[PATCH 1/2] doc|www: flesh out POP3 documentation for servers and users

[Eric Wong <e@80x24.org>]

Hopefully it makes sense to new users deploying or using POP3...
---
 Documentation/public-inbox-config.pod |  7 +++++++
 lib/PublicInbox/Inbox.pm              | 30 +++++++++++++++++++++++----
 lib/PublicInbox/WwwText.pm            | 26 +++++++++++++++++------
 3 files changed, 53 insertions(+), 10 deletions(-)

diff --git a/Documentation/public-inbox-config.pod b/Documentation/public-inbox-config.pod
index ed99b188..d8504e61 100644
--- a/Documentation/public-inbox-config.pod
+++ b/Documentation/public-inbox-config.pod
@@ -228,6 +228,13 @@ L<public-inbox-nntpd(1)> instance.
 
 Default: none
 
+=item publicinbox.pop3server
+
+Same as C<publicinbox.imapserver>, but for the hostname(s) of the
+L<public-inbox-pop3d(1)> instance.
+
+Default: none
+
 =item publicinbox.pop3state
 
 See L<public-inbox-pop3d(1)/publicinbox.pop3state>
diff --git a/lib/PublicInbox/Inbox.pm b/lib/PublicInbox/Inbox.pm
index da81fb67..0ad68810 100644
--- a/lib/PublicInbox/Inbox.pm
+++ b/lib/PublicInbox/Inbox.pm
@@ -28,7 +28,7 @@ sub do_cleanup {
 		check_inodes($ibx);
 	} else {
 		delete(@$ibx{qw(over mm description cloneurl
-				-imap_url -nntp_url)});
+				-imap_url -nntp_url -pop3_url)});
 	}
 	my $srch = $ibx->{search} // $ibx;
 	delete @$srch{qw(xdb qp)};
@@ -230,9 +230,9 @@ sub base_url {
 	$url;
 }
 
-# imapserver, nntpserver, and pop3server configs are used here:
+# imapserver, nntpserver configs are used here:
 sub _x_url ($$$) {
-	my ($self, $x, $ctx) = @_; # $x is "imap", "nntp", or "pop3"
+	my ($self, $x, $ctx) = @_; # $x is "imap" or "nntp"
 	# 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"} //
@@ -276,7 +276,29 @@ EOM
 # my ($self, $ctx) = @_;
 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', $_[1]) }
+
+sub pop3_url {
+	my ($self, $ctx) = @_;
+	$self->{-pop3_url} //= do {
+		my $ps = $self->{'pop3server'} //
+		       $ctx->{www}->{pi_cfg}->get_all('publicinbox.pop3server');
+		my $group = $self->{newsgroup};
+		my @urls;
+		($ps && $group) and
+			@urls = map { m!\Apops?://! ? $_ : "pop://$_" } @$ps;
+		if (my $mi = $self->{'pop3mirror'}) {
+			my @m = map { m!\Apops?://! ? $_ : "pop://$_" } @$mi;
+			my %seen; # List::Util::uniq requires Perl 5.26+
+			@urls = grep { !$seen{$_}++ } (@urls, @m);
+		}
+		my $n = 0;
+		for (@urls) { $n += s!/+\z!! }
+		warn <<EOM if $n;
+W: pop3server and/or pop3mirror URLs should not end with trailing slash `/'
+EOM
+		\@urls;
+	}
+}
 
 sub nntp_usable {
 	my ($self) = @_;
diff --git a/lib/PublicInbox/WwwText.pm b/lib/PublicInbox/WwwText.pm
index 2b4e69fe..2937c333 100644
--- a/lib/PublicInbox/WwwText.pm
+++ b/lib/PublicInbox/WwwText.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>
 
 # used for displaying help texts and other non-mail content
@@ -272,7 +272,7 @@ EOF
 	@ret; # may be empty, this sub is called as an arg for join()
 }
 
-sub _add_imap_nntp_urls ($$) {
+sub _add_non_http_urls ($$) {
 	my ($ctx, $txt) = @_;
 	$ctx->{ibx}->can('nntp_url') or return; # TODO extindex can have IMAP
 	my $urls = $ctx->{ibx}->imap_url($ctx);
@@ -286,11 +286,25 @@ EOM
 	}
 	$urls = $ctx->{ibx}->nntp_url($ctx);
 	if (@$urls) {
-		$$txt .= "\n";
-		$$txt .= @$urls == 1 ? 'Newsgroup' : 'Newsgroups are';
+		$$txt .= @$urls == 1 ? "\nNewsgroup" : "\nNewsgroups are";
 		$$txt .= ' available over NNTP:';
 		$$txt .= "\n  " . join("\n  ", @$urls) . "\n";
 	}
+	$urls = $ctx->{ibx}->pop3_url($ctx);
+	if (@$urls) {
+		$urls = join("\n  ", @$urls);
+		$$txt .= <<EOM;
+
+POP3 access is available:
+  $urls
+
+The password is: anonymous
+The username is: \$(uuidgen)\@$ctx->{ibx}->{newsgroup}
+where \$(uuidgen) in the output of the `uuidgen' command on your system.
+The UUID in the username functions as a private cookie (don't share it).
+Idle accounts will expire periodically.
+EOM
+	}
 }
 
 sub _add_onion_note ($) {
@@ -379,7 +393,7 @@ EOM
 
 Example config snippet for mirrors: $cfg_link
 EOF
-	_add_imap_nntp_urls($ctx, $txt);
+	_add_non_http_urls($ctx, $txt);
 	_add_onion_note($txt);
 
 	my $code_url = prurl($ctx->{env}, $PublicInbox::WwwStream::CODE_URL);
@@ -508,7 +522,7 @@ message threading
 EOF
 	} # $over
 
-	_add_imap_nntp_urls($ctx, \(my $note = ''));
+	_add_non_http_urls($ctx, \(my $note = ''));
 	$note and $note =~ s/^/  /gms and $$txt .= <<EOF;
 additional protocols
 --------------------