First hack at fixing #509.

servant-foreign/servant-foreign.cabal

@@ -31,6 +31,7 @@ library
                      , Servant.Foreign.Internal
                      , Servant.Foreign.Inflections
   build-depends:       base       == 4.*
+                     , http-media == 0.7.*
                      , lens       == 4.*
                      , servant    == 0.11.*
                      , text       >= 1.2  && < 1.3

servant-foreign/src/Servant/Foreign/Internal.hs

@@ -18,8 +18,10 @@ import           Data.Text
 import           Data.Text.Encoding (decodeUtf8)
 import           GHC.TypeLits
 import qualified Network.HTTP.Types as HTTP
+import           Network.HTTP.Media.MediaType
 import           Prelude hiding (concat)
 import           Servant.API
+import           Servant.API.ContentTypes (AllMime, allMime)
 import           Servant.API.TypeLevel
 
 
@@ -125,6 +127,7 @@ data Req f = Req
   , _reqBody       :: Maybe f
   , _reqReturnType :: Maybe f
   , _reqFuncName   :: FunctionName
+  , _reqReturnContentTypes :: [MediaType]
   }
 
 deriving instance Eq f => Eq (Req f)
@@ -133,7 +136,7 @@ deriving instance Show f => Show (Req f)
 makeLenses ''Req
 
 defReq :: Req ftype
-defReq = Req defUrl "GET" [] Nothing Nothing (FunctionName [])
+defReq = Req defUrl "GET" [] Nothing Nothing (FunctionName []) []
 
 -- | 'HasForeignType' maps Haskell types with types in the target
 -- language of your backend. For example, let's say you're
@@ -224,7 +227,7 @@ instance (KnownSymbol sym, HasForeignType lang ftype [t], HasForeign lang ftype
         { _argName = PathSegment str
         , _argType = ftype }
 
-instance (Elem JSON list, HasForeignType lang ftype a, ReflectMethod method)
+instance (AllMime list, HasForeignType lang ftype a, ReflectMethod method)
   => HasForeign lang ftype (Verb method status list a) where
   type Foreign ftype (Verb method status list a) = Req ftype
 
@@ -232,10 +235,12 @@ instance (Elem JSON list, HasForeignType lang ftype a, ReflectMethod method)
     req & reqFuncName . _FunctionName %~ (methodLC :)
         & reqMethod .~ method
         & reqReturnType .~ Just retType
+        & reqReturnContentTypes .~ cTypes
     where
       retType  = typeFor lang (Proxy :: Proxy ftype) (Proxy :: Proxy a)
       method   = reflectMethod (Proxy :: Proxy method)
       methodLC = toLower $ decodeUtf8 method
+      cTypes   = allMime (Proxy :: Proxy list)
 
 instance (KnownSymbol sym, HasForeignType lang ftype a, HasForeign lang ftype api)
   => HasForeign lang ftype (Header sym a :> api) where

servant-foreign/test/Servant/ForeignSpec.hs

@@ -3,6 +3,7 @@
 
 module Servant.ForeignSpec where
 
+import Data.List.NonEmpty (toList)
 import Data.Monoid ((<>))
 import Data.Proxy
 import Servant.Foreign
@@ -57,6 +58,7 @@ type TestApi
  :<|> "test" :> QueryParams "params" Int :> ReqBody '[JSON] String :> Put '[JSON] NoContent
  :<|> "test" :> Capture "id" Int :> Delete '[JSON] NoContent
  :<|> "test" :> CaptureAll "ids" Int :> Get '[JSON] [Int]
+ :<|> "test" :> "text" :> Get '[PlainText] String
  :<|> "test" :> EmptyAPI
 
 testApi :: [Req String]
@@ -65,9 +67,9 @@ testApi = listFromAPI (Proxy :: Proxy LangX) (Proxy :: Proxy String) (Proxy :: P
 listFromAPISpec :: Spec
 listFromAPISpec = describe "listFromAPI" $ do
   it "generates 5 endpoints for TestApi" $ do
-    length testApi `shouldBe` 5
+    length testApi `shouldBe` 6
 
-  let [getReq, postReq, putReq, deleteReq, captureAllReq] = testApi
+  let [getReq, postReq, putReq, deleteReq, captureAllReq, getTextReq] = testApi
 
   it "collects all info for get request" $ do
     shouldBe getReq $ defReq
@@ -79,6 +81,7 @@ listFromAPISpec = describe "listFromAPI" $ do
       , _reqBody       = Nothing
       , _reqReturnType = Just "intX"
       , _reqFuncName   = FunctionName ["get", "test"]
+      , _reqReturnContentTypes = toList $ contentTypes (Proxy :: Proxy JSON)
       }
 
   it "collects all info for post request" $ do
@@ -91,6 +94,7 @@ listFromAPISpec = describe "listFromAPI" $ do
       , _reqBody       = Just "listX of stringX"
       , _reqReturnType = Just "voidX"
       , _reqFuncName   = FunctionName ["post", "test"]
+      , _reqReturnContentTypes = toList $ contentTypes (Proxy :: Proxy JSON)
       }
 
   it "collects all info for put request" $ do
@@ -104,6 +108,7 @@ listFromAPISpec = describe "listFromAPI" $ do
       , _reqBody       = Just "stringX"
       , _reqReturnType = Just "voidX"
       , _reqFuncName   = FunctionName ["put", "test"]
+      , _reqReturnContentTypes = toList $ contentTypes (Proxy :: Proxy JSON)
       }
 
   it "collects all info for delete request" $ do
@@ -117,6 +122,7 @@ listFromAPISpec = describe "listFromAPI" $ do
       , _reqBody       = Nothing
       , _reqReturnType = Just "voidX"
       , _reqFuncName   = FunctionName ["delete", "test", "by", "id"]
+      , _reqReturnContentTypes = toList $ contentTypes (Proxy :: Proxy JSON)
       }
 
   it "collects all info for capture all request" $ do
@@ -130,4 +136,20 @@ listFromAPISpec = describe "listFromAPI" $ do
       , _reqBody       = Nothing
       , _reqReturnType = Just "listX of intX"
       , _reqFuncName   = FunctionName ["get", "test", "by", "ids"]
+      , _reqReturnContentTypes = toList $ contentTypes (Proxy :: Proxy JSON)
       }
+
+  it "collects all info for plaintext request" $ do
+    shouldBe getTextReq $ defReq
+      { _reqUrl        = Url
+          [ Segment $ Static "test"
+          , Segment $ Static "text" ]
+          []
+      , _reqMethod     = "GET"
+      , _reqHeaders    = []
+      , _reqBody       = Nothing
+      , _reqReturnType = Just "stringX"
+      , _reqFuncName   = FunctionName ["get", "test", "text"]
+      , _reqReturnContentTypes = toList $ contentTypes (Proxy :: Proxy PlainText)
+      }
+