public-inbox-pop3d - a mostly read-only POP3 server

Old account expiry has not been implemented, but it seems to
work well with both mpop(1) and getmail(1).  The strictness of
mpop was particularly helpful in ironing out bugs in our
implementation of (dreaded) message sequence numbers.

"EXPIRE 0" (RFC 2449) can theoretically save numerous "DELE"
commands, but that's untested by real-world clients.  mpop
supports PIPELINING which is effective in hiding latency,
and the core networking functionality is already well-tested
from our NNTP and IMAP implementations.

Configuration requires "publicinbox.pop3state" to point to
a directory writable by the otherwise read-only daemon.
See public-inbox-pop3d(1) manpage for more usage details.

1 files changed, 6 insertions, 4 deletions

diff --git a/lib/PublicInbox/Inbox.pm b/lib/PublicInbox/Inbox.pm
index 1579d500..da81fb67 100644
--- a/lib/PublicInbox/Inbox.pm
+++ b/lib/PublicInbox/Inbox.pm
@@ -1,4 +1,4 @@
-# Copyright (C) 2016-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 #
 # Represents a public-inbox (which may have multiple mailing addresses)
@@ -230,8 +230,9 @@ sub base_url {
         $url;
 }
 
+# imapserver, nntpserver, and pop3server configs are used here:
 sub _x_url ($$$) {
-        my ($self, $x, $ctx) = @_; # $x is "nntp" or "imap"
+        my ($self, $x, $ctx) = @_; # $x is "imap", "nntp", or "pop3"
         # no checking for nntp_usable here, we can point entirely
         # to non-local servers or users run by a different user
         my $ns = $self->{"${x}server"} //
@@ -253,7 +254,7 @@ sub _x_url ($$$) {
                                 if ($group) {
                                         $u .= '/' if $u !~ m!/\z!;
                                         $u .= $group;
-                                } else { # n.b. IMAP uses "newsgroup"
+                                } else { # n.b. IMAP and POP3 use "newsgroup"
                                         warn <<EOM;
 publicinbox.$self->{name}.${x}mirror=$_ missing newsgroup name
 EOM
@@ -273,8 +274,9 @@ EOM
 }
 
 # my ($self, $ctx) = @_;
-sub nntp_url { $_[0]->{-nntp_url} //= _x_url($_[0], 'nntp', $_[1]) }
 sub imap_url { $_[0]->{-imap_url} //= _x_url($_[0], 'imap', $_[1]) }
+sub nntp_url { $_[0]->{-nntp_url} //= _x_url($_[0], 'nntp', $_[1]) }
+sub pop3_url { $_[0]->{-pop3_url} //= _x_url($_[0], 'pop3', $_[1]) }
 
 sub nntp_usable {
         my ($self) = @_;