msg_iter: make ->each_part method for PublicInbox::MIME

The reliance on Email::MIME->subparts is a tad inefficient with
a work-in-progress module to replace Email::MIME.  So move
towards using ->each_part as a class-specific iterator which can
take advantage of more class-specific optimizations in the
yet-to-be-revealed PublicInbox::Eml and PublicInbox::Gmime
classes.

The msg_iter() sub remains for compatibility with existing
3rd-party scripts/modules which use our small public Perl API
and Email::MIME.

1 files changed, 13 insertions, 2 deletions

diff --git a/lib/PublicInbox/MsgIter.pm b/lib/PublicInbox/MsgIter.pm
index fa25564a..cd5a5d99 100644
--- a/lib/PublicInbox/MsgIter.pm
+++ b/lib/PublicInbox/MsgIter.pm
@@ -7,12 +7,12 @@ use strict;
 use warnings;
 use base qw(Exporter);
 our @EXPORT = qw(msg_iter msg_part_text);
-use PublicInbox::MIME;
 
+# This becomes PublicInbox::MIME->each_part:
 # Like Email::MIME::walk_parts, but this is:
 # * non-recursive
 # * passes depth and indices to the iterator callback
-sub msg_iter ($$;$$) {
+sub em_each_part ($$;$$) {
         my ($mime, $cb, $cb_arg, $do_undef) = @_;
         my @parts = $mime->subparts;
         if (@parts) {
@@ -36,6 +36,17 @@ sub msg_iter ($$;$$) {
         }
 }
 
+# Use this when we may accept Email::MIME from user scripts
+# (not just PublicInbox::MIME)
+sub msg_iter ($$;$$) { # $_[0] = PublicInbox::MIME/Email::MIME-like obj
+        my (undef, $cb, $cb_arg, $once) = @_;
+        if (my $ep = $_[0]->can('each_part')) { # PublicInbox::{MIME,*}
+                $ep->($_[0], $cb, $cb_arg, $once);
+        } else { # for compatibility with existing Email::MIME users:
+                em_each_part($_[0], $cb, $cb_arg, $once);
+        }
+}
+
 sub msg_part_text ($$) {
         my ($part, $ct) = @_;