[PATCH 12/29] t/common: introduce run_script wrapper for t/cgi.t

[Eric Wong <e@80x24.org>]

This will give us a consistent interface for running
test scripts in more performant ways while still giving
us a consistent interface to recreate real-world behavior
via spawn() (fork + execve), if needed.

The default run_mode (1) is faster and can run within the test
process with some minor adjustments to our code to avoid global
state.

This avoids the significante overhead of Perl code loading,
parsing and compilation phases.
---
 t/cgi.t       |  16 ++-----
 t/common.perl | 125 +++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 129 insertions(+), 12 deletions(-)

diff --git a/t/cgi.t b/t/cgi.t
index 1b4b06cb..3c09ecd6 100644
--- a/t/cgi.t
+++ b/t/cgi.t
@@ -7,10 +7,7 @@ use warnings;
 use Test::More;
 use Email::MIME;
 use File::Temp qw/tempdir/;
-eval { require IPC::Run };
-plan skip_all => "missing IPC::Run for t/cgi.t" if $@;
-
-use constant CGI => "blib/script/public-inbox.cgi";
+require './t/common.perl';
 my $tmpdir = tempdir('pi-cgi-XXXXXX', TMPDIR => 1, CLEANUP => 1);
 my $home = "$tmpdir/pi-home";
 my $pi_home = "$home/.public-inbox";
@@ -145,11 +142,6 @@ EOF
 
 done_testing();
 
-sub run_with_env {
-	my ($env, @args) = @_;
-	IPC::Run::run(@args, init => sub { %ENV = (%ENV, %$env) });
-}
-
 sub cgi_run {
 	my %env = (
 		PATH_INFO => $_[0],
@@ -162,7 +154,9 @@ sub cgi_run {
 		HTTP_HOST => 'test.example.com',
 	);
 	my ($in, $out, $err) = ("", "", "");
-	my $rc = run_with_env(\%env, [CGI], \$in, \$out, \$err);
+	my $rdr = { 0 => \$in, 1 => \$out, 2 => \$err };
+	run_script(['.cgi'], \%env, $rdr);
+	die "unexpected error: \$?=$?" if $?;
 	my ($head, $body) = split(/\r\n\r\n/, $out, 2);
-	{ head => $head, body => $body, rc => $rc, err => $err }
+	{ head => $head, body => $body, err => $err }
 }
diff --git a/t/common.perl b/t/common.perl
index d4a0fcd2..c5693080 100644
--- a/t/common.perl
+++ b/t/common.perl
@@ -1,7 +1,7 @@
 # Copyright (C) 2015-2019 all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 
-use Fcntl qw(FD_CLOEXEC F_SETFD F_GETFD);
+use Fcntl qw(FD_CLOEXEC F_SETFD F_GETFD :seek);
 use POSIX qw(dup2);
 use strict;
 use warnings;
@@ -68,4 +68,127 @@ sub require_git ($;$) {
 	1;
 }
 
+my %cached_scripts;
+sub key2script ($) {
+	my ($key) = @_;
+	return $key if $key =~ m!\A/!;
+	# n.b. we may have scripts which don't start with "public-inbox" in
+	# the future:
+	$key =~ s/\A([-\.])/public-inbox$1/;
+	'blib/script/'.$key;
+}
+
+sub _prepare_redirects ($) {
+	my ($fhref) = @_;
+	my @x = ([ \*STDIN, '<&' ], [ \*STDOUT, '>&' ], [ \*STDERR, '>&' ]);
+	for (my $fd = 0; $fd <= $#x; $fd++) {
+		my $fh = $fhref->[$fd] or next;
+		my ($oldfh, $mode) = @{$x[$fd]};
+		open $oldfh, $mode, $fh or die "$$oldfh $mode redirect: $!";
+	}
+}
+
+# $opt->{run_mode} (or $ENV{TEST_RUN_MODE}) allows chosing between
+# three ways to spawn our own short-lived Perl scripts for testing:
+#
+# 0 - (fork|vfork) + execve, the most realistic but slowest
+# 1 - preloading and running in a forked subprocess (fast)
+# 2 - preloading and running in current process (slightly faster than 1)
+#
+# 2 is not compatible with scripts which use "exit" (which we'll try to
+# avoid in the future).
+# The default is 2.
+our $run_script_exit_code;
+sub RUN_SCRIPT_EXIT () { "RUN_SCRIPT_EXIT\n" };
+sub run_script_exit (;$) {
+	$run_script_exit_code = $_[0] // 0;
+	die RUN_SCRIPT_EXIT;
+}
+
+sub run_script ($;$$) {
+	my ($cmd, $env, $opt) = @_;
+	my ($key, @argv) = @$cmd;
+	my $run_mode = $ENV{TEST_RUN_MODE} // $opt->{run_mode} // 1;
+	my $sub = $run_mode == 0 ? undef : ($cached_scripts{$key} //= do {
+		my $f = key2script($key);
+		open my $fh, '<', $f or die "open $f: $!";
+		my $str = do { local $/; <$fh> };
+		my ($fc, $rest) = ($key =~ m/([a-z])([a-z0-9]+)\z/);
+		$fc = uc($fc);
+		my $pkg = "PublicInbox::TestScript::$fc$rest";
+		eval <<EOF;
+package $pkg;
+use strict;
+use subs qw(exit);
+
+*exit = *::run_script_exit;
+sub main {
+$str
+	0;
+}
+1;
+EOF
+		$pkg->can('main');
+	}); # do
+
+	my $fhref = [];
+	my $spawn_opt = {};
+	for my $fd (0..2) {
+		my $redir = $opt->{$fd};
+		next unless ref($redir);
+		open my $fh, '+>', undef or die "open: $!";
+		$fhref->[$fd] = $fh;
+		$spawn_opt->{$fd} = fileno($fh);
+		next if $fd > 0;
+		$fh->autoflush(1);
+		print $fh $$redir or die "print: $!";
+		seek($fh, 0, SEEK_SET) or die "seek: $!";
+	}
+	if ($run_mode == 0) {
+		# spawn an independent new process, like real-world use cases:
+		require PublicInbox::Spawn;
+		my $cmd = [ key2script($key), @argv ];
+		my $pid = PublicInbox::Spawn::spawn($cmd, $env, $spawn_opt);
+		defined($pid) or die "spawn: $!";
+		if (defined $pid) {
+			my $r = waitpid($pid, 0);
+			defined($r) or die "waitpid: $!";
+			$r == $pid or die "waitpid: expected $pid, got $r";
+		}
+	} else { # localize and run everything in the same process:
+		local *STDIN = *STDIN;
+		local *STDOUT = *STDOUT;
+		local *STDERR = *STDERR;
+		local %ENV = $env ? (%ENV, %$env) : %ENV;
+		local %SIG = %SIG;
+		_prepare_redirects($fhref);
+		local @ARGV = @argv;
+		$run_script_exit_code = undef;
+		my $exit_code = eval { $sub->(@argv) };
+		if ($@ eq RUN_SCRIPT_EXIT) {
+			$@ = '';
+			$exit_code = $run_script_exit_code;
+			$? = ($exit_code << 8);
+		} elsif (defined($exit_code)) {
+			$? = ($exit_code << 8);
+		} elsif ($@) { # mimic die() behavior when uncaught
+			warn "E: eval-ed $key: $@\n";
+			$? = ($! << 8) if $!;
+			$? = (255 << 8) if $? == 0;
+		} else {
+			die "BUG: eval-ed $key: no exit code or \$@\n";
+		}
+	}
+
+	# slurp the redirects back into user-supplied strings
+	for my $fd (1..2) {
+		my $fh = $fhref->[$fd] or next;
+		seek($fh, 0, SEEK_SET) or die "seek: $!";
+		my $redir = $opt->{$fd};
+		local $/;
+		$$redir = <$fh>;
+	}
+	$? == 0;
+}
+
 1;