Multi-part Form Support

Sources/Endpoints/Endpoint+URLRequest.swift

@@ -125,14 +125,23 @@ extension Endpoint {
         urlRequest.url = url
 
         if !(body is EmptyCodable) {
+            let encoder = Self.bodyEncoder
             do {
-                urlRequest.httpBody = try Self.bodyEncoder.encode(body)
+                urlRequest.httpBody = try encoder.encode(body)
             } catch {
                 throw EndpointError.invalidBody(error)
             }
 
             if headerItems[Header.contentType.name] == nil {
-                urlRequest.addValue("application/json", forHTTPHeaderField: Header.contentType.name)
+                let encoderType = type(of: encoder)
+                if let contentType = encoderType.contentType {
+                    if contentType.lowercased().hasPrefix("multipart/form-data"),
+                       let multipartEncoder = encoder as? MultipartFormEncoder {
+                        urlRequest.addValue(multipartEncoder.contentType, forHTTPHeaderField: Header.contentType.name)
+                    } else {
+                        urlRequest.addValue(contentType, forHTTPHeaderField: Header.contentType.name)
+                    }
+                }
             }
         } else if !bodyFormItems.isEmpty {
             urlRequest.httpBody = bodyFormItems.formString.data(using: .utf8)

Sources/Endpoints/Endpoint.swift

@@ -36,11 +36,20 @@ public enum HeaderField<T> {
 public struct EmptyCodable: Codable { }
 
 public protocol EncoderType {
+    static var contentType: String? { get }
     func encode<T: Encodable>(_ value: T) throws -> Data
 }
 
+public extension EncoderType {
+    static var contentType: String? { nil }
+}
+
 extension JSONEncoder: EncoderType { }
 
+extension JSONEncoder {
+    public static var contentType: String? { "application/json" }
+}
+
 public protocol DecoderType {
     func decode<T: Decodable>(_ type: T.Type, from data: Data) throws -> T
 }