Include response headers in the API type

Author: 7omb

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/HaskellServantCodegen.java

@@ -577,6 +577,25 @@ public CodegenOperation fromOperation(String resourcePath, String httpMethod, Op
             returnType = "(" + returnType + ")";
         }
 
+        List<CodegenProperty> headers = new ArrayList<>();
+        for (CodegenResponse r : op.responses) {
+            headers.addAll(r.headers);
+        }
+        if (!headers.isEmpty()) {
+            List<String> headerContents = new ArrayList<>();
+            for (CodegenProperty h : headers) {
+                // Because headers is a Map multiple Set-Cookie headers are currently not possible. If someone
+                // uses the workaround with null bytes, remove them and add add each header to the list:
+                // https://github.com/OAI/OpenAPI-Specification/issues/1237#issuecomment-906603675
+                String headerName = h.baseName.replaceAll("\0", "");
+                String headerType = h.dataType;
+                headerContents.add("Header \"" + headerName + "\" " + headerType);
+            }
+            String headerContent = String.join(", ", headerContents);
+
+            returnType = "(Headers '[" + headerContent + "] " + returnType + ")";
+        }
+
         String code = "200";
         for (CodegenResponse r : op.responses) {
             if (r.code.matches("2[0-9][0-9]")) {

samples/server/petstore/haskell-servant/lib/OpenAPIPetstore/API.hs

@@ -163,7 +163,7 @@ type OpenAPIPetstoreAPI
     :<|> "user" :> "createWithList" :> ReqBody '[JSON] [User] :> Verb 'POST 200 '[JSON] NoContent -- 'createUsersWithListInput' route
     :<|> "user" :> Capture "username" Text :> Verb 'DELETE 200 '[JSON] NoContent -- 'deleteUser' route
     :<|> "user" :> Capture "username" Text :> Verb 'GET 200 '[JSON] User -- 'getUserByName' route
-    :<|> "user" :> "login" :> QueryParam "username" Text :> QueryParam "password" Text :> Verb 'GET 200 '[JSON] Text -- 'loginUser' route
+    :<|> "user" :> "login" :> QueryParam "username" Text :> QueryParam "password" Text :> Verb 'GET 200 '[JSON] (Headers '[Header "X-Rate-Limit" Int, Header "X-Expires-After" UTCTime] Text) -- 'loginUser' route
     :<|> "user" :> "logout" :> Verb 'GET 200 '[JSON] NoContent -- 'logoutUser' route
     :<|> "user" :> Capture "username" Text :> ReqBody '[JSON] User :> Verb 'PUT 200 '[JSON] NoContent -- 'updateUser' route
     :<|> Raw
@@ -203,7 +203,7 @@ data OpenAPIPetstoreBackend a m = OpenAPIPetstoreBackend
   , createUsersWithListInput :: [User] -> m NoContent{- ^  -}
   , deleteUser :: Text -> m NoContent{- ^ This can only be done by the logged in user. -}
   , getUserByName :: Text -> m User{- ^  -}
-  , loginUser :: Maybe Text -> Maybe Text -> m Text{- ^  -}
+  , loginUser :: Maybe Text -> Maybe Text -> m (Headers '[Header "X-Rate-Limit" Int, Header "X-Expires-After" UTCTime] Text){- ^  -}
   , logoutUser :: m NoContent{- ^  -}
   , updateUser :: Text -> User -> m NoContent{- ^ This can only be done by the logged in user. -}
   }