wkd: Implement --blacklist option for gpg-wks-client

* tools/gpg-wks-client.c (blacklist_array, blacklist_array_len): New.
(parse_arguments): Install blacklist.
(read_file): New.
(cmp_blacklist, add_blacklist, is_in_blacklist): New.
(mirror_one_key): Check list.
* tools/gpg-wks.h (opt): Remove field blacklist.
--

GnuPG-bug-id: 6224
(cherry picked from commit b0b4e24c4f)

doc/wks.texi

@@ -53,6 +53,26 @@ Directory.
 .B gpg-wks-client
 .RI [ options ]
 .B \-\-read
+.br
+.B gpg-wks-client
+.RI [ options ]
+.B \-\-mirror
+.br
+.B gpg-wks-client
+.RI [ options ]
+.B \-\-install-key
+.br
+.B gpg-wks-client
+.RI [ options ]
+.B \-\-remove-key
+.br
+.B gpg-wks-client
+.RI [ options ]
+.B \-\-print-wkd-hash
+.br
+.B gpg-wks-client
+.RI [ options ]
+.B \-\-print-wkd-url
 @end ifset
 
 @mansect description
@@ -101,6 +121,13 @@ fingerprint and the mailbox separated by a space.  The command
 @option{--remove-key} removes a key from that directory, its only
 argument is a user-id.
 
+The command @option{--mirror} is similar to @option{--install-key} but
+takes the keys from the the LDAP server configured for Dirmngr.  If no
+arguments are given all keys and user ids are installed.  If arguments
+are given they are taken as domain names to limit the to be installed
+keys.  The option @option{--blacklist} may be used to further limit
+the to be installed keys.
+
 The command @option{--print-wkd-hash} prints the WKD user-id identifiers
 and the corresponding mailboxes from the user-ids given on the command
 line or via stdin (one user-id per line).
@@ -184,8 +211,16 @@ easily get the return code of the process.
 @itemx --directory @var{dir}
 @opindex directory
 Use @var{dir} as top level directory for the commands
-@option{--install-key} and @option{--remove-key}.  The default is
-@file{openpgpkey}.
+@option{--mirror}, @option{--install-key} and @option{--remove-key}.
+The default is @file{openpgpkey}.
+
+
+@item --blacklist @var{file}
+@opindex blacklist
+This option is used to exclude certain mail addresses from a mirror
+operation.  The format of @var{file} is one mail address (just the
+addrspec, e.g. "postel@@isi.edu") per line.  Empty lines and lines
+starting with a '#' are ignored.
 
 @item --verbose
 @opindex verbose