send-email: validate patches before sending anything

We try to catch errors early so that we don't end up sending
half of a broken patch series. Right now the only validation
is checking that line-lengths are under the SMTP-mandated
limit of 998.

The validation parsing is very crude (it just checks each
line length without understanding the mailbox format) but
should work fine for this simple check.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-send-email.perl

@@ -332,6 +332,11 @@ for my $f (@ARGV) {
 	}
 }
 
+foreach my $f (@files) {
+	my $error = validate_patch($f);
+	$error and die "fatal: $f: $error\nwarning: no patches were sent\n";
+}
+
 if (@files) {
 	unless ($quiet) {
 		print $_,"\n" for (@files);
@@ -837,3 +842,15 @@ sub unique_email_list(@) {
 	}
 	return @emails;
 }
+
+sub validate_patch {
+	my $fn = shift;
+	open(my $fh, '<', $fn)
+		or die "unable to open $fn: $!\n";
+	while (my $line = <$fh>) {
+		if (length($line) > 998) {
+			return "$.: patch contains a line longer than 998 characters";
+		}
+	}
+	return undef;
+}

t/t9001-send-email.sh

@@ -78,4 +78,24 @@ test_expect_success 'Show all headers' '
 	diff -u expected-show-all-headers actual-show-all-headers
 '
 
+z8=zzzzzzzz
+z64=$z8$z8$z8$z8$z8$z8$z8$z8
+z512=$z64$z64$z64$z64$z64$z64$z64$z64
+test_expect_success 'reject long lines' '
+	rm -f commandline &&
+	cp $patches longline.patch &&
+	echo $z512$z512 >>longline.patch &&
+	! git send-email \
+		--from="Example <nobody@example.com>" \
+		--to=nobody@example.com \
+		--smtp-server="$(pwd)/fake.sendmail" \
+		$patches longline.patch \
+		2>errors &&
+	grep longline.patch errors
+'
+
+test_expect_success 'no patch was sent' '
+	! test -e commandline
+'
+
 test_done