Fix threading

SignalServiceKit/src/Loki/API/Onion Requests/OnionRequestAPI.swift

@@ -173,15 +173,17 @@ internal enum OnionRequestAPI {
     // MARK: Internal API
     /// Sends an onion request to `snode`. Builds new paths as needed.
     internal static func invoke(_ method: LokiAPITarget.Method, on snode: LokiAPITarget, parameters: JSON) -> Promise<Any> {
+        let (promise, seal) = Promise<Any>.pending()
+        workQueue.async {
             let parameters: JSON = [ "method" : method.rawValue, "params" : parameters ]
             let payload: Data
             do {
-            guard JSONSerialization.isValidJSONObject(parameters) else { return Promise<Any> { $0.reject(Error.invalidJSON) } }
+                guard JSONSerialization.isValidJSONObject(parameters) else { return seal.reject(Error.invalidJSON) }
                 payload = try JSONSerialization.data(withJSONObject: parameters, options: [])
             } catch (let error) {
-            return Promise<Any> { $0.reject(error) }
+                return seal.reject(error)
             }
-        return buildOnion(around: payload, targetedAt: snode).then(on: workQueue) { intermediate -> Promise<Any> in
+            buildOnion(around: payload, targetedAt: snode).done(on: workQueue) { intermediate in
                 let guardSnode = intermediate.guardSnode
                 let encryptionResult = intermediate.encryptionResult
                 let onion = encryptionResult.ciphertext
@@ -192,10 +194,9 @@ internal enum OnionRequestAPI {
                     "ciphertext" : onion.base64EncodedString(),
                     "ephemeral_key" : encryptionResult.ephemeralPublicKey.toHexString()
                 ]
-            guard JSONSerialization.isValidJSONObject(parameters) else { throw Error.invalidJSON }
+                guard JSONSerialization.isValidJSONObject(parameters) else { return seal.reject(Error.invalidJSON) }
                 request.httpBody = try JSONSerialization.data(withJSONObject: parameters, options: [])
                 request.timeoutInterval = timeout
-            let (promise, seal) = Promise<Any>.pending()
                 print("[Loki] [Onion Request API] Sending onion request.")
                 let task = urlSession.dataTask(with: request) { response, result, error in
                     if let error = error {
@@ -207,7 +208,8 @@ internal enum OnionRequestAPI {
                     }
                 }
                 task.resume()
-            return promise
             }
         }
+        return promise
+    }
 }