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//
// RelaySelector.swift
// RelaySelector
//
// Created by pronebird on 11/06/2019.
// Copyright © 2019 Mullvad VPN AB. All rights reserved.
//
import Foundation
import MullvadREST
import MullvadTypes
public enum RelaySelector {
public static func evaluate(
relays: REST.ServerRelaysResponse,
constraints: RelayConstraints
) throws -> RelaySelectorResult {
let filteredRelays = applyConstraints(constraints, relays: Self.parseRelaysResponse(relays))
guard let relayWithLocation = pickRandomRelay(relays: filteredRelays),
let port = pickRandomPort(rawPortRanges: relays.wireguard.portRanges)
else {
throw NoRelaysSatisfyingConstraintsError()
}
let endpoint = MullvadEndpoint(
ipv4Relay: IPv4Endpoint(
ip: relayWithLocation.relay.ipv4AddrIn,
port: port
),
ipv6Relay: nil,
ipv4Gateway: relays.wireguard.ipv4Gateway,
ipv6Gateway: relays.wireguard.ipv6Gateway,
publicKey: relayWithLocation.relay.publicKey
)
return RelaySelectorResult(
endpoint: endpoint,
relay: relayWithLocation.relay,
location: relayWithLocation.location
)
}
/// Produce a list of `RelayWithLocation` items satisfying the given constraints
private static func applyConstraints(
_ constraints: RelayConstraints,
relays: [RelayWithLocation]
) -> [RelayWithLocation] {
return relays.filter { relayWithLocation -> Bool in
switch constraints.location {
case .any:
return true
case let .only(relayConstraint):
switch relayConstraint {
case let .country(countryCode):
return relayWithLocation.location.countryCode == countryCode &&
relayWithLocation.relay.includeInCountry
case let .city(countryCode, cityCode):
return relayWithLocation.location.countryCode == countryCode &&
relayWithLocation.location.cityCode == cityCode
case let .hostname(countryCode, cityCode, hostname):
return relayWithLocation.location.countryCode == countryCode &&
relayWithLocation.location.cityCode == cityCode &&
relayWithLocation.relay.hostname == hostname
}
}
}.filter { relayWithLocation -> Bool in
return relayWithLocation.relay.active
}
}
private static func pickRandomRelay(relays: [RelayWithLocation]) -> RelayWithLocation? {
let totalWeight = relays.reduce(0) { accummulatedWeight, relayWithLocation in
return accummulatedWeight + relayWithLocation.relay.weight
}
// Return random relay when all relays within the list have zero weight.
guard totalWeight > 0 else {
return relays.randomElement()
}
// Pick a random number in the range 1 - totalWeight. This choses the relay with a
// non-zero weight.
var i = (1 ... totalWeight).randomElement()!
let randomRelay = relays.first { relayWithLocation -> Bool in
let (result, isOverflow) = i
.subtractingReportingOverflow(relayWithLocation.relay.weight)
i = isOverflow ? 0 : result
return i == 0
}
assert(randomRelay != nil, "At least one relay must've had a weight above 0")
return randomRelay
}
private static func pickRandomPort(rawPortRanges: [[UInt16]]) -> UInt16? {
let portRanges = parseRawPortRanges(rawPortRanges)
let portAmount = portRanges.reduce(0) { partialResult, closedRange in
return partialResult + closedRange.count
}
guard var portIndex = (0 ..< portAmount).randomElement() else {
return nil
}
for range in portRanges {
if portIndex < range.count {
return UInt16(portIndex) + range.lowerBound
} else {
portIndex -= range.count
}
}
assertionFailure("Port selection algorithm is broken!")
return nil
}
private static func parseRawPortRanges(_ rawPortRanges: [[UInt16]]) -> [ClosedRange<UInt16>] {
return rawPortRanges.compactMap { inputRange -> ClosedRange<UInt16>? in
guard inputRange.count == 2 else { return nil }
let startPort = inputRange[0]
let endPort = inputRange[1]
if startPort <= endPort {
return startPort ... endPort
} else {
return nil
}
}
}
private static func parseRelaysResponse(
_ response: REST
.ServerRelaysResponse
) -> [RelayWithLocation] {
return response.wireguard.relays.compactMap { serverRelay -> RelayWithLocation? in
guard let serverLocation = response.locations[serverRelay.location] else { return nil }
let locationComponents = serverRelay.location.split(separator: "-")
guard locationComponents.count > 1 else { return nil }
let location = Location(
country: serverLocation.country,
countryCode: String(locationComponents[0]),
city: serverLocation.city,
cityCode: String(locationComponents[1]),
latitude: serverLocation.latitude,
longitude: serverLocation.longitude
)
return RelayWithLocation(relay: serverRelay, location: location)
}
}
}
public struct NoRelaysSatisfyingConstraintsError: LocalizedError {
public var errorDescription: String? {
return "No relays satisfying constraints."
}
}
public struct RelaySelectorResult: Codable {
public var endpoint: MullvadEndpoint
public var relay: REST.ServerRelay
public var location: Location
public var packetTunnelRelay: PacketTunnelRelay {
return PacketTunnelRelay(
ipv4Relay: endpoint.ipv4Relay,
ipv6Relay: endpoint.ipv6Relay,
hostname: relay.hostname,
location: location
)
}
}
private struct RelayWithLocation {
var relay: REST.ServerRelay
var location: Location
}
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