POEM support array result

Author: ningyougang

proposals/POEM-support-array-result.md

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+# Title
+
+Currently, openwhisk supports return json object only, e.g.
+```shell
+# wsk action invoke hello -r
+{
+    "greeting": "Hello stranger!"
+}
+```
+It is necessary to support return array, e.g.
+```shell
+# wsk action invoke hello-array -r
+[
+    "a",
+    "b"
+]
+```
+
+## Status
+* Current state: In-progress
+* Author(s): @ningyougang
+
+## Summary and Motivation
+
+This POEM proposes a new feature that allows user to write their own action which supports array result.
+So the result will support object and array both in future.
+
+## Proposed changes
+### Openwhisk main repo
+Make controller and invoker support array result both.
+
+### Runtime repos
+All runtime images should support array result. e.g.
+
+* nodejs
+* go
+* java
+* python
+* php
+* shell
+* docker
+* ruby
+* dotnet
+* rust
+* swift 
+
+### Openwhisk-cli repo
+* When use wsk to execute action, need to support parse array result.
+* When use wsk to get activation, need to support parse array result as well.