+ chop($x = <<EOM);
+<hr><pre>glossary
+--------
+<dfn
+id=commit>Commit</dfn> objects reference one tree, and zero or more parents.
+
+Single <dfn
+id=parent>parent</dfn> commits can typically generate a patch in
+unified diff format via `git format-patch'.
+
+Multiple <dfn id=parents>parents</dfn> means the commit is a merge.
+
+<dfn id=root_commit>Root commits</dfn> have no ancestor. Note that it is
+possible to have multiple root commits when merging independent histories.
+
+Every commit references one top-level <dfn id=tree>tree</dfn> object.</pre>
+EOM
+ delete($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);