+Multiple <dfn id=parents>parents</dfn> means the commit is a merge.
+
+<dfn id=root_commit>Root commits</dfn> have no ancestor. Note that it is
+possible to have multiple root commits when merging independent histories.
+
+Every commit references one top-level <dfn id=tree>tree</dfn> object.</pre>
+EOM
+ delete($ctx->{-wcb})->($ctx->html_done($x));
+}
+
+sub stream_patch_parse_hdr { # {parse_hdr} for Qspawn
+ my ($r, $bref, $ctx) = @_;
+ if (!defined $r) { # sysread error
+ html_page($ctx, 500, dbg_log($ctx));
+ } elsif (index($$bref, "\n\n") >= 0) {
+ my $eml = bless { hdr => $bref }, 'PublicInbox::Eml';
+ my $fn = to_filename($eml->header('Subject') // '');
+ $fn = substr($fn // 'PATCH-no-subject', 6); # drop "PATCH-"
+ return [ 200, [ 'Content-Type', 'text/plain; charset=UTF-8',
+ 'Content-Disposition',
+ qq(inline; filename=$fn.patch) ] ];
+ } elsif ($r == 0) {
+ my $log = dbg_log($ctx);
+ warn "premature EOF on $ctx->{patch_oid} $log";
+ return html_page($ctx, 500, $log);
+ } else {
+ undef; # bref keeps growing until "\n\n"
+ }
+}
+
+sub show_patch ($$) {
+ my ($ctx, $res) = @_;
+ my ($git, $oid) = @$res;
+ my @cmd = ('git', "--git-dir=$git->{git_dir}",
+ qw(format-patch -1 --stdout -C),
+ "--signature=git format-patch -1 --stdout -C $oid", $oid);
+ my $qsp = PublicInbox::Qspawn->new(\@cmd);
+ $ctx->{env}->{'qspawn.wcb'} = $ctx->{-wcb};
+ $ctx->{patch_oid} = $oid;
+ $qsp->psgi_return($ctx->{env}, undef, \&stream_patch_parse_hdr, $ctx);
+}
+
+sub show_commit ($$) {
+ my ($ctx, $res) = @_;
+ return show_patch($ctx, $res) if ($ctx->{fn} // '') =~ /\.patch\z/;
+ my ($git, $oid) = @$res;
+ # patch-id needs two passes, and we use the initial show to ensure
+ # a patch embedded inside the commit message body doesn't get fed
+ # to patch-id:
+ my $cmd = [ '/bin/sh', '-c',
+ "git show --encoding=UTF-8 '$SHOW_FMT'".
+ " -z --no-notes --no-patch $oid >h && ".
+ 'git show --encoding=UTF-8 --pretty=format:%n -M'.
+ " --stat -p $oid >p && ".
+ "git patch-id --stable <p" ];
+ my $e = { GIT_DIR => $git->{git_dir} };
+ my $qsp = PublicInbox::Qspawn->new($cmd, $e, { -C => "$ctx->{-tmp}" });
+ $qsp->{qsp_err} = \($ctx->{-qsp_err} = '');
+ $ctx->{env}->{'qspawn.wcb'} = $ctx->{-wcb};
+ $ctx->{git} = $git;
+ $qsp->psgi_qx($ctx->{env}, undef, \&show_commit_start, $ctx);
+}
+
+sub show_other ($$) { # just in case...
+ my ($ctx, $res) = @_;
+ my ($git, $oid, $type, $size) = @$res;
+ $size > $MAX_SIZE and return html_page($ctx, 200,
+ ascii_html($type)." $oid is too big to show\n". dbg_log($ctx));
+ my $cmd = ['git', "--git-dir=$git->{git_dir}",
+ qw(show --encoding=UTF-8 --no-color --no-abbrev), $oid ];
+ my $qsp = PublicInbox::Qspawn->new($cmd);
+ $qsp->{qsp_err} = \($ctx->{-qsp_err} = '');
+ $qsp->psgi_qx($ctx->{env}, undef, \&show_other_result, $ctx);
+}
+
+sub show_tree_result ($$) {
+ my ($bref, $ctx) = @_;
+ if (my $qsp_err = delete $ctx->{-qsp_err}) {
+ return html_page($ctx, 500, dbg_log($ctx) .
+ "git ls-tree -z error:$qsp_err");
+ }
+ my @ent = split(/\0/, $$bref);
+ my $qp = delete $ctx->{qp};
+ my $l = $ctx->{-linkify} //= PublicInbox::Linkify->new;
+ my $pfx = $qp->{b};
+ $$bref = "<pre><a href=#tree>tree</a> $ctx->{tree_oid}";
+ if (defined $pfx) {
+ if ($pfx eq '') {
+ $$bref .= " (root)\n";
+ } else {
+ my $x = ascii_html($pfx);
+ $pfx .= '/';
+ $$bref .= qq( <a href=#path>path</a>: $x</a>\n);
+ }
+ } else {
+ $pfx = '';
+ $$bref .= qq[ (<a href=#path>path</a> unknown)\n];
+ }
+ my ($x, $m, $t, $oid, $sz, $f, $n);
+ $$bref .= "\n size name";
+ for (@ent) {
+ ($x, $f) = split(/\t/, $_, 2);
+ undef $_;
+ ($m, $t, $oid, $sz) = split(/ +/, $x, 4);
+ $m = $GIT_MODE{$m} // '?';
+ utf8::decode($f);
+ $n = ascii_html($f);
+ if ($m eq 'g') { # gitlink submodule commit
+ $$bref .= "\ng\t\t$n @ <a\nhref=#g>commit</a>$oid";
+ next;
+ }
+ my $q = 'b='.ascii_html(uri_escape_path($pfx.$f));
+ if ($m eq 'd') { $n .= '/' }
+ elsif ($m eq 'x') { $n = "<b>$n</b>" }
+ elsif ($m eq 'l') { $n = "<i>$n</i>" }
+ $$bref .= qq(\n$m\t$sz\t<a\nhref="../../$oid/s/?$q">$n</a>);