A private messenger for iOS.
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import CryptoSwift
import PromiseKit
import SessionUtilitiesKit
/// See the "Onion Requests" section of [The Session Whitepaper](https://arxiv.org/pdf/2002.04609.pdf) for more information.
public enum OnionRequestAPI {
/// - Note: Should only be accessed from `Threading.workQueue` to avoid race conditions.
private static var pathFailureCount: [Path:UInt] = [:]
/// - Note: Should only be accessed from `Threading.workQueue` to avoid race conditions.
private static var snodeFailureCount: [Snode:UInt] = [:]
/// - Note: Should only be accessed from `Threading.workQueue` to avoid race conditions.
public static var guardSnodes: Set<Snode> = []
public static var paths: [Path] = [] // Not a set to ensure we consistently show the same path to the user
// MARK: Settings
public static let maxFileSize = 10_000_000 // 10 MB
/// The number of snodes (including the guard snode) in a path.
private static let pathSize: UInt = 3
/// The number of times a path can fail before it's replaced.
private static let pathFailureThreshold: UInt = 3
/// The number of times a snode can fail before it's replaced.
private static let snodeFailureThreshold: UInt = 3
/// The number of paths to maintain.
public static let targetPathCount: UInt = 2
/// The number of guard snodes required to maintain `targetPathCount` paths.
private static var targetGuardSnodeCount: UInt { return targetPathCount } // One per path
// MARK: Destination
public enum Destination {
case snode(Snode)
case server(host: String, target: String, x25519PublicKey: String)
}
// MARK: Error
public enum Error : LocalizedError {
case httpRequestFailedAtDestination(statusCode: UInt, json: JSON)
case insufficientSnodes
case invalidURL
case missingSnodeVersion
case snodePublicKeySetMissing
case unsupportedSnodeVersion(String)
public var errorDescription: String? {
switch self {
case .httpRequestFailedAtDestination(let statusCode, _): return "HTTP request failed at destination with status code: \(statusCode)."
case .insufficientSnodes: return "Couldn't find enough Service Nodes to build a path."
case .invalidURL: return "Invalid URL"
case .missingSnodeVersion: return "Missing Service Node version."
case .snodePublicKeySetMissing: return "Missing Service Node public key set."
case .unsupportedSnodeVersion(let version): return "Unsupported Service Node version: \(version)."
}
}
}
// MARK: Path
public typealias Path = [Snode]
// MARK: Onion Building Result
private typealias OnionBuildingResult = (guardSnode: Snode, finalEncryptionResult: AESGCM.EncryptionResult, destinationSymmetricKey: Data)
// MARK: Private API
/// Tests the given snode. The returned promise errors out if the snode is faulty; the promise is fulfilled otherwise.
private static func testSnode(_ snode: Snode) -> Promise<Void> {
let (promise, seal) = Promise<Void>.pending()
DispatchQueue.global(qos: .userInitiated).async {
let url = "\(snode.address):\(snode.port)/get_stats/v1"
let timeout: TimeInterval = 3 // Use a shorter timeout for testing
HTTP.execute(.get, url, timeout: timeout).done2 { json in
guard let version = json["version"] as? String else { return seal.reject(Error.missingSnodeVersion) }
if version >= "2.0.7" {
seal.fulfill(())
} else {
SNLog("Unsupported snode version: \(version).")
seal.reject(Error.unsupportedSnodeVersion(version))
}
}.catch2 { error in
seal.reject(error)
}
}
return promise
}
/// Finds `targetGuardSnodeCount` guard snodes to use for path building. The returned promise errors out with `Error.insufficientSnodes`
/// if not enough (reliable) snodes are available.
private static func getGuardSnodes(reusing reusableGuardSnodes: [Snode]) -> Promise<Set<Snode>> {
if guardSnodes.count >= targetGuardSnodeCount {
return Promise<Set<Snode>> { $0.fulfill(guardSnodes) }
} else {
SNLog("Populating guard snode cache.")
return SnodeAPI.getRandomSnode().then2 { _ -> Promise<Set<Snode>> in // Just used to populate the snode pool
var unusedSnodes = SnodeAPI.snodePool.subtracting(reusableGuardSnodes) // Sync on LokiAPI.workQueue
let reusableGuardSnodeCount = UInt(reusableGuardSnodes.count)
guard unusedSnodes.count >= (targetGuardSnodeCount - reusableGuardSnodeCount) else { throw Error.insufficientSnodes }
func getGuardSnode() -> Promise<Snode> {
// randomElement() uses the system's default random generator, which is cryptographically secure
guard let candidate = unusedSnodes.randomElement() else { return Promise<Snode> { $0.reject(Error.insufficientSnodes) } }
unusedSnodes.remove(candidate) // All used snodes should be unique
SNLog("Testing guard snode: \(candidate).")
// Loop until a reliable guard snode is found
return testSnode(candidate).map2 { candidate }.recover(on: DispatchQueue.main) { _ in
withDelay(0.1, completionQueue: Threading.workQueue) { getGuardSnode() }
}
}
let promises = (0..<(targetGuardSnodeCount - reusableGuardSnodeCount)).map { _ in getGuardSnode() }
return when(fulfilled: promises).map2 { guardSnodes in
let guardSnodesAsSet = Set(guardSnodes + reusableGuardSnodes)
OnionRequestAPI.guardSnodes = guardSnodesAsSet
return guardSnodesAsSet
}
}
}
}
/// Builds and returns `targetPathCount` paths. The returned promise errors out with `Error.insufficientSnodes`
/// if not enough (reliable) snodes are available.
@discardableResult
private static func buildPaths(reusing reusablePaths: [Path]) -> Promise<[Path]> {
SNLog("Building onion request paths.")
DispatchQueue.main.async {
NotificationCenter.default.post(name: .buildingPaths, object: nil)
}
return SnodeAPI.getRandomSnode().then2 { _ -> Promise<[Path]> in // Just used to populate the snode pool
let reusableGuardSnodes = reusablePaths.map { $0[0] }
return getGuardSnodes(reusing: reusableGuardSnodes).map2 { guardSnodes -> [Path] in
var unusedSnodes = SnodeAPI.snodePool.subtracting(guardSnodes).subtracting(reusablePaths.flatMap { $0 })
let reusableGuardSnodeCount = UInt(reusableGuardSnodes.count)
let pathSnodeCount = (targetGuardSnodeCount - reusableGuardSnodeCount) * pathSize - (targetGuardSnodeCount - reusableGuardSnodeCount)
guard unusedSnodes.count >= pathSnodeCount else { throw Error.insufficientSnodes }
// Don't test path snodes as this would reveal the user's IP to them
return guardSnodes.subtracting(reusableGuardSnodes).map { guardSnode in
let result = [ guardSnode ] + (0..<(pathSize - 1)).map { _ in
// randomElement() uses the system's default random generator, which is cryptographically secure
let pathSnode = unusedSnodes.randomElement()! // Safe because of the pathSnodeCount check above
unusedSnodes.remove(pathSnode) // All used snodes should be unique
return pathSnode
}
SNLog("Built new onion request path: \(result.prettifiedDescription).")
return result
}
}.map2 { paths in
OnionRequestAPI.paths = paths + reusablePaths
SNSnodeKitConfiguration.shared.storage.writeSync { transaction in
SNLog("Persisting onion request paths to database.")
SNSnodeKitConfiguration.shared.storage.setOnionRequestPaths(to: paths, using: transaction)
}
DispatchQueue.main.async {
NotificationCenter.default.post(name: .pathsBuilt, object: nil)
}
return paths
}
}
}
/// Returns a `Path` to be used for building an onion request. Builds new paths as needed.
private static func getPath(excluding snode: Snode?) -> Promise<Path> {
guard pathSize >= 1 else { preconditionFailure("Can't build path of size zero.") }
var paths = OnionRequestAPI.paths
if paths.isEmpty {
paths = SNSnodeKitConfiguration.shared.storage.getOnionRequestPaths()
OnionRequestAPI.paths = paths
if !paths.isEmpty {
guardSnodes.formUnion([ paths[0][0] ])
if paths.count >= 2 {
guardSnodes.formUnion([ paths[1][0] ])
}
}
}
// randomElement() uses the system's default random generator, which is cryptographically secure
if paths.count >= targetPathCount {
if let snode = snode {
return Promise { $0.fulfill(paths.filter { !$0.contains(snode) }.randomElement()!) }
} else {
return Promise { $0.fulfill(paths.randomElement()!) }
}
} else if !paths.isEmpty {
if let snode = snode {
if let path = paths.first(where: { !$0.contains(snode) }) {
buildPaths(reusing: paths) // Re-build paths in the background
return Promise { $0.fulfill(path) }
} else {
return buildPaths(reusing: paths).map2 { paths in
return paths.filter { !$0.contains(snode) }.randomElement()!
}
}
} else {
buildPaths(reusing: paths) // Re-build paths in the background
return Promise { $0.fulfill(paths.randomElement()!) }
}
} else {
return buildPaths(reusing: []).map2 { paths in
if let snode = snode {
return paths.filter { !$0.contains(snode) }.randomElement()!
} else {
return paths.randomElement()!
}
}
}
}
private static func dropGuardSnode(_ snode: Snode) {
#if DEBUG
dispatchPrecondition(condition: .onQueue(Threading.workQueue))
#endif
guardSnodes = guardSnodes.filter { $0 != snode }
}
private static func drop(_ snode: Snode) throws {
#if DEBUG
dispatchPrecondition(condition: .onQueue(Threading.workQueue))
#endif
// We repair the path here because we can do it sync. In the case where we drop a whole
// path we leave the re-building up to getPath(excluding:) because re-building the path
// in that case is async.
OnionRequestAPI.snodeFailureCount[snode] = 0
var oldPaths = paths
guard let pathIndex = oldPaths.firstIndex(where: { $0.contains(snode) }) else { return }
var path = oldPaths[pathIndex]
guard let snodeIndex = path.firstIndex(of: snode) else { return }
path.remove(at: snodeIndex)
let unusedSnodes = SnodeAPI.snodePool.subtracting(oldPaths.flatMap { $0 })
guard !unusedSnodes.isEmpty else { throw Error.insufficientSnodes }
// randomElement() uses the system's default random generator, which is cryptographically secure
path.append(unusedSnodes.randomElement()!)
// Don't test the new snode as this would reveal the user's IP
oldPaths.remove(at: pathIndex)
let newPaths = oldPaths + [ path ]
paths = newPaths
SNSnodeKitConfiguration.shared.storage.writeSync { transaction in
SNLog("Persisting onion request paths to database.")
SNSnodeKitConfiguration.shared.storage.setOnionRequestPaths(to: newPaths, using: transaction)
}
}
private static func drop(_ path: Path) {
#if DEBUG
dispatchPrecondition(condition: .onQueue(Threading.workQueue))
#endif
OnionRequestAPI.pathFailureCount[path] = 0
var paths = OnionRequestAPI.paths
guard let pathIndex = paths.firstIndex(of: path) else { return }
paths.remove(at: pathIndex)
OnionRequestAPI.paths = paths
SNSnodeKitConfiguration.shared.storage.writeSync { transaction in
if !paths.isEmpty {
SNLog("Persisting onion request paths to database.")
SNSnodeKitConfiguration.shared.storage.setOnionRequestPaths(to: paths, using: transaction)
} else {
SNLog("Clearing onion request paths.")
SNSnodeKitConfiguration.shared.storage.setOnionRequestPaths(to: [], using: transaction)
}
}
}
/// Builds an onion around `payload` and returns the result.
private static func buildOnion(around payload: JSON, targetedAt destination: Destination) -> Promise<OnionBuildingResult> {
var guardSnode: Snode!
var targetSnodeSymmetricKey: Data! // Needed by invoke(_:on:with:) to decrypt the response sent back by the destination
var encryptionResult: AESGCM.EncryptionResult!
var snodeToExclude: Snode?
if case .snode(let snode) = destination { snodeToExclude = snode }
return getPath(excluding: snodeToExclude).then2 { path -> Promise<AESGCM.EncryptionResult> in
guardSnode = path.first!
// Encrypt in reverse order, i.e. the destination first
return encrypt(payload, for: destination).then2 { r -> Promise<AESGCM.EncryptionResult> in
targetSnodeSymmetricKey = r.symmetricKey
// Recursively encrypt the layers of the onion (again in reverse order)
encryptionResult = r
var path = path
var rhs = destination
func addLayer() -> Promise<AESGCM.EncryptionResult> {
if path.isEmpty {
return Promise<AESGCM.EncryptionResult> { $0.fulfill(encryptionResult) }
} else {
let lhs = Destination.snode(path.removeLast())
return OnionRequestAPI.encryptHop(from: lhs, to: rhs, using: encryptionResult).then2 { r -> Promise<AESGCM.EncryptionResult> in
encryptionResult = r
rhs = lhs
return addLayer()
}
}
}
return addLayer()
}
}.map2 { _ in (guardSnode, encryptionResult, targetSnodeSymmetricKey) }
}
// MARK: Public API
/// Sends an onion request to `snode`. Builds new paths as needed.
public static func sendOnionRequest(to snode: Snode, invoking method: Snode.Method, with parameters: JSON, associatedWith publicKey: String) -> Promise<JSON> {
let payload: JSON = [ "method" : method.rawValue, "params" : parameters ]
return sendOnionRequest(with: payload, to: Destination.snode(snode)).recover2 { error -> Promise<JSON> in
guard case OnionRequestAPI.Error.httpRequestFailedAtDestination(let statusCode, let json) = error else { throw error }
throw SnodeAPI.handleError(withStatusCode: statusCode, json: json, forSnode: snode, associatedWith: publicKey) ?? error
}
}
/// Sends an onion request to `server`. Builds new paths as needed.
public static func sendOnionRequest(_ request: NSURLRequest, to server: String, target: String = "/loki/v3/lsrpc", using x25519PublicKey: String, isJSONRequired: Bool = true) -> Promise<JSON> {
var rawHeaders = request.allHTTPHeaderFields ?? [:]
rawHeaders.removeValue(forKey: "User-Agent")
var headers: JSON = rawHeaders.mapValues { value in
switch value.lowercased() {
case "true": return true
case "false": return false
default: return value
}
}
guard let url = request.url?.absoluteString, let host = request.url?.host else { return Promise(error: Error.invalidURL) }
var endpoint = ""
if server.count < url.count {
guard let serverEndIndex = url.range(of: server)?.upperBound else { return Promise(error: Error.invalidURL) }
let endpointStartIndex = url.index(after: serverEndIndex)
endpoint = String(url[endpointStartIndex..<url.endIndex])
}
let parametersAsString: String
if let tsRequest = request as? TSRequest {
headers["Content-Type"] = "application/json"
let tsRequestParameters = tsRequest.parameters
if !tsRequestParameters.isEmpty {
guard let parameters = try? JSONSerialization.data(withJSONObject: tsRequestParameters, options: [ .fragmentsAllowed ]) else {
return Promise(error: HTTP.Error.invalidJSON)
}
parametersAsString = String(bytes: parameters, encoding: .utf8) ?? "null"
} else {
parametersAsString = "null"
}
} else {
headers["Content-Type"] = request.allHTTPHeaderFields!["Content-Type"]
if let parametersAsInputStream = request.httpBodyStream, let parameters = try? Data(from: parametersAsInputStream) {
parametersAsString = "{ \"fileUpload\" : \"\(String(data: parameters.base64EncodedData(), encoding: .utf8) ?? "null")\" }"
} else {
parametersAsString = "null"
}
}
let payload: JSON = [
"body" : parametersAsString,
"endpoint" : endpoint,
"method" : request.httpMethod!,
"headers" : headers
]
let destination = Destination.server(host: host, target: target, x25519PublicKey: x25519PublicKey)
let promise = sendOnionRequest(with: payload, to: destination, isJSONRequired: isJSONRequired)
promise.catch2 { error in
SNLog("Couldn't reach server: \(url) due to error: \(error).")
}
return promise
}
public static func sendOnionRequest(with payload: JSON, to destination: Destination, isJSONRequired: Bool = true) -> Promise<JSON> {
let (promise, seal) = Promise<JSON>.pending()
var guardSnode: Snode?
Threading.workQueue.async { // Avoid race conditions on `guardSnodes` and `paths`
buildOnion(around: payload, targetedAt: destination).done2 { intermediate in
guardSnode = intermediate.guardSnode
let url = "\(guardSnode!.address):\(guardSnode!.port)/onion_req/v2"
let finalEncryptionResult = intermediate.finalEncryptionResult
let onion = finalEncryptionResult.ciphertext
if case Destination.server = destination, Double(onion.count) > 0.75 * Double(maxFileSize) {
SNLog("Approaching request size limit: ~\(onion.count) bytes.")
}
let parameters: JSON = [
"ephemeral_key" : finalEncryptionResult.ephemeralPublicKey.toHexString()
]
let body: Data
do {
body = try encode(ciphertext: onion, json: parameters)
} catch {
return seal.reject(error)
}
let destinationSymmetricKey = intermediate.destinationSymmetricKey
HTTP.execute(.post, url, body: body).done2 { json in
guard let base64EncodedIVAndCiphertext = json["result"] as? String,
let ivAndCiphertext = Data(base64Encoded: base64EncodedIVAndCiphertext), ivAndCiphertext.count >= AESGCM.ivSize else { return seal.reject(HTTP.Error.invalidJSON) }
do {
let data = try AESGCM.decrypt(ivAndCiphertext, with: destinationSymmetricKey)
guard let json = try JSONSerialization.jsonObject(with: data, options: [ .fragmentsAllowed ]) as? JSON,
let statusCode = json["status"] as? Int else { return seal.reject(HTTP.Error.invalidJSON) }
if statusCode == 406 { // Clock out of sync
SNLog("The user's clock is out of sync with the service node network.")
seal.reject(SnodeAPI.Error.clockOutOfSync)
} else if let bodyAsString = json["body"] as? String {
let body: JSON
if !isJSONRequired {
body = [ "result" : bodyAsString ]
} else {
guard let bodyAsData = bodyAsString.data(using: .utf8),
let b = try JSONSerialization.jsonObject(with: bodyAsData, options: [ .fragmentsAllowed ]) as? JSON else { return seal.reject(HTTP.Error.invalidJSON) }
body = b
}
guard 200...299 ~= statusCode else { return seal.reject(Error.httpRequestFailedAtDestination(statusCode: UInt(statusCode), json: body)) }
seal.fulfill(body)
} else {
guard 200...299 ~= statusCode else { return seal.reject(Error.httpRequestFailedAtDestination(statusCode: UInt(statusCode), json: json)) }
seal.fulfill(json)
}
} catch {
seal.reject(error)
}
}.catch2 { error in
seal.reject(error)
}
}.catch2 { error in
seal.reject(error)
}
}
promise.catch2 { error in // Must be invoked on Threading.workQueue
guard case HTTP.Error.httpRequestFailed(let statusCode, let json) = error, let guardSnode = guardSnode else { return }
let path = paths.first { $0.contains(guardSnode) }
func handleUnspecificError() {
guard let path = path else { return }
var pathFailureCount = OnionRequestAPI.pathFailureCount[path] ?? 0
pathFailureCount += 1
if pathFailureCount >= pathFailureThreshold {
dropGuardSnode(guardSnode)
path.forEach { snode in
SnodeAPI.handleError(withStatusCode: statusCode, json: json, forSnode: snode) // Intentionally don't throw
}
drop(path)
} else {
OnionRequestAPI.pathFailureCount[path] = pathFailureCount
}
}
let prefix = "Next node not found: "
if let message = json?["result"] as? String, message.hasPrefix(prefix) {
let ed25519PublicKey = message[message.index(message.startIndex, offsetBy: prefix.count)..<message.endIndex]
if let path = path, let snode = path.first(where: { $0.publicKeySet.ed25519Key == ed25519PublicKey }) {
var snodeFailureCount = OnionRequestAPI.snodeFailureCount[snode] ?? 0
snodeFailureCount += 1
if snodeFailureCount >= snodeFailureThreshold {
SnodeAPI.handleError(withStatusCode: statusCode, json: json, forSnode: snode) // Intentionally don't throw
do {
try drop(snode)
} catch {
handleUnspecificError()
}
} else {
OnionRequestAPI.snodeFailureCount[snode] = snodeFailureCount
}
} else {
// Do nothing
}
} else if let message = json?["result"] as? String, message == "Loki Server error" {
// Do nothing
} else if statusCode == 0 { // Timeout
// Do nothing
} else {
handleUnspecificError()
}
}
return promise
}
}