Update content-length header on setting response body (#425)

* Update content-length header on setting response body

* Add createHeadResponse

Sources/Hummingbird/Router/EndpointResponder.swift

@@ -35,9 +35,8 @@ struct EndpointResponders<Context: BaseRequestContext>: Sendable {
     mutating func autoGenerateHeadEndpoint() {
         if self.methods[.head] == nil, let get = methods[.get] {
             self.methods[.head] = CallbackResponder { request, context in
-                var response = try await get.respond(to: request, context: context)
-                response.body = .init()
-                return response
+                let response = try await get.respond(to: request, context: context)
+                return response.createHeadResponse()
             }
         }
     }

Sources/HummingbirdCore/Response/Response.swift

@@ -17,7 +17,13 @@ import HTTPTypes
 /// Holds all the required to generate a HTTP Response
 public struct Response: Sendable {
     public var head: HTTPResponse
-    public var body: ResponseBody
+    public var body: ResponseBody {
+        didSet {
+            if let contentLength = body.contentLength {
+                self.head.headerFields[.contentLength] = String(describing: contentLength)
+            }
+        }
+    }
 
     public init(status: HTTPResponse.Status, headers: HTTPFields = .init(), body: ResponseBody = .init()) {
         self.head = .init(status: status, headerFields: headers)
@@ -36,6 +42,11 @@ public struct Response: Sendable {
         get { self.head.headerFields }
         set { self.head.headerFields = newValue }
     }
+
+    /// Return HEAD response based off this response
+    public func createHeadResponse() -> Response {
+        .init(status: self.status, headers: self.headers, body: .init())
+    }
 }
 
 extension Response: CustomStringConvertible {