send-email: add an auto option for transfer encoding

For most patches, using a transfer encoding of 8bit provides good
compatibility with most servers and makes it as easy as possible to view
patches.  However, there are some patches for which 8bit is not a valid
encoding: RFC 5322 specifies that a message must not have lines
exceeding 998 octets.

Add a transfer encoding value, auto, which indicates that a patch should
use 8bit where allowed and quoted-printable otherwise.  Choose
quoted-printable instead of base64, since base64-encoded plain text is
treated as suspicious by some spam filters.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/t/t9001-send-email.sh b/t/t9001-send-email.sh
index e80eacbb1b..a35cba6a4c 100755
--- a/t/t9001-send-email.sh
+++ b/t/t9001-send-email.sh
@@ -456,6 +456,29 @@ test_expect_success $PREREQ 'allow long lines with --no-validate' '
 		2>errors
 '
 
+test_expect_success $PREREQ 'short lines with auto encoding are 8bit' '
+	clean_fake_sendmail &&
+	git send-email \
+		--from="A <author@example.com>" \
+		--to=nobody@example.com \
+		--smtp-server="$(pwd)/fake.sendmail" \
+		--transfer-encoding=auto \
+		$patches &&
+	grep "Content-Transfer-Encoding: 8bit" msgtxt1
+'
+
+test_expect_success $PREREQ 'long lines with auto encoding are quoted-printable' '
+	clean_fake_sendmail &&
+	git send-email \
+		--from="Example <nobody@example.com>" \
+		--to=nobody@example.com \
+		--smtp-server="$(pwd)/fake.sendmail" \
+		--transfer-encoding=auto \
+		--no-validate \
+		longline.patch &&
+	grep "Content-Transfer-Encoding: quoted-printable" msgtxt1
+'
+
 test_expect_success $PREREQ 'Invalid In-Reply-To' '
 	clean_fake_sendmail &&
 	git send-email \