Mihaela Mihaljevic
fe0400c3df
Third profile-guided pass (#139, docs/benchmarks.md pass 27), targeting scanContentMarkup(), which inlines the start-tag/attribute/namespace scanners and carries ~46% of parse time. scanAttributeValue's opening and closing quote checks ran on the Character path (peek + advance, buffering the quote as a Character only to compare and discard it) on every attribute value in the document; both now check the raw byte first, reaching the byte fast path with no Character buffering, with the Character path kept as the off-fast-path fallback for streaming sources. The quote bytes are ASCII and non-CR/LF, so the raw byte and the normalized stream agree, the same reasoning peekByte's other callers already rely on. NamespaceContext.checkExpandedNames allocated a Set's native storage and built a concatenated URI+local key string per element even when at most one attribute carries a namespace URI, where no duplicate is possible (the default namespace never applies to attributes, and xmlns declarations carry no URI). Counting URI-bearing attributes first, with no allocation, and returning early below two skips all of it on the overwhelming majority of elements; for xml:* attributes specifically the key exceeded the small-string limit, so this also removes a real per-element heap allocation. EntityDecoder.decode/decodeLenient guarded with raw.contains("&"), a grapheme-by-grapheme walk to find one ASCII byte, once per ampersand-bearing text node or attribute value; raw.utf8.contains(0x26) finds the same byte without decoding graphemes, the same shape as checkNameShape's colon check. The quote-handling extraction into two helpers also resolves the cyclomatic complexity the inline version tripped. Six new regression tests pin the quote edge cases (empty value, single-quoted, a quote kind nested inside the other, unterminated at end of input) plus byte/Character-path agreement for each in the parser path differential. Verified: full local suite (1858 tests) and full W3C XSTS suite (14383 groups) pass unchanged. Parse ~6.00x -> ~4.75x versus libxml2 at the 20000-item corpus, best of 5.
361 lines
16 KiB
Swift
361 lines
16 KiB
Swift
extension PureXML.Parsing {
|
|
/// Decodes XML references inside text and attribute values: the five
|
|
/// predefined entities, decimal/hex character references, and declared
|
|
/// internal general entities.
|
|
///
|
|
/// Declared-entity expansion is the billion-laughs vector, so it is bounded:
|
|
/// only characters produced by expansion count against a shared budget, and a
|
|
/// set of in-progress entity names detects recursive references. Literal
|
|
/// document text never consumes the budget.
|
|
enum EntityDecoder {
|
|
/// Decodes references in `raw`. `entities` is the declared internal-entity
|
|
/// table (empty unless a DTD was processed). `budget` is the remaining
|
|
/// expansion allowance, shared across the document and decremented as
|
|
/// expansion produces characters.
|
|
static func decode(
|
|
_ raw: String,
|
|
entities: [String: String],
|
|
budget: inout Int,
|
|
at mark: Mark,
|
|
) throws -> String {
|
|
// A `Character` literal here resolves to `Sequence.contains(_:)`,
|
|
// walking extended grapheme clusters to find one ASCII byte; called
|
|
// once per ampersand-bearing text node or attribute value in the
|
|
// whole document. `utf8.contains(0x26)` finds the same `&` via the
|
|
// UTF-8 byte view, since 0x26 is never a lead or continuation byte
|
|
// of a multi-byte sequence (matches the reasoning already applied
|
|
// to `NamespaceContext.checkNameShape`'s colon check).
|
|
guard raw.utf8.contains(0x26) else { return raw }
|
|
var expander = EntityExpander(entities: entities, mark: mark, budget: budget)
|
|
try expander.expand(raw, visiting: [], counts: false)
|
|
budget = expander.budget
|
|
return expander.result
|
|
}
|
|
|
|
/// Decodes like ``decode(_:entities:budget:at:)`` but treats an
|
|
/// undeclared entity as a validity finding instead of a fatal error
|
|
/// (production 68: with an external subset or parameter entities in
|
|
/// play, Entity Declared is a VC): the reference is kept literally and
|
|
/// its name appended to `undeclared`.
|
|
static func decodeLenient(
|
|
_ raw: String,
|
|
entities: [String: String],
|
|
budget: inout Int,
|
|
at mark: Mark,
|
|
undeclared: inout [String],
|
|
) throws -> String {
|
|
// See `decode(_:entities:budget:at:)`'s matching guard: byte-level
|
|
// scan, not a grapheme walk, for the same reason.
|
|
guard raw.utf8.contains(0x26) else { return raw }
|
|
var expander = EntityExpander(entities: entities, mark: mark, budget: budget, undeclared: [])
|
|
try expander.expand(raw, visiting: [], counts: false)
|
|
budget = expander.budget
|
|
undeclared += expander.undeclared ?? []
|
|
return expander.result
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Content splicing (4.4.2 Included): a declared general entity whose
|
|
/// replacement text, directly or through entities it references, contains
|
|
/// markup must be reparsed as content, not included as character data. The
|
|
/// event reader uses these helpers to find such references in a text run, to
|
|
/// validate and budget the inclusion, and to splice the replacement back into
|
|
/// its character stream.
|
|
extension PureXML.Parsing.EntityDecoder {
|
|
private static let predefined: Set<String> = ["amp", "lt", "gt", "quot", "apos"]
|
|
|
|
/// A text run split at a markup-producing entity reference: the text
|
|
/// before the reference, the entity name, and the unconsumed text after.
|
|
struct MarkupSplit {
|
|
let prefix: String
|
|
let name: String
|
|
let remainder: String
|
|
}
|
|
|
|
/// Splits `raw` at the first reference to a declared entity whose
|
|
/// replacement produces markup. Nil when no such reference occurs and
|
|
/// plain decoding suffices.
|
|
static func splitAtMarkupEntity(_ raw: String, entities: [String: String]) -> MarkupSplit? {
|
|
guard !entities.isEmpty else { return nil }
|
|
var markupCache: [String: Bool] = [:]
|
|
var index = raw.startIndex
|
|
while index < raw.endIndex, let amp = raw[index...].firstIndex(of: "&") {
|
|
guard let semicolon = raw[amp...].firstIndex(of: ";") else { return nil }
|
|
let name = String(raw[raw.index(after: amp) ..< semicolon])
|
|
if !name.hasPrefix("#"), !predefined.contains(name), producesMarkup(name, entities: entities, cache: &markupCache) {
|
|
return MarkupSplit(
|
|
prefix: String(raw[..<amp]),
|
|
name: name,
|
|
remainder: String(raw[raw.index(after: semicolon)...]),
|
|
)
|
|
}
|
|
index = raw.index(after: semicolon)
|
|
}
|
|
return nil
|
|
}
|
|
|
|
/// Validates and budgets one content inclusion of `name`, returning its
|
|
/// replacement text for splicing: the replacement must reparse as balanced
|
|
/// content (the reference-time WFC), the reference chain must not recurse,
|
|
/// and the replacement's size counts against the amplification budget.
|
|
static func includeForContent(
|
|
_ name: String,
|
|
entities: [String: String],
|
|
budget: inout Int,
|
|
at mark: PureXML.Parsing.Mark,
|
|
) throws -> String {
|
|
guard let replacement = entities[name] else {
|
|
throw PureXML.Parsing.ParseError.undefinedEntity(name: name, mark)
|
|
}
|
|
if PureXML.Parsing.EntityReplacementGrammar.violation(inValue: replacement) != nil {
|
|
throw PureXML.Parsing.ParseError.invalidReference("&\(name);", mark)
|
|
}
|
|
try checkRecursion(name, entities: entities, visiting: [name], at: mark)
|
|
guard budget >= replacement.count else {
|
|
throw PureXML.Parsing.ParseError.amplificationLimitExceeded(mark)
|
|
}
|
|
budget -= replacement.count
|
|
return replacement
|
|
}
|
|
|
|
/// Whether `name`'s replacement contains markup, directly or transitively.
|
|
/// Memoized per entity name: the property depends only on the (fixed) entity
|
|
/// graph, so a deeply-nested reference chain resolves in O(entities) rather
|
|
/// than O(references^depth), which a billion-laughs document otherwise forces.
|
|
/// A tentative `false` recorded before the recursion breaks any cycle (a
|
|
/// cyclic entity is an error caught when the reference is expanded).
|
|
private static func producesMarkup(_ name: String, entities: [String: String], cache: inout [String: Bool]) -> Bool {
|
|
if let cached = cache[name] { return cached }
|
|
guard let replacement = entities[name] else {
|
|
cache[name] = false
|
|
return false
|
|
}
|
|
cache[name] = false
|
|
let result = replacement.contains("<")
|
|
|| declaredReferences(in: replacement).contains { producesMarkup($0, entities: entities, cache: &cache) }
|
|
cache[name] = result
|
|
return result
|
|
}
|
|
|
|
private static func checkRecursion(
|
|
_ name: String,
|
|
entities: [String: String],
|
|
visiting: Set<String>,
|
|
at mark: PureXML.Parsing.Mark,
|
|
) throws {
|
|
var verified: Set<String> = []
|
|
try checkRecursion(name, entities: entities, visiting: visiting, verified: &verified, at: mark)
|
|
}
|
|
|
|
/// Three-colour DFS for the No-Recursion WFC. `visiting` is the grey set
|
|
/// (entities on the current reference chain; revisiting one is the cycle).
|
|
/// `verified` is the black set: an entity is added only after its whole
|
|
/// reachable subgraph returns acyclic, so it can never reach a chain node
|
|
/// that reaches it. Skipping a black entity is therefore sound and collapses
|
|
/// the otherwise O(references^depth) revisits of a billion-laughs graph to
|
|
/// one pass over the distinct edges.
|
|
private static func checkRecursion(
|
|
_ name: String,
|
|
entities: [String: String],
|
|
visiting: Set<String>,
|
|
verified: inout Set<String>,
|
|
at mark: PureXML.Parsing.Mark,
|
|
) throws {
|
|
guard let replacement = entities[name] else { return }
|
|
for reference in declaredReferences(in: replacement) where !verified.contains(reference) {
|
|
guard !visiting.contains(reference) else {
|
|
throw PureXML.Parsing.ParseError.recursiveEntity(name: reference, mark)
|
|
}
|
|
try checkRecursion(reference, entities: entities, visiting: visiting.union([reference]), verified: &verified, at: mark)
|
|
verified.insert(reference)
|
|
}
|
|
}
|
|
|
|
/// The declared-entity names referenced in `text`: `&name;` forms that are
|
|
/// neither predefined nor character references. References inside CDATA
|
|
/// sections are shielded and not counted.
|
|
private static func declaredReferences(in text: String) -> [String] {
|
|
var names: [String] = []
|
|
var index = text.startIndex
|
|
while index < text.endIndex {
|
|
if text[index...].hasPrefix("<![CDATA[") {
|
|
var cursor = text.index(index, offsetBy: 9)
|
|
while cursor < text.endIndex, !text[cursor...].hasPrefix("]]>") {
|
|
cursor = text.index(after: cursor)
|
|
}
|
|
index = cursor < text.endIndex ? text.index(cursor, offsetBy: 3) : text.endIndex
|
|
continue
|
|
}
|
|
guard text[index] == "&" else {
|
|
index = text.index(after: index)
|
|
continue
|
|
}
|
|
guard let semicolon = text[index...].firstIndex(of: ";") else { return names }
|
|
let name = String(text[text.index(after: index) ..< semicolon])
|
|
if !name.hasPrefix("#"), !predefined.contains(name) {
|
|
names.append(name)
|
|
}
|
|
index = text.index(after: semicolon)
|
|
}
|
|
return names
|
|
}
|
|
}
|
|
|
|
/// Carries the mutable state of one decode pass (output and remaining budget) so
|
|
/// the recursive expansion stays a few small methods. File-scope and private.
|
|
///
|
|
/// Two independent bounds defend against expansion attacks: the character
|
|
/// `budget` caps total output, and the `visiting` set caps recursion depth,
|
|
/// since each entity name may appear at most once per chain, the expansion
|
|
/// depth is bounded by the number of declared entities (a cycle is an error).
|
|
private struct EntityExpander {
|
|
let entities: [String: String]
|
|
let mark: PureXML.Parsing.Mark
|
|
var budget: Int
|
|
/// When non-nil, an undeclared entity is recorded here and kept literal
|
|
/// instead of throwing.
|
|
var undeclared: [String]?
|
|
var result = ""
|
|
|
|
mutating func expand(_ raw: String, visiting: Set<String>, counts: Bool) throws {
|
|
var iterator = raw.startIndex
|
|
while iterator < raw.endIndex {
|
|
// Copy the literal run up to the next reference or markup character
|
|
// in bulk rather than one character at a time: only '&' (a
|
|
// reference) and '<' (a possible CDATA section) need per-character
|
|
// handling, and the text between them is the bulk of any run. The
|
|
// scan is at the byte level (both are ASCII, so a UTF-8 index is a
|
|
// valid string index), which avoids decoding every literal byte into
|
|
// a grapheme just to look for two markers.
|
|
guard let special = raw.utf8[iterator...].firstIndex(where: { $0 == 0x26 || $0 == 0x3C }) else {
|
|
try appendRun(raw[iterator...], counts: counts)
|
|
return
|
|
}
|
|
if special > iterator {
|
|
try appendRun(raw[iterator ..< special], counts: counts)
|
|
iterator = special
|
|
}
|
|
let character = raw[iterator]
|
|
if character == "<" {
|
|
// A CDATA section inside replacement text shields its content
|
|
// from reference recognition: copy it verbatim through the
|
|
// terminator. A '<' that does not open CDATA is literal content.
|
|
if raw[iterator...].hasPrefix("<![CDATA[") {
|
|
let openEnd = raw.index(iterator, offsetBy: 9)
|
|
var end = raw.endIndex
|
|
var cursor = openEnd
|
|
while cursor < raw.endIndex {
|
|
if raw[cursor...].hasPrefix("]]>") {
|
|
end = raw.index(cursor, offsetBy: 3)
|
|
break
|
|
}
|
|
cursor = raw.index(after: cursor)
|
|
}
|
|
try appendRun(raw[iterator ..< end], counts: counts)
|
|
iterator = end
|
|
continue
|
|
}
|
|
try append(character, counts: counts)
|
|
iterator = raw.index(after: iterator)
|
|
continue
|
|
}
|
|
guard let semicolon = raw.utf8[iterator...].firstIndex(of: 0x3B) else {
|
|
throw PureXML.Parsing.ParseError.invalidReference(String(raw[iterator...]), mark)
|
|
}
|
|
let body = String(raw[raw.index(after: iterator) ..< semicolon])
|
|
try resolve(body, visiting: visiting, counts: counts)
|
|
iterator = raw.index(after: semicolon)
|
|
}
|
|
}
|
|
|
|
/// Appends a verbatim run, charging its whole length against the
|
|
/// amplification budget at once when counting (the per-character
|
|
/// ``append(_:counts:)`` charges one at a time; for a run the effect is
|
|
/// identical, the budget reaching the same value and the same overrun
|
|
/// throwing, only without the per-character work).
|
|
private mutating func appendRun(_ run: Substring, counts: Bool) throws {
|
|
if counts {
|
|
let length = run.count
|
|
guard budget >= length else {
|
|
throw PureXML.Parsing.ParseError.amplificationLimitExceeded(mark)
|
|
}
|
|
budget -= length
|
|
}
|
|
result += run
|
|
}
|
|
|
|
private mutating func resolve(_ body: String, visiting: Set<String>, counts: Bool) throws {
|
|
if let predefined = Self.predefinedValue(body) {
|
|
try append(predefined, counts: counts)
|
|
return
|
|
}
|
|
if body.hasPrefix("#") {
|
|
try append(Self.characterReference(body, at: mark), counts: counts)
|
|
return
|
|
}
|
|
guard let replacement = entities[body] else {
|
|
if undeclared != nil {
|
|
undeclared?.append(body)
|
|
result += "&\(body);"
|
|
return
|
|
}
|
|
throw PureXML.Parsing.ParseError.undefinedEntity(name: body, mark)
|
|
}
|
|
guard !visiting.contains(body) else {
|
|
throw PureXML.Parsing.ParseError.recursiveEntity(name: body, mark)
|
|
}
|
|
// The replacement-text well-formedness constraint binds here, at the
|
|
// reference: the included text must reparse as balanced content in
|
|
// isolation (so '&' alone, an incomplete reference, or tags spanning
|
|
// the entity boundary are rejected on use, not on declaration).
|
|
if PureXML.Parsing.EntityReplacementGrammar.violation(inValue: replacement) != nil {
|
|
throw PureXML.Parsing.ParseError.invalidReference("&\(body);", mark)
|
|
}
|
|
// Expanding a declared entity: every produced character now counts against
|
|
// the amplification budget.
|
|
try expand(replacement, visiting: visiting.union([body]), counts: true)
|
|
}
|
|
|
|
private mutating func append(_ character: Character, counts: Bool) throws {
|
|
if counts {
|
|
guard budget > 0 else {
|
|
throw PureXML.Parsing.ParseError.amplificationLimitExceeded(mark)
|
|
}
|
|
budget -= 1
|
|
}
|
|
result.append(character)
|
|
}
|
|
|
|
private static func predefinedValue(_ body: String) -> Character? {
|
|
switch body {
|
|
case "amp": "&"
|
|
case "lt": "<"
|
|
case "gt": ">"
|
|
case "quot": "\""
|
|
case "apos": "'"
|
|
default: nil
|
|
}
|
|
}
|
|
|
|
private static func characterReference(_ body: String, at mark: PureXML.Parsing.Mark) throws -> Character {
|
|
let digits = String(body.dropFirst())
|
|
// XML 1.0: only lowercase 'x' introduces a hex reference, and the
|
|
// referenced code point must be a valid XML Char (rejecting NUL, bare
|
|
// control characters, surrogates, and U+FFFE/U+FFFF).
|
|
let scalarValue: UInt32? = if digits.hasPrefix("x") {
|
|
UInt32(digits.dropFirst(), radix: 16)
|
|
} else if digits.hasPrefix("X") {
|
|
nil
|
|
} else {
|
|
UInt32(digits, radix: 10)
|
|
}
|
|
guard let value = scalarValue, let scalar = Unicode.Scalar(value),
|
|
PureXML.Parsing.XMLCharacter.isChar(scalar)
|
|
else {
|
|
throw PureXML.Parsing.ParseError.invalidReference("&\(body);", mark)
|
|
}
|
|
return Character(scalar)
|
|
}
|
|
}
|