SpamAssassin rule to match IPFS urls

21_uri_ipfs.cf

## these are the IPFS gateways I've seen most frequently in spam/phishing.
## Others can be found via https://ipfs.github.io/public-gateway-checker/
## We assume the string "/ipfs/" followed by a Base36/Base32 string of at least 20 chars is an IPFS url.

uri             __URI_IPFS_LIKELY m,/ipfs/[a-z0-9]{20,}=?,i
uri             __URI_IPFS_1    m,://ipfs.io/ipfs/,i
uri             __URI_IPFS_2    m,://ipfs.fleek.co/ipfs/,i

meta            HEX_IPFS_URI    ( __URI_IPFS_1 || __URI_IPFS_2 )
describe        HEX_IPFS_URI    Contains a known IPFS public gateway URI
score           HEX_IPFS_URI    1.0

meta            HEX_IPFS_LIKELY __URI_IPFS_LIKELY && !HEX_IPFS_URI
describe        HEX_IPFS_LIKELY Probably contains an IPFS public gateway URI
score           HEX_IPFS_LIKELY 0.2