www: implement generic help text

Begin documenting some basic help functionality.
I may tweak the anchor names of the various HTML endpoints
to be more consistent with each other (old ones will be
supported for a short while), so I'm not documenting
those, for now.

This may become part of a builtin key-value store for
basic texts, but this probably shouldn't become a wiki
engine, either.

1 files changed, 203 insertions, 0 deletions

diff --git a/lib/PublicInbox/WwwText.pm b/lib/PublicInbox/WwwText.pm
new file mode 100644
index 00000000..b8beb97c
--- /dev/null
+++ b/lib/PublicInbox/WwwText.pm
@@ -0,0 +1,203 @@
+# Copyright (C) 2016 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+#
+# serves the /$INBOX/_/* endpoints from :text/* of the git tree
+package PublicInbox::WwwText;
+use strict;
+use warnings;
+use PublicInbox::Linkify;
+use PublicInbox::WwwStream;
+use PublicInbox::Hval qw(ascii_html);
+our $QP_URL = 'https://xapian.org/docs/queryparser.html';
+our $WIKI_URL = 'https://en.wikipedia.org/wiki';
+
+# /$INBOX/_/text/$KEY/ # KEY may contain slashes
+# For now, "help" is the only supported $KEY
+sub get_text {
+        my ($ctx, $key) = @_;
+        my $code = 200;
+
+        $key = 'help' if !defined $key; # this 302s to _/text/help/
+
+        # get the raw text the same way we get mboxrds
+        my $raw = ($key =~ s!/raw\z!!);
+        my $have_tslash = ($key =~ s!/\z!!) if !$raw;
+
+        my $txt = '';
+        if (!_default_text($ctx, $key, \$txt)) {
+                $code = 404;
+                $txt = "404 Not Found ($key)\n";
+        }
+        if ($raw) {
+                return [ $code, [ 'Content-Type', 'text/plain',
+                                  'Content-Length', bytes::length($txt) ],
+                        [ $txt ] ]
+        }
+
+        # enforce trailing slash for "wget -r" compatibility
+        if (!$have_tslash && $code == 200) {
+                my $url = $ctx->{-inbox}->base_url($ctx->{env});
+                $url .= "_/text/$key/";
+
+                return [ 302, [ 'Content-Type', 'text/plain',
+                                'Location', $url ],
+                        [ "Redirecting to $url\n" ] ];
+        }
+
+        # Follow git commit message conventions,
+        # first line is the Subject/title
+        my ($title) = ($txt =~ /\A([^\n]*)/s);
+        _do_linkify($txt);
+        $ctx->{-title_html} = ascii_html($title);
+
+        my $nslash = ($key =~ tr!/!/!);
+        $ctx->{-upfx} = '../../../' . ('../' x $nslash);
+
+        PublicInbox::WwwStream->response($ctx, $code, sub {
+                my ($nr, undef) = @_;
+                $nr == 1 ? '<pre>'.$txt.'</pre>' : undef
+        });
+}
+
+sub _do_linkify {
+        my $l = PublicInbox::Linkify->new;
+        $_[0] = $l->linkify_2(ascii_html($l->linkify_1($_[0])));
+}
+
+sub _srch_prefix ($$) {
+        my ($srch, $txt) = @_;
+        my $pad = 0;
+        my $htxt = '';
+        my $help = $srch->help;
+        my $i;
+        for ($i = 0; $i < @$help; $i += 2) {
+                my $pfx = $help->[$i];
+                my $n = length($pfx);
+                $pad = $n if $n > $pad;
+                $htxt .= $pfx . "\0";
+                $htxt .= $help->[$i + 1];
+                $htxt .= "\f\n";
+        }
+        $pad += 2;
+        my $padding = ' ' x ($pad + 8);
+        $htxt =~ s/^/$padding/gms;
+        $htxt =~ s/^$padding(\S+)\0/"        $1".
+                                (' ' x ($pad - length($1)))/egms;
+        $htxt =~ s/\f\n/\n/gs;
+        $$txt .= $htxt;
+        1;
+}
+
+
+sub _default_text ($$$) {
+        my ($ctx, $key, $txt) = @_;
+        return if $key ne 'help'; # TODO more keys?
+
+        my $ibx = $ctx->{-inbox};
+        my $base_url = $ibx->base_url($ctx->{env});
+        $$txt .= "public-inbox help for $base_url\n";
+        $$txt .= <<EOF;
+
+overview
+--------
+
+    public-inbox uses Message-ID identifiers in URLs.
+    One may look up messages by substituting Message-IDs
+    (without the leading '<' or trailing '>') into the URL.
+    Forward slash ('/') characters in the Message-IDs
+    need to be escaped as "%2F" (without quotes).
+
+    Thus, it is possible to retrieve any message by its
+    Message-ID by going to:
+
+        $base_url<Message-ID>/
+
+        (without the '<' or '>')
+
+    Message-IDs are described at:
+
+        $WIKI_URL/Message-ID
+
+EOF
+
+        # n.b. we use the Xapian DB for any regeneratable,
+        # order-of-arrival-independent data.
+        my $srch = $ibx->search;
+        if ($srch) {
+                $$txt .= <<EOF;
+search
+------
+
+    This public-inbox has search functionality provided by Xapian.
+
+    It supports typical AND, OR, NOT, '+', '-' queries present
+    in other search engines.
+
+    We also support search prefixes to limit the scope of the
+    search to certain fields using prefixes.
+
+    Prefixes supported in this installation include:
+
+EOF
+                _srch_prefix($srch, $txt);
+
+                $$txt .= <<EOF;
+    The upstream Xapian query parser documentation fully explains
+    the query syntax:
+
+        $QP_URL
+
+message threading
+-----------------
+
+    Message threading is enabled for this public-inbox,
+    additional endpoints for message threads are available:
+
+    * $base_url<Message-ID>/T/#u
+
+      Loads the thread belonging to the given <Message-ID>
+      in flat chronological order.  The "#u" anchor
+      focuses the browser on the given <Message-ID>.
+
+    * $base_url<Message-ID>/t/#u
+
+      Loads the thread belonging to the given <Message-ID>
+      in threaded order with nesting.  For deep threads,
+      this requires a wide display or horizontal scrolling.
+
+    Both of these HTML endpoints are suitable for offline reading
+    using the thread overview at the bottom of each page.
+
+    Users of feed readers may follow a particular thread using:
+
+    * $base_url<Message-ID>/t.atom
+
+      Which loads the thread in Atom Syndication Standard
+      described at Wikipedia and RFC4287:
+
+        $WIKI_URL/Atom_(standard)
+        https://tools.ietf.org/html/rfc4287
+
+    Finally, the gzipped mbox for a thread is available for
+    downloading and importing into your favorite mail client:
+
+    * $base_url<Message-ID>/t.mbox.gz
+
+    We use the mboxrd variant of the mbox format described
+    at:
+
+        $WIKI_URL/Mbox
+
+contact
+-------
+
+    This help text is maintained by public-inbox developers
+    reachable via plain-text email at: meta\@public-inbox.org
+
+EOF
+        # TODO: support admin contact info in ~/.public-inbox/config
+        }
+        1;
+}
+
+1;