feat(emqx.erl): Add a help function to load debug secret

src/emqx.erl

@@ -63,12 +63,39 @@
         , reboot/0
         ]).
 
+%% Troubleshooting
+-export([ set_debug_secret/1
+        ]).
+
 -define(APP, ?MODULE).
 
 -define(COPYRIGHT, "Copyright (c) 2020 EMQ Technologies Co., Ltd").
 
 -define(LICENSE_MESSAGE, "Licensed under the Apache License, Version 2.0").
 
+%% @hidden Path to the file which has debug_info encryption secret in it.
+%% Evaluate this function if there is a need to access encrypted debug_info.
+%% NOTE: Do not change the API to accept the secret text because it may
+%% get logged everywhere.
+set_debug_secret(PathToSecretFile) ->
+    SecretText =
+        case file:read_file(PathToSecretFile) of
+            {ok, Secret} ->
+                try string:trim(binary_to_list(Secret))
+                catch _ : _ -> error({badfile, PathToSecretFile})
+                end;
+            {error, Reason} ->
+                io:format("Failed to read debug_info encryption key file ~s: ~p~n",
+                          [PathToSecretFile, Reason]),
+                error(Reason)
+        end,
+    F = fun(init) -> ok;
+           (clear) -> ok;
+           ({debug_info, _Mode, _Module, _Filename}) -> SecretText
+        end,
+    _ = beam_lib:clear_crypto_key_fun(),
+    ok = beam_lib:crypto_key_fun(F).
+
 %%--------------------------------------------------------------------
 %% Bootstrap, is_running...
 %%--------------------------------------------------------------------