www: use PerlIO::scalar (zfh) for buffering

Calling Compress::Raw::Zlib::deflate is fairly expensive.
Relying on the `.=' (concat) operator inside ->zadd operator is
faster, but the method dispatch overhead is noticeable compared
to the original code where we had bare `.=' littered throughout.

Fortunately, `print' and `say' with the PerlIO::scalar IO layer
appears to offer better performance without high method dispatch
overhead.  This doesn't allow us to save as much memory as I
originally hoped, but does allow us to rely less on concat
operators in other places and just pass a list of args to
`print' and `say' as a appropriate.

This does reduce scratchpad use, however, allowing for large
memory savings, and we still ->deflate every single $eml.

1 files changed, 34 insertions, 35 deletions

diff --git a/lib/PublicInbox/ViewDiff.pm b/lib/PublicInbox/ViewDiff.pm
index 95b615dc..5d23881b 100644
--- a/lib/PublicInbox/ViewDiff.pm
+++ b/lib/PublicInbox/ViewDiff.pm
@@ -67,8 +67,8 @@ sub oid ($$$) {
 }
 
 # returns true if diffstat anchor written, false otherwise
-sub anchor0 ($$$$) {
-        my ($dst, $ctx, $fn, $rest) = @_;
+sub anchor0 ($$$) {
+        my ($ctx, $fn, $rest) = @_;
 
         my $orig = $fn;
 
@@ -84,15 +84,12 @@ sub anchor0 ($$$$) {
         # long filenames will require us to check in anchor1()
         push(@{$ctx->{-long_path}}, $fn) if $fn =~ s!\A\.\.\./?!!;
 
-        if (defined(my $attr = to_attr($ctx->{-apfx}.$fn))) {
-                $ctx->{-anchors}->{$attr} = 1;
-                my $spaces = ($orig =~ s/( +)\z//) ? $1 : '';
-                $$dst .= " <a\nid=i$attr\nhref=#$attr>" .
-                        ascii_html($orig) . '</a>' . $spaces .
+        my $attr = to_attr($ctx->{-apfx}.$fn) // return;
+        $ctx->{-anchors}->{$attr} = 1;
+        my $spaces = ($orig =~ s/( +)\z//) ? $1 : '';
+        print { $ctx->{zfh} } " <a\nid=i$attr\nhref=#$attr>",
+                        ascii_html($orig), '</a>', $spaces,
                         $ctx->{-linkify}->to_html($rest);
-                return 1;
-        }
-        undef;
 }
 
 # returns "diff --git" anchor destination, undef otherwise
@@ -156,33 +153,34 @@ sub diff_header ($$$) {
                 warn "BUG? <$$x> had no ^index line";
         }
         $$x =~ s!^diff --git!anchor1($ctx, $pb) // 'diff --git'!ems;
-        $ctx->zadd(qq(<span\nclass="head">$$x</span>));
+        print { $ctx->{zfh} } qq(<span\nclass="head">), $$x, '</span>';
         $dctx;
 }
 
 sub diff_before_or_after ($$) {
         my ($ctx, $x) = @_;
-        if (exists $ctx->{-anchors} && $$x =~ /\A(.*?) # likely "---\n"
+        if (exists $ctx->{-anchors} && $$x =~ /\A(.*?) # likely "---\n" # \$1
                         # diffstat lines:
                         ((?:^\x20(?:[^\n]+?)(?:\x20+\|\x20[^\n]*\n))+)
                         (\x20[0-9]+\x20files?\x20)changed,([^\n]+\n)
                         (.*?)\z/msx) { # notes, commit message, etc
                 my @x = ($5, $4, $3, $2, $1);
+                undef $$x;
                 my $lnk = $ctx->{-linkify};
-                $$x = $lnk->to_html(pop @x); # uninteresting prefix
-                for my $l (split(/^/m, pop(@x))) { # per-file diffstat lines
+                my $zfh = $ctx->{zfh};
+                print $zfh $lnk->to_html(pop @x); # $1 uninteresting prefix
+                for my $l (split(/^/m, pop(@x))) { # $2 per-file stat lines
                         $l =~ /^ (.+)( +\| .*\z)/s and
-                                anchor0($x, $ctx, $1, $2) and next;
-                        $$x .= $lnk->to_html($l);
+                                anchor0($ctx, $1, $2) and next;
+                         print $zfh $lnk->to_html($l);
                 }
-                $$x .= pop @x; # $3 /^ \d+ files? /
                 my $ch = $ctx->{changed_href} // '#related';
-                $$x .= qq(<a href="$ch">changed</a>,);
-                $$x .= ascii_html(pop @x); # $4: insertions/deletions
-                # notes, commit message, etc
-                $ctx->zadd($$x .= $lnk->to_html(pop @x));
+                print $zfh pop(@x), # $3 /^ \d+ files? /
+                        qq(<a href="$ch">changed</a>,),
+                        ascii_html(pop @x), # insertions/deletions
+                        $lnk->to_html(@x); # notes, commit message, etc
         } else {
-                $ctx->zadd($ctx->{-linkify}->to_html($$x));
+                print { $ctx->{zfh} } $ctx->{-linkify}->to_html($$x);
         }
 }
 
@@ -195,6 +193,7 @@ sub flush_diff ($$) {
 
         my $lnk = $ctx->{-linkify};
         my $dctx; # {}, keys: Q, oid_a, oid_b
+        my $zfh = $ctx->zfh;
 
         while (defined(my $x = shift @top)) {
                 if (scalar(@top) >= 4 &&
@@ -202,7 +201,7 @@ sub flush_diff ($$) {
                                 $top[0] =~ $IS_OID) {
                         $dctx = diff_header(\$x, $ctx, \@top);
                 } elsif ($dctx) {
-                        my $after = '';
+                        open(my $afh, '>>', \(my $after='')) or die "open: $!";
 
                         # Quiet "Complex regular subexpression recursion limit"
                         # warning.  Perl will truncate matches upon hitting
@@ -218,25 +217,25 @@ sub flush_diff ($$) {
                                         (?:(?:^-[^\n]*\n)+)|
                                         (?:^@@ [^\n]+\n))/xsm, $x)) {
                                 if (!defined($dctx)) {
-                                        $after .= $s;
+                                        print $afh $s;
                                 } elsif ($s =~ s/\A@@ (\S+) (\S+) @@//) {
-                                        $ctx->zadd(qq(<span\nclass="hunk">) .
-                                                diff_hunk($dctx, $1, $2) .
-                                                $lnk->to_html($s) .
-                                                '</span>');
+                                        print $zfh qq(<span\nclass="hunk">),
+                                                diff_hunk($dctx, $1, $2),
+                                                $lnk->to_html($s),
+                                                '</span>';
                                 } elsif ($s =~ /\A\+/) { # $s may be huge
-                                        $ctx->zadd(qq(<span\nclass="add">),
+                                        print $zfh qq(<span\nclass="add">),
                                                         $lnk->to_html($s),
-                                                        '</span>');
+                                                        '</span>';
                                 } elsif ($s =~ /\A-- $/sm) { # email sig starts
                                         $dctx = undef;
-                                        $after .= $s;
+                                        print $afh $s;
                                 } elsif ($s =~ /\A-/) { # $s may be huge
-                                        $ctx->zadd(qq(<span\nclass="del">),
-                                                $lnk->to_html($s),
-                                                '</span>');
+                                        print $zfh qq(<span\nclass="del">),
+                                                        $lnk->to_html($s),
+                                                        '</span>';
                                 } else { # $s may be huge
-                                        $ctx->zadd($lnk->to_html($s));
+                                        print $zfh $lnk->to_html($s);
                                 }
                         }
                         diff_before_or_after($ctx, \$after) if !$dctx;