Add special casing of Data return type (#30)

* Special case data when decoding

* Update README

PapyrusCore/Sources/Response.swift

@@ -8,29 +8,32 @@ public protocol Response {
 }
 
 extension Response {
+    /// Validates the status code of a Response, as well as any transport errors that may have occurred.
     @discardableResult
     public func validate() throws -> Self {
-        if let statusCode {
-            guard (200..<300).contains(statusCode) else {
-                throw PapyrusError("Unsuccessful status code: \(statusCode).")
-            }
-        }
-
-        guard let error else {
-            return self
+        if let error { throw error }
+        if let statusCode, !(200..<300).contains(statusCode) { throw PapyrusError("Unsuccessful status code: \(statusCode).") }
+        return self
+    }
+
+    public func decode(_ type: Data?.Type = Data?.self, using decoder: ResponseDecoder) throws -> Data? {
+        try validate().body
+    }
+
+    public func decode(_ type: Data.Type = Data.self, using decoder: ResponseDecoder) throws -> Data {
+        guard let body = try decode(Data?.self, using: decoder) else {
+            throw PapyrusError("Unable to return the body of a `Response`; the body was nil.")
         }
 
-        throw error
+        return body
     }
-
+    
     public func decode<D: Decodable>(_ type: D.Type = D.self, using decoder: ResponseDecoder) throws -> D {
-        try validate()
-
-        guard let data = body else {
+        guard let body = try validate().body else {
             throw PapyrusError("Unable to decode `\(Self.self)` from a `Response`; body was nil.")
         }
-
-        return try decoder.decode(type, from: data)
+        
+        return try decoder.decode(type, from: body)
     }
 }
 

README.md

@@ -307,6 +307,22 @@ Endpoint functions should return a type that conforms to `Decodable`. It will au
 func getUser() async throws -> User
 ```
 
+### Accessing just the body
+
+If you only need a response's raw body bytes, you can just return `Data` from your function.  
+
+```swift
+@GET("/bytes")
+func getBytes() async throws -> Data
+```
+
+The above will throw if the request body is empty, even if the status code is successful. If you don't want to throw in that case, set the response as `Data?`; it will successfully return nil if the response body is empty.
+
+```swift
+@GET("/bytes")
+func getBytes() async throws -> Data?
+```
+
 ### Empty responses
 
 If you don't need to decode something from the response and just want to confirm it was successful, you may leave out the return type.