change guids to fixed-size binariesbug22647

This change was cherry-picked from the bug21673 branch and brings
'default' closer to that branch.

2 files changed, 6 insertions, 8 deletions

diff --git a/include/rabbit.hrl b/include/rabbit.hrl
index 552aec67..a4abc1ff 100644
--- a/include/rabbit.hrl
+++ b/include/rabbit.hrl
@@ -87,7 +87,7 @@
 -type(file_path() :: string()).
 
 %% this is really an abstract type, but dialyzer does not support them
--type(guid() :: any()).
+-type(guid() :: binary()).
 -type(txn() :: guid()).
 -type(pkey() :: guid()).
 -type(r(Kind) ::
diff --git a/src/rabbit_guid.erl b/src/rabbit_guid.erl
index 2fa531a7..2d632d9d 100644
--- a/src/rabbit_guid.erl
+++ b/src/rabbit_guid.erl
@@ -78,7 +78,7 @@ update_disk_serial() ->
     end,
     Serial.
 
-%% generate a guid that is monotonically increasing per process.
+%% generate a GUID.
 %%
 %% The id is only unique within a single cluster and as long as the
 %% serial store hasn't been deleted.
@@ -92,20 +92,18 @@ guid() ->
     %% A persisted serial number, in combination with self/0 (which
     %% includes the node name) uniquely identifies a process in space
     %% and time. We combine that with a process-local counter to give
-    %% us a GUID that is monotonically increasing per process.
+    %% us a GUID.
     G = case get(guid) of
             undefined -> {{gen_server:call(?SERVER, serial, infinity), self()},
                           0};
             {S, I}   -> {S, I+1}
         end,
     put(guid, G),
-    G.
+    erlang:md5(term_to_binary(G)).
 
-%% generate a readable string representation of a guid. Note that any
-%% monotonicity of the guid is not preserved in the encoding.
+%% generate a readable string representation of a GUID.
 string_guid(Prefix) ->
-    Prefix ++ "-" ++ base64:encode_to_string(
-                       erlang:md5(term_to_binary(guid()))).
+    Prefix ++ "-" ++ base64:encode_to_string(guid()).
 
 binstring_guid(Prefix) ->
     list_to_binary(string_guid(Prefix)).