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use std::iter::FusedIterator;
use std::ops::Range;
use crate::buffer::Buffer;
/// Either a field that is missing or has an invalid value.
#[derive(Debug, thiserror::Error)]
pub enum FieldValueError<E> {
/// No such field was found.
#[error("Missing field tag")]
Missing,
/// The field was found, but can't be parsed.
#[error("Invalid field value: {0}")]
Invalid(#[from] E),
}
impl<E> PartialEq<FieldValueError<E>> for FieldValueError<E> {
fn eq(&self, other: &FieldValueError<E>) -> bool {
matches!(
(self, other),
(FieldValueError::Missing, FieldValueError::Missing)
)
}
}
impl<E> From<Option<E>> for FieldValueError<E> {
fn from(e: Option<E>) -> Self {
match e {
Some(e) => FieldValueError::Invalid(e),
None => FieldValueError::Missing,
}
}
}
/// Provides (de)serialization logic for a Rust type as FIX field values.
///
/// See the [`field_types`](crate::field_types) module for more information.
pub trait FieldType<'a>
where
Self: Sized,
{
/// The error type that can arise during deserialization.
type Error;
/// A type with values that customize the serialization algorithm, e.g.
/// padding information.
type SerializeSettings: Default;
/// Writes `self` to `buffer` using default settings.
#[inline]
fn serialize<B>(&self, buffer: &mut B) -> usize
where
B: Buffer,
{
self.serialize_with(buffer, Self::SerializeSettings::default())
}
/// Writes `self` to `buffer` using custom serialization `settings`.
fn serialize_with<B>(&self, buffer: &mut B, settings: Self::SerializeSettings) -> usize
where
B: Buffer;
/// Parses and deserializes from `data`.
fn deserialize(data: &'a [u8]) -> Result<Self, Self::Error>;
/// Like [`FieldType::deserialize`], but it's allowed to skip *some* amount of
/// input checking. Invalid inputs might not trigger errors and instead be
/// deserialized as random values.
///
/// # Safety
///
/// This method remains 100% safe even on malformed inputs.
fn deserialize_lossy(data: &'a [u8]) -> Result<Self, Self::Error> {
Self::deserialize(data)
}
/// Serializes `self` to a [`Vec`] of bytes, allocated on the fly.
fn to_bytes(&self) -> Vec<u8> {
let mut buffer = Vec::new();
self.serialize(&mut buffer);
buffer
}
/// Allocates a [`String`] representation of `self`, using [`FieldType::to_bytes`].
///
/// # Panics
///
/// This function will panic if the underlying byte representation is not
/// valid UTF-8. As such, you should only *ever* use this function for
/// [`FieldType`] implementors that are guaranteed to be representable with
/// valid UTF-8 (like numbers with ASCII digits).
fn to_string(&self) -> String {
String::from_utf8(self.to_bytes()).expect("Invalid UTF-8 representation of FIX field.")
}
}
/// Provides random (i.e. non-sequential) access to FIX fields and groups within
/// messages.
///
/// # Methods
///
/// [`FieldMap`] provides two kinds of methods:
///
/// 1. Group getters: [`FieldMap::group`] and
/// [`FieldMap::group_opt`].
///
/// 2. Field getters: [`FieldMap::get_raw`], [`FieldMap::get`],
/// etc..
///
/// The most basic form of field access is done via
/// [`FieldMap::get_raw`], which performs no deserialization at all: it
/// simply returns the bytes contents associated with a FIX field, if found.
///
/// Building upon [`FieldMap::get_raw`] and [`FieldType`], the other
/// field access methods all provide some utility deserialization logic. These
/// methods all have the `get_` prefix, with the following considerations:
///
/// - `get_lossy` methods perform "lossy" deserialization via
/// [`FieldType::deserialize_lossy`]. Unlike lossless deserialization, these
/// methods may skip some error checking logic and thus prove to be faster.
/// Memory-safety is still guaranteed, but malformed FIX fields won't be
/// detected 100% of the time.
/// - `get_opt` methods work exactly like their non-`_opt` counterparties, but they
/// have a different return type: instead of returning [`Err(None)`] for missing
/// fields, these methods return [`None`] for missing fields and
/// [`Some(Ok(field))`] for existing fields.
///
/// # Type parameters
///
/// This trait is generic over a type `F`, which must univocally identify FIX
/// fields (besides FIX repeating groups, which allow repetitions).
pub trait FieldMap<F> {
/// The type returned by [`FieldMap::group`] and
/// [`FieldMap::group_opt`].
type Group: RepeatingGroup<Entry = Self>;
/// Looks for a `field` within `self` and then returns its raw byte
/// contents, if it exists.
fn get_raw(&self, field: F) -> Option<&[u8]>;
/// Looks for a group that starts with `field` within `self`.
fn group(&self, field: F) -> Result<Self::Group, FieldValueError<<usize as FieldType>::Error>>;
/// Like [`FieldMap::group`], but doesn't return an [`Err`] if the
/// group is missing.
#[inline]
fn group_opt(&self, field: F) -> Result<Option<Self::Group>, <usize as FieldType>::Error> {
match self.group(field) {
Ok(group) => Ok(Some(group)),
Err(FieldValueError::Missing) => Ok(None),
Err(FieldValueError::Invalid(e)) => Err(e),
}
}
/// Looks for a `field` within `self` and then decodes its raw byte contents
/// via [`FieldType::deserialize`], if found.
#[inline]
fn get<'a, V>(&'a self, field: F) -> Result<V, FieldValueError<V::Error>>
where
V: FieldType<'a>,
{
self.get_opt(field)
.map_err(FieldValueError::Invalid)
.and_then(|opt| opt.ok_or(FieldValueError::Missing))
}
/// Like [`FieldMap::get`], but with lossy deserialization.
#[inline]
fn get_lossy<'a, V>(&'a self, field: F) -> Result<V, FieldValueError<V::Error>>
where
V: FieldType<'a>,
{
self.get_lossy_opt(field)
.map_err(FieldValueError::Invalid)
.and_then(|opt| opt.ok_or(FieldValueError::Missing))
}
/// Like [`FieldMap::get`], but doesn't return an [`Err`] if `field`
/// is missing.
#[inline]
fn get_opt<'a, V>(&'a self, field: F) -> Result<Option<V>, V::Error>
where
V: FieldType<'a>,
{
self.get_raw(field).map(V::deserialize).transpose()
}
/// Like [`FieldMap::get_opt`], but with lossy deserialization.
#[inline]
fn get_lossy_opt<'a, V>(&'a self, field: F) -> Result<Option<V>, V::Error>
where
V: FieldType<'a>,
{
self.get_raw(field).map(V::deserialize_lossy).transpose()
}
}
/// Provides access to entries within a FIX repeating group.
pub trait RepeatingGroup: Sized {
/// The type of entries in this FIX repeating group. Must implement
/// [`FieldMap`].
type Entry;
/// Returns the number of FIX group entries in `self`.
fn len(&self) -> usize;
fn is_empty(&self) -> bool;
/// Returns the `i` -th entry in `self`, if present.
fn get(&self, i: usize) -> Option<Self::Entry>;
/// Creates and returns an [`Iterator`] over the entries in `self`.
/// Iteration MUST be done in sequential order, i.e. in which they appear in
/// the original FIX message.
fn entries(&self) -> GroupEntries<Self> {
GroupEntries {
group: self,
range: 0..self.len(),
}
}
}
/// An [`Iterator`] over the entries of a FIX repeating group.
///
/// This `struct` is created by the method [`RepeatingGroup::entries`]. It
/// also implements [`FusedIterator`], [`DoubleEndedIterator`], and
/// [`ExactSizeIterator`].
#[derive(Debug, Clone)]
pub struct GroupEntries<'a, G> {
group: &'a G,
range: Range<usize>,
}
impl<'a, G> Iterator for GroupEntries<'a, G>
where
G: RepeatingGroup,
{
type Item = G::Entry;
fn next(&mut self) -> Option<Self::Item> {
let i = self.range.next()?;
self.group.get(i)
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.range.size_hint()
}
}
impl<'a, G> FusedIterator for GroupEntries<'a, G> where G: RepeatingGroup {}
impl<'a, G> ExactSizeIterator for GroupEntries<'a, G> where G: RepeatingGroup {}
impl<'a, G> DoubleEndedIterator for GroupEntries<'a, G>
where
G: RepeatingGroup,
{
fn next_back(&mut self) -> Option<Self::Item> {
let i = self.range.next_back()?;
self.group.get(i)
}
}