Fix error reporting when fetching replication filtersfix-replicator-filter-fetch-error

Don't unnecessarily unwrap the fetch error since `error_info/1` can already
handle the current shape. Also, make sure to translate the reason to binary for
consistency with the other filter fetching errors in the
`couch_replicator_filters` module.

Add a test to ensure we return the `filter_fetch_error` term as that is
explicitly turned into a 404 error in chttpd, so we try to maintain
compatibility with CouchDB <= 3.x code.

3 files changed, 18 insertions, 6 deletions

diff --git a/src/couch_replicator/src/couch_replicator_filters.erl b/src/couch_replicator/src/couch_replicator_filters.erl
index 50c37335d..1cadce1dd 100644
--- a/src/couch_replicator/src/couch_replicator_filters.erl
+++ b/src/couch_replicator/src/couch_replicator_filters.erl
@@ -150,7 +150,7 @@ fetch_internal(DDocName, FilterName, Source) ->
                      couch_replicator_api_wrap:db_uri(Source),
                      couch_util:to_binary(CodeError)]
                  ),
-                 throw({fetch_error, CodeErrorMsg})
+                 throw({fetch_error, iolist_to_binary(CodeErrorMsg)})
          end
     after
         couch_replicator_api_wrap:db_close(Db)
diff --git a/src/couch_replicator/src/couch_replicator_job.erl b/src/couch_replicator/src/couch_replicator_job.erl
index ed3d00d7b..eaa661e77 100644
--- a/src/couch_replicator/src/couch_replicator_job.erl
+++ b/src/couch_replicator/src/couch_replicator_job.erl
@@ -810,9 +810,8 @@ get_rep_id(JTx, Job, #{} = JobData) ->
     try
         couch_replicator_ids:replication_id(Rep)
     catch
-        throw:{filter_fetch_error, Error} ->
-            Error1 = io_lib:format("Filter fetch error ~p", [Error]),
-            reschedule_on_error(JTx, Job, JobData, Error1),
+        throw:{filter_fetch_error, _} = Error ->
+            reschedule_on_error(JTx, Job, JobData, {error, Error}),
             exit({shutdown, finished})
     end.
 
diff --git a/src/couch_replicator/test/eunit/couch_replicator_transient_jobs_tests.erl b/src/couch_replicator/test/eunit/couch_replicator_transient_jobs_tests.erl
index 25fc6a3ff..222d13809 100644
--- a/src/couch_replicator/test/eunit/couch_replicator_transient_jobs_tests.erl
+++ b/src/couch_replicator/test/eunit/couch_replicator_transient_jobs_tests.erl
@@ -31,7 +31,8 @@ transient_jobs_test_() ->
                 fun teardown/1,
                 [
                     ?TDEF_FE(transient_job_is_removed, 10),
-                    ?TDEF_FE(posting_same_job_is_a_noop, 10)
+                    ?TDEF_FE(posting_same_job_is_a_noop, 10),
+                    ?TDEF_FE(transient_job_with_a_bad_filter, 10)
                 ]
             }
         }
@@ -79,7 +80,19 @@ posting_same_job_is_a_noop({Source, Target}) ->
     ?assertEqual(Pid1, Pid2),
     couch_replicator_test_helper:cancel(RepId1).
 
-   
+
+transient_job_with_a_bad_filter({Source, Target}) ->
+    DDoc = #{<<"_id">> => <<"_design/myddoc">>},
+    couch_replicator_test_helper:create_docs(Source, [DDoc]),
+    Result = couch_replicator:replicate(#{
+        <<"source">> => couch_replicator_test_helper:db_url(Source),
+        <<"target">> => couch_replicator_test_helper:db_url(Target),
+        <<"continuous">> => true,
+        <<"filter">> => <<"myddoc/myfilter">>
+    }, ?ADMIN_USER),
+    ?assertMatch({error, #{<<"error">> := <<"filter_fetch_error">>}}, Result).
+
+
 get_rep_id(Source, Target) ->
     {ok, Id, _} = couch_replicator_parse:parse_transient_rep(#{
         <<"source">> => couch_replicator_test_helper:db_url(Source),