eml: speed up common LF-only emails

Emails a *nix MTA are typically LF-only, so we don't need the
complexity of the RE engine when a simple index() works.  We
still need to ensure there's no "\r\n\r\n" before the first
"\n\n", but two calls to index() is still faster than a RE
match.

This gives a 2-5% speedup in some informal tests and saves ~30MB
when scanning a 30MB spam message on newer versions of Perl.
I'll have to diagnose why Perl wastes so much memory doing
RE matches on giant strings, though.

diff --git a/lib/PublicInbox/Eml.pm b/lib/PublicInbox/Eml.pm
index 80e7c1afe90db6dd4e7753c5cbe516997ba53c9c..f022516c12cd091cd2ee6bc77212208f399b7522 100644 (file)
--- a/lib/PublicInbox/Eml.pm
+++ b/lib/PublicInbox/Eml.pm
@@ -71,10 +71,18 @@ sub re_memo ($) {
 # compatible with our uses of Email::MIME
 sub new {
        my $ref = ref($_[1]) ? $_[1] : \(my $cpy = $_[1]);
-       if ($$ref =~ /\r?\n(\r?\n)/s) { # likely
-               # This can modify $$ref in-place and to avoid memcpy/memmove
-               # on a potentially large $$ref.  It does need to make a
-               # copy for $hdr, though.  Idea stolen from Email::Simple
+       # substr() can modify the first arg in-place and to avoid
+       # memcpy/memmove on a potentially large scalar.  It does need
+       # to make a copy for $hdr, though.  Idea stolen from Email::Simple.
+
+       # We also prefer index() on common LFLF emails since it's faster
+       # and re scan can bump RSS by length($$ref) on big strings
+       if (index($$ref, "\r\n") < 0 && (my $pos = index($$ref, "\n\n")) >= 0) {
+               # likely on *nix
+               my $hdr = substr($$ref, 0, $pos + 2, ''); # sv_chop on $$ref
+               chop($hdr); # lower SvCUR
+               bless { hdr => \$hdr, crlf => "\n", bdy => $ref }, __PACKAGE__;
+       } elsif ($$ref =~ /\r?\n(\r?\n)/s) {
                my $hdr = substr($$ref, 0, $+[0], ''); # sv_chop on $$ref
                substr($hdr, -(length($1))) = ''; # lower SvCUR
                bless { hdr => \$hdr, crlf => $1, bdy => $ref }, __PACKAGE__;