net/v2: meta bug for v2 changes

[bradfitz]

This is a meta/index bug for things we might change in a possible future net/v2 (~ "Go 2") package, including both links to other issues, or just comments with API problems/cleanups that are too little to warrant their own bugs.

(This is not about net/http, net/mail, net/rpc, net/smtp, net/nextproto, or net/url. Those should have their own bugs if/when needed.)

[bradfitz]

There's probably at least 1 too many ways to read from a UDP Conn:

go1.txt:pkg net, method (*UDPConn) Read([]uint8) (int, error)
go1.txt:pkg net, method (*UDPConn) ReadFrom([]uint8) (int, Addr, error)
go1.txt:pkg net, method (*UDPConn) ReadFromUDP([]uint8) (int, *UDPAddr, error)
go1.1.txt:pkg net, method (*UDPConn) ReadMsgUDP([]uint8, []uint8) (int, int, int, *UDPAddr, error)

Likewise with UnixConn and IPConn.

And maybe they're still not sufficient because it says at:

https://golang.org/pkg/net/#UDPConn.ReadMsgUDP

The packages golang.org/x/net/ipv4 and golang.org/x/net/ipv6 can be used to manipulate IP-level socket options in oob.

Maybe we can get it right in one place and remove some of the redundant ones.

[bradfitz]

• net: add mechanism to wait for readability on a TCPConn #15735 - net: add mechanism to wait for readability on a TCPConn
• proposal: net: ParseIP should return an error, like other Parse functions #18757 - net: change ParseIP to return (IP, error)

[cespare]

Also the more general

• proposal: net: reconsider representation of IP #18804 - net: reconsider representation of IP

[networkimprov]

This is now tagged for 1.13, but has been open since 2012

• net: errClosing not exported #4373 - net: errClosing not exported

[mikioh]

A few things in my mind, though each of these must be an individual proposal and I still have no concrete draft-proposals yet:

1. A buffering mechanism between packages close to users and packages close to protocol stacks, for example, the packages net/http, crypto/tls and net. The motivation behind this is, a) to achieve efficient layered buffering interacting with transport-layer protocol properties, as in, link/path MTUs and capsulation overhead, b) to provide a way to handle both partial reads/writes on connection-oriented protocols and message reads/writes on connection-less protocols seamlessly, to help applications using io.Reader interface over datagram/message-based protocols.

2. A printer for network-specific types, for example, net.IP and net.HardwareAddr. The motivation behind this is to provide a way to control various output forms of the types for people who need to work on systems using pipelines of various text forms.

[cristaloleg]

• proposal: net/v2: add SetDeadline to Listener interface #6892 proposal: net: add SetDeadline to Listener interface

[networkimprov]

• net: KeepAlive is disabled by write to dead link #31490 - TCP KeepAlive is disabled by write to dead link

[mateusz834]

Few thoughts after my contributions to the net package:

• net/netip the default and only IP address.

• LookupAddr returns a []string, should []netip.Addr.

• net: LookupCNAME inconsistency on unix systems #59943, net: make LookupCNAME consistent between Unix and Windows, document #50101 - provide a way to query the CNAME resource properly, add an ability to get the Canonical Name of the host.

func LookupCNAME(string) ([]string, error) {/*...*/}

// Struct, insted of returning multiple values in LookupHostInfo, so that we can add more field in the future.
type HostInfo struct {
    Addrs         []netip.Addr
    CanonicalName string
}

func LookupHostInfo(string) (HostInfo, error) {/*...*/}

func LookupCanonicalName(h string) (string, error) {
    hi, err := LookupHostInfo(h)
    if err != nil {
        return "", err
    }
    return hi.CanonicalName, nil
}

• network is passed as a string, should be a special type, like:

type Network uint8

const (
    NetworkUDP Network = iota
    NetworkUDP4
    NetworkUDP6
    NetworkTCP
    NetworkTCP4
    NetworkTCP6

    // ....
)

• We have bunch of methods for resolving hostnames to IP Addresses (LookupHost, LookupIP, LookupIPAddr, LookupNetIP), there should be exactly one:

func LookupIP(network Network, host string) ([]netip.Addr, error) {
    hi, err := LookupHostInfo(h)
    if err != nil {
        return nil, err
    }
    return hi.Addrs, nil
}

• support all DNS names, not just Preferred name syntax https://datatracker.ietf.org/doc/html/rfc1035#section-2.3.1 (with escapes).

• remove Err, IsTimeout, IsTemporary, IsNotFound fields from the DNSError, leave methods for retrieving them from the unwrapErr. Make all fields unexported, name and server are usefull for constructing nice-error message, but not sure how useful they are in real code (we can even make the DNSError unexported).

type DNSError struct {
    name      string
    server    netip.Addr
    unwrapErr error
}

Keep the bevhaviour of only returing few error conditions in Unwrap, this logic is moved into the Unwrap method:

go/src/net/net.go

Lines 686 to 690 in 3959d54

	// At this time, the only errors we wrap are context errors, to allow
	// users to check for canceled/timed out requests.
	if errors.Is(err, context.DeadlineExceeded) || errors.Is(err, context.Canceled) {
	unwrapErr = err
	}

Instead of the IsNotFound field, define a global error and return it through the (*DNSError).Unwrap method. It would be then used as errors.Is(err, net.ErrHostNotFound).

    ErrHostNotFound = errors.New("no such host")

• remove unused error types, like: DNSConfigError.

• DefaultResolver should be an unexported atomic.Pointer with a global getter and setter.