Tentative suport for sending exploded series

I've been working on a way to automatically convert pull requests into
series, complete with mailing them out to arbitrary destinations. This
would allow folks to send a pull request to a dedicated list and have it
automatically converted into a well-formed series.

This is a tentative implementation that relies on git-send-email to do
most of the heavy lifting. I have misgivings about using git-send-email
for this purpose, but it does reduce the amount of duplicated code we
would have otherwise had to write, and allows us to hook into things
like tocmd/cccmd, etc.

For example, adding the following to your .git/config:

    [sendemail "autopr"]
        smtpserver = [your.server.here]
        smtpserverport = 587
        smtpencryption = tls
        smtpuser = [your-user]
        smtppass = [your-pass]
        transferEncoding = 8bit
        suppressFrom = yes
        confirm = never
        validate = no
        tocmd = "$(git rev-parse --show-toplevel)/scripts/get_maintainer.pl --norolestats --nol"
        cccmd = "$(git rev-parse --show-toplevel)/scripts/get_maintainer.pl --norolestats --nom"

This would allow doing the following:

    b4 pr -e -f "AutoPR Exploder <autopr@yourdomain.here>" -s autopr [--dry-run]

The pull request will be exploded into a patch series and sent to all
the proper destinations as returned by get_maintainer.pl. We construct
the message headers in a way that allow regular code review and "b4 am"
usage after the auto-exploded series is sent out.

If testing goes well, we'll implement this as a kernel.org service and
then hook a similar implementation via Gitlab/Github.

Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>

2 files changed, 66 insertions, 33 deletions

diff --git a/b4/command.py b/b4/command.py
index 3f130c8..2d6994d 100644
--- a/b4/command.py
+++ b/b4/command.py
@@ -160,6 +160,11 @@ def cmd():
                        help='Attempt to retrieve any Link: URLs (use with -e)')
     sp_pr.add_argument('-f', '--from-addr', dest='mailfrom', default=None,
                        help='Use this From: in exploded messages (use with -e)')
+    sp_pr.add_argument('-s', '--send-as-identity', dest='sendidentity', default=None,
+                       help=('Use git-send-email to send exploded series (use with -e);'
+                             'the identity must match a [sendemail "identity"] config section'))
+    sp_pr.add_argument('--dry-run', dest='dryrun', action='store_true', default=False,
+                       help='Force a --dry-run on git-send-email invocation (use with -s)')
     sp_pr.add_argument('msgid', nargs='?',
                        help='Message ID to process, or pipe a raw message')
     sp_pr.set_defaults(func=cmd_pr)
diff --git a/b4/pr.py b/b4/pr.py
index 98de07b..1e308d8 100644
--- a/b4/pr.py
+++ b/b4/pr.py
@@ -322,19 +322,22 @@ def explode(gitdir, lmsg, mailfrom=None, retrieve_links=True, fpopts=None):
             # Is this the cover letter?
             if msubj.counter == 0:
                 # We rebuild the message from scratch
-                cmsg = MIMEMultipart()
-                cmsg.add_header('From', mailfrom)
-                cmsg.add_header('Subject', '[' + ' '.join(msubj.prefixes) + '] ' + lmsg.subject)
-                cmsg.add_header('Date', lmsg.msg.get('Date'))
-
                 # The cover letter body is the pull request body, plus a few trailers
                 body = '%s\n\nbase-commit: %s\nPR-Link: %s\n' % (
                     lmsg.body.strip(), lmsg.pr_base_commit, config['linkmask'] % lmsg.msgid)
-                cmsg.attach(MIMEText(body, 'plain'))
 
-                # now we attach the original request
-                # XXX: seems redundant, so turned off for now
-                # cmsg.attach(MIMEMessage(lmsg.msg))
+                # Make it a multipart if we're doing retrieve_links
+                if retrieve_links:
+                    cmsg = MIMEMultipart()
+                    cmsg.attach(MIMEText(body, 'plain'))
+                else:
+                    cmsg = email.message.EmailMessage()
+                    cmsg.set_payload(body)
+
+                cmsg.add_header('From', mailfrom)
+                cmsg.add_header('Subject', '[' + ' '.join(msubj.prefixes) + '] ' + lmsg.subject)
+                cmsg.add_header('Date', lmsg.msg.get('Date'))
+
                 msg = cmsg
 
             else:
@@ -456,20 +459,6 @@ def main(cmdargs):
         lmsg.pr_tip_commit = lmsg.pr_remote_tip_commit
 
     if cmdargs.explode:
-        config = b4.get_main_config()
-        if config.get('save-maildirs', 'no') == 'yes':
-            save_maildir = True
-            dftext = 'maildir'
-        else:
-            save_maildir = False
-            dftext = 'mbx'
-        savefile = cmdargs.outmbox
-        if savefile is None:
-            savefile = f'{lmsg.msgid}.{dftext}'
-        if os.path.exists(savefile):
-            logger.info('File exists: %s', savefile)
-            sys.exit(1)
-
         # Set up a temporary clone
         with b4.git_temp_clone(gitdir) as tc:
             try:
@@ -478,19 +467,58 @@ def main(cmdargs):
                 logger.critical('Nothing exploded.')
                 sys.exit(1)
 
-            if msgs:
-                if save_maildir:
-                    b4.save_maildir(msgs, savefile)
-                else:
-                    with open(savefile, 'wb') as fh:
-                        b4.save_git_am_mbox(msgs, fh)
-                logger.info('---')
-                logger.info('Saved %s', savefile)
-                sys.exit(0)
+        if msgs:
+            if cmdargs.sendidentity:
+                # Pass exploded series via git-send-email
+                config = b4.get_config_from_git(rf'sendemail\.{cmdargs.sendidentity}\..*')
+                if not len(config):
+                    logger.critical('Not able to find sendemail.%s configuration', cmdargs.sendidentity)
+                    sys.exit(1)
+                # Make sure from is not overridden by current user
+                mailfrom = msgs[0].get('from')
+                gitargs = ['send-email', '--identity', cmdargs.sendidentity, '--from', mailfrom]
+                if cmdargs.dryrun:
+                    gitargs.append('--dry-run')
+                # Write out everything into a temporary dir
+                counter = 0
+                with tempfile.TemporaryDirectory() as tfd:
+                    for msg in msgs:
+                        outfile = os.path.join(tfd, '%04d' % counter)
+                        with open(outfile, 'wb') as tfh:
+                            tfh.write(msg.as_string(policy=b4.emlpolicy).encode())
+                        gitargs.append(outfile)
+                        counter += 1
+                    ecode, out = b4.git_run_command(cmdargs.gitdir, gitargs, logstderr=True)
+                    if cmdargs.dryrun:
+                        logger.info(out)
+                    sys.exit(ecode)
+
+            config = b4.get_main_config()
+            if config.get('save-maildirs', 'no') == 'yes':
+                save_maildir = True
+                dftext = 'maildir'
             else:
-                logger.critical('Nothing exploded.')
+                save_maildir = False
+                dftext = 'mbx'
+            savefile = cmdargs.outmbox
+            if savefile is None:
+                savefile = f'{lmsg.msgid}.{dftext}'
+            if os.path.exists(savefile):
+                logger.info('File exists: %s', savefile)
                 sys.exit(1)
 
+            if save_maildir:
+                b4.save_maildir(msgs, savefile)
+            else:
+                with open(savefile, 'wb') as fh:
+                    b4.save_git_am_mbox(msgs, fh)
+            logger.info('---')
+            logger.info('Saved %s', savefile)
+            sys.exit(0)
+        else:
+            logger.critical('Nothing exploded.')
+            sys.exit(1)
+
     exists = b4.git_commit_exists(gitdir, lmsg.pr_tip_commit)
     if exists:
         # Is it in any branch, or just flapping in the wind?