Bug 895306: REST endpoint returns both JSON and HTML errors when running under mod_perl

mod_perl.pl

@@ -115,6 +115,7 @@ use strict;
 
 use parent qw(ModPerl::Registry);
 use Bugzilla;
+use Bugzilla::Constants qw(USAGE_MODE_REST);
 
 sub handler : method {
     my $class = shift;
@@ -132,7 +133,13 @@ sub handler : method {
     use warnings;
 
     Bugzilla::init_page();
-    return $class->SUPER::handler(@_);
+    my $result = $class->SUPER::handler(@_);
+
+    # When returning data from the REST api, tell Apache not to append its
+    # error html documents to the response.
+    return Bugzilla->usage_mode == USAGE_MODE_REST
+           ? Apache2::Const::OK
+           : $result;
 }