	}
	}
	}

	// TODO(cneo): Use <f..>::from_le_bytes when we move past rustc 1.39.
	fn f32_from_le_bytes(bytes: [u8; 4]) -> f32 {
	let bits = <u32>::from_le_bytes(bytes);
	<f32>::from_bits(bits)
	}
	fn f64_from_le_bytes(bytes: [u8; 8]) -> f64 {
	let bits = <u64>::from_le_bytes(bytes);
	<f64>::from_bits(bits)
	}

	fn read_usize(buffer: &[u8], address: usize, width: BitWidth) -> usize {
	let cursor = &buffer[address..];
	match width {
	BitWidth::W8 => cursor[0] as usize,
	BitWidth::W16 => cursor
	.get(0..2)
	.and_then(\|s\| s.try_into().ok())
	.map(<u16>::from_le_bytes)
	.unwrap_or_default() as usize,
	BitWidth::W32 => cursor
	.get(0..4)
	.and_then(\|s\| s.try_into().ok())
	.map(<u32>::from_le_bytes)
	.unwrap_or_default() as usize,
	BitWidth::W64 => cursor
	.get(0..8)
	.and_then(\|s\| s.try_into().ok())
	.map(<u64>::from_le_bytes)
	.unwrap_or_default() as usize,
	}
	}

	fn unpack_type(ty: u8) -> Result<(FlexBufferType, BitWidth), Error> {
	let w = BitWidth::try_from(ty & 3u8).map_err(\|_\| Error::InvalidPackedType)?;
	let t = FlexBufferType::try_from(ty >> 2).map_err(\|_\| Error::InvalidPackedType)?;
	Ok((t, w))
	}