base64url-encode for string guid generation

this works well for AMQP (with its restrictions on queue name
characters) but also when used as part of filenames, urls, etc

1 files changed, 8 insertions, 1 deletions

diff --git a/src/rabbit_guid.erl b/src/rabbit_guid.erl
index 523af7492d..2d0f5014f2 100644
--- a/src/rabbit_guid.erl
+++ b/src/rabbit_guid.erl
@@ -89,8 +89,15 @@ guid() ->
     erlang:md5(term_to_binary(G)).
 
 %% generate a readable string representation of a GUID.
+%%
+%% employs base64url encoding, which is safer in more contexts than
+%% plain base64.
 string_guid(Prefix) ->
-    Prefix ++ "-" ++ base64:encode_to_string(guid()).
+    Prefix ++ "-" ++ lists:foldl(fun ($\+, Acc) -> [$\- | Acc];
+                                     ($\/, Acc) -> [$\_ | Acc];
+                                     ($\=, Acc) -> Acc;
+                                     (Chr, Acc) -> [Chr | Acc]
+                                 end, [], base64:encode_to_string(guid())).
 
 binstring_guid(Prefix) ->
     list_to_binary(string_guid(Prefix)).