Merge header fields when calling setDefaultEnvironmentalProperties()

`HTTPManagerRequest.setDefaultEnvironmentalProperties()` now merges the
environment's default headers into the request headers, giving priority
to the existing request headers in the case of a conflict.

Fixes #36.

README.md

@@ -414,6 +414,8 @@ work by you shall be dual licensed as above, without any additional terms or con
 
 * Add `HTTPHeaders.merge(_:uniquingKeysWith:)` and `HTTPHeaders.merging(_:uniquingKeysWith:)`.
 * Deprecate `HTTPHeaders.append(contentsOf:)`.
+* Merge header fields when calling `HTTPManagerRequest.setDefaultEnvironmentalProperties()`, giving priority to existing request header fields in the case
+  of a conflict.
 
 #### v4.1.0 (2018-06-15)
 

Sources/HTTPManager.swift

@@ -1174,7 +1174,9 @@ extension HTTPManager {
                 request.auth = auth
             }
             request.serverRequiresContentLength = inner.defaultServerRequiresContentLength
-            request.headerFields = inner.defaultHeaderFields
+            if !inner.defaultHeaderFields.isEmpty {
+                request.headerFields.merge(inner.defaultHeaderFields, uniquingKeysWith: { (current, _) in current })
+            }
         }
     }
 

Tests/PMHTTPTests.swift

@@ -1810,8 +1810,8 @@ final class PMHTTPTests: PMHTTPTestCase {
 
     func testHeaderFieldsEnvironmentDefaults() {
         HTTP.environment = HTTPManagerEnvironment(string: "http://\(httpServer.address)/v1")!
-
         HTTP.defaultHeaderFields = ["X-Foo": "Bar"]
+
         var req = HTTP.request(GET: "foo")!
         XCTAssertEqual(req.headerFields, ["X-Foo": "Bar"], "request headerFields")
         req = HTTP.request(GET: "")!
@@ -1829,6 +1829,23 @@ final class PMHTTPTests: PMHTTPTestCase {
         XCTAssertEqual(req.headerFields, ["X-Foo": "Bar"], "request headerFields")
     }
 
+    func testSetDefaultEnvironmentalPropertiesHeaderFieldsMerge() {
+        HTTP.defaultHeaderFields = ["X-Foo": "Bar", "Quux": "Grably"]
+
+        var req = HTTP.request(GET: "http://apple.com/v1")!
+        req.headerFields.addValue("Foo", forHeaderField: "X-Bar")
+        XCTAssertEqual(req.headerFields, ["X-Bar": "Foo"], "request headerFields")
+        req.setDefaultEnvironmentalProperties()
+        XCTAssertEqual(req.headerFields, ["X-Bar": "Foo", "X-Foo": "Bar", "Quux": "Grably"], "request headerFields")
+
+        req = HTTP.request(GET: "http://apple.com/v1")
+        req.headerFields.addValue("Foo", forHeaderField: "X-Bar")
+        req.headerFields.addValue("Qux", forHeaderField: "X-Foo")
+        XCTAssertEqual(req.headerFields, ["X-Bar": "Foo", "X-Foo": "Qux"], "request headerFields")
+        req.setDefaultEnvironmentalProperties()
+        XCTAssertEqual(req.headerFields, ["X-Bar": "Foo", "X-Foo": "Qux", "Quux": "Grably"], "request headerFields")
+    }
+
     func testResetSessionWithStoppedTask() {
         _ = expectationForRequestCanceled(HTTP.request(GET: "foo"), startAutomatically: false)
         HTTP.resetSession()