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ASN1Parser.swift
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ASN1Parser.swift
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import Foundation
protocol ASN1ParserDelegate : AnyObject {
func asn1Parser(_ parser: ASN1.Parser, didParse token: ASN1.Parser.Token)
}
extension ASN1 {
/// Parses any ASN1 data in an event-driven manner. Data is relayed as a stream of tokens to the delegate.
/// The aim of the parser is to never fatally trap. All errors should be funneled through the API. This aim is not yet fully implemented.
class Parser {
weak var delegate: ASN1ParserDelegate?
private let data: Data
private var didAbort: Bool = false
init(data: Data) {
self.data = data
}
enum Token : Equatable {
case contextStart(type: UInt8)
case contextEnd(type: UInt8)
case containerStart(type: ASN1.BufferType)
case containerEnd(type: ASN1.BufferType)
case value(ASN1.BufferValue)
}
func parse() throws {
defer {
self.reset()
}
if self.data.isEmpty { throw Error.emptyData }
var remainingData = self.data
while !remainingData.isEmpty {
remainingData = try self._parse(subdata: remainingData)
}
}
// You can call this partway through parsing, but it is not guaranteed to stop token events to the delegate. The parse() method will bubble up an `Error.abort` at termination.
func abortParsing() {
self.didAbort = true
}
enum Error : Swift.Error {
case emptyData
case aborted
case unknownASN1Type(UInt8)
case usesLongFormNotSupported
case malformedLengthForData
case cannotResolveIndefiniteLengthForData
}
}
}
extension ASN1.Parser {
internal struct PayloadDescriptor {
internal let domain: Domain
internal let tag: Tag
internal let valueKind: ValueKind
internal init(domain: Domain, tag: Tag, valueKind: ValueKind) {
self.domain = domain
self.tag = tag
self.valueKind = valueKind
}
internal init(from byte: UInt8) {
// Octet: | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 |
// Decoded: |Domain_|IsC|TagNumber__________|
// Domain is first two bits, one of Domain values
// isConstructed is 0 or 1 bit, 1 for true
// Remaining bits is tag number, can be custom if domain is context specific
let domainRawValue = byte >> 6
let domain = Domain(rawValue: domainRawValue)!
let isConstructed = ((byte >> 5) & 1) == 1
let valueKind: ValueKind = isConstructed ? .constructed : .primitive
let tagRawValue = byte & 0x1f
let tag: Tag = ASN1.BufferType(rawValue: tagRawValue).map { .type($0) } ?? .custom(tagRawValue)
self.init(domain: domain, tag: tag, valueKind: valueKind)
}
enum Domain : UInt8, Equatable {
case universal = 0x0
case application = 0x1
case contextSpecific = 0x2
case `private` = 0x3
}
enum ValueKind : Equatable {
case primitive
case constructed
}
enum Tag : Equatable {
case custom(UInt8)
case type(ASN1.BufferType)
var type: ASN1.BufferType? {
switch self {
case .type(let type): return type
default: return nil
}
}
var rawType: UInt8 {
switch self {
case .type(let type): return type.rawValue
case .custom(let type): return type
}
}
}
func withTag(_ tag: Tag) -> PayloadDescriptor {
return PayloadDescriptor(domain: self.domain, tag: tag, valueKind: self.valueKind)
}
}
private func reset() {
self.didAbort = false
}
private func _parse(subdata: Data) throws -> Data {
var shouldStopParsing = false
var stopParsingError: Swift.Error!
if self.didAbort {
throw Error.aborted
}
var descriptor = PayloadDescriptor(from: subdata.first!)
if descriptor.tag.type == ASN1.BufferType.usesLongForm {
throw Error.usesLongFormNotSupported
}
let (parsedLength, subdata) = try ASN1.consumeLength(from: subdata[subdata.index(after: subdata.startIndex)...])
let length: Int
let skipByteCountAfterBuffer: Int
switch parsedLength {
case .definite(let value):
length = value
skipByteCountAfterBuffer = 0
case .indefinite:
let result = try self.resolveIndefiniteLength(from: subdata)
length = result.bufferLength
skipByteCountAfterBuffer = result.skipBytes
}
guard let bufferEndIndex = subdata.index(subdata.startIndex, offsetBy: length, limitedBy: subdata.endIndex) else {
throw Error.malformedLengthForData
}
let buffer = subdata[..<bufferEndIndex]
if descriptor.domain == .contextSpecific {
self.delegate?.asn1Parser(self, didParse: .contextStart(type: descriptor.tag.rawType))
// parser did start context with tag
if descriptor.valueKind == .primitive {
descriptor = descriptor.withTag(.type(.octetString))
}
}
if descriptor.valueKind == .constructed {
// did start container with type
if let type = descriptor.tag.type {
self.delegate?.asn1Parser(self, didParse: .containerStart(type: type))
}
if !buffer.isEmpty {
do {
var buffer = buffer
while !buffer.isEmpty && !self.didAbort {
buffer = try self._parse(subdata: buffer)
}
} catch let error {
shouldStopParsing = true
stopParsingError = error
}
}
// did end container
if let type = descriptor.tag.type {
self.delegate?.asn1Parser(self, didParse: .containerEnd(type: type))
}
} else {
do {
guard let type = descriptor.tag.type else { throw Error.unknownASN1Type(descriptor.tag.rawType) }
let value = try ASN1.value(convertedFrom: buffer, as: type)
self.delegate?.asn1Parser(self, didParse: .value(value))
} catch let error {
shouldStopParsing = true
stopParsingError = error
}
}
if descriptor.domain == .contextSpecific {
self.delegate?.asn1Parser(self, didParse: .contextEnd(type: descriptor.tag.rawType))
// did end context with tag
}
if shouldStopParsing {
throw stopParsingError
}
guard let newStartIndex = subdata.index(buffer.endIndex, offsetBy: skipByteCountAfterBuffer, limitedBy: subdata.endIndex) else {
throw Error.malformedLengthForData
}
return subdata[newStartIndex...]
}
private func resolveIndefiniteLength(from data: Data) throws -> IndefiniteLengthResult {
var data = data
let startingAt = data.startIndex
while !data.isEmpty {
let descriptor = PayloadDescriptor(from: data.first!)
if descriptor.tag == .type(.eoc) && descriptor.domain == .universal {
let length = data.startIndex - startingAt
return IndefiniteLengthResult(bufferLength: length, skipBytes: 2)
}
let (parsedLength, buffer) = try ASN1.consumeLength(from: data[data.index(after: data.startIndex)...])
let length: Int
let skipBytesCount: Int
switch parsedLength {
case .definite(let value):
length = value
skipBytesCount = 0
case .indefinite:
let result = try self.resolveIndefiniteLength(from: buffer)
length = result.bufferLength
skipBytesCount = result.skipBytes
}
guard let bufferEndIndex = buffer.index(buffer.startIndex, offsetBy: length + skipBytesCount, limitedBy: buffer.endIndex) else {
throw Error.malformedLengthForData
}
data = buffer[bufferEndIndex...]
}
throw Error.cannotResolveIndefiniteLengthForData
}
struct IndefiniteLengthResult {
let bufferLength: Int
let skipBytes: Int
}
}