script: support multiple header values (#3013)

Introduce `add` and `values` methods to set and get multiple header values.

Signed-off-by: Alexander Yastrebov <alexander.yastrebov@zalando.de>

docs/reference/scripts.md

@@ -137,6 +137,32 @@ ctx.request.header["Authorization"] = nil -- delete authorization header
 
 Response headers `ctx.response.header` work the same way - this is of course only valid in the `response()` phase.
 
+### Multiple header values
+
+Request and response header tables provide access to a first value of a header.
+
+To access multiple values use `add` and `values` methods:
+
+```lua
+function request(ctx, params)
+	ctx.request.header.add("X-Foo", "Bar")
+	ctx.request.header.add("X-Foo", "Baz")
+
+	-- all X-Foo values
+	for _, v in pairs(ctx.request.header.values("X-Foo")) do
+		print(v)
+	end
+
+	-- all values
+	for k, _ in ctx.request.header() do
+		for _, v in pairs(ctx.request.header.values(k)) do
+			print(k, "=", v)
+		end
+	end
+end
+```
+
+
 ## Other request fields
 
 * `backend_url` - (read only) returns the backend url specified in the route

script/script.go

@@ -465,7 +465,10 @@ func getRequestValue(f filters.FilterContext) func(*lua.LState) int {
 		switch key {
 		case "header":
 			if header == nil {
-				header = s.CreateTable(0, 0)
+				header = s.CreateTable(0, 2)
+				header.RawSetString("add", s.NewFunction(addRequestHeader(f)))
+				header.RawSetString("values", s.NewFunction(requestHeaderValues(f)))
+
 				mt := s.CreateTable(0, 3)
 				mt.RawSetString("__index", s.NewFunction(getRequestHeader(f)))
 				mt.RawSetString("__newindex", s.NewFunction(setRequestHeader(f)))
@@ -556,7 +559,10 @@ func getResponseValue(f filters.FilterContext) func(*lua.LState) int {
 		switch key {
 		case "header":
 			if header == nil {
-				header = s.CreateTable(0, 0)
+				header = s.CreateTable(0, 2)
+				header.RawSetString("add", s.NewFunction(addResponseHeader(f)))
+				header.RawSetString("values", s.NewFunction(responseHeaderValues(f)))
+
 				mt := s.CreateTable(0, 3)
 				mt.RawSetString("__index", s.NewFunction(getResponseHeader(f)))
 				mt.RawSetString("__newindex", s.NewFunction(setResponseHeader(f)))
@@ -677,6 +683,30 @@ func setRequestHeader(f filters.FilterContext) func(*lua.LState) int {
 	}
 }
 
+func addRequestHeader(f filters.FilterContext) func(*lua.LState) int {
+	return func(s *lua.LState) int {
+		value := s.ToString(-1)
+		name := s.ToString(-2)
+		if name != "" && value != "" {
+			f.Request().Header.Add(name, value)
+		}
+		return 0
+	}
+}
+
+func requestHeaderValues(f filters.FilterContext) func(*lua.LState) int {
+	return func(s *lua.LState) int {
+		name := s.ToString(-1)
+		values := f.Request().Header.Values(name)
+		res := s.CreateTable(len(values), 0)
+		for _, v := range values {
+			res.Append(lua.LString(v))
+		}
+		s.Push(res)
+		return 1
+	}
+}
+
 func iterateRequestHeader(f filters.FilterContext) func(*lua.LState) int {
 	// https://www.lua.org/pil/7.2.html
 	return func(s *lua.LState) int {
@@ -755,6 +785,30 @@ func setResponseHeader(f filters.FilterContext) func(*lua.LState) int {
 	}
 }
 
+func addResponseHeader(f filters.FilterContext) func(*lua.LState) int {
+	return func(s *lua.LState) int {
+		value := s.ToString(-1)
+		name := s.ToString(-2)
+		if name != "" && value != "" {
+			f.Response().Header.Add(name, value)
+		}
+		return 0
+	}
+}
+
+func responseHeaderValues(f filters.FilterContext) func(*lua.LState) int {
+	return func(s *lua.LState) int {
+		name := s.ToString(-1)
+		values := f.Response().Header.Values(name)
+		res := s.CreateTable(len(values), 0)
+		for _, v := range values {
+			res.Append(lua.LString(v))
+		}
+		s.Push(res)
+		return 1
+	}
+}
+
 func iterateResponseHeader(f filters.FilterContext) func(*lua.LState) int {
 	return func(s *lua.LState) int {
 		s.Push(s.NewFunction(nextHeader(f.Response().Header)))