[PATCH v3 3/3] send-email: detect empty blank lines in command output

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

The email format does not allow blank lines in headers; detect such
input and report it as malformed and add a test for it.

Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>
---
 git-send-email.perl   | 12 ++++++++++--
 t/t9001-send-email.sh | 17 +++++++++++++++++
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/git-send-email.perl b/git-send-email.perl
index 666b37adc9..5adcbbeb49 100755
--- a/git-send-email.perl
+++ b/git-send-email.perl
@@ -2008,14 +2008,22 @@ sub process_file {
 	}
 }
 
-# Execute a command and return its output lines as an array.
+# Execute a command and return its output lines as an array.  Blank
+# lines which do not appear at the end of the output are reported as
+# errors.
 sub execute_cmd {
 	my ($prefix, $cmd, $file) = @_;
 	my @lines = ();
+	my $seen_blank_line = 0;
 	open my $fh, "-|", "$cmd \Q$file\E"
 		or die sprintf(__("(%s) Could not execute '%s'"), $prefix, $cmd);
 	while (my $line = <$fh>) {
-		last if $line =~ /^$/;
+		die sprintf(__("(%s) Malformed output from '%s'"), $prefix, $cmd)
+		    if $seen_blank_line;
+		if ($line =~ /^$/) {
+			$seen_blank_line = $line =~ /^$/;
+			next;
+		}
 		push @lines, $line;
 	}
 	close $fh
diff --git a/t/t9001-send-email.sh b/t/t9001-send-email.sh
index 230f436f23..6701dd8848 100755
--- a/t/t9001-send-email.sh
+++ b/t/t9001-send-email.sh
@@ -445,6 +445,23 @@ FoldedField: This is a tale
 	grep "^FoldedField: This is a tale best told using multiple lines.$" msgtxt1
 '
 
+# Blank lines in the middle of the output of a command are invalid.
+test_expect_success $PREREQ 'malform output reported on blank lines in command output' '
+	clean_fake_sendmail &&
+	cp $patches headercmd.patch &&
+	write_script headercmd-malformed-output <<-\EOF &&
+	echo "X-Debbugs-CC: someone@example.com
+
+SomeOtherField: someone-else@example.com"
+	EOF
+	! git send-email \
+		--from="Example <nobody@example.com>" \
+		--to=nobody@example.com \
+		--header-cmd=./headercmd-malformed-output \
+		--smtp-server="$(pwd)/fake.sendmail" \
+		headercmd.patch
+'
+
 test_expect_success $PREREQ 'reject long lines' '
 	z8=zzzzzzzz &&
 	z64=$z8$z8$z8$z8$z8$z8$z8$z8 &&
-- 
2.39.2