eml: reduce RE captures and possible side effects

Since Perl 5.6, the `@-' (aka @LAST_MATCH_START) and `@+' (aka
@LAST_MATCH_END) arrays provides integer offsets for every match
as documented in perlvar(1), regardless of regexp modifiers.

We can avoid relying on $1 in the epilogue scan, entirely.

So use these instead of relying on m//g and pos(), since the `g'
modifier can be affected by m//g matches performed in other
places.

Unrelated, but while we're in the area: remove some unnecessary
use of (?:...), too.

1 files changed, 6 insertions, 6 deletions

diff --git a/lib/PublicInbox/Eml.pm b/lib/PublicInbox/Eml.pm
index 4508bd84..80e7c1af 100644
--- a/lib/PublicInbox/Eml.pm
+++ b/lib/PublicInbox/Eml.pm
@@ -71,11 +71,11 @@ sub re_memo ($) {
 # compatible with our uses of Email::MIME
 sub new {
         my $ref = ref($_[1]) ? $_[1] : \(my $cpy = $_[1]);
-        if ($$ref =~ /(?:\r?\n(\r?\n))/gs) { # likely
+        if ($$ref =~ /\r?\n(\r?\n)/s) { # likely
                 # This can modify $$ref in-place and to avoid memcpy/memmove
                 # on a potentially large $$ref.  It does need to make a
                 # copy for $hdr, though.  Idea stolen from Email::Simple
-                my $hdr = substr($$ref, 0, pos($$ref), ''); # sv_chop on $$ref
+                my $hdr = substr($$ref, 0, $+[0], ''); # sv_chop on $$ref
                 substr($hdr, -(length($1))) = ''; # lower SvCUR
                 bless { hdr => \$hdr, crlf => $1, bdy => $ref }, __PACKAGE__;
         } elsif ($$ref =~ /^[a-z0-9-]+[ \t]*:/ims && $$ref =~ /(\r?\n)\z/s) {
@@ -90,8 +90,8 @@ sub new {
 sub new_sub {
         my (undef, $ref) = @_;
         # special case for messages like <85k5su9k59.fsf_-_@lola.goethe.zz>
-        $$ref =~ /\A(?:(\r?\n))/gs or goto &new;
-        my $hdr = substr($$ref, 0, pos($$ref), ''); # sv_chop on $$ref
+        $$ref =~ /\A(\r?\n)/s or goto &new;
+        my $hdr = substr($$ref, 0, $+[0], ''); # sv_chop on $$ref
         bless { hdr => \$hdr, crlf => $1, bdy => $ref }, __PACKAGE__;
 }
 
@@ -132,8 +132,8 @@ sub mp_descend ($$) {
         # *sigh* just the regexp match alone seems to bump RSS by
         # length($$bdy) on a ~30M string:
         my $epilogue_missing;
-        if ($$bdy =~ /((?:\r?\n)?^--$bnd--[ \t]*\r?$)/gsm) {
-                substr($$bdy, pos($$bdy) - length($1)) = '';
+        if ($$bdy =~ /(?:\r?\n)?^--$bnd--[ \t]*\r?$/sm) {
+                substr($$bdy, $-[0]) = '';
         } else {
                 $epilogue_missing = 1;
         }