[PATCH v3] git-send-email: add option to specify sendmail command

[Gregory Anders <greg@gpanders.com>]

The sendemail.smtpServer configuration option and --smtp-server command
line option both support using a sendmail-like program to send emails by
specifying an absolute file path. However, this is not ideal for the
following reasons:

1. It overloads the meaning of smtpServer (now a program is being used
   for the server?)
2. It doesn't allow for non-absolute paths, arguments, or arbitrary
   scripting

Requiring an absolute path is bad for portability, as the same program
may be in different locations on different systems. If a user wishes to
pass arguments to their program, they have to use the smtpServerOption
option, which is cumbersome (as it must be repeated for each option) and
doesn't adhere to normal git conventions.

Introduce a new configuration option sendemail.sendmailCmd as well as a
command line option --sendmail-cmd that can be used to specify a command
(with or without arguments) or shell expression to run to send email.
The name of this option is consistent with --to-cmd and --cc-cmd. This
invocation honors the user's $PATH so that absolute paths are not
necessary. Arbitrary shell expressions are also supported, allowing
users to do basic scripting.

Give this option a higher precedence over --smtp-server and
sendemail.smtpServer, as the new interface is more flexible. For
backward compatibility, continue to support absolute paths in
--smtp-server and sendemail.smtpServer.

Signed-off-by: Gregory Anders <greg@gpanders.com>
---

Fix and reword the documentation to hopefully be more consistent between 
--sendmail-cmd and --smtp-server.

Update the invocation of "sendmail_cmd" to ensure that parameters are 
not expanded by the shell (the parameters may contain any number of 
special characters that are not intended to be interpreted by the 
shell).

Use a block scoped variable to print the sendmail invocation at the end 
of the 'send_message' subroutine. Assigning directly to $sendmail_cmd 
(as in the v2 patch) causes some bizarre problems; namely, it seems to 
affect the value of $sendmail_cmd that is read at earlier points in the 
same subroutine, which causes test invocations of the form

    git send-email --smtp-server="$(pwd)/fake.sendmail"

to fail. The value passed to --smtp-server was assigned to $sendmail_cmd 
at the end of the 'send_message' subprocedure, but somehow this caused 
the 'if (defined $sendmail_cmd)' condition earlier in the subproc to 
evaluate to true. This would fail because $sendmail_cmd is expanded in 
the shell, and since $(pwd) contains a space the command was being 
split, resulting in a "command not found" error. I don't have enough 
Perl experience to explain what's happening in this case, but using a 
scoped variable resolves the issue.

 Documentation/git-send-email.txt | 25 ++++++++++++++++-------
 git-send-email.perl              | 34 +++++++++++++++++++++++++-------
 t/t9001-send-email.sh            | 31 +++++++++++++++++++++++++++++
 3 files changed, 76 insertions(+), 14 deletions(-)

diff --git a/Documentation/git-send-email.txt b/Documentation/git-send-email.txt
index 93708aefea..3db4eab4ba 100644
--- a/Documentation/git-send-email.txt
+++ b/Documentation/git-send-email.txt
@@ -167,6 +167,14 @@ Sending
 	`sendemail.envelopeSender` configuration variable; if that is
 	unspecified, choosing the envelope sender is left to your MTA.
 
+--sendmail-cmd=<command>::
+	Specify a command to run to send the email. The command should
+	be sendmail-like; specifically, it must support the `-i` option.
+	The command will be executed in the shell if necessary.  Default
+	is the value of `sendemail.sendmailcmd`.  If unspecified, and if
+	--smtp-server is also unspecified, git-send-email will search
+	for `sendmail` in `/usr/sbin`, `/usr/lib` and $PATH.
+
 --smtp-encryption=<encryption>::
 	Specify the encryption to use, either 'ssl' or 'tls'.  Any other
 	value reverts to plain SMTP.  Default is the value of
@@ -211,13 +219,16 @@ a password is obtained using 'git-credential'.
 
 --smtp-server=<host>::
 	If set, specifies the outgoing SMTP server to use (e.g.
-	`smtp.example.com` or a raw IP address).  Alternatively it can
-	specify a full pathname of a sendmail-like program instead;
-	the program must support the `-i` option.  Default value can
-	be specified by the `sendemail.smtpServer` configuration
-	option; the built-in default is to search for `sendmail` in
-	`/usr/sbin`, `/usr/lib` and $PATH if such program is
-	available, falling back to `localhost` otherwise.
+	`smtp.example.com` or a raw IP address).  If unspecified, and if
+	`--sendmail-cmd` is also unspecified, the default is to search
+	for `sendmail` in `/usr/sbin`, `/usr/lib` and $PATH if such a
+	program is available, falling back to `localhost` otherwise.
++
+For backward compatibility, this option can also specify a full pathname
+of a sendmail-like program instead; the program must support the `-i`
+option.  This method does not support passing arguments or using plain
+command names.  For those use cases, consider using `--sendmail-cmd`
+instead.
 
 --smtp-server-port=<port>::
 	Specifies a port different from the default port (SMTP
diff --git a/git-send-email.perl b/git-send-email.perl
index 175da07d94..dbb144aa11 100755
--- a/git-send-email.perl
+++ b/git-send-email.perl
@@ -70,6 +70,7 @@ sub usage {
 
   Sending:
     --envelope-sender       <str>  * Email envelope sender.
+    --sendmail-cmd          <str>  * Command to run to send email.
     --smtp-server       <str:int>  * Outgoing SMTP server to use. The port
                                      is optional. Default 'localhost'.
     --smtp-server-option    <str>  * Outgoing SMTP server option to use.
@@ -252,6 +253,7 @@ sub do_edit {
 my (@suppress_cc);
 my ($auto_8bit_encoding);
 my ($compose_encoding);
+my ($sendmail_cmd);
 # Variables with corresponding config settings & hardcoded defaults
 my ($debug_net_smtp) = 0;		# Net::SMTP, see send_message()
 my $thread = 1;
@@ -299,6 +301,7 @@ sub do_edit {
     "assume8bitencoding" => \$auto_8bit_encoding,
     "composeencoding" => \$compose_encoding,
     "transferencoding" => \$target_xfer_encoding,
+    "sendmailcmd" => \$sendmail_cmd,
 );
 
 my %config_path_settings = (
@@ -432,6 +435,7 @@ sub read_config {
 		    "no-bcc" => \$no_bcc,
 		    "chain-reply-to!" => \$chain_reply_to,
 		    "no-chain-reply-to" => sub {$chain_reply_to = 0},
+		    "sendmail-cmd=s" => \$sendmail_cmd,
 		    "smtp-server=s" => \$smtp_server,
 		    "smtp-server-option=s" => \@smtp_server_options,
 		    "smtp-server-port=s" => \$smtp_server_port,
@@ -1003,16 +1007,19 @@ sub expand_one_alias {
 	$reply_to = sanitize_address($reply_to);
 }
 
-if (!defined $smtp_server) {
+if (!defined $sendmail_cmd && !defined $smtp_server) {
 	my @sendmail_paths = qw( /usr/sbin/sendmail /usr/lib/sendmail );
 	push @sendmail_paths, map {"$_/sendmail"} split /:/, $ENV{PATH};
 	foreach (@sendmail_paths) {
 		if (-x $_) {
-			$smtp_server = $_;
+			$sendmail_cmd = $_;
 			last;
 		}
 	}
-	$smtp_server ||= 'localhost'; # could be 127.0.0.1, too... *shrug*
+
+	if (!defined $sendmail_cmd) {
+		$smtp_server = 'localhost'; # could be 127.0.0.1, too... *shrug*
+	}
 }
 
 if ($compose && $compose > 0) {
@@ -1492,11 +1499,17 @@ sub send_message {
 
 	if ($dry_run) {
 		# We don't want to send the email.
-	} elsif (file_name_is_absolute($smtp_server)) {
+	} elsif (defined $sendmail_cmd || file_name_is_absolute($smtp_server)) {
 		my $pid = open my $sm, '|-';
 		defined $pid or die $!;
 		if (!$pid) {
-			exec($smtp_server, @sendmail_parameters) or die $!;
+			if (defined $sendmail_cmd) {
+				exec ("sh", "-c", "$sendmail_cmd \"\$@\"", "-", @sendmail_parameters)
+					or die $!;
+			} else {
+				exec ($smtp_server, @sendmail_parameters)
+					or die $!;
+			}
 		}
 		print $sm "$header\n$message";
 		close $sm or die $!;
@@ -1592,14 +1605,21 @@ sub send_message {
 		printf($dry_run ? __("Dry-Sent %s\n") : __("Sent %s\n"), $subject);
 	} else {
 		print($dry_run ? __("Dry-OK. Log says:\n") : __("OK. Log says:\n"));
-		if (!file_name_is_absolute($smtp_server)) {
+		if (!defined $sendmail_cmd && !file_name_is_absolute($smtp_server)) {
 			print "Server: $smtp_server\n";
 			print "MAIL FROM:<$raw_from>\n";
 			foreach my $entry (@recipients) {
 			    print "RCPT TO:<$entry>\n";
 			}
 		} else {
-			print "Sendmail: $smtp_server ".join(' ',@sendmail_parameters)."\n";
+			my $sm;
+			if (defined $sendmail_cmd) {
+				$sm = $sendmail_cmd;
+			} else {
+				$sm = $smtp_server;
+			}
+
+			print "Sendmail: $sm ".join(' ',@sendmail_parameters)."\n";
 		}
 		print $header, "\n";
 		if ($smtp) {
diff --git a/t/t9001-send-email.sh b/t/t9001-send-email.sh
index 65b3035371..583fbba410 100755
--- a/t/t9001-send-email.sh
+++ b/t/t9001-send-email.sh
@@ -2148,6 +2148,37 @@ test_expect_success $PREREQ 'leading and trailing whitespaces are removed' '
 	test_cmp expected-list actual-list
 '
 
+test_expect_success $PREREQ 'test using command name with --sendmail-cmd' '
+	clean_fake_sendmail &&
+	PATH="$(pwd):$PATH" \
+	git send-email \
+		--from="Example <nobody@example.com>" \
+		--to=nobody@example.com \
+		--sendmail-cmd="fake.sendmail" \
+		HEAD^ &&
+	test_path_is_file commandline1
+'
+
+test_expect_success $PREREQ 'test using arguments with --sendmail-cmd' '
+	clean_fake_sendmail &&
+	git send-email \
+		--from="Example <nobody@example.com>" \
+		--to=nobody@example.com \
+		--sendmail-cmd="\"$(pwd)/fake.sendmail\" -f nobody@example.com" \
+		HEAD^ &&
+	test_path_is_file commandline1
+'
+
+test_expect_success $PREREQ 'test shell expression with --sendmail-cmd' '
+	clean_fake_sendmail &&
+	git send-email \
+		--from="Example <nobody@example.com>" \
+		--to=nobody@example.com \
+		--sendmail-cmd="f() { \"$(pwd)/fake.sendmail\" \"\$@\"; };f" \
+		HEAD^ &&
+	test_path_is_file commandline1
+'
+
 test_expect_success $PREREQ 'invoke hook' '
 	mkdir -p .git/hooks &&
 
-- 
2.31.1