Enable sd_listen_fds(3)-style socket-activation support

I've added straightforward systemd unit files in
system/socket-activation/ that make use of this approach, and a
README.md in the same location that describes the tradeoffs.

.gitignore

@@ -1,3 +1,4 @@
 dist
 dkimpy_milter.egg-info
 *.pyc
+*~

dkimpy_milter/__init__.py

@@ -1,4 +1,4 @@
-#! /usr/bin/python2
+#! /usr/bin/python3
 # Original dkim-milter.py code:
 # Author: Stuart D. Gathman <stuart@bmsi.com>
 # Copyright 2007 Business Management Systems, Inc.
@@ -28,8 +28,9 @@ import dkim
 import authres
 import os
 import tempfile
-import StringIO
+import io
 import re
+import codecs
 from Milter.utils import parse_addr, parseaddr
 import dkimpy_milter.config as config
 from dkimpy_milter.util import drop_privileges
@@ -61,7 +62,9 @@ class dkimMilter(Milter.Base):
         self.external_connection = False
         self.hello_name = None
         # sometimes people put extra space in sendmail config, so we strip
-        self.receiver = self.getsymval('j').strip()
+        self.receiver = self.getsymval('j')
+        if self.receiver is not None:
+            self.receiver = self.receiver.strip()
         try:
             self.AuthservID = milterconfig['AuthservID']
         except:
@@ -108,7 +111,7 @@ class dkimMilter(Milter.Base):
     def envfrom(self, f, *str):
         if milterconfig.get('Syslog') and milterconfig.get('debugLevel') >= 2:
             syslog.syslog("mail from: {0} {1}".format(f, str))
-        self.fp = StringIO.StringIO()
+        self.fp = io.BytesIO()
         self.mailfrom = f
         t = parse_addr(f)
         if len(t) == 2:
@@ -140,13 +143,13 @@ class dkimMilter(Milter.Base):
         elif lname == 'authentication-results':
             self.arheaders.append(val)
         if self.fp:
-            self.fp.write("%s: %s\n" % (name, val))
+            self.fp.write(b"%s: %s\n" % (codecs.encode(name, 'ascii'), codecs.encode(val, 'ascii')))
         return Milter.CONTINUE
 
     @Milter.noreply
     def eoh(self):
         if self.fp:
-            self.fp.write("\n")   # terminate headers
+            self.fp.write(b"\n")   # terminate headers
         self.bodysize = 0
         return Milter.CONTINUE
 
@@ -193,20 +196,20 @@ class dkimMilter(Milter.Base):
             h = authres.AuthenticationResultsHeader(authserv_id=
                                                     self.AuthservID,
                                                     results=self.arresults)
-            h = fold(str(h))
+            h = fold(codecs.encode(str(h), 'ascii'))
             if (milterconfig.get('Syslog') and
                     milterconfig.get('debugLevel') >= 2):
-                syslog.syslog(str(h))
-            name, val = str(h).split(': ', 1)
+                syslog.syslog(codecs.decode(h, 'ascii'))
+            name, val = codecs.decode(h, 'ascii').split(': ', 1)
             self.addheader(name, val, 0)
         return Milter.CONTINUE
 
     def sign_dkim(self, txt):
-        canon = milterconfig.get('Canonicalization')
+        canon = codecs.encode(milterconfig.get('Canonicalization'), 'ascii')
         canonicalize = []
-        if len(canon.split('/')) == 2:
-            canonicalize.append(canon.split('/')[0])
-            canonicalize.append(canon.split('/')[1])
+        if len(canon.split(b'/')) == 2:
+            canonicalize.append(canon.split(b'/')[0])
+            canonicalize.append(canon.split(b'/')[1])
         else:
             canonicalize.append(canon)
             canonicalize.append(canon)
@@ -216,11 +219,12 @@ class dkimMilter(Milter.Base):
         try:
             if privateRSA:
                 d = dkim.DKIM(txt)
-                h = d.sign(milterconfig.get('Selector'), self.fdomain,
-                           privateRSA, canonicalize=(canonicalize[0],
-                                                     canonicalize[1]))
-                name, val = h.split(': ', 1)
-                self.addheader(name, val.strip().replace('\r\n', '\n'), 0)
+                h = d.sign(codecs.encode(milterconfig.get('Selector'), 'ascii'), codecs.encode(self.fdomain, 'ascii'),
+                           codecs.encode(privateRSA, 'ascii'),
+                           canonicalize=(canonicalize[0],
+                                         canonicalize[1]))
+                name, val = h.split(b': ', 1)
+                self.addheader(codecs.decode(name, 'ascii'), codecs.decode(val, 'ascii').strip().replace('\r\n', '\n'), 0)
                 if (milterconfig.get('Syslog') and
                     (milterconfig.get('SyslogSuccess')
                      or milterconfig.get('debugLevel') >= 1)):
@@ -231,12 +235,12 @@ class dkimMilter(Milter.Base):
                                                   d.domain.lower()))
             if privateEd25519:
                 d = dkim.DKIM(txt)
-                h = d.sign(milterconfig.get('SelectorEd25519'), self.fdomain,
+                h = d.sign(codecs.encode(milterconfig.get('SelectorEd25519'), 'ascii'), codecs.encode(self.fdomain, 'ascii'),
                            privateEd25519, canonicalize=(canonicalize[0],
                                                          canonicalize[1]),
-                           signature_algorithm='ed25519-sha256')
-                name, val = h.split(': ', 1)
-                self.addheader(name, val.strip().replace('\r\n', '\n'), 0)
+                           signature_algorithm=b'ed25519-sha256')
+                name, val = h.split(b': ', 1)
+                self.addheader(codecs.decode(name, 'ascii'), codecs.decode(val, 'ascii').strip().replace('\r\n', '\n'), 0)
                 if (milterconfig.get('Syslog') and
                     (milterconfig.get('SyslogSuccess')
                      or milterconfig.get('debugLevel') >= 1)):
@@ -258,21 +262,23 @@ class dkimMilter(Milter.Base):
         for y in range(self.has_dkim):  # Verify _ALL_ the signatures
             d = dkim.DKIM(txt)
             try:
-                res = d.verify(idx=y)
+                dnsoverride = milterconfig.get('DNSOverride')
+                if isinstance(dnsoverride, str):
+                    syslog.syslog("DNSOverride: {0}".format(dnsoverride))
+                    res = d.verify(idx=y, dnsfunc=lambda _x: dnsoverride)
+                else:
+                    res = d.verify(idx=y)
+                algo = codecs.decode(d.signature_fields.get(b'a'), 'ascii')
                 if res:
-                    if d.signature_fields.get(b'a') == 'ed25519-sha256':
+                    if algo == 'ed25519-sha256':
                         self.dkim_comment = ('Good {0} signature'
-                                             .format(d.signature_fields
-                                                     .get(b'a')))
+                                             .format(algo))
                     else:
                         self.dkim_comment = ('Good {0} bit {1} signature'
-                                             .format(d.keysize,
-                                                     d.signature_fields
-                                                     .get(b'a')))
+                                             .format(d.keysize, algo))
                 else:
                     self.dkim_comment = ('Bad {0} bit {1} signature.'
-                                         .format(d.keysize,
-                                                 d.signature_fields.get(b'a')))
+                                         .format(d.keysize, algo))
             except dkim.DKIMException as x:
                 self.dkim_comment = str(x)
                 if milterconfig.get('Syslog'):
@@ -281,9 +287,9 @@ class dkimMilter(Milter.Base):
                 self.dkim_comment = str(x)
                 if milterconfig.get('Syslog'):
                     syslog.syslog("check_dkim: {0}".format(x))
-            self.header_i = d.signature_fields.get(b'i')
-            self.header_d = d.signature_fields.get(b'd')
-            self.header_a = d.signature_fields.get(b'a')
+            self.header_i = codecs.decode(d.signature_fields.get(b'i'), 'ascii')
+            self.header_d = codecs.decode(d.signature_fields.get(b'd'), 'ascii')
+            self.header_a = codecs.decode(d.signature_fields.get(b'a'), 'ascii')
             if res:
                 if (milterconfig.get('Syslog') and
                         (milterconfig.get('SyslogSuccess') or
@@ -348,7 +354,18 @@ def main():
     Milter.set_flags(Milter.CHGHDRS + Milter.ADDHDRS)
     miltername = 'dkimpy-filter'
     socketname = milterconfig.get('Socket')
-    own_socketfile(milterconfig)
+    if socketname is None:
+        if int(os.environ.get('LISTEN_PID', '0')) == os.getpid():
+            lfds = os.environ.get('LISTEN_FDS')
+            if lfds is not None:
+                if lfds != '1':
+                    syslog.syslog('LISTEN_FDS is set to "{0}", but we only know how to deal with "1", ignoring it'.
+                                  format(lfds))
+                else:
+                    socketname = 'fd:3'
+        if socketname is None:
+            socketname = 'local:/var/run/dkimpy-milter/dkimpy-milter.sock'
+    own_socketfile(milterconfig, socketname)
     drop_privileges(milterconfig)
     sys.stdout.flush()
     Milter.runmilter(miltername, socketname, 240)

dkimpy_milter/__main__.py

@@ -0,0 +1,6 @@
+#!/usr/bin/python3
+
+from dkimpy_milter import main
+
+if __name__ == "__main__":
+    main()

dkimpy_milter/config.py

@@ -31,16 +31,16 @@ import stat
 import dkim
 import socket
 import ipaddress
-from dnsplug import Session
+from .dnsplug import Session
 
 #  default values
 defaultConfigData = {
     'Syslog': 'yes',
     'SyslogFacility': 'mail',
-    'UMask': 007,
+    'UMask': 0o07,
     'Mode': 'sv',
-    'Socket': 'local:/var/run/dkimpy-milter/dkimpy-milter.sock',
-    'PidFile': '/var/run/dkimpy-milter/dkimpy-milter.pid',
+    'Socket': None,
+    'PidFile': None,
     'UserID': 'dkimpy-milter',
     'Canonicalization': 'relaxed/simple',
     'InternalHosts': '127.0.0.1',
@@ -48,6 +48,7 @@ defaultConfigData = {
     'DiagnosticDirectory': '',
     'MacroList': '',
     'MacroListVerify': '',
+    'DNSOverride': None,
     'debugLevel': 0  # Undocumented config item for developer use
     }
 
@@ -84,14 +85,14 @@ class HostsDataset(object):
                 self.item = item[1:]
                 self.negative = True
             try:
-                self.item = ipaddress.ip_address(unicode(self.item, "utf-8"))
+                self.item = ipaddress.ip_address(str(self.item, "utf-8"))
                 if isinstance(self.item, ipaddress.IPv4Address):
                     self.isipv4 = True
                 elif isinstance(self.item, ipaddress.IPv6Address):
                     self.isipv6 = True
             except ValueError as e:
                 try:
-                    self.item = ipaddress.ip_network(unicode
+                    self.item = ipaddress.ip_network(str
                                                      (self.item, "utf-8"),
                                                      strict=False)
                     if isinstance(self.item, ipaddress.IPv4Network):
@@ -109,7 +110,7 @@ class HostsDataset(object):
 
     def match(self, connectip):
         '''Check if the connect IP is part of the dataset'''
-        source = ipaddress.ip_address(unicode(connectip, "utf-8"))
+        source = ipaddress.ip_address(str(connectip, "utf-8"))
         for item in self.dataset:
             if item.isdomain or item.ishostname:
                 result = self.matchname(source)   # Match host/domains first
@@ -159,13 +160,13 @@ class HostsDataset(object):
             if isinstance(source, ipaddress.IPv4Address):
                 ips = s.dns(name, 'A')
                 for ip in ips:
-                    ip = ipaddress.IPv4Address(unicode(ip, 'UTF-8'))
+                    ip = ipaddress.IPv4Address(str(ip, 'UTF-8'))
                     if ip == source:
                         results.append(name)
             if isinstance(source, ipaddress.IPv6Address):
                 ips = s.dns(name, 'AAAA')
                 for ip in ips:
-                    ip = ipaddress.IPv6Address(unicode(ip, 'UTF-8'))
+                    ip = ipaddress.IPv6Address(str(ip, 'UTF-8'))
                 if ip == source:
                     results.append(name)
         return results
@@ -224,13 +225,13 @@ def _processConfigFile(filename=None, configdata=None, useSyslog=1,
     '''Load the specified config file, exit and log errors if it fails,
     otherwise return a config dictionary.'''
 
-    import config
+    from . import config
     if configdata is None:
         configdata = config.defaultConfigData
     if filename is not None:
         try:
             _readConfigFile(filename, configdata)
-        except Exception, e:
+        except Exception as e:
             raise
             if useSyslog:
                 syslog.syslog(e.args[0])
@@ -334,13 +335,14 @@ def _readConfigFile(path, configData=None, configGlobal={}):
         'DiagnosticDirectory': 'str',
         'MacroList': 'dataset',
         'MacroListVerify': 'dataset',
+        'DNSOverride': 'str',
         'debugLevel': 'int'
         }
 
     #  check to see if it's a file
     try:
         mode = os.stat(path)[0]
-    except OSError, e:
+    except OSError as e:
         syslog.syslog(syslog.LOG_ERR, 'ERROR stating "%s": %s'
                       % (path, e.strerror))
         return(configData)
@@ -388,7 +390,10 @@ def _readConfigFile(path, configData=None, configGlobal={}):
         if conversion == 'bool':
             configData[name] = _find_boolean(value)
         elif conversion == 'str':
-            configData[name] = str(value)
+            if isinstance(value, list):
+                configData[name] = line.split(None, 1)[1]
+            else:
+                configData[name] = str(value)
         elif conversion == 'int':
             configData[name] = int(value)
         elif conversion == 'dataset':
@@ -399,7 +404,7 @@ def _readConfigFile(path, configData=None, configGlobal={}):
             configData[name] = conversion(value)
     fp.close()
     try:
-        configData['AuthservID'] = _make_authserv_id(configData['AuthservID'])
+        configData['AuthservID'] = _make_authserv_id(configData.get('AuthservID', 'HOSTNAME'))
         configData['IntHosts'] = HostsDataset(configData['InternalHosts'])
     except:
         pass

dkimpy_milter/dnsplug.py

@@ -84,7 +84,7 @@ class Session(object):
             raise DNSError('Length of CNAME chain exceeds %d' % MAX_CNAME)
         cnames[name] = cname
         if cname in cnames:
-            raise DNSError, 'CNAME loop'
+            raise DNSError('CNAME loop')
         result = self.dns(cname, qtype, cnames=cnames)
     return result
 
@@ -103,16 +103,16 @@ def DNSLookup_pydns(name, qtype, tcpfallback=True, timeout=30):
         #
         if resp.header['tc'] == True:
           if not tcpfallback:
-              raise DNS.DNSError, 'DNS: Truncated UDP Reply, SPF records should fit in a UDP packet'
+              raise DNS.DNSError('DNS: Truncated UDP Reply, SPF records should fit in a UDP packet')
           try:
               req = DNS.DnsRequest(name, qtype=qtype, protocol='tcp',
                         timeout=timeout)
               resp = req.req()
-          except DNS.DNSError, x:
-              raise DNS.DNSError, 'TCP Fallback error: ' + str(x)
+          except DNS.DNSError as x:
+              raise DNS.DNSError('TCP Fallback error: ' + str(x))
         return [((a['name'], a['typename']), a['data']) for a in resp.answers]
-    except IOError, x:
-        raise DNS.DNSError, 'DNS: ' + str(x)
+    except IOError as x:
+        raise DNS.DNSError('DNS: ' + str(x))
 
 def DNSLookup_dnspython(name,qtype,tcpfallback=True,timeout=30):
   retVal = []
@@ -164,5 +164,5 @@ if __name__ == '__main__':
   import sys
   s = Session()
   for n,t in zip(*[iter(sys.argv[1:])]*2):
-    print n,t
-    print s.dns(n,t)
+    print(n,t)
+    print(s.dns(n,t))

dkimpy_milter/util.py

@@ -115,45 +115,59 @@ def write_pid(milterconfig):
     """Write PID in pidfile.  Will not overwrite an existing file."""
     import os
     import syslog
-    if not os.path.isfile(milterconfig.get('PidFile')):
+    pidfile = milterconfig.get('PidFile')
+    if pidfile is None:
+        return
+    if not os.path.isfile(pidfile):
         pid = str(os.getpid())
         try:
-            f = open(milterconfig.get('PidFile'), 'w')
+            f = open(pidfile, 'w')
         except IOError as e:
             if str(e)[:35] == '[Errno 2] No such file or directory':
-                piddir = milterconfig.get('PidFile').rsplit('/', 1)[0]
+                piddir = pidfile.rsplit('/', 1)[0]
                 os.mkdir(piddir)
                 user, group = user_group(milterconfig.get('UserID'))
                 os.chown(piddir, user, group)
-                f = open(milterconfig.get('PidFile'), 'w')
+                f = open(pidfile, 'w')
                 if milterconfig.get('Syslog'):
                     syslog.syslog('PID dir created: {0}'.format(piddir))
             else:
                 if milterconfig.get('Syslog'):
                     syslog.syslog('Unable to write pidfle {0}.  IOError: {1}'
-                                  .format(milterconfig.get('PidFile'), e))
+                                  .format(pidfile, e))
                 raise
         f.write(pid)
         f.close()
         user, group = user_group(milterconfig.get('UserID'))
-        os.chown(milterconfig.get('PidFile'), user, group)
+        os.chown(pidfile, user, group)
     else:
         if milterconfig.get('Syslog'):
             syslog.syslog('Unable to write pidfle {0}.  File exists.'
-                          .format(milterconfig.get('PidFile')))
+                          .format(pidfile))
         raise RuntimeError('Unable to write pidfle {0}.  File exists.'
-                           .format(milterconfig.get('PidFile')))
+                           .format(pidfile))
     return pid
 
 
-def own_socketfile(milterconfig):
+def own_socketfile(milterconfig, sockname=None):
     """If socket is Unix socket, chown to UserID before dropping privileges"""
     import os
     user, group = user_group(milterconfig.get('UserID'))
-    if milterconfig.get('Socket')[:1] == '/':
-        os.chown(milterconfig.get('Socket')[1:], user, group)
-    if milterconfig.get('Socket')[:6] == "local:":
-        os.chown(milterconfig.get('Socket')[6:], user, group)
+    offset = None
+    if sockname is None:
+        sockname = milterconfig.get('Socket')
+    if sockname is None:
+        return
+    if sockname[:1] == '/':
+        offset = 0
+    elif sockname[:6] == "local:":
+        offset = 6
+    elif sockname[:5] == "unix:":
+        offset = 5
+
+    if offset is not None:
+        if os.path.exists(sockname[offset:]):
+            os.chown(sockname[offset:], user, group)
 
 
 def read_keyfile(milterconfig, keytype):

man/dkimpy-milter.conf.5

@@ -311,6 +311,13 @@ be set:
 (b) KeyTable, SigningTable, no Domain, no KeyFile, no Selector;
 [fooTable options NOT IMPLEMENTED]
 
+.TP 
+.I DNSOverride (string)
+Provide a text string that a verifying milter should use instead of
+consulting the DNS on each message.  This is useful primarily for
+testing purposes in environments where it is awkward to modify the
+system DNS resolution.  It should not be used in production.
+
 .TP
 .I PeerList (dataset)
 Identifies a set of "peers" that identifies clients whose connections
@@ -331,7 +338,7 @@ will be checked. [PeerList NOT IMPLEMENTED - included for reference only]
 .TP
 .I PidFile (string)
 Specifies the path to a file that should be created at process start
-containing the process ID.
+containing the process ID.  If not specified, no such file will be created.
 
 .TP
 .I Selector (string)

setup.py

@@ -1,4 +1,4 @@
-#! /usr/bin/python
+#! /usr/bin/python3
 # dkimpy-milter: A DKIM signing/verification Milter application
 # Author: Scott Kitterman <scott@kitterman.com>
 # Copyright 2018 Scott Kitterman
@@ -23,10 +23,10 @@ description = "Domain Keys Identified Mail (DKIM) signing/verifying milter for P
 
 kw = {}  # Work-around for lack of 'or' requires in setuptools.
 try:
-    import DNS
-    kw['install_requires'] = ['dkimpy>=0.7', 'pymilter', 'authres>=1.1.0', 'PyNaCl', 'ipaddress', 'PyDNS']
+    import dns
+    kw['install_requires'] = ['dkimpy>=0.7', 'pymilter', 'authres>=1.1.0', 'PyNaCl', 'dnspython']
 except ImportError:  # If PyDNS is not installed, prefer dnspython
-    kw['install_requires'] = ['dkimpy>=0.7', 'pymilter', 'authres>=1.1.0', 'PyNaCl', 'ipaddress', 'dnspython']
+    kw['install_requires'] = ['dkimpy>=0.7', 'pymilter', 'authres>=1.1.0', 'PyNaCl', 'PyDNS']
 
 setup(
     name='dkimpy-milter',
@@ -43,7 +43,7 @@ setup(
         'License :: OSI Approved :: GNU General Public License (GPL)',
         'Natural Language :: English',
         'Operating System :: POSIX',
-        'Programming Language :: Python :: 2 :: Only',
+        'Programming Language :: Python :: 3 :: Only',
         'Topic :: Communications :: Email :: Mail Transport Agents',
         'Topic :: Communications :: Email :: Filters',
         'Topic :: Security',

system/socket-activation/README.md

@@ -0,0 +1,32 @@
+This directory contains example systemd unit files for running a
+supervised, socket-activated instance of dkimpy-milter.
+
+There are several advantages of using socket activation:
+
+- dkimpy-milter never runs with elevated privileges, they are dropped
+  before any dkimpy-milter code is executed.
+   
+- The socket is opened before dkimpy-milter runs.  This means that
+  clients can connect() to the socket immediately.  So even if there
+  is a delay in dkimpy-milter startup, or in libmilter itself, the
+  connection will not fail.
+  
+- You can set the privileges of a listening Unix-domain socket by an
+  override of ListenGroup= in dkimpy-milter.socket (see
+  systemd.unit(5) for how to override).  This lets you control who has
+  access to the daemon with finer granularity than is available with
+  dkimpy-milter on its own.
+  
+- dkimpy-milter will not consume system resources if it is not used.
+
+- A fully-supervised dkimpy-milter needs no PIDFile, UMask, UserID, or
+  Socket configuation.  This eliminates common race conditions and
+  startup failures, and simplifies the resulting configuration file.
+  
+There is one downside to using socket activation:
+
+- it will only work on systems where libmilter can support connection
+  strings like "fd:3".  This has been supported on Debian and derived
+  systems since sendmail 8.14.4-6 (before Debian Jessie, in early
+  2014), see for example:
+  https://sources.debian.org/src/sendmail/8.15.2-8/debian/patches/socket_activation.patch/

system/socket-activation/dkimpy-milter.service

@@ -0,0 +1,11 @@
+[Unit]
+Description=DKIMpy Milter
+Documentation=man:dkimpy-milter(8) man:dkimpy-milter.conf(5)
+Requires=dkimpy-milter.socket
+
+[Service]
+ExecStart=/usr/bin/dkimpy-milter /etc/dkimpy-milter.conf
+User=dkimpy-milter
+
+[Install]
+Also=dkimpy-milter.socket

system/socket-activation/dkimpy-milter.socket

@@ -0,0 +1,12 @@
+[Unit]
+Description=DKIMpy Milter socket
+Documentation=man:dkimpy-milter(8) man:dkimpy-milter.conf(5)
+
+[Socket]
+ListenStream=/run/dkimpy-milter/dkimpy-milter.sock
+SocketMode=0660
+# override SocketGroup to grant access to members of another system group:
+SocketGroup=dkimpy-milter
+
+[Install]
+WantedBy=sockets.target

tests/00_minimal.miltertest

@@ -0,0 +1,12 @@
+-- -*- lua -*-
+for _, keytype in ipairs({"ed25519", "rsa"}) do
+   for _, func in ipairs({"signing", "verify"}) do
+      mt.echo("testing "..keytype.." "..func)
+      conn = mt.connect("unix:"..keytype.."."..func..".sock")
+      if conn == nil then
+         error("mt.connect() failed "..keytype.." "..func)
+      end
+      mt.disconnect(conn)
+      mt.echo(keytype.." "..func.." complete")
+   end
+end

tests/01_connect.miltertest

@@ -0,0 +1,40 @@
+-- -*- lua -*-
+for _, keytype in ipairs({"ed25519", "rsa"}) do
+   for _, func in ipairs({"signing", "verify"}) do
+      mt.echo("testing "..keytype.." "..func)
+      conn = mt.connect("unix:"..keytype.."."..func..".sock")
+      if conn == nil then
+         error("mt.connect() failed "..keytype.." "..func)
+      end
+      if mt.conninfo(conn, "localhost", "127.0.0.1") ~= nil then
+         error("mt.conninfo() failed "..keytype.." "..func)
+      end
+      if mt.getreply(conn) ~= SMFIR_CONTINUE then
+         error("mt.conninfo() unexpected reply "..keytype.." "..func)
+      end
+
+      if mt.test_action(conn, SMFIF_ADDHDRS) then
+         print("could add headers "..keytype.." "..func)
+      else
+         error("mt.test_action() says could not add headers "..keytype.." "..func)
+      end
+
+      if mt.test_action(conn, SMFIF_CHGHDRS) then
+         print("could change headers "..keytype.." "..func)
+      else
+         error("mt.test_action() says could not change headers "..keytype.." "..func)
+      end
+
+-- -- FIXME: this part of the test fails, as apparently the
+-- -- dkimpy-milter claims the right to change the body of a message,
+-- -- even though it shouldn't.  How can we fix the negotiation?
+--      if mt.test_action(conn, SMFIF_CHGBODY) then
+--         error("mt.test_action() says could change body "..keytype.." "..func)
+--      else
+--         print("could not change body "..keytype.." "..func)
+--      end
+
+      mt.disconnect(conn)
+      mt.echo(keytype.." "..func.." test complete")
+   end
+end

tests/02_sign_message.miltertest

@@ -0,0 +1,100 @@
+-- -*- lua -*-
+
+msg = {
+   ['headers'] = {
+      ['From'] = 'Alice <alice@example.net>',
+      ['Message-Id'] = '<dkimpy-milter-test-02@example.net>',
+      ['To'] = 'Bob <bob@example.biz>',
+      ['Date'] = 'Mon, 18 Feb 2019 08:32:50 -0500',
+      ['Subject'] = 'Signing test',
+      ['Content-Type'] = 'text/plain',
+   },
+   ['body'] = "This is a test!\r\n",
+}
+
+-- returns miltertest connection object
+function connect_and_send (sockname, headers, body)
+   conn = mt.connect(sockname)
+   if conn == nil then
+      error "mt.connect() failed"
+   end
+   if mt.conninfo(conn, "localhost", "127.0.0.1") ~= nil then
+      error "mt.conninfo() failed"
+   end
+   if mt.getreply(conn) ~= SMFIR_CONTINUE then
+      error "mt.conninfo() unexpected reply"
+   end
+
+   -- mt.macro(conn, SMFIC_MAIL, "i", "simple-message")
+   if mt.mailfrom(conn, "<alice@example.net>") ~= nil then
+      error "mt.mailfrom() failed"
+   end
+   if mt.getreply(conn) ~= SMFIR_CONTINUE then
+      error "mt.mailfrom() unexpected reply"
+   end
+   -- mt.rcptto() is called implicitly
+
+   -- send headers
+   for key,value in pairs(headers) do
+      if mt.header(conn, key, value) ~= nil then
+         error("mt.header(" .. key .. ") failed")
+      end
+      if mt.getreply(conn) ~= SMFIR_CONTINUE then
+         error("mt.header(" .. key .. ") unexpected reply")
+      end
+   end
+   -- send EOH
+   if mt.eoh(conn) ~= nil then
+      error "mt.eoh() failed"
+   end
+   if mt.getreply(conn) ~= SMFIR_CONTINUE then
+      error "mt.eoh() unexpected reply"
+   end
+
+   -- send body
+   if mt.bodystring(conn, body) ~= nil then
+      error "mt.bodystring() failed"
+   end
+   if mt.getreply(conn) ~= SMFIR_CONTINUE then
+      error "mt.bodystring() unexpected reply"
+   end
+   -- end of message; let the filter react
+   if mt.eom(conn) ~= nil then
+      error "mt.eom() failed"
+   end
+   reply = mt.getreply(conn)
+   if reply ~= SMFIR_CONTINUE then
+      error ("mt.eom() unexpected reply: " .. reply)
+   end
+   return conn
+end
+
+for _, keytype in ipairs({"ed25519", "rsa"}) do
+   mt.echo("testing "..keytype)
+   signing = connect_and_send("unix:"..keytype..".signing.sock", msg.headers, msg.body)
+   -- verify that a test header field got added
+   if not mt.eom_check(signing, MT_HDRINSERT) then
+      error "no header added by signer"
+   end
+
+   signature = mt.getheader(signing, "DKIM-Signature", 0)
+
+   mt.disconnect(signing)
+
+   mt.echo("DKIM-Signature: " .. signature)
+
+   msg.headers['DKIM-Signature'] = signature
+
+   verify = connect_and_send("unix:"..keytype..".verify.sock", msg.headers, msg.body)
+
+   if not mt.eom_check(verify, MT_HDRINSERT) then
+      error "no header added in verify"
+   end
+
+   authres = mt.getheader(verify, "Authentication-Results", 0)
+   mt.echo("Authentication-Results: "..authres)
+
+   mt.disconnect(verify)
+
+   mt.echo(keytype.." complete")
+end

tests/dkimpy-milter

@@ -0,0 +1,2 @@
+#!/bin/sh
+python3 -m dkimpy_milter "$@"

tests/runtests

@@ -0,0 +1,84 @@
+#!/bin/bash
+
+set -e
+WORKDIR=$(mktemp -d)
+TESTDIR=$(realpath "$(dirname "$0")")
+DKIMPY_MILTER=${DKIMPY_MILTER:-"$TESTDIR/dkimpy-milter"}
+KEY_TYPES=(ed25519 rsa)
+
+cd "$WORKDIR"
+
+printf "Testing %s from directory %s\n" "$DKIMPY_MILTER" "$WORKDIR"
+
+for keytype in "${KEY_TYPES[@]}"; do
+    dknewkey --ktype "$keytype" "testkey.$keytype"
+    if [ "$keytype" = ed25519 ]; then
+        keyfile=KeyFileEd25519
+        selector=SelectorEd25519
+    else
+        keyfile=KeyFile
+        selector=Selector
+    fi
+    cat > "$keytype.signing.conf" <<EOF
+Domain example.net
+$keyfile testkey.$keytype.key
+$selector testkey
+Socket unix:$keytype.signing.sock
+PidFile $keytype.signing.pid
+Mode s
+UserID $(id --name --user):$(id --name --group)
+EOF
+
+    cat > "$keytype.verify.conf" <<EOF
+Socket unix:$keytype.verify.sock
+PidFile $keytype.verify.pid
+Mode v
+DNSOverride $(cat testkey.$keytype.dns)
+UserID $(id --name --user):$(id --name --group)
+EOF
+done
+
+cleanup() {
+    echo cleaning up jobs:
+    jobs
+    for keytype in "${KEY_TYPES[@]}"; do
+        for func in signing verify; do
+            if [ -s "$keytype.$func.pid" ] && kill -0 "$(cat "$keytype.$func.pid")"; then
+                kill "$(cat $keytype.$func.pid)"
+            fi
+        done
+    done
+    wait
+    for keytype in "${KEY_TYPES[@]}"; do
+        for func in signing verify; do
+            errdata="$keytype.$func.stderr"
+            if [ -s "$errdata" ]; then
+                printf -- "-> %s:\n" "$errdata"
+                cat "$errdata"
+                printf -- "-> end %s\n" "$errdata"
+            fi
+        done
+    done
+    rm -rf "$WORKDIR"
+}
+
+for keytype in "${KEY_TYPES[@]}"; do
+    for func in signing verify; do
+        PYTHONPATH="$(dirname "$TESTDIR")" "$DKIMPY_MILTER" "$keytype.$func.conf" 2>"$keytype.$func.stderr" &
+    done
+done
+trap cleanup EXIT
+
+# ugly ugly (how are we supposed to know that the milters are all ready?):
+sleep 2
+
+# uses miltertest from opendkim:
+for x in ${TESTS:-"$TESTDIR"/*.miltertest}; do
+    if ! [ -e "$x" ]; then
+        if [ -e "$TESTDIR/$x" ]; then
+            x="$TESTDIR/$x"
+        fi
+    fi
+    printf -- "-> running %s...\n" "$x"
+    miltertest -s "$x"
+done