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dc08641128
Remove `Ipv6Addr::is_unicast_link_local_strict` Removes the unstable method `Ipv6Addr::is_unicast_link_local_strict` and keeps the behaviour of `Ipv6Addr::is_unicast_link_local`, see also #85604 where I have tried to summarize related discussion so far. My intent is for `is_unicast_link_local`, `is_unicast_site_local` and `is_unicast_global` to have the semantics of checking if an address has Link-Local, Site-Local or Global scope, see also #85696 which changes the behaviour of `is_unicast_global` and renames these methods to `has_unicast_XXX_scope` to reflect this. For checking Link-Local scope we currently have two methods: `is_unicast_link_local` and `is_unicast_link_local_strict`. This is because of what appears to be conflicting definitions in [IETF RFC 4291](https://datatracker.ietf.org/doc/html/rfc4291). From [IETF RFC 4291 section 2.4](https://datatracker.ietf.org/doc/html/rfc4291#section-2.4): "Link-Local unicast" (`FE80::/10`) ```text Address type Binary prefix IPv6 notation Section ------------ ------------- ------------- ------- Unspecified 00...0 (128 bits) ::/128 2.5.2 Loopback 00...1 (128 bits) ::1/128 2.5.3 Multicast 11111111 FF00::/8 2.7 Link-Local unicast 1111111010 FE80::/10 2.5.6 Global Unicast (everything else) ``` From [IETF RFC 4291 section 2.5.6](https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.6): "Link-Local IPv6 Unicast Addresses" (`FE80::/64`) ```text | 10 bits | 54 bits | 64 bits | +----------+-------------------------+----------------------------+ |1111111010| 0 | interface ID | +----------+-------------------------+----------------------------+ ``` With `is_unicast_link_local` checking `FE80::/10` and `is_unicast_link_local_strict` checking `FE80::/64`. There is also [IETF RFC 5156 section 2.4](https://datatracker.ietf.org/doc/html/rfc5156#section-2.4) which defines "Link-Scoped Unicast" as `FE80::/10`. It has been pointed out that implementations in other languages and the linux kernel all use `FE80::/10` (https://github.com/rust-lang/rust/pull/76098#issuecomment-706916840, https://github.com/rust-lang/rust/pull/76098#issuecomment-705928605). Given all of this I believe the correct interpretation to be the following: All addresses in `FE80::/10` are defined as having Link-Local scope, however currently only the block `FE80::/64` has been allocated for "Link-Local IPv6 Unicast Addresses". This might change in the future however; more addresses in `FE80::/10` could be allocated and those will have Link-Local scope. I therefore believe the current behaviour of `is_unicast_link_local` to be correct (if interpreting it to have the semantics of `has_unicast_link_local_scope`) and `is_unicast_link_local_strict` to be unnecessary, confusing and even a potential source of future bugs: Currently there is no real difference in checking `FE80::/10` or `FE80::/64`, since any address in practice will be `FE80::/64`. However if an application uses `is_unicast_link_local_strict` to implement link-local (so non-global) behaviour, it will be incorrect in the future if addresses outside of `FE80::/64` are allocated. r? `@joshtriplett` as reviewer of all the related PRs |
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