RewriteEngine On
# Force the trailing slash for all pages unless they end in .html
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
# Skipping pages with the .html extension is necessary to avoid an infinite chain of .html. See the note at the bottom.
RewriteCond %{REQUEST_URI} !.html$
RewriteRule ^(.*[^/])$ /$1/ [R=301,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
# If the HTML file doesn't exist don't attempt to rewrite, or we'll get an infinite loop
RewriteCond %{REQUEST_FILENAME}.html -f
# If we've already tried appending HTML and the file still doesn't exist, don't do it again. See the note at the bottom.
RewriteCond %{REQUEST_URI} !.html$
RewriteRule ^(.*)/$ $1.html
ErrorDocument 404 /404.html
ErrorDocument 422 /422.html
ErrorDocument 500 /500.html
# Note on infinite .html appending loops: We have to take pains to ensure that if a certain file, say foo.html, exists,
# then a path like /foo/bar won't get .html appended an infinite number of times. This can happen because %{REQUEST_FILENAME}
# would match /foo/bar/ to foo.html. Our redirect to force trailing slashes then sends us through an infinite loop.
