再現できません。ドメインの直後の余分なスラッシュは、DirectorySlashes がオフの場合でも mod_rewrite に渡されることはありません。スラッシュを削除しているのは Opera か Apache かは確認していません)。それ以外の場合は、すべて正常に動作します。
RewriteBase /
RewriteCond %{REQUEST_URI} ^//+(.*)$ [OR]
RewriteCond %{REQUEST_URI} ^(.*/)/+$
RewriteRule .* http://domain/%1 [R=301,L]
http://localhost//abc/b//のリクエスト
127.0.0.1 - - [17/May/2010:12:26:36 +0100] [localhost/sid#c08fb0][rid#2756540/initial] (3) [perdir C:/HTTP/htdocs/] add path info postfix: C:/HTTP/htdocs/abc -> C:/HTTP/htdocs/abc/b/
127.0.0.1 - - [17/May/2010:12:26:36 +0100] [localhost/sid#c08fb0][rid#2756540/initial] (3) [perdir C:/HTTP/htdocs/] strip per-dir prefix: C:/HTTP/htdocs/abc/b/ -> abc/b/
127.0.0.1 - - [17/May/2010:12:26:36 +0100] [localhost/sid#c08fb0][rid#2756540/initial] (3) [perdir C:/HTTP/htdocs/] applying pattern '.*' to uri 'abc/b/'
127.0.0.1 - - [17/May/2010:12:26:36 +0100] [localhost/sid#c08fb0][rid#2756540/initial] (4) [perdir C:/HTTP/htdocs/] RewriteCond: input='/abc//b//' pattern='^//+(.*)$' => not-matched
127.0.0.1 - - [17/May/2010:12:26:36 +0100] [localhost/sid#c08fb0][rid#2756540/initial] (4) [perdir C:/HTTP/htdocs/] RewriteCond: input='/abc//b//' pattern='^(.*/)/+$' => matched
127.0.0.1 - - [17/May/2010:12:26:36 +0100] [localhost/sid#c08fb0][rid#2756540/initial] (2) [perdir C:/HTTP/htdocs/] rewrite 'abc/b/' -> 'http://domain//abc//b/'
127.0.0.1 - - [17/May/2010:12:26:36 +0100] [localhost/sid#c08fb0][rid#2756540/initial] (2) [perdir C:/HTTP/htdocs/] explicitly forcing redirect with http://domain//abc//b/
127.0.0.1 - - [17/May/2010:12:26:36 +0100] [localhost/sid#c08fb0][rid#2756540/initial] (1) [perdir C:/HTTP/htdocs/] escaping http://domain//abc//b/ for redirect
127.0.0.1 - - [17/May/2010:12:26:36 +0100] [localhost/sid#c08fb0][rid#2756540/initial] (1) [perdir C:/HTTP/htdocs/] redirect to http://domain//abc//b/ [REDIRECT/301]
注: ホストをハードコーディングしないことを検討してください。
RewriteCond %{HTTP_HOST} !=""
RewriteCond %{REQUEST_URI} ^//+(.*)$ [OR]
RewriteCond %{REQUEST_URI} ^(.*/)/+$
RewriteRule .* http://%{HTTP_HOST}/%1 [R=301,L]
また、内側の「//」が置き換えられていないことにも注意してください。内側のスラッシュを置き換える別のルールを追加します。
新しい編集: OK、これは // で始まるまたは終わる URL を防ぐために機能するようです:
RewriteEngine on
RewriteBase /
RewriteCond %{HTTP_HOST} !=""
RewriteCond %{THE_REQUEST} ^[A-Z]+\s//+(.*)\sHTTP/[0-9.]+$ [OR]
RewriteCond %{THE_REQUEST} ^[A-Z]+\s(.*/)/+\sHTTP/[0-9.]+$
RewriteRule .* http://%{HTTP_HOST}/%1 [R=301,L]