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, 7 insertions, 5 deletions

diff --git a/git-send-email.perl b/git-send-email.perl
index 8ec70e5..1736a09 100755
--- a/git-send-email.perl
+++ b/git-send-email.perl
@@ -1739,9 +1739,8 @@ sub process_file {
 	}
 	if (defined $target_xfer_encoding) {
 		$xfer_encoding = '8bit' if not defined $xfer_encoding;
-		$message = apply_transfer_encoding(
+		($message, $xfer_encoding) = apply_transfer_encoding(
 			$message, $xfer_encoding, $target_xfer_encoding);
-		$xfer_encoding = $target_xfer_encoding;
 	}
 	if (defined $xfer_encoding) {
 		push @xh, "Content-Transfer-Encoding: $xfer_encoding";
@@ -1852,13 +1851,16 @@ sub apply_transfer_encoding {
 	$message = MIME::Base64::decode($message)
 		if ($from eq 'base64');
 
+	$to = ($message =~ /.{999,}/) ? 'quoted-printable' : '8bit'
+		if $to eq 'auto';
+
 	die __("cannot send message as 7bit")
 		if ($to eq '7bit' and $message =~ /[^[:ascii:]]/);
-	return $message
+	return ($message, $to)
 		if ($to eq '7bit' or $to eq '8bit');
-	return MIME::QuotedPrint::encode($message, "\n", 0)
+	return (MIME::QuotedPrint::encode($message, "\n", 0), $to)
 		if ($to eq 'quoted-printable');
-	return MIME::Base64::encode($message, "\n")
+	return (MIME::Base64::encode($message, "\n"), $to)
 		if ($to eq 'base64');
 	die __("invalid transfer encoding");
 }