send-email: --batch-size to work around some SMTP server limit

Some email servers (e.g. smtp.163.com) limit the number emails to be
sent per session (connection) and this will lead to a faliure when
sending many messages.

Teach send-email to disconnect after sending a number of messages
(configurable via the --batch-size=<num> option), wait for a few
seconds (configurable via the --relogin-delay=<seconds> option) and
reconnect, to work around such a limit.

Also add two configuration variables to give these options the default.

Note:

  We will use this as a band-aid for now, but in the longer term, we
  should look at and react to the SMTP error code from the server;
  Xianqiang reports that 450 and 451 are returned by problematic
  servers.

  cf. https://public-inbox.org/git/7993e188.d18d.15c3560bcaf.Coremail.zxq_yx_007@163.com/

Signed-off-by: xiaoqiang zhao <zxq_yx_007@163.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -2914,6 +2914,16 @@ sendemail.xmailer::
 sendemail.signedoffcc (deprecated)::
 	Deprecated alias for `sendemail.signedoffbycc`.
 
+sendemail.smtpBatchSize::
+	Number of messages to be sent per connection, after that a relogin
+	will happen.  If the value is 0 or undefined, send all messages in
+	one connection.
+	See also the `--batch-size` option of linkgit:git-send-email[1].
+
+sendemail.smtpReloginDelay::
+	Seconds wait before reconnecting to smtp server.
+	See also the `--relogin-delay` option of linkgit:git-send-email[1].
+
 showbranch.default::
 	The default set of branches for linkgit:git-show-branch[1].
 	See linkgit:git-show-branch[1].

Documentation/git-send-email.txt

@@ -248,6 +248,21 @@ must be used for each option.
 	commands and replies will be printed. Useful to debug TLS
 	connection and authentication problems.
 
+--batch-size=<num>::
+	Some email servers (e.g. smtp.163.com) limit the number emails to be
+	sent per session (connection) and this will lead to a faliure when
+	sending many messages.  With this option, send-email will disconnect after
+	sending $<num> messages and wait for a few seconds (see --relogin-delay)
+	and reconnect, to work around such a limit.  You may want to
+	use some form of credential helper to avoid having to retype
+	your password every time this happens.  Defaults to the
+	`sendemail.smtpBatchSize` configuration variable.
+
+--relogin-delay=<int>::
+	Waiting $<int> seconds before reconnecting to SMTP server. Used together
+	with --batch-size option.  Defaults to the `sendemail.smtpReloginDelay`
+	configuration variable.
+
 Automating
 ~~~~~~~~~~
 

contrib/completion/git-completion.bash

@@ -2608,6 +2608,8 @@ _git_config ()
 		sendemail.thread
 		sendemail.to
 		sendemail.validate
+		sendemail.smtpbatchsize
+		sendemail.smtprelogindelay
 		showbranch.default
 		status.relativePaths
 		status.showUntrackedFiles

git-send-email.perl

@@ -81,6 +81,10 @@ sub usage {
                                      This setting forces to use one of the listed mechanisms.
     --smtp-debug            <0|1>  * Disable, enable Net::SMTP debug.
 
+    --batch-size            <int>  * send max <int> message per connection.
+    --relogin-delay         <int>  * delay <int> seconds between two successive login.
+                                     This option can only be used with --batch-size
+
   Automating:
     --identity              <str>  * Use the sendemail.<id> options.
     --to-cmd                <str>  * Email To: via `<str> \$patch_path`
@@ -153,6 +157,7 @@ sub format_2822_time {
 my $have_mail_address = eval { require Mail::Address; 1 };
 my $smtp;
 my $auth;
+my $num_sent = 0;
 
 # Regexes for RFC 2047 productions.
 my $re_token = qr/[^][()<>@,;:\\"\/?.= \000-\037\177-\377]+/;
@@ -216,6 +221,7 @@ sub do_edit {
 my ($to_cmd, $cc_cmd);
 my ($smtp_server, $smtp_server_port, @smtp_server_options);
 my ($smtp_authuser, $smtp_encryption, $smtp_ssl_cert_path);
+my ($batch_size, $relogin_delay);
 my ($identity, $aliasfiletype, @alias_files, $smtp_domain, $smtp_auth);
 my ($validate, $confirm);
 my (@suppress_cc);
@@ -247,6 +253,8 @@ sub do_edit {
     "smtppass" => \$smtp_authpass,
     "smtpdomain" => \$smtp_domain,
     "smtpauth" => \$smtp_auth,
+    "smtpbatchsize" => \$batch_size,
+    "smtprelogindelay" => \$relogin_delay,
     "to" => \@initial_to,
     "tocmd" => \$to_cmd,
     "cc" => \@initial_cc,
@@ -358,6 +366,8 @@ sub signal_handler {
 		    "force" => \$force,
 		    "xmailer!" => \$use_xmailer,
 		    "no-xmailer" => sub {$use_xmailer = 0},
+		    "batch-size=i" => \$batch_size,
+		    "relogin-delay=i" => \$relogin_delay,
 	 );
 
 usage() if $help;
@@ -1664,6 +1674,14 @@ sub send_message {
 		}
 	}
 	$message_id = undef;
+	$num_sent++;
+	if (defined $batch_size && $num_sent == $batch_size) {
+		$num_sent = 0;
+		$smtp->quit if defined $smtp;
+		undef $smtp;
+		undef $auth;
+		sleep($relogin_delay) if defined $relogin_delay;
+	}
 }
 
 # Execute a command (e.g. $to_cmd) to get a list of email addresses