/*!
Types and routines specific to sparse DFAs.
This module is the home of [`sparse::DFA`](DFA).
Unlike the [`dense`](super::dense) module, this module does not contain a
builder or configuration specific for sparse DFAs. Instead, the intended
way to build a sparse DFA is either by using a default configuration with
its constructor [`sparse::DFA::new`](DFA::new), or by first configuring the
construction of a dense DFA with [`dense::Builder`](super::dense::Builder)
and then calling [`dense::DFA::to_sparse`](super::dense::DFA::to_sparse). For
example, this configures a sparse DFA to do an overlapping search:
```
use regex_automata::{
dfa::{Automaton, OverlappingState, dense},
HalfMatch, Input, MatchKind,
};
let dense_re = dense::Builder::new()
.configure(dense::Config::new().match_kind(MatchKind::All))
.build(r"Samwise|Sam")?;
let sparse_re = dense_re.to_sparse()?;
// Setup our haystack and initial start state.
let input = Input::new("Samwise");
let mut state = OverlappingState::start();
// First, 'Sam' will match.
sparse_re.try_search_overlapping_fwd(&input, &mut state)?;
assert_eq!(Some(HalfMatch::must(0, 3)), state.get_match());
// And now 'Samwise' will match.
sparse_re.try_search_overlapping_fwd(&input, &mut state)?;
assert_eq!(Some(HalfMatch::must(0, 7)), state.get_match());
# Ok::<(), Box<dyn std::error::Error>>(())
```
*/
#[cfg(feature = "dfa-build")]
use core::iter;
use core::{
convert::{TryFrom, TryInto},
fmt,
mem::size_of,
};
#[cfg(feature = "dfa-build")]
use alloc::{vec, vec::Vec};
#[cfg(feature = "dfa-build")]
use crate::dfa::dense::{self, BuildError};
use crate::{
dfa::{
automaton::{fmt_state_indicator, Automaton},
dense::Flags,
special::Special,
StartKind, DEAD,
},
util::{
alphabet::{ByteClasses, ByteSet},
escape::DebugByte,
int::{Pointer, Usize, U16, U32},
prefilter::Prefilter,
primitives::{PatternID, StateID},
search::{Anchored, Input, MatchError},
start::{Start, StartByteMap},
wire::{self, DeserializeError, Endian, SerializeError},
},
};
const LABEL: &str = "rust-regex-automata-dfa-sparse";
const VERSION: u32 = 2;
/// A sparse deterministic finite automaton (DFA) with variable sized states.
///
/// In contrast to a [dense::DFA](crate::dfa::dense::DFA), a sparse DFA uses
/// a more space efficient representation for its transitions. Consequently,
/// sparse DFAs may use much less memory than dense DFAs, but this comes at a
/// price. In particular, reading the more space efficient transitions takes
/// more work, and consequently, searching using a sparse DFA is typically
/// slower than a dense DFA.
///
/// A sparse DFA can be built using the default configuration via the
/// [`DFA::new`] constructor. Otherwise, one can configure various aspects
/// of a dense DFA via [`dense::Builder`](crate::dfa::dense::Builder),
/// and then convert a dense DFA to a sparse DFA using
/// [`dense::DFA::to_sparse`](crate::dfa::dense::DFA::to_sparse).
///
/// In general, a sparse DFA supports all the same search operations as a dense
/// DFA.
///
/// Making the choice between a dense and sparse DFA depends on your specific
/// work load. If you can sacrifice a bit of search time performance, then a
/// sparse DFA might be the best choice. In particular, while sparse DFAs are
/// probably always slower than dense DFAs, you may find that they are easily
/// fast enough for your purposes!
///
/// # Type parameters
///
/// A `DFA` has one type parameter, `T`, which is used to represent the parts
/// of a sparse DFA. `T` is typically a `Vec<u8>` or a `&[u8]`.
///
/// # The `Automaton` trait
///
/// This type implements the [`Automaton`] trait, which means it can be used
/// for searching. For example:
///
/// ```
/// use regex_automata::{dfa::{Automaton, sparse::DFA}, HalfMatch, Input};
///
/// let dfa = DFA::new("foo[0-9]+")?;
/// let expected = Some(HalfMatch::must(0, 8));
/// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[derive(Clone)]
pub struct DFA<T> {
// When compared to a dense DFA, a sparse DFA *looks* a lot simpler
// representation-wise. In reality, it is perhaps more complicated. Namely,
// in a dense DFA, all information needs to be very cheaply accessible
// using only state IDs. In a sparse DFA however, each state uses a
// variable amount of space because each state encodes more information
// than just its transitions. Each state also includes an accelerator if
// one exists, along with the matching pattern IDs if the state is a match
// state.
//
// That is, a lot of the complexity is pushed down into how each state
// itself is represented.
tt: Transitions<T>,
st: StartTable<T>,
special: Special,
pre: Option<Prefilter>,
quitset: ByteSet,
flags: Flags,
}
#[cfg(feature = "dfa-build")]
impl DFA<Vec<u8>> {
/// Parse the given regular expression using a default configuration and
/// return the corresponding sparse DFA.
///
/// If you want a non-default configuration, then use
/// the [`dense::Builder`](crate::dfa::dense::Builder)
/// to set your own configuration, and then call
/// [`dense::DFA::to_sparse`](crate::dfa::dense::DFA::to_sparse) to create
/// a sparse DFA.
///
/// # Example
///
/// ```
/// use regex_automata::{dfa::{Automaton, sparse}, HalfMatch, Input};
///
/// let dfa = sparse::DFA::new("foo[0-9]+bar")?;
///
/// let expected = Some(HalfMatch::must(0, 11));
/// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345bar"))?);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[cfg(feature = "syntax")]
pub fn new(pattern: &str) -> Result<DFA<Vec<u8>>, BuildError> {
dense::Builder::new()
.build(pattern)
.and_then(|dense| dense.to_sparse())
}
/// Parse the given regular expressions using a default configuration and
/// return the corresponding multi-DFA.
///
/// If you want a non-default configuration, then use
/// the [`dense::Builder`](crate::dfa::dense::Builder)
/// to set your own configuration, and then call
/// [`dense::DFA::to_sparse`](crate::dfa::dense::DFA::to_sparse) to create
/// a sparse DFA.
///
/// # Example
///
/// ```
/// use regex_automata::{dfa::{Automaton, sparse}, HalfMatch, Input};
///
/// let dfa = sparse::DFA::new_many(&["[0-9]+", "[a-z]+"])?;
/// let expected = Some(HalfMatch::must(1, 3));
/// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345bar"))?);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[cfg(feature = "syntax")]
pub fn new_many<P: AsRef<str>>(
patterns: &[P],
) -> Result<DFA<Vec<u8>>, BuildError> {
dense::Builder::new()
.build_many(patterns)
.and_then(|dense| dense.to_sparse())
}
}
#[cfg(feature = "dfa-build")]
impl DFA<Vec<u8>> {
/// Create a new DFA that matches every input.
///
/// # Example
///
/// ```
/// use regex_automata::{
/// dfa::{Automaton, sparse},
/// HalfMatch, Input,
/// };
///
/// let dfa = sparse::DFA::always_match()?;
///
/// let expected = Some(HalfMatch::must(0, 0));
/// assert_eq!(expected, dfa.try_search_fwd(&Input::new(""))?);
/// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo"))?);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn always_match() -> Result<DFA<Vec<u8>>, BuildError> {
dense::DFA::always_match()?.to_sparse()
}
/// Create a new sparse DFA that never matches any input.
///
/// # Example
///
/// ```
/// use regex_automata::{dfa::{Automaton, sparse}, Input};
///
/// let dfa = sparse::DFA::never_match()?;
/// assert_eq!(None, dfa.try_search_fwd(&Input::new(""))?);
/// assert_eq!(None, dfa.try_search_fwd(&Input::new("foo"))?);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn never_match() -> Result<DFA<Vec<u8>>, BuildError> {
dense::DFA::never_match()?.to_sparse()
}
/// The implementation for constructing a sparse DFA from a dense DFA.
pub(crate) fn from_dense<T: AsRef<[u32]>>(
dfa: &dense::DFA<T>,
) -> Result<DFA<Vec<u8>>, BuildError> {
// In order to build the transition table, we need to be able to write
// state identifiers for each of the "next" transitions in each state.
// Our state identifiers correspond to the byte offset in the
// transition table at which the state is encoded. Therefore, we do not
// actually know what the state identifiers are until we've allocated
// exactly as much space as we need for each state. Thus, construction
// of the transition table happens in two passes.
//
// In the first pass, we fill out the shell of each state, which
// includes the transition length, the input byte ranges and
// zero-filled space for the transitions and accelerators, if present.
// In this first pass, we also build up a map from the state identifier
// index of the dense DFA to the state identifier in this sparse DFA.
//
// In the second pass, we fill in the transitions based on the map
// built in the first pass.
// The capacity given here reflects a minimum. (Well, the true minimum
// is likely even bigger, but hopefully this saves a few reallocs.)
let mut sparse = Vec::with_capacity(StateID::SIZE * dfa.state_len());
// This maps state indices from the dense DFA to StateIDs in the sparse
// DFA. We build out this map on the first pass, and then use it in the
// second pass to back-fill our transitions.
let mut remap: Vec<StateID> = vec![DEAD; dfa.state_len()];
for state in dfa.states() {
let pos = sparse.len();
remap[dfa.to_index(state.id())] = StateID::new(pos)
.map_err(|_| BuildError::too_many_states())?;
// zero-filled space for the transition length
sparse.push(0);
sparse.push(0);
let mut transition_len = 0;
for (unit1, unit2, _) in state.sparse_transitions() {
match (unit1.as_u8(), unit2.as_u8()) {
(Some(b1), Some(b2)) => {
transition_len += 1;
sparse.push(b1);
sparse.push(b2);
}
(None, None) => {}
(Some(_), None) | (None, Some(_)) => {
// can never occur because sparse_transitions never
// groups EOI with any other transition.
unreachable!()
}
}
}
// Add dummy EOI transition. This is never actually read while
// searching, but having space equivalent to the total number
// of transitions is convenient. Otherwise, we'd need to track
// a different number of transitions for the byte ranges as for
// the 'next' states.
//
// N.B. The loop above is not guaranteed to yield the EOI
// transition, since it may point to a DEAD state. By putting
// it here, we always write the EOI transition, and thus
// guarantee that our transition length is >0. Why do we always
// need the EOI transition? Because in order to implement
// Automaton::next_eoi_state, this lets us just ask for the last
// transition. There are probably other/better ways to do this.
transition_len += 1;
sparse.push(0);
sparse.push(0);
// Check some assumptions about transition length.
assert_ne!(
transition_len, 0,
"transition length should be non-zero",
);
assert!(
transition_len <= 257,
"expected transition length {} to be <= 257",
transition_len,
);
// Fill in the transition length.
// Since transition length is always <= 257, we use the most
// significant bit to indicate whether this is a match state or
// not.
let ntrans = if dfa.is_match_state(state.id()) {
transition_len | (1 << 15)
} else {
transition_len
};
wire::NE::write_u16(ntrans, &mut sparse[pos..]);
// zero-fill the actual transitions.
// Unwraps are OK since transition_length <= 257 and our minimum
// support usize size is 16-bits.
let zeros = usize::try_from(transition_len)
.unwrap()
.checked_mul(StateID::SIZE)
.unwrap();
sparse.extend(iter::repeat(0).take(zeros));
// If this is a match state, write the pattern IDs matched by this
// state.
if dfa.is_match_state(state.id()) {
let plen = dfa.match_pattern_len(state.id());
// Write the actual pattern IDs with a u32 length prefix.
// First, zero-fill space.
let mut pos = sparse.len();
// Unwraps are OK since it's guaranteed that plen <=
// PatternID::LIMIT, which is in turn guaranteed to fit into a
// u32.
let zeros = size_of::<u32>()
.checked_mul(plen)
.unwrap()
.checked_add(size_of::<u32>())
.unwrap();
sparse.extend(iter::repeat(0).take(zeros));
// Now write the length prefix.
wire::NE::write_u32(
// Will never fail since u32::MAX is invalid pattern ID.
// Thus, the number of pattern IDs is representable by a
// u32.
plen.try_into().expect("pattern ID length fits in u32"),
&mut sparse[pos..],
);
pos += size_of::<u32>();
// Now write the pattern IDs.
for &pid in dfa.pattern_id_slice(state.id()) {
pos += wire::write_pattern_id::<wire::NE>(
pid,
&mut sparse[pos..],
);
}
}
// And now add the accelerator, if one exists. An accelerator is
// at most 4 bytes and at least 1 byte. The first byte is the
// length, N. N bytes follow the length. The set of bytes that
// follow correspond (exhaustively) to the bytes that must be seen
// to leave this state.
let accel = dfa.accelerator(state.id());
sparse.push(accel.len().try_into().unwrap());
sparse.extend_from_slice(accel);
}
let mut new = DFA {
tt: Transitions {
sparse,
classes: dfa.byte_classes().clone(),
state_len: dfa.state_len(),
pattern_len: dfa.pattern_len(),
},
st: StartTable::from_dense_dfa(dfa, &remap)?,
special: dfa.special().remap(|id| remap[dfa.to_index(id)]),
pre: dfa.get_prefilter().map(|p| p.clone()),
quitset: dfa.quitset().clone(),
flags: dfa.flags().clone(),
};
// And here's our second pass. Iterate over all of the dense states
// again, and update the transitions in each of the states in the
// sparse DFA.
for old_state in dfa.states() {
let new_id = remap[dfa.to_index(old_state.id())];
let mut new_state = new.tt.state_mut(new_id);
let sparse = old_state.sparse_transitions();
for (i, (_, _, next)) in sparse.enumerate() {
let next = remap[dfa.to_index(next)];
new_state.set_next_at(i, next);
}
}
debug!(
"created sparse DFA, memory usage: {} (dense memory usage: {})",
new.memory_usage(),
dfa.memory_usage(),
);
Ok(new)
}
}
impl<T: AsRef<[u8]>> DFA<T> {
/// Cheaply return a borrowed version of this sparse DFA. Specifically, the
/// DFA returned always uses `&[u8]` for its transitions.
pub fn as_ref<'a>(&'a self) -> DFA<&'a [u8]> {
DFA {
tt: self.tt.as_ref(),
st: self.st.as_ref(),
special: self.special,
pre: self.pre.clone(),
quitset: self.quitset,
flags: self.flags,
}
}
/// Return an owned version of this sparse DFA. Specifically, the DFA
/// returned always uses `Vec<u8>` for its transitions.
///
/// Effectively, this returns a sparse DFA whose transitions live on the
/// heap.
#[cfg(feature = "alloc")]
pub fn to_owned(&self) -> DFA<alloc::vec::Vec<u8>> {
DFA {
tt: self.tt.to_owned(),
st: self.st.to_owned(),
special: self.special,
pre: self.pre.clone(),
quitset: self.quitset,
flags: self.flags,
}
}
/// Returns the starting state configuration for this DFA.
///
/// The default is [`StartKind::Both`], which means the DFA supports both
/// unanchored and anchored searches. However, this can generally lead to
/// bigger DFAs. Therefore, a DFA might be compiled with support for just
/// unanchored or anchored searches. In that case, running a search with
/// an unsupported configuration will panic.
pub fn start_kind(&self) -> StartKind {
self.st.kind
}
/// Returns true only if this DFA has starting states for each pattern.
///
/// When a DFA has starting states for each pattern, then a search with the
/// DFA can be configured to only look for anchored matches of a specific
/// pattern. Specifically, APIs like [`Automaton::try_search_fwd`] can
/// accept a [`Anchored::Pattern`] if and only if this method returns true.
/// Otherwise, an error will be returned.
///
/// Note that if the DFA is empty, this always returns false.
pub fn starts_for_each_pattern(&self) -> bool {
self.st.pattern_len.is_some()
}
/// Returns the equivalence classes that make up the alphabet for this DFA.
///
/// Unless [`dense::Config::byte_classes`] was disabled, it is possible
/// that multiple distinct bytes are grouped into the same equivalence
/// class if it is impossible for them to discriminate between a match and
/// a non-match. This has the effect of reducing the overall alphabet size
/// and in turn potentially substantially reducing the size of the DFA's
/// transition table.
///
/// The downside of using equivalence classes like this is that every state
/// transition will automatically use this map to convert an arbitrary
/// byte to its corresponding equivalence class. In practice this has a
/// negligible impact on performance.
pub fn byte_classes(&self) -> &ByteClasses {
&self.tt.classes
}
/// Returns the memory usage, in bytes, of this DFA.
///
/// The memory usage is computed based on the number of bytes used to
/// represent this DFA.
///
/// This does **not** include the stack size used up by this DFA. To
/// compute that, use `std::mem::size_of::<sparse::DFA>()`.
pub fn memory_usage(&self) -> usize {
self.tt.memory_usage() + self.st.memory_usage()
}
}
/// Routines for converting a sparse DFA to other representations, such as raw
/// bytes suitable for persistent storage.
impl<T: AsRef<[u8]>> DFA<T> {
/// Serialize this DFA as raw bytes to a `Vec<u8>` in little endian
/// format.
///
/// The written bytes are guaranteed to be deserialized correctly and
/// without errors in a semver compatible release of this crate by a
/// `DFA`'s deserialization APIs (assuming all other criteria for the
/// deserialization APIs has been satisfied):
///
/// * [`DFA::from_bytes`]
/// * [`DFA::from_bytes_unchecked`]
///
/// Note that unlike a [`dense::DFA`](crate::dfa::dense::DFA)'s
/// serialization methods, this does not add any initial padding to the
/// returned bytes. Padding isn't required for sparse DFAs since they have
/// no alignment requirements.
///
/// # Example
///
/// This example shows how to serialize and deserialize a DFA:
///
/// ```
/// use regex_automata::{dfa::{Automaton, sparse::DFA}, HalfMatch, Input};
///
/// // Compile our original DFA.
/// let original_dfa = DFA::new("foo[0-9]+")?;
///
/// // N.B. We use native endianness here to make the example work, but
/// // using to_bytes_little_endian would work on a little endian target.
/// let buf = original_dfa.to_bytes_native_endian();
/// // Even if buf has initial padding, DFA::from_bytes will automatically
/// // ignore it.
/// let dfa: DFA<&[u8]> = DFA::from_bytes(&buf)?.0;
///
/// let expected = Some(HalfMatch::must(0, 8));
/// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[cfg(feature = "dfa-build")]
pub fn to_bytes_little_endian(&self) -> Vec<u8> {
self.to_bytes::<wire::LE>()
}
/// Serialize this DFA as raw bytes to a `Vec<u8>` in big endian
/// format.
///
/// The written bytes are guaranteed to be deserialized correctly and
/// without errors in a semver compatible release of this crate by a
/// `DFA`'s deserialization APIs (assuming all other criteria for the
/// deserialization APIs has been satisfied):
///
/// * [`DFA::from_bytes`]
/// * [`DFA::from_bytes_unchecked`]
///
/// Note that unlike a [`dense::DFA`](crate::dfa::dense::DFA)'s
/// serialization methods, this does not add any initial padding to the
/// returned bytes. Padding isn't required for sparse DFAs since they have
/// no alignment requirements.
///
/// # Example
///
/// This example shows how to serialize and deserialize a DFA:
///
/// ```
/// use regex_automata::{dfa::{Automaton, sparse::DFA}, HalfMatch, Input};
///
/// // Compile our original DFA.
/// let original_dfa = DFA::new("foo[0-9]+")?;
///
/// // N.B. We use native endianness here to make the example work, but
/// // using to_bytes_big_endian would work on a big endian target.
/// let buf = original_dfa.to_bytes_native_endian();
/// // Even if buf has initial padding, DFA::from_bytes will automatically
/// // ignore it.
/// let dfa: DFA<&[u8]> = DFA::from_bytes(&buf)?.0;
///
/// let expected = Some(HalfMatch::must(0, 8));
/// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[cfg(feature = "dfa-build")]
pub fn to_bytes_big_endian(&self) -> Vec<u8> {
self.to_bytes::<wire::BE>()
}
/// Serialize this DFA as raw bytes to a `Vec<u8>` in native endian
/// format.
///
/// The written bytes are guaranteed to be deserialized correctly and
/// without errors in a semver compatible release of this crate by a
/// `DFA`'s deserialization APIs (assuming all other criteria for the
/// deserialization APIs has been satisfied):
///
/// * [`DFA::from_bytes`]
/// * [`DFA::from_bytes_unchecked`]
///
/// Note that unlike a [`dense::DFA`](crate::dfa::dense::DFA)'s
/// serialization methods, this does not add any initial padding to the
/// returned bytes. Padding isn't required for sparse DFAs since they have
/// no alignment requirements.
///
/// Generally speaking, native endian format should only be used when
/// you know that the target you're compiling the DFA for matches the
/// endianness of the target on which you're compiling DFA. For example,
/// if serialization and deserialization happen in the same process or on
/// the same machine. Otherwise, when serializing a DFA for use in a
/// portable environment, you'll almost certainly want to serialize _both_
/// a little endian and a big endian version and then load the correct one
/// based on the target's configuration.
///
/// # Example
///
/// This example shows how to serialize and deserialize a DFA:
///
/// ```
/// use regex_automata::{dfa::{Automaton, sparse::DFA}, HalfMatch, Input};
///
/// // Compile our original DFA.
/// let original_dfa = DFA::new("foo[0-9]+")?;
///
/// let buf = original_dfa.to_bytes_native_endian();
/// // Even if buf has initial padding, DFA::from_bytes will automatically
/// // ignore it.
/// let dfa: DFA<&[u8]> = DFA::from_bytes(&buf)?.0;
///
/// let expected = Some(HalfMatch::must(0, 8));
/// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[cfg(feature = "dfa-build")]
pub fn to_bytes_native_endian(&self) -> Vec<u8> {
self.to_bytes::<wire::NE>()
}
/// The implementation of the public `to_bytes` serialization methods,
/// which is generic over endianness.
#[cfg(feature = "dfa-build")]
fn to_bytes<E: Endian>(&self) -> Vec<u8> {
let mut buf = vec![0; self.write_to_len()];
// This should always succeed since the only possible serialization
// error is providing a buffer that's too small, but we've ensured that
// `buf` is big enough here.
self.write_to::<E>(&mut buf).unwrap();
buf
}
/// Serialize this DFA as raw bytes to the given slice, in little endian
/// format. Upon success, the total number of bytes written to `dst` is
/// returned.
///
/// The written bytes are guaranteed to be deserialized correctly and
/// without errors in a semver compatible release of this crate by a
/// `DFA`'s deserialization APIs (assuming all other criteria for the
/// deserialization APIs has been satisfied):
///
/// * [`DFA::from_bytes`]
/// * [`DFA::from_bytes_unchecked`]
///
/// # Errors
///
/// This returns an error if the given destination slice is not big enough
/// to contain the full serialized DFA. If an error occurs, then nothing
/// is written to `dst`.
///
/// # Example
///
/// This example shows how to serialize and deserialize a DFA without
/// dynamic memory allocation.
///
/// ```
/// use regex_automata::{dfa::{Automaton, sparse::DFA}, HalfMatch, Input};
///
/// // Compile our original DFA.
/// let original_dfa = DFA::new("foo[0-9]+")?;
///
/// // Create a 4KB buffer on the stack to store our serialized DFA.
/// let mut buf = [0u8; 4 * (1<<10)];
/// // N.B. We use native endianness here to make the example work, but
/// // using write_to_little_endian would work on a little endian target.
/// let written = original_dfa.write_to_native_endian(&mut buf)?;
/// let dfa: DFA<&[u8]> = DFA::from_bytes(&buf[..written])?.0;
///
/// let expected = Some(HalfMatch::must(0, 8));
/// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn write_to_little_endian(
&self,
dst: &mut [u8],
) -> Result<usize, SerializeError> {
self.write_to::<wire::LE>(dst)
}
/// Serialize this DFA as raw bytes to the given slice, in big endian
/// format. Upon success, the total number of bytes written to `dst` is
/// returned.
///
/// The written bytes are guaranteed to be deserialized correctly and
/// without errors in a semver compatible release of this crate by a
/// `DFA`'s deserialization APIs (assuming all other criteria for the
/// deserialization APIs has been satisfied):
///
/// * [`DFA::from_bytes`]
/// * [`DFA::from_bytes_unchecked`]
///
/// # Errors
///
/// This returns an error if the given destination slice is not big enough
/// to contain the full serialized DFA. If an error occurs, then nothing
/// is written to `dst`.
///
/// # Example
///
/// This example shows how to serialize and deserialize a DFA without
/// dynamic memory allocation.
///
/// ```
/// use regex_automata::{dfa::{Automaton, sparse::DFA}, HalfMatch, Input};
///
/// // Compile our original DFA.
/// let original_dfa = DFA::new("foo[0-9]+")?;
///
/// // Create a 4KB buffer on the stack to store our serialized DFA.
/// let mut buf = [0u8; 4 * (1<<10)];
/// // N.B. We use native endianness here to make the example work, but
/// // using write_to_big_endian would work on a big endian target.
/// let written = original_dfa.write_to_native_endian(&mut buf)?;
/// let dfa: DFA<&[u8]> = DFA::from_bytes(&buf[..written])?.0;
///
/// let expected = Some(HalfMatch::must(0, 8));
/// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn write_to_big_endian(
&self,
dst: &mut [u8],
) -> Result<usize, SerializeError> {
self.write_to::<wire::BE>(dst)
}
/// Serialize this DFA as raw bytes to the given slice, in native endian
/// format. Upon success, the total number of bytes written to `dst` is
/// returned.
///
/// The written bytes are guaranteed to be deserialized correctly and
/// without errors in a semver compatible release of this crate by a
/// `DFA`'s deserialization APIs (assuming all other criteria for the
/// deserialization APIs has been satisfied):
///
/// * [`DFA::from_bytes`]
/// * [`DFA::from_bytes_unchecked`]
///
/// Generally speaking, native endian format should only be used when
/// you know that the target you're compiling the DFA for matches the
/// endianness of the target on which you're compiling DFA. For example,
/// if serialization and deserialization happen in the same process or on
/// the same machine. Otherwise, when serializing a DFA for use in a
/// portable environment, you'll almost certainly want to serialize _both_
/// a little endian and a big endian version and then load the correct one
/// based on the target's configuration.
///
/// # Errors
///
/// This returns an error if the given destination slice is not big enough
/// to contain the full serialized DFA. If an error occurs, then nothing
/// is written to `dst`.
///
/// # Example
///
/// This example shows how to serialize and deserialize a DFA without
/// dynamic memory allocation.
///
/// ```
/// use regex_automata::{dfa::{Automaton, sparse::DFA}, HalfMatch, Input};
///
/// // Compile our original DFA.
/// let original_dfa = DFA::new("foo[0-9]+")?;
///
/// // Create a 4KB buffer on the stack to store our serialized DFA.
/// let mut buf = [0u8; 4 * (1<<10)];
/// let written = original_dfa.write_to_native_endian(&mut buf)?;
/// let dfa: DFA<&[u8]> = DFA::from_bytes(&buf[..written])?.0;
///
/// let expected = Some(HalfMatch::must(0, 8));
/// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn write_to_native_endian(
&self,
dst: &mut [u8],
) -> Result<usize, SerializeError> {
self.write_to::<wire::NE>(dst)
}
/// The implementation of the public `write_to` serialization methods,
/// which is generic over endianness.
fn write_to<E: Endian>(
&self,
dst: &mut [u8],
) -> Result<usize, SerializeError> {
let mut nw = 0;
nw += wire::write_label(LABEL, &mut dst[nw..])?;
nw += wire::write_endianness_check::<E>(&mut dst[nw..])?;
nw += wire::write_version::<E>(VERSION, &mut dst[nw..])?;
nw += {
// Currently unused, intended for future flexibility
E::write_u32(0, &mut dst[nw..]);
size_of::<u32>()
};
nw += self.flags.write_to::<E>(&mut dst[nw..])?;
nw += self.tt.write_to::<E>(&mut dst[nw..])?;
nw += self.st.write_to::<E>(&mut dst[nw..])?;
nw += self.special.write_to::<E>(&mut dst[nw..])?;
nw += self.quitset.write_to::<E>(&mut dst[nw..])?;
Ok(nw)
}
/// Return the total number of bytes required to serialize this DFA.
///
/// This is useful for determining the size of the buffer required to pass
/// to one of the serialization routines:
///
/// * [`DFA::write_to_little_endian`]
/// * [`DFA::write_to_big_endian`]
/// * [`DFA::write_to_native_endian`]
///
/// Passing a buffer smaller than the size returned by this method will
/// result in a serialization error.
///
/// # Example
///
/// This example shows how to dynamically allocate enough room to serialize
/// a sparse DFA.
///
/// ```
/// use regex_automata::{dfa::{Automaton, sparse::DFA}, HalfMatch, Input};
///
/// // Compile our original DFA.
/// let original_dfa = DFA::new("foo[0-9]+")?;
///
/// let mut buf = vec![0; original_dfa.write_to_len()];
/// let written = original_dfa.write_to_native_endian(&mut buf)?;
/// let dfa: DFA<&[u8]> = DFA::from_bytes(&buf[..written])?.0;
///
/// let expected = Some(HalfMatch::must(0, 8));
/// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn write_to_len(&self) -> usize {
wire::write_label_len(LABEL)
+ wire::write_endianness_check_len()
+ wire::write_version_len()
+ size_of::<u32>() // unused, intended for future flexibility
+ self.flags.write_to_len()
+ self.tt.write_to_len()
+ self.st.write_to_len()
+ self.special.write_to_len()
+ self.quitset.write_to_len()
}
}
impl<'a> DFA<&'a [u8]> {
/// Safely deserialize a sparse DFA with a specific state identifier
/// representation. Upon success, this returns both the deserialized DFA
/// and the number of bytes read from the given slice. Namely, the contents
/// of the slice beyond the DFA are not read.
///
/// Deserializing a DFA using this routine will never allocate heap memory.
/// For safety purposes, the DFA's transitions will be verified such that
/// every transition points to a valid state. If this verification is too
/// costly, then a [`DFA::from_bytes_unchecked`] API is provided, which
/// will always execute in constant time.
///
/// The bytes given must be generated by one of the serialization APIs
/// of a `DFA` using a semver compatible release of this crate. Those
/// include:
///
/// * [`DFA::to_bytes_little_endian`]
/// * [`DFA::to_bytes_big_endian`]
/// * [`DFA::to_bytes_native_endian`]
/// * [`DFA::write_to_little_endian`]
/// * [`DFA::write_to_big_endian`]
/// * [`DFA::write_to_native_endian`]
///
/// The `to_bytes` methods allocate and return a `Vec<u8>` for you. The
/// `write_to` methods do not allocate and write to an existing slice
/// (which may be on the stack). Since deserialization always uses the
/// native endianness of the target platform, the serialization API you use
/// should match the endianness of the target platform. (It's often a good
/// idea to generate serialized DFAs for both forms of endianness and then
/// load the correct one based on endianness.)
///
/// # Errors
///
/// Generally speaking, it's easier to state the conditions in which an
/// error is _not_ returned. All of the following must be true:
///
/// * The bytes given must be produced by one of the serialization APIs
/// on this DFA, as mentioned above.
/// * The endianness of the target platform matches the endianness used to
/// serialized the provided DFA.
///
/// If any of the above are not true, then an error will be returned.
///
/// Note that unlike deserializing a
/// [`dense::DFA`](crate::dfa::dense::DFA), deserializing a sparse DFA has
/// no alignment requirements. That is, an alignment of `1` is valid.
///
/// # Panics
///
/// This routine will never panic for any input.
///
/// # Example
///
/// This example shows how to serialize a DFA to raw bytes, deserialize it
/// and then use it for searching.
///
/// ```
/// use regex_automata::{dfa::{Automaton, sparse::DFA}, HalfMatch, Input};
///
/// let initial = DFA::new("foo[0-9]+")?;
/// let bytes = initial.to_bytes_native_endian();
/// let dfa: DFA<&[u8]> = DFA::from_bytes(&bytes)?.0;
///
/// let expected = Some(HalfMatch::must(0, 8));
/// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
///
/// # Example: loading a DFA from static memory
///
/// One use case this library supports is the ability to serialize a
/// DFA to disk and then use `include_bytes!` to store it in a compiled
/// Rust program. Those bytes can then be cheaply deserialized into a
/// `DFA` structure at runtime and used for searching without having to
/// re-compile the DFA (which can be quite costly).
///
/// We can show this in two parts. The first part is serializing the DFA to
/// a file:
///
/// ```no_run
/// use regex_automata::dfa::sparse::DFA;
///
/// let dfa = DFA::new("foo[0-9]+")?;
///
/// // Write a big endian serialized version of this DFA to a file.
/// let bytes = dfa.to_bytes_big_endian();
/// std::fs::write("foo.bigendian.dfa", &bytes)?;
///
/// // Do it again, but this time for little endian.
/// let bytes = dfa.to_bytes_little_endian();
/// std::fs::write("foo.littleendian.dfa", &bytes)?;
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
///
/// And now the second part is embedding the DFA into the compiled program
/// and deserializing it at runtime on first use. We use conditional
/// compilation to choose the correct endianness. We do not need to employ
/// any special tricks to ensure a proper alignment, since a sparse DFA has
/// no alignment requirements.
///
/// ```no_run
/// use regex_automata::{
/// dfa::{Automaton, sparse::DFA},
/// util::lazy::Lazy,
/// HalfMatch, Input,
/// };
///
/// // This crate provides its own "lazy" type, kind of like
/// // lazy_static! or once_cell::sync::Lazy. But it works in no-alloc
/// // no-std environments and let's us write this using completely
/// // safe code.
/// static RE: Lazy<DFA<&'static [u8]>> = Lazy::new(|| {
/// # const _: &str = stringify! {
/// #[cfg(target_endian = "big")]
/// static BYTES: &[u8] = include_bytes!("foo.bigendian.dfa");
/// #[cfg(target_endian = "little")]
/// static BYTES: &[u8] = include_bytes!("foo.littleendian.dfa");
/// # };
/// # static BYTES: &[u8] = b"";
///
/// let (dfa, _) = DFA::from_bytes(BYTES)
/// .expect("serialized DFA should be valid");
/// dfa
/// });
///
/// let expected = Ok(Some(HalfMatch::must(0, 8)));
/// assert_eq!(expected, RE.try_search_fwd(&Input::new("foo12345")));
/// ```
///
/// Alternatively, consider using
/// [`lazy_static`](
https://crates.io/crates/lazy_static)
/// or
/// [`once_cell`](
https://crates.io/crates/once_cell),
/// which will guarantee safety for you.
pub fn from_bytes(
slice: &'a [u8],
) -> Result<(DFA<&'a [u8]>, usize), DeserializeError> {
// SAFETY: This is safe because we validate both the sparse transitions
// (by trying to decode every state) and start state ID list below. If
// either validation fails, then we return an error.
let (dfa, nread) = unsafe { DFA::from_bytes_unchecked(slice)? };
dfa.tt.validate(&dfa.special)?;
dfa.st.validate(&dfa.special, &dfa.tt)?;
// N.B. dfa.special doesn't have a way to do unchecked deserialization,
// so it has already been validated.
Ok((dfa, nread))
}
/// Deserialize a DFA with a specific state identifier representation in
/// constant time by omitting the verification of the validity of the
/// sparse transitions.
///
/// This is just like [`DFA::from_bytes`], except it can potentially return
/// a DFA that exhibits undefined behavior if its transitions contains
/// invalid state identifiers.
///
/// This routine is useful if you need to deserialize a DFA cheaply and
/// cannot afford the transition validation performed by `from_bytes`.
///
/// # Safety
///
/// This routine is not safe because it permits callers to provide
/// arbitrary transitions with possibly incorrect state identifiers. While
/// the various serialization routines will never return an incorrect
/// DFA, there is no guarantee that the bytes provided here are correct.
/// While `from_bytes_unchecked` will still do several forms of basic
/// validation, this routine does not check that the transitions themselves
/// are correct. Given an incorrect transition table, it is possible for
/// the search routines to access out-of-bounds memory because of explicit
/// bounds check elision.
///
/// # Example
///
/// ```
/// use regex_automata::{dfa::{Automaton, sparse::DFA}, HalfMatch, Input};
///
/// let initial = DFA::new("foo[0-9]+")?;
/// let bytes = initial.to_bytes_native_endian();
/// // SAFETY: This is guaranteed to be safe since the bytes given come
/// // directly from a compatible serialization routine.
/// let dfa: DFA<&[u8]> = unsafe { DFA::from_bytes_unchecked(&bytes)?.0 };
///
/// let expected = Some(HalfMatch::must(0, 8));
/// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub unsafe fn from_bytes_unchecked(
slice: &'a [u8],
) -> Result<(DFA<&'a [u8]>, usize), DeserializeError> {
let mut nr = 0;
nr += wire::read_label(&slice[nr..], LABEL)?;
nr += wire::read_endianness_check(&slice[nr..])?;
nr += wire::read_version(&slice[nr..], VERSION)?;
let _unused = wire::try_read_u32(&slice[nr..], "unused space")?;
nr += size_of::<u32>();
let (flags, nread) = Flags::from_bytes(&slice[nr..])?;
nr += nread;
let (tt, nread) = Transitions::from_bytes_unchecked(&slice[nr..])?;
nr += nread;
let (st, nread) = StartTable::from_bytes_unchecked(&slice[nr..])?;
nr += nread;
let (special, nread) = Special::from_bytes(&slice[nr..])?;
nr += nread;
if special.max.as_usize() >= tt.sparse().len() {
return Err(DeserializeError::generic(
"max should not be greater than or equal to sparse bytes",
));
}
let (quitset, nread) = ByteSet::from_bytes(&slice[nr..])?;
nr += nread;
// Prefilters don't support serialization, so they're always absent.
let pre = None;
Ok((DFA { tt, st, special, pre, quitset, flags }, nr))
}
}
impl<T: AsRef<[u8]>> fmt::Debug for DFA<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
writeln!(f, "sparse::DFA(")?;
for state in self.tt.states() {
fmt_state_indicator(f, self, state.id())?;
writeln!(f, "{:06?}: {:?}", state.id().as_usize(), state)?;
}
writeln!(f, "")?;
for (i, (start_id, anchored, sty)) in self.st.iter().enumerate() {
if i % self.st.stride == 0 {
match anchored {
Anchored::No => writeln!(f, "START-GROUP(unanchored)")?,
Anchored::Yes => writeln!(f, "START-GROUP(anchored)")?,
Anchored::Pattern(pid) => writeln!(
f,
"START_GROUP(pattern: {:?})",
pid.as_usize()
)?,
}
}
writeln!(f, " {:?} => {:06?}", sty, start_id.as_usize())?;
}
writeln!(f, "state length: {:?}", self.tt.state_len)?;
writeln!(f, "pattern length: {:?}", self.pattern_len())?;
writeln!(f, "flags: {:?}", self.flags)?;
writeln!(f, ")")?;
Ok(())
}
}
// SAFETY: We assert that our implementation of each method is correct.
unsafe impl<T: AsRef<[u8]>> Automaton for DFA<T> {
#[inline]
fn is_special_state(&self, id: StateID) -> bool {
self.special.is_special_state(id)
}
#[inline]
fn is_dead_state(&self, id: StateID) -> bool {
self.special.is_dead_state(id)
}
#[inline]
fn is_quit_state(&self, id: StateID) -> bool {
self.special.is_quit_state(id)
}
#[inline]
fn is_match_state(&self, id: StateID) -> bool {
self.special.is_match_state(id)
}
#[inline]
fn is_start_state(&self, id: StateID) -> bool {
self.special.is_start_state(id)
}
#[inline]
fn is_accel_state(&self, id: StateID) -> bool {
self.special.is_accel_state(id)
}
// This is marked as inline to help dramatically boost sparse searching,
// which decodes each state it enters to follow the next transition.
#[cfg_attr(feature = "perf-inline", inline(always))]
fn next_state(&self, current: StateID, input: u8) -> StateID {
let input = self.tt.classes.get(input);
self.tt.state(current).next(input)
}
#[inline]
unsafe fn next_state_unchecked(
&self,
current: StateID,
input: u8,
) -> StateID {
self.next_state(current, input)
}
#[inline]
fn next_eoi_state(&self, current: StateID) -> StateID {
self.tt.state(current).next_eoi()
}
#[inline]
fn pattern_len(&self) -> usize {
self.tt.pattern_len
}
#[inline]
fn match_len(&self, id: StateID) -> usize {
self.tt.state(id).pattern_len()
}
#[inline]
fn match_pattern(&self, id: StateID, match_index: usize) -> PatternID {
// This is an optimization for the very common case of a DFA with a
// single pattern. This conditional avoids a somewhat more costly path
// that finds the pattern ID from the state machine, which requires
// a bit of slicing/pointer-chasing. This optimization tends to only
// matter when matches are frequent.
if self.tt.pattern_len == 1 {
return PatternID::ZERO;
}
self.tt.state(id).pattern_id(match_index)
}
#[inline]
fn has_empty(&self) -> bool {
self.flags.has_empty
}
#[inline]
fn is_utf8(&self) -> bool {
self.flags.is_utf8
}
#[inline]
fn is_always_start_anchored(&self) -> bool {
self.flags.is_always_start_anchored
}
#[inline]
fn start_state_forward(
&self,
input: &Input<'_>,
) -> Result<StateID, MatchError> {
if !self.quitset.is_empty() && input.start() > 0 {
let offset = input.start() - 1;
let byte = input.haystack()[offset];
if self.quitset.contains(byte) {
return Err(MatchError::quit(byte, offset));
}
}
let start = self.st.start_map.fwd(&input);
self.st.start(input, start)
}
#[inline]
fn start_state_reverse(
&self,
input: &Input<'_>,
) -> Result<StateID, MatchError> {
if !self.quitset.is_empty() && input.end() < input.haystack().len() {
let offset = input.end();
let byte = input.haystack()[offset];
if self.quitset.contains(byte) {
return Err(MatchError::quit(byte, offset));
}
}
let start = self.st.start_map.rev(&input);
self.st.start(input, start)
}
#[inline]
fn universal_start_state(&self, mode: Anchored) -> Option<StateID> {
match mode {
Anchored::No => self.st.universal_start_unanchored,
Anchored::Yes => self.st.universal_start_anchored,
Anchored::Pattern(_) => None,
}
}
#[inline]
fn accelerator(&self, id: StateID) -> &[u8] {
self.tt.state(id).accelerator()
}
#[inline]
fn get_prefilter(&self) -> Option<&Prefilter> {
self.pre.as_ref()
}
}
/// The transition table portion of a sparse DFA.
///
/// The transition table is the core part of the DFA in that it describes how
/// to move from one state to another based on the input sequence observed.
///
/// Unlike a typical dense table based DFA, states in a sparse transition
/// table have variable size. That is, states with more transitions use more
/// space than states with fewer transitions. This means that finding the next
/// transition takes more work than with a dense DFA, but also typically uses
/// much less space.
#[derive(Clone)]
struct Transitions<T> {
/// The raw encoding of each state in this DFA.
///
/// Each state has the following information:
///
/// * A set of transitions to subsequent states. Transitions to the dead
/// state are omitted.
/// * If the state can be accelerated, then any additional accelerator
/// information.
/// * If the state is a match state, then the state contains all pattern
/// IDs that match when in that state.
///
/// To decode a state, use Transitions::state.
///
/// In practice, T is either Vec<u8> or &[u8].
sparse: T,
/// A set of equivalence classes, where a single equivalence class
/// represents a set of bytes that never discriminate between a match
/// and a non-match in the DFA. Each equivalence class corresponds to a
/// single character in this DFA's alphabet, where the maximum number of
/// characters is 257 (each possible value of a byte plus the special
/// EOI transition). Consequently, the number of equivalence classes
/// corresponds to the number of transitions for each DFA state. Note
/// though that the *space* used by each DFA state in the transition table
/// may be larger. The total space used by each DFA state is known as the
/// stride and is documented above.
///
/// The only time the number of equivalence classes is fewer than 257 is
/// if the DFA's kind uses byte classes which is the default. Equivalence
/// classes should generally only be disabled when debugging, so that
/// the transitions themselves aren't obscured. Disabling them has no
/// other benefit, since the equivalence class map is always used while
/// searching. In the vast majority of cases, the number of equivalence
/// classes is substantially smaller than 257, particularly when large
/// Unicode classes aren't used.
///
/// N.B. Equivalence classes aren't particularly useful in a sparse DFA
/// in the current implementation, since equivalence classes generally tend
/// to correspond to continuous ranges of bytes that map to the same
/// transition. So in a sparse DFA, equivalence classes don't really lead
/// to a space savings. In the future, it would be good to try and remove
/// them from sparse DFAs entirely, but requires a bit of work since sparse
/// DFAs are built from dense DFAs, which are in turn built on top of
/// equivalence classes.
classes: ByteClasses,
/// The total number of states in this DFA. Note that a DFA always has at
/// least one state---the dead state---even the empty DFA. In particular,
/// the dead state always has ID 0 and is correspondingly always the first
/// state. The dead state is never a match state.
state_len: usize,
/// The total number of unique patterns represented by these match states.
pattern_len: usize,
}
impl<'a> Transitions<&'a [u8]> {
unsafe fn from_bytes_unchecked(
mut slice: &'a [u8],
) -> Result<(Transitions<&'a [u8]>, usize), DeserializeError> {
let slice_start = slice.as_ptr().as_usize();
let (state_len, nr) =
wire::try_read_u32_as_usize(&slice, "state length")?;
slice = &slice[nr..];
let (pattern_len, nr) =
wire::try_read_u32_as_usize(&slice, "pattern length")?;
slice = &slice[nr..];
let (classes, nr) = ByteClasses::from_bytes(&slice)?;
slice = &slice[nr..];
let (len, nr) =
wire::try_read_u32_as_usize(&slice, "sparse transitions length")?;
slice = &slice[nr..];
wire::check_slice_len(slice, len, "sparse states byte length")?;
let sparse = &slice[..len];
slice = &slice[len..];
let trans = Transitions { sparse, classes, state_len, pattern_len };
Ok((trans, slice.as_ptr().as_usize() - slice_start))
}
}
impl<T: AsRef<[u8]>> Transitions<T> {
/// Writes a serialized form of this transition table to the buffer given.
/// If the buffer is too small, then an error is returned. To determine
/// how big the buffer must be, use `write_to_len`.
fn write_to<E: Endian>(
&self,
mut dst: &mut [u8],
) -> Result<usize, SerializeError> {
let nwrite = self.write_to_len();
if dst.len() < nwrite {
return Err(SerializeError::buffer_too_small(
"sparse transition table",
));
}
dst = &mut dst[..nwrite];
// write state length
E::write_u32(u32::try_from(self.state_len).unwrap(), dst);
dst = &mut dst[size_of::<u32>()..];
// write pattern length
E::write_u32(u32::try_from(self.pattern_len).unwrap(), dst);
dst = &mut dst[size_of::<u32>()..];
// write byte class map
let n = self.classes.write_to(dst)?;
dst = &mut dst[n..];
// write number of bytes in sparse transitions
E::write_u32(u32::try_from(self.sparse().len()).unwrap(), dst);
dst = &mut dst[size_of::<u32>()..];
// write actual transitions
let mut id = DEAD;
while id.as_usize() < self.sparse().len() {
let state = self.state(id);
let n = state.write_to::<E>(&mut dst)?;
dst = &mut dst[n..];
// The next ID is the offset immediately following `state`.
id = StateID::new(id.as_usize() + state.write_to_len()).unwrap();
}
Ok(nwrite)
}
/// Returns the number of bytes the serialized form of this transition
/// table will use.
fn write_to_len(&self) -> usize {
size_of::<u32>() // state length
+ size_of::<u32>() // pattern length
+ self.classes.write_to_len()
+ size_of::<u32>() // sparse transitions length
+ self.sparse().len()
}
/// Validates that every state ID in this transition table is valid.
///
/// That is, every state ID can be used to correctly index a state in this
/// table.
fn validate(&self, sp: &Special) -> Result<(), DeserializeError> {
// In order to validate everything, we not only need to make sure we
// can decode every state, but that every transition in every state
// points to a valid state. There are many duplicative transitions, so
// we record state IDs that we've verified so that we don't redo the
// decoding work.
//
// Except, when in no_std mode, we don't have dynamic memory allocation
// available to us, so we skip this optimization. It's not clear
// whether doing something more clever is worth it just yet. If you're
// profiling this code and need it to run faster, please file an issue.
//
// OK, so we also use this to record the set of valid state IDs. Since
// it is possible for a transition to point to an invalid state ID that
// still (somehow) deserializes to a valid state. So we need to make
// sure our transitions are limited to actually correct state IDs.
// The problem is, I'm not sure how to do this verification step in
// no-std no-alloc mode. I think we'd *have* to store the set of valid
// state IDs in the DFA itself. For now, we don't do this verification
// in no-std no-alloc mode. The worst thing that can happen is an
// incorrect result. But no panics or memory safety problems should
// result. Because we still do validate that the state itself is
// "valid" in the sense that everything it points to actually exists.
//
// ---AG
struct Seen {
#[cfg(feature = "alloc")]
set: alloc::collections::BTreeSet<StateID>,
#[cfg(not(feature = "alloc"))]
set: core::marker::PhantomData<StateID>,
}
#[cfg(feature = "alloc")]
impl Seen {
fn new() -> Seen {
Seen { set: alloc::collections::BTreeSet::new() }
}
fn insert(&mut self, id: StateID) {
self.set.insert(id);
}
fn contains(&self, id: &StateID) -> bool {
self.set.contains(id)
}
}
#[cfg(not(feature = "alloc"))]
impl Seen {
fn new() -> Seen {
Seen { set: core::marker::PhantomData }
}
fn insert(&mut self, _id: StateID) {}
fn contains(&self, _id: &StateID) -> bool {
false
}
}
let mut verified: Seen = Seen::new();
// We need to make sure that we decode the correct number of states.
// Otherwise, an empty set of transitions would validate even if the
// recorded state length is non-empty.
let mut len = 0;
// We can't use the self.states() iterator because it assumes the state
// encodings are valid. It could panic if they aren't.
let mut id = DEAD;
while id.as_usize() < self.sparse().len() {
// Before we even decode the state, we check that the ID itself
// is well formed. That is, if it's a special state then it must
// actually be a quit, dead, accel, match or start state.
if sp.is_special_state(id) {
let is_actually_special = sp.is_dead_state(id)
|| sp.is_quit_state(id)
|| sp.is_match_state(id)
|| sp.is_start_state(id)
|| sp.is_accel_state(id);
if !is_actually_special {
// This is kind of a cryptic error message...
return Err(DeserializeError::generic(
"found sparse state tagged as special but \
wasn't actually special",
));
}
}
let state = self.try_state(sp, id)?;
verified.insert(id);
// The next ID should be the offset immediately following `state`.
id = StateID::new(wire::add(
id.as_usize(),
state.write_to_len(),
"next state ID offset",
)?)
.map_err(|err| {
DeserializeError::state_id_error(err, "next state ID offset")
})?;
len += 1;
}
// Now that we've checked that all top-level states are correct and
// importantly, collected a set of valid state IDs, we have all the
// information we need to check that all transitions are correct too.
//
// Note that we can't use `valid_ids` to iterate because it will
// be empty in no-std no-alloc contexts. (And yes, that means our
// verification isn't quite as good.) We can use `self.states()`
// though at least, since we know that all states can at least be
// decoded and traversed correctly.
for state in self.states() {
// Check that all transitions in this state are correct.
for i in 0..state.ntrans {
let to = state.next_at(i);
// For no-alloc, we just check that the state can decode. It is
// technically possible that the state ID could still point to
// a non-existent state even if it decodes (fuzzing proved this
// to be true), but it shouldn't result in any memory unsafety
// or panics in non-debug mode.
#[cfg(not(feature = "alloc"))]
{
let _ = self.try_state(sp, to)?;
}
#[cfg(feature = "alloc")]
{
if !verified.contains(&to) {
return Err(DeserializeError::generic(
"found transition that points to a \
non-existent state",
));
}
}
}
}
if len != self.state_len {
return Err(DeserializeError::generic(
"mismatching sparse state length",
));
}
Ok(())
}
/// Converts these transitions to a borrowed value.
fn as_ref(&self) -> Transitions<&'_ [u8]> {
Transitions {
sparse: self.sparse(),
classes: self.classes.clone(),
state_len: self.state_len,
pattern_len: self.pattern_len,
}
}
/// Converts these transitions to an owned value.
#[cfg(feature = "alloc")]
fn to_owned(&self) -> Transitions<alloc::vec::Vec<u8>> {
Transitions {
sparse: self.sparse().to_vec(),
classes: self.classes.clone(),
state_len: self.state_len,
pattern_len: self.pattern_len,
}
}
/// Return a convenient representation of the given state.
///
/// This panics if the state is invalid.
///
/// This is marked as inline to help dramatically boost sparse searching,
/// which decodes each state it enters to follow the next transition. Other
/// functions involved are also inlined, which should hopefully eliminate
/// a lot of the extraneous decoding that is never needed just to follow
/// the next transition.
#[cfg_attr(feature = "perf-inline", inline(always))]
fn state(&self, id: StateID) -> State<'_> {
let mut state = &self.sparse()[id.as_usize()..];
let mut ntrans = wire::read_u16(&state).as_usize();
let is_match = (1 << 15) & ntrans != 0;
ntrans &= !(1 << 15);
state = &state[2..];
let (input_ranges, state) = state.split_at(ntrans * 2);
let (next, state) = state.split_at(ntrans * StateID::SIZE);
let (pattern_ids, state) = if is_match {
let npats = wire::read_u32(&state).as_usize();
state[4..].split_at(npats * 4)
} else {
(&[][..], state)
};
let accel_len = usize::from(state[0]);
let accel = &state[1..accel_len + 1];
State { id, is_match, ntrans, input_ranges, next, pattern_ids, accel }
}
/// Like `state`, but will return an error if the state encoding is
/// invalid. This is useful for verifying states after deserialization,
/// which is required for a safe deserialization API.
///
/// Note that this only verifies that this state is decodable and that
/// all of its data is consistent. It does not verify that its state ID
/// transitions point to valid states themselves, nor does it verify that
/// every pattern ID is valid.
fn try_state(
&self,
sp: &Special,
id: StateID,
) -> Result<State<'_>, DeserializeError> {
if id.as_usize() > self.sparse().len() {
return Err(DeserializeError::generic(
"invalid caller provided sparse state ID",
));
}
let mut state = &self.sparse()[id.as_usize()..];
// Encoding format starts with a u16 that stores the total number of
// transitions in this state.
let (mut ntrans, _) =
wire::try_read_u16_as_usize(state, "state transition length")?;
let is_match = ((1 << 15) & ntrans) != 0;
ntrans &= !(1 << 15);
state = &state[2..];
if ntrans > 257 || ntrans == 0 {
return Err(DeserializeError::generic(
"invalid transition length",
));
}
--> --------------------
--> maximum size reached
--> --------------------
