fix(aws-lambda): add null handling for multiValueHeaders (Kong#13533)

A small PR for adding a null handling code for the multiValueHeaders field. Also contains a small refactor to put isBase64Encode check into the validate function to keep consistency with other fields

FTI-6168

changelog/unreleased/kong/fix-aws-lambda-multi-value-header-null.yml

@@ -0,0 +1,3 @@
+message: "**AWS-Lambda**: Fixed an issue in proxy integration mode that caused internal server error when the `multiValueHeaders` is null."
+type: bugfix
+scope: Plugin

kong/plugins/aws-lambda/request-util.lua

@@ -1,6 +1,7 @@
 local kong = kong
 local ngx_encode_base64 = ngx.encode_base64
 local ngx_decode_base64 = ngx.decode_base64
+local null = ngx.null
 local cjson = require "cjson.safe"
 
 local date = require("date")
@@ -89,6 +90,10 @@ local function validate_custom_response(response)
     return nil, "body must be a string"
   end
 
+  if response.isBase64Encoded ~= nil and type(response.isBase64Encoded) ~= "boolean" then
+    return nil, "isBase64Encoded must be a boolean"
+  end
+
   return true
 end
 
@@ -118,13 +123,10 @@ local function extract_proxy_response(content)
   local isBase64Encoded = serialized_content.isBase64Encoded
   if isBase64Encoded == true then
     body = ngx_decode_base64(body)
-
-  elseif isBase64Encoded ~= false and isBase64Encoded ~= nil then
-    return nil, "isBase64Encoded must be a boolean"
   end
 
   local multiValueHeaders = serialized_content.multiValueHeaders
-  if multiValueHeaders then
+  if multiValueHeaders and multiValueHeaders ~= null then
     for header, values in pairs(multiValueHeaders) do
       headers[header] = values
     end

spec/03-plugins/27-aws-lambda/99-access_spec.lua

@@ -194,6 +194,12 @@ for _, strategy in helpers.each_strategy() do
         service     = null,
       }
 
+      local route29 = bp.routes:insert {
+        hosts       = { "lambda29.test" },
+        protocols   = { "http", "https" },
+        service     = null,
+      }
+
       bp.plugins:insert {
         name     = "aws-lambda",
         route    = { id = route1.id },
@@ -580,6 +586,19 @@ for _, strategy in helpers.each_strategy() do
         }
       }
 
+      bp.plugins:insert {
+        name     = "aws-lambda",
+        route    = { id = route29.id },
+        config                 = {
+          port                 = 10001,
+          aws_key              = "mock-key",
+          aws_secret           = "mock-secret",
+          aws_region           = "us-east-1",
+          function_name        = "functionWithNullMultiValueHeaders",
+          is_proxy_integration = true,
+        }
+      }
+
       fixtures.dns_mock:A({
         name = "custom.lambda.endpoint",
         address = "127.0.0.1",
@@ -1154,6 +1173,25 @@ for _, strategy in helpers.each_strategy() do
           assert.equal("Bad Gateway", b.message)
         end)
 
+        it("do not throw error when 'multiValueHeaders' is JSON null", function ()
+          local res = assert(proxy_client:send {
+            method  = "POST",
+            path    = "/post",
+            headers = {
+              ["Host"]         = "lambda11.test",
+              ["Content-Type"] = "application/json",
+            },
+            body = {
+              statusCode = 201,
+              body = "test",
+              multiValueHeaders = cjson.null,
+            }
+          })
+
+          local body = assert.res_status(201, res)
+          assert.same(body, "test")
+        end)
+
         it("returns HTTP 502 with when response from lambda is not valid JSON", function()
           local res = assert(proxy_client:send {
             method  = "POST",