Return empty data on error in multipart datatask.

Author: NeoTeo

Cartfile

@@ -1 +1,2 @@
 github "NeoTeo/SwiftMultiaddr"
+#git "file:///Users/teo/source/Apple/macOS/Libraries/SwiftMultiaddr" "test"

SwiftIpfsApi.xcodeproj/project.pbxproj

@@ -402,7 +402,7 @@
 				GCC_WARN_UNUSED_VARIABLE = YES;
 				IPHONEOS_DEPLOYMENT_TARGET = 8.0;
 				LD_RUNPATH_SEARCH_PATHS = "@loader_path/Frameworks";
-				MACOSX_DEPLOYMENT_TARGET = 10.11;
+				MACOSX_DEPLOYMENT_TARGET = 10.13;
 				MTL_ENABLE_DEBUG_INFO = YES;
 				ONLY_ACTIVE_ARCH = YES;
 				SDKROOT = macosx;
@@ -471,7 +471,7 @@
 				GCC_WARN_UNUSED_VARIABLE = YES;
 				IPHONEOS_DEPLOYMENT_TARGET = 8.0;
 				LD_RUNPATH_SEARCH_PATHS = "@loader_path/Frameworks";
-				MACOSX_DEPLOYMENT_TARGET = 10.11;
+				MACOSX_DEPLOYMENT_TARGET = 10.13;
 				MTL_ENABLE_DEBUG_INFO = NO;
 				SDKROOT = macosx;
 				SUPPORTED_PLATFORMS = "macosx iphonesimulator iphoneos";

SwiftIpfsApi/Multipart.swift

@@ -154,11 +154,14 @@ extension Multipart {
         let task = URLSession.shared.dataTask(with: (multipart.request as URLRequest)) {
             (data: Data?, response: URLResponse?, error: Error?) -> Void in
 
-            guard error == nil && data != nil else {
-                print("Error in dataTaskWithRequest: \(String(describing: error))")//throw HttpIoError.TransmissionError("fail: \(error)")
+            // FIXME: use Swift 5 Result type rather than passing nil data.
+            if error != nil || data == nil {
+                print("Error in dataTaskWithRequest: \(String(describing: error))")
+                let emptyData = Data()
+                completionHandler(emptyData)
                 return
             }
-            
+
             completionHandler(data!)
 
         }

SwiftIpfsApiTests/SwiftIpfsApiTests.swift

@@ -60,7 +60,10 @@ class SwiftIpfsApiTests: XCTestCase {
             try api.refs.local() { (localRefs: [Multihash]) in
 
                 for mh in localRefs {
-                    print(b58String(mh))
+                    // Bad assumption that the string is necessarily in base 58.
+                    // Check first.
+                    print("multihash string :\(mh.string())")
+//                    print(b58String(mh))
                 }
 
                 expectation.fulfill()