Pass plugin key from embedders to PluginBase. (proxy-wasm#178)

Signed-off-by: Takeshi Yoneda <[email protected]>

Author: mathetake

include/proxy-wasm/context.h

@@ -45,13 +45,16 @@ class WasmVm;
  * @param vm_id is a string used to differentiate VMs with the same code and VM configuration.
  * @param plugin_configuration is configuration for this plugin.
  * @param fail_open if true the plugin will pass traffic as opposed to close all streams.
+ * @param key is used to uniquely identify this plugin instance.
  */
 struct PluginBase {
   PluginBase(std::string_view name, std::string_view root_id, std::string_view vm_id,
-             std::string_view runtime, std::string_view plugin_configuration, bool fail_open)
+             std::string_view runtime, std::string_view plugin_configuration, bool fail_open,
+             std::string_view key)
       : name_(std::string(name)), root_id_(std::string(root_id)), vm_id_(std::string(vm_id)),
         runtime_(std::string(runtime)), plugin_configuration_(plugin_configuration),
-        fail_open_(fail_open), key_(root_id_ + "||" + plugin_configuration_),
+        fail_open_(fail_open),
+        key_(root_id_ + "||" + plugin_configuration_ + "||" + std::string(key)),
         log_prefix_(makeLogPrefix()) {}
 
   const std::string name_;