imap: *SEARCH: use Parse::RecDescent

For properly parsing IMAP search requests, it's easier to use a
recursive descent parser generator to deal with subqueries and
the "OR" statement.

Parse::RecDescent was chosen since it's mature, well-known,
widely available and already used by our optional dependencies:
Inline::C and Mail::IMAPClient.  While it's possible to build
Xapian queries without using the Xapian string query parser;
this iteration of the IMAP parser still builds a string which is
passed to Xapian's query parser for ease-of-diagnostics.

Since this is a recursive descent parser dealing with untrusted
inputs, subqueries have a nesting limit of 10.  I expect that is
more than adequate for real-world use.

1 files changed, 276 insertions, 0 deletions

diff --git a/lib/PublicInbox/IMAPsearchqp.pm b/lib/PublicInbox/IMAPsearchqp.pm
new file mode 100644
index 00000000..fba3bacc
--- /dev/null
+++ b/lib/PublicInbox/IMAPsearchqp.pm
@@ -0,0 +1,276 @@
+# Copyright (C) 2020 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+# IMAP search query parser.  cf RFC 3501
+
+# We currently compile Xapian queries to a string which is fed
+# to Xapian's query parser.  However, we may use Xapian-provided
+# Query object API to build an optree, instead.
+package PublicInbox::IMAPsearchqp;
+use strict;
+use Parse::RecDescent;
+use Time::Local qw(timegm);
+use POSIX qw(strftime);
+our $q = bless {}, __PACKAGE__; # singleton, reachable in generated P::RD
+my @MoY = qw(JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC);
+my %MM = map {; $MoY[$_-1] => sprintf('%02u', $_) } (1..12);
+
+# IMAP to Xapian header search key mapping
+my %IH2X = (
+        TEXT => '',
+        SUBJECT => 's:',
+        BODY => 'b:',
+        FROM => 'f:',
+        TO => 't:',
+        CC => 'c:',
+        # BCC => 'bcc:', # TODO
+
+        # IMAP allows searching arbitrary headers via
+        # "HEADER $field_name $string" which gets silly expensive.
+        # We only allow the headers we already index.
+        'MESSAGE-ID' => 'm:',
+        'LIST-ID' => 'l:',
+        # KEYWORD # TODO ? dfpre,dfpost,...
+);
+
+sub uid_set_xap ($$) {
+        my ($self, $seq_set) = @_;
+        my @u;
+        do {
+                my $u = $self->{imap}->range_step(\$seq_set);
+                die $u unless ref($u); # break out of the parser on error
+                push @u, "uid:$u->[0]..$u->[1]";
+        } while ($seq_set);
+        push(@{$q->{xap}}, @u > 1 ? '('.join(' OR ', @u).')' : $u[0]);
+}
+
+sub xap_only ($;$) {
+        my ($self, $query) = @_;
+        delete $self->{sql}; # query too complex for over.sqlite3
+        push @{$self->{xap}}, $query if defined($query);
+
+        # looks like we can't use SQLite-only, convert SQLite UID
+        # ranges to Xapian:
+        if (my $uid = delete $self->{uid}) {
+                uid_set_xap($self, $_) for @$uid;
+        }
+        1;
+}
+
+sub ih2x {
+        my ($self, $field_name, $s) = @_; # $self == $q
+        $s =~ /\A"(.*?)"\z/s and $s = $1;
+
+        # AFAIK Xapian can't handle [*"] in probabilistic terms,
+        # and it relies on lowercase
+        my $xk = defined($field_name) ? ($IH2X{$field_name} // '') : '';
+        xap_only($self,
+                lc(join(' ', map { qq[$xk"$_"] } split(/[\*"\s]+/, $s))));
+        1;
+}
+
+sub subq_enter {
+        xap_only($q);
+        my $old = delete($q->{xap}) // [];
+        my $nr = push @{$q->{stack}}, $old;
+        die 'BAD deep recursion' if $nr > 10;
+        $q->{xap} = [];
+}
+
+sub subq_leave {
+        my $child = delete $q->{xap};
+        my $parent = $q->{xap} = pop @{$q->{stack}};
+        push(@$parent, @$child > 1 ? '('.join(' ', @$child).')' : $child->[0]);
+        1;
+}
+
+sub yyyymmdd ($) {
+        my ($item) = @_;
+        my ($dd, $mon, $yyyy) = split(/-/, $item->{date}, 3);
+        my $mm = $MM{$mon} // die "BAD month: $mon";
+        wantarray ? ($yyyy, $mm, sprintf('%02u', $dd))
+                : timegm(0, 0, 0, $dd, $mm - 1, $yyyy);
+}
+
+sub SENTSINCE {
+        my ($self, $item) = @_;
+        my ($yyyy, $mm, $dd) = yyyymmdd($item);
+        push @{$self->{xap}}, "d:$yyyy$mm$dd..";
+        my $sql = $self->{sql} or return 1;
+        my $ds = timegm(0, 0, 0, $dd, $mm - 1, $yyyy);
+        $$sql .= " AND ds >= $ds";
+}
+
+sub SENTON {
+        my ($self, $item) = @_;
+        my ($yyyy, $mm, $dd) = yyyymmdd($item);
+        my $ds = timegm(0, 0, 0, $dd, $mm - 1, $yyyy);
+        my $end = $ds + 86399; # no leap day
+        my $dt_end = strftime('%Y%m%d%H%M%S', gmtime($end));
+        push @{$self->{xap}}, "dt:$yyyy$mm$dd"."000000..$dt_end";
+        my $sql = $self->{sql} or return 1;
+        $$sql .= " AND ds >= $ds AND ds <= $end";
+}
+
+sub SENTBEFORE {
+        my ($self, $item) = @_;
+        my ($yyyy, $mm, $dd) = yyyymmdd($item);
+        push @{$self->{xap}}, "d:..$yyyy$mm$dd";
+        my $sql = $self->{sql} or return 1;
+        my $ds = timegm(0, 0, 0, $dd, $mm - 1, $yyyy);
+        $$sql .= " AND ds <= $ds";
+}
+
+sub ON {
+        my ($self, $item) = @_;
+        my $ts = yyyymmdd($item);
+        my $end = $ts + 86399; # no leap day
+        push @{$self->{xap}}, "ts:$ts..$end";
+        my $sql = $self->{sql} or return 1;
+        $$sql .= " AND ts >= $ts AND ts <= $end";
+}
+
+sub BEFORE {
+        my ($self, $item) = @_;
+        my $ts = yyyymmdd($item);
+        push @{$self->{xap}}, "ts:..$ts";
+        my $sql = $self->{sql} or return 1;
+        $$sql .= " AND ts <= $ts";
+}
+
+sub SINCE {
+        my ($self, $item) = @_;
+        my $ts = yyyymmdd($item);
+        push @{$self->{xap}}, "ts:$ts..";
+        my $sql = $self->{sql} or return 1;
+        $$sql .= " AND ts >= $ts";
+}
+
+sub uid_set ($$) {
+        my ($self, $seq_set) = @_;
+        if ($self->{sql}) {
+                push @{$q->{uid}}, $seq_set;
+        } else { # we've gone Xapian-only
+                uid_set_xap($self, $seq_set);
+        }
+        1;
+}
+
+sub msn_set {
+        my ($self, $seq_set) = @_;
+        PublicInbox::IMAP::msn_to_uid_range(
+                $self->{msn2uid} //= $self->{imap}->msn2uid, $seq_set);
+        uid_set($self, $seq_set);
+}
+
+my $prd = Parse::RecDescent->new(<<'EOG');
+<nocheck>
+{ my $q = $PublicInbox::IMAPsearchqp::q; }
+search_key : search_key1(s) { $return = $q }
+search_key1 : "ALL" | "RECENT" | "UNSEEN" | "NEW"
+        | OR_search_keys
+        | NOT_search_key
+        | LARGER_number
+        | SMALLER_number
+        | SENTSINCE_date
+        | SENTON_date
+        | SENTBEFORE_date
+        | SINCE_date
+        | ON_date
+        | BEFORE_date
+        | FROM_string
+        | HEADER_field_name_string
+        | TO_string
+        | CC_string
+        | BCC_string
+        | SUBJECT_string
+        | UID_set
+        | MSN_set
+        | sub_query
+        | <error>
+
+SENTSINCE_date : 'SENTSINCE' date { $q->SENTSINCE(\%item) }
+SENTON_date : 'SENTON' date { $q->SENTON(\%item) }
+SENTBEFORE_date : 'SENTBEFORE' date { $q->SENTBEFORE(\%item) }
+
+SINCE_date : 'SINCE' date { $q->SINCE(\%item) }
+ON_date : 'ON' date { $q->ON(\%item) }
+BEFORE_date : 'BEFORE' date { $q->BEFORE(\%item) }
+
+MSN_set : sequence_set { $q->msn_set($item{sequence_set}) }
+UID_set : "UID" sequence_set { $q->uid_set($item{sequence_set}) }
+LARGER_number : "LARGER" number { $q->xap_only("bytes:$item{number}..") }
+SMALLER_number : "SMALLER" number { $q->xap_only("bytes:..$item{number}") }
+# pass "NOT" through XXX is this right?
+OP_NOT : "NOT" { $q->xap_only('NOT') }
+NOT_search_key : OP_NOT search_key1
+OP_OR : "OR" {
+        $q->xap_only('OP_OR');
+        my $cur = delete $q->{xap};
+        push @{$q->{stack}}, $cur;
+        $q->{xap} = [];
+}
+search_key_a : search_key1
+{
+        my $ka = delete $q->{xap};
+        $q->{xap} = [];
+        push @{$q->{stack}}, $ka;
+}
+OR_search_keys : OP_OR search_key_a search_key1
+{
+        my $kb = delete $q->{xap};
+        my $ka = pop @{$q->{stack}};
+        my $xap = $q->{xap} = pop @{$q->{stack}};
+        my $op = pop @$xap;
+        $op eq 'OP_OR' or die "BAD expected OR: $op";
+        $ka = @$ka > 1 ? '('.join(' ', @$ka).')' : $ka->[0];
+        $kb = @$kb > 1 ? '('.join(' ', @$kb).')' : $kb->[0];
+        push @$xap, "($ka OR $kb)";
+}
+HEADER_field_name_string : "HEADER" field_name string
+{
+        $q->ih2x($item{field_name}, $item{string});
+}
+FROM_string : "FROM" string { $q->ih2x('FROM', $item{string}) }
+TO_string : "TO" string { $q->ih2x('TO', $item{string}) }
+CC_string : "CC" string { $q->ih2x('CC', $item{string}) }
+BCC_string : "BCC" string { $q->ih2x('BCC', $item{string}) }
+SUBJECT_string : "SUBJECT" string { $q->ih2x('SUBJECT', $item{string}) }
+op_subq_enter : '(' { $q->subq_enter }
+sub_query : op_subq_enter search_key1(s) ')' { $q->subq_leave }
+
+field_name : /[\x21-\x39\x3b-\x7e]+/
+string : quoted | literal
+literal : /[^"\(\) \t]+/ # bogus, I know
+quoted : /"[^"]*"/
+number : /[0-9]+/
+date : /[0123]?[0-9]-[A-Z]{3}-[0-9]{4,}/
+sequence_set : /\A[0-9][0-9,:]*[0-9\*]?\z/
+EOG
+
+sub parse {
+        my ($imap, $query) = @_;
+        my $sql = '';
+        %$q = (sql => \$sql, imap => $imap); # imap = PublicInbox::IMAP obj
+        # $::RD_TRACE = 1;
+        my $res = eval { $prd->search_key(uc($query)) };
+        return $@ if $@ && $@ =~ /\ABAD /;
+        return 'BAD unexpected result' if !$res || $res != $q;
+        if (exists $q->{sql}) {
+                delete $q->{xap};
+                if (my $uid = delete $q->{uid}) {
+                        my @u;
+                        for my $uid_set (@$uid) {
+                                my $u = $q->{imap}->range_step(\$uid_set);
+                                return $u if !ref($u);
+                                push @u, "num >= $u->[0] AND num <= $u->[1]";
+                        }
+                        $sql .= ' AND ('.join(' OR ', @u).')';
+                }
+        } else {
+                $q->{xap} = join(' ', @{$q->{xap}});
+        }
+        delete @$q{qw(imap msn2uid)};
+        $q;
+}
+
+1