Support platforms back to macOS 10.15, iOS 13, tvOS 13, and watchOS 6 (#7)

### Motivation

Reduce deployment target by 3 versions to gain more adoption.

### Modifications

- Added new deployment targets
- Refactor `invokeSession` method to support iOS 13+
- Update `swift-openapi-runtime` version once changes are done
[there](apple/swift-openapi-runtime#18).

### Result

Deployment target will be reduced by 3 versions.

Author: denil-ct

Package.swift

@@ -18,7 +18,7 @@ import PackageDescription
 let package = Package(
     name: "swift-openapi-urlsession",
     platforms: [
-        .macOS(.v13), .iOS(.v16), .tvOS(.v16), .watchOS(.v9),
+        .macOS(.v10_15), .iOS(.v13), .tvOS(.v13), .watchOS(.v6),
     ],
     products: [
         .library(
@@ -27,7 +27,7 @@ let package = Package(
         ),
     ],
     dependencies: [
-        .package(url: "https://github.com/apple/swift-openapi-runtime", .upToNextMinor(from: "0.1.0")),
+        .package(url: "https://github.com/apple/swift-openapi-runtime", .upToNextMinor(from: "0.1.3")),
         .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0"),
     ],
     targets: [

README.md

@@ -4,6 +4,11 @@ A client transport that uses the [URLSession](https://developer.apple.com/docume
 
 Use the transport with client code generated by [Swift OpenAPI Generator](https://github.com/apple/swift-openapi-generator).
 
+## Supported platforms and minimum versions
+ | macOS | Linux | iOS | tvOS | watchOS |
+ | :-: | :-: | :-: | :-: | :-: |
+ | ✅ 10.15+  | ✅     | ✅ 13+ | ✅ 13+ | ✅ 6+ |
+
 ## Usage
 
 Add the package dependency in your `Package.swift`:

Sources/OpenAPIURLSession/Documentation.docc/Documentation.md

@@ -8,6 +8,11 @@ A client transport that uses the [URLSession](https://developer.apple.com/docume
 
 Use the transport with client code generated by [Swift OpenAPI Generator](https://github.com/apple/swift-openapi-generator).
 
+### Supported platforms and minimum versions
+| macOS | Linux | iOS | tvOS | watchOS |
+| :-: | :-: | :-: | :-: | :-: |
+| ✅ 10.15+  | ✅     | ✅ 13+ | ✅ 13+ | ✅ 6+ |
+
 ### Usage
 
 Add the package dependency in your `Package.swift`:

Sources/OpenAPIURLSession/URLSessionTransport.swift

@@ -90,23 +90,28 @@ public struct URLSessionTransport: ClientTransport {
     }
 
     private func invokeSession(_ urlRequest: URLRequest) async throws -> (Data, URLResponse) {
-        #if canImport(FoundationNetworking)
+        // Using `dataTask(with:completionHandler:)` instead of the async method `data(for:)` of URLSession because the latter is not available on linux platforms
         return try await withCheckedThrowingContinuation { continuation in
             configuration.session
                 .dataTask(with: urlRequest) { data, response, error in
-                    if let error = error {
+                    if let error {
                         continuation.resume(with: .failure(error))
                         return
                     }
+
+                    guard let response else {
+                        continuation.resume(
+                            with: .failure(URLSessionTransportError.noResponse(url: urlRequest.url))
+                        )
+                        return
+                    }
+
                     continuation.resume(
-                        with: .success((data ?? Data(), response!))
+                        with: .success((data ?? Data(), response))
                     )
                 }
                 .resume()
         }
-        #else
-        return try await configuration.session.data(for: urlRequest)
-        #endif
     }
 }
 
@@ -118,6 +123,9 @@ internal enum URLSessionTransportError: Error {
 
     /// Returned `URLResponse` could not be converted to `HTTPURLResponse`.
     case notHTTPResponse(URLResponse)
+
+    /// Returned `URLResponse` was nil
+    case noResponse(url: URL?)
 }
 
 extension OpenAPIRuntime.Response {
@@ -170,6 +178,8 @@ extension URLSessionTransportError: CustomStringConvertible {
                 "Invalid request URL from request path: \(request.path), query: \(request.query ?? "<nil>") relative to base URL: \(baseURL.absoluteString)"
         case .notHTTPResponse(let response):
             return "Received a non-HTTP response, of type: \(String(describing: type(of: response)))"
+        case .noResponse(let url):
+            return "Received a nil response for \(url?.absoluteString ?? "<nil URL>")"
         }
     }
 }