Re: [quicwg/base-drafts] Allow servers to send a preferred address of each address family (#2296)

[Kazuho Oku <[e-mail]>]

kazuho commented on this pull request.

@DavidSchinazi Thank you for working on this.

>  
 ~~~
    struct {
-     enum { IPv4(4), IPv6(6), (15) } ipVersion;
-     opaque ipAddress<4..2^8-1>;
+     opaque ipv4Address<0..2^8-1>;
+     opaque ipv6Address<0..2^8-1>;
      uint16 port;

The PR seems to assume that:
* IPv4 and IPv6 are the only two types of underlying protocols that we care, while the current draft provides extensibility (i.e. we can add new types to the ipVersion enumeration).
* All the addresses share the same port number.

Are we fine with that?

If the intent here is to add support for IPv6 address:port without having any impact on other aspects, I believe that the struct should look like:

```
struct {
    enum { IPv4(4), IPv6(6), (15) } ipVersion;
    struct {
        select (ipVersion) {
        case IPv4:
            struct {
                opaque address[4];
                uint16 port;
            };
        case IPv6:
            struct {
                opaque address[16];
                uint16 port;
            };
        }
    } <0..2^8-1>;
} AddressPort;

struct {
    AddressPort address<0..2^8-1>;
    uint16 port;
    opaque connectionId<0..18>;
    opaque statelessResetToken[16];
} PreferredAddress;

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