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// Copyright 2019-2024 ChainSafe Systems
// SPDX-License-Identifier: Apache-2.0, MIT
mod empty_map;
use std::ops::SubAssign;
use indexmap::IndexMap;
use serde::{Deserialize, Serialize};
#[cfg(test)]
use super::Ipld;
#[cfg(test)]
use Selector::*;
/// Selectors are expressions that identify and select a subset of data from an
/// IPLD DAG. Selectors are themselves IPLD and can be serialized and
/// de-serialized as such.
#[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
pub enum Selector {
/// `Matcher` marks a node to be included in the "result" set.
/// (All nodes traversed by a selector are in the "covered" set (which is
/// a.k.a. "the Merkle proof"); the "result" set is a subset of the
/// "covered" set.)
///
/// In libraries using selectors, the "result" set is typically provided to
/// some user-specified callback.
///
/// A selector tree with only "explore*"-type selectors and no `Matcher`
/// selectors is valid; it will just generate a "covered" set of nodes
/// and no "result" set.
#[serde(rename = ".", with = "empty_map")]
Matcher,
/// `ExploreAll` is similar to a `*` -- it traverses all elements of an
/// array, or all entries in a map, and applies a next selector to the
/// reached nodes.
#[serde(rename = "a")]
ExploreAll {
#[serde(rename = ">")]
next: Box<Selector>,
},
/// `ExploreFields` traverses named fields in a map (or equivalently,
/// structure, if traversing on typed/schema nodes) and applies a next
/// selector to the reached nodes.
///
/// Note that a concept of exploring a whole path (e.g. "path/to/file") can
/// be represented as a set of three nested `ExploreFields` selectors,
/// each specifying one field.
///
/// Fields insertion order is maintained and traversed using that order.
#[serde(rename = "f")]
ExploreFields {
#[serde(rename = "f>")]
fields: IndexMap<String, Selector>,
},
/// `ExploreIndex` traverses a specific index in a list, and applies a next
/// selector to the reached node.
#[serde(rename = "i")]
ExploreIndex {
#[serde(rename = "i")]
index: usize,
#[serde(rename = ">")]
next: Box<Selector>,
},
/// `ExploreRange` traverses a list, and for each element in the range
/// specified, will apply a next selector to those reached nodes.
#[serde(rename = "r")]
ExploreRange {
#[serde(rename = "^")]
start: usize,
#[serde(rename = "$")]
end: usize,
#[serde(rename = ">")]
next: Box<Selector>,
},
/// `ExploreRecursive` traverses some structure recursively.
/// To guide this exploration, it uses a "sequence", which is another
/// Selector tree; some leaf node in this sequence should contain an
/// `ExploreRecursiveEdge` selector, which denotes the place recursion
/// should occur.
///
/// In implementation, whenever evaluation reaches an `ExploreRecursiveEdge`
/// marker in the recursion sequence's Selector tree, the implementation
/// logically produces another new Selector which is a copy of the
/// original `ExploreRecursive` selector, but with a decremented depth
/// parameter for limit (if limit is of type depth), and continues
/// evaluation.
///
/// It is not valid for an `ExploreRecursive` selector's sequence to contain
/// no instances of `ExploreRecursiveEdge`; it *is* valid for it to contain
/// more than one `ExploreRecursiveEdge`.
///
/// `ExploreRecursive` can contain a nested `ExploreRecursive`!
/// This is comparable to a nested for-loop.
/// In these cases, any `ExploreRecursiveEdge` instance always refers to the
/// nearest parent `ExploreRecursive` (in other words,
/// `ExploreRecursiveEdge` can be thought of like the 'continue'
/// statement, or end of a for-loop body; it is *not* a `goto`
/// statement).
///
/// Be careful when using `ExploreRecursive` with a large depth limit
/// parameter; it can easily cause very large traversals (especially if
/// used in combination with selectors like `ExploreAll` inside the
/// sequence).
///
/// limit is a union type -- it can have an integer depth value (key
/// "depth") or no value (key "none"). If limit has no value it is up to
/// the implementation library using selectors to identify an
/// appropriate max depth as necessary so that recursion is not infinite
#[serde(rename = "R")]
ExploreRecursive {
#[serde(rename = ":>")]
sequence: Box<Selector>,
#[serde(rename = "l")]
limit: RecursionLimit,
/// if a node matches, we won't match it nor explore its children.
#[serde(rename = "!")]
stop_at: Option<Condition>,
#[serde(skip_deserializing)]
/// Used to index current
current: Option<Box<Selector>>,
},
/// `ExploreUnion` allows selection to continue with two or more distinct
/// selectors while exploring the same tree of data.
///
/// `ExploreUnion` can be used to apply a `Matcher` on one node (causing it
/// to be considered part of a (possibly labeled) result set), while
/// simultaneously continuing to explore deeper parts of the tree with
/// another selector, for example.
#[serde(rename = "|")]
ExploreUnion(Vec<Selector>),
/// `ExploreRecursiveEdge` is a special sentinel value which is used to mark
/// the end of a sequence started by an `ExploreRecursive` selector: the
/// recursion goes back to the initial state of the earlier
/// `ExploreRecursive` selector, and proceeds again (with a decremented
/// `maxDepth` value).
///
/// An `ExploreRecursive` selector that doesn't contain an
/// `ExploreRecursiveEdge` is nonsensical. Containing more than one
/// `ExploreRecursiveEdge` is valid. An `ExploreRecursiveEdge` without
/// an enclosing `ExploreRecursive` is an error.
#[serde(rename = "@", with = "empty_map")]
ExploreRecursiveEdge,
//* No conditional explore impl exists, ignore for now
// #[serde(rename = "&")]
// ExploreConditional {
// #[serde(rename = "&")]
// condition: Option<Condition>,
// #[serde(rename = ">")]
// next: Box<Selector>,
// },
}
#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, Copy)]
pub enum RecursionLimit {
#[serde(rename = "none", with = "empty_map")]
None,
#[serde(rename = "depth")]
Depth(u64),
}
impl SubAssign<u64> for RecursionLimit {
fn sub_assign(&mut self, other: u64) {
if let RecursionLimit::Depth(v) = self {
*v -= other;
}
}
}
/// Condition is expresses a predicate with a boolean result.
///
/// Condition clauses are used several places:
/// - in `Matcher`, to determine if a node is selected.
/// - in `ExploreRecursive`, to halt exploration.
/// - in `ExploreConditional`,
#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, Copy)]
pub enum Condition {
#[serde(rename = "hasField")]
HasField,
#[serde(rename = "=")]
HasValue,
#[serde(rename = "%")]
HasKind,
#[serde(rename = "/")]
IsLink,
#[serde(rename = "greaterThan")]
GreaterThan,
#[serde(rename = "lessThan")]
LessThan,
#[serde(rename = "and")]
And,
#[serde(rename = "or")]
Or,
}
#[cfg(test)]
impl Selector {
/// Processes and returns resultant selector node
pub fn explore(self, ipld: &Ipld, p: &str) -> Option<Selector> {
match self {
ExploreAll { next } => Some(*next),
ExploreFields { mut fields } => match ipld {
Ipld::Map(m) => {
m.get(p)?;
fields.swap_remove(p)
}
,
// Using ExploreFields for list is supported feature in go impl
Ipld::List(l) => {
// Check to make sure index is within bounds
if p.parse::<usize>().ok()? >= l.len() {
return None;
}
fields.swap_remove(p)
}
_ => None,
},
ExploreIndex { index, next } => match ipld {
Ipld::List(l) => {
let i = p.parse::<usize>().ok()?;
if i != index || i >= l.len() {
None
} else {
// Path segment matches selector index
Some(*next)
}
}
_ => None,
},
ExploreRange { start, end, next } => {
match ipld {
Ipld::List(l) => {
let i = p.parse::<usize>().ok()?;
// Check to make sure index is within list bounds
if i < start || i >= end || i >= l.len() {
None
} else {
// Path segment is within the selector range
Some(*next)
}
}
_ => None,
}
}
ExploreRecursive {
current,
sequence,
mut limit,
stop_at,
} => {
let next = current
.unwrap_or_else(|| sequence.clone())
.explore(ipld, p)?;
if !has_recursive_edge(&next) {
return Some(ExploreRecursive {
sequence,
current: Some(next.into()),
limit,
stop_at,
});
}
if let RecursionLimit::Depth(depth) = limit {
if depth < 2 {
// Replaces recursive edge with None on last iteration
return replace_recursive_edge(next, None);
}
limit -= 1;
}
Some(ExploreRecursive {
current: replace_recursive_edge(next, Some(*sequence.clone())).map(Box::new),
sequence,
limit,
stop_at,
})
}
ExploreUnion(selectors) => {
// Push all valid explored selectors to new vector
let replace_selectors: Vec<_> = selectors
.into_iter()
.filter_map(|s| s.explore(ipld, p))
.collect();
Selector::from_selectors(replace_selectors)
}
// Go impl panics here, but panic on exploring malformed selector seems bad
ExploreRecursiveEdge => None,
// Matcher is terminal selector
Matcher => None,
}
}
fn from_selectors(mut vec: Vec<Self>) -> Option<Self> {
match vec.len() {
0 | 1 => vec.pop(),
_ => Some(ExploreUnion(vec)),
}
}
}
#[cfg(test)]
fn replace_recursive_edge(next_sel: Selector, replace: Option<Selector>) -> Option<Selector> {
match next_sel {
ExploreRecursiveEdge => replace,
ExploreUnion(selectors) => {
// Push all valid explored selectors to new vector
let replace_selectors: Vec<_> = selectors
.into_iter()
.filter_map(|s| replace_recursive_edge(s, replace.clone()))
.collect();
Selector::from_selectors(replace_selectors)
}
_ => Some(next_sel),
}
}
#[cfg(test)]
fn has_recursive_edge(next_sel: &Selector) -> bool {
match next_sel {
ExploreRecursiveEdge { .. } => true,
ExploreUnion(selectors) => selectors.iter().any(has_recursive_edge),
_ => false,
}
}